Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

NASA Astrophysics Data System (ADS)

Batterman, Sarah A.; Hedin, Lars O.; van Breugel, Michiel; Ransijn, Johannes; Craven, Dylan J.; Hall, Jefferson S.

2013-10-01

Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2 may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N2), but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use, or expand in response to rising CO2 (refs 6, 8). Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystem-scale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests. Over a 300-year chronosequence in Panama, N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbours (greatest difference in youngest forests), and showed species-specific differences in the amount and timing of fixation. As a result of fast growth and high fixation, fixers provided a large fraction of the nitrogen needed to support net forest growth (50,000kg carbon per hectare) in the first 12years. A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence. These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development, with potentially important implications for the ability of tropical forests to sequester CO2.

Key role of symbiotic dinitrogen fixation in tropical forest secondary succession.

PubMed

Batterman, Sarah A; Hedin, Lars O; van Breugel, Michiel; Ransijn, Johannes; Craven, Dylan J; Hall, Jefferson S

2013-10-10

Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2 may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N2), but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use, or expand in response to rising CO2 (refs 6, 8). Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystem-scale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests. Over a 300-year chronosequence in Panama, N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbours (greatest difference in youngest forests), and showed species-specific differences in the amount and timing of fixation. As a result of fast growth and high fixation, fixers provided a large fraction of the nitrogen needed to support net forest growth (50,000 kg carbon per hectare) in the first 12 years. A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence. These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development, with potentially important implications for the ability of tropical forests to sequester CO2.

Symbiotic Nitrogen Fixation in the Fungus Gardens of Leaf-Cutter Ants

USDA-ARS?s Scientific Manuscript database

Bacteria-mediated acquisition of atmospheric dinitrogen by plants serves as a critical nitrogen source in terrestrial ecosystems, and through its key role in agriculture, this phenomenon has shaped the development of human civilizations. Here we show that, paralleling human agriculture, cultivation ...

Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic

NASA Astrophysics Data System (ADS)

Li, Yang; Li, Ying; Wang, Baomin; Luo, Yi; Yang, Dawei; Tong, Peng; Zhao, Jinfeng; Luo, Lun; Zhou, Yuhan; Chen, Si; Cheng, Fang; Qu, Jingping

2013-04-01

Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber-Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3- and NH2- species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed.

The small unicellular diazotrophic symbiont, UCYN-A, is a key player in the marine nitrogen cycle.

PubMed

Martínez-Pérez, Clara; Mohr, Wiebke; Löscher, Carolin R; Dekaezemacker, Julien; Littmann, Sten; Yilmaz, Pelin; Lehnen, Nadine; Fuchs, Bernhard M; Lavik, Gaute; Schmitz, Ruth A; LaRoche, Julie; Kuypers, Marcel M M

2016-09-12

Microbial dinitrogen (N 2 ) fixation, the nitrogenase enzyme-catalysed reduction of N 2 gas into biologically available ammonia, is the main source of new nitrogen (N) in the ocean. For more than 50 years, oceanic N 2 fixation has mainly been attributed to the activity of the colonial cyanobacterium Trichodesmium 1,2 . Other smaller N 2 -fixing microorganisms (diazotrophs)-in particular the unicellular cyanobacteria group A (UCYN-A)-are, however, abundant enough to potentially contribute significantly to N 2 fixation in the surface waters of the oceans 3-6 . Despite their abundance, the contribution of UCYN-A to oceanic N 2 fixation has so far not been directly quantified. Here, we show that in one of the main areas of oceanic N 2 fixation, the tropical North Atlantic 7 , the symbiotic cyanobacterium UCYN-A contributed to N 2 fixation similarly to Trichodesmium. Two types of UCYN-A, UCYN-A1 and -A2, were observed to live in symbioses with specific eukaryotic algae. Single-cell analyses showed that both algae-UCYN-A symbioses actively fixed N 2 , contributing ∼20% to N 2 fixation in the tropical North Atlantic, revealing their significance in this region. These symbioses had growth rates five to ten times higher than Trichodesmium, implying a rapid transfer of UCYN-A-fixed N into the food web that might significantly raise their actual contribution to N 2 fixation. Our analysis of global 16S rRNA gene databases showed that UCYN-A occurs in surface waters from the Arctic to the Antarctic Circle and thus probably contributes to N 2 fixation in a much larger oceanic area than previously thought. Based on their high rates of N 2 fixation and cosmopolitan distribution, we hypothesize that UCYN-A plays a major, but currently overlooked role in the oceanic N cycle.

Agglomeration Determines Effects of Carbonaceous Nanomaterials on Soybean Nodulation, Dinitrogen Fixation Potential, and Growth in Soil

EPA Science Inventory

The potential effects of carbonaceous nanomaterials (CNMs) on agricultural plants are of concern. However, little research has been performed using plants cultivated to maturity in soils contaminated with various CNMs at different concentrations. Here, we grew soybean for 39 days...

Microbial dinitrogen fixation in coral holobionts exposed to thermal stress and bleaching.

PubMed

Cardini, Ulisse; van Hoytema, Nanne; Bednarz, Vanessa N; Rix, Laura; Foster, Rachel A; Al-Rshaidat, Mamoon M D; Wild, Christian

2016-09-01

Coral holobionts (i.e., coral-algal-prokaryote symbioses) exhibit dissimilar thermal sensitivities that may determine which coral species will adapt to global warming. Nonetheless, studies simultaneously investigating the effects of warming on all holobiont members are lacking. Here we show that exposure to increased temperature affects key physiological traits of all members (herein: animal host, zooxanthellae and diazotrophs) of both Stylophora pistillata and Acropora hemprichii during and after thermal stress. S. pistillata experienced severe loss of zooxanthellae (i.e., bleaching) with no net photosynthesis at the end of the experiment. Conversely, A. hemprichii was more resilient to thermal stress. Exposure to increased temperature (+ 6°C) resulted in a drastic increase in daylight dinitrogen (N2 ) fixation, particularly in A. hemprichii (threefold compared with controls). After the temperature was reduced again to in situ levels, diazotrophs exhibited a reversed diel pattern of activity, with increased N2 fixation rates recorded only in the dark, particularly in bleached S. pistillata (twofold compared to controls). Concurrently, both animal hosts, but particularly bleached S. pistillata, reduced both organic matter release and heterotrophic feeding on picoplankton. Our findings indicate that physiological plasticity by coral-associated diazotrophs may play an important role in determining the response of coral holobionts to ocean warming. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Dinitrogen fixation associated with shoots of aquatic carnivorous plants: is it ecologically important?

PubMed Central

Sirová, Dagmara; Šantrůček, Jiří; Adamec, Lubomír; Bárta, Jiří; Borovec, Jakub; Pech, Jiří; Owens, Sarah M.; Šantrůčková, Hana; Schäufele, Rudi; Štorchová, Helena; Vrba, Jaroslav

2014-01-01

Background and Aims Rootless carnivorous plants of the genus Utricularia are important components of many standing waters worldwide, as well as suitable model organisms for studying plant–microbe interactions. In this study, an investigation was made of the importance of microbial dinitrogen (N2) fixation in the N acquisition of four aquatic Utricularia species and another aquatic carnivorous plant, Aldrovanda vesiculosa. Methods 16S rRNA amplicon sequencing was used to assess the presence of micro-organisms with known ability to fix N2. Next-generation sequencing provided information on the expression of N2 fixation-associated genes. N2 fixation rates were measured following 15N2-labelling and were used to calculate the plant assimilation rate of microbially fixed N2. Key Results Utricularia traps were confirmed as primary sites of N2 fixation, with up to 16 % of the plant-associated microbial community consisting of bacteria capable of fixing N2. Of these, rhizobia were the most abundant group. Nitrogen fixation rates increased with increasing shoot age, but never exceeded 1·3 μmol N g–1 d. mass d–1. Plant assimilation rates of fixed N2 were detectable and significant, but this fraction formed less than 1 % of daily plant N gain. Although trap fluid provides conditions favourable for microbial N2 fixation, levels of nif gene transcription comprised <0·01 % of the total prokaryotic transcripts. Conclusions It is hypothesized that the reason for limited N2 fixation in aquatic Utricularia, despite the large potential capacity, is the high concentration of NH4-N (2·0–4·3 mg L–1) in the trap fluid. Resulting from fast turnover of organic detritus, it probably inhibits N2 fixation in most of the microorganisms present. Nitrogen fixation is not expected to contribute significantly to N nutrition of aquatic carnivorous plants under their typical growth conditions; however, on an annual basis the plant–microbe system can supply nitrogen in the order of hundreds of mg m–2 into the nutrient-limited littoral zone, where it may thus represent an important N source. PMID:24817095

Binding of isolated plant lectin by rhizobia during episodes of reduced gravity obtained by parabolic flight

NASA Technical Reports Server (NTRS)

Henry, R. L.; Green, P. D.; Wong, P. P.; Guikema, J. A.; Spooner, B. S. (Principal Investigator)

1990-01-01

Development of a legume root nodule is a complex process culminating in a plant/bacterial symbiosis possessing the capacity for biological dinitrogen fixation. Formation of root nodules is initiated by the binding and stabilization of rhizobia to plant root hairs, mediated in part by a receptor/ligand recognition system composed of lectins on the plant root surface and lectin-binding sites on the rhizobial cell surface. The dinitrogen fixation activity of these root nodules may be an important feature of enclosed, space-based life support systems, and may provide an ecological method to recycle nitrogen for amino acid production. However, the effects on nodule development of varied gravitational fields, or of root nutrient delivery hardware, remain unknown. We have investigated the effects of microgravity on root nodule formation, with preliminary experiments focused upon the receptor/ligand component. Microgravity, obtained during parabolic flight aboard NASA 930, has no apparent effect on the binding of purified lectin to rhizobia, a result that will facilitate forthcoming experiments using intact root tissues.

Facets of diazotrophy in the oxygen minimum zone waters off Peru

PubMed Central

Loescher, Carolin R; Großkopf, Tobias; Desai, Falguni D; Gill, Diana; Schunck, Harald; Croot, Peter L; Schlosser, Christian; Neulinger, Sven C; Pinnow, Nicole; Lavik, Gaute; Kuypers, Marcel M M; LaRoche, Julie; Schmitz, Ruth A

2014-01-01

Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4+), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2− and PO43− are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the future. PMID:24813564

Facets of diazotrophy in the oxygen minimum zone waters off Peru.

PubMed

Loescher, Carolin R; Großkopf, Tobias; Desai, Falguni D; Gill, Diana; Schunck, Harald; Croot, Peter L; Schlosser, Christian; Neulinger, Sven C; Pinnow, Nicole; Lavik, Gaute; Kuypers, Marcel M M; LaRoche, Julie; Schmitz, Ruth A

2014-11-01

Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4(+)), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2(-) and PO4(3-) are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the future.

High-nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas)

NASA Astrophysics Data System (ADS)

Berthelot, H.; Benavides, M.; Moisander, P. H.; Grosso, O.; Bonnet, S.

2017-08-01

Dinitrogen (N2) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using 15N2 incubation assays taking into account both the particulate and the dissolved pools. Average depth-integrated particulate N2 fixation rates were 203 (range 43-399) and 1396 (range 176-3132) μmol N m-2 d-1 in the Bismarck and Solomon Seas, respectively. In both seas, N2 fixation measured in the dissolved pool was similar to particulate N2 fixation, highlighting the potentially substantial underestimation of N2 fixation in oceanic budgets when only particulate N2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant. Regression analyses suggest that it accounted for the major proportion of N2 fixation. However, unicellular cyanobacterial and non-cyanobacterial diazotrophs were also occasionally abundant. This study reports high pelagic N2 fixation rates and confirms that the Western Tropical South Pacific is a hot spot for marine N2 fixation.

Measurement of dinitrogen fixation by Biological soil crust (BSC) from the Sahelian zone: an isotopic method.

NASA Astrophysics Data System (ADS)

Ehrhardt, F.; Alavoine, G.; Bertrand, I.

2012-04-01

Amongst the described ecological roles of Biological Soil Crust, N fixation is of importance for soil fertility, especially in arid and semi-arid ecosystems with low inputs. In BSC, the quantification of N fixation fluxes using an indirect method is widespread, usually with the Acetylene Reduction Assay (ARA) which consists in measuring the nitrogenase activity through the process of acetylene reduction into ethylene. A converting factor, still discussed in the literature and greatly depending of the constitutive organisms of the BSC, is the tool used to convert the amount of reduced ethylene into quantitative fixed Nitrogen. The aim of this poster is to describe an isotopic direct method to quantify the atmospheric dinitrogen fixation fluxes in BSC, while minimizing the variability due to manipulations. Nine different BSC from the Sahelian zone were selected and placed in an incubation room at 28° C in dark and light conditions during three days, while moisture equivalent to pF=2 was regularly adjusted using the gravimetric method with needles and deionized water, in order to activate and reach a dynamic stability of their metabolisms. Subsequently, each crust was placed into a gas-tight glass vial for incubation with a reconstituted 15N2 enriched atmosphere (31.61 % atom 15N, while the proportion of each main gas present in the air was conserved, i.e. 78% N2, 21% O2 and 0.04% CO2). Principal difficulties are to guarantee the airtighness of the system, to avoid crust desiccation and to keep the crust metabolically active under stable conditions for six hours. Several tests were performed to determine the optimum time for 15N2 incubation. Three replicated control samples per crust were also stabilized for three days and then dried at 105° C, without any incubation with 15N2 enriched atmosphere. Total N and 15N were then measured in the grounded (80μm) and dried (105° C) crust, using a Flash EA elemental analyzer (Eurovector, Milan, Italy) coupled to a DeltaPlus Advantage mass spectrometer (Finnigan Thermo Fisher Scientific, Bremen, Germany). N2fixation fluxes were calculated from the difference between the amount of 15N in incubated and in control samples. Mean values ranged from 1.32.10-3 ± 1.02.10-4 to 8.47.10-2 ± 2.63.10-3 mgN.m-2.h-1. Concerning the variability, differences observed between crusts and between replicates are probably related to the characteristic of each crust as well as to field sampling which integrates the important heterogeneity and sensitivity of the material.

Nitrogen fixation rates associated with the invasive macroalgae Sargassum horneri around Catalina Island, CA

NASA Astrophysics Data System (ADS)

DeLiberto, A.

2016-02-01

Nitrogen fixation is an important process which allows organisms access to biologically unavailable dinitrogen gas. Bacteria, known as diazotrophs use the enzyme nitrogenase to convert N2 to NH3. These bacteria, including certain species of heterotrophic bacteria and cyanobacteria, can be symbiotically associated with marine macroalgae, facilitating nutrient cycling in oligotrophic regions. As many species within the genera Sargassum are associated with nitrogen fixation, this study hypothesized that nitrogenase activity would be associated with the benthic invasive Sargassum horneri on Catalina Island. In the past decade, Sargassum horneri, an invasive from Japan, has spread throughout the waters around Catalina Island. Using the acetylene reduction procedure using flame ionization detection, initial nitrogenase activity of S. horneri sampled from Indian Rock was observed. Nitrogen fixation rates increased with decomposition, particularly in dark/anaerobic treatments, suggesting the presence of heterotrophic bacteria. In addition, acetate additions greatly increase nitrogen fixation rates, once again indicating heterotrophic nitrogen fixing bacteria.

Appraisal of the nitrogen-15 natural-abundance method for quantifying dinitrogen fixation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bremer, E.; van Kessel, C.

Several investigators have questioned the use of the {sup 15}N natural-abundance method of estimating N{sub 2} fixation because of variability in soil {delta}{sup 15}N and small differences between the {delta}{sup 15}N of soil N and atmospheric N. Investigations were conducted to compare the {sup 15}N natural-abundance and {sup 15}N-isotope-dilution methods for estimating N{sub 2} fixation of field-grown pea (Pisum sativum L.) and lentil (Lens culinaris Medik.). Spatial variability was assessed at three sites by determining the {delta}{sup 15}N of non-N{sub 2}-fixing plants. Seasonal variation in {delta}{sup 15}N for spring and winter wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), barleymore » (Hordeum vulgare L.), rape (Brassica napus L.) and lentil was determined at one site. Comparisons between {delta}{sup 15}N and {sup 15}N-enriched isotope-dilution methods for estimating N{sub 2} fixation by lentil were conducted at several sites over a 3-yr period. Variability in {delta}{sup 15}N of the reference plant was site dependent: the {delta}{sup 15}N ranged from 2.8 to 9.3 at the first site, 3.4 to 8.8 at the second site, and 3.5 to 6.2 at the third site. The average {delta}{sup 15}N of four of the five non-N{sub 2}-fixing plants increased from 5.4 at 42 d after planting to 6.9 at the final harvest. The fifth non-N{sub 2}-fixing plant, rape, accumulated most of its N during the first 42 d after planting, and its {delta}{sup 15}N value declined from 8.1 at 42 d after planting to 7.3 at the final harvest. Estimates of N{sub 2} fixation were not significantly different in 18 out of 21 comparisons; in two comparisons in the {delta}{sup 15}N method and in one comparison the {sup 15}N-enriched method provided higher estimates of N{sub 2} fixation. Overall, both methods appeared to provide equally reliable estimates of N{sub 2} fixation for lentil.« less

Nitrogen fixation in the mucus of Red Sea corals.

PubMed

Grover, Renaud; Ferrier-Pagès, Christine; Maguer, Jean-François; Ezzat, Leila; Fine, Maoz

2014-11-15

Scleractinian corals are essential constituents of tropical reef ecological diversity. They live in close association with diazotrophs [dinitrogen (N2)-fixing microbes], which can fix high rates of N2. Whether corals benefit from this extrinsic nitrogen source is still under debate. Until now, N2 fixation rates have been indirectly estimated using the acetylene reduction assay, which does not permit assessment of the amount of nitrogen incorporated into the different compartments of the coral holobiont. In the present study, the (15)N2 technique was applied for the first time on three Red Sea coral species. Significant (15)N enrichment was measured in particles released by corals to the surrounding seawater. N2 fixation rates were species specific and as high as 1.6-2 ng N day(-1) l(-1). However, no significant enrichment was measured in the symbiotic dinoflagellates or the coral host tissues, suggesting that corals do not benefit from diazotrophic N2 fixation. © 2014. Published by The Company of Biologists Ltd.

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

NASA Technical Reports Server (NTRS)

Klingler, J. M.; Mancinelli, R. L.; White, M. R.

1989-01-01

One of the most striking differences between the conditions on early Mars and earth was a low (18 mb) partial pressure of N2 (pN2) on early Mars, as opposed to 780 mb N2 on earth. To investigate the possibility of biological nitrogen fixation under conditions of early Mars, experiments were carried out on the growth of Azotobacter vinelandii and Azomonas agilis in nitrogen-free synthetic medium under various partial pressures of N2 (ranging from 780 to 0 mb). It was found that, although the biomass, cell number, and growth rate of these bacteria decreased with decreasing pN2 values below pN2 of 400 mb, both microorganisms were capable of growing at pN2 as low as 5 mb (but not at of below 1 mb), indicating that biological fixation of nitrogen could have occurred on primordial Mars.

Molybdenum and Phosphorus Interact to Constrain Asymbiotic Nitrogen Fixation in Tropical Forests

PubMed Central

Wurzburger, Nina; Bellenger, Jean Philippe; Kraepiel, Anne M. L.; Hedin, Lars O.

2012-01-01

Biological di-nitrogen fixation (N2) is the dominant natural source of new nitrogen to land ecosystems. Phosphorus (P) is thought to limit N2 fixation in many tropical soils, yet both molybdenum (Mo) and P are crucial for the nitrogenase reaction (which catalyzes N2 conversion to ammonia) and cell growth. We have limited understanding of how and when fixation is constrained by these nutrients in nature. Here we show in tropical forests of lowland Panama that the limiting element on asymbiotic N2 fixation shifts along a broad landscape gradient in soil P, where Mo limits fixation in P-rich soils while Mo and P co-limit in P-poor soils. In no circumstance did P alone limit fixation. We provide and experimentally test a mechanism that explains how Mo and P can interact to constrain asymbiotic N2 fixation. Fixation is uniformly favored in surface organic soil horizons - a niche characterized by exceedingly low levels of available Mo relative to P. We show that soil organic matter acts to reduce molybdate over phosphate bioavailability, which, in turn, promotes Mo limitation in sites where P is sufficient. Our findings show that asymbiotic N2 fixation is constrained by the relative availability and dynamics of Mo and P in soils. This conceptual framework can explain shifts in limitation status across broad landscape gradients in soil fertility and implies that fixation depends on Mo and P in ways that are more complex than previously thought. PMID:22470462

Light-driven dinitrogen reduction catalyzed by a CdS:nitrogenase MoFe protein biohybrid.

PubMed

Brown, Katherine A; Harris, Derek F; Wilker, Molly B; Rasmussen, Andrew; Khadka, Nimesh; Hamby, Hayden; Keable, Stephen; Dukovic, Gordana; Peters, John W; Seefeldt, Lance C; King, Paul W

2016-04-22

The splitting of dinitrogen (N2) and reduction to ammonia (NH3) is a kinetically complex and energetically challenging multistep reaction. In the Haber-Bosch process, N2 reduction is accomplished at high temperature and pressure, whereas N2 fixation by the enzyme nitrogenase occurs under ambient conditions using chemical energy from adenosine 5'-triphosphate (ATP) hydrolysis. We show that cadmium sulfide (CdS) nanocrystals can be used to photosensitize the nitrogenase molybdenum-iron (MoFe) protein, where light harvesting replaces ATP hydrolysis to drive the enzymatic reduction of N2 into NH3 The turnover rate was 75 per minute, 63% of the ATP-coupled reaction rate for the nitrogenase complex under optimal conditions. Inhibitors of nitrogenase (i.e., acetylene, carbon monoxide, and dihydrogen) suppressed N2 reduction. The CdS:MoFe protein biohybrids provide a photochemical model for achieving light-driven N2 reduction to NH3. Copyright © 2016, American Association for the Advancement of Science.

Light-driven dinitrogen reduction catalyzed by a CdS:nitrogenase MoFe protein biohybrid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, K. A.; Harris, D. F.; Wilker, M. B.

The splitting of dinitrogen (N2) and reduction to ammonia (NH3) is a kinetically complex and energetically challenging multistep reaction. In the Haber-Bosch process, N2 reduction is accomplished at high temperature and pressure, whereas N2 fixation by the enzyme nitrogenase occurs under ambient conditions using chemical energy from adenosine 5'-triphosphate (ATP) hydrolysis. We show that cadmium sulfide (CdS) nanocrystals can be used to photosensitize the nitrogenase molybdenum-iron (MoFe) protein, where light harvesting replaces ATP hydrolysis to drive the enzymatic reduction of N2 into NH3. The turnover rate was 75 per minute, 63% of the ATP-coupled reaction rate for the nitrogenase complexmore » under optimal conditions. Inhibitors of nitrogenase (i.e., acetylene, carbon monoxide, and dihydrogen) suppressed N2 reduction. The CdS:MoFe protein biohybrids provide a photochemical model for achieving light-driven N2 reduction to NH3.« less

Factors affecting the photoproduction of ammonia from dinitrogen and water by the cyanobacterium Anabaena sp. strain ATCC 33047.

PubMed

Ramos, J L; Guerrero, M G; Losada, M

1987-04-01

Synthesis of ammonia from dinitrogen and water by suspensions of Anabaena sp. Strain ATCC 33047 treated with the glutamine synthetase inhibitor L-methionine-D,L-sulfoximine is strictly dependent on light. Under otherwise optimal conditions, the yield of ammonia production is influenced by irradiance, as well as by the density, depth, and turbulence of the cell suspension. The interaction among these factors seems to determine the actual amount of light available to each single cell or filament in the suspension for the photoproduction process. Under convenient illumination, the limiting factor in the synthesis of ammonia seems to be the cellular nitrogenase activity level, but under limiting light conditions the limiting factor could, however, be the assimilatory power required for nitrogen fixation. Photosynthetic ammonia production from atmospheric nitrogen and water can operate with an efficiency of ca. 10% of its theoretical maximum, representing a remarkable process for the conversion of light energy into chemical energy.

The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium.

PubMed

Hong, Haizheng; Shen, Rong; Zhang, Futing; Wen, Zuozhu; Chang, Siwei; Lin, Wenfang; Kranz, Sven A; Luo, Ya-Wei; Kao, Shuh-Ji; Morel, François M M; Shi, Dalin

2017-05-05

Acidification of seawater caused by anthropogenic carbon dioxide (CO 2 ) is anticipated to influence the growth of dinitrogen (N 2 )-fixing phytoplankton, which contribute a large fraction of primary production in the tropical and subtropical ocean. We found that growth and N 2 -fixation of the ubiquitous cyanobacterium Trichodesmium decreased under acidified conditions, notwithstanding a beneficial effect of high CO 2 Acidification resulted in low cytosolic pH and reduced N 2 -fixation rates despite elevated nitrogenase concentrations. Low cytosolic pH required increased proton pumping across the thylakoid membrane and elevated adenosine triphosphate production. These requirements were not satisfied under field or experimental iron-limiting conditions, which greatly amplified the negative effect of acidification. Copyright © 2017, American Association for the Advancement of Science.

Efficient Nitrogen Fixation via a Redox-Flexible Single-Iron Site with Reverse-Dative Iron → Boron σ Bonding.

PubMed

Lu, Jun-Bo; Ma, Xue-Lu; Wang, Jia-Qi; Liu, Jin-Cheng; Xiao, Hai; Li, Jun

2018-05-10

Model systems of the FeMo cofactor of nitrogenase have been explored extensively in catalysis to gain insights into their ability for nitrogen fixation that is of vital importance to the human society. Here we investigate the trigonal pyramidal borane-ligand Fe complex by first-principles calculations, and find that the variation of oxidation state of Fe along the reaction path correlates with that of the reverse-dative Fe → B bonding. The redox-flexibility of the reverse-dative Fe → B bonding helps to provide an electron reservoir that buffers and stabilizes the evolution of Fe oxidation state, which is essential for forming the key intermediates of N 2 activation. Our work provides insights for understanding and optimizing homogeneous and surface single-atom catalysts with reverse-dative donating ligands for efficient dinitrogen fixation. The extension of this kind of molecular catalytic active center to heterogeneous catalysts with surface single-clusters is also discussed.

Biome-scale nitrogen fixation strategies selected by climatic constraints on nitrogen cycle.

PubMed

Sheffer, Efrat; Batterman, Sarah A; Levin, Simon A; Hedin, Lars O

2015-11-23

Dinitrogen fixation by plants (in symbiosis with root bacteria) is a major source of new nitrogen for land ecosystems(1). A long-standing puzzle(2) is that trees capable of nitrogen fixation are abundant in nitrogen-rich tropical forests, but absent or restricted to early successional stages in nitrogen-poor extra-tropical forests. This biome-scale pattern presents an evolutionary paradox(3), given that the physiological cost(4) of nitrogen fixation predicts the opposite pattern: fixers should be out-competed by non-fixers in nitrogen-rich conditions, but competitively superior in nitrogen-poor soils. Here we evaluate whether this paradox can be explained by the existence of different fixation strategies in tropical versus extra-tropical trees: facultative fixers (capable of downregulating fixation(5,6) by sanctioning mutualistic bacteria(7)) are common in the tropics, whereas obligate fixers (less able to downregulate fixation) dominate at higher latitudes. Using a game-theoretic approach, we assess the ecological and evolutionary conditions under which these fixation strategies emerge, and examine their dependence on climate-driven differences in the nitrogen cycle. We show that in the tropics, transient soil nitrogen deficits following disturbance and rapid tree growth favour a facultative strategy and the coexistence of fixers and non-fixers. In contrast, sustained nitrogen deficits following disturbance in extra-tropical forests favour an obligate fixation strategy, and cause fixers to be excluded in late successional stages. We conclude that biome-scale differences in the abundance of nitrogen fixers can be explained by the interaction between individual plant strategies and climatic constraints on the nitrogen cycle over evolutionary time.

Oscillating behavior of carbohydrate granule formation and dinitrogen fixation in the cyanobacterium Cyanothece sp. strain ATCC 51142

NASA Technical Reports Server (NTRS)

Schneegurt, M. A.; Sherman, D. M.; Nayar, S.; Sherman, L. A.; Mitchell, C. A. (Principal Investigator)

1994-01-01

It has been shown that some aerobic, unicellular, diazotrophic cyanobacteria temporally separate photosynthetic O2 evolution and oxygen-sensitive N2 fixation. Cyanothece sp. ATCC strain 51142 is an aerobic, unicellular, diazotrophic cyanobacterium that fixes N2 during discrete periods of its cell cycle. When the bacteria are maintained under diurnal light-dark cycles, N2 fixation occurs in the dark. Similar cycling is observed in continuous light, implicating a circadian rhythm. Under N2-fixing conditions, large inclusion granules form between the thylakoid membranes. Maximum granulation, as observed by electron microscopy, occurs before the onset of N2 fixation, and the granules decrease in number during the period of N2 fixation. The granules can be purified from cell homogenates by differential centrifugation. Biochemical analyses of the granules indicate that these structures are primarily carbohydrate, with some protein. Further analyses of the carbohydrate have shown that it is a glucose polymer with some characteristics of glycogen. It is proposed that N2 fixation is driven by energy and reducing power stored in these inclusion granules. Cyanothece sp. strain ATCC 51142 represents an excellent experimental organism for the study of the protective mechanisms of nitrogenase, metabolic events in cyanobacteria under normal and stress conditions, the partitioning of resources between growth and storage, and biological rhythms.

Nitrogen Cycling in Seagrass Beds Dominated by Thalassia testudinum and Halodule wrightii: the Role of Nitrogen Fixation and Ammonium Oxidation in Regulating Ammonium Availability

NASA Astrophysics Data System (ADS)

Capps, R.; Caffrey, J. M.; Hester, C.

2016-02-01

Seagrass meadows provide key ecosystem services including nursery and foraging grounds, storm and erosion buffers, biodiversity enhancers and global carbon and nutrient cycling. Nitrogen concentrations are often very low in coastal waters and sediments, which may limit primary productivity. Biological nitrogen fixation is a microbial process that converts dinitrogen to ammonium, which is readily taken up by seagrasses. In the oxygenated rhizospheres, diazotrophs provide the plant with ammonium and use root exudates as an energy source. Nitrogen fixation rates and nutrient concentrations differ between seagrass species and substrate types. Thalassia testudinum has a higher biomass and is a climax species than Halodule wrightii, which is a pioneer species. Nitrogen fixation rates are relatively consistent in Thalassia testudinum dominated sediments. However, it is relatively variable in sediments occupied by Halodule wrightii. Nitrogen fixation rates are higher in bare substrate compared to areas with Thalassia testudinum, which may be due to T. testudinum's greater efficiency in nutrient retention because it is a climax species. We hypothesize that seasonal shifts in nitrogen fixation will coincide with seasonal shifts in seagrass biomass due to higher nutrient requirements during peak growth and lower requirements during senescence and dormancy. The ratio of porewater ammonium to phosphate suggests that seagrass growth may be nitrogen limited as does nitrogen demand, estimated from gross primary productivity. Significant rates of ammonium oxidation in both surface and rhizosphere sediments contribute to this imbalance. Thus, nitrogen fixation may be critical in supporting plant growth.

Nitrogen fixation in denitrified marine waters.

PubMed

Fernandez, Camila; Farías, Laura; Ulloa, Osvaldo

2011-01-01

Nitrogen fixation is an essential process that biologically transforms atmospheric dinitrogen gas to ammonia, therefore compensating for nitrogen losses occurring via denitrification and anammox. Currently, inputs and losses of nitrogen to the ocean resulting from these processes are thought to be spatially separated: nitrogen fixation takes place primarily in open ocean environments (mainly through diazotrophic cyanobacteria), whereas nitrogen losses occur in oxygen-depleted intermediate waters and sediments (mostly via denitrifying and anammox bacteria). Here we report on rates of nitrogen fixation obtained during two oceanographic cruises in 2005 and 2007 in the eastern tropical South Pacific (ETSP), a region characterized by the presence of coastal upwelling and a major permanent oxygen minimum zone (OMZ). Our results show significant rates of nitrogen fixation in the water column; however, integrated rates from the surface down to 120 m varied by ∼30 fold between cruises (7.5±4.6 versus 190±82.3 µmol m(-2) d(-1)). Moreover, rates were measured down to 400 m depth in 2007, indicating that the contribution to the integrated rates of the subsurface oxygen-deficient layer was ∼5 times higher (574±294 µmol m(-2) d(-1)) than the oxic euphotic layer (48±68 µmol m(-2) d(-1)). Concurrent molecular measurements detected the dinitrogenase reductase gene nifH in surface and subsurface waters. Phylogenetic analysis of the nifH sequences showed the presence of a diverse diazotrophic community at the time of the highest measured nitrogen fixation rates. Our results thus demonstrate the occurrence of nitrogen fixation in nutrient-rich coastal upwelling systems and, importantly, within the underlying OMZ. They also suggest that nitrogen fixation is a widespread process that can sporadically provide a supplementary source of fixed nitrogen in these regions.

GROWTH, PRIMARY PRODUCTIVITY, AND NITROGEN FIXATION POTENTIAL OF NODULARIA SPP. (CYANOPHYCEAE) IN WATER FROM A SUBTROPICAL ESTUARY IN THE UNITED STATES .

PubMed

Moisander, Pia H; Paerl, Hans W

2000-08-26

Nodularia is a halotolerant, filamentous, dinitrogen-fixing cyanobacterium that forms massive blooms in some coastal oceans, estuaries, and saline lakes worldwide. Although the genus is globally distributed, its blooms are sporadic and appear to be confined to certain water bodies. Blooms are frequently associated with phosphorus enrichment; therefore Nodularia may benefit from increased anthropogenic nutrient loading to coastal waters. We studied the potential for Nodularia to grow in the nitrogen-limited Neuse River Estuary (North Carolina, U.S.A.) with laboratory growth experiments in Neuse River Estuary water and by examining physico-chemical data from the estuary. Analysis of nutrients (nitrogen and phosphorus), salinity, and temperature data from the Neuse River Estuary between 1994 and 1998 revealed that suitable conditions for Nodularia prevailed during the summer of each of these years for time spans ranging from 1.5 to 5 months. Growth of two laboratory strains in Neuse River Estuary water was as fast or slightly slower than in artificial growth medium, as long as the culture inoculum had phosphorus reserves. Phosphorus addition did not stimulate growth of already phosphorus-sufficient inocula. Phosphorus starvation of the inoculum before the experiment decreased growth rates in the estuarine water unless additional phosphorus was supplied. Although phosphorus addition had a stimulatory effect on dinitrogen fixation and productivity, the effect differed for the two Nodularia strains. Results suggest that growth of Nodularia in North Carolinian estuaries is possible, and that such growth would be phosphorus-limited at times. Phosphorus availability may determine the times and locations for potential establishment of Nodularia in this and similar estuarine ecosystems.

Synthesis of hydrogen cyanide under simulated hydrothermal conditions

NASA Astrophysics Data System (ADS)

Pinedo-González, Paulina

Nitrogen is a fundamental element for life, where is present in structural (e.g., proteins), catalytic (e.g., enzymes and ribozymes), energy transfer (e.g., ATP) and information storage (RNA and DNA) biomolecules. Atmospheric and planetary models suggest that nitrogen was abundant in the early atmospheres of Earth as dinitrogen (N2 ), an inert gas under normal atmospheric conditions. To be available for prebiotic synthesis it must be converted into hydrogen cyanide (HCN), ammonia (NH3 ) and/or nitric oxide (NO), in a process referred to as nitrogen fixation. Due to the strength of the triple bond in N2 , nitrogen fixation, while thermodynamically favored is kinetically restricted. In a reducing atmosphere dominated by CH4 -N2 , thunderstorm lightning efficiently produces HCN and NH3 (Stribling and Miller, 1987). Nevertheless, photochemical and geochemical constraints strongly suggest that the early atmosphere was weakly reducing, dominated by CO2 and N2 with traces of CH4 , CO, and H2 (Kasting, 1993). Under these conditions, HCN is no longer synthesized in the lightning channel and instead NO is formed (Navarro-Gonźlez, et al., 2001). In volcanic plumes, where magmatic gases a were more reducing than in the atmosphere, NO can also be formed by the lava heat (Mather et al., 2004) or volcanic lightning (Navarro-Gonźlez et al., 1998). Surprisingly, dinitrogen can be a reduced to NH3 in hydrothermal systems (Brandes et al., 1998), but the formation of HCN and its derivates were not investigated. The present work explores the possibility of the formation of HCN as well as other nitrile derivatives catalyzed by mineral surfaces in hydrothermal vents. To simulate a hydrothermal atmosphere, the experiments were carried out in a stainless steel Parr R minireactor with a 0.1 M NH4 HCO3 solution (200 ml) with or without a mineral surface exposed at 1 bar at temperatures ranging from 100 to 375° C. Different mineral matrices are been investigated. Our preliminary results have been conducted with pyrite and quantified by headspace-gas chromatography-mass spectrometry. These results indicate that catalysis induced by the mineral surface under hydrothermal conditions does not stop with the production of HCN, but the reaction continues leading to more complex nitriles. The experiments also reveal a clear trend between time and the production of more complex molecules, which are measurable by the chromatographic method. Brandes, J.A., Boctor, N.Z., Cody, G.D., Cooper, B. A., Hazen, R. M. and Yoder Jr, H.S. (1998). Abiotic nitrogen reduction on the early Earth. Nature 395, 365-367. Kasting J.F. (1993) Earth's early atmosphere. Science 259, 920-926. Mather, T.A., Pyle, D.M., and Allen, A.G. (2004) Volcanic source of fixed nitrogen in the early Earth's atmosphere. Geology 32, 905-908. Navarro-Gonźlez, R., Molina, M.J. and. Molina, L.T. (1998) Nitrogen fixation by volcanic a lightning in the early Earth. Geophys. Res. Lett. 25, 3123-3126. Navarro-Gonźlez, R., McKay, C.P. and Nna Mvondo, D. ( 2001) A possible nitrogen crisis for a Archean life due to reduced nitrogen fixation by lightning. Nature 412, 61-64. Stribling, R., and Miller, S.L. (1987) Energy yields for the hydrogen cyanide and formaldehyde synthesis: the HCN and amino acid concentrations in the primitive ocean. Origins Life 17, 261-273.

Preface: The Oligotrophy to the UlTra-oligotrophy PACific Experiment (OUTPACE cruise, 18 February to 3 April 2015)

NASA Astrophysics Data System (ADS)

Moutin, Thierry; Michelangelo Doglioli, Andrea; de Verneil, Alain; Bonnet, Sophie

2017-07-01

The overall goal of OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) was to obtain a successful representation of the interactions between planktonic organisms and the cycle of biogenic elements in the western tropical South Pacific Ocean across trophic and N2 fixation gradients. Within the context of climate change, it is necessary to better quantify the ability of the oligotrophic ocean to sequester carbon through biological processes. OUTPACE was organized around three main objectives, which were (1) to perform a zonal characterization of the biogeochemistry and biological diversity of the western tropical South Pacific during austral summer conditions, (2) to study the production and fate of organic matter (including carbon export) in three contrasting trophic regimes (increasing oligotrophy) with a particular emphasis on the role of dinitrogen fixation, and (3) to obtain a representation of the main biogeochemical fluxes and dynamics of the planktonic trophic network. The international OUTPACE cruise took place between 18 February and 3 April 2015 aboard the RV L'Atalante and involved 60 scientists (30 onboard). The west-east transect covered ˜ 4000 km from the western part of the Melanesian archipelago (New Caledonia) to the western boundary of the South Pacific gyre (French Polynesia). Following an adaptive strategy, the transect initially designed along the 19° S parallel was adapted along-route to incorporate information coming from satellite measurements of sea surface temperature, chlorophyll a concentration, currents, and diazotroph quantification. After providing a general context and describing previous work done in this area, this introductory paper elucidates the objectives of OUTPACE, the implementation plan of the cruise and water mass and climatological characteristics and concludes with a general overview of the other papers that will be published in this special issue.

Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation.

PubMed

Mohr, Wiebke; Vagner, Tomas; Kuypers, Marcel M M; Ackermann, Martin; Laroche, Julie

2013-01-01

Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N2 fixation and photosynthesis commonly observed. However, N2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell.

Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation

PubMed Central

Mohr, Wiebke; Vagner, Tomas; Kuypers, Marcel M. M.; Ackermann, Martin; LaRoche, Julie

2013-01-01

Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N2 fixation and photosynthesis commonly observed. However, N2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell. PMID:23805199

Bond Order and Chemical Properties of BF, CO, and N[subscript 2

ERIC Educational Resources Information Center

Martinie, Ryan J.; Bultema, Jarred J.; Vander Wal, Mark N.; Burkhart, Brandon J.; Vander Griend, Douglas A.; DeKock, Roger L.

2011-01-01

The traditional chemical approaches, Lewis electron dot structures and molecular orbital theory, predict the relative bond orders of boron monofluoride, carbon monoxide, and dinitrogen to be BF less than CO less than N[subscript 2]. This is quantified by quantum mechanical, theoretical studies that show the bond orders to be approximately 1.4,…

Benthic N2 fixation in coral reefs and the potential effects of human-induced environmental change

PubMed Central

Cardini, Ulisse; Bednarz, Vanessa N; Foster, Rachel A; Wild, Christian

2014-01-01

Tropical coral reefs are among the most productive and diverse ecosystems, despite being surrounded by ocean waters where nutrients are in short supply. Benthic dinitrogen (N2) fixation is a significant internal source of “new” nitrogen (N) in reef ecosystems, but related information appears to be sparse. Here, we review the current state (and gaps) of knowledge on N2 fixation associated with coral reef organisms and their ecosystems. By summarizing the existing literature, we show that benthic N2 fixation is an omnipresent process in tropical reef environments. Highest N2 fixation rates are detected in reef-associated cyanobacterial mats and sea grass meadows, clearly showing the significance of these functional groups, if present, to the input of new N in reef ecosystems. Nonetheless, key benthic organisms such as hard corals also importantly contribute to benthic N2 fixation in the reef. Given the usually high coral coverage of healthy reef systems, these results indicate that benthic symbiotic associations may be more important than previously thought. In fact, mutualisms between carbon (C) and N2 fixers have likely evolved that may enable reef communities to mitigate N limitation. We then explore the potential effects of the increasing human interferences on the process of benthic reef N2 fixation via changes in diazotrophic populations, enzymatic activities, or availability of benthic substrates favorable to these microorganisms. Current knowledge indicates positive effects of ocean acidification, warming, and deoxygenation and negative effects of increased ultraviolet radiation on the amount of N fixed in coral reefs. Eutrophication may either boost or suppress N2 fixation, depending on the nutrient becoming limiting. As N2 fixation appears to play a fundamental role in nutrient-limited reef ecosystems, these assumptions need to be expanded and confirmed by future research efforts addressing the knowledge gaps identified in this review. PMID:24967086

Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Benavides, Mar; Shoemaker, Katyanne M.; Moisander, Pia H.; Niggemann, Jutta; Dittmar, Thorsten; Duhamel, Solange; Grosso, Olivier; Pujo-Pay, Mireille; Hélias-Nunige, Sandra; Fumenia, Alain; Bonnet, Sophie

2018-05-01

The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L-1 d-1) but consistently detected across all depths and stations, representing ˜ 6-88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.

Dinitrogen and Cyanide Fixation by Methane Seep Microorganisms Revealed by FISH- SIMS And Implications for AOM Productivity and Nitrogenase Evolution

NASA Astrophysics Data System (ADS)

Dekas, A.; Orphan, V.

2008-12-01

The anaerobic oxidation of methane (AOM), mediated by methane oxidizing archaea (ANME) and sulfate reducing bacterial symbionts (SRB), minimizes the flux of methane from marine sediment to the overlying water column. Understanding the factors determining AOM productivity, and particularly the rates of methane catabolism and anabolism, is of interest to both modern and ancient investigations of climate and bulk carbon isotopic change. It has been hypothesized that nitrogen availability in methane seeps is temporally variable, and that the seep biomass may be at least partially nitrogen limited. The recent finding of nif genes, those necessary for the production of nitrogenase, in enrichments of ANME and SRB consortia suggested that the organisms mediating AOM have the potential to fix dinitrogen. In the present study we incubated methane seep sediment with nitrogen-deplete artificial marine media and a headspace of methane (CH4) and either 15N-labeled dinitrogen (15N2), cyanide (C15N-), or ammonia (15NH3) in order to (1) test the ability of these currently unculturable microorganisms to fix nitrogen and other triple bonded substrates, (2) investigate which AOM partner was responsible for the fixation, (3) compare growth rates on different nitrogen sources, and (4) characterize the phylogeny of these methane seep-associated nitrogenases. Fluorescence in situ hybridization coupled to nano-scale Secondary Ion Mass Spectroscopy imaging (FISH-SIMS) revealed incorporation of 15N into ANME and SRB biomass of up to 0.06 15N fractional abundance in the 15N2 incubation, and up to 0.02 in the C15N- incubation, after 6 and 4 months, respectively. This represents a nearly ten-fold enrichment of 15N compared to the measured natural 15N fractional abundance (0.0036). The NanoSIMS ion images of ANME/SRB aggregates from 15N2 incubations show evidence for 15N enrichment in both partners with the highest incorporation of 15N within the methanotrophic ANME cells. Cyanide incubations revealed a more heterogeneous pattern of 15N distribution, with localized zones of enrichment within both the SRB and the ANME biomass. From these findings, two alternative explanations are considered: (1) both partners are capable of nitrogenase production, but express the nif genes under different conditions, and (2) the distribution of fixed nitrogen within the ANME and SRB is driven by intimate metabolic coupling and resource sharing, with only one partner serving as the primary diazotroph. In incubations with 15NH3, the AOM biomass 15N fractional abundance was nearly 1.0 after 6 months, demonstrating a much faster growth rate when NH3 rather than N2 or CN- is the nitrogen source, consistent with what is observed in other diazotrophic organisms. Nitrogenase genes recovered from these incubations primarily were associated with the nifH group III clade, but the majority were diverged from known nifH sequences. This suggests that novel nitrogenases are responsible for the N2 fixation observed, and the poor substrate specificity and the potential use as a CN- detoxification mechanism could imply that they are similar to the first nitrogenases. The finding that nitrogen fixation occurs within these potentially ancient organisms therefore may provide a window for examining the history and functional diversity of nitrogenase, and the variable growth rates depending on nitrogen substrate could have implications for AOM productivity through time.

Assessing planetary and regional nitrogen boundaries related to food security and adverse environmental impacts

NASA Astrophysics Data System (ADS)

de Vries, Wim; Kros, Hans; Kroeze, Carolien; Seitzinger, Sybil

2014-05-01

In this presentation, we first discuss the concept of -, governance interest in- and criticism on planetary boundaries, specifically with respect to the nitrogen (N) cycle. We then systematically evaluate the criticism and argue that planetary N boundaries need to include both the benefits and adverse impacts of reactive N (Nr) and the spatial variability of Nr impacts, in terms of shortage and surplus, being main arguments for not deriving such boundaries. Next, we present an holistic approach for an updated planetary N boundary by considering the need to: (i) avoid adverse impacts of elevated Nr emissions to water, air and soils, and (ii) feed the world population in an adequate way. The derivation of a planetary N boundary, in terms of anthropogenic fixation of di-nitrogen (N2) by growing legumes and production of N fertilizer, is illustrated by (i) identification of multiple threat N indicators and setting critical limits for them, (ii) back calculating critical N losses from critical limits for N indicators, while accounting for the spatial variability of indicators and their exceedance and (iii) back calculating critical N fixation rates from critical N losses. The derivation of the needed planetary N fixation is assessed from the global population, the recommended dietary N consumption per capita and the N use efficiency in the complete chain from N fixation to N consumption. Results of example applications show that the previously suggested planetary N boundary of 25% of the current value is too low in view of needed N fixation and also unnecessary in view of most environmental impacts. We also illustrate the impacts of changes in the N use efficiency on planetary boundaries in terms of critical N fixation rates.

Coordinated regulation of growth, activity and transcription in natural populations of the unicellular nitrogen-fixing cyanobacterium Crocosphaera.

PubMed

Wilson, Samuel T; Aylward, Frank O; Ribalet, Francois; Barone, Benedetto; Casey, John R; Connell, Paige E; Eppley, John M; Ferrón, Sara; Fitzsimmons, Jessica N; Hayes, Christopher T; Romano, Anna E; Turk-Kubo, Kendra A; Vislova, Alice; Armbrust, E Virginia; Caron, David A; Church, Matthew J; Zehr, Jonathan P; Karl, David M; DeLong, Edward F

2017-07-31

The temporal dynamics of phytoplankton growth and activity have large impacts on fluxes of matter and energy, yet obtaining in situ metabolic measurements of sufficient resolution for even dominant microorganisms remains a considerable challenge. We performed Lagrangian diel sampling with synoptic measurements of population abundances, dinitrogen (N 2 ) fixation, mortality, productivity, export and transcription in a bloom of Crocosphaera over eight days in the North Pacific Subtropical Gyre (NPSG). Quantitative transcriptomic analyses revealed clear diel oscillations in transcript abundances for 34% of Crocosphaera genes identified, reflecting a systematic progression of gene expression in diverse metabolic pathways. Significant time-lagged correspondence was evident between nifH transcript abundance and maximal N 2 fixation, as well as sepF transcript abundance and cell division, demonstrating the utility of transcriptomics to predict the occurrence and timing of physiological and biogeochemical processes in natural populations. Indirect estimates of carbon fixation by Crocosphaera were equivalent to 11% of net community production, suggesting that under bloom conditions this diazotroph has a considerable impact on the wider carbon cycle. Our cross-scale synthesis of molecular, population and community-wide data underscores the tightly coordinated in situ metabolism of the keystone N 2 -fixing cyanobacterium Crocosphaera, as well as the broader ecosystem-wide implications of its activities.

Nitrogen fixation and hydrogen metabolism in cyanobacteria.

PubMed

Bothe, Hermann; Schmitz, Oliver; Yates, M Geoffrey; Newton, William E

2010-12-01

This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N(2) fixation and/or H(2) formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H(2) as a source of combustible energy. To enhance the rates of H(2) production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H(2) formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.

Diversity and Activity of Diazotrophs in Great Barrier Reef Surface Waters.

PubMed

Messer, Lauren F; Brown, Mark V; Furnas, Miles J; Carney, Richard L; McKinnon, A D; Seymour, Justin R

2017-01-01

Discrepancies between bioavailable nitrogen (N) concentrations and phytoplankton growth rates in the oligotrophic waters of the Great Barrier Reef (GBR) suggest that undetermined N sources must play a significant role in supporting primary productivity. One such source could be biological dinitrogen (N 2 ) fixation through the activity of "diazotrophic" bacterioplankton. Here, we investigated N 2 fixation and diazotroph community composition over 10° S of latitude within GBR surface waters. Qualitative N 2 fixation rates were found to be variable across the GBR but were relatively high in coastal, inner and outer GBR waters, reaching 68 nmol L -1 d -1 . Diazotroph assemblages, identified by amplicon sequencing of the nifH gene, were dominated by the cyanobacterium Trichodesmium erythraeum , γ-proteobacteria from the Gamma A clade, and δ-proteobacterial phylotypes related to sulfate-reducing genera. However, diazotroph communities exhibited significant spatial heterogeneity, correlated with shifts in dissolved inorganic nutrient concentrations. Specifically, heterotrophic diazotrophs generally increased in relative abundance with increasing concentrations of phosphate and N, while Trichodesmium was proportionally more abundant when concentrations of these nutrients were low. This study provides the first in-depth characterization of diazotroph community composition and N 2 fixation dynamics within the oligotrophic, N-limited surface waters of the GBR. Our observations highlight the need to re-evaluate N cycling dynamics within oligotrophic coral reef systems, to include diverse N 2 fixing assemblages as a potentially significant source of dissolved N within the water column.

Environmental forcing of nitrogen fixation in the eastern tropical and sub-tropical North Atlantic Ocean.

PubMed

Rijkenberg, Micha J A; Langlois, Rebecca J; Mills, Matthew M; Patey, Matthew D; Hill, Polly G; Nielsdóttir, Maria C; Compton, Tanya J; Laroche, Julie; Achterberg, Eric P

2011-01-01

During the winter of 2006 we measured nifH gene abundances, dinitrogen (N(2)) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 10(6) L(-1)nifH gene copies, unicellular group A cyanobacteria with up to 10(5) L(-1)nifH gene copies and gamma A proteobacteria with up to 10(4) L(-1)nifH gene copies. N(2) fixation rates were low and ranged between 0.032-1.28 nmol N L(-1) d(-1) with a mean of 0.30 ± 0.29 nmol N L(-1) d(-1) (1σ, n = 65). CO(2)-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2 ± 3.2 in surface waters. Nevertheless, N(2) fixation rates contributed only 0.55 ± 0.87% (range 0.03-5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N(2) fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N(2) fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the consequences of climate warming for N(2) fixation in the North Atlantic.

Wet season cyanobacterial N enrichment highly correlated with species richness and Nostoc in the northern Australian savannah

NASA Astrophysics Data System (ADS)

Williams, Wendy; Büdel, Burkhard; Williams, Stephen

2018-04-01

The Boodjamulla National Park research station is situated in the north-western Queensland dry savannah, where the climate is dominated by summer monsoons and virtually dry winters. Under shrub canopies and in between the tussock grasses cyanobacterial crusts almost entirely cover the flood plain soil surfaces. Seasonality drives N fixation, and in the savannah this has a large impact on both plant and soil function. Many cyanobacteria fix dinitrogen that is liberated into the soil in both inorganic and organic N forms. We examined cyanobacterial species richness and bioavailable N spanning 7 months of a typical wet season. Over the wet season cyanobacterial richness ranged from 6 to 19 species. N-fixing Scytonema accounted for seasonal averages between 51 and 93 % of the biocrust. Cyanobacterial richness was highly correlated with N fixation and bioavailable N in 0-1 cm. Key N-fixing species such as Nostoc, Symploca and Gloeocapsa significantly enriched soil N although Nostoc was the most influential. Total seasonal N fixation by cyanobacteria demonstrated the variability in productivity according to the number of wet days as well as the follow-on days where the soil retained adequate moisture. Based on total active days per month we estimated that N soil enrichment via cyanobacteria would be ˜ 5.2 kg ha-1 annually which is comparable to global averages. This is a substantial contribution to the nutrient-deficient savannah soils that are almost entirely reliant on the wet season for microbial turnover of organic matter. Such well-defined seasonal trends and synchronisation in cyanobacterial species richness, N fixation, bioavailable N and C fixation (Büdel et al., 2018) provide important contributions to multifunctional microprocesses and soil fertility.

Volcano fixes nitrogen into plant-available forms

USGS Publications Warehouse

Huebert, B.; Vitousek, P.; Sutton, J.; Elias, T.; Heath, J.; Coeppicus, S.; Howell, S.; Blomquist, B.

1999-01-01

Hawaiian montane ecosystems developing on recent tephra deposits contain more fixed nitrogen than conventional sources can explain. Heath and Huebert (1999) demonstrated that cloud water interception is the mechanism by which this extra nitrogen is deposited, but could not identify its source. We show here that atmospheric dinitrogen is fixed at the surface of active lava flows, producing concentrations of NO which are higher than those found in most urban rush hour air pollution. Over a period of hours this NO is blown away from the island and oxidized to nitrate. Interruptions in the trade wind flow can return this nitrate to the island to be deposited in cloud water. Thus, fixation on active lava flows is able to provide nitrogen to developing ecosystems on flows emplaced earlier.

Catalytic reduction of dinitrogen to ammonia at a single molybdenum center

PubMed Central

Weare, Walter W.; Dai, Xuliang; Byrnes, Matthew J.; Chin, Jia Min; Schrock, Richard R.; Müller, Peter

2006-01-01

Since our discovery of the catalytic reduction of dinitrogen to ammonia at a single molybdenum center, we have embarked on a variety of studies designed to further understand this complex reaction cycle. These include studies of both individual reaction steps and of ligand variations. An important step in the reaction sequence is exchange of ammonia for dinitrogen in neutral molybdenum(III) compounds. We have found that this exchange reaction is first order in dinitrogen and relatively fast (complete in <1 h) at 1 atm of dinitrogen. Variations of the terphenyl substituents in the triamidoamine ligand demonstrate that the original ligand is not unique in its ability to yield successful catalysts. However, complexes that contain sterically less demanding ligands fail to catalyze formation of ammonia from dinitrogen; it is proposed as a consequence of a base-catalyzed decomposition of a diazenido (MoNNH) intermediate. PMID:17085586

Significance of Herbaspirillum seropedicae inoculation and/or straw amendment on growth and dinitrogen fixation of wheat using 15N-dilution method.

PubMed

el-Komy, H M; Saad, O A; Hetta, A M

2003-01-01

The effect of Herbaspirillum seropedicae inoculation and/or maize straw (0, 5 and 10 Mg/hm2) amendment on the growth and N2 fixation of wheat was determined in pot experiments using 15N-dilution method. Inoculation resulted in accumulation of fixed nitrogen, and % N from atmosphere being 24.6 and 26.5% in wheat shoot and grain, respectively. Straw amendment reduced % Natm to 16.1 and 20.2% at high straw level (10 Mg/hm2). Rational nitrogen fertilization (180 kg N/hm2) completely inhibited N2 fixation by H. seropedicae inoculation. Bacterial inoculation increased dry shoot and grain yield up to 23 and 31%, respectively. The highest levels of shoot and grain dry mass (46.5 and 42.4%) were obtained by N-fertilization in both inoculated and uninoculated plants. Total shoot and grain N-yield increased irrespective of organic matter amendment by inoculation up to 9 and 25%, respectively. N-fertilized plants recorded a maximum increase in N-yield (57 and 51%). H. seropedicae was reisolated from inoculated wheat histosphere after harvesting (90 d from sowing). Neither organic matter nor mineral nitrogen applications had any marked effect on bacterial total counts colonizing wheat histosphere. Moreover, no symptoms of mottled stripe disease were observed on leaves and stems of inoculated plants.

Application of stable‐isotope labelling techniques for the detection of active diazotrophs

PubMed Central

Angel, Roey; Panhölzl, Christopher; Gabriel, Raphael; Herbold, Craig; Wanek, Wolfgang; Richter, Andreas; Eichorst, Stephanie A.

2017-01-01

Summary Investigating active participants in the fixation of dinitrogen gas is vital as N is often a limiting factor for primary production. Biological nitrogen fixation is performed by a diverse guild of bacteria and archaea (diazotrophs), which can be free‐living or symbionts. Free‐living diazotrophs are widely distributed in the environment, yet our knowledge about their identity and ecophysiology is still limited. A major challenge in investigating this guild is inferring activity from genetic data as this process is highly regulated. To address this challenge, we evaluated and improved several 15N‐based methods for detecting N2 fixation activity (with a focus on soil samples) and studying active diazotrophs. We compared the acetylene reduction assay and the 15N2 tracer method and demonstrated that the latter is more sensitive in samples with low activity. Additionally, tracing 15N into microbial RNA provides much higher sensitivity compared to bulk soil analysis. Active soil diazotrophs were identified with a 15N‐RNA‐SIP approach optimized for environmental samples and benchmarked to 15N‐DNA‐SIP. Lastly, we investigated the feasibility of using SIP‐Raman microspectroscopy for detecting 15N‐labelled cells. Taken together, these tools allow identifying and investigating active free‐living diazotrophs in a highly sensitive manner in diverse environments, from bulk to the single‐cell level. PMID:29027346

49 CFR 173.336 - Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 2 2013-10-01 2013-10-01 false Nitrogen dioxide, liquefied, or dinitrogen....336 Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied. (a) Nitrogen dioxide, liquefied... with nitrogen dioxide. Each valve opening must be closed by a solid metal plug with tapered thread...

49 CFR 173.336 - Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 2 2012-10-01 2012-10-01 false Nitrogen dioxide, liquefied, or dinitrogen....336 Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied. (a) Nitrogen dioxide, liquefied... with nitrogen dioxide. Each valve opening must be closed by a solid metal plug with tapered thread...

49 CFR 173.336 - Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 2 2010-10-01 2010-10-01 false Nitrogen dioxide, liquefied, or dinitrogen....336 Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied. (a) Nitrogen dioxide, liquefied... with nitrogen dioxide. Each valve opening must be closed by a solid metal plug with tapered thread...

High potential of nitrogen fixation in pristine, ombrotrophic bogs in Southern Patagonia

NASA Astrophysics Data System (ADS)

Knorr, Klaus-Holger; Horn, Marcus A.; Bahamonde Aguilar, Nelson A.; Borken, Werner

2015-04-01

Nitrogen (N) input in pristine peatlands occurs via natural input of inorganic N through atmospheric deposition or biological dinitrogen (N2) fixation. However, N2 fixation is to date mostly attributed to bacteria and algae associated to Sphagnum and its contribution to plant productivity and peat buildup has been often underestimated in previous studies. Based on net N storage, exceptionally low N deposition, and high abundance of vascular plants at pristine peatlands in Southern Patagonia, we hypothesized that there must be a high potential of non-symbiotic N2 fixation not limited to the occurrence of Sphagnum. To this end, we chose two ombrotrophic bogs with spots that are dominated either by Sphagnum or by vascular, cushion-forming plants and sampled peat from different depths for incubation with 15N2 to determine N2 fixation potentials. Moreover, we analyzed 15N2 fixation by a nodule-forming, endemic conifer inhabiting the peatlands. Results from 15N2 uptake were compared to the conventional approach to study N2 fixation by the acetylene reduction assay (ARA). Using 15N2 as a tracer, high non-symbiotic N2 fixation rates of 0.3-1.4 μmol N g-1 d-1 were found down to 50 cm under micro-oxic conditions (2 vol.%) in samples from both plots either covered by Sphagnum magellanicum or by vascular cushion plants. Peat N concentrations suggested a higher potential of non-symbiotic N2 fixation under cushion plants, likely because of the availability of easily decomposable organic compounds as substrates and oxic conditions in the rhizosphere. In the Sphagnum plots, high N2 fixation below 10 cm depth would rather reflect a potential fixation that may switch on during periods of low water levels when oxygen penetrates deeper into the peat. 15N natural abundance of live Sphagnum from 0-10 cm pointed to N uptake solely from atmospheric deposition and non-symbiotic N2 fixation. 15N signatures of peat from the cushion plant plots indicated additional N supply from N mineralization. Nitrogen fixation by the conifer Lepidothamnus fonkii was exceptionally high, reaching 3.1 μmol N g-1 d.w. d-1 detected in roots, stems, and green biomass. For L. fonkii, we could identify a specific association with Beijerinckiaceae as N2 fixing bacteria in the root nodules, whereas the rhizosphere peat was dominated by other diazotrophs. The ARA considerably underestimated N2 fixation and can thus not be recommended for peatland studies. Our findings suggest that non-symbiotic or associative N2 fixation overcomes N deficiency in different vegetation communities and has great significance for N cycling and peat accumulation in pristine peatlands.

Nitrogenase Reduction of Carbon-Containing Compounds

PubMed Central

Seefeldt, Lance C.; Yang, Zhi-Yong; Duval, Simon; Dean, Dennis R.

2013-01-01

Nitrogenase is an enzyme found in many bacteria and archaea that catalyzes biological dinitrogen fixation, the reduction of N2 to NH3, accounting for the major input of fixed nitrogen into the biogeochemical N cycle. In addition to reducing N2 and protons, nitrogenase can reduce a number of small, non-physiological substrates. Among these alternative substrates are included a wide array of carbon containing compounds. These compounds have provided unique insights into aspects of the nitrogenase mechanism. Recently, it was shown that carbon monoxide (CO) and carbon dioxide (CO2) can also be reduced by nitrogenase to yield hydrocarbons, opening new insights into the mechanism of small molecule activation and reduction by this complex enzyme as well as providing clues for the design of novel molecular catalysts. PMID:23597875

Growth Characteristics of an Estuarine Heterocystous Cyanobacterium

PubMed Central

Guimarães, Pablo; Yunes, João S.; Cretoiu, Mariana Silvia; Stal, Lucas J.

2017-01-01

A new estuarine filamentous heterocystous cyanobacterium was isolated from intertidal sediment of the Lagoa dos Patos estuary (Brazil). The isolate may represent a new genus related to Cylindrospermopsis. While the latter is planktonic, contains gas vesicles, and is toxic, the newly isolated strain is benthic and does not contain gas vesicles. It is not known whether the new strain is toxic. It grows equally well in freshwater, brackish and full salinity growth media, in the absence of inorganic or organic combined nitrogen, with a growth rate 0.6 d-1. Nitrogenase, the enzyme complex responsible for fixing dinitrogen, was most active during the initial growth phase and its activity was not different between the different salinities tested (freshwater, brackish, and full salinity seawater). Salinity shock also did not affect nitrogenase activity. The frequency of heterocysts was high, coinciding with high nitrogenase activity during the initial growth phase, but decreased subsequently. However, the frequency of heterocysts decreased considerably more at higher salinity, while no change in nitrogenase activity occurred, indicating a higher efficiency of dinitrogen fixation. Akinete frequency was low in the initial growth phase and higher in the late growth phase. Akinete frequency was much lower at high salinity, which might indicate better growth conditions or that akinete differentiation was under the same control as heterocyst differentiation. These trends have hitherto not been reported for heterocystous cyanobacteria but they seem to be well fitted for an estuarine life style. PMID:28670308

Global terrestrial carbon and nitrogen cycling insensitive to estimates of biological N fixation

NASA Astrophysics Data System (ADS)

Steinkamp, J.; Weber, B.; Werner, C.; Hickler, T.

2015-12-01

Dinitrogen (N2) is the most abundant molecule in the atmosphere and incorporated in other molecules an essential nutrient for life on earth. However, only few natural processes can initiate a reaction of N2. These natural processes are fire, lightning and biological nitrogen fixation (BNF) with BNF being the largest source. In the course of the last century humans have outperformed the natural processes of nitrogen fixation by the production of fertilizer. Industrial and other human emission of reactive nitrogen, as well as fire and lightning lead to a deposition of 63 Tg (N) per year. This is twice the amount of BNF estimated by the default setup of the dynamic global vegetation model LPJ-GUESS (30 Tg), which is a conservative approach. We use different methods and parameterizations for BNF in LPJ-GUESS: 1.) varying total annual amount; 2.) annual evenly distributed and daily calculated fixation rates; 3.) an improved dataset of BNF by cryptogamic covers (free-living N-fixers). With this setup BNF is ranging from 30 Tg to 60 Tg. We assess the impact of BNF on carbon storage and grand primary production (GPP) of the natural vegetation. These results are compared to and evaluated against available independent datasets. We do not see major differences in the productivity and carbon stocks with these BNF estimates, suggesting that natural vegetation is insensitive to BNF on a global scale and the vegetation can compensate for the different nitrogen availabilities. Current deposition of nitrogen compounds and internal cycling through mineralization and uptake is sufficient for natural vegetation productivity. However, due to the coarse model grid and spatial heterogeneity in the real world this conclusion does not exclude the existence of habitats constrained by BNF.

Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria.

PubMed

Garcia, Nathan S; Fu, Feixue; Sedwick, Peter N; Hutchins, David A

2015-01-01

Marine dinitrogen (N2)-fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide (CO2) and fertilize oligotrophic ocean waters with new nitrogen. Iron (Fe) and phosphorus (P) are the two most important limiting nutrients for marine biological N2 fixation, and their availabilities vary between major ocean basins and regions. A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria, unicellular Crocosphaera and filamentous Trichodesmium, to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce. We show that under P-deficient conditions, cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete. In addition, growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations. In Crocosphaera, this effect is accompanied by a reduction in cell sizes and elemental quotas. Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P, low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers. The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past, present and future oceans could have large consequences for global carbon and nitrogen cycles.

Nitrogen fixation is not the only trait that determines the success of tropical legumes during secondary succession

NASA Astrophysics Data System (ADS)

Gei, Maria G.; Powers, Jennifer S.

2017-04-01

Legumes trees are well represented throughout the entire precipitation gradient of tropical forests. Many of these species are able to fix atmospheric dinitrogen through symbiosis and offer a mechanism to overcome nitrogen limitation typical of initial stages of secondary forest succession. While it is often assumed the success of legumes is linked to their fixation ability, the variation of other functional traits within this large group has received considerably less attention. Here we assessed legume abundance in secondary forest plots in 42 Neotropical chronosequences (the 2ndFOR network) that span a broad gradient of precipitation regimes and identified those traits that are favored in distinct successional environments. Our main finding is that in young secondary dry forests (5-20 years), legumes that have the potential to fix nitrogen and have small leaflet size become exceptionally abundant (up to 17-99% relative basal area). We suggest that in those species, reduced leaf area could help regulate leaf temperature and minimize water loss, and the cost of reduced total leaf area may be compensated by high photosynthetic rates maximized with nitrogen obtained through fixation. Overall, our study underscores great functional heterogeneity within tropical legumes, which likely translates into diverse biogeochemical cycles. In addition, these results provide a useful framework for active restoration of degraded areas, as it identifies a group of species that accumulate carbon at fast rates under warm and dry environments, conditions that are expected to become more common in the tropics.

Changing nutrient stoichiometry affects phytoplankton production, DOP accumulation and dinitrogen fixation - a mesocosm experiment in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Meyer, J.; Löscher, C. R.; Neulinger, S. C.; Reichel, A. F.; Loginova, A.; Borchard, C.; Schmitz, R. A.; Hauss, H.; Kiko, R.; Riebesell, U.

2016-02-01

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low nitrogen to phosphorus (N : P) ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified nitrate availability as a control of primary production, while a possible co-limitation of nitrate and phosphate could not be ruled out. To better understand the impact of changing N : P ratios on primary production and N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67-48). Silicic acid was supplied at 15 µmol L-1 in all mesocosms. We monitored nutrient drawdown, biomass accumulation and nitrogen fixation in response to variable nutrient stoichiometry. Our results confirmed nitrate to be the key factor determining primary production. We found that excess phosphate was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low inorganic phosphate availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where nitrate was still available, indicating that bioavailable N does not necessarily suppress N2 fixation. We observed a shift from a mixed cyanobacteria-proteobacteria dominated active diazotrophic community towards a diatom-diazotrophic association of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially influencing primary productivity and carbon export.

Molecular Ecological and Stable Isotopic Studies of Nitrogen Fixation in Modern Microbial Mats

NASA Technical Reports Server (NTRS)

Bebout, B. M.; Crumbliss, L. L.; DesMarais, D. J.; Hogan, M. E.; Omoregie, E.; Turk, K. A.; Zehr, J. P.

2003-01-01

Nitrogen is usually the element limiting biological productivity in the marine environment. Microbial mats, laminated microbial communities analogous to some of the oldest forms of life on Earth, are often the sites of high rates of N fixation (the energetically expensive conversion of atmospheric dinitrogen into a biologically useful form). The N fixing enzyme nitrogenase is generally considered to be of ancient origin, and is widely distributed throughout the Bacterial and Archaeal domains of life, indicating an important role for this process over evolutionary time. The stable isotopic signature of N fixation is purportedly recognizable in organic matter (ancient kerogens as well as present-day microbial mats) as a delta (15)N(sub organic) near zero. We studied two microbial mats exhibiting different rates of N fixation in order to better understand the impact of N fixation on the delta (15)N (sub organic) of the mats, as well as what organisms are important in this process. Mats dominated by the cyanobacterium Microcoleus chthonoplastes grow in permanently submerged hypersaline salterns, and exhibit low rates of N fixation, whereas mats dominated by the cyanobacterium Lyngbya spp grow in an intertidal area, and exhibit rates of N fixation an order of magnitude higher. To examine successional stages in mat growth, both developing and established mats at each location were sampled. PCR and RT-PCR based approaches were used to identify, respectively, the organisms containing nifH (one of the genes that encode nitrogenase) as well as those expressing nifH in these mats. Both mats exhibited a distinct diel cycle of N fixation, with highest rates occurring at night. The delta (15)N(sub organic) of the subtidal Microcoleus mats is near zero whereas the delta (15)N(sub organic) is slightly more positive (+ 2-3%), in the intertidal Lyngbya mats, an interesting difference in view of the fact that overall rates of activity in the intertidal mats are much higher that those in the submerged hypersaline mats. Developing mats in both the subtidal and intertidal locations had delta (15)N(sub organic) values very near those of the established mats. Further work is necessary in order to determine the importance of other transformations of nitrogen on the delta (15)N(sub organic) signature of the mats.

Symbiosis revisited: phosphorus and acid buffering stimulate N2 fixation but not Sphagnum growth

NASA Astrophysics Data System (ADS)

van den Elzen, Eva; Kox, Martine A. R.; Harpenslager, Sarah F.; Hensgens, Geert; Fritz, Christian; Jetten, Mike S. M.; Ettwig, Katharina F.; Lamers, Leon P. M.

2017-03-01

In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha-1 yr-1), we found that diazotrophic activity (as measured by 15 - 15N2 labeling) was still present at a rate of 40 nmol N gDW-1 h-1. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha-1 yr-1 on top of the high nitrogen deposition in these ecosystems.

Structural analysis of the coordination of dinitrogen to transition metal complexes.

PubMed

Peigné, Benjamin; Aullón, Gabriel

2015-06-01

Transition-metal complexes show a wide variety of coordination modes for the nitrogen molecule. A structural database study has been undertaken for dinitrogen complexes, and geometrical parameters around the L(n)M-N2 unit are retrieved from the Cambridge Structural Database. These data were classified in families of compounds, according to metal properties, to determine the degree of lengthening for the dinitrogen bonding. The importance of the nature of the metal center, such as coordination number and electronic configuration, is reported. Our study reveals poor activation by coordination of dinitrogen in mononuclear complexes, always having end-on coordination. However, partial weakening of nitrogen-nitrogen bonding is found for end-on binuclear complexes, whereas side-on complexes can be completely activated.

Feathermoss and epiphytic Nostoc cooperate differently: expanding the spectrum of plant-cyanobacteria symbiosis.

PubMed

Warshan, Denis; Espinoza, Josh L; Stuart, Rhona K; Richter, R Alexander; Kim, Sea-Yong; Shapiro, Nicole; Woyke, Tanja; C Kyrpides, Nikos; Barry, Kerrie; Singan, Vasanth; Lindquist, Erika; Ansong, Charles; Purvine, Samuel O; M Brewer, Heather; Weyman, Philip D; Dupont, Christopher L; Rasmussen, Ulla

2017-12-01

Dinitrogen (N 2 )-fixation by cyanobacteria in symbiosis with feathermosses is the primary pathway of biological nitrogen (N) input into boreal forests. Despite its significance, little is known about the cyanobacterial gene repertoire and regulatory rewiring needed for the establishment and maintenance of the symbiosis. To determine gene acquisitions and regulatory changes allowing cyanobacteria to form and maintain this symbiosis, we compared genomically closely related symbiotic-competent and -incompetent Nostoc strains using a proteogenomics approach and an experimental set up allowing for controlled chemical and physical contact between partners. Thirty-two gene families were found only in the genomes of symbiotic strains, including some never before associated with cyanobacterial symbiosis. We identified conserved orthologs that were differentially expressed in symbiotic strains, including protein families involved in chemotaxis and motility, NO regulation, sulfate/phosphate transport, and glycosyl-modifying and oxidative stress-mediating exoenzymes. The physical moss-cyanobacteria epiphytic symbiosis is distinct from other cyanobacteria-plant symbioses, with Nostoc retaining motility, and lacking modulation of N 2 -fixation, photosynthesis, GS-GOGAT cycle and heterocyst formation. The results expand our knowledge base of plant-cyanobacterial symbioses, provide a model of information and material exchange in this ecologically significant symbiosis, and suggest new currencies, namely nitric oxide and aliphatic sulfonates, may be involved in establishing and maintaining the cyanobacteria-feathermoss symbiosis.

Feathermoss and epiphytic Nostoc cooperate differently: expanding the spectrum of plant–cyanobacteria symbiosis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warshan, Denis; Espinoza, Josh L.; Stuart, Rhona

Dinitrogen (N2)-fixation by cyanobacteria in symbiosis with feather mosses represents the main pathway of biological N input into boreal forests. Despite its significance, little is known about the gene repertoire needed for the establishment and maintenance of the symbiosis. To determine gene acquisitions or regulatory rewiring allowing cyanobacteria to form this symbiosis, we compared closely related Nostoc strains that were either symbiosis-competent or non-competent, using a proteogenomics approach and a unique experimental setup allowing for controlled chemical and physical contact between partners. Thirty-two protein families were only in the genomes of competent strains, including some never before associated with symbiosis.more » We identified conserved orthologs that were differentially expressed in competent strains, including gene families involved in chemotaxis and motility, NO regulation, sulfate/phosphate transport, sugar metabolism, and glycosyl-modifying and oxidative stress-mediating exoenzymes. In contrast to other cyanobacteria-plant symbioses, the moss-cyanobacteria epiphytic symbiosis is distinct, with the symbiont retaining motility and chemotaxis, and not modulating N-fixation, photosynthesis, GS-GOGAT cycle, and heterocyst formation. Our work expands our knowledge of plant cyanobacterial symbioses, provides an interaction model of this ecologically significant symbiosis, and suggests new currencies, namely nitric oxide and aliphatic sulfonates, may be involved in establishing and maintaining this symbiosis.« less

Validation of Ocean Color Satellite Data Products in Under Sampled Marine Areas. Chapter 6

NASA Technical Reports Server (NTRS)

Subramaniam, Ajit; Hood, Raleigh R.; Brown, Christopher W.; Carpenter, Edward J.; Capone, Douglas G.

2001-01-01

The planktonic marine cyanobacterium, Trichodesmium sp., is broadly distributed throughout the oligotrophic marine tropical and sub-tropical oceans. Trichodesmium, which typically occurs in macroscopic bundles or colonies, is noteworthy for its ability to form large surface aggregations and to fix dinitrogen gas. The latter is important because primary production supported by N2 fixation can result in a net export of carbon from the surface waters to deep ocean and may therefore play a significant role in the global carbon cycle. However, information on the distribution and density of Trichodesmium from shipboard measurements through the oligotrophic oceans is very sparse. Such estimates are required to quantitatively estimate total global rates of N2 fixation. As a result current global rate estimates are highly uncertain. Thus in order to understand the broader biogeochemical importance of Trichodesmium and N2 fixation in the oceans, we need better methods to estimate the global temporal and spatial variability of this organism. One approach that holds great promise is satellite remote sensing. Satellite ocean color sensors are ideal instruments for estimating global phytoplankton biomass, especially that due to episodic blooms, because they provide relatively high frequency synoptic information over large areas. Trichodesmium has a combination of specific ultrastructural and biochemical features that lend themselves to identification of this organism by remote sensing. Specifically, these features are high backscatter due to the presence of gas vesicles, and absorption and fluorescence of phycoerythrin. The resulting optical signature is relatively unique and should be detectable with satellite ocean color sensors such as the Sea-Viewing Wide Field-of-view Sensor (SeaWiFS).

Dinitrogen fixation by legume shade trees and direct transfer of fixed N to associated cacao in a tropical agroforestry system.

PubMed

Nygren, Pekka; Leblanc, Humberto A

2015-02-01

Natural abundance of (15)N (δ (15)N) was determined in bulk soil, rhizospheric soil and vegetation in an organically managed cacao (Theobroma cacao L.) plantation with Inga edulis Mart. legume trees (inga) as the principal shade for studying the nitrogen (N) cycle in the system. Cacao without contact with legumes in an adjacent plantation was used as the reference for N2 fixation and direct N transfer calculations. Bulk and rhizospheric soils contained 72 and 20%, respectively, of whole- system N. No vegetation effect on δ (15)N in rhizospheric soil was detected, probably due to the high native soil N pool. Fine roots of the cacaos associated with inga contained ∼35% of N fixed from the atmosphere (Nf) out of the total N. Leaves of all species had significantly higher δ (15)N than fine roots. Twenty percent of system Nf was found in cacao suggesting direct N transfer from inga via a common mycelial network of mycorrhizal fungi or recycling of N-rich root exudates of inga. Inga had accumulated 98 kg [Nf] ha(-1) during the 14-year history of the plantation. The conservative estimate of current N2 fixation rate was 41 kg [Nf] ha(-1) year(-1) based on inga biomass only and 50 kg [Nf] ha(-1) year(-1) based on inga and associated trees. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Nitrogenase-mimic iron-containing chalcogels for photochemical reduction of dinitrogen to ammonia.

PubMed

Liu, Jian; Kelley, Matthew S; Wu, Weiqiang; Banerjee, Abhishek; Douvalis, Alexios P; Wu, Jinsong; Zhang, Yongbo; Schatz, George C; Kanatzidis, Mercouri G

2016-05-17

A nitrogenase-inspired biomimetic chalcogel system comprising double-cubane [Mo2Fe6S8(SPh)3] and single-cubane (Fe4S4) biomimetic clusters demonstrates photocatalytic N2 fixation and conversion to NH3 in ambient temperature and pressure conditions. Replacing the Fe4S4 clusters in this system with other inert ions such as Sb(3+), Sn(4+), Zn(2+) also gave chalcogels that were photocatalytically active. Finally, molybdenum-free chalcogels containing only Fe4S4 clusters are also capable of accomplishing the N2 fixation reaction with even higher efficiency than their Mo2Fe6S8(SPh)3-containing counterparts. Our results suggest that redox-active iron-sulfide-containing materials can activate the N2 molecule upon visible light excitation, which can be reduced all of the way to NH3 using protons and sacrificial electrons in aqueous solution. Evidently, whereas the Mo2Fe6S8(SPh)3 is capable of N2 fixation, Mo itself is not necessary to carry out this process. The initial binding of N2 with chalcogels under illumination was observed with in situ diffuse-reflectance Fourier transform infrared spectroscopy (DRIFTS). (15)N2 isotope experiments confirm that the generated NH3 derives from N2 Density functional theory (DFT) electronic structure calculations suggest that the N2 binding is thermodynamically favorable only with the highly reduced active clusters. The results reported herein contribute to ongoing efforts of mimicking nitrogenase in fixing nitrogen and point to a promising path in developing catalysts for the reduction of N2 under ambient conditions.

Gene function analysis in extremophiles: the "nif" regulon of the strict iron oxidizing bacterium "Leptospirillum ferrooxidans"

NASA Astrophysics Data System (ADS)

Parro, Victor; Moreno-Paz, Mercedes

2004-03-01

In Centro de Astrobiologia it has been considered the Tinto river as a model ecosystem to study life based on iron. The final goal is to study the biological and metabolic diversity in microorganisms living there, following a genomic approach, to get insights to the mechanisms of adaptation to this environment. The Gram-negative bacterium Leptospirillum ferrooxidans is one of the most abundant microorganisms in the river, and it is one of the main responsible in maintenance of pH balance and, as a consequence, the physico-chemical properties of the exosystem. We have constructed a Shotgun DNA microarrays from this bacterium and we have used it to studied its genetic capacity for nitrogen fixation. With this approach we have identified most of the genes necessary for dinitrogen (N2) reduction, confirming the capacity of L. ferrooxidans as a free diazotrophic (nitrogen fixer) microorganism.

Fixation stability of the upward gaze in patients with myasthenia gravis: an eye-tracker study

PubMed Central

Mihara, Miharu; Hayashi, Atsushi; Fujita, Kazuya; Kakeue, Ken; Tamura, Ryoi

2017-01-01

Objective To quantify fixation stability of the upward gaze in patients with myasthenia gravis (MG) using an eye tracker. Methods and analysis In this study, 21 normal subjects, 5 patients with MG with diplopia, 5 patients with MG without diplopia and 6 patients with superior oblique (SO) palsy were included. Subjects fixated on a target in the upward direction for 1 min. The horizontal (X) and vertical (Y) eye positions were recorded using an eye tracker. Fixation stability was first quantified using the bivariate contour ellipse areas (BCEA) of fixation points as an index of whole stability. Then, the SDs of the X and Y eye positions (SDX and SDY, respectively) were quantified as indices of directional stability, with the data divided into three 20 s fractions to detect temporal fixation fluctuation. Results BCEAs were larger in patients with MG (both with and without diplopia) than normal subjects and patients with SO palsy, without significant differences among the three 20 s fractions. Compared with normal subjects, SDXs were larger only in patients with MG with diplopia; SDYs were larger in both patients with MG with and without diplopia. In addition, SDYs in patients with MG with diplopia were larger than those in patients with MG without diplopia and patients with SO palsy. Furthermore, a significant difference among the three 20 s fractions was detected for SDYs in patients with MG with diplopia. Conclusion Patients with MG, especially those with diplopia, exhibit fixation instability in the upward gaze. Non-invasive quantification of fixation stability with an eye tracker is useful for precisely identifying MG-specific fatigue characteristics. Trial registration number UMIN000023468; pre-results. PMID:29354719

Changing nutrient stoichiometry affects phytoplankton production, DOP build up and dinitrogen fixation - a mesocosm experiment in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Meyer, J.; Löscher, C. R.; Neulinger, S. C.; Reichel, A. F.; Loginova, A.; Borchard, C.; Schmitz, R. A.; Hauss, H.; Kiko, R.; Riebesell, U.

2015-07-01

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially-driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low N : P ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified N availability as controlling of primary production, while a possible co-limitation of nitrate and phosphate (P) could not be ruled out. To better understand the impact of changing N : P ratios on primary production and on N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67-48). Silicate was supplied at 15 μmol L-1 in all mesocosms. We monitored nutrient drawdown, bloom formation, biomass build up and diazotrophic feedback in response to variable nutrient stoichiometry. Our results confirmed N to be limiting to primary production. We found that excess P was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low P availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where inorganic N was still available, indicating that bioavailable N does not necessarily has to have a negative impact on N2 fixation. We observed a shift from a mixed cyanobacterial/proteobacterial dominated active diazotrophic community towards diazotrophic diatom symbionts of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially modifying primary productivity.

Regulation of nif expression in Methanococcus maripaludis: roles of the euryarchaeal repressor NrpR, 2-oxoglutarate, and two operators.

PubMed

Lie, Thomas J; Wood, Gwendolyn E; Leigh, John A

2005-02-18

The methanogenic archaean Methanococcus maripaludis can use ammonia, alanine, or dinitrogen as a nitrogen source for growth. The euryarchaeal nitrogen repressor NrpR controls the expression of the nif (nitrogen fixation) operon, resulting in full repression with ammonia, intermediate repression with alanine, and derepression with dinitrogen. NrpR binds to two tandem operators in the nif promoter region, nifOR(1) and nifOR(2). Here we have undertaken both in vivo and in vitro approaches to study the way in which NrpR, nifOR(1), nifOR(2), and the effector 2-oxoglutarate (2OG) combine to regulate nif expression, leading to a comprehensive understanding of this archaeal regulatory system. We show that NrpR binds as a dimer to nifOR(1) and cooperatively as two dimers to both operators. Cooperative binding occurs only with both operators present. nifOR(1) has stronger binding and by itself can mediate the repression of nif transcription during growth on ammonia, unlike the weakly binding nifOR(2). However, nifOR(2) in combination with nifOR(1) is critical for intermediate repression during growth on alanine. Accordingly, NrpR binds to both operators together with higher affinity than to nifOR(1) alone. NrpR responds directly to 2OG, which weakens its binding to the operators. Hence, 2OG is an intracellular indicator of nitrogen deficiency and acts as an inducer of nif transcription via NrpR. This model is upheld by the recent finding (J. A. Dodsworth and J. A. Leigh, submitted for publication) in our laboratory that 2OG levels in M. maripaludis vary with growth on different nitrogen sources.

Experimental assessment of diazotroph responses to elevated seawater pCO2 in the North Pacific Subtropical Gyre

NASA Astrophysics Data System (ADS)

Böttjer, Daniela; Karl, David M.; Letelier, Ricardo M.; Viviani, Donn A.; Church, Matthew J.

2014-06-01

We examined short-term (24-72 h) responses of naturally occurring marine N2 fixing microorganisms (termed diazotrophs) to abrupt increases in the partial pressure of carbon dioxide (pCO2) in seawater during nine incubation experiments conducted between May 2010 and September 2012 at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) (22°45'N, 158°W) in the North Pacific Subtropical Gyre (NPSG). Rates of N2 fixation, nitrogenase (nifH) gene abundances and transcripts of six major groups of cyanobacterial diazotrophs (including both unicellular and filamentous phylotypes), and rates of primary productivity (as measured by 14C-bicarbonate assimilation into plankton biomass) were determined under contemporary (~390 ppm) and elevated pCO2 conditions (~1100 ppm). Quantitative polymerase chain reaction (QPCR) amplification of planktonic nifH genes revealed that unicellular cyanobacteria phylotypes dominated gene abundances during these experiments. In the majority of experiments (seven out of nine), elevated pCO2 did not significantly influence rates of dinitrogen (N2) fixation or primary productivity (two-way analysis of variance (ANOVA), P > 0.05). During two experiments, rates of N2 fixation and primary productivity were significantly lower (by 79 to 82% and 52 to 72%, respectively) in the elevated pCO2 treatments relative to the ambient controls (two-way ANOVA, P < 0.05). QPCR amplification of nifH genes and gene transcripts revealed that diazotroph abundances and nifH gene expression were largely unchanged by the perturbation of the seawater pCO2. Our results suggest that naturally occurring N2 fixing plankton assemblages in the NPSG are relatively resilient to large, short-term increases in pCO2.

Nitrogenase-mimic iron-containing chalcogels for photochemical reduction of dinitrogen to ammonia

DOE PAGES

Liu, Jian; Kelley, Matthew S.; Wu, Weiqiang; ...

2016-05-02

A nitrogenase-inspired biomimetic chalcogel system comprising double-cubane [Mo 2Fe 6S 8(SPh) 3] and single-cubane (Fe 4S 4) biomimetic clusters demonstrates photocatalytic N 2 fixation and conversion to NH 3 in ambient temperature and pressure conditions. Replacing the Fe 4S 4 clusters in this system with other inert ions such as Sb 3+, Sn 4+, Zn 2+ also gave chalcogels that were photocatalytically active. Finally, molybdenum-free chalcogels containing only Fe 4S 4 clusters are also capable of accomplishing the N2 fixation reaction with even higher efficiency than their Mo 2Fe 6S 8(SPh) 3-containing counterparts. In this study, our results suggest thatmore » redox-active iron-sulfide–containing materials can activate the N 2 molecule upon visible light excitation, which can be reduced all of the way to NH 3 using protons and sacrificial electrons in aqueous solution. Evidently, whereas the Mo 2Fe 6S 8(SPh) 3 is capable of N 2 fixation, Mo itself is not necessary to carry out this process. The initial binding of N 2 with chalcogels under illumination was observed with in situ diffuse-reflectance Fourier transform infrared spectroscopy (DRIFTS). 15N 2 isotope experiments confirm that the generated NH 3 derives from N 2. Density functional theory (DFT) electronic structure calculations suggest that the N 2 binding is thermodynamically favorable only with the highly reduced active clusters. Finally, the results reported herein contribute to ongoing efforts of mimicking nitrogenase in fixing nitrogen and point to a promising path in developing catalysts for the reduction of N 2 under ambient conditions.« less

Comparative assessment of nitrogen fixation methodologies, conducted in the oligotrophic North Pacific Ocean.

PubMed

Wilson, Samuel T; Böttjer, Daniela; Church, Matthew J; Karl, David M

2012-09-01

Resolution of the nitrogen (N) cycle in the marine environment requires an accurate assessment of dinitrogen (N(2)) fixation. We present here an update on progress in conducting field measurements of acetylene reduction (AR) and (15)N(2) tracer assimilation in the oligotrophic North Pacific Subtropical Gyre (NPSG). The AR assay was conducted on discrete seawater samples using a headspace analysis system, followed by quantification of ethylene (C(2)H(4)) with a reducing compound photodetector. The rates of C(2)H(4) production were measurable for nonconcentrated seawater samples after an incubation period of 3 to 4 h. The (15)N(2) tracer measurements compared the addition of (15)N(2) as a gas bubble and dissolved as (15)N(2) enriched seawater. On all sampling occasions and at all depths, a 2- to 6-fold increase in the rate of (15)N(2) assimilation was measured when (15)N(2)-enriched seawater was added to the seawater sample compared to the addition of (15)N(2) as a gas bubble. In addition, we show that the (15)N(2)-enriched seawater can be prepared prior to its use with no detectable loss (<1.7%) of dissolved (15)N(2) during 4 weeks of storage, facilitating its use in the field. The ratio of C(2)H(4) production to (15)N(2) assimilation varied from 7 to 27 when measured simultaneously in surface seawater samples. Collectively, the modifications to the AR assay and the (15)N(2) assimilation technique present opportunities for more accurate and high frequency measurements (e.g., diel scale) of N(2) fixation, providing further insight into the contribution of different groups of diazotrophs to the input of N in the global oceans.

Biological dinitrogen fixation by selected soil cyanobacteria as affected by strain origin, morphotype, and light conditions.

PubMed

Hrčková, K; Simek, M; Hrouzek, P; Lukešová, A

2010-09-01

The potential for N(2) fixation by heterocystous cyanobacteria isolated from soils of different geographical areas was determined as nitrogenase activity (NA) using the acetylene reduction assay. Morphology of cyanobacteria had the largest influence on NA determined under light conditions. NA was generally higher in species lacking thick slime sheaths. The highest value (1446 nmol/h C(2)H(4) per g fresh biomass) was found in the strain of branched cyanobacterium Hassalia (A Has1) from the polar region. A quadratic relationship between NA and biomass was detected in the Tolypothrix group under light conditions. The decline of NA in dark relative to light conditions ranged from 37 to 100 % and differed among strains from distinct geographical areas. Unlike the NA of temperate and tropical strains, whose decline in dark relative to light was 24 and 17 %, respectively, the NA of polar strains declined to 1 % in the dark. This difference was explained by adaptation to different light conditions in temperate, tropical, and polar habitats. NA was not related to the frequency of heterocysts in strains of the colony-forming cyanobacterium Nostoc. Colony morphology and life cycle are therefore more important for NA then heterocyst frequency. NA values probably reflect the environmental conditions where the cyanobacterium was isolated and the physiological and morphological state of the strain.

Nodule-enhanced expression of a sucrose phosphate synthase gene member (MsSPSA) has a role in carbon and nitrogen metabolism in the nodules of alfalfa (Medicago sativa L.)

PubMed Central

Aleman, Lorenzo; Ortega, Jose Luis; Martinez-Grimes, Martha; Seger, Mark; Holguin, Francisco Omar; Uribe, Diana J.; Garcia-Ibilcieta, David

2013-01-01

Sucrose phosphate synthase (SPS) catalyzes the first step in the synthesis of sucrose in photosynthetic tissues. We characterized the expression of three different isoforms of SPS belonging to two different SPS gene families in alfalfa (Medicago sativa L.), a previously identified SPS (MsSPSA) and two novel isoforms belonging to class B (MsSPSB and MsSPSB3). While MsSPSA showed nodule-enhanced expression, both MsSPSB genes exhibited leaf-enhanced expression. Alfalfa leaf and nodule SPS enzymes showed differences in chromatographic and electrophoretic migration and differences in Vmax and allosteric regulation. The root nodules in legume plants are a strong sink for photosynthates with its need for ATP, reducing power and carbon skeletons for dinitrogen fixation and ammonia assimilation. The expression of genes encoding SPS and other key enzymes in sucrose metabolism, sucrose phosphate phosphatase and sucrose synthase, was analyzed in the leaves and nodules of plants inoculated with Sinorhizobium meliloti. Based on the expression pattern of these genes, the properties of the SPS isoforms and the concentration of starch and soluble sugars in nodules induced by a wild type and a nitrogen fixation deficient strain, we propose that SPS has an important role in the control of carbon flux into different metabolic pathways in the symbiotic nodules. PMID:19898977

Feathermoss and epiphytic Nostoc cooperate differently: expanding the spectrum of plant–cyanobacteria symbiosis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warshan, Denis; Espinoza, Josh L.; Stuart, Rhona K.

Dinitrogen (N 2)-fixation by cyanobacteria in symbiosis with feathermosses is the primary pathway of biological nitrogen (N) input into boreal forests. Despite its significance, little is known about the cyanobacterial gene repertoire and regulatory rewiring needed for the establishment and maintenance of the symbiosis. To determine gene acquisitions and regulatory changes allowing cyanobacteria to form and maintain this symbiosis, we compared genomically closely related symbiotic-competent and -incompetent Nostoc strains using a proteogenomics approach and an experimental set up allowing for controlled chemical and physical contact between partners. Thirty-two gene families were found only in the genomes of symbiotic strains, includingmore » some never before associated with cyanobacterial symbiosis. We identified conserved orthologs that were differentially expressed in symbiotic strains, including protein families involved in chemotaxis and motility, NO regulation, sulfate/phosphate transport, and glycosyl-modifying and oxidative stress-mediating exoenzymes. The physical moss–cyanobacteria epiphytic symbiosis is distinct from other cyanobacteria–plant symbioses, with Nostoc retaining motility, and lacking modulation of N 2-fixation, photosynthesis, GS-GOGAT cycle and heterocyst formation. The results expand our knowledge base of plant–cyanobacterial symbioses, provide a model of information and material exchange in this ecologically significant symbiosis, and suggest new currencies, namely nitric oxide and aliphatic sulfonates, may be involved in establishing and maintaining the cyanobacteria–feathermoss symbiosis.« less

Feathermoss and epiphytic Nostoc cooperate differently: expanding the spectrum of plant–cyanobacteria symbiosis

PubMed Central

Warshan, Denis; Espinoza, Josh L; Stuart, Rhona K; Richter, R Alexander; Kim, Sea-Yong; Shapiro, Nicole; Woyke, Tanja; C Kyrpides, Nikos; Barry, Kerrie; Singan, Vasanth; Lindquist, Erika; Ansong, Charles; Purvine, Samuel O; M Brewer, Heather; Weyman, Philip D; Dupont, Christopher L; Rasmussen, Ulla

2017-01-01

Dinitrogen (N2)-fixation by cyanobacteria in symbiosis with feathermosses is the primary pathway of biological nitrogen (N) input into boreal forests. Despite its significance, little is known about the cyanobacterial gene repertoire and regulatory rewiring needed for the establishment and maintenance of the symbiosis. To determine gene acquisitions and regulatory changes allowing cyanobacteria to form and maintain this symbiosis, we compared genomically closely related symbiotic-competent and -incompetent Nostoc strains using a proteogenomics approach and an experimental set up allowing for controlled chemical and physical contact between partners. Thirty-two gene families were found only in the genomes of symbiotic strains, including some never before associated with cyanobacterial symbiosis. We identified conserved orthologs that were differentially expressed in symbiotic strains, including protein families involved in chemotaxis and motility, NO regulation, sulfate/phosphate transport, and glycosyl-modifying and oxidative stress-mediating exoenzymes. The physical moss–cyanobacteria epiphytic symbiosis is distinct from other cyanobacteria–plant symbioses, with Nostoc retaining motility, and lacking modulation of N2-fixation, photosynthesis, GS-GOGAT cycle and heterocyst formation. The results expand our knowledge base of plant–cyanobacterial symbioses, provide a model of information and material exchange in this ecologically significant symbiosis, and suggest new currencies, namely nitric oxide and aliphatic sulfonates, may be involved in establishing and maintaining the cyanobacteria–feathermoss symbiosis. PMID:28800136

Feathermoss and epiphytic Nostoc cooperate differently: expanding the spectrum of plant–cyanobacteria symbiosis

DOE PAGES

Warshan, Denis; Espinoza, Josh L.; Stuart, Rhona K.; ...

2017-08-11

Dinitrogen (N 2)-fixation by cyanobacteria in symbiosis with feathermosses is the primary pathway of biological nitrogen (N) input into boreal forests. Despite its significance, little is known about the cyanobacterial gene repertoire and regulatory rewiring needed for the establishment and maintenance of the symbiosis. To determine gene acquisitions and regulatory changes allowing cyanobacteria to form and maintain this symbiosis, we compared genomically closely related symbiotic-competent and -incompetent Nostoc strains using a proteogenomics approach and an experimental set up allowing for controlled chemical and physical contact between partners. Thirty-two gene families were found only in the genomes of symbiotic strains, includingmore » some never before associated with cyanobacterial symbiosis. We identified conserved orthologs that were differentially expressed in symbiotic strains, including protein families involved in chemotaxis and motility, NO regulation, sulfate/phosphate transport, and glycosyl-modifying and oxidative stress-mediating exoenzymes. The physical moss–cyanobacteria epiphytic symbiosis is distinct from other cyanobacteria–plant symbioses, with Nostoc retaining motility, and lacking modulation of N 2-fixation, photosynthesis, GS-GOGAT cycle and heterocyst formation. The results expand our knowledge base of plant–cyanobacterial symbioses, provide a model of information and material exchange in this ecologically significant symbiosis, and suggest new currencies, namely nitric oxide and aliphatic sulfonates, may be involved in establishing and maintaining the cyanobacteria–feathermoss symbiosis.« less

Phytoplankton Productivity in an Arctic Fjord (West Greenland): Estimating Electron Requirements for Carbon Fixation and Oxygen Production

PubMed Central

Hancke, Kasper; Dalsgaard, Tage; Sejr, Mikael Kristian; Markager, Stiig; Glud, Ronnie Nøhr

2015-01-01

Accurate quantification of pelagic primary production is essential for quantifying the marine carbon turnover and the energy supply to the food web. Knowing the electron requirement (Κ) for carbon (C) fixation (Κ C) and oxygen (O2) production (Κ O2), variable fluorescence has the potential to quantify primary production in microalgae, and hereby increasing spatial and temporal resolution of measurements compared to traditional methods. Here we quantify Κ C and Κ O2 through measures of Pulse Amplitude Modulated (PAM) fluorometry, C fixation and O2 production in an Arctic fjord (Godthåbsfjorden, W Greenland). Through short- (2h) and long-term (24h) experiments, rates of electron transfer (ETRPSII), C fixation and/or O2 production were quantified and compared. Absolute rates of ETR were derived by accounting for Photosystem II light absorption and spectral light composition. Two-hour incubations revealed a linear relationship between ETRPSII and gross 14C fixation (R2 = 0.81) during light-limited photosynthesis, giving a Κ C of 7.6 ± 0.6 (mean ± S.E.) mol é (mol C)−1. Diel net rates also demonstrated a linear relationship between ETRPSII and C fixation giving a Κ C of 11.2 ± 1.3 mol é (mol C)−1 (R2 = 0.86). For net O2 production the electron requirement was lower than for net C fixation giving 6.5 ± 0.9 mol é (mol O2)−1 (R2 = 0.94). This, however, still is an electron requirement 1.6 times higher than the theoretical minimum for O2 production [i.e. 4 mol é (mol O2)−1]. The discrepancy is explained by respiratory activity and non-photochemical electron requirements and the variability is discussed. In conclusion, the bio-optical method and derived electron requirement support conversion of ETR to units of C or O2, paving the road for improved spatial and temporal resolution of primary production estimates. PMID:26218096

Selective Electrocatalytic Reduction of Nitrite to Dinitrogen Based on Decoupled Proton-Electron Transfer.

PubMed

He, Daoping; Li, Yamei; Ooka, Hideshi; Go, Yoo Kyung; Jin, Fangming; Kim, Sun Hee; Nakamura, Ryuhei

2018-02-14

The development of denitrification catalysts which can reduce nitrate and nitrite to dinitrogen is critical for sustaining the nitrogen cycle. However, regulating the selectivity has proven to be a challenge, due to the difficulty of controlling complex multielectron/proton reactions. Here we report that utilizing sequential proton-electron transfer (SPET) pathways is a viable strategy to enhance the selectivity of electrochemical reactions. The selectivity of an oxo-molybdenum sulfide electrocatalyst toward nitrite reduction to dinitrogen exhibited a volcano-type pH dependence with a maximum at pH 5. The pH-dependent formation of the intermediate species (distorted Mo(V) oxo species) identified using operando electron paramagnetic resonance (EPR) and Raman spectroscopy was in accord with a mathematical prediction that the pK a of the reaction intermediates determines the pH-dependence of the SPET-derived product. By utilizing this acute pH dependence, we achieved a Faradaic efficiency of 13.5% for nitrite reduction to dinitrogen, which is the highest value reported to date under neutral conditions.

N2-fixing tropical legume evolution: a contributor to enhanced weathering through the Cenozoic?

PubMed Central

Hedin, Lars O.; Leake, Jonathan R.

2017-01-01

Fossil and phylogenetic evidence indicates legume-rich modern tropical forests replaced Late Cretaceous palm-dominated tropical forests across four continents during the early Cenozoic (58–42 Ma). Tropical legume trees can transform ecosystems via their ability to fix dinitrogen (N2) and higher leaf N compared with non-legumes (35–65%), but it is unclear how their evolutionary rise contributed to silicate weathering, the long-term sink for atmospheric carbon dioxide (CO2). Here we hypothesize that the increasing abundance of N2-fixing legumes in tropical forests amplified silicate weathering rates by increased input of fixed nitrogen (N) to terrestrial ecosystems via interrelated mechanisms including increasing microbial respiration and soil acidification, and stimulating forest net primary productivity. We suggest the high CO2 early Cenozoic atmosphere further amplified legume weathering. Evolution of legumes with high weathering rates was probably driven by their high demand for phosphorus and micronutrients required for N2-fixation and nodule formation. PMID:28814651

Life sciences and space research XXIII(2): Planetary biology and origins of life; Proceedings of the Topical Meeting and Workshops XX, XXI and XXIII of the 27th COSPAR Plenary Meeting, Espoo, Finland, July 18-29, 1988

NASA Technical Reports Server (NTRS)

Schwartz, A. W. (Editor); Dose, K. (Editor); Raup, D. M. (Editor); Klein, H. P. (Editor); Devincenzi, D. L. (Editor)

1989-01-01

This volume includes chapters on exobiology in space, chemical and early biochemical evolution, life without oxygen, potential for chemical evolution in the early environment of Mars, planetary protection issues and sample return missions, and the modulation of biological evolution by astrophysical phenomena. Papers are presented on the results of spaceflight missions, the action of some factors of space medium on the abiogenic synthesis of nucleotides, early peptidic enzymes, microbiology and biochemistry of the methanogenic archaeobacteria, and present-day biogeochemical activities of anaerobic bacteria and their relevance to future exobiological investigations. Consideration is also given to the development of the Alba Patera volcano on Mars, biological nitrogen fixation under primordial Martian partial pressures of dinitrogen, the planetary protection issues in advance of human exploration of Mars, and the difficulty with astronomical explanations of periodic mass extinctions.

N2-fixing tropical legume evolution: a contributor to enhanced weathering through the Cenozoic?

PubMed

Epihov, Dimitar Z; Batterman, Sarah A; Hedin, Lars O; Leake, Jonathan R; Smith, Lisa M; Beerling, David J

2017-08-16

Fossil and phylogenetic evidence indicates legume-rich modern tropical forests replaced Late Cretaceous palm-dominated tropical forests across four continents during the early Cenozoic (58-42 Ma). Tropical legume trees can transform ecosystems via their ability to fix dinitrogen (N 2 ) and higher leaf N compared with non-legumes (35-65%), but it is unclear how their evolutionary rise contributed to silicate weathering, the long-term sink for atmospheric carbon dioxide (CO 2 ). Here we hypothesize that the increasing abundance of N 2 -fixing legumes in tropical forests amplified silicate weathering rates by increased input of fixed nitrogen (N) to terrestrial ecosystems via interrelated mechanisms including increasing microbial respiration and soil acidification, and stimulating forest net primary productivity. We suggest the high CO 2 early Cenozoic atmosphere further amplified legume weathering. Evolution of legumes with high weathering rates was probably driven by their high demand for phosphorus and micronutrients required for N 2 -fixation and nodule formation. © 2017 The Author(s).

The effect of hubs and shortcuts on fixation time in evolutionary graphs

NASA Astrophysics Data System (ADS)

Askari, Marziyeh; Moradi Miraghaei, Zeinab; Aghababaei Samani, Keivan

2017-07-01

How can a new species (like a gene, an idea, or a strategy) take over the whole of a population? This process, which is called fixation, is considerably affected by the structure of the population. There are two key quantities to quantify the fixation process, namely fixation probability and fixation time. Fixation probability has been vastly studied in recent years, but fixation time has not been completely explored, yet. This is because the discovery of a relationship between fixation time and network structure is quite challenging. In this paper we investigate this relationship for a number of well-known complex networks. We show that the existence of a few high-degree nodes (hubs) in the network results in a longer fixation time, while the existence of a few short-cuts decreases the fixation time. Furthermore we investigate the effect of network parameters, such as connection probability, on fixation time. We show that by increasing the density of edges, fixation time decreases for all types of studied networks. Finally, we survey the effect of rewiring probability in a Watts-Strogatz network on fixation time.

Landscape scale estimation of denitrification rate and nitrous oxide to dinitrogen ratio at Georgia and Pennsylvania sites

USDA-ARS?s Scientific Manuscript database

Denitrification results in a significant loss of plant-available nitrogen from agricultural systems and contributes to climate change, due to the emissions of both the potent greenhouse gas nitrous oxide and environmentally benign dinitrogen. However total quantities of the gases emitted and the ra...

Infrared studies of autoionization of thin films of dinitrogen tetroxidea)

NASA Astrophysics Data System (ADS)

Jones, L. H.; Swanson, B. I.; Agnew, S. F.

1985-05-01

The autoionization of dinitrogen tetroxide to form nitrosonium nitrate in thin films at 150-200 K has been studied using infrared absorption spectroscopy. It is found that at these temperatures and low pressure the process is intramolecular, involving only one of two isomers of the nitrite form (ONONO2). (AIP)

Exploring the effects of black mangrove (Avicennia germinans) expansions on nutrient cycling in smooth cordgrass (Spartina alterniflora) marsh sediments of southern Louisiana, USA

NASA Astrophysics Data System (ADS)

Henry, K. M.; Twilley, R. R.

2011-12-01

Located at the northernmost extent of mangroves in the Gulf of Mexico, coastal Louisiana (LA) provides an excellent opportunity to study the effects of a climate-induced vegetation shift on nutrient cycling within an ecosystem. Climate throughout the Gulf Coast region is experiencing a general warming trend and scientists predict both hotter summers (+1.5 to 4 °C) and warmer winters (+1.5 to 5.5 °C) by 2100. Over the last two decades, mild winter temperatures have facilitated the expansion of black mangrove trees (Avicennia germinans) into the smooth cordgrass (Spartina alterniflora) along parts of the LA coast. Due to differences in morphology and physiology between these two species, the expansion of Avicennia has the potential to greatly alter sediment biogeochemistry, especially nutrient cycling. With such an extensive history of coastal nutrient enrichment and eutrophication in the Mississippi River delta, it is important to understand how nutrient cycling, retention, and removal in this region will be affected by this climate-induced vegetation expansion. We examined the effect of this species shift on porewater salinity, sulfide, and dissolved inorganic nutrient concentrations (nitrite, nitrate, ammonium, and phosphate) as well as sediment oxidation-reduction potential, bulk density, and nutrient content (carbon, nitrogen, phosphorus). We also measured net dinitrogen (N2:Ar), oxygen, and dissolved inorganic nutrient fluxes on intact, non-vegetated sediment cores collected from both Spartina and Avicennia habitats. Spartina sediments were more reducing, with higher concentrations of sulfides and ammonium. We found no significant difference between Spartina and Avicennia sediment dinitrogen, oxygen, or dissolved inorganic nutrient fluxes. Net dinitrogen fluxes for both habitat types were predominately positive, indicating higher rates of denitrification than nitrogen fixation at these sites. Sediments were primarily a nitrate sink, but functioned as both a source and sink of nitrite, ammonium, and phosphate depending on the season and light conditions. Further sediment analysis showed no significant difference in bulk density, carbon, nitrogen, or phosphorus content between Spartina and Avicennia sediments. Marine sediments high in bulk density and phosphorus content and low carbon and nitrogen content dominated the top several centimeters in both Spartina and Avicennia habitats. These surprising but reassuring results suggest that in a region where allochthonous sediment input dominates organic accretion from the primary producers, the climate-induced shift from Spartina to Avicennia will have little to no affect on littoral nutrient cycling.

Chemical microenvironments and single-cell carbon and nitrogen uptake in field-collected colonies of Trichodesmium under different pCO2

PubMed Central

Eichner, Meri J; Klawonn, Isabell; Wilson, Samuel T; Littmann, Sten; Whitehouse, Martin J; Church, Matthew J; Kuypers, Marcel MM; Karl, David M; Ploug, Helle

2017-01-01

Gradients of oxygen (O2) and pH, as well as small-scale fluxes of carbon (C), nitrogen (N) and O2 were investigated under different partial pressures of carbon dioxide (pCO2) in field-collected colonies of the marine dinitrogen (N2)-fixing cyanobacterium Trichodesmium. Microsensor measurements indicated that cells within colonies experienced large fluctuations in O2, pH and CO2 concentrations over a day–night cycle. O2 concentrations varied with light intensity and time of day, yet colonies exposed to light were supersaturated with O2 (up to ~200%) throughout the light period and anoxia was not detected. Alternating between light and dark conditions caused a variation in pH levels by on average 0.5 units (equivalent to 15 nmol l−1 proton concentration). Single-cell analyses of C and N assimilation using secondary ion mass spectrometry (SIMS; large geometry SIMS and nanoscale SIMS) revealed high variability in metabolic activity of single cells and trichomes of Trichodesmium, and indicated transfer of C and N to colony-associated non-photosynthetic bacteria. Neither O2 fluxes nor C fixation by Trichodesmium were significantly influenced by short-term incubations under different pCO2 levels, whereas N2 fixation increased with increasing pCO2. The large range of metabolic rates observed at the single-cell level may reflect a response by colony-forming microbial populations to highly variable microenvironments. PMID:28398346

Nutrient acquisition, soil phosphorus partitioning and competition among trees in a lowland tropical rain forest.

PubMed

Nasto, Megan K; Osborne, Brooke B; Lekberg, Ylva; Asner, Gregory P; Balzotti, Christopher S; Porder, Stephen; Taylor, Philip G; Townsend, Alan R; Cleveland, Cory C

2017-06-01

We hypothesized that dinitrogen (N 2 )- and non-N 2 -fixing tropical trees would have distinct phosphorus (P) acquisition strategies allowing them to exploit different P sources, reducing competition. We measured root phosphatase activity and arbuscular mycorrhizal (AM) colonization among two N 2 - and two non-N 2 -fixing seedlings, and grew them alone and in competition with different inorganic and organic P forms to assess potential P partitioning. We found an inverse relationship between root phosphatase activity and AM colonization in field-collected seedlings, indicative of a trade-off in P acquisition strategies. This correlated with the predominantly exploited P sources in the seedling experiment: the N 2 fixer with high N 2 fixation and root phosphatase activity grew best on organic P, whereas the poor N 2 fixer and the two non-N 2 fixers with high AM colonization grew best on inorganic P. When grown in competition, however, AM colonization, root phosphatase activity and N 2 fixation increased in the N 2 fixers, allowing them to outcompete the non-N 2 fixers regardless of P source. Our results indicate that some tropical trees have the capacity to partition soil P, but this does not eliminate interspecific competition. Rather, enhanced P and N acquisition strategies may increase the competitive ability of N 2 fixers relative to non-N 2 fixers. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Is there foul play in the leaf pocket? The metagenome of floating fern Azolla reveals endophytes that do not fix N2 but may denitrify.

PubMed

Dijkhuizen, Laura W; Brouwer, Paul; Bolhuis, Henk; Reichart, Gert-Jan; Koppers, Nils; Huettel, Bruno; Bolger, Anthony M; Li, Fay-Wei; Cheng, Shifeng; Liu, Xin; Wong, Gane Ka-Shu; Pryer, Kathleen; Weber, Andreas; Bräutigam, Andrea; Schluepmann, Henriette

2018-01-01

Dinitrogen fixation by Nostoc azollae residing in specialized leaf pockets supports prolific growth of the floating fern Azolla filiculoides. To evaluate contributions by further microorganisms, the A. filiculoides microbiome and nitrogen metabolism in bacteria persistently associated with Azolla ferns were characterized. A metagenomic approach was taken complemented by detection of N 2 O released and nitrogen isotope determinations of fern biomass. Ribosomal RNA genes in sequenced DNA of natural ferns, their enriched leaf pockets and water filtrate from the surrounding ditch established that bacteria of A. filiculoides differed entirely from surrounding water and revealed species of the order Rhizobiales. Analyses of seven cultivated Azolla species confirmed persistent association with Rhizobiales. Two distinct nearly full-length Rhizobiales genomes were identified in leaf-pocket-enriched samples from ditch grown A. filiculoides. Their annotation revealed genes for denitrification but not N 2 -fixation. 15 N 2 incorporation was active in ferns with N. azollae but not in ferns without. N 2 O was not detectably released from surface-sterilized ferns with the Rhizobiales. N 2 -fixing N. azollae, we conclude, dominated the microbiome of Azolla ferns. The persistent but less abundant heterotrophic Rhizobiales bacteria possibly contributed to lowering O 2 levels in leaf pockets but did not release detectable amounts of the strong greenhouse gas N 2 O. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant.

PubMed

Horváth, Beatrix; Domonkos, Ágota; Kereszt, Attila; Szűcs, Attila; Ábrahám, Edit; Ayaydin, Ferhan; Bóka, Károly; Chen, Yuhui; Chen, Rujin; Murray, Jeremy D; Udvardi, Michael K; Kondorosi, Éva; Kaló, Péter

2015-12-08

Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula.

Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant

PubMed Central

Horváth, Beatrix; Domonkos, Ágota; Szűcs, Attila; Ábrahám, Edit; Ayaydin, Ferhan; Bóka, Károly; Chen, Yuhui; Chen, Rujin; Murray, Jeremy D.; Udvardi, Michael K.; Kondorosi, Éva; Kaló, Péter

2015-01-01

Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula. PMID:26401023

Perturbation-free measurement of in situ di-nitrogen emissions from denitrification in nitrate-rich aquatic ecosystems.

PubMed

Qin, Shuping; Clough, Timothy; Luo, Jiafa; Wrage-Mönnig, Nicole; Oenema, Oene; Zhang, Yuming; Hu, Chunsheng

2017-02-01

Increased production of reactive nitrogen (Nr) from atmospheric di-nitrogen (N 2 ) has greatly contributed to increased food production. However, enriching the biosphere with Nr has also caused a series of negative effects on global ecosystems, especially aquatic ecosystems. The main pathway converting Nr back into the atmospheric N 2 pool is the last step in the denitrification process. Despite several attempts, there is still a need for perturbation-free methods for measuring in situ N 2 fluxes from denitrification in aquatic ecosystems at the field scale. Such a method is needed to comprehensively quantify the N 2 fluxes from aquatic ecosystems. Here we observed linear relationships between the δ 15 N-N 2 O signatures and the logarithmically transformed N 2 O/(N 2 +N 2 O) emission ratios. Through independent measurements, we verified that the perturbation-free N 2 flux from denitrification in nitrate-rich aquatic ecosystems can be inferred from these linear relationships. Our method allowed the determination of field-scale in situ N 2 fluxes from nitrate-rich aquatic ecosystems both with and without overlaying water. The perturbation-free in situ N 2 fluxes observed by the new method were almost one order of magnitude higher than those by the sediment core method. The ability of aquatic ecosystems to remove Nr may previously have been severely underestimated. Copyright © 2016 Elsevier Ltd. All rights reserved.

Plant, Microbiome, and Biogeochemistry: Quantifying moss-associated N fixation in Alaska

NASA Astrophysics Data System (ADS)

Stuart, J.; Mack, M. C.; Holland Moritz, H.; Fierer, N.; McDaniels, S.; Lewis, L.

2017-12-01

The future carbon (C) sequestration potential of the Arctic and boreal zones, currently the largest terrestrial C sink globally, is linked to nitrogen (N) cycling and N availability vis-a-vis C accumulation and plant species composition. Pristine environments in Alaska have low anthropogenic N deposition (<1 kg N ha-1 yr-1), and the main source of new N to these ecosystems is through previously overlooked N-fixation from microbial communities on mosses. Despite the importance of moss associated N-fixation, the relationship between moss species, microbial communities, and fixation rates remains ambiguous. In the summer of 2016, the fixation rates of 20 moss species from sites around both Fairbanks and Toolik Lake were quantified using 15N2 incubations. Subsequently, the microbial community and moss genome of the samples were also analyzed by collaborators. The most striking result is that all sampled moss genera fixed N, including well-studied feather mosses such as Hylocomium splendens and Pleurozium schreberi as well as less common but ecologically relevant mosses such as Aulacomnium spp., Dicranum spp., Ptilium crista-castrensis, and Tomentypnum nitens. Across all samples, preliminary fixation rates ranged from 0.004-19.994 µg N g-1 moss d-1. Depending upon percent cover, moss-associated N fixation is the largest input of new N to the ecosystem. Given this, linking variation in N-fixation rates to microbial and moss community structures can be helpful in predicting future trends of C and N cycling in northern latitudes. Vegetation changes, alterations in downstream biogeochemical N processes, and anthropogenic N deposition could all interact with or alter moss associated N-fixation, thereby changing ecosystem N inputs. Further elucidation of the species level signal in N-fixation rates and microbial community will augment our knowledge of N cycling in northern latitudes, both current and future.

Differential Responses of Dinitrogen Fixation, Diazotrophic Cyanobacteria and Ammonia Oxidation Reveal a Potential Warming-Induced Imbalance of the N-Cycle in Biological Soil Crusts.

PubMed

Zhou, Xiaobing; Smith, Hilda; Giraldo Silva, Ana; Belnap, Jayne; Garcia-Pichel, Ferran

2016-01-01

N2 fixation and ammonia oxidation (AO) are the two most important processes in the nitrogen (N) cycle of biological soil crusts (BSCs). We studied the short-term response of acetylene reduction assay (ARA) rates, an indicator of potential N2 fixation, and AO rates to temperature (T, -5°C to 35°C) in BSC of different successional stages along the BSC ecological succession and geographic origin (hot Chihuahuan and cooler Great Basin deserts). ARA in all BSCs increased with T until saturation occurred between 15 and 20°C, and declined at 30-35°C. Culture studies using cyanobacteria isolated from these crusts indicated that the saturating effect was traceable to their inability to grow well diazotrophically within the high temperature range. Below saturation, temperature response was exponential, with Q10 significantly different in the two areas (~ 5 for Great Basin BSCs; 2-3 for Chihuahuan BSCs), but similar between the two successional stages. However, in contrast to ARA, AO showed a steady increase to 30-35°C in Great Basin, and Chihuhuan BSCs showed no inhibition at any tested temperature. The T response of AO also differed significantly between Great Basin (Q10 of 4.5-4.8) and Chihuahuan (Q10 of 2.4-2.6) BSCs, but not between successional stages. Response of ARA rates to T did not differ from that of AO in either desert. Thus, while both processes scaled to T in unison until 20°C, they separated to an increasing degree at higher temperature. As future warming is likely to occur in the regions where BSCs are often the dominant living cover, this predicted decoupling is expected to result in higher proportion of nitrates in soil relative to ammonium. As nitrate is more easily lost as leachate or to be reduced to gaseous forms, this could mean a depletion of soil N over large landscapes globally.

Physiological and isotopic characteristics of nitrogen fixation by hyperthermophilic methanogens: Key insights into nitrogen anabolism of the microbial communities in Archean hydrothermal systems

NASA Astrophysics Data System (ADS)

Nishizawa, Manabu; Miyazaki, Junichi; Makabe, Akiko; Koba, Keisuke; Takai, Ken

2014-08-01

Hyperthermophilic hydrogenotrophic methanogens are considered to be one of the most predominant primary producers in hydrogen (H2)-abundant hydrothermal environments in the present-day ocean and throughout the history of the Earth. However, the nitrogen sources supporting the development of microbial communities in hydrothermal environments remain poorly understood. We have investigated, for the first time, methanogenic archaea commonly found in deep-sea hydrothermal environments to understand their physiological properties (growth kinetics, energetics, and metal requirements) and isotopic characteristics during the fixation of dinitrogen (N2), which is an abundant but less-bioavailable compound in hydrothermal fluids. Culture experiments showed that Methanocaldococcus strain (Mc 1-85N) (Topt = 85 °C) and Methanothermococcus strain (Mt 5-55N) (Topt = 55 °C) assimilated N2 and ammonium, but not nitrate. Previous phylogenetic studies have predicted that the Methanocaldococcus and Methanothermococcus lineages have nitrogenases, key enzymes for N2 fixation, with biochemically uncharacterised active site metal cofactors. We showed that Mt 5-55N required molybdenum for the nitrogenase to function, implying a molybdenum-bearing cofactor in the strain. Molybdenum also stimulated diazotrophic (i.e., N2-fixing) growth of Mc 1-85N, though further experiments are required to test whether the strain contains a molybdenum-dependent nitrogenase. Importantly, Mc 1-85N exhibited an apparently lower requirement of and higher tolerance to molybdenum and iron than Mt 5-55N. Furthermore, both strains produced more 15N-depleted biomass (-4‰ relative to N2) than that previously reported for diazotrophic photosynthetic prokaryotes. These results demonstrate that diazotrophic hyperthermophilic methanogens can be broadly distributed in seafloor and subseafloor hydrothermal environments, where the availability of transition metals is variable and where organic carbon, organic nitrogen, and ammonium are generally scarce. The emergence and function of diazotrophy, coupled with methanogenesis, in the early Earth is also consistent with the nitrogen isotopic records of 3.5 billion-year-old hydrothermal deposits.

Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

NASA Astrophysics Data System (ADS)

Lu, Yangyang; Wen, Zuozhu; Shi, Dalin; Chen, Mingming; Zhang, Yao; Bonnet, Sophie; Li, Yuhang; Tian, Jiwei; Kao, Shuh-Ji

2018-01-01

Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotroph-derived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient) range of 193 to 315 µE m-2 s-1, with light saturation at around 400 µE m-2 s-1. The proportion of DDN net release ranged from ˜ 6 to ˜ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF / NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m-2 s-1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term ( < 24 h) light change modulates the physiological state, which subsequently determined the C / N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

Measurement of undisturbed di-nitrogen emissions from aquatic ecosystems

NASA Astrophysics Data System (ADS)

Qin, Shuping, Clough, Timothy, Lou, Jiafa; Hu, Chunsheng; Oenema, Oene; Wrage-Mönnig, Nicole; Zhang, Yuming

2016-04-01

Increased production of reactive nitrogen (Nr) from atmospheric di-nitrogen (N2) during the last century has greatly contributed to increased food production1-4. However, enriching the biosphere with Nr through N fertilizer production, combustion, and biological N2 fixation has also caused a series of negative effects on global ecosystems 5,6, especially aquatic ecosystems7. The main pathway converting Nr back into the atmospheric N2 pool is the last step of the denitrification process, i.e., the reduction of nitrous oxide (N2O) into N2 by micro-organisms7,8. Despite several attempts9,10, there is not yet an accurate, fast and direct method for measuring undisturbed N2 fluxes from denitrification in aquatic sediments at the field scale11-14. Such a method is essential to study the feedback of aquatic ecosystems to Nr inputs1,2,7. Here we show that the measurement of both N2O emission and its isotope signature can be used to infer the undisturbed N2 fluxes from aquatic ecosystems. The microbial reduction of N2O increases the natural abundance of 15N-N2O relative to 14N-N2O (δ15N-N2O). We observed linear relationships between δ15N-N2O and the logarithmic transformed N2O/(N2+N2O) emission ratios. Through independent measurements, we verified that the undisturbed N2 flux from aquatic ecosystems can be inferred from measurements of N2O emissions and the δ15N-N2O signature. Our method allows the determination of field-scale N2 fluxes from undisturbed aquatic ecosystems, and thereby allows model predictions of denitrification rates to be tested. The undisturbed N2 fluxes observed are almost one order of magnitude higher than those estimated by the traditional method, where perturbation of the system occurs, indicating that the ability of aquatic ecosystems to remove Nr may have been severely underestimated.

Ecogenomic sensor reveals controls on N2-fixing microorganisms in the North Pacific Ocean.

PubMed

Robidart, Julie C; Church, Matthew J; Ryan, John P; Ascani, François; Wilson, Samuel T; Bombar, Deniz; Marin, Roman; Richards, Kelvin J; Karl, David M; Scholin, Christopher A; Zehr, Jonathan P

2014-06-01

Nitrogen-fixing microorganisms (diazotrophs) are keystone species that reduce atmospheric dinitrogen (N2) gas to fixed nitrogen (N), thereby accounting for much of N-based new production annually in the oligotrophic North Pacific. However, current approaches to study N2 fixation provide relatively limited spatiotemporal sampling resolution; hence, little is known about the ecological controls on these microorganisms or the scales over which they change. In the present study, we used a drifting robotic gene sensor to obtain high-resolution data on the distributions and abundances of N2-fixing populations over small spatiotemporal scales. The resulting measurements demonstrate that concentrations of N2 fixers can be highly variable, changing in abundance by nearly three orders of magnitude in less than 2 days and 30 km. Concurrent shipboard measurements and long-term time-series sampling uncovered a striking and previously unrecognized correlation between phosphate, which is undergoing long-term change in the region, and N2-fixing cyanobacterial abundances. These results underscore the value of high-resolution sampling and its applications for modeling the effects of global change.

Modeling pathways of riverine nitrogen and phosphorus in the Baltic Sea

NASA Astrophysics Data System (ADS)

Radtke, H.; Neumann, T.; Voss, M.; Fennel, W.

2012-09-01

A better understanding of the fate of nutrients entering the Baltic Sea ecosystem is an important issue with implications for environmental management. There are two sources of nitrogen and phosphorus: riverine input and atmospheric deposition. In the case of nitrogen, the fixation of dinitrogen by diazotrophic bacteria represents a third source. From an analysis of stable nitrogen isotope ratios it was suggested that most of the riverine nitrogen is sequestered in the coastal rim, specifically along the southern Baltic Sea coast with its coarse sediments, whereas nitrogen from fixation dominates the central basins. However, pathways of nutrients and timescales between the input of the nutrients and their arrival in different basins are difficult to obtain from direct measurements. To elucidate this problem, we use a source attribution technique in a three-dimensional ecosystem model, ERGOM, to track nutrients originating from various rivers. An “age” variable is attributed to the marked elements to indicate their propagation speeds and residence times. In this paper, we specifically investigate the spreading of nitrogen and phosphorus from the riverine discharges of the Oder, Vistula, Neman and Daugava. We demonstrate which regions they are transported to and for how long they remain in the ecosystem. The model results show good agreement with source estimations from observed δ15N values in sediments. The model results suggest that 95% of nitrogen is lost by denitrification in sediments, after an average time of 1.4 years for riverine nitrogen. The residence time of riverine phosphorus is much longer and exceeds our simulated period of 35 years.

Simple approach for the preparation of (15-15)N2-enriched water for nitrogen fixation assessments: evaluation, application and recommendations.

PubMed

Klawonn, Isabell; Lavik, Gaute; Böning, Philipp; Marchant, Hannah K; Dekaezemacker, Julien; Mohr, Wiebke; Ploug, Helle

2015-01-01

Recent findings revealed that the commonly used (15)N2 tracer assay for the determination of dinitrogen (N2) fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared (15-15)N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of (15-15)N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add (15-15)N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥ 5 min). Optionally, water can be degassed at low-pressure (≥950 mbar) for 10 min prior to the (15-15)N2 gas addition to indirectly enhance the (15-15)N2 concentration. This preparation of (15-15)N2-enriched water can be done within 1 h using standard laboratory equipment. The final (15)N-atom% excess was 5% after replacing 2-5% of the incubation volume with (15-15)N2-enriched water. Notably, the addition of (15-15)N2-enriched water can alter levels of trace elements in the incubation water due to the contact of (15-15)N2-enriched water with glass, plastic and rubber ware. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn) increased by up to 0.1 nmol L(-1) in the final incubation volume, which may bias rate measurements in regions where N2 fixation is limited by trace elements. For these regions, we tested an alternative way to enrich water with (15-15)N2. The (15-15)N2 was injected as a bubble directly to the incubation water, followed by gentle shaking. Immediately thereafter, the bubble was replaced with water to stop the (15-15)N2 equilibration. This approach achieved a (15)N-atom% excess of 6.6 ± 1.7% when adding 2 mL (15-15)N2 per liter of incubation water. The herein presented methodological tests offer guidelines for the (15)N2 tracer assay and thus, are crucial to circumvent methodological draw-backs for future N2 fixation assessments.

Simple approach for the preparation of 15−15N2-enriched water for nitrogen fixation assessments: evaluation, application and recommendations

PubMed Central

Klawonn, Isabell; Lavik, Gaute; Böning, Philipp; Marchant, Hannah K.; Dekaezemacker, Julien; Mohr, Wiebke; Ploug, Helle

2015-01-01

Recent findings revealed that the commonly used 15N2 tracer assay for the determination of dinitrogen (N2) fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared 15−15N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of 15−15N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add 15−15N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥ 5 min). Optionally, water can be degassed at low-pressure (≥950 mbar) for 10 min prior to the 15−15N2 gas addition to indirectly enhance the 15−15N2 concentration. This preparation of 15−15N2-enriched water can be done within 1 h using standard laboratory equipment. The final 15N-atom% excess was 5% after replacing 2–5% of the incubation volume with 15−15N2-enriched water. Notably, the addition of 15−15N2-enriched water can alter levels of trace elements in the incubation water due to the contact of 15−15N2-enriched water with glass, plastic and rubber ware. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn) increased by up to 0.1 nmol L−1 in the final incubation volume, which may bias rate measurements in regions where N2 fixation is limited by trace elements. For these regions, we tested an alternative way to enrich water with 15−15N2. The 15−15N2 was injected as a bubble directly to the incubation water, followed by gentle shaking. Immediately thereafter, the bubble was replaced with water to stop the 15−15N2 equilibration. This approach achieved a 15N-atom% excess of 6.6 ± 1.7% when adding 2 mL 15−15N2 per liter of incubation water. The herein presented methodological tests offer guidelines for the 15N2 tracer assay and thus, are crucial to circumvent methodological draw-backs for future N2 fixation assessments. PMID:26300853

Establishment of process technology for the manufacture of dinitrogen pentoxide and its utility for the synthesis of most powerful explosive of today--CL-20.

PubMed

Talawar, M B; Sivabalan, R; Polke, B G; Nair, U R; Gore, G M; Asthana, S N

2005-09-30

This paper reviews the recent work done on the synthesis as well as characterization of dinitrogen pentoxide (DNPO). The physico-chemical characteristics of DNPO are also discussed. The review brings out the key aspects of N2O5 technology with relevance to realize modern and novel HEMs. The paper also includes the aspects related with establishing the synthesis facility of dinitrogen pentoxide at HEMRL by gas phase interaction of N2O4 with O3. The process parameters for the synthesis of N2O5 at 50 g/batch have been optimized. The synthesized dinitrogen pentoxide has been characterized by UV [204, 213, 258 nm (pi-->pi*) 378 and 384 nm (n-->pi*)] and IR (1428, 1266, 1249, 1206, 1044, 822, 750, 546 and 454 cm(-1)) spectroscopy. The DSC clearly showed the sublimation of N2O5 at 32 degrees C. The nitration studies on 2,6,8,12-tetraacetylhexaaza tetracyclo[5,5,0,0(3,11)0(5,9)]dodecane (TAIW) proved its viability in 2,4,6,8,10,12-hexanitro-2,4,6,8(10,12))-hexaazatetracyclo [5,5,0,0(3,11)0(5,9)]dodecane (CL-20) synthesis. The synthesized CL-20 and its precursors have also been subjected to hyphenated TG-FTIR studies to understand decomposition pattern.

The nitrogen cycle in anaerobic methanotrophic mats of the Black Sea is linked to sulfate reduction and biomass decomposition.

PubMed

Siegert, Michael; Taubert, Martin; Seifert, Jana; von Bergen-Tomm, Martin; Basen, Mirko; Bastida, Felipe; Gehre, Matthias; Richnow, Hans-Hermann; Krüger, Martin

2013-11-01

Anaerobic methanotrophic (ANME) mats host methane-oxidizing archaea and sulfate-reducing prokaryotes. Little is known about the nitrogen cycle in these communities. Here, we link the anaerobic oxidation of methane (AOM) to the nitrogen cycle in microbial mats of the Black Sea by using stable isotope probing. We used four different (15)N-labeled sources of nitrogen: dinitrogen, nitrate, nitrite and ammonium. We estimated the nitrogen incorporation rates into the total biomass and the methyl coenzyme M reductase (MCR). Dinitrogen played an insignificant role as nitrogen source. Assimilatory and dissimilatory nitrate reduction occurred. High rates of nitrate reduction to dinitrogen were stimulated by methane and sulfate, suggesting that oxidation of reduced sulfur compounds such as sulfides was necessary for AOM with nitrate as electron acceptor. Nitrate reduction to dinitrogen occurred also in the absence of methane as electron donor but at six times slower rates. Dissimilatory nitrate reduction to ammonium was independent of AOM. Ammonium was used for biomass synthesis under all conditions. The pivotal enzyme in AOM coupled to sulfate reduction, MCR, was synthesized from nitrate and ammonium. Results show that AOM coupled to sulfate reduction along with biomass decomposition drive the nitrogen cycle in the ANME mats of the Black Sea and that MCR enzymes are involved in this process. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Microperimetry in patients with central serous retinopathy.

PubMed

Toonen, F; Remky, A; Janssen, V; Wolf, S; Reim, M

1995-09-01

In patients with acute central serous retinopathy (CSR), evaluation of visual acuity alone may not represent visual function. In patients with acute CSR, visual function may be disturbed by localized scotomas, distortion, and waviness. For the assessment of localized light sensitivity and stability of fixation, patients with CSR were evaluated by fundus perimetry with a scanning laser ophthalmoscope (SLO 101, Rodenstock Instruments). In all, 21 patients with acute CSR and 19 healthy volunteers were included in the study. Diagnosis of CSR was established by ophthalmoscopy and digital video fluorescein angiography. All patients and volunteers underwent static suprathreshold perimetry with the SLO. Light sensitivity was quantified by presenting stimuli with different light intensities (intensity, 0-27.9 dB above background; size, Goldmann III; wavelength, 633 nm) using an automatic staircase strategy. Stimuli were presented with simultaneous real-time monitoring of the retina. Fixation stability was quantified by measuring the area encompassing 75% of all points of fixation. Light sensitivity was 18-20 dB in affected areas, whereas in healthy eyes and outside the affected area, values of 22-24 dB were obtained. Fixation stability was significantly decreased in the affected eye as compared with normal eyes (33 +/- 12 versus 21 +/- 4 min of arc; P < 0.01). Static perimetry with an SLO is a useful technique for the assessment of localized light sensitivity and fixation stability in patients with macular disease. This technique could provide helpful information in the management of CSR.

Abnormal Fixational Eye Movements in Amblyopia.

PubMed

Shaikh, Aasef G; Otero-Millan, Jorge; Kumar, Priyanka; Ghasia, Fatema F

2016-01-01

Fixational saccades shift the foveal image to counteract visual fading related to neural adaptation. Drifts are slow eye movements between two adjacent fixational saccades. We quantified fixational saccades and asked whether their changes could be attributed to pathologic drifts seen in amblyopia, one of the most common causes of blindness in childhood. Thirty-six pediatric subjects with varying severity of amblyopia and eleven healthy age-matched controls held their gaze on a visual target. Eye movements were measured with high-resolution video-oculography during fellow eye-viewing and amblyopic eye-viewing conditions. Fixational saccades and drifts were analyzed in the amblyopic and fellow eye and compared with controls. We found an increase in the amplitude with decreased frequency of fixational saccades in children with amblyopia. These alterations in fixational eye movements correlated with the severity of their amblyopia. There was also an increase in eye position variance during drifts in amblyopes. There was no correlation between the eye position variance or the eye velocity during ocular drifts and the amplitude of subsequent fixational saccade. Our findings suggest that abnormalities in fixational saccades in amblyopia are independent of the ocular drift. This investigation of amblyopia in pediatric age group quantitatively characterizes the fixation instability. Impaired properties of fixational saccades could be the consequence of abnormal processing and reorganization of the visual system in amblyopia. Paucity in the visual feedback during amblyopic eye-viewing condition can attribute to the increased eye position variance and drift velocity.

Abnormal Fixational Eye Movements in Amblyopia

PubMed Central

Shaikh, Aasef G.; Otero-Millan, Jorge; Kumar, Priyanka; Ghasia, Fatema F.

2016-01-01

Purpose Fixational saccades shift the foveal image to counteract visual fading related to neural adaptation. Drifts are slow eye movements between two adjacent fixational saccades. We quantified fixational saccades and asked whether their changes could be attributed to pathologic drifts seen in amblyopia, one of the most common causes of blindness in childhood. Methods Thirty-six pediatric subjects with varying severity of amblyopia and eleven healthy age-matched controls held their gaze on a visual target. Eye movements were measured with high-resolution video-oculography during fellow eye-viewing and amblyopic eye-viewing conditions. Fixational saccades and drifts were analyzed in the amblyopic and fellow eye and compared with controls. Results We found an increase in the amplitude with decreased frequency of fixational saccades in children with amblyopia. These alterations in fixational eye movements correlated with the severity of their amblyopia. There was also an increase in eye position variance during drifts in amblyopes. There was no correlation between the eye position variance or the eye velocity during ocular drifts and the amplitude of subsequent fixational saccade. Our findings suggest that abnormalities in fixational saccades in amblyopia are independent of the ocular drift. Discussion This investigation of amblyopia in pediatric age group quantitatively characterizes the fixation instability. Impaired properties of fixational saccades could be the consequence of abnormal processing and reorganization of the visual system in amblyopia. Paucity in the visual feedback during amblyopic eye-viewing condition can attribute to the increased eye position variance and drift velocity. PMID:26930079

Measuring N2 Pressure Using Cyanobacteria Discipline: Geomicrobiology

NASA Technical Reports Server (NTRS)

Silverman, Shaelyn N.; Kopf, Sebastian; Gordon, Richard; Bebout, Brad M.; Som, Sanjoy

2017-01-01

The evolution of Earth's atmosphere has been governed by biological evolution. Dinitrogen (N2) has been a major constituent of Earth's atmosphere throughout the planet's history, yet only a few constraints exist for the partial pressure of N2 (pN2). In this study we evaluate two new potential proxies for pN2: the physical spacing between heterocysts and the isotopic signature of nitrogen fixation in filamentous cyanobacteria. Heterocyst-forming filamentous cyanobacteria are some of the oldest photosynthetic microorganisms on Earth, and debated fossilized specimens have been found in sedimentary rocks as old as 2 Ga. These organisms overcome nitrogen limitation in their aqueous environment through cellular differentiation along their filaments. The specialized cells that develop, known as heterocysts, fix the nitrogen and laterally distribute it to neighboring cells along the filaments. Because the concentration of the dissolved N2 available to the filaments correlates directly with pN2, any preservable physiological response of the organism to the changed N2 availability constitutes a potential proxy for pN2. In the laboratory, we have examined how pN2 is reflected in the heterocyst spacing pattern and in the isotopic signature of nitrogen fixation by subjecting the representative species Anabaena cylindrica and Anabaena variabilis to different N2 partial pressures during growth at constant temperature and lighting (in media free of combined nitrogen). We show experimentally that the distance between heterocysts and the nitrogen isotope fractionation measured in bulk biomass reflect the pN2 experienced by Anabaena cylindrica. Current work is investigating these responses in Anabaena variabilis. When heterocystous cyanobacteria fossilize, these morphological and isotopic signatures should preserve information about pN2 at that time. Application of this relationship to the rock record may provide a paleoproxy to complement the two existing geobarometers.

Differential responses of dinitrogen fixation, diazotrophic cyanobacteria and ammonia oxidation reveal a potential warming-induced imbalance of the N-cycle in biological soil crusts

USGS Publications Warehouse

Zhou, Xiaobing; Smith, Hilda J.; Giraldo Silva, Ana; Belnap, Jayne; Garcia-Pichel, Ferran

2017-01-01

N2 fixation and ammonia oxidation (AO) are the two most important processes in the nitrogen (N) cycle of biological soil crusts (BSCs). We studied the short-term response of acetylene reduction assay (ARA) rates, an indicator of potential N2 fixation, and AO rates to temperature (T, -5°C to 35°C) in BSC of different successional stages along the BSC ecological succession and geographic origin (hot Chihuahuan and cooler Great Basin deserts). ARA in all BSCs increased with T until saturation occurred between 15 and 20°C, and declined at 30–35°C. Culture studies using cyanobacteria isolated from these crusts indicated that the saturating effect was traceable to their inability to grow well diazotrophically within the high temperature range. Below saturation, temperature response was exponential, with Q10 significantly different in the two areas (~ 5 for Great Basin BSCs; 2–3 for Chihuahuan BSCs), but similar between the two successional stages. However, in contrast to ARA, AO showed a steady increase to 30–35°C in Great Basin, and Chihuhuan BSCs showed no inhibition at any tested temperature. The T response of AO also differed significantly between Great Basin (Q10 of 4.5–4.8) and Chihuahuan (Q10 of 2.4–2.6) BSCs, but not between successional stages. Response of ARA rates to T did not differ from that of AO in either desert. Thus, while both processes scaled to T in unison until 20°C, they separated to an increasing degree at higher temperature. As future warming is likely to occur in the regions where BSCs are often the dominant living cover, this predicted decoupling is expected to result in higher proportion of nitrates in soil relative to ammonium. As nitrate is more easily lost as leachate or to be reduced to gaseous forms, this could mean a depletion of soil N over large landscapes globally.

Differential Responses of Dinitrogen Fixation, Diazotrophic Cyanobacteria and Ammonia Oxidation Reveal a Potential Warming-Induced Imbalance of the N-Cycle in Biological Soil Crusts

PubMed Central

Zhou, Xiaobing; Smith, Hilda; Giraldo Silva, Ana; Belnap, Jayne; Garcia-Pichel, Ferran

2016-01-01

N2 fixation and ammonia oxidation (AO) are the two most important processes in the nitrogen (N) cycle of biological soil crusts (BSCs). We studied the short-term response of acetylene reduction assay (ARA) rates, an indicator of potential N2 fixation, and AO rates to temperature (T, -5°C to 35°C) in BSC of different successional stages along the BSC ecological succession and geographic origin (hot Chihuahuan and cooler Great Basin deserts). ARA in all BSCs increased with T until saturation occurred between 15 and 20°C, and declined at 30–35°C. Culture studies using cyanobacteria isolated from these crusts indicated that the saturating effect was traceable to their inability to grow well diazotrophically within the high temperature range. Below saturation, temperature response was exponential, with Q10 significantly different in the two areas (~ 5 for Great Basin BSCs; 2–3 for Chihuahuan BSCs), but similar between the two successional stages. However, in contrast to ARA, AO showed a steady increase to 30–35°C in Great Basin, and Chihuhuan BSCs showed no inhibition at any tested temperature. The T response of AO also differed significantly between Great Basin (Q10 of 4.5–4.8) and Chihuahuan (Q10 of 2.4–2.6) BSCs, but not between successional stages. Response of ARA rates to T did not differ from that of AO in either desert. Thus, while both processes scaled to T in unison until 20°C, they separated to an increasing degree at higher temperature. As future warming is likely to occur in the regions where BSCs are often the dominant living cover, this predicted decoupling is expected to result in higher proportion of nitrates in soil relative to ammonium. As nitrate is more easily lost as leachate or to be reduced to gaseous forms, this could mean a depletion of soil N over large landscapes globally. PMID:27776160

Structural principles for computational and de novo design of 4Fe-4S metalloproteins

PubMed Central

Nanda, Vikas; Senn, Stefan; Pike, Douglas H.; Rodriguez-Granillo, Agustina; Hansen, Will; Khare, Sagar D.; Noy, Dror

2017-01-01

Iron-sulfur centers in metalloproteins can access multiple oxidation states over a broad range of potentials, allowing them to participate in a variety of electron transfer reactions and serving as catalysts for high-energy redox processes. The nitrogenase FeMoCO cluster converts di-nitrogen to ammonia in an eight-electron transfer step. The 2(Fe4S4) containing bacterial ferredoxin is an evolutionarily ancient metalloprotein fold and is thought to be a primordial progenitor of extant oxidoreductases. Controlling chemical transformations mediated by iron-sulfur centers such as nitrogen fixation, hydrogen production as well as electron transfer reactions involved in photosynthesis are of tremendous importance for sustainable chemistry and energy production initiatives. As such, there is significant interest in the design of iron-sulfur proteins as minimal models to gain fundamental understanding of complex natural systems and as lead-molecules for industrial and energy applications. Herein, we discuss salient structural characteristics of natural iron-sulfur proteins and how they guide principles for design. Model structures of past designs are analyzed in the context of these principles and potential directions for enhanced designs are presented, and new areas of iron-sulfur protein design are proposed. PMID:26449207

Interdecadal Trichodesmium variability in cold North Atlantic waters

NASA Astrophysics Data System (ADS)

Rivero-Calle, Sara; Del Castillo, Carlos E.; Gnanadesikan, Anand; Dezfuli, Amin; Zaitchik, Benjamin; Johns, David G.

2016-11-01

Studies of the nitrogen cycle in the ocean generally assume that the distribution of the marine diazotroph, Trichodesmium, is restricted to warm, tropical, and subtropical oligotrophic waters. Here we show evidence that Trichodesmium are widely distributed in the North Atlantic. We report an approximately fivefold increase during the 1980s and 1990s in Trichodesmium presence near the British Isles with respect to the average over the last 50 years. A potential explanation is an increase in the Saharan dust source starting in the 1980s, coupled with changes in North Atlantic winds that opened a pathway for dust transport. Results from a coarse-resolution model in which winds vary but iron deposition is climatologically fixed suggest frequent nitrogen limitation in the region and reversals of the Portugal current, but it does not simulate the observed changes in Trichodesmium. Our results suggest that Trichodesmium may be capable of growth at temperatures below 20°C and challenge assumptions about their latitudinal distribution. Therefore, we need to reevaluate assumptions about the temperature limitations of Trichodesmium and the dinitrogen (N2) fixation capabilities of extratropical strains, which may have important implications for the global nitrogen budget.

The Pattern of Visual Fixation Eccentricity and Instability in Optic Neuropathy and Its Spatial Relationship to Retinal Ganglion Cell Layer Thickness.

PubMed

Mallery, Robert M; Poolman, Pieter; Thurtell, Matthew J; Wang, Jui-Kai; Garvin, Mona K; Ledolter, Johannes; Kardon, Randy H

2016-07-01

The purpose of this study was to assess whether clinically useful measures of fixation instability and eccentricity can be derived from retinal tracking data obtained during optical coherence tomography (OCT) in patients with optic neuropathy (ON) and to develop a method for relating fixation to the retinal ganglion cell complex (GCC) thickness. Twenty-nine patients with ON underwent macular volume OCT with 30 seconds of confocal scanning laser ophthalmoscope (cSLO)-based eye tracking during fixation. Kernel density estimation quantified fixation instability and fixation eccentricity from the distribution of fixation points on the retina. Preferred ganglion cell layer loci (PGCL) and their relationship to the GCC thickness map were derived, accounting for radial displacement of retinal ganglion cell soma from their corresponding cones. Fixation instability was increased in ON eyes (0.21 deg2) compared with normal eyes (0.06982 deg2; P < 0.001), and fixation eccentricity was increased in ON eyes (0.48°) compared with normal eyes (0.24°; P = 0.03). Fixation instability and eccentricity each correlated moderately with logMAR acuity and were highly predictive of central visual field loss. Twenty-six of 35 ON eyes had PGCL skewed toward local maxima of the GCC thickness map. Patients with bilateral dense central scotomas had PGCL in homonymous retinal locations with respect to the fovea. Fixation instability and eccentricity measures obtained during cSLO-OCT assess the function of perifoveal retinal elements and predict central visual field loss in patients with ON. A model relating fixation to the GCC thickness map offers a method to assess the structure-function relationship between fixation and areas of preserved GCC in patients with ON.

The Pattern of Visual Fixation Eccentricity and Instability in Optic Neuropathy and Its Spatial Relationship to Retinal Ganglion Cell Layer Thickness

PubMed Central

M. Mallery, Robert; Poolman, Pieter; J. Thurtell, Matthew; Wang, Jui-Kai; K. Garvin, Mona; Ledolter, Johannes; Kardon, Randy H.

2016-01-01

Purpose The purpose of this study was to assess whether clinically useful measures of fixation instability and eccentricity can be derived from retinal tracking data obtained during optical coherence tomography (OCT) in patients with optic neuropathy (ON) and to develop a method for relating fixation to the retinal ganglion cell complex (GCC) thickness. Methods Twenty-nine patients with ON underwent macular volume OCT with 30 seconds of confocal scanning laser ophthalmoscope (cSLO)-based eye tracking during fixation. Kernel density estimation quantified fixation instability and fixation eccentricity from the distribution of fixation points on the retina. Preferred ganglion cell layer loci (PGCL) and their relationship to the GCC thickness map were derived, accounting for radial displacement of retinal ganglion cell soma from their corresponding cones. Results Fixation instability was increased in ON eyes (0.21 deg2) compared with normal eyes (0.06982 deg2; P < 0.001), and fixation eccentricity was increased in ON eyes (0.48°) compared with normal eyes (0.24°; P = 0.03). Fixation instability and eccentricity each correlated moderately with logMAR acuity and were highly predictive of central visual field loss. Twenty-six of 35 ON eyes had PGCL skewed toward local maxima of the GCC thickness map. Patients with bilateral dense central scotomas had PGCL in homonymous retinal locations with respect to the fovea. Conclusions Fixation instability and eccentricity measures obtained during cSLO-OCT assess the function of perifoveal retinal elements and predict central visual field loss in patients with ON. A model relating fixation to the GCC thickness map offers a method to assess the structure–function relationship between fixation and areas of preserved GCC in patients with ON. PMID:27409502

Nutrient availability and the ultimate control of the biological carbon pump in the western tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Moutin, Thierry; Wagener, Thibaut; Caffin, Mathieu; Fumenia, Alain; Gimenez, Audrey; Baklouti, Melika; Bouruet-Aubertot, Pascale; Pujo-Pay, Mireille; Leblanc, Karine; Lefevre, Dominique; Helias Nunige, Sandra; Leblond, Nathalie; Grosso, Olivier; de Verneil, Alain

2018-05-01

Surface waters (0-200 m) of the western tropical South Pacific (WTSP) were sampled along a longitudinal 4000 km transect (OUTPACE cruise, DOI: 10.17600/15000900) during the austral summer (stratified) period (18 February to 3 April 2015) between the Melanesian Archipelago (MA) and the western part of the SP gyre (WGY). Two distinct areas were considered for the MA, the western MA (WMA), and the eastern MA (EMA). The main carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes provide a basis for the characterization of the expected trend from oligotrophy to ultra-oligotrophy, and the building of first-order budgets at the daily and seasonal timescales (using climatology). Sea surface chlorophyll a well reflected the expected oligotrophic gradient with higher values obtained at WMA, lower values at WGY, and intermediate values at EMA. As expected, the euphotic zone depth, the deep chlorophyll maximum, and nitracline depth deepen from west to east. Nevertheless, phosphaclines and nitraclines did not match. The decoupling between phosphacline and nitracline depths in the MA allows for excess P to be locally provided in the upper water by winter mixing. We found a significant biological soft tissue carbon pump in the MA sustained almost exclusively by dinitrogen (N2) fixation and essentially controlled by phosphate availability in this iron-rich environment. The MA appears to be a net sink for atmospheric CO2, while the WGY is in quasi-steady state. We suggest that the necessary excess P, allowing the success of nitrogen fixers and subsequent carbon production and export, is mainly brought to the upper surface by local deep winter convection at an annual timescale rather than by surface circulation. While the origin of the decoupling between phosphacline and nitracline remains uncertain, the direct link between local P upper water enrichment, N2 fixation, and organic carbon production and export, offers a possible shorter timescale than previously thought between N input by N2 fixation and carbon export. The low iron availability in the SP gyre and P availability in the MA during the stratified period may appear as the ultimate control of N input by N2 fixation. Because of the huge volume of water to consider, and because the SP Ocean is the place of intense denitrification in the east (N sink) and N2 fixation in the west (N source), precise seasonal C, N, P, and iron (Fe) budgets would be of prime interest to understand the efficiency, at the present time and in the future, of the oceanic biological carbon pump.

Phase-contrast Hounsfield units of fixated and non-fixated soft-tissue samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willner, Marian; Fior, Gabriel; Marschner, Mathias

X-ray phase-contrast imaging is a novel technology that achieves high soft-tissue contrast. Although its clinical impact is still under investigation, the technique may potentially improve clinical diagnostics. In conventional attenuation-based X-ray computed tomography, radiological diagnostics are quantified by Hounsfield units. Corresponding Hounsfield units for phase-contrast imaging have been recently introduced, enabling a setup-independent comparison and standardized interpretation of imaging results. Thus far, the experimental values of few tissue types have been reported; these values have been determined from fixated tissue samples. This study presents phase-contrast Hounsfield units for various types of non-fixated human soft tissues. A large variety of tissuemore » specimens ranging from adipose, muscle and connective tissues to liver, kidney and pancreas tissues were imaged by a grating interferometer with a rotating-anode X-ray tube and a photon-counting detector. In addition, we investigated the effects of formalin fixation on the quantitative phase-contrast imaging results.« less

Phase-Contrast Hounsfield Units of Fixated and Non-Fixated Soft-Tissue Samples

PubMed Central

Willner, Marian; Fior, Gabriel; Marschner, Mathias; Birnbacher, Lorenz; Schock, Jonathan; Braun, Christian; Fingerle, Alexander A.; Noël, Peter B.; Rummeny, Ernst J.; Pfeiffer, Franz; Herzen, Julia

2015-01-01

X-ray phase-contrast imaging is a novel technology that achieves high soft-tissue contrast. Although its clinical impact is still under investigation, the technique may potentially improve clinical diagnostics. In conventional attenuation-based X-ray computed tomography, radiological diagnostics are quantified by Hounsfield units. Corresponding Hounsfield units for phase-contrast imaging have been recently introduced, enabling a setup-independent comparison and standardized interpretation of imaging results. Thus far, the experimental values of few tissue types have been reported; these values have been determined from fixated tissue samples. This study presents phase-contrast Hounsfield units for various types of non-fixated human soft tissues. A large variety of tissue specimens ranging from adipose, muscle and connective tissues to liver, kidney and pancreas tissues were imaged by a grating interferometer with a rotating-anode X-ray tube and a photon-counting detector. Furthermore, we investigated the effects of formalin fixation on the quantitative phase-contrast imaging results. PMID:26322638

Phase-contrast Hounsfield units of fixated and non-fixated soft-tissue samples

DOE PAGES

Willner, Marian; Fior, Gabriel; Marschner, Mathias; ...

2015-08-31

X-ray phase-contrast imaging is a novel technology that achieves high soft-tissue contrast. Although its clinical impact is still under investigation, the technique may potentially improve clinical diagnostics. In conventional attenuation-based X-ray computed tomography, radiological diagnostics are quantified by Hounsfield units. Corresponding Hounsfield units for phase-contrast imaging have been recently introduced, enabling a setup-independent comparison and standardized interpretation of imaging results. Thus far, the experimental values of few tissue types have been reported; these values have been determined from fixated tissue samples. This study presents phase-contrast Hounsfield units for various types of non-fixated human soft tissues. A large variety of tissuemore » specimens ranging from adipose, muscle and connective tissues to liver, kidney and pancreas tissues were imaged by a grating interferometer with a rotating-anode X-ray tube and a photon-counting detector. In addition, we investigated the effects of formalin fixation on the quantitative phase-contrast imaging results.« less

Spontaneous eye movements in goldfish: oculomotor integrator performance, plasticity, and dependence on visual feedback.

PubMed

Mensh, B D; Aksay, E; Lee, D D; Seung, H S; Tank, D W

2004-03-01

To quantify performance of the goldfish oculomotor neural integrator and determine its dependence on visual feedback, we measured the relationship between eye drift-velocity and position during spontaneous gaze fixations in the light and in the dark. In the light, drift-velocities were typically less than 1 deg/s, similar to those observed in humans. During brief periods in darkness, drift-velocities were only slightly larger, but showed greater variance. One hour in darkness degraded fixation-holding performance. These findings suggest that while visual feedback is not essential for online fixation stability, it may be used to tune the mechanism of persistent neural activity in the oculomotor integrator.

A Rare Terminal Dinitrogen Complex of Chromium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mock, Michael T.; Chen, Shentan; Rousseau, Roger J.

The reduction of dinitrogen to ammonia from N2 and H2 is currently carried out by the Haber-Bosch process, an energy intensive process that requires high pressures and high temperatures and accounts for the production of millions of tons of ammonia per year. The development of a catalytic, energy-efficient process for N2 reduction is of great interest and remains a formidable challenge. In this communication, we are reporting the preparation, characterization and computational electronic structure analysis of a rare 'Chatt-type' ((P-P)2M(N2)2, P-P = diphosphine ligand) complex of chromium, cis-[Cr(N2)2(PPh2NBn2)2] and its reactivity with CO. This complex is supported by the diphosphinemore » ligand PPh2NBn2, containing non-coordinating pendant amine bases, to serve as proton relays. Future studies for this complex are aimed at answering fundamental questions regarding the role of proton relays in the second coordination sphere in their ability to facilitate proton movement from an external acid to metal-bound dinitrogen ligands in the challenging multi-proton/electron reduction of N2 to ammonia.« less

Heterobimetallic Ti/Co Complexes That Promote Catalytic N-N Bond Cleavage.

PubMed

Wu, Bing; Gramigna, Kathryn M; Bezpalko, Mark W; Foxman, Bruce M; Thomas, Christine M

2015-11-16

Treatment of the tris(phosphinoamide) titanium precursor ClTi(XylNP(i)Pr2)3 (1) with CoI2 leads to the heterobimetallic complex (η(2)-(i)Pr2PNXyl)Ti(XylNP(i)Pr2)2(μ-Cl)CoI (2). One-electron reduction of 2 affords (η(2)-(i)Pr2PNXyl)Ti(XylNP(i)Pr2)2CoI (3), which can be reduced by another electron under dinitrogen to generate the reduced diamagnetic complex (THF)Ti(XylNP(i)Pr2)3CoN2 (4). The removal of the dinitrogen ligand from 4 under vacuum affords (THF)Ti(XylNP(i)Pr2)3Co (5), which features a Ti-Co triple bond. Treatment of 4 with hydrazine or methyl hydrazine results in N-N bond cleavage and affords the new diamagnetic complexes (L)Ti(XylNP(i)Pr2)3CoN2 (L = NH3 (6), MeNH2 (7)). Complexes 4, 5, and 6 have been shown to catalyze the disproportionation of hydrazine into ammonia and dinitrogen gas through a mechanism involving a diazene intermediate.

Evolutionary games on cycles with strong selection

NASA Astrophysics Data System (ADS)

Altrock, P. M.; Traulsen, A.; Nowak, M. A.

2017-02-01

Evolutionary games on graphs describe how strategic interactions and population structure determine evolutionary success, quantified by the probability that a single mutant takes over a population. Graph structures, compared to the well-mixed case, can act as amplifiers or suppressors of selection by increasing or decreasing the fixation probability of a beneficial mutant. Properties of the associated mean fixation times can be more intricate, especially when selection is strong. The intuition is that fixation of a beneficial mutant happens fast in a dominance game, that fixation takes very long in a coexistence game, and that strong selection eliminates demographic noise. Here we show that these intuitions can be misleading in structured populations. We analyze mean fixation times on the cycle graph under strong frequency-dependent selection for two different microscopic evolutionary update rules (death-birth and birth-death). We establish exact analytical results for fixation times under strong selection and show that there are coexistence games in which fixation occurs in time polynomial in population size. Depending on the underlying game, we observe inherence of demographic noise even under strong selection if the process is driven by random death before selection for birth of an offspring (death-birth update). In contrast, if selection for an offspring occurs before random removal (birth-death update), then strong selection can remove demographic noise almost entirely.

Community structure and soil pH determine chemoautotrophic carbon dioxide fixation in drained paddy soils.

PubMed

Long, Xi-En; Yao, Huaiying; Wang, Juan; Huang, Ying; Singh, Brajesh K; Zhu, Yong-Guan

2015-06-16

Previous studies suggested that microbial photosynthesis plays a potential role in paddy fields, but little is known about chemoautotrophic carbon fixers in drained paddy soils. We conducted a microcosm study using soil samples from five paddy fields to determine the environmental factors and quantify key functional microbial taxa involved in chemoautotrophic carbon fixation. We used stable isotope probing in combination with phospholipid fatty acid (PLFA) and molecular approaches. The amount of microbial (13)CO2 fixation was determined by quantification of (13)C-enriched fatty acid methyl esters and ranged from 21.28 to 72.48 ng of (13)C (g of dry soil)(-1), and the corresponding ratio (labeled PLFA-C:total PLFA-C) ranged from 0.06 to 0.49%. The amount of incorporationof (13)CO2 into PLFAs significantly increased with soil pH except at pH 7.8. PLFA and high-throughput sequencing results indicated a dominant role of Gram-negative bacteria or proteobacteria in (13)CO2 fixation. Correlation analysis indicated a significant association between microbial community structure and carbon fixation. We provide direct evidence of chemoautotrophic C fixation in soils with statistical evidence of microbial community structure regulation of inorganic carbon fixation in the paddy soil ecosystem.

A simple and rapid latex fixation test for measuring immunoglobulins produced in cell cultures.

PubMed

Kasahara, T; Harada, H; Enomoto, H; Itoh, Y; Kawai, T; Shioiri-Nakano, K

1981-01-01

A rapid and simple latex fixation test (LFT), which quantifies immunoglobulin (Ig) released into culture supernatants is described. Latex particles are coated with rabbit anti-human IgG, IgA or IgM antibodies. With this LFT technique the concentration of Ig is determined within a few minutes. The LFT is as sensitive and quantitative as double-antibody radioimmunoassay and is capable of detecting 35, 68 and 225 ng/ml of IgG, IgA and IgM, respectively.

Quantifying nitrogen-fixation in feather moss carpets of boreal forests.

PubMed

DeLuca, Thomas H; Zackrisson, Olle; Nilsson, Marie-Charlotte; Sellstedt, Anita

2002-10-31

Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests.

Fixation light hue bias revisited: implications for using adaptive optics to study color vision.

PubMed

Hofer, H J; Blaschke, J; Patolia, J; Koenig, D E

2012-03-01

Current vision science adaptive optics systems use near infrared wavefront sensor 'beacons' that appear as red spots in the visual field. Colored fixation targets are known to influence the perceived color of macroscopic visual stimuli (Jameson, D., & Hurvich, L. M. (1967). Fixation-light bias: An unwanted by-product of fixation control. Vision Research, 7, 805-809.), suggesting that the wavefront sensor beacon may also influence perceived color for stimuli displayed with adaptive optics. Despite its importance for proper interpretation of adaptive optics experiments on the fine scale interaction of the retinal mosaic and spatial and color vision, this potential bias has not yet been quantified or addressed. Here we measure the impact of the wavefront sensor beacon on color appearance for dim, monochromatic point sources in five subjects. The presence of the beacon altered color reports both when used as a fixation target as well as when displaced in the visual field with a chromatically neutral fixation target. This influence must be taken into account when interpreting previous experiments and new methods of adaptive correction should be used in future experiments using adaptive optics to study color. Copyright © 2012 Elsevier Ltd. All rights reserved.

Biomechanical Comparison of External Fixation and Compression Screws for Transverse Tarsal Joint Arthrodesis.

PubMed

Latt, L Daniel; Glisson, Richard R; Adams, Samuel B; Schuh, Reinhard; Narron, John A; Easley, Mark E

2015-10-01

Transverse tarsal joint arthrodesis is commonly performed in the operative treatment of hindfoot arthritis and acquired flatfoot deformity. While fixation is typically achieved using screws, failure to obtain and maintain joint compression sometimes occurs, potentially leading to nonunion. External fixation is an alternate method of achieving arthrodesis site compression and has the advantage of allowing postoperative compression adjustment when necessary. However, its performance relative to standard screw fixation has not been quantified in this application. We hypothesized that external fixation could provide transverse tarsal joint compression exceeding that possible with screw fixation. Transverse tarsal joint fixation was performed sequentially, first with a circular external fixator and then with compression screws, on 9 fresh-frozen cadaveric legs. The external fixator was attached in abutting rings fixed to the tibia and the hindfoot and a third anterior ring parallel to the hindfoot ring using transverse wires and half-pins in the tibial diaphysis, calcaneus, and metatarsals. Screw fixation comprised two 4.3 mm headless compression screws traversing the talonavicular joint and 1 across the calcaneocuboid joint. Compressive forces generated during incremental fixator foot ring displacement to 20 mm and incremental screw tightening were measured using a custom-fabricated instrumented miniature external fixator spanning the transverse tarsal joint. The maximum compressive force generated by the external fixator averaged 186% of that produced by the screws (range, 104%-391%). Fixator compression surpassed that obtainable with screws at 12 mm of ring displacement and decreased when the tibial ring was detached. No correlation was found between bone density and the compressive force achievable by either fusion method. The compression across the transverse tarsal joint that can be obtained with a circular external fixator including a tibial ring exceeds that which can be obtained with 3 headless compression screws. Screw and external fixator performance did not correlate with bone mineral density. This study supports the use of external fixation as an alternative method of generating compression to help stimulate fusion across the transverse tarsal joints. The findings provide biomechanical evidence to support the use of external fixation as a viable option in transverse tarsal joint fusion cases in which screw fixation has failed or is anticipated to be inadequate due to suboptimal bone quality. © The Author(s) 2015.

Quantifying manganese and nitrogen cycle coupling in manganese-rich, organic carbon-starved marine sediments: Examples from the Clarion-Clipperton fracture zone

NASA Astrophysics Data System (ADS)

Mogollón, José M.; Mewes, Konstantin; Kasten, Sabine

2016-07-01

Extensive deep-sea sedimentary areas are characterized by low organic carbon contents and thus harbor suboxic sedimentary environments where secondary (autotrophic) redox cycling becomes important for microbial metabolic processes. Simulation results for three stations in the Eastern Equatorial Pacific with low organic carbon content (<0.5 dry wt %) and low sedimentation rates (10-1-100 mm ky-1) show that ammonium generated during organic matter degradation may act as a reducing agent for manganese oxides below the oxic zone. Likewise, at these sedimentary depths, dissolved reduced manganese may act as a reducing agent for oxidized nitrogen species. These manganese-coupled transformations provide a suboxic conversion pathway of ammonium and nitrate to dinitrogen. These manganese-nitrogen interactions further explain the presence and production of dissolved reduced manganese (up to tens of μM concentration) in sediments with high nitrate (>20 μM) concentrations.

Numerical Simulation of Callus Healing for Optimization of Fracture Fixation Stiffness

PubMed Central

Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

2014-01-01

The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000–2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction. PMID:24991809

Numerical simulation of callus healing for optimization of fracture fixation stiffness.

PubMed

Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

2014-01-01

The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000-2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction.

Art Expertise Reduces Influence of Visual Salience on Fixation in Viewing Abstract-Paintings

PubMed Central

Koide, Naoko; Kubo, Takatomi; Nishida, Satoshi; Shibata, Tomohiro; Ikeda, Kazushi

2015-01-01

When viewing a painting, artists perceive more information from the painting on the basis of their experience and knowledge than art novices do. This difference can be reflected in eye scan paths during viewing of paintings. Distributions of scan paths of artists are different from those of novices even when the paintings contain no figurative object (i.e. abstract paintings). There are two possible explanations for this difference of scan paths. One is that artists have high sensitivity to high-level features such as textures and composition of colors and therefore their fixations are more driven by such features compared with novices. The other is that fixations of artists are more attracted by salient features than those of novices and the fixations are driven by low-level features. To test these, we measured eye fixations of artists and novices during the free viewing of various abstract paintings and compared the distribution of their fixations for each painting with a topological attentional map that quantifies the conspicuity of low-level features in the painting (i.e. saliency map). We found that the fixation distribution of artists was more distinguishable from the saliency map than that of novices. This difference indicates that fixations of artists are less driven by low-level features than those of novices. Our result suggests that artists may extract visual information from paintings based on high-level features. This ability of artists may be associated with artists’ deep aesthetic appreciation of paintings. PMID:25658327

Quantifying the competing relationship between adduction range of motion and baseplate micromotion with lateralization of reverse total shoulder arthroplasty.

PubMed

Elwell, Josie; Choi, Joseph; Willing, Ryan

2017-02-08

Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) could improve functional outcomes and mitigate scapular notching, a commonly occurring complication of the procedure. However, resulting increases in torque at the bone-implant interface may negatively affect initial fixation of the glenoid-side component, especially if only two fixation screws can be placed. Shoulder-specific finite element (FE) models of four fresh-frozen cadaveric shoulders were constructed. Scapular geometry and material property distributions were derived from CT data. Generic baseplates with two and four fixation screws were virtually implanted, after which superiorly-oriented shear loads, accompanied by a compressive load, were applied incrementally further from the glenoid surface to simulate lateralization of the COR. Relationships between lateralization, adduction range of motion (ROM), the number of fixation screws and micromotion of the baseplate (initial implant fixation) were characterized. Lateralization significantly increases micromotion (p=0.015) and adduction ROM (p=0.001). Using two, versus four, baseplate fixation screws significantly increases micromotion (p=0.008). The effect of lateralization and the number of screws on adduction ROM and baseplate fixation is variable on a shoulder-specific basis. Trade-offs exist between functional outcomes, namely adduction ROM, and initial implant fixation and the negative effect of lateralization on implant fixation is amplified when only two fixation screws are used. The possibility of lateralizing the COR in order to improve functional outcomes of the procedure should be considered on a patient-specific basis accounting for factors such as availability and quality of bone stock. Copyright © 2016 Elsevier Ltd. All rights reserved.

Toward FRP-Based Brain-Machine Interfaces—Single-Trial Classification of Fixation-Related Potentials

PubMed Central

Finke, Andrea; Essig, Kai; Marchioro, Giuseppe; Ritter, Helge

2016-01-01

The co-registration of eye tracking and electroencephalography provides a holistic measure of ongoing cognitive processes. Recently, fixation-related potentials have been introduced to quantify the neural activity in such bi-modal recordings. Fixation-related potentials are time-locked to fixation onsets, just like event-related potentials are locked to stimulus onsets. Compared to existing electroencephalography-based brain-machine interfaces that depend on visual stimuli, fixation-related potentials have the advantages that they can be used in free, unconstrained viewing conditions and can also be classified on a single-trial level. Thus, fixation-related potentials have the potential to allow for conceptually different brain-machine interfaces that directly interpret cortical activity related to the visual processing of specific objects. However, existing research has investigated fixation-related potentials only with very restricted and highly unnatural stimuli in simple search tasks while participant’s body movements were restricted. We present a study where we relieved many of these restrictions while retaining some control by using a gaze-contingent visual search task. In our study, participants had to find a target object out of 12 complex and everyday objects presented on a screen while the electrical activity of the brain and eye movements were recorded simultaneously. Our results show that our proposed method for the classification of fixation-related potentials can clearly discriminate between fixations on relevant, non-relevant and background areas. Furthermore, we show that our classification approach generalizes not only to different test sets from the same participant, but also across participants. These results promise to open novel avenues for exploiting fixation-related potentials in electroencephalography-based brain-machine interfaces and thus providing a novel means for intuitive human-machine interaction. PMID:26812487

The coxBAC Operon Encodes a Cytochrome c Oxidase Required for Heterotrophic Growth in the Cyanobacterium Anabaena variabilis Strain ATCC 29413

PubMed Central

Schmetterer, Georg; Valladares, Ana; Pils, Dietmar; Steinbach, Susanne; Pacher, Margit; Muro-Pastor, Alicia M.; Flores, Enrique; Herrero, Antonia

2001-01-01

Three genes, coxB, coxA, and coxC, found in a clone from a gene library of the cyanobacterium Anabaena variabilis strain ATCC 29413, were identified by hybridization with an oligonucleotide specific for aa3-type cytochrome c oxidases. Deletion of these genes from the genome of A. variabilis strain ATCC 29413 FD yielded strain CSW1, which displayed no chemoheterotrophic growth and an impaired cytochrome c oxidase activity. Photoautotrophic growth of CSW1, however, was unchanged, even with dinitrogen as the nitrogen source. A higher cytochrome c oxidase activity was detected in membrane preparations from dinitrogen-grown CSW1 than from nitrate-grown CSW1, but comparable activities of respiratory oxygen uptake were found in the wild type and in CSW1. Our data indicate that the identified cox gene cluster is essential for fructose-dependent growth in the dark, but not for growth on dinitrogen, and that other terminal respiratory oxidases are expressed in this cyanobacterium. Transcription analysis showed that coxBAC constitutes an operon which is expressed from two transcriptional start points. The use of one of them was stimulated by fructose. PMID:11591688

Mechanical evaluation of external skeletal fixator-intramedullary pin tie-in configurations applied to cadaveral humeri from red-tailed hawks (Buteo jamaicensis).

PubMed

Van Wettere, Arnaud J; Redig, Patrick T; Wallace, Larry J; Bourgeault, Craig A; Bechtold, Joan E

2009-12-01

Use of external skeletal fixator-intramedullary pin (ESF-IM) tie-in fixators is an adjustable and effective method of fracture fixation in birds. The objective of this study was to determine the contribution of each of the following parameters to the compressive and torsional rigidity of an ESF-IM pin tie-in applied to avian bones with an osteotomy gap: (1) varying the fixation pin position in the proximal bone segment and (2) increasing the number of fixation pins in one or both bone segments. ESF-IM pin tie-in constructs were applied to humeri harvested from red-tailed hawks (Buteo jamaicensis) (n=24) that had been euthanatized for clinical reasons. Constructs with a variation in the placement of the proximal fixation pin and with 2, 3, or 4 fixation pins applied to avian bone with an osteotomy gap were loaded to a defined displacement in torque and axial compression. Response variables were determined from resulting load-displacement curves (construct stiffness, load at 1-mm displacement). Increasing the number of fixation pins from 1 to 2 per bone segment significantly increased the stiffness in torque (110%) and compression (60%), and the safe load in torque (107%) and compression (50%). Adding a fixation pin to the distal bone segment to form a 3-pin fixator significantly increased the stiffness (27%) and safe load (20%) in torque but not in axial compression. In the configuration with 2 fixation pins, placing the proximal pin distally in the proximal bone segment significantly increased the stiffness in torque (28%), and the safe load in torque (23%) and in axial compression (32%). Results quantified the relative importance of specific parameters affecting the rigidity of ESF-IM pin tie-in constructs as applied to unstable bone fracture models in birds.

Characterization and crop production efficiency of diazotrophic bacterial isolates from coastal saline soils.

PubMed

Barua, Shilajit; Tripathi, Sudipta; Chakraborty, Ashis; Ghosh, Sagarmoy; Chakrabarti, Kalyan

2012-01-20

Use of eco-friendly area specific salt tolerant bioinoculants is better alternatives to chemical fertilizer for sustainable agriculture in coastal saline soils. We isolated diverse groups of diazotrophic bacteria from coastal saline soils of different forest and agricultural lands in the Sundarbans, West Bengal, India, to study their effect on crop productivity in saline soils. Phenotypic, biochemical and molecular identifications of the isolates were performed. The isolates produced indole acetic acid, phosphatase, and solubilized insoluble phosphates. Sequence analysis of 16S rDNA identified the SUND_BDU1 strain as Agrobacterium and the strains SUND_LM2, Can4 and Can6 belonging to the genus Bacillus. The ARA activity, dinitrogen fixation and presence of nifH genes indicated they were diazotrophs. Field trials with these strains as bioinoculants were carried out during 2007-2009, with rice during August-December followed by Lady's finger during April-June. Microplots, amended with FYM inoculated with four bioinoculants individually were compared against sole FYM (5 t ha(-1)) and a sole chemical fertilizer (60:30:30 kg ha(-1) NPK) treated plot. The strain Can6 was by far the best performer in respect of yield attributes and productivity of studied crops. Copyright © 2011 Elsevier GmbH. All rights reserved.

Exact Markov chain and approximate diffusion solution for haploid genetic drift with one-way mutation.

PubMed

Hössjer, Ola; Tyvand, Peder A; Miloh, Touvia

2016-02-01

The classical Kimura solution of the diffusion equation is investigated for a haploid random mating (Wright-Fisher) model, with one-way mutations and initial-value specified by the founder population. The validity of the transient diffusion solution is checked by exact Markov chain computations, using a Jordan decomposition of the transition matrix. The conclusion is that the one-way diffusion model mostly works well, although the rate of convergence depends on the initial allele frequency and the mutation rate. The diffusion approximation is poor for mutation rates so low that the non-fixation boundary is regular. When this happens we perturb the diffusion solution around the non-fixation boundary and obtain a more accurate approximation that takes quasi-fixation of the mutant allele into account. The main application is to quantify how fast a specific genetic variant of the infinite alleles model is lost. We also discuss extensions of the quasi-fixation approach to other models with small mutation rates. Copyright © 2015 Elsevier Inc. All rights reserved.

Transfer of diazotroph-derived nitrogen towards non-diazotrophic planktonic communities: a comparative study between Trichodesmium erythraeum, Crocosphaera watsonii and Cyanothece sp.

NASA Astrophysics Data System (ADS)

Berthelot, Hugo; Bonnet, Sophie; Grosso, Olivier; Cornet, Véronique; Barani, Aude

2016-07-01

Biological dinitrogen (N2) fixation is the major source of new nitrogen (N) for the open ocean, and thus promotes marine productivity, in particular in the vast N-depleted regions of the surface ocean. Yet, the fate of the diazotroph-derived N (DDN) in marine ecosystems is poorly understood, and its transfer to auto- and heterotrophic surrounding plankton communities is rarely measured due to technical limitations. Moreover, the different diazotrophs involved in N2 fixation (Trichodesmium spp. vs. UCYN) exhibit distinct patterns of N2 fixation and inhabit different ecological niches, thus having potentially different fates in the marine food webs that remain to be explored. Here we used nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labelling and flow cytometry cell sorting to examine the DDN transfer to specific groups of natural phytoplankton and bacteria during artificially induced diazotroph blooms in New Caledonia (southwestern Pacific). The fate of the DDN was compared according to the three diazotrophs: the filamentous and colony-forming Trichodesmium erythraeum (IMS101), and the unicellular strains Crocosphaera watsonii WH8501 and Cyanothece ATCC51142. After 48 h, 7-17 % of the N2 fixed during the experiment was transferred to the dissolved pool and 6-12 % was transferred to non-diazotrophic plankton. The transfer was twice as high in the T. erythraeum bloom than in the C. watsonii and Cyanothece blooms, which shows that filamentous diazotrophs blooms are more efficient at promoting non-diazotrophic production in N-depleted areas. The amount of DDN released in the dissolved pool did not appear to be a good indicator of the DDN transfer efficiency towards the non-diazotrophic plankton. In contrast, the 15N-enrichment of the extracellular ammonium (NH4+) pool was a good indicator of the DDN transfer efficiency: it was significantly higher in the T. erythraeum than in unicellular diazotroph blooms, leading to a DDN transfer twice as efficient. This suggests that NH4+ was the main pathway of the DDN transfer from diazotrophs to non-diazotrophs. The three simulated diazotroph blooms led to significant increases in non-diazotrophic plankton biomass. This increase in biomass was first associated with heterotrophic bacteria followed by phytoplankton, indicating that heterotrophs took the most advantage of the DDN in this oligotrophic ecosystem.

The Co-Distribution of Nitrifying Archaea and Diazotrophic Bacteria in Geothermal Springs

NASA Astrophysics Data System (ADS)

Hamilton, T. L.; Jewell, T. N. M.; de la Torre, J. R.; Boyd, E. S.

2014-12-01

Microbial processes that regulate availability of nutrients play key roles in shaping community composition. All life requires fixed nitrogen (N), and its bioavailability is what often limits ecosystem productivity. Biological nitrogen fixation, or the reduction of dinitrogen (N2) to ammonia (NH3), is a keystone process in N limited ecosystems, providing nitrogen for members of the community. N2 fixing organisms likely represent a 'bottom up control' on the structure of communities that develop in N limited environments. N2 fixation is catalyzed by a limited number of metabolically diverse bacteria and some methanogenic archaea and occurs in a variety of physically and geochemically diverse environments. Nitrification, or the sequential oxidation of NH4+ to nitrite (NO2-) and ultimately nitrate (NO3-), is catalyzed by several lineages of Proteobacteria at temperatures of < 62°C and by members of the Thaumarcheota at temperatures up to 90°C. Nitrification can thus be considered a 'top down control' on the structure of communities that develop in N limited environments. Our research in Yellowstone National Park (YNP) reveals a strong correspondence between the distribution of ammonia oxidizing archaea (AOA) and nitrogen fixing aquificae (NFA) in nitrogen-limited geothermal hot springs over large environmental gradients. Based on the physiology of AOA and NFA, we propose that the strong co-distributional pattern results from interspecies interactions, namely competition for bioavailable ammonia. Our recent work has shown that in springs where the niche dimension of AOA and NFA overlap (e.g., Perpetual Spouter; pH 7.1, 86.4°C), the dissimilar affinities for NH4 result in AOA metabolism maintaining a low NH4(T) pool and selecting for inclusion of NFA during the assembly of these communities. Here, we examine in situ physiological interactions of AOA and NFA, tracking changes in transcript levels of key genes involved in nitrogen metabolism and carbon fixation of these organisms in springs where the niche dimension of AOA and NFA overlap (e.g., Perpetual Spouter). These data suggest affinity for substrate and electron donor use play key roles in structuring the biodiversity of this hydrothermal community, and likely influences the structure of other N limited hydrothermal and non-hydrothermal ecosystems.

Monoaxial external fixation of the calcaneus: An anatomical study assessing the safety of monoaxial pin insertion.

PubMed

Thomson, Callum M; Esparon, Tom; Rea, Paul M; Jamal, Bilal

2016-10-01

The use of external fixation for intra-articular calcaneal fractures is increasing in popularity. Studies have shown fine wire and monoaxial external fixation to be a viable surgical alternative to more invasive methods of open reduction and internal fixation of the calcaneus. However, there is an absence of literature that quantifies the risk of pin insertion for monoaxial fixation. This study aimed to determine the safety of inserting monoaxial pins within the calcaneus to house the Orthofix Calcaneal Mini-Fixator. Five formalin embalmed cadaveric ankle and lower leg specimens were inserted with six monoaxial pins. Careful dissection then revealed the presence of the tendons of peroneus longus and brevis, the sural nerve and the small saphenous vein in relation to these pins. Measurements from each pin to each of these structures were made as the structures transected lines drawn from each pin to two palpable bony landmarks: the inferior tip of the lateral malleolus and the posterosuperior calcaneus. In doing this, the risk posed by each pin could be evaluated. We found that two particular pins, those used to hold the articular surface of the subtalar joint in a reduced position, posed a larger risk of injury to surrounding structures than the remaining pins. These findings therefore suggest that monoaxial fixation of the calcaneus using a six pin approach is a relatively safe method of rectifying calcaneal fractures and thus may serve as a welcome alternative to other methods of calcaneal fixation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Perifoveal function in patients with North Carolina macular dystrophy: the importance of accounting for fixation locus.

PubMed

Seiple, William; Szlyk, Janet P; Paliga, Jennifer; Rabb, Maurice F

2006-04-01

To quantify the extent of visual function losses in patients with North Carolina Macular Dystrophy (NCMD) and to demonstrate the importance of accounting for eccentric fixation when making comparisons with normal data. Five patients with NCMD who were from a single family were examined. Multifocal electroretinograms (mfERGs) and psychophysical assessments of acuity and luminance visual field sensitivities were measured throughout the central retina. Comparisons of responses from equivalent retinal areas were accomplished by shifting normal templates to be centered at the locus of fixation for each patient. Losses of psychophysically measured visual function in patients with NCMD extend to areas adjacent to the locations of visible lesions. The multifocal ERG amplitude was reduced only within the area of visible lesion. Multifocal ERG implicit times were delayed throughout the entire central retinal area assessed. ERG timing is a sensitive assay of retinal function, and our results indicate that NCMD has a widespread effect at the level of the mid and outer retina. The findings also demonstrated that it is necessary to account for fixation locus and to ensure that equivalent retinal areas are compared when testing patients with macular disease who have eccentric fixation.

Ultraviolet Light Enhances the Bovine Serum Albumin Fixation for Acid Fast Bacilli Stain

PubMed Central

Lai, Pei-Yin; Lee, Shih-Yi; Chou, Yu-Ching; Fu, Yung-Chieh; Wu, Chen-Cheng; Chiueh, Tzong-Shi

2014-01-01

The use of a liquid culture system such as MGIT broth has greatly improved the sensitivity of isolating mycobacteria in clinical laboratories. Microscopic visualization of acid fast bacilli (AFB) in the culture positive MGIT broth remains the first routine step for rapidly indicating the presence of mycobacteria. We modified an ultraviolet (UV) light fixation process to increase AFB cells adherence to the slide. The retained haze proportion of a 1-cm circle marked area on the smear slide was quantified after the staining procedure indicating the adherence degree of AFB cells. More AFB cells were preserved on the slide after exposure to UV light of either germicidal lamp or UV crosslinker in a time-dependent manner. We demonstrated both the bovine serum albumin (BSA) in MGIT media and UV light exposure were required for enhancing fixation of AFB cells. While applying to AFB stains for 302 AFB positive MGIT broths in clinics, more AFB cells were retained and observed on smear slides prepared by the modified fixation procedure rather than by the conventional method. The modified fixation procedure was thus recommended for improving the sensitivity of microscopic diagnosis of AFB cells in culture positive MGIT broth. PMID:24586725

Single-cell sequencing of Thiomargarita reveals genomic flexibility for adaptation to dynamic redox conditions

DOE PAGES

Winkel, Matthias; Salman-Carvalho, Verena; Woyke, Tanja; ...

2016-06-21

Large, colorless sulfur-oxidizing bacteria (LSB) of the family Beggiatoaceae form thick mats at sulfidic sediment surfaces, where they efficiently detoxify sulfide before it enters the water column. The genus Thiomargarita harbors the largest known free-living bacteria with cell sizes of up to 750 μm in diameter. In addition to their ability to oxidize reduced sulfur compounds, some Thiornargarita spp. are known to store large amounts of nitrate, phosphate and elemental sulfur internally. To date little is known about their energy yielding metabolic pathways, and how these pathways compare to other Beggiatoaceae. Here, we present a draft single-cell genome of amore » chain-forming " Candidatus Thiomargarita nelsonii Thio36", and conduct a comparative analysis to five draft and one full genome of other members of the Beggiatoaceae. " Ca. T. nelsonii Thio36" is able to respire nitrate to both ammonium and dinitrogen, which allows them to flexibly respond to environmental changes. Genes for sulfur oxidation and inorganic carbon fixation confirmed that " Ca. T. nelsonii Thio36" can function as a chemolithoautotroph. Carbon can be fixed via the Calvin-Benson-Bassham cycle, which is common among the Beggiatoaceae. In addition we found key genes of the reductive tricarboxylic acid cycle that point toward an alternative CO 2 fixation pathway. Surprisingly, " Ca. T. nelsonii Thio36" also encodes key genes of the C2-cycle that convert 2-phosphoglycolate to 3-phosphoglycerate during photorespiration in higher plants and cyanobacteria. Moreover, we identified a novel trait of a flavin-based energy bifurcation pathway coupled to a Na +-translocating membrane complex (Rnf). The coupling of these pathways may be key to surviving long periods of anoxia. As other Beggiatoaceae " Ca. T. nelsonii Thio36" encodes many genes similar to those of (filamentous) cyanobacteria. In conclusion, the genome of " Ca. T. nelsonii Thio36" provides additional insight into the ecology of giant sulfur-oxidizing bacteria, and reveals unique genomic features for the Thiomargarita lineage within the Beggiatoaceae.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winkel, Matthias; Salman-Carvalho, Verena; Woyke, Tanja

Large, colorless sulfur-oxidizing bacteria (LSB) of the family Beggiatoaceae form thick mats at sulfidic sediment surfaces, where they efficiently detoxify sulfide before it enters the water column. The genus Thiomargarita harbors the largest known free-living bacteria with cell sizes of up to 750 μm in diameter. In addition to their ability to oxidize reduced sulfur compounds, some Thiornargarita spp. are known to store large amounts of nitrate, phosphate and elemental sulfur internally. To date little is known about their energy yielding metabolic pathways, and how these pathways compare to other Beggiatoaceae. Here, we present a draft single-cell genome of amore » chain-forming " Candidatus Thiomargarita nelsonii Thio36", and conduct a comparative analysis to five draft and one full genome of other members of the Beggiatoaceae. " Ca. T. nelsonii Thio36" is able to respire nitrate to both ammonium and dinitrogen, which allows them to flexibly respond to environmental changes. Genes for sulfur oxidation and inorganic carbon fixation confirmed that " Ca. T. nelsonii Thio36" can function as a chemolithoautotroph. Carbon can be fixed via the Calvin-Benson-Bassham cycle, which is common among the Beggiatoaceae. In addition we found key genes of the reductive tricarboxylic acid cycle that point toward an alternative CO 2 fixation pathway. Surprisingly, " Ca. T. nelsonii Thio36" also encodes key genes of the C2-cycle that convert 2-phosphoglycolate to 3-phosphoglycerate during photorespiration in higher plants and cyanobacteria. Moreover, we identified a novel trait of a flavin-based energy bifurcation pathway coupled to a Na +-translocating membrane complex (Rnf). The coupling of these pathways may be key to surviving long periods of anoxia. As other Beggiatoaceae " Ca. T. nelsonii Thio36" encodes many genes similar to those of (filamentous) cyanobacteria. In conclusion, the genome of " Ca. T. nelsonii Thio36" provides additional insight into the ecology of giant sulfur-oxidizing bacteria, and reveals unique genomic features for the Thiomargarita lineage within the Beggiatoaceae.« less

Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.

PubMed

Raveendran, Rajkumar Nallour; Babu, Raiju J; Hess, Robert F; Bobier, William R

2014-03-01

To test the hypothesis that fixational stability of the amblyopic eye in strabismics will improve when viewing provides both bifoveal fixation and reduced inter-ocular suppression by reducing the contrast to the fellow eye. Seven strabismic amblyopes (Age: 29.2 ± 9 years; five esotropes and two exotropes) showing clinical characteristics of central suppression were recruited. Interocular suppression was measured by a global motion task. For each participant, a balance point was determined which defined contrast levels for each eye where binocular combination was optimal (interocular suppression minimal). When the balance point could not be determined, this participant was excluded. Bifoveal fixation was established by ocular alignment using a haploscope. Participants dichoptically viewed similar targets (a cross of 2.3° surrounded by a square of 11.3°) at 40 cm. Target contrasts presented to each eye were either high contrast (100% to both eyes) or balanced contrast (attenuated contrast in the fellow fixing eye). Fixation stability was measured over a 5 min period and quantified using bivariate contour ellipse areas in four different binocular conditions; unaligned/high contrast, unaligned/balance point, aligned/high contrast and aligned/balance point. Fixation stability was also measured in six control subjects (Age: 25.3 ± 4 years). Bifoveal fixation in the strabismics was transient (58.15 ± 15.7 s). Accordingly, fixational stability was analysed over the first 30 s using repeated measures anova. Post hoc analysis revealed that for the amblyopic subjects, the fixational stability of the amblyopic eye was significantly improved in aligned/high contrast (p = 0.01) and aligned/balance point (p < 0.01) conditions. Fixational stability of the fellow fixing eye was not different statistically across conditions. Bivariate contour ellipse areas of the amblyopic and fellow fixing eyes were therefore averaged for each amblyope in the four conditions and compared with normals. This averaged bivariate contour ellipse area was significantly greater (reduced fixational stability, p = 0.04) in amblyopes compared to controls except in the case of aligned and balanced contrast (aligned/balance point, p = 0.19). Fixation stability in the amblyopic eye appears to improve with bifoveal fixation and reduced interocular suppression. However, once initiated, bifoveal fixation is transient with the strabismic eye drifting away from foveal alignment, thereby increasing the angle of strabismus. © 2014 The Authors Ophthalmic & Physiological Optics © 2014 The College of Optometrists.

Carbon and nitrogen fixation differ between successional stages of biological soil crusts in the Colorado Plateau and Chihuahuan Desert

USGS Publications Warehouse

Housman, D.C.; Powers, H.H.; Collins, A.D.; Belnap, J.

2006-01-01

Biological soil crusts (cyanobacteria, mosses and lichens collectively) perform essential ecosystem services, including carbon (C) and nitrogen (N) fixation. Climate and land-use change are converting later successional soil crusts to early successional soil crusts with lower C and N fixation rates. To quantify the effect of such conversions on C and N dynamics in desert ecosystems we seasonally measured diurnal fixation rates in different biological soil crusts. We classified plots on the Colorado Plateau (Canyonlands) and Chihuahuan Desert (Jornada) as early (Microcoleus) or later successional (Nostoc/Scytonema or Placidium/Collema) and measured photosynthesis (Pn), nitrogenase activity (NA), and chlorophyll fluorescence (Fv/Fm) on metabolically active (moist) soil crusts. Later successional crusts typically had greater Pn, averaging 1.2-1.3-fold higher daily C fixation in Canyonlands and 2.4-2.8-fold higher in the Jornada. Later successional crusts also had greater NA, averaging 1.3-7.5-fold higher daily N fixation in Canyonlands and 1.3-25.0-fold higher in the Jornada. Mean daily Fv/Fm was also greater in later successional Canyonlands crusts during winter, and Jornada crusts during all seasons except summer. Together these findings indicate conversion of soil crusts back to early successional stages results in large reductions of C and N inputs into these ecosystems.

Biological Nitrogen Fixation In Tropical Dry Forests Of Costa Rica

NASA Astrophysics Data System (ADS)

Gei, M. G.; Powers, J. S.

2012-12-01

Evidence suggests that tropical dry forests (TDF) are not nitrogen (N) deficient. This evidence includes: high losses of gaseous nitrogen during the rainy season, high ecosystem soil N stocks and high N concentrations in leaves and litterfall. Its been commonly hypothesized that biological nitrogen fixation is responsible for the high availability of N in tropical soils. However, the magnitude of this flux has rarely if ever been measured in tropical dry forests. Because of the high cost of fixing N and the ubiquity of N fixing legume trees in the TDF, at the individual tree level symbiotic fixation should be a strategy down-regulated by the plant. Our main goal was to determine the rates of and controls over symbiotic N fixation. We hypothesized that legume tree species employ a facultative strategy of nitrogen fixation and that this process responds to changes in light availability, soil moisture and nutrient supply. We tested this hypothesis both on naturally established trees in a forest and under controlled conditions in a shade house by estimating the quantities of N fixed annually using the 15N natural abundance method, counting nodules, and quantifying (field) or manipulating (shade house) the variation in important environmental variables (soil nutrients, soil moisture, and light). We found that in both in our shade house experiment and in the forest, nodulation varied among different legume species. For both settings, the 15N natural abundance approach successfully detected differences in nitrogen fixation among species. The legume species that we studied were able to regulate fixation depending on the environmental conditions. They showed to have different strategies of nitrogen fixation that follow a gradient of facultative to obligate fixation. Our data suggest that there exists a continuum of nitrogen fixation strategies among species. Any efforts to define tropical legume trees as a functional group need to incorporate this variation.

Patient-specific in silico models can quantify primary implant stability in elderly human bone.

PubMed

Steiner, Juri A; Hofmann, Urs A T; Christen, Patrik; Favre, Jean M; Ferguson, Stephen J; van Lenthe, G Harry

2018-03-01

Secure implant fixation is challenging in osteoporotic bone. Due to the high variability in inter- and intra-patient bone quality, ex vivo mechanical testing of implants in bone is very material- and time-consuming. Alternatively, in silico models could substantially reduce costs and speed up the design of novel implants if they had the capability to capture the intricate bone microstructure. Therefore, the aim of this study was to validate a micro-finite element model of a multi-screw fracture fixation system. Eight human cadaveric humerii were scanned using micro-CT and mechanically tested to quantify bone stiffness. Osteotomy and fracture fixation were performed, followed by mechanical testing to quantify displacements at 12 different locations on the instrumented bone. For each experimental case, a micro-finite element model was created. From the micro-finite element analyses of the intact model, the patient-specific bone tissue modulus was determined such that the simulated apparent stiffness matched the measured stiffness of the intact bone. Similarly, the tissue modulus of a small damage region around each screw was determined for the instrumented bone. For validation, all in silico models were rerun using averaged material properties, resulting in an average coefficient of determination of 0.89 ± 0.04 with a slope of 0.93 ± 0.19 and a mean absolute error of 43 ± 10 μm when correlating in silico marker displacements with the ex vivo test. In conclusion, we validated a patient-specific computer model of an entire organ bone-implant system at the tissue-level at high resolution with excellent overall accuracy. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:954-962, 2018. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Immunofluorescence detection of nitrogenase proteins in whole cells.

PubMed

Rennie, R J

1976-12-01

Fluorescent antibodies (FA) prepared against the Mo-Fe and Fe proteins of nitrogenase from Klebsiella pneumoniae M5aI were used to detect these protein components in toluene-treated whole cells that were actively reducing acetylene. The FA were highly specific, staining only nitrogenase component proteins originating from Klebsiella. Cross-reactions between the FA and purified nitrogenase proteins from other dinitrogen-fixing micro-organisms did not occur, except in the case of Bacillus polymyxa. The tests rapidly and accurately assayed the component proteins in Klebsiella mutants and derivatives to which Klebsiella nif genes had been transferred either by plasmid or by other means. Cross-reactions also indicated the degree of relatedness between nitrogenase proteins from dinitrogen-fixing micro-organisms of various origins.

Rotational spectrum of 14N 2 · H 35Cl and 14N 2 · H 37Cl: electric field gradients at the nitrogen nuclei

NASA Astrophysics Data System (ADS)

Kisiel, Z.; Pszczólkowski, L.; Fowler, P. W.; Legon, A. C.

1997-09-01

Rotational spectra of the most abundant isotopic species of the weakly bound dimer formed between dinitrogen and hydrogen chloride were investigated. Spectroscopic constants for 14N 2 · H 37Cl were determined for the first time and those for 14N 2 · H 35Cl improved. Analysis of observed nuclear quadrupole spliting patterns within the framework of coupling of three nonequivalent nuclear spins allowed determination of splitting constants for both nuclei in the complexed dinitrogen molecule. Electric field gradient calculations at the SCF supermolecule level for the dimer are presented and account for the observed values of the nitrogen splitting constants.

Flexibility and fatigue evaluation of oblique as compared with anterior lumbar interbody cages with integrated endplate fixation.

PubMed

Freeman, Andrew L; Camisa, William J; Buttermann, Glenn R; Malcolm, James R

2016-01-01

This study was undertaken to quantify the in vitro range of motion (ROM) of oblique as compared with anterior lumbar interbody devices, pullout resistance, and subsidence in fatigue. Anterior and oblique cages with integrated plate fixation (IPF) were tested using lumbar motion segments. Flexibility tests were conducted on the intact segments, cage, cage + IPF, and cage + IPF + pedicle screws (6 anterior, 7 oblique). Pullout tests were then performed on the cage + IPF. Fatigue testing was conducted on the cage + IPF specimens for 30,000 cycles. No ROM differences were observed in any test group between anterior and oblique cage constructs. The greatest reduction in ROM was with supplemental pedicle screw fixation. Peak pullout forces were 637 ± 192 N and 651 ± 127 N for the anterior and oblique implants, respectively. The median cage subsidence was 0.8 mm and 1.4 mm for the anterior and oblique cages, respectively. Anterior and oblique cages similarly reduced ROM in flexibility testing, and the integrated fixation prevented device displacement. Subsidence was minimal during fatigue testing, most of which occurred in the first 2500 cycles.

Isolating Discriminant Neural Activity in the Presence of Eye Movements and Concurrent Task Demands

PubMed Central

Touryan, Jon; Lawhern, Vernon J.; Connolly, Patrick M.; Bigdely-Shamlo, Nima; Ries, Anthony J.

2017-01-01

A growing number of studies use the combination of eye-tracking and electroencephalographic (EEG) measures to explore the neural processes that underlie visual perception. In these studies, fixation-related potentials (FRPs) are commonly used to quantify early and late stages of visual processing that follow the onset of each fixation. However, FRPs reflect a mixture of bottom-up (sensory-driven) and top-down (goal-directed) processes, in addition to eye movement artifacts and unrelated neural activity. At present there is little consensus on how to separate this evoked response into its constituent elements. In this study we sought to isolate the neural sources of target detection in the presence of eye movements and over a range of concurrent task demands. Here, participants were asked to identify visual targets (Ts) amongst a grid of distractor stimuli (Ls), while simultaneously performing an auditory N-back task. To identify the discriminant activity, we used independent components analysis (ICA) for the separation of EEG into neural and non-neural sources. We then further separated the neural sources, using a modified measure-projection approach, into six regions of interest (ROIs): occipital, fusiform, temporal, parietal, cingulate, and frontal cortices. Using activity from these ROIs, we identified target from non-target fixations in all participants at a level similar to other state-of-the-art classification techniques. Importantly, we isolated the time course and spectral features of this discriminant activity in each ROI. In addition, we were able to quantify the effect of cognitive load on both fixation-locked potential and classification performance across regions. Together, our results show the utility of a measure-projection approach for separating task-relevant neural activity into meaningful ROIs within more complex contexts that include eye movements. PMID:28736519

The impact of simulated chronic nitrogen deposition on the biomass and N₂-fixation activity of two boreal feather moss-cyanobacteria associations.

PubMed

Gundale, Michael J; Bach, Lisbet H; Nordin, Annika

2013-01-01

Bryophytes achieve substantial biomass and play several key functional roles in boreal forests that can influence how carbon (C) and nitrogen (N) cycling respond to atmospheric deposition of reactive nitrogen (Nr). They associate with cyanobacteria that fix atmospheric N₂, and downregulation of this process may offset anthropogenic Nr inputs to boreal systems. Bryophytes also promote soil C accumulation by thermally insulating soils, and changes in their biomass influence soil C dynamics. Using a unique large-scale (0.1 ha forested plots), long-term experiment (16 years) in northern Sweden where we simulated anthropogenic Nr deposition, we measured the biomass and N₂-fixation response of two bryophyte species, the feather mosses Hylocomium splendens and Pleurozium schreberi. Our data show that the biomass declined for both species; however, N₂-fixation rates per unit mass and per unit area declined only for H. splendens. The low and high treatments resulted in a 29% and 54% reduction in total feather moss biomass, and a 58% and 97% reduction in total N₂-fixation rate per unit area, respectively. These results help to quantify the sensitivity of feather moss biomass and N₂ fixation to chronic Nr deposition, which is relevant for modelling ecosystem C and N balances in boreal ecosystems.

Internal versus external fixation of the anterior component in unstable fractures of the pelvic ring: pooled results from a systematic review.

PubMed

Wardle, B; Eslick, G D; Sunner, P

2016-10-01

Improving reduction of the pelvic ring improves long-term functional outcomes for patients. It has been demonstrated that posterior internal fixation is necessary to adequately control fractures to the posterior ring and there is evidence that supplementing this with fixation of the anterior ring improves stability. It is accepted that internal fixation provides greater stability than external fixation of the anterior ring but long-term differences in radiographic and functional outcomes have not yet been quantified. A search of electronic databases, reference lists and review articles from 1989 to 2015 yielded 18 studies (n = 884) that met our inclusion criteria. We included studies that discussed pelvic ring injuries in adults, reported functional or radiological outcomes or complications by anterior ring intervention and exceeded 14 patients. We excluded biomechanical and cadaver studies. Internal fixation of the anterior pelvic ring had better functional and radiographic outcomes. Residual displacement of >10 mm was less common with internal fixation (ER 0.12, 95 % CI 0.06-0.24) than external fixation (ER 0.31, 95 % CI 0.11-0.62). Unsatisfactory outcomes also occurred at a lower rate (ER 0.09, 95 % CI 0.03-0.22) compared to external fixation (ER 0.32, 95 % CI 0.18-0.50). Losses of reduction (ER 0.02, 95 % CI 0.01-0.04 versus ER 0.07, 95 % CI 0.02-0.21), malunions (ER 0.03, 95 % CI 0.01-0.08 versus ER 0.07, 95 % CI 0.02-0.21) and delayed/non-unions (ER 0.02, 95 % CI 0.01-0.05 versus ER 0.04, 95 % CI 0.02-0.07). Internal fixation of the anterior pelvic ring as supplementary fixation for unstable injuries to the pelvic ring appears to result in better radiographic and functional outcomes as well as fewer complications. However, data that separated outcomes and complications in relation to interventions of the anterior pelvic ring were limited. More studies looking specifically at outcomes in relation to the type of anterior ring intervention are needed.

Phytoplankton plasticity drives large variability in carbon fixation efficiency

NASA Astrophysics Data System (ADS)

Ayata, Sakina-Dorothée.; Lévy, Marina; Aumont, Olivier; Resplandy, Laure; Tagliabue, Alessandro; Sciandra, Antoine; Bernard, Olivier

2014-12-01

Phytoplankton C:N stoichiometry is highly flexible due to physiological plasticity, which could lead to high variations in carbon fixation efficiency (carbon consumption relative to nitrogen). However, the magnitude, as well as the spatial and temporal scales of variability, remains poorly constrained. We used a high-resolution biogeochemical model resolving various scales from small to high, spatially and temporally, in order to quantify and better understand this variability. We find that phytoplankton C:N ratio is highly variable at all spatial and temporal scales (5-12 molC/molN), from mesoscale to regional scale, and is mainly driven by nitrogen supply. Carbon fixation efficiency varies accordingly at all scales (±30%), with higher values under oligotrophic conditions and lower values under eutrophic conditions. Hence, phytoplankton plasticity may act as a buffer by attenuating carbon sequestration variability. Our results have implications for in situ estimations of C:N ratios and for future predictions under high CO2 world.

Quantification of pilot workload via instrument scan

NASA Technical Reports Server (NTRS)

Tole, J. R.; Stephens, A. T.; Harris, R. L., Sr.; Ephrath, A.

1982-01-01

The use of visual scanning behavior as an indicator of pilot workload is described. The relationship between level of performance on a constant piloting task under simulated IFR conditions, the skill of the pilot the level of mental workload induced by an additional verbal task imposed on the basic control task, and visual scanning behavior is investigated. An increase in fixation dwell times, especially on the primary instrument with increased mental loading is indicated. Skilled subjects 'stared' less under increased loading than did novice pilots. Sequences of instrument fixations were also examined. The percentage occurrence of the subject's most used sequences decreased with increased task difficulty for novice subjects but not for highly skilled subjects. Entropy rate (bits/sec) of the sequence of fixations was also used to quantify the scan pattern. It consistently decreased for most subjects as the four loading levels used increased.

Reverse shoulder glenoid baseplate fixation: a comparison of flat-back versus curved-back designs and oval versus circular designs with 2 different offset glenospheres.

PubMed

Roche, Christopher P; Stroud, Nicholas J; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D; DiPaola, Matthew J

2014-09-01

In this glenoid loosening study, we compared the fixation strength of multiple generic reverse shoulder glenoid baseplates that differed only in backside geometry and shape and size to optimize design from a fixation perspective. The fixation strength of 4 generic baseplates was quantified in a low-density polyurethane substrate to isolate the contribution of baseplate profile and size (25 mm circular vs 25 × 34 mm oval) and backside geometry (flat back vs curved back) on fixation using 2 center-of-rotation glenospheres (0 mm and 10 mm lateral). The cyclic test simulated 55° of abduction as a 750 N load was continuously applied to induce a variable shear and compressive load. Before and after cyclic loading, baseplate displacement was measured in the directions of the applied static shear and compressive loads. Each generic baseplate was cyclically tested 7 times with each offset glenosphere for a total of 56 samples. Circular baseplates were associated with significantly more shear displacement in both the superior-inferior (SI) and anterior-posterior (AP) directions after cyclic loading than oval baseplates. No such significant differences in fixation were observed between flat-back and curved-back baseplates. Circular baseplates were also associated with significantly more SI and AP shear displacement with 10 mm glenospheres than with 0 mm glenospheres. No significant difference in SI or AP motion was observed with oval baseplates between 0 mm and 10 mm glenospheres. Our results suggest that baseplate shape and size affects fixation strength more than backside geometry. The 25 × 34 mm oval baseplates showed better fixation characteristics than their 25 mm circular counterparts; no discernible difference in fixation was observed between flat-back and curved-back baseplates. Copyright © 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

Dimension and bridging ligand effects on Mo-mediated catalytic transformation of dinitrogen to ammonia: Chain-like extended models of Nishibayashi’s catalyst

DOE PAGES

Sheng, Xiao -Lan; Batista, Enrique Ricardo; Duan, Yi -Xiang; ...

2016-11-01

Previous studies suggested that in Nishibayashi’s homogenous catalytic systems based on molybdenum (Mo) complexes, the bimetallic structure facilitated dinitrogen to ammonia conversion in comparison to the corresponding monometallic complexes, likely due to the through-bond interactions between the two Mo centers. However, more detailed model systems are necessary to support this bimetallic hypothesis, and to elucidate the multi-metallic effects on the catalytic mechanism. In this work, we computationally examined the effects of dimension as well as the types of bridging ligands on the catalytic activities of molybdenum-dinitrogen complexes by using a set of extended model systems based on Nishibayashi’s bimetallic structure.more » The polynuclear chains containing four ([Mo] 4) or more Mo centers were found to drastically enhance the catalytic performance by comparing with both the monometallic and bimetallic complexes. Carbide ([:C≡C:] 2–) was found to be a more effective bridging ligand than N 2 in terms of electronic charges dispersion between metal centers thereby facilitating reactions in the catalytic cycle. Furthermore, the mechanistic modelling suggests that in principle, more efficient catalytic system for N 2 to NH 3 transformation might be obtained by extending the polynuclear chain to a proper size in combination with an effective bridging ligand for charge dispersion.« less

Dimension and bridging ligand effects on Mo-mediated catalytic transformation of dinitrogen to ammonia: Chain-like extended models of Nishibayashi’s catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheng, Xiao -Lan; Batista, Enrique Ricardo; Duan, Yi -Xiang

Previous studies suggested that in Nishibayashi’s homogenous catalytic systems based on molybdenum (Mo) complexes, the bimetallic structure facilitated dinitrogen to ammonia conversion in comparison to the corresponding monometallic complexes, likely due to the through-bond interactions between the two Mo centers. However, more detailed model systems are necessary to support this bimetallic hypothesis, and to elucidate the multi-metallic effects on the catalytic mechanism. In this work, we computationally examined the effects of dimension as well as the types of bridging ligands on the catalytic activities of molybdenum-dinitrogen complexes by using a set of extended model systems based on Nishibayashi’s bimetallic structure.more » The polynuclear chains containing four ([Mo] 4) or more Mo centers were found to drastically enhance the catalytic performance by comparing with both the monometallic and bimetallic complexes. Carbide ([:C≡C:] 2–) was found to be a more effective bridging ligand than N 2 in terms of electronic charges dispersion between metal centers thereby facilitating reactions in the catalytic cycle. Furthermore, the mechanistic modelling suggests that in principle, more efficient catalytic system for N 2 to NH 3 transformation might be obtained by extending the polynuclear chain to a proper size in combination with an effective bridging ligand for charge dispersion.« less

Effects of tungsten and titanium oxide nanoparticles on the diazotrophic growth and metals acquisition by Azotobacter vinelandii under molybdenum limiting condition.

PubMed

Allard, Patrick; Darnajoux, Romain; Phalyvong, Karine; Bellenger, Jean-Philippe

2013-02-19

The acquisition of essential metals, such as the metal cofactors (molybdenum (Mo) and iron (Fe)) of the nitrogenase, the enzyme responsible for the reduction of dinitrogen (N(2)) to ammonium, is critical to N(2) fixing bacteria in soil. The release of metal nanoparticles (MNPs) to the environment could be detrimental to N(2) fixing bacteria by introducing a new source of toxic metals and by interfering with the acquisition of essential metals such as Mo. Since Mo has been reported to limit nonsymbiotic N(2) fixation in many ecosystems from tropical to cold temperate, this question is particularly acute in the context of Mo limitation. Using a combination of microbiology and analytical chemistry techniques, we have evaluated the effect of titanium (Ti) and tungsten (W) oxide nanoparticles on the diazotrophic growth and metals acquisition in pure culture of the ubiquitous N(2) fixing bacterium Azotobacter vinelandii under Mo replete and Mo limiting conditions. We report that under our conditions (≤10 mg·L(-1)) TiO(2) NPs have no effects on the diazotrophic growth of A. vinelandii while WO(3) NPs are highly detrimental to the growth especially under Mo limiting conditions. Our results show that the toxicity of WO(3) NPs to A. vinelandii is due to an interference with the catechol-metalophores assisted uptake of Mo.

Fixation and mounting of porcine aortic valves for use in mock circuits.

PubMed

Schlöglhofer, Thomas; Aigner, Philipp; Stoiber, Martin; Schima, Heinrich

2013-10-01

Investigations of the circulatory system in vitro use mock circuits that require valves to mimic the cardiac situation. Whereas mechanical valves increase water hammer effects due to inherent stiffness and do not allow the use of pressure lines or catheters, bioprosthetic valves are expensive and of limited durability in test fluids. Therefore, we developed a cheap, fast, alternative method to mount valves obtained from the slaughterhouse in mock circuits. Porcine aortic roots were obtained from the abattoir and used either in native condition or after fixation. Fixation was performed at a constant retrograde pressure to ensure closed valve position. Fixation time was 4 h in a 0.5%-glutaraldehyde phosphate buffer. The fixed valves were molded into a modular mock circulation connector using a fast curing silicone. Valve functionality was evaluated in a pulsatile setting (cardiac output = 4.7 l/min, heart rate = 80 beats/min) and compared before and after fixation. Leaflet motion was recorded with a high-speed camera and valve insufficiency was quantified by leakage flow under steady pressure application (80 mmHg). Under physiological conditions the aortic valves showed almost equal leaflet motion in native and fixed conditions. However, the leaflets of the native valves showed lower stiffness and more fluttering during systole than the fixed specimens. Under retrograde pressure, fresh and fixed valves showed small leakage flows of <30 ml/min. The new mounting and fixation procedure is a fast method to fabricate low cost biologic valves for the use in mock circuits.

Is nitrogen transfer among plants enhanced by contrasting nutrient-acquisition strategies?

PubMed

Teste, François P; Veneklaas, Erik J; Dixon, Kingsley W; Lambers, Hans

2015-01-01

Nitrogen (N) transfer among plants has been found where at least one plant can fix N2 . In nutrient-poor soils, where plants with contrasting nutrient-acquisition strategies (without N2 fixation) co-occur, it is unclear if N transfer exists and what promotes it. A novel multi-species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non-mycorrhizal cluster-rooted plants in nutrient-poor soils with mycorrhizal mesh barriers. We foliar-fed plants with a K(15) NO3 solution to quantify one-way N transfer from 'donor' to 'receiver' plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient-acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N2 fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM-only plants. We demonstrate N transfer between plants of contrasting nutrient-acquisition strategies, and a preferential enrichment of cluster-rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient-poor soils. © 2014 John Wiley & Sons Ltd.

New, national bottom-up estimate for tree-based biological nitrogen fixation in the US

EPA Science Inventory

Nitrogen is a limiting nutrient in many ecosystems, but is also a chief pollutant from human activity. Quantifying human impacts on the nitrogen cycle and investigating natural ecosystem nitrogen cycling both require an understanding of the magnitude of nitrogen inputs from biolo...

Temporal Sequences Quantify the Contributions of Individual Fixations in Complex Perceptual Matching Tasks

ERIC Educational Resources Information Center

Busey, Thomas; Yu, Chen; Wyatte, Dean; Vanderkolk, John

2013-01-01

Perceptual tasks such as object matching, mammogram interpretation, mental rotation, and satellite imagery change detection often require the assignment of correspondences to fuse information across views. We apply techniques developed for machine translation to the gaze data recorded from a complex perceptual matching task modeled after…

Hemiarthroplasty compared to internal fixation with percutaneous cannulated screws as treatment of displaced femoral neck fractures in the elderly: cost-utility analysis performed alongside a randomized, controlled trial.

PubMed

Waaler Bjørnelv, G M; Frihagen, F; Madsen, J E; Nordsletten, L; Aas, E

2012-06-01

We estimated the cost-effectiveness of hemiarthroplasty compared to internal fixation for elderly patients with displaced femoral neck fractures. Over 2 years, patients treated with hemiarthroplasty gained more quality-adjusted life years than patients treated with internal fixation. In addition, costs for hemiarthroplasty were lower. Hemiarthroplasty was thus cost effective. Estimating the cost utility of hemiarthroplasty compared to internal fixation in the treatment of displaced femoral neck fractures in the elderly. A cost-utility analysis (CUA) was conducted alongside a clinical randomized controlled trial at a university hospital in Norway; 166 patients, 124 (75%) women with a mean age of 82 years were randomized to either internal fixation (n = 86) or hemiarthroplasty (n = 80). Patients were followed up at 4, 12, and 24 months. Health-related quality of life was assessed with the EQ-5D, and in combination with time used to calculate patients' quality-adjusted life years (QALYs). Resource use was identified, quantified, and valued for direct and indirect hospital costs and for societal costs. Results were expressed in incremental cost-effectiveness ratios. Over the 2-year period, patients treated with hemiarthroplasty gained 0.15-0.20 more QALYs than patients treated with internal fixation. For the hemiarthroplasty group, the direct hospital costs, total hospital costs, and total costs were non-significantly less costly compared with the internal fixation group, with an incremental cost of €2,731 (p = 0.81), €2,474 (p = 0.80), and €14,160 (p = 0.07), respectively. Thus, hemiarthroplasty was the dominant treatment. Sensitivity analyses by bootstrapping supported these findings. Hemiarthroplasty was a cost-effective treatment. Trial registration, NCT00464230.

Assessing nitrogen fixation in mixed- and single-species plantations of Eucalyptus globulus and Acacia mearnsii.

PubMed

Forrester, David I; Schortemeyer, Marcus; Stock, William D; Bauhus, Jürgen; Khanna, Partap K; Cowie, Annette L

2007-09-01

Mixtures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman are twice as productive as E. globulus monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N(2) fixation by A. mearnsii. To investigate whether N(2) fixation by A. mearnsii could account for the mixed-species growth responses, we assessed N(2) fixation by the accretion method and the (15)N natural abundance method. Nitrogen gained by E. globulus and A. mearnsii mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that A. mearnsii influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing A. mearnsii compared with E. globulus monocultures were due to N(2) fixation, the 10-year annual mean rates of N(2) fixation were 38 and 86 kg ha(-1) year(-1) in 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation by A. mearnsii could not be quantified on the basis of the natural abundance of (15)N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that A. mearnsii fixed significant quantities of N(2) when mixed with E. globulus. A decline in delta(15)N values of E. globulus and A. mearnsii with time, from 2 to 10 years, is further evidence that N(2) was fixed and cycled through the stands. The increased aboveground biomass production of E. globulus trees in mixtures when compared with monocultures can be attributed to increases in N availability.

Structural symmetry in evolutionary games.

PubMed

McAvoy, Alex; Hauert, Christoph

2015-10-06

In evolutionary game theory, an important measure of a mutant trait (strategy) is its ability to invade and take over an otherwise-monomorphic population. Typically, one quantifies the success of a mutant strategy via the probability that a randomly occurring mutant will fixate in the population. However, in a structured population, this fixation probability may depend on where the mutant arises. Moreover, the fixation probability is just one quantity by which one can measure the success of a mutant; fixation time, for instance, is another. We define a notion of homogeneity for evolutionary games that captures what it means for two single-mutant states, i.e. two configurations of a single mutant in an otherwise-monomorphic population, to be 'evolutionarily equivalent' in the sense that all measures of evolutionary success are the same for both configurations. Using asymmetric games, we argue that the term 'homogeneous' should apply to the evolutionary process as a whole rather than to just the population structure. For evolutionary matrix games in graph-structured populations, we give precise conditions under which the resulting process is homogeneous. Finally, we show that asymmetric matrix games can be reduced to symmetric games if the population structure possesses a sufficient degree of symmetry. © 2015 The Author(s).

Structural symmetry in evolutionary games

PubMed Central

McAvoy, Alex; Hauert, Christoph

2015-01-01

In evolutionary game theory, an important measure of a mutant trait (strategy) is its ability to invade and take over an otherwise-monomorphic population. Typically, one quantifies the success of a mutant strategy via the probability that a randomly occurring mutant will fixate in the population. However, in a structured population, this fixation probability may depend on where the mutant arises. Moreover, the fixation probability is just one quantity by which one can measure the success of a mutant; fixation time, for instance, is another. We define a notion of homogeneity for evolutionary games that captures what it means for two single-mutant states, i.e. two configurations of a single mutant in an otherwise-monomorphic population, to be ‘evolutionarily equivalent’ in the sense that all measures of evolutionary success are the same for both configurations. Using asymmetric games, we argue that the term ‘homogeneous’ should apply to the evolutionary process as a whole rather than to just the population structure. For evolutionary matrix games in graph-structured populations, we give precise conditions under which the resulting process is homogeneous. Finally, we show that asymmetric matrix games can be reduced to symmetric games if the population structure possesses a sufficient degree of symmetry. PMID:26423436

The impact of simulated chronic nitrogen deposition on the biomass and N2-fixation activity of two boreal feather moss–cyanobacteria associations

PubMed Central

Gundale, Michael J.; Bach, Lisbet H.; Nordin, Annika

2013-01-01

Bryophytes achieve substantial biomass and play several key functional roles in boreal forests that can influence how carbon (C) and nitrogen (N) cycling respond to atmospheric deposition of reactive nitrogen (Nr). They associate with cyanobacteria that fix atmospheric N2, and downregulation of this process may offset anthropogenic Nr inputs to boreal systems. Bryophytes also promote soil C accumulation by thermally insulating soils, and changes in their biomass influence soil C dynamics. Using a unique large-scale (0.1 ha forested plots), long-term experiment (16 years) in northern Sweden where we simulated anthropogenic Nr deposition, we measured the biomass and N2-fixation response of two bryophyte species, the feather mosses Hylocomium splendens and Pleurozium schreberi. Our data show that the biomass declined for both species; however, N2-fixation rates per unit mass and per unit area declined only for H. splendens. The low and high treatments resulted in a 29% and 54% reduction in total feather moss biomass, and a 58% and 97% reduction in total N2-fixation rate per unit area, respectively. These results help to quantify the sensitivity of feather moss biomass and N2 fixation to chronic Nr deposition, which is relevant for modelling ecosystem C and N balances in boreal ecosystems. PMID:24196519

Effects of Cementing on Ligament Balance During Total Knee Arthroplasty.

PubMed

Chow, Jimmy; Wang, Kevin; Elson, Leah; Anderson, Christopher; Roche, Martin

2017-05-01

Complications related to joint imbalance may contribute to some of the most predominant modes of failure in total knee arthroplasty (TKA). These complications include instability, aseptic loosening, asymmetric component wear, and idiopathic pain. Fixation may represent a step that introduces unchecked variability into the procedure and may contribute to the incidence of joint imbalance-related complications. The ability to quantify in vivo loading in the medial and lateral compartments would allow for the ability to confirm balance after fixation and prior to wound closure. This retrospective study sought to capture any variability and imbalance associated with cementing technique. A total of 93 patients underwent sensor-assisted TKA. All patients were confirmed to have quantifiably balanced joints prior to cementation. After cementing and final component placement, the sensor was reinserted into the joint to capture any cementation-induced changes in loading. Imbalance was observed in 44% of patients after cementation. There was no difference in the proportion of imbalance due to surgeon experience (P=.456), cement type (P=.429), or knee system (P=.792). A majority of knees exhibited loading increase in the medial compartment. It was concluded that cementation technique contributes to a significant amount of balance-related variability at the fixation stage of the procedure. The use of the sensor in this study allowed for the correction of all instances of imbalance prior to closure. More objective methods of balance verification may be important for ensuring optimal surgical outcomes. [Orthopedics. 2017; 40(3):e455-e459.]. Copyright 2017, SLACK Incorporated.

Ubiquitous Gammaproteobacteria dominate dark carbon fixation in coastal sediments.

PubMed

Dyksma, Stefan; Bischof, Kerstin; Fuchs, Bernhard M; Hoffmann, Katy; Meier, Dimitri; Meyerdierks, Anke; Pjevac, Petra; Probandt, David; Richter, Michael; Stepanauskas, Ramunas; Mußmann, Marc

2016-08-01

Marine sediments are the largest carbon sink on earth. Nearly half of dark carbon fixation in the oceans occurs in coastal sediments, but the microorganisms responsible are largely unknown. By integrating the 16S rRNA approach, single-cell genomics, metagenomics and transcriptomics with (14)C-carbon assimilation experiments, we show that uncultured Gammaproteobacteria account for 70-86% of dark carbon fixation in coastal sediments. First, we surveyed the bacterial 16S rRNA gene diversity of 13 tidal and sublittoral sediments across Europe and Australia to identify ubiquitous core groups of Gammaproteobacteria mainly affiliating with sulfur-oxidizing bacteria. These also accounted for a substantial fraction of the microbial community in anoxic, 490-cm-deep subsurface sediments. We then quantified dark carbon fixation by scintillography of specific microbial populations extracted and flow-sorted from sediments that were short-term incubated with (14)C-bicarbonate. We identified three distinct gammaproteobacterial clades covering diversity ranges on family to order level (the Acidiferrobacter, JTB255 and SSr clades) that made up >50% of dark carbon fixation in a tidal sediment. Consistent with these activity measurements, environmental transcripts of sulfur oxidation and carbon fixation genes mainly affiliated with those of sulfur-oxidizing Gammaproteobacteria. The co-localization of key genes of sulfur and hydrogen oxidation pathways and their expression in genomes of uncultured Gammaproteobacteria illustrates an unknown metabolic plasticity for sulfur oxidizers in marine sediments. Given their global distribution and high abundance, we propose that a stable assemblage of metabolically flexible Gammaproteobacteria drives important parts of marine carbon and sulfur cycles.

National Institute for Petroleum and Energy Research quarterly technical report, July 1--September 30, 1992. [Dinitrogen compound 1,10-phenanthroline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

Progress reports are presented for the following two fuel research programs: (1) development of analytical methodology for analysis of heavy crudes; and (2) thermochemistry and thermophysical properties of organic nitrogen and diheteroatom-containing compounds. For the first research program, gasoline range (82--43[degree]) components in liquid products from catalytic cracking whole Wilmington >650[degree]F resid, Wilmington >650[degree]F neutrals, and blends of neutrals plus 650--1000[degree]F acids and bases were determined by gas chromatography/mass spectroscopy. For the second research program, density measurements were completed for thianthrene between 450 K and near 570 K, and for phenoxathiin between 348 K and 548 K. Heat capacity measurementsmore » were begun for the dinitrogen compound 1,10-phenanthroline.« less

Quantifying Three-Dimensional Morphology and RNA from Individual Embryos

PubMed Central

Green, Rebecca M.; Leach, Courtney L.; Hoehn, Natasha; Marcucio, Ralph S.; Hallgrímsson, Benedikt

2017-01-01

Quantitative analysis of morphogenesis aids our understanding of developmental processes by providing a method to link changes in shape with cellular and molecular processes. Over the last decade many methods have been developed for 3D imaging of embryos using microCT scanning to quantify the shape of embryos during development. These methods generally involve a powerful, cross-linking fixative such as paraformaldehyde to limit shrinkage during the CT scan. However, the extended time frames that these embryos are incubated in such fixatives prevent use of the tissues for molecular analysis after microCT scanning. This is a significant problem because it limits the ability to correlate variation in molecular data with morphology at the level of individual embryos. Here, we outline a novel method that allows RNA, DNA or protein isolation following CT scan while also allowing imaging of different tissue layers within the developing embryo. We show shape differences early in craniofacial development (E11.5) between common mouse genetic backgrounds, and demonstrate that we are able to generate RNA from these embryos after CT scanning that is suitable for downstream RT-PCR and RNAseq analyses. PMID:28152580

Effects of Anthropogenic Nitrogen Loading on Riverine Nitrogen Export in the Northeastern USA

NASA Astrophysics Data System (ADS)

Boyer, E. W.; Goodale, C. L.; Howarth, R. W.

2001-05-01

Human activities have greatly altered the nitrogen (N) cycle, accelerating the rate of N fixation in landscapes and delivery of N to water bodies. To examine the effects of anthropogenic N inputs on riverine N export, we quantified N inputs and riverine N loss for 16 catchments along a latitudinal profile from Maine to Virginia, which encompass a range of climatic variability and are major drainages to the coast of the North Atlantic Ocean. We quantified inputs of N to each catchment: atmospheric deposition, fertilizer application, agricultural and forest biological N fixation, and the net import of N in food and feed. We compared these inputs with N losses from the system in riverine export. The importance of the relative sources varies widely by watershed and is related to land use. Atmospheric deposition was the largest source (>60%) to the forested catchments of northern New England (e.g., Penobscot and Kennebec); import of N in food was the largest source of N to the more populated regions of southern New England (e.g., Charles and Blackstone); and agricultural inputs were the dominant N sources in the Mid-Atlantic region (e.g., Schuylkill and Potomac). Total N inputs to each catchment increased with percent cover in agriculture and urban land, and decreased with percent forest. Over the combined area of the catchments, net atmospheric deposition was the largest single source input (34%), followed by imports of N in food and feed (24%), fixation in agricultural lands (21%), fertilizer use (15%), and fixation in forests (6%). Riverine export of N is well correlated with N inputs, but it accounts for only a fraction (28%) of the total N inputs. This work provides an understanding of the sources of N in landscapes, and highlights how human activities impact N cycling in the northeast region.

Oxygen and the light-dark cycle of nitrogenase activity in two unicellular cyanobacteria.

PubMed

Compaoré, Justine; Stal, Lucas J

2010-01-01

Cyanobacteria capable of fixing dinitrogen exhibit various strategies to protect nitrogenase from inactivation by oxygen. The marine Crocosphaera watsonii WH8501 and the terrestrial Gloeothece sp. PCC6909 are unicellular diazotrophic cyanobacteria that are capable of aerobic nitrogen fixation. These cyanobacteria separate the incompatible processes of oxygenic photosynthesis and nitrogen fixation temporally, confining the latter to the dark. Although these cyanobacteria thrive in fully aerobic environments and can be cultivated diazotrophically under aerobic conditions, the effect of oxygen is not precisely known due to methodological limitations. Here we report the characteristics of nitrogenase activity with respect to well-defined levels of oxygen to which the organisms are exposed, using an online and near real-time acetylene reduction assay combined with sensitive laser-based photoacoustic ethylene detection. The cultures were grown under an alternating 12-12 h light-dark cycle and acetylene reduction was recorded continuously. Acetylene reduction was assayed at 20%, 15%, 10%, 7.5%, 5% and 0% oxygen and at photon flux densities of 30 and 76 mumol m(-2) s(-1) provided at the same light-dark cycle as during cultivation. Nitrogenase activity was predominantly but not exclusively confined to the dark. At 0% oxygen nitrogenase activity in Gloeothece sp. was not detected during the dark and was shifted completely to the light period, while C. watsonii did not exhibit nitrogenase activity at all. Oxygen concentrations of 15% and higher did not support nitrogenase activity in either of the two cyanobacteria. The highest nitrogenase activities were at 5-7.5% oxygen. The highest nitrogenase activities in C. watsonii and Gloeothece sp. were observed at 29 degrees C. At 31 degrees C and above, nitrogenase activity was not detected in C. watsonii while the same was the case at 41 degrees C and above in Gloeothece sp. The differences in the behaviour of nitrogenase activity in these cyanobacteria are discussed with respect to their presumed physiological strategies to protect nitrogenase from oxygen inactivation and to the environment in which they thrive.

Heterozygosity-fitness correlations among wild populations of European tree frog (Hyla arborea) detect fixation load.

PubMed

Luquet, E; David, P; Lena, J-P; Joly, P; Konecny, L; Dufresnes, C; Perrin, N; Plenet, S

2011-05-01

Quantifying the impacts of inbreeding and genetic drift on fitness traits in fragmented populations is becoming a major goal in conservation biology. Such impacts occur at different levels and involve different sets of loci. Genetic drift randomly fixes slightly deleterious alleles leading to different fixation load among populations. By contrast, inbreeding depression arises from highly deleterious alleles in segregation within a population and creates variation among individuals. A popular approach is to measure correlations between molecular variation and phenotypic performances. This approach has been mainly used at the individual level to detect inbreeding depression within populations and sometimes at the population level but without consideration about the genetic processes measured. For the first time, we used in this study a molecular approach considering both the interpopulation and intrapopulation level to discriminate the relative importance of inbreeding depression vs. fixation load in isolated and non-fragmented populations of European tree frog (Hyla arborea), complemented with interpopulational crosses. We demonstrated that the positive correlations observed between genetic heterozygosity and larval performances on merged data were mainly caused by co-variations in genetic diversity and fixation load among populations rather than by inbreeding depression and segregating deleterious alleles within populations. Such a method is highly relevant in a conservation perspective because, depending on how populations lose fitness (inbreeding vs. fixation load), specific management actions may be designed to improve the persistence of populations. © 2011 Blackwell Publishing Ltd.

X-ray emission spectroscopy evidences a central carbon in the nitrogenase iron-molybdenum cofactor.

PubMed

Lancaster, Kyle M; Roemelt, Michael; Ettenhuber, Patrick; Hu, Yilin; Ribbe, Markus W; Neese, Frank; Bergmann, Uwe; DeBeer, Serena

2011-11-18

Nitrogenase is a complex enzyme that catalyzes the reduction of dinitrogen to ammonia. Despite insight from structural and biochemical studies, its structure and mechanism await full characterization. An iron-molybdenum cofactor (FeMoco) is thought to be the site of dinitrogen reduction, but the identity of a central atom in this cofactor remains unknown. Fe Kβ x-ray emission spectroscopy (XES) of intact nitrogenase MoFe protein, isolated FeMoco, and the FeMoco-deficient nifB protein indicates that among the candidate atoms oxygen, nitrogen, and carbon, it is carbon that best fits the XES data. The experimental XES is supported by computational efforts, which show that oxidation and spin states do not affect the assignment of the central atom to C(4-). Identification of the central atom will drive further studies on its role in catalysis.

Millennial-scale plankton regime shifts in the subtropical North Pacific Ocean.

PubMed

McMahon, Kelton W; McCarthy, Matthew D; Sherwood, Owen A; Larsen, Thomas; Guilderson, Thomas P

2015-12-18

Climate change is predicted to alter marine phytoplankton communities and affect productivity, biogeochemistry, and the efficacy of the biological pump. We reconstructed high-resolution records of changing plankton community composition in the North Pacific Ocean over the past millennium. Amino acid-specific δ(13)C records preserved in long-lived deep-sea corals revealed three major plankton regimes corresponding to Northern Hemisphere climate periods. Non-dinitrogen-fixing cyanobacteria dominated during the Medieval Climate Anomaly (950-1250 Common Era) before giving way to a new regime in which eukaryotic microalgae contributed nearly half of all export production during the Little Ice Age (~1400-1850 Common Era). The third regime, unprecedented in the past millennium, began in the industrial era and is characterized by increasing production by dinitrogen-fixing cyanobacteria. This picoplankton community shift may provide a negative feedback to rising atmospheric carbon dioxide concentrations. Copyright © 2015, American Association for the Advancement of Science.

Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines.

PubMed

Alajarin, Mateo; Bonillo, Baltasar; Ortin, Maria-Mar; Orenes, Raul-Angel; Vidal, Angel

2011-10-07

N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.

Catalytic reduction of dinitrogen to ammonia at a single molybdenum center.

PubMed

Yandulov, Dmitry V; Schrock, Richard R

2003-07-04

Dinitrogen (N2) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN3N]3- triamidoamine ligands (such as [HIPTN3N]Mo(N2), where [HIPTN3N]3- is [(3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N]3-) in heptane. Slow addition of the proton source [(2,6-lutidinium)(BAr'4), where Ar' is 3,5-(CF3)2C6H3]and reductant (decamethyl chromocene) was critical for achieving high efficiency ( approximately 66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.

Abundance and distribution of archaeal acetyl-CoA/propionyl-CoA carboxylase genes indicative for putatively chemoautotrophic Archaea in the tropical Atlantic's interior.

PubMed

Bergauer, Kristin; Sintes, Eva; van Bleijswijk, Judith; Witte, Harry; Herndl, Gerhard J

2013-06-01

Recently, evidence suggests that dark CO2 fixation in the pelagic realm of the ocean does not only occur in the suboxic and anoxic water bodies but also in the oxygenated meso- and bathypelagic waters of the North Atlantic. To elucidate the significance and phylogeny of the key organisms mediating dark CO2 fixation in the tropical Atlantic, we quantified functional genes indicative for CO2 fixation. We used a Q-PCR-based assay targeting the bifunctional acetyl-CoA/propionyl-CoA carboxylase (accA subunit), a key enzyme powering inter alia the 3-hydroxypropionate/4-hydroxybutyrate cycle (HP/HB) and the archaeal ammonia monooxygenase (amoA). Quantification of accA-like genes revealed a consistent depth profile in the upper mesopelagial with increasing gene abundances from subsurface layers towards the oxygen minimum zone (OMZ), coinciding with an increase in archaeal amoA gene abundance. Gene abundance profiles of metabolic marker genes (accA, amoA) were correlated with thaumarchaeal 16S rRNA gene abundances as well as CO2 fixation rates to link the genetic potential to actual rate measurements. AccA gene abundances correlated with archaeal amoA gene abundance throughout the water column (r(2)  = 0.309, P < 0.0001). Overall, a substantial genetic predisposition of CO2 fixation was present in the dark realm of the tropical Atlantic in both Archaea and Bacteria. Hence, dark ocean CO2 fixation might be more widespread among prokaryotes inhabiting the oxygenated water column of the ocean's interior than hitherto assumed. © 2013 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Quantitative framework for prospective motion correction evaluation.

PubMed

Pannetier, Nicolas A; Stavrinos, Theano; Ng, Peter; Herbst, Michael; Zaitsev, Maxim; Young, Karl; Matson, Gerald; Schuff, Norbert

2016-02-01

Establishing a framework to evaluate performances of prospective motion correction (PMC) MRI considering motion variability between MRI scans. A framework was developed to obtain quantitative comparisons between different motion correction setups, considering that varying intrinsic motion patterns between acquisitions can induce bias. Intrinsic motion was considered by replaying in a phantom experiment the recorded motion trajectories from subjects. T1-weighted MRI on five volunteers and two different marker fixations (mouth guard and nose bridge fixations) were used to test the framework. Two metrics were investigated to quantify the improvement of the image quality with PMC. Motion patterns vary between subjects as well as between repeated scans within a subject. This variability can be approximated by replaying the motion in a distinct phantom experiment and used as a covariate in models comparing motion corrections. We show that considering the intrinsic motion alters the statistical significance in comparing marker fixations. As an example, two marker fixations, a mouth guard and a nose bridge, were evaluated in terms of their effectiveness for PMC. A mouth guard achieved better PMC performance. Intrinsic motion patterns can bias comparisons between PMC configurations and must be considered for robust evaluations. A framework for evaluating intrinsic motion patterns in PMC is presented. © 2015 Wiley Periodicals, Inc.

A Proteomic Network for Symbiotic Nitrogen Fixation Efficiency in Bradyrhizobium elkanii.

PubMed

Cooper, Bret; Campbell, Kimberly B; Beard, Hunter S; Garrett, Wesley M; Mowery, Joseph; Bauchan, Gary R; Elia, Patrick

2018-03-01

Rhizobia colonize legumes and reduce N 2 to NH 3 in root nodules. The current model is that symbiotic rhizobia bacteroids avoid assimilating this NH 3 . Instead, host legume cells form glutamine from NH 3 , and the nitrogen is returned to the bacteroid as dicarboxylates, peptides, and amino acids. In soybean cells surrounding bacteroids, glutamine also is converted to ureides. One problem for soybean cultivation is inefficiency in symbiotic N 2 fixation, the biochemical basis of which is unknown. Here, the proteomes of bacteroids of Bradyrhizobium elkanii USDA76 isolated from N 2 fixation-efficient Peking and -inefficient Williams 82 soybean nodules were analyzed by mass spectrometry. Nearly half of the encoded bacterial proteins were quantified. Efficient bacteroids produced greater amounts of enzymes to form Nod factors and had increased amounts of signaling proteins, transporters, and enzymes needed to generate ATP to power nitrogenase and to acquire resources. Parallel investigation of nodule proteins revealed that Peking had no significantly greater accumulation of enzymes needed to assimilate NH 3 than Williams 82. Instead, efficient bacteroids had increased amounts of enzymes to produce amino acids, including glutamine, and to form ureide precursors. These results support a model for efficient symbiotic N 2 fixation in soybean where the bacteroid assimilates NH 3 for itself.

First synthesis of 2'-deoxyfluoropuromycin analogues: experimental insight into the mechanism of the Staudinger reaction.

PubMed

Charafeddine, Adib; Dayoub, Wissam; Chapuis, Hubert; Strazewski, Peter

2007-01-01

The N(6),N(6)-dedimethyl-2'-deoxyfluoro analogue of puromycin (= 3'-deoxy-N(6),N(6)-dimethyl-3'-[O-methyltyrosylamido]adenosine), its 2',3'-regioisomer and a 3'-cytidyl-5'-(2'-deoxyfluoro)puromycyl dinucleotide analogue were synthesized following an approach involving i) the diastereospecific nitrite-assisted formation of a lyxo nucleosidic 2',3'-epoxide from an adenosine-2',3'-ditriflate derivative in a biphasic solvent mixture; ii) the regio- and stereoselective epoxide ring opening with sodium azide under mildly acidic aqueous conditions, iii) the stereospecific introduction of the fluor atom using DAST and iv) the reaction between the nucleosidyl or dinucleotidyl azide and an active ester of the N-protected amino acid using highly efficient solution conditions for the Staudinger-Vilarrasa coupling, to obtain the corresponding carboxamide directly from the in situ formed iminophosphorane. This coupling reaction furnished sterically quite demanding amides in 94 % isolated yields under very mild conditions and should therefore be of a more general value. Under certain reaction conditions we isolated (amino)acyltriazene derivatives from which dinitrogen was not eliminated. These secondary products are trapped and stabilized witnesses of the first intermediate of the Staudinger reaction, the phosphatriazenes (phosphazides, triazaphosphadienes) which usually eliminate dinitrogen in situ and rapidly rearrange into iminophosphoranes, unless they are derived from conjugated or sterically bulky azides and phosphines. The acyltriazenes could either be thermally decomposed or converted to the corresponding N-alkyl carboxamides through proton-assisted elimination of dinitrogen. All compounds were carefully characterized through MS spectrometry, (1)H, (19)F, (31)P and (13)C NMR spectroscopy.

Revision ulnar collateral ligament reconstruction using a suspension button fixation technique.

PubMed

Lee, Gregory H; Limpisvasti, Orr; Park, Maxwell C; McGarry, Michelle H; Yocum, Lewis A; Lee, Thay Q

2010-03-01

Revision ulnar collateral ligament reconstruction remains a challenging problem. The objective of this study was to biomechanically evaluate an ulnar collateral ligament reconstruction technique using a suspension button fixation technique that can be used even in the case of ulnar cortical bone loss. An ulnar suspension fixation technique for ulnar collateral ligament reconstruction can restore elbow kinematics and demonstrate failure strength comparable to that of currently available techniques. Controlled laboratory study. Nine pairs of cadaveric elbows were dissected free of soft tissue and potted. After simulating ulnar cortical bone loss, ulnar collateral ligament reconstruction was performed in 1 elbow of each pair using palmaris longus autograft and a 30-mm RetroButton suspended from the far (lateralmost) ulnar cortex. A docking technique was used for humeral fixation of the graft. Elbow valgus angle was quantified using a Microscribe 3DLX digitizer at multiple elbow flexion angles. Valgus angle was measured with the ulnar collateral ligament intact, transected, and reconstructed. In addition, load-to-failure testing was performed in 1 elbow of each pair. Release of the ulnar collateral ligament caused a significant increase in valgus angle at each flexion angle tested (P < .002). Reconstructed elbows demonstrated no significant differences in valgus angle from the intact elbow at all flexion angles tested. Load-to-failure tests showed that reconstructed elbows had an ultimate torque (10.3 + or - 5.7 N x m) significantly less than intact elbows (26.4 + or - 10.6 N x m) (P = .001). Ulnar collateral ligament reconstruction using a suspension button fixation technique reliably restored elbow kinematics to the intact state. Load-to-failure testing demonstrated comparable fixation strength to several historic controls of primary reconstruction techniques despite the simulated ulnar cortical bone loss. Ulnar collateral ligament reconstruction using a suspension button fixation technique can be considered in the case of ulnar cortical bone loss in a primary or revision setting.

Vanadium Nitrogenase Reduces CO*

PubMed Central

Lee, Chi Chung; Hu, Yilin; Ribbe, Markus W.

2011-01-01

Vanadium nitrogenase not only reduces dinitrogen to ammonia but also reduces carbon monoxide to ethylene, ethane, and propane. The parallelism between the two reactions suggests a potential link in mechanism and evolution between the carbon and nitrogen cycles on Earth. PMID:20689010

49 CFR 173.336 - Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied.

Code of Federal Regulations, 2014 CFR

2014-10-01

... rail. (b) Each UN pressure receptacle must be cleaned in accordance with the requirements of ISO 11621... agent must not be capable of reacting with oxygen. One cylinder selected at random from a group of 200...

49 CFR 173.336 - Nitrogen dioxide, liquefied, or dinitrogen tetroxide, liquefied.

Code of Federal Regulations, 2011 CFR

2011-10-01

... rail. (b) Each UN pressure receptacle must be cleaned in accordance with the requirements of ISO 11621... agent must not be capable of reacting with oxygen. One cylinder selected at random from a group of 200...

Synthesis and X-ray crystal structures of (Mo(CO)(Et{sub 2}PC{sub 2}H{sub 4}PEt{sub 2}){sub 2}){sub 2}({mu}-N{sub 2}) with an end-on bridging dinitrogen ligand and Mo(CO)(Bu{sup i}{sub 2}PC{sub 2}H{sub 4}PBu{sup i}{sub 2}){sub 2} containing an agostic Mo...H-C interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, X.L.; Kubas, G.J.; Burns, C.J.

1995-12-20

The compound formed by the reaction of trans-Mo(N{sub 2})(Et{sub 2}PC{sub 2}H{sub 4}PEt{sub 2}){sub 2} with ethyl acetate in refluxing toluene under argon has been formulated as the bridging dinitrogen complex (Mo(CO)(Et{sub 2}PC{sub 2}H{sub 4}PEt{sub 2}){sub 2}){sub 2}({mu}-N{sub 2}) (1), in contrast with the previously proposed formulation of Mo(CO)(Et{sub 2}PC{sub 2}H{sub 4}PEt{sub 2}){sub 2} (2). In refluxing p-xylene and under argon, compound 1 eliminates the bridging dinitrogen ligand to form the nitrogen-free compound 2. The reaction of trans-Mo(N{sub 2})(Bu{sup i}{sub 2}PC{sub 2}H{sub 4}PBu{sup i}{sub 2}){sub 2} (3). The molecular structures of compounds 1 and 3 have been determined by single-crystal X-raymore » diffraction studies. Compound 1 contains an end-on bridging dinitrogen ligand. Compound 3 attains a formal 18-electron configuration by virtue of an agostic Mo...H-C interaction between the molybdenum atom and an alphiatic {gamma}-C-H bond of the alkyldiphosphine ligand. On the basis of the agostic Mo...C and Mo...H distances, the agostic interaction in 3 appears to be stronger than that in the related compound Mo(CO)(Ph{sub 2}PC{sub 2}H{sub 4}PPh{sub 2}){sub 2} which involves an ortho aromatic C-H bond of the diphosphine ligand. Crystallographic data for 1: monoclinic, space group C2/c, a=24.270(2){angstrom}, b=44.233(4){angstrom}, c=20.378(2){angstrom}, {beta}=90.725(9){angstrom}, V=21875(3){angstrom}{sup 3}, Z=16, and R=0.048. Crystallographic data for 3: orthorhombic, space group Pna2{sub 1}, a=18.332(4){angstrom}, b=22.0664(4){angstrom}, c=10.589(2){angstrom}, V=4283(2){angstrom}{sup 3}, Z=4, and R=0.034.« less

Usefullness of three-dimensional templating software to quantify the contact state between implant and femur in total hip arthroplasty.

PubMed

Inoue, Daisuke; Kabata, Tamon; Maeda, Toru; Kajino, Yoshitomo; Fujita, Kenji; Hasegawa, Kazuhiro; Yamamoto, Takashi; Takagi, Tomoharu; Ohmori, Takaaki; Tsuchiya, Hiroyuki

2015-12-01

It would be ideal if surgeons could precisely confirm whether the planned femoral component achieves the best fit and fill of implant and femur. However, the cortico-cancellous interfaces can be difficult to standardize using plain radiography, and therefore, determining the contact state is a subjective decision by the examiner. Few reports have described the use of CT-based three-dimensional templating software to quantify the contact state of stem and femur in detail. The purpose of this study was to use three-dimensional templating software to quantify the implant-femur contact state and develop a technique to analyze the initial fixation pattern of a cementless femoral stem. We conducted a retrospective review of 55 hips in 53 patients using a short proximal fit-and-fill anatomical stem (APS Natural-Hip™ System). All femurs were examined by density mapping which can visualize and digitize the contact state. We evaluated the contact state of implant and femur by using density mapping. The varus group (cases that had changed varus 2° by 3 months after surgery) consisted of 11 hips. The varus group showed no significant difference with regard to cortical contact in the proximal medial portion (Gruen 7), but the contact area in the distal portion (Gruen 3 and Gruen 5) was significantly lower than that of non-varus group. Density mapping showed that the stem only has to be press-fit to the medial calcar, but also must fill the distal portion of the implant in order to achieve the ideal contact state. Our results indicated that quantifying the contact state of implant and femur by using density mapping is a useful technique to accurately analyze the fixation pattern of a cementless femoral stem.

Importance of tropospheric ClNO2 chemistry across the Northern Hemisphere

EPA Science Inventory

Laboratory and field experiments have revealed that the heterogeneous hydrolysis of dinitrogen pentoxide produces nitryl chloride and nitric acid in the presence of particulate chloride. We incorporate the heterogeneous chemistry of nitryl chloride into the hemispheric Community ...

Chemistry Notes

ERIC Educational Resources Information Center

School Science Review, 1976

1976-01-01

Describes several chemistry projects, including solubility, formula for magnesium oxide, dissociation of dinitrogen tetroxide, use of 1-chloro-2, 4-dinitrobenzene, migration of ions, heats of neutralizations, use of pocket calculators, sonic cleaning, oxidation states of manganese, and cell potentials. Includes an extract from Chemical Age on…

Experimental investigations of pupil accommodation factors.

PubMed

Lee, Eui Chul; Lee, Ji Woo; Park, Kang Ryoung

2011-08-17

PURPOSE. The contraction and dilation of the iris muscle that controls the amount of light entering the retina causes pupil accommodation. In this study, experiments were performed and two of the three factors that influence pupil accommodation were analyzed: lighting conditions and depth fixations. The psychological benefits were not examined, because they could not be quantified. METHODS. A head-wearable eyeglasses-based, eye-capturing device was designed to measure pupil size. It included a near-infrared (NIR) camera and an NIR light-emitting diode. Twenty-four subjects watched two-dimensional (2D) and three-dimensional (3D) stereoscopic videos of the same content, and the changes in pupil size were measured by using the eye-capturing device and image-processing methods: RESULTS. The pupil size changed with the intensity of the videos and the disparities between the left and right images of a 3D stereoscopic video. There was correlation between the pupil size and average intensity. The pupil diameter could be estimated as being contracted from approximately 5.96 to 4.25 mm as the intensity varied from 0 to 255. Further, from the changes in the depth fixation for the pupil accommodation, it was confirmed that the depth fixation also affected accommodation of pupil size. CONCLUSIONS. It was confirmed that the lighting condition was an even more significant factor in pupil accommodation than was depth fixation (significance ratio: approximately 3.2:1) when watching 3D stereoscopic video. Pupil accommodation was more affected by depth fixation in the real world than was the binocular convergence in the 3D stereoscopic display.

Mechanical torque measurement for in vivo quantification of bone strength in the proximal femur.

PubMed

Mueller, Marc Andreas; Hengg, Clemens; Hirschmann, Michael; Schmid, Denise; Sprecher, Christoph; Audigé, Laurent; Suhm, Norbert

2012-10-01

Bone strength determines fracture risk and fixation strength of osteosynthesis implants. In vivo, bone strength is currently measured indirectly by quantifying bone mineral density (BMD) which is however only one determinant of the bone's biomechanical competence besides the bone's macro- and micro-architecture and tissue related parameters. We have developed a measurement principle (DensiProbe™ Hip) for direct, mechanical quantification of bone strength within the proximal femur upon hip fracture fixation. Previous cadaver tests indicated a close correlation between DensiProbe™ Hip measurements, 3D micro-CT analysis and biomechanical indicators of bone strength. The goal of this study was to correlate DensiProbe™ Hip measurements with areal bone mineral density (BMD). Forty-three hip fracture patients were included in this study. Intraoperatively, DensiProbe™ Hip was inserted to the subsequent hip screw tip position within the femoral head. Peak torque to breakaway of local cancellous bone was registered. Thirty-seven patients underwent areal BMD measurements of the contralateral proximal femur. Failure of fixation was assessed radio graphically 6 and 12 weeks postoperatively. Peak torque and femoral neck BMD showed significant correlations (R=0.60, P=0.0001). In regression analysis, areal BMD explained 46% of femoral neck BMD variance in a quadratic relationship. Throughout the 12-week follow-up period, no failure of fixation was observed. DensiProbe™ Hip may capture variations of bone strength beyond areal BMD which are currently difficult to measure in vivo. A multicenter study will clarify if peak torque predicts fixation failure. Copyright © 2012 Elsevier Ltd. All rights reserved.

How Do We See Art: An Eye-Tracker Study

PubMed Central

Quiroga, Rodrigo Quian; Pedreira, Carlos

2011-01-01

We describe the pattern of fixations of subjects looking at figurative and abstract paintings from different artists (Molina, Mondrian, Rembrandt, della Francesca) and at modified versions in which different aspects of these art pieces were altered with simple digital manipulations. We show that the fixations of the subjects followed some general common principles (e.g., being attracted to saliency regions) but with a large variability for the figurative paintings, according to the subject’s personal appreciation and knowledge. In particular, we found different gazing patterns depending on whether the subject saw the original or the modified version of the painting first. We conclude that the study of gazing patterns obtained by using the eye-tracker technology gives a useful approach to quantify how subjects observe art. PMID:21941476

Patella Fracture Fixation with Suture and Wire: you Reap what you Sew

PubMed Central

Egol, Kenneth; Howard, Daniel; Monroy, Alexa; Crespo, Alexander; Tejwani, Nirmal; Davidovitch, Roy

2014-01-01

Introduction Operative fixation of displaced inferior pole patella fractures has now become the standard of care. This study aims to quantify clinical, radiographic and functional outcomes, as well as identify complications in a cohort of patients treated with non-absorbable braided suture fixation for inferior pole patellar fractures. These patients were then compared to a control group of patients treated for mid-pole fractures with K-wires or cannulated screws with tension band wiring. Methods In this IRB approved study, we identified a cohort of patients who were diagnosed and treated surgically for a displaced patella fracture. Demographic, injury, and surgical information were recorded. All patients were treated with a standard surgical technique utilizing non-absorbable braided suture woven through the patellar tendon and placed through drill holes to achieve reduction and fracture fixation. All patients were treated with a similar post-operative protocol and followed up at standard intervals. Data were collected concurrently at follow up visits. For purpose of comparison, we identified a control cohort with middle third patella fractures treated with either k-wires or cannulated screws and tension band technique. Patients were followed by the treating surgeon at regular follow-up intervals. Outcomes included self-reported function and knee range of motion compared to the uninjured side. Results Forty-nine patients with 49 patella fractures identified retrospectively were treated over 9 years. This cohort consisted of 31 females (63.3%) and 18 males (36.7%) with an average age of 57.1 years (range 26 - 88 years). Patients had an average BMI of 26.48 (range 19 - 44.08). Thirteen patients with inferior pole fractures underwent suture fixation and 36 patients with mid-pole fractures underwent tension band fixation (K-wire or cannulated screws with tension band). In the suture cohort, one fracture failed open repair (7.6%), which was revised again with sutures and progressed to union. Of the 36 fractures repaired with a tension band fixation, 11 underwent secondary surgery due to hardware pain or fixation failure (30.6%). At one year, no difference was seen in knee range of motion between cohorts. All fractures healed radiographically. Those patients who required reoperation or removal of hardware had significantly diminished range of motion about their injured knee (p > 0.005). Conclusions Patients who sustain inferior pole patella fractures have limited options for fracture fixation. Suture repair is clinically acceptable, yielding similar results to patella fractures repaired with metal implants. Importantly, patients undergoing suture repair appear to have fewer hardware related postoperative complications than those receiving wire fixation for midpole fractures. PMID:25328461

Patella fracture fixation with suture and wire: you reap what you sew.

PubMed

Egol, Kenneth; Howard, Daniel; Monroy, Alexa; Crespo, Alexander; Tejwani, Nirmal; Davidovitch, Roy

2014-01-01

Operative fixation of displaced inferior pole patella fractures has now become the standard of care. This study aims to quantify clinical, radiographic and functional outcomes, as well as identify complications in a cohort of patients treated with non-absorbable braided suture fixation for inferior pole patellar fractures. These patients were then compared to a control group of patients treated for mid-pole fractures with K-wires or cannulated screws with tension band wiring. In this IRB approved study, we identified a cohort of patients who were diagnosed and treated surgically for a displaced patella fracture. Demographic, injury, and surgical information were recorded. All patients were treated with a standard surgical technique utilizing non-absorbable braided suture woven through the patellar tendon and placed through drill holes to achieve reduction and fracture fixation. All patients were treated with a similar post-operative protocol and followed up at standard intervals. Data were collected concurrently at follow up visits. For purpose of comparison, we identified a control cohort with middle third patella fractures treated with either k-wires or cannulated screws and tension band technique. Patients were followed by the treating surgeon at regular follow-up intervals. Outcomes included self-reported function and knee range of motion compared to the uninjured side. Forty-nine patients with 49 patella fractures identified retrospectively were treated over 9 years. This cohort consisted of 31 females (63.3%) and 18 males (36.7%) with an average age of 57.1 years (range 26-88 years). Patients had an average BMI of 26.48 (range 19-44.08). Thirteen patients with inferior pole fractures underwent suture fixation and 36 patients with mid-pole fractures underwent tension band fixation (K-wire or cannulated screws with tension band). In the suture cohort, one fracture failed open repair (7.6%), which was revised again with sutures and progressed to union. Of the 36 fractures repaired with a tension band fixation, 11 underwent secondary surgery due to hardware pain or fixation failure (30.6%). At one year, no difference was seen in knee range of motion between cohorts. All fractures healed radiographically. Those patients who required reoperation or removal of hardware had significantly diminished range of motion about their injured knee (p > 0.005). Patients who sustain inferior pole patella fractures have limited options for fracture fixation. Suture repair is clinically acceptable, yielding similar results to patella fractures repaired with metal implants. Importantly, patients undergoing suture repair appear to have fewer hardware related postoperative complications than those receiving wire fixation for midpole fractures.

REVISED TREATMENT OF N2 O5 HYDROLYSIS IN CMAQ

EPA Science Inventory

In this presentation, revised treatment of homogeneous and heterogeneous hydrolysis of dinitrogen pentoxide in the Community Multiscale Air Quality model version 4.6 are described. A series of model sensitivity tests are conducted and compared with observations of total atmosphe...

Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

NASA Astrophysics Data System (ADS)

Hunt, Brian P. V.; Bonnet, Sophie; Berthelot, Hugo; Conroy, Brandon J.; Foster, Rachel A.; Pagano, Marc

2016-05-01

In oligotrophic tropical and subtropical oceans, where strong stratification can limit the replenishment of surface nitrate, dinitrogen (N2) fixation by diazotrophs can represent a significant source of nitrogen (N) for primary production. The VAHINE (VAriability of vertical and tropHIc transfer of fixed N2 in the south-wEst Pacific) experiment was designed to examine the fate of diazotroph-derived nitrogen (DDN) in such ecosystems. In austral summer 2013, three large ( ˜ 50 m3) in situ mesocosms were deployed for 23 days in the New Caledonia lagoon, an ecosystem that typifies the low-nutrient, low-chlorophyll environment, to stimulate diazotroph production. The zooplankton component of the study aimed to measure the incorporation of DDN into zooplankton biomass, and assess the role of direct diazotroph grazing by zooplankton as a DDN uptake pathway. Inside the mesocosms, the diatom-diazotroph association (DDA) het-1 predominated during days 5-15 while the unicellular diazotrophic cyanobacteria UCYN-C predominated during days 15-23. A Trichodesmium bloom was observed in the lagoon (outside the mesocosms) towards the end of the experiment. The zooplankton community was dominated by copepods (63 % of total abundance) for the duration of the experiment. Using two-source N isotope mixing models we estimated a mean ˜ 28 % contribution of DDN to zooplankton nitrogen biomass at the start of the experiment, indicating that the natural summer peak of N2 fixation in the lagoon was already contributing significantly to the zooplankton. Stimulation of N2 fixation in the mesocosms corresponded with a generally low-level enhancement of DDN contribution to zooplankton nitrogen biomass, but with a peak of ˜ 73 % in mesocosm 1 following the UCYN-C bloom. qPCR analysis targeting four of the common diazotroph groups present in the mesocosms (Trichodesmium, het-1, het-2, UCYN-C) demonstrated that all four were ingested by copepod grazers, and that their abundance in copepod stomachs generally corresponded with their in situ abundance. 15N2 labelled grazing experiments therefore provided evidence for direct ingestion and assimilation of UCYN-C-derived N by the zooplankton, but not for het-1 and Trichodesmium, supporting an important role of secondary pathways of DDN to the zooplankton for the latter groups, i.e. DDN contributions to the dissolved N pool and uptake by nondiazotrophs. This study appears to provide the first evidence of direct UCYN-C grazing by zooplankton, and indicates that UCYN-C-derived N contributes significantly to the zooplankton food web in the New Caledonia lagoon through a combination of direct grazing and secondary pathways.

Teredinibacter turnerae gen. nov., sp. nov., a dinitrogen-fixing, cellulolytic, endosymbiotic gamma-proteobacterium isolated from the gills of wood-boring molluscs (Bivalvia: Teredinidae).

PubMed

Distel, Daniel L; Morrill, Wendy; MacLaren-Toussaint, Noelle; Franks, Dianna; Waterbury, John

2002-11-01

A cellulolytic, dinitrogen-fixing bacterium isolated from the gill tissue of a wood-boring mollusc (shipworm) Lyrodus pedicellatus of the bivalve family Teredinidae and 58 additional strains with similar properties, isolated from gills of 24 bivalve species representing 9 of 14 genera of Teredinidae, are described. The cells are Gram-negative, rigid, rods (0.4-0.6 x 3-6 microm) that bear a single polar flagellum. All isolates are capable of chemoheterotrophic growth in a simple mineral medium supplemented with cellulose as a sole source of carbon and energy. Xylan, pectin, carboxymethylcellulose, cellobiose and a variety of sugars and organic acids also support growth. Growth requires addition of combined nitrogen when cultures are vigorously aerated, but all isolates fix dinitrogen under microaerobic conditions. The pH, temperature and salinity optima for growth were determined for six isolates and are approximately 8.5, 30-35 degrees C and 0.3 M NaCl respectively. The isolates are marine. In addition to NaCl, growth requires elevated concentrations of Ca2+ and Mg2+ that reflect the chemistry of seawater. The DNA G+C content ranged from 49 to 51 mol%. Four isolates were identical with respect to small-subunit rRNA sequence over 891 positions compared and fall within a unique clade in the gamma-subclass of the Proteobacteria. Based on morphological, physiological and phylogenetic characteristics and specific symbiotic association with teredinid bivalves, a new genus and species, Teredinibacter turnerae gen. nov., sp. nov., is proposed. The type strain is T7902(T) (= ATCC 39867(T) = DSM 15152(T)).

High-resolution elemental mapping of human placental chorionic villi using synchrotron X-ray fluorescence spectroscopy

DOE PAGES

Punshon, Tracy; Chen, Si; Finney, Lydia; ...

2015-07-03

The placenta is the organ that mediates transport of nutrients and waste materials between mother and fetus. Synchrotron X-ray fluorescence (SXRF) microanalysis is a tool for imaging the distribution and quantity of elements in biological tissue, which can be used to study metal transport across biological membranes. Our aims were to pilot placental biopsy specimen preparation techniques that could be integrated into an ongoing epidemiology birth cohort study without harming rates of sample acquisition. We studied the effects of fixative (formalin or glutaraldehyde) and storage duration (30 days or immediate processing) on metal distribution and abundance and investigated a thaw-fixationmore » protocol for archived specimens stored at -80° C. We measured fixative elemental composition with and without a placental biopsy via inductively coupled plasma mass spectrometry (ICP-MS) to quantify fixative-induced elemental changes. Formalin-fixed specimens showed hemolysis of erythrocytes. The glutaraldehyde-paraformaldehyde solution in HEPES buffer (GTA-HEPES) had superior anatomical preservation, avoided hemolysis, and minimized elemental loss, although some cross-linking of exogenous Zn was evident. Elemental loss from tissue stored in fixative for 1 month showed variable losses (≈ 40 % with GTA-HEPES), suggesting storage duration be controlled for. Lastly, thawing of tissue held at -80 °C in a GTA-HEPES solution provided high-quality visual images and elemental images« less

Electrochemical reduction of nitrate and nitrite in concentrated sodium hydroxide at platinum and nickel electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu Lin Li; Robertson, D.H.; Chambers, J.Q.

1996-10-01

This work describes the electrochemical reduction of nitrate in alkaline solutions. Conditions which maximize the current efficiency for the production of dinitrogen and/or ammonia gases could be very important for the treatment of radioactive waste solutions.

Streamlined ammonia removal from wastewater using biological deammonification process

USDA-ARS?s Scientific Manuscript database

In this work we evaluated biological deammonification process to more economically remove ammonia from livestock wastewater. The process combines partial nitritation (PN) and anammox. The anammox is a biologically mediated reaction that oxidizes ammonia (NH4+) and releases di-nitrogen gas (N2) unde...

Symphyseal fixation in open book injuries cannot fully compensate anterior SI joint injury-A biomechanical study in a two-leg alternating load model.

PubMed

Stuby, Fabian M; Lenz, Mark; Doebele, Stefan; Agarwal, Yash; Skulev, Hristo; Ochs, Björn G; Zwingmann, Jörn; Gueorguiev, Boyko

2017-01-01

In open book injuries type Tile B1.1 or B1.2 also classified as APC II (anteroposterior compression), it remains controversial, if a fixation of the anterior ring provides sufficient stability or a fixation of the posterior ring should be included. Therefore the relative motion at the sacroiliac joint was quantified in a two-leg alternating load biomechanical pelvis model in the intact, the injured and the restored pelvis. Fresh-frozen intact (I) pelvises (n = 6) were subjected to a non-destructive cyclic test under sinosuidal axial two-leg alternating load with progressively increasing amplitude. Afterwards an open book injury (J) including the anterior ligament complex of the left sacroiliac joint, the sacrospinal and sacrotuberal ligaments (Tile B1.1) was created and the specimens were retested. Finally, the symphysis was stabilized with a modular fixation system (1-, 2- or 4-rod configuration) (R) and specimens were cyclically retested. Relative motion at the sacroiliac joint was captured at both sacroiliac joints by motion tracking system at two load levels of 170 N and 340 N during all tests. Relative sacroiliac joint movements at both load levels were significantly higher in the J-state compared to the I-state, excluding superoinferior translational movement. With exception of the anteroposterior translational movement at 340N, the relative sacroiliac joint movements after each of the three reconstructions (1-, 2-, 4-rod fixation) were significantly smaller compared to the J-state and did not differ significantly to the I-state, but stayed above the values of the latter. Relative movements did not differ significantly in a direct comparison between the 1-rod, 2-rod and 4-rod fixations. Symphyseal locked plating significantly reduces relative movement of the sacroiliac joint in open book injuries type Tile B1.1 or B1.2 (APC II) but cannot fully restore the situation of the intact sacroiliac joint.

Symphyseal fixation in open book injuries cannot fully compensate anterior SI joint injury—A biomechanical study in a two-leg alternating load model

PubMed Central

Stuby, Fabian M.; Lenz, Mark; Agarwal, Yash; Skulev, Hristo; Ochs, Björn G.; Zwingmann, Jörn; Gueorguiev, Boyko

2017-01-01

Introduction In open book injuries type Tile B1.1 or B1.2 also classified as APC II (anteroposterior compression), it remains controversial, if a fixation of the anterior ring provides sufficient stability or a fixation of the posterior ring should be included. Therefore the relative motion at the sacroiliac joint was quantified in a two-leg alternating load biomechanical pelvis model in the intact, the injured and the restored pelvis. Methods Fresh-frozen intact (I) pelvises (n = 6) were subjected to a non-destructive cyclic test under sinosuidal axial two-leg alternating load with progressively increasing amplitude. Afterwards an open book injury (J) including the anterior ligament complex of the left sacroiliac joint, the sacrospinal and sacrotuberal ligaments (Tile B1.1) was created and the specimens were retested. Finally, the symphysis was stabilized with a modular fixation system (1-, 2- or 4-rod configuration) (R) and specimens were cyclically retested. Relative motion at the sacroiliac joint was captured at both sacroiliac joints by motion tracking system at two load levels of 170 N and 340 N during all tests. Results Relative sacroiliac joint movements at both load levels were significantly higher in the J-state compared to the I-state, excluding superoinferior translational movement. With exception of the anteroposterior translational movement at 340N, the relative sacroiliac joint movements after each of the three reconstructions (1-, 2-, 4-rod fixation) were significantly smaller compared to the J-state and did not differ significantly to the I-state, but stayed above the values of the latter. Relative movements did not differ significantly in a direct comparison between the 1-rod, 2-rod and 4-rod fixations. Conclusion Symphyseal locked plating significantly reduces relative movement of the sacroiliac joint in open book injuries type Tile B1.1 or B1.2 (APC II) but cannot fully restore the situation of the intact sacroiliac joint. PMID:29176772

The fate of nitrogen fixed by diazotrophs in the ocean

NASA Astrophysics Data System (ADS)

Mulholland, M. R.

2007-01-01

While we now know that N2 fixation is a significant source of new nitrogen (N) in the marine environment, little is known about the fate of this N (and associated C), despite the importance of diazotrophs to global carbon and nutrient cycles. Specifically, does N fixed during N2 fixation fuel autotrophic or heterotrophic growth and thus facilitate carbon (C) export from the euphotic zone, or does it contribute primarily to bacterial productivity and respiration in the euphotic zone? For Trichodesmium, the diazotroph we know the most about, the transfer of recently fixed N2 (and C) appears to be primarily through dissolved pools. The release of N varies among and within populations and as a result of the changing physiological state of cells and populations. The net result of trophic transfers appears to depend on the co-occurring organisms and the complexity of the colonizing community. In order to understand the impact of diazotrophy on carbon flow and export in marine systems, we need a better understanding of the trophic flow of elements in Trichodesmium-dominated communities and other diazotrophic communities under various defined physiological states. Nitrogen and carbon fixation rates themselves vary by orders of magnitude within and among studies of Trichodesmium, highlighting the difficulty in extrapolating global rates of N2 fixation from direct measurements. Because the stoichiometry of N2 and C fixation does not appear to be in balance with that of particles, and the relationship between C and N2 fixation rates is also variable, it is equally difficult to derive global rates of one from the other. This paper seeks to synthesize what is known about the fate of diazotrophic production in the environment. A better understanding of the physiology and physiological ecology of Trichodesmium and other marine diazotrophs is necessary to quantify and predict the effects of increased or decreased diazotrophy in the context of the carbon cycle and global change.

Feedback Interactions between Trace Metal Nutrients and Phytoplankton in the Ocean

PubMed Central

Sunda, William G.

2012-01-01

In addition to control by major nutrient elements (nitrogen, phosphorus, and silicon) the productivity and species composition of marine phytoplankton communities are also regulated by a number of trace metal nutrients (iron, zinc, cobalt, manganese, copper, and cadmium). Of these, iron is most limiting to phytoplankton growth and has the greatest effect on algal species diversity. It also plays an important role in limiting di-nitrogen (N2) fixation rates, and thus is important in controlling ocean inventories of fixed nitrogen. Because of these effects, iron is thought to play a key role in regulating biological cycles of carbon and nitrogen in the ocean, including the biological transfer of carbon to the deep sea, the so-called biological CO2 pump, which helps regulate atmospheric CO2 and CO2-linked global warming. Other trace metal nutrients (zinc, cobalt, copper, and manganese) have lesser effects on productivity; but may exert an important influence on the species composition of algal communities because of large differences in metal requirements among species. The interactions between trace metals and ocean plankton are reciprocal: not only do the metals control the plankton, but the plankton regulate the distributions, chemical speciation, and cycling of these metals through cellular uptake and recycling processes, downward flux of biogenic particles, biological release of organic chelators, and mediation of redox reactions. This two way interaction has influenced not only the biology and chemistry of the modern ocean, but has had a profound influence on biogeochemistry of the ocean and earth system as a whole, and on the evolution of marine and terrestrial biology over geologic history. PMID:22701115

Bioturbation and the role of microniches for sulfate reduction in coastal marine sediments.

PubMed

Bertics, Victoria J; Ziebis, Wiebke

2010-11-01

The effects of bioturbation in marine sediments are mainly associated with an increase in oxic and oxidized zones through an influx of oxygen-rich water deeper into the sediment and the rapid transport of particles between oxic and anoxic conditions. However, macrofaunal activity also can increase the occurrence of reduced microniches and anaerobic processes, such as sulfate reduction. Our goal was to determine the two-dimensional distribution of microniches associated with burrows of a ghost shrimp (Neotrypaea californiensis) and to determine microbial activities. In laboratory experiments, detailed measurements of sulfate reduction rates (SRR) were measured by injecting, in a 1 cm grid, radiolabelled sulfate directly into a narrow aquarium (40 cm × 30 cm × 3 cm) containing the complex burrow of an actively burrowing shrimp. Light-coloured oxidized burrow walls, along with black reduced microniches, were clearly visible through the aquarium walls. Direct injection of radiotracers allowed for whole-aquarium incubation to obtain two-dimensional documentation of sulfate reduction. Results indicated SRR were up to three orders of magnitude higher (140-790 nmol SO(4) (2-) cm(-3) day(-1) ) in reduced microniches associated with burrows when compared with the surrounding sediment. Additionally, some of the subsurface sulfate-reducing microniches associated with the burrow system appeared to be zones of dinitrogen fixation. Bioturbation may also lead to decreased sulfate reduction in other microniches and the sum of the activity in all microniches might not result in a total increase of sulfate reduction compared with non-bioturbated control sediments. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Ecological consequences of the expansion of N₂-fixing plants in cold biomes.

PubMed

Hiltbrunner, Erika; Aerts, Rien; Bühlmann, Tobias; Huss-Danell, Kerstin; Magnusson, Borgthor; Myrold, David D; Reed, Sasha C; Sigurdsson, Bjarni D; Körner, Christian

2014-09-01

Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N2)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N2O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N2-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N2 fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N2-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N2-fixing plants and a rapid subsequent saturation in the ecosystem's capacity to retain N. Therefore, analogous to increases in N deposition, N2-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.

Selenium hyperaccumulation by Astragalus (Fabaceae) does not inhibit root nodule symbiosis.

PubMed

Alford, Elan R; Pilon-Smits, Elizabeth A H; Fakra, Sirine C; Paschke, Mark W

2012-12-01

A survey of the root-nodule symbiosis in Astragalus and its interaction with selenium (Se) has not been conducted before. Such studies can provide insight into how edaphic conditions modify symbiotic interactions and influence partner coevolution. In this paper plant-organ Se concentration ([Se]) was investigated to assess potential Se exposure to endophytes. • Selenium distribution and molecular speciation of root nodules from Se-hyperaccumulators Astragalus bisulcatus, A. praelongus, and A. racemosus was determined by Se K-edge x-ray absorption spectroscopy. A series of greenhouse experiments were conducted to characterize the response of root-nodule symbiosis in Se-hyperaccumulators and nonhyperaccumulators. • Nodules in three Se-hyperaccumulators (Astragalus crotalariae, A. praelongus, and A. preussii) are reported for the first time. Leaves, flowers, and fruits from Se-hyperaccumulators were routinely above the hyperaccumulator threshold (1,000 µg Se g(-1) DW), but root samples rarely contained that amount, and nodules never exceeded 110 µg Se g(-1) DW. Nodules from A. bisulcatus, A. praelongus, and A. racemosus had Se throughout, with a majority stored in C-Se-C form. Finally, an evaluation of nodulation in Se-hyperaccumulators and nonhyperaccumulators indicated that there was no nodulation inhibition because of plant Se tolerance. Rather, we found that in Se-hyperaccumulators higher levels of Se treatment (up to 100 µM Se) corresponded with higher nodule counts, indicating a potential role for dinitrogen fixation in Se-hyperaccumulation. The effect was not found in nonhyperaccumulators. • As the evolution of Se hyperaccumulation in Astragalus developed, root-nodule symbiosis may have played an integral role.

Ecological consequences of the expansion of N2-fixing plants in cold biomes

USGS Publications Warehouse

Hiltbrunner, Erika; Aerts, Rien; Bühlmann, Tobias; Huss-Danell, Kerstin; Magnusson, Borgthor; Myrold, David D.; Reed, Sasha C.; Sigurdsson, Bjarni D.; Körner, Christian

2014-01-01

Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N2)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N2O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N2-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N2 fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N2-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N2-fixing plants and a rapid subsequent saturation in the ecosystem’s capacity to retain N. Therefore, analogous to increases in N deposition, N2-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.

Applicability, usability, and limitations of murine embryonic imaging with optical coherence tomography and optical projection tomography

PubMed Central

Singh, Manmohan; Raghunathan, Raksha; Piazza, Victor; Davis-Loiacono, Anjul M.; Cable, Alex; Vedakkan, Tegy J.; Janecek, Trevor; Frazier, Michael V.; Nair, Achuth; Wu, Chen; Larina, Irina V.; Dickinson, Mary E.; Larin, Kirill V.

2016-01-01

We present an analysis of imaging murine embryos at various embryonic developmental stages (embryonic day 9.5, 11.5, and 13.5) by optical coherence tomography (OCT) and optical projection tomography (OPT). We demonstrate that while OCT was capable of rapid high-resolution live 3D imaging, its limited penetration depth prevented visualization of deeper structures, particularly in later stage embryos. In contrast, OPT was able to image the whole embryos, but could not be used in vivo because the embryos must be fixed and cleared. Moreover, the fixation process significantly altered the embryo morphology, which was quantified by the volume of the eye-globes before and after fixation. All of these factors should be weighed when determining which imaging modality one should use to achieve particular goals of a study. PMID:27375945

Torsional stiffness after subtalar arthrodesis using second generation headless compression screws: Biomechanical comparison of 2-screw and 3-screw fixation.

PubMed

Riedl, Markus; Glisson, Richard R; Matsumoto, Takumi; Hofstaetter, Stefan G; Easley, Mark E

2017-06-01

Subtalar joint arthrodesis is a common operative treatment for symptomatic subtalar arthrosis. Because excessive relative motion between the talus and calcaneus can delay or prohibit fusion, fixation should be optimized, particularly in patients at risk for subtalar arthrodesis nonunion. Tapered, fully-threaded, variable pitch screws are gaining popularity for this application, but the mechanical properties of joints fixed with these screws have not been characterized completely. We quantified the torsion resistance of 2-screw and 3-screw subtalar joint fixation using this type of screw. Ten pairs of cadaveric subtalar joints were prepared for arthrodesis and fixed using Acutrak 2-7.5 screws. One specimen from each pair was fixed with two diverging posterior screws, and the contralateral joint was fixed using two posterior screws and a third screw directed through the anterior calcaneus into the talar neck. Internal and external torsional loads were applied and joint rotation and torsional stiffness were measured at two torque levels. Internal rotation was significantly less in specimens fixed with three screws. No difference was detectable between 2-screw and 3-screw fixation in external rotation or torsional stiffness in either rotation direction. Both 2-screw and 3-screw fixation exhibited torsion resistance surpassing that reported previously for subtalar joints fixed with two diverging conventional lag screws. Performance of the tapered, fully threaded, variable pitch screws exceeded that of conventional lag screws regardless of whether two or three screws were used. Additional resistance to internal rotation afforded by a third screw placed anteriorly may offer some advantage in patients at risk for nonunion. Copyright © 2017. Published by Elsevier Ltd.

How task demands influence scanpath similarity in a sequential number-search task.

PubMed

Dewhurst, Richard; Foulsham, Tom; Jarodzka, Halszka; Johansson, Roger; Holmqvist, Kenneth; Nyström, Marcus

2018-06-07

More and more researchers are considering the omnibus eye movement sequence-the scanpath-in their studies of visual and cognitive processing (e.g. Hayes, Petrov, & Sederberg, 2011; Madsen, Larson, Loschky, & Rebello, 2012; Ni et al., 2011; von der Malsburg & Vasishth, 2011). However, it remains unclear how recent methods for comparing scanpaths perform in experiments producing variable scanpaths, and whether these methods supplement more traditional analyses of individual oculomotor statistics. We address this problem for MultiMatch (Jarodzka et al., 2010; Dewhurst et al., 2012), evaluating its performance with a visual search-like task in which participants must fixate a series of target numbers in a prescribed order. This task should produce predictable sequences of fixations and thus provide a testing ground for scanpath measures. Task difficulty was manipulated by making the targets more or less visible through changes in font and the presence of distractors or visual noise. These changes in task demands led to slower search and more fixations. Importantly, they also resulted in a reduction in the between-subjects scanpath similarity, demonstrating that participants' gaze patterns became more heterogenous in terms of saccade length and angle, and fixation position. This implies a divergent strategy or random component to eye-movement behaviour which increases as the task becomes more difficult. Interestingly, the duration of fixations along aligned vectors showed the opposite pattern, becoming more similar between observers in 2 of the 3 difficulty manipulations. This provides important information for vision scientists who may wish to use scanpath metrics to quantify variations in gaze across a spectrum of perceptual and cognitive tasks. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pseudo-Fovea Formation After Gene Therapy for RPE65-LCA

PubMed Central

Cideciyan, Artur V.; Aguirre, Geoffrey K.; Jacobson, Samuel G.; Butt, Omar H.; Schwartz, Sharon B.; Swider, Malgorzata; Roman, Alejandro J.; Sadigh, Sam; Hauswirth, William W.

2015-01-01

Purpose. The purpose of this study was to evaluate fixation location and oculomotor characteristics of 15 patients with Leber congenital amaurosis (LCA) caused by RPE65 mutations (RPE65-LCA) who underwent retinal gene therapy. Methods. Eye movements were quantified under infrared imaging of the retina while the subject fixated on a stationary target. In a subset of patients, letter recognition under retinal imaging was performed. Cortical responses to visual stimulation were measured using functional magnetic resonance imaging (fMRI) in two patients before and after therapy. Results. All patients were able to fixate on a 1° diameter visible target in the dark. The preferred retinal locus of fixation was either at the anatomical fovea or at an extrafoveal locus. There were a wide range of oculomotor abnormalities. Natural history showed little change in oculomotor abnormalities if target illuminance was increased to maintain target visibility as the disease progressed. Eleven of 15 study eyes treated with gene therapy showed no differences from baseline fixation locations or instability over an average of follow-up of 3.5 years. Four of 15 eyes developed new pseudo-foveas in the treated retinal regions 9 to 12 months after therapy that persisted for up to 6 years; patients used their pseudo-foveas for letter identification. fMRI studies demonstrated that preservation of light sensitivity was restricted to the cortical projection zone of the pseudo-foveas. Conclusions. The slow emergence of pseudo-foveas many months after the initial increases in light sensitivity points to a substantial plasticity of the adult visual system and a complex interaction between it and the progression of underlying retinal disease. The visual significance of pseudo-foveas suggests careful consideration of treatment zones for future gene therapy trials. (ClinicalTrials.gov number, NCT00481546.) PMID:25537204

Accurate Quantification of T Cells by Measuring Loss of Germline T-Cell Receptor Loci with Generic Single Duplex Droplet Digital PCR Assays.

PubMed

Zoutman, Willem H; Nell, Rogier J; Versluis, Mieke; van Steenderen, Debby; Lalai, Rajshri N; Out-Luiting, Jacoba J; de Lange, Mark J; Vermeer, Maarten H; Langerak, Anton W; van der Velden, Pieter A

2017-03-01

Quantifying T cells accurately in a variety of tissues of benign, inflammatory, or malignant origin can be of great importance in a variety of clinical applications. Flow cytometry and immunohistochemistry are considered to be gold-standard methods for T-cell quantification. However, these methods require fresh, frozen, or fixated cells and tissue of a certain quality. In addition, conventional and droplet digital PCR (ddPCR), whether followed by deep sequencing techniques, have been used to elucidate T-cell content by focusing on rearranged T-cell receptor (TCR) genes. These approaches typically target the whole TCR repertoire, thereby supplying additional information about TCR use. We alternatively developed and validated two novel generic single duplex ddPCR assays to quantify T cells accurately by measuring loss of specific germline TCR loci and compared them with flow cytometry-based quantification. These assays target sequences between the Dδ2 and Dδ3 genes (TRD locus) and Dβ1 and Jβ1.1 genes (TRB locus) that become deleted systematically early during lymphoid differentiation. Because these ddPCR assays require small amounts of DNA instead of freshly isolated, frozen, or fixated material, initially unanalyzable (scarce) specimens can be assayed from now on, supplying valuable information about T-cell content. Our ddPCR method provides a novel and sensitive way for quantifying T cells relatively fast, accurate, and independent of the cellular context. Copyright © 2017 American Society for Investigative Pathology and the Association for Molecular Pathology. Published by Elsevier Inc. All rights reserved.

Development of the eye-movement response in the trainee radiologist

NASA Astrophysics Data System (ADS)

Wooding, David S.; Roberts, Geraint M.; Phillips-Hughes, Jane

1999-05-01

In order to explore the initial response of the visual system to radiological images in groups of individuals with increasing degrees of radiological training and experience, the locations of fixations made during visual inspection of digitized chest radiographs were examined for 4 groups of observers: 10 experienced radiologists, 9 first-year 'novice' radiologists, 11 'trainee' radiologists in the second and third years of their training, and 7 native controls. Each observer viewed 12 digitized chest radiographs (6 normal and 6 showing some abnormality) in a VDU for 8s each. Eye movements were recorded throughout and observers indicated via a button box whether they thought the radiograph to be normal or abnormal. A least squares index was utilized in order to quantify the similarity in fixation location between pairs of eye movement traces over the first 1.5 and 3 seconds of an inspection. The similarities thus produced were then averaged to give intra- and inter-group similarities in fixation location. The fixation locations of experienced radiologists were found to be highly similar as a group, as were those of the novices. While the fixation locations of controls showed less similarity, it was the fixations of trainees which were the least similar (i.e. showed the most variability) within their group. The fixation locations of novices showed a greater similarity to those of radiologists than those of controls, and a decreased similarity to those of controls than those of the controls themselves. However, rather than showing that the fixation locations of individuals become increasing similar to those of radiologists as training progresses, the data show that the more variable fixation locations of trainees are the least similar to those of radiologists than those of any of the groups, even the controls. Control observers examine every day images in a similar way and this is also true of radiological images. Experienced radiologists view radiological images in a similar way to each other, but their training has resulted in differences between them and controls. In becoming experienced radiologists, it appears that trainees may move through a developmental phase characterized by more idiosyncratic eye movements; their eye movements becoming less similar to controls or experienced radiologists than they were. With experience the eye movements of trainee radiologists may become more similar to both groups, but the transition of the trainee from novice to experienced radiologist is not a simple one: the change involves a period of some disorder.

Chain Reaction: A Detailed look at Reactive Nitrogen and Possible Management Approaches

EPA Science Inventory

Nitrogen is one of the building blocks of life, yet excessive amounts in the environment can cause problems in various ecosystems. Abundant in the atmosphere as dinitrogen (N₂), nitrogen needs to be combined with other elements such as hydrogen or oxygen to...

Examining the impact of heterogeneous nitryl chloride production on air quality across the United States

EPA Science Inventory

The heterogeneous hydrolysis of dinitrogen pentoxide (N₂O₅) has typically been modeled as only producing nitric acid. However, recent field studies have confirmed that the presence of particulate chloride can alter the reaction product to produce nitryl chlo...

Nitrous oxide emission from denitrification in stream and river networks

Treesearch

J.J. Beaulieu; J.L. Tank; S.K. Hamilton; W.M. Wollheim; R.O. Hall; P.J. Mulholland; B.J. Peterson; L.R. Ashkenas; L.W. Cooper; C.N. Dahm; W.K. Dodds; N.B. Grimm; S.L. Johnson; W.H. McDowell; G.C. Poole; H.M. Valett; C.P. Arango; M.J. Bernot; A.J. Burgin; C.L. Crenshaw; A.M. Helton; L.T. Johnson; J.M. O' Brien; J.D. Potter; R.W. Sheibley; D.J. Sobota; S.M. Thomas

2011-01-01

Nitrous oxide (N20) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N20 via microbial denitrification that converts N to N20 and dinitrogen (N2...

Inoculation of Bacillus sphaericus UPMB-10 to Young Oil Palm and Measurement of Its Uptake of Fixed Nitrogen Using the 15N Isotope Dilution Technique

PubMed Central

Zakry, Fitri Abdul Aziz; Shamsuddin, Zulkifli H.; Rahim, Khairuddin Abdul; Zakaria, Zin Zawawi; Rahim, Anuar Abdul

2012-01-01

There are increasing applications of diazotrophic rhizobacteria in the sustainable agriculture system. A field experiment on young immature oil palm was conducted to quantify the uptake of N derived from N2 fixation by the diazotroph Bacillus sphaericus strain UPMB-10, using the 15N isotope dilution method. Eight months after 15N application, young immature oil palms that received 67% of standard N fertilizer application together with B. sphaericus inoculation had significantly lower 15N enrichment than uninoculated palms that received similar N fertilizers. The dilution of labeled N served as a marker for the occurrence of biological N2 fixation. The proportion of N uptake that was derived from the atmosphere was estimated as 63% on the whole plant basis. The inoculation process increased the N and dry matter yields of the palm leaflets and rachis significantly. Field planting of young, immature oil palm in soil inoculated with B. sphaericus UPMB-10 might mitigate inorganic fertilizer-N application through supplementation by biological nitrogen fixation. This could be a new and important source of nitrogen biofertilizer in the early phase of oil palm cultivation in the field. PMID:22446306

Live interaction distinctively shapes social gaze dynamics in rhesus macaques.

PubMed

Dal Monte, Olga; Piva, Matthew; Morris, Jason A; Chang, Steve W C

2016-10-01

The dynamic interaction of gaze between individuals is a hallmark of social cognition. However, very few studies have examined social gaze dynamics after mutual eye contact during real-time interactions. We used a highly quantifiable paradigm to assess social gaze dynamics between pairs of monkeys and modeled these dynamics using an exponential decay function to investigate sustained attention after mutual eye contact. When monkeys were interacting with real partners compared with static images and movies of the same monkeys, we found a significant increase in the proportion of fixations to the eyes and a smaller dispersion of fixations around the eyes, indicating enhanced focal attention to the eye region. Notably, dominance and familiarity between the interacting pairs induced separable components of gaze dynamics that were unique to live interactions. Gaze dynamics of dominant monkeys after mutual eye contact were associated with a greater number of fixations to the eyes, whereas those of familiar pairs were associated with a faster rate of decrease in this eye-directed attention. Our findings endorse the notion that certain key aspects of social cognition are only captured during interactive social contexts and dependent on the elapsed time relative to socially meaningful events. Copyright © 2016 the American Physiological Society.

Live interaction distinctively shapes social gaze dynamics in rhesus macaques

PubMed Central

Piva, Matthew; Morris, Jason A.; Chang, Steve W. C.

2016-01-01

The dynamic interaction of gaze between individuals is a hallmark of social cognition. However, very few studies have examined social gaze dynamics after mutual eye contact during real-time interactions. We used a highly quantifiable paradigm to assess social gaze dynamics between pairs of monkeys and modeled these dynamics using an exponential decay function to investigate sustained attention after mutual eye contact. When monkeys were interacting with real partners compared with static images and movies of the same monkeys, we found a significant increase in the proportion of fixations to the eyes and a smaller dispersion of fixations around the eyes, indicating enhanced focal attention to the eye region. Notably, dominance and familiarity between the interacting pairs induced separable components of gaze dynamics that were unique to live interactions. Gaze dynamics of dominant monkeys after mutual eye contact were associated with a greater number of fixations to the eyes, whereas those of familiar pairs were associated with a faster rate of decrease in this eye-directed attention. Our findings endorse the notion that certain key aspects of social cognition are only captured during interactive social contexts and dependent on the elapsed time relative to socially meaningful events. PMID:27486105

Carbon sequestration in soybean crop soils: the role of hydrogen-coupled CO2 fixation

NASA Astrophysics Data System (ADS)

Graham, A.; Layzell, D. B.; Scott, N. A.; Cen, Y.; Kyser, T. K.

2011-12-01

Conversion of native vegetation to agricultural land in order to support the world's growing population is a key factor contributing to global climate change. However, the extent to which agricultural activities contribute to greenhouse gas emissions compared to carbon storage is difficult to ascertain, especially for legume crops, such as soybeans. Soybean establishment often leads to an increase in N2O emissions because N-fixation leads to increased soil available N during decomposition of the low C:N legume biomass. However, soybean establishment may also reduce net greenhouse gas emissions by increasing soil fertility, plant growth, and soil carbon storage. The mechanism behind increased carbon storage, however, remains unclear. One explanation points to hydrogen coupled CO2 fixation; the process by which nitrogen fixation releases H2 into the soil system, thereby promoting chemoautotrophic carbon fixation by soil microbes. We used 13CO2 as a tracer to track the amount and fate of carbon fixed by hydrogen coupled CO2 fixation during one-year field and laboratory incubations. The objectives of the research are to 1) quantify rates of 13CO2 fixation in soil collected from a field used for long-term soybean production 2) examine the impact of H2 gas concentration on rates of 13CO2 fixation, and 3) measure changes in δ13C signature over time in 3 soil fractions: microbial biomass, light fraction, and acid stable fraction. If this newly-fixed carbon is incorporated into the acid-stable soil C fraction, it has a good chance of contributing to long-term soil C sequestration under soybean production. Soil was collected in the field both adjacent to root nodules (nodule soil) and >3cm away (root soil) and labelled with 13CO2 (1% v/v) in the presence and absence of H2 gas. After a two week labelling period, δ13C signatures already revealed differences in the four treatments of bulk soil: -17.1 for root, -17.6 for nodule, -14.2 for root + H2, and -6.1 for nodule + H2. Labelled soil was then placed in nylon mesh bags and buried in the field at a depth of 15cm in a soybean field at the Central Experiment Farm in Ottawa, Ontario. Samples will be removed at intervals of 1,2,3,6,9,12, and 15 months, and the δ13C of three soil fractions will be examined to reveal changes in carbon storage over time. Our results will provide insights into the fate of carbon fixed during hydrogen coupled CO2 fixation, and demonstrate whether this CO2 fixation can contribute to the long-term greenhouse gas balance of soybean production systems.

Programmed cell death in the marine cyanobacterium Trichodesmium mediates carbon and nitrogen export

PubMed Central

Bar-Zeev, Edo; Avishay, Itamar; Bidle, Kay D; Berman-Frank, Ilana

2013-01-01

The extent of carbon (C) and nitrogen (N) export to the deep ocean depends upon the efficacy of the biological pump that transports primary production to depth, thereby preventing its recycling in the upper photic zone. The dinitrogen-fixing (diazotrophic) Trichodesmium spp. contributes significantly to oceanic C and N cycling by forming extensive blooms in nutrient-poor tropical and subtropical regions. These massive blooms generally collapse several days after forming, but the cellular mechanism responsible, along with the magnitude of associated C and N export processes, are as yet unknown. Here, we used a custom-made, 2-m high water column to simulate a natural bloom and to specifically test and quantify whether the programmed cell death (PCD) of Trichodesmium mechanistically regulates increased vertical flux of C and N. Our findings demonstrate that extremely rapid development and abrupt, PCD-induced demise (within 2–3 days) of Trichodesmium blooms lead to greatly elevated excretions of transparent exopolymers and a massive downward pulse of particulate organic matter. Our results mechanistically link autocatalytic PCD and bloom collapse to quantitative C and N export fluxes, suggesting that PCD may have an impact on the biological pump efficiency in the oceans. PMID:23887173

Understanding Nitrogen Fixation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul J. Chirik

The purpose of our program is to explore fundamental chemistry relevant to the discovery of energy efficient methods for the conversion of atmospheric nitrogen (N{sub 2}) into more value-added nitrogen-containing organic molecules. Such transformations are key for domestic energy security and the reduction of fossil fuel dependencies. With DOE support, we have synthesized families of zirconium and hafnium dinitrogen complexes with elongated and activated N-N bonds that exhibit rich N{sub 2} functionalization chemistry. Having elucidated new methods for N-H bond formation from dihydrogen, C-H bonds and Broensted acids, we have since turned our attention to N-C bond construction. These reactionsmore » are particularly important for the synthesis of amines, heterocycles and hydrazines with a range of applications in the fine and commodity chemicals industries and as fuels. One recent highlight was the discovery of a new N{sub 2} cleavage reaction upon addition of carbon monoxide which resulted in the synthesis of an important fertilizer, oxamide, from the diatomics with the two strongest bonds in chemistry. Nitrogen-carbon bonds form the backbone of many important organic molecules, especially those used in the fertilizer and pharamaceutical industries. During the past year, we have continued our work in the synthesis of hydrazines of various substitution patterns, many of which are important precursors for heterocycles. In most instances, the direct functionalization of N{sub 2} offers a more efficient synthetic route than traditional organic methods. In addition, we have also discovered a unique CO-induced N{sub 2} bond cleavage reaction that simultaneously cleaves the N-N bond of the metal dinitrogen compound and assembles new C-C bond and two new N-C bonds. Treatment of the CO-functionalized core with weak Broensted acids liberated oxamide, H{sub 2}NC(O)C(O)NH{sub 2}, an important slow release fertilizer that is of interest to replace urea in many applications. The synthesis of ammonia, NH{sub 3}, from its elements, H{sub 2} and N{sub 2}, via the venerable Haber-Bosch process is one of the most significant technological achievements of the past century. Our research program seeks to discover new transition metal reagents and catalysts to disrupt the strong N {triple_bond} N bond in N{sub 2} and create new, fundamental chemical linkages for the construction of molecules with application as fuels, fertilizers and fine chemicals. With DOE support, our group has discovered a mild method for ammonia synthesis in solution as well as new methods for the construction of nitrogen-carbon bonds directly from N{sub 2}. Ideally these achievements will evolve into more efficient nitrogen fixation schemes that circumvent the high energy demands of industrial ammonia synthesis. Industrially, atmospheric nitrogen enters the synthetic cycle by the well-established Haber-Bosch process whereby N{sub 2} is hydrogenated to ammonia at high temperature and pressure. The commercialization of this reaction represents one of the greatest technological achievements of the 20th century as Haber-Bosch ammonia is responsible for supporting approximately 50% of the world's population and serves as the source of half of the nitrogen in the human body. The extreme reaction conditions required for an economical process have significant energy consequences, consuming 1% of the world's energy supply mostly in the form of pollution-intensive coal. Moreover, industrial H{sub 2} synthesis via the water gas shift reaction and the steam reforming of methane is fossil fuel intensive and produces CO{sub 2} as a byproduct. New synthetic methods that promote this thermodynamically favored transformation ({Delta}G{sup o} = -4.1 kcal/mol) under milder conditions or completely obviate it are therefore desirable. Most nitrogen-containing organic molecules are derived from ammonia (and hence rely on the Haber-Bosch and H{sub 2} synthesis processes) and direct synthesis from atmospheric nitrogen could, in principle, be more energy-efficient. This is particularly attractive given the interest in direct hydrazine fuel cells.« less

Electron transfer to nitrogenase in different genomic and metabolic backgrounds.

PubMed

Poudel, Saroj; Colman, Daniel R; Fixen, Kathryn R; Ledbetter, Rhesa N; Zheng, Yanning; Pence, Natasha; Seefeldt, Lance C; Peters, John W; Harwood, Caroline S; Boyd, Eric S

2018-02-26

Nitrogenase catalyzes the reduction of dinitrogen (N 2 ) using low potential electrons from ferredoxin (Fd) or flavodoxin (Fld) through an ATP dependent process. Since its emergence in an anaerobic chemoautotroph, this oxygen (O 2 ) sensitive enzyme complex has evolved to operate in a variety of genomic and metabolic backgrounds including those of aerobes, anaerobes, chemotrophs, and phototrophs. However, whether pathways of electron delivery to nitrogenase are influenced by these different metabolic backgrounds is not well understood. Here, we report the distribution of homologs of Fds, Flds, and Fd/Fld-reducing enzymes in 359 genomes of putative N 2 fixers (diazotrophs). Six distinct lineages of nitrogenase were identified and their distributions largely corresponded to differences in the host cells' ability to integrate O 2 or light into energy metabolism. Predicted pathways of electron transfer to nitrogenase in aerobes, facultative anaerobes, and phototrophs varied from those in anaerobes at the level of Fds/Flds used to reduce nitrogenase, the enzymes that generate reduced Fds/Flds, and the putative substrates of these enzymes. Proteins that putatively reduce Fd with hydrogen or pyruvate were enriched in anaerobes, while those that reduce Fd with NADH/NADPH were enriched in aerobes, facultative anaerobes, and anoxygenic phototrophs. The energy metabolism of aerobic, facultatively anaerobic, and anoxygenic phototrophic diazotrophs often yields reduced NADH/NADPH that is not sufficiently reduced to drive N 2 reduction. At least two mechanisms have been acquired by these taxa to overcome this limitation and to generate electrons with potentials capable of reducing Fd. These include the bifurcation of electrons or the coupling of Fd reduction to reverse ion translocation. IMPORTANCE Nitrogen fixation supplies fixed nitrogen to cells from a variety of genomic and metabolic backgrounds including those of aerobes, facultative anaerobes, chemotrophs, and phototrophs. Here, using informatics approaches applied to genomic data, we show that pathways of electron transfer to nitrogenase in metabolically diverse diazotrophic taxa have diversified primarily in response to host cells' acquired ability to integrate O 2 or light into their energy metabolism. Acquisition of two key enzyme complexes enabled aerobic and facultatively anaerobic phototrophic taxa to generate electrons of sufficiently low potential to reduce nitrogenase: the bifurcation of electrons via the Fix complex or the coupling of Fd reduction to reverse ion translocation via the Rhodobacter nitrogen fixation (Rnf) complex. Copyright © 2018 American Society for Microbiology.

Achieving fixation in glenoids with superior wear using reverse shoulder arthroplasty.

PubMed

Roche, Christopher P; Stroud, Nicholas J; Martin, Brian L; Steiler, Cindy A; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D; Dipaola, Matthew J

2013-12-01

Superior glenoid wear is a common challenge with reverse shoulder arthroplasty and, if left uncorrected, can result in superior glenoid tilt, which increases the risk of aseptic glenoid loosening. This study evaluates the impact of an E2 superior defect on reverse shoulder glenoid fixation in composite scapulae after correction of glenoid tilt by use of 2 different glenoid reaming techniques: eccentric reaming and off-axis reaming. A superior glenoid defect was created in 14 composite scapulae. The superior defect was corrected by 2 different glenoid reaming techniques: (1) eccentric reaming with implantation of a standard glenoid baseplate and (2) off-axis reaming with implantation of a superior-augment glenoid baseplate. Each corrected superior-defect scapula was then cyclically loaded (along with a control group consisting of 7 non-worn scapulae) for 10,000 cycles at 750 N; glenoid baseplate displacement was measured for each group to quantify fixation before and after cyclic loading. Regardless of the glenoid reaming technique or the glenoid baseplate type, each standard and superior-augment glenoid baseplate remained well fixed in this superior-defect model scenario after cyclic loading. No differences in baseplate displacement were observed either before or after cyclic loading between groups. Our results suggest that either glenoid reaming technique may be used to achieve fixation in the clinically challenging situation of superior wear with reverse shoulder arthroplasty. Basic science, biomechanical study. Copyright © 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

Unicompartmental knee prostheses: in vitro wear assessment of the menisci tibial insert after two different fixation methods

NASA Astrophysics Data System (ADS)

Affatato, S.; Spinelli, M.; Zavalloni, M.; Carmignato, S.; Lopomo, N.; Marcacci, M.; Viceconti, M.

2008-10-01

Knee osteoarthritis is a complex clinical scenario where many biological and mechanical factors influence the severity of articular degenerative changes. Minimally invasive knee prosthetic surgery, with only a compartment replacement (unicompartmental knee replacement), might be a good compromise between osteotomy and total knee prosthesis. The focus of this study was to develop and validate a protocol to assess the fixation method of the femoral components in mechanical simulation, for pre-clinical validation; the wear behaviour of two different fixation frames was quantified and compared. In particular, two different wear tests were conducted using the same knee simulator, the same load profiles and the same kinematics; two different fixation methods were applied to the femoral sleds (synthetic femur and metal block). Surface characterization on both articulating bearings was performed by a roughness measuring machine and coordinate measuring machine. The wear produced by the tibial inserts using the synthetic femur was considerably higher than the wear registered by the metal-block holder. Roughness measurements on femoral sleds showed a limited number of scratches with high Rt values for the metal-block set-up; the damaged surface broadened in the case of femoral condyles and tibial inserts mounted on composite bone, but lower Rt and linear penetration values were measured. The two holding frames showed different wear activities as a consequence of dissimilar dynamic performance. Further observations should be made in vivo to prove the actual importance of synthetic bone simulations and specific material behaviour.

A Locally Weighted Fixation Density-Based Metric for Assessing the Quality of Visual Saliency Predictions

NASA Astrophysics Data System (ADS)

Gide, Milind S.; Karam, Lina J.

2016-08-01

With the increased focus on visual attention (VA) in the last decade, a large number of computational visual saliency methods have been developed over the past few years. These models are traditionally evaluated by using performance evaluation metrics that quantify the match between predicted saliency and fixation data obtained from eye-tracking experiments on human observers. Though a considerable number of such metrics have been proposed in the literature, there are notable problems in them. In this work, we discuss shortcomings in existing metrics through illustrative examples and propose a new metric that uses local weights based on fixation density which overcomes these flaws. To compare the performance of our proposed metric at assessing the quality of saliency prediction with other existing metrics, we construct a ground-truth subjective database in which saliency maps obtained from 17 different VA models are evaluated by 16 human observers on a 5-point categorical scale in terms of their visual resemblance with corresponding ground-truth fixation density maps obtained from eye-tracking data. The metrics are evaluated by correlating metric scores with the human subjective ratings. The correlation results show that the proposed evaluation metric outperforms all other popular existing metrics. Additionally, the constructed database and corresponding subjective ratings provide an insight into which of the existing metrics and future metrics are better at estimating the quality of saliency prediction and can be used as a benchmark.

Enhanced Soft Tissue Attachment and Fixation Using a Mechanically-Stimulated Cytoselective Tissue-Specific ECM Coating

DTIC Science & Technology

2013-01-01

of stimulation parameters . The deposited ECM was quantified. It was observed that the entirely strained stretching regime produced slightly higher... parameters (such as, % strain, strain duration, number of cycles, lag between cycles, etc.) that were commonly reported in the literature. There are many... hydroxyapatite . Biomaterials 2007;28(3):383-92. 18. Johnson GA, Tramaglini DM, Levine RE, Ohno K, Choi NY, Woo SL. Tensile and viscoelastic

Comparative fixation methods of cervical disc arthroplasty versus conventional methods of anterior cervical arthrodesis: serration, teeth, keels, or screws?

PubMed

Cunningham, Bryan W; Hu, Nianbin; Zorn, Candace M; McAfee, Paul C

2010-02-01

Using a synthetic vertebral model, the authors quantified the comparative fixation strengths and failure mechanisms of 6 cervical disc arthroplasty devices versus 2 conventional methods of cervical arthrodesis, highlighting biomechanical advantages of prosthetic endplate fixation properties. Eight cervical implant configurations were evaluated in the current investigation: 1) PCM Low Profile; 2) PCM V-Teeth; 3) PCM Modular Flange; 4) PCM Fixed Flange; 5) Prestige LP; 6) Kineflex/C disc; 7) anterior cervical plate + interbody cage; and 8) tricortical iliac crest. All PCM treatments contained a serrated implant surface (0.4 mm). The PCM V-Teeth and Prestige contained 2 additional rows of teeth, which were 1 mm and 2 mm high, respectively. The PCM Modular and Fixed Flanged devices and anterior cervical plate were augmented with 4 vertebral screws. Eight pullout tests were performed for each of the 8 conditions by using a synthetic fixation model consisting of solid rigid polyurethane foam blocks. Biomechanical testing was conducted using an 858 Bionix test system configured with an unconstrained testing platform. Implants were positioned between testing blocks, using a compressive preload of -267 N. Tensile load-to-failure testing was performed at 2.5 mm/second, with quantification of peak load at failure (in Newtons), implant surface area (in square millimeters), and failure mechanisms. The mean loads at failure for the 8 implants were as follows: 257.4 +/- 28.54 for the PCM Low Profile; 308.8 +/- 15.31 for PCM V-Teeth; 496.36 +/- 40.01 for PCM Modular Flange; 528.03+/- 127.8 for PCM Fixed Flange; 306.4 +/- 31.3 for Prestige LP; 286.9 +/- 18.4 for Kineflex/C disc; 635.53 +/- 112.62 for anterior cervical plate + interbody cage; and 161.61 +/- 16.58 for tricortical iliac crest. The anterior plate exhibited the highest load at failure compared with all other treatments (p < 0.05). The PCM Modular and Fixed Flange PCM constructs in which screw fixation was used exhibited higher pullout loads than all other treatments except the anterior plate (p < 0.05). The PCM VTeeth and Prestige and Kineflex/C implants exhibited higher pullout loads than the PCM Low Profile and tricortical iliac crest (p < 0.05). Tricortical iliac crest exhibited the lowest pullout strength, which was different from all other treatments (p < 0.05). The surface area of endplate contact, measuring 300 mm(2) (PCM treatments), 275 mm(2) (Prestige LP), 250 mm(2) (Kineflex/C disc), 180 mm(2) (plate + cage), and 235 mm(2) (tricortical iliac crest), did not correlate with pullout strength (p > 0.05). The PCM, Prestige, and Kineflex constructs, which did not use screw fixation, all failed by direct pullout. Screw fixation devices, including anterior plates, led to test block fracture, and tricortical iliac crest failed by direct pullout. These results demonstrate a continuum of fixation strength based on prosthetic endplate design. Disc arthroplasty constructs implanted using vertebral body screw fixation exhibited the highest pullout strength. Prosthetic endplates containing toothed ridges (>or= 1 mm) or keels placed second in fixation strength, whereas endplates containing serrated edges exhibited the lowest fixation strength. All treatments exhibited greater fixation strength than conventional tricortical iliac crest. The current study offers insights into the benefits of various prosthetic endplate designs, which may potentially improve acute fixation following cervical disc arthroplasty.

Using a Microcomputer in the Teaching of Gas-Phase Equilibria: A Numerical Simulation.

ERIC Educational Resources Information Center

Hayward, Roger

1995-01-01

Describes a computer program that can model the equilibrium processes in the production of ammonia from hydrogen and nitrogen, sulfur trioxide from sulfur dioxide and oxygen, and the nitrogen dioxide-dinitrogen tetroxide equilibrium. Provides information about downloading the program ChemEquilibrium from the World Wide Web. (JRH)

Using soil isotopes as an indicator of site-specific to national-scale denitrification in wetlands

EPA Science Inventory

Denitrification is an anaerobic, microbial process that converts nitrate to inert dinitrogen (N2) gas and nitrous oxide (N2O), a potent greenhouse and ozone depleting gas. High rates of denitrification can be found in wetlands, resulting in the removal of large quantities of nitr...

Denitrification alternates between a source and sink of nitrous oxide in the hypolimnion of a thermally stratified reservoir

EPA Science Inventory

Nitrogen loading from developed watersheds to aquatic ecosystems can stimulate microbial denitrification, a process which reduces nitrate (NO3-) to dinitrogen (N2) or nitrous oxide (N2O), the latter a potent greenhouse gas. While aquatic ecosystems are a globally significant sou...

Catalysis-dependent selenium incorporation and migration in the nitrogenase active site iron-molybdenum cofactor.

PubMed

Spatzal, Thomas; Perez, Kathryn A; Howard, James B; Rees, Douglas C

2015-12-16

Dinitrogen reduction in the biological nitrogen cycle is catalyzed by nitrogenase, a two-component metalloenzyme. Understanding of the transformation of the inert resting state of the active site FeMo-cofactor into an activated state capable of reducing dinitrogen remains elusive. Here we report the catalysis dependent, site-selective incorporation of selenium into the FeMo-cofactor from selenocyanate as a newly identified substrate and inhibitor. The 1.60 Å resolution structure reveals selenium occupying the S2B site of FeMo-cofactor in the Azotobacter vinelandii MoFe-protein, a position that was recently identified as the CO-binding site. The Se2B-labeled enzyme retains substrate reduction activity and marks the starting point for a crystallographic pulse-chase experiment of the active site during turnover. Through a series of crystal structures obtained at resolutions of 1.32-1.66 Å, including the CO-inhibited form of Av1-Se2B, the exchangeability of all three belt-sulfur sites is demonstrated, providing direct insights into unforeseen rearrangements of the metal center during catalysis.

Denitrification in Shallow Groundwater Below Different Arable Land Systems in a High Nitrogen-Loading Region

NASA Astrophysics Data System (ADS)

Zhou, Wei; Ma, Yuchun; Well, Reinhard; Wang, Hua; Yan, Xiaoyuan

2018-03-01

To evaluate the risk of nitrate (NO3--N) in groundwater, it is necessary to know the denitrification capacity. In this study, observations were carried out for 2 years to investigate the groundwater denitrification capacity below three arable land systems in eastern China. Denitrification capacity was assessed by measuring the concentration and distribution patterns of nitrous oxide (N2O) and dinitrogen (N2) in groundwater. The results revealed that groundwater denitrification activity was high and consumed 76%, 83%, and 65% of the NO3--N in the vineyard (VY), vegetable field (VF), and paddy field (PF), respectively. The high denitrification activity might be attributed to the strong reducing conditions, with high dissolved oxygen concentrations in groundwater, which promotes denitrification. During the sampling period, we observed high dinitrogen (excess N2) accumulation in groundwater, which exceeded the total reactive nitrogen (N) in the deep layer. The large amount of excess N2 observed in VY and VF indicated that considerable N was stored as gaseous N2 in groundwater and should not be ignored when balancing N budgets in aquifers where denitrification is high.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia

In this study, the adsorption of N 2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N 2 in H 2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N 2. Four supported species formed in various flowing gases: Ir(N 2), Ir(N 2)(N 2), Ir(C 2H 5)(N 2), and Ir(H)(N 2). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N 2, Ir(N 2) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N 2)more » formed transiently in flowing CO, and in the presence of H 2, rather stable iridium hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.« less

Matrix isolation infrared spectroscopic studies and density functional theory calculations of the MNN, (MN)2 (M = Y and La), and Y3NN molecules.

PubMed

Teng, Yun-Lei; Xu, Qiang

2008-04-24

The reactions of yttrium and lanthanum with dinitrogen were reinvestigated. Laser-ablated yttrium and lanthanum atoms were co-deposited at 4 K with dinitrogen in excess argon, and the low-temperature reactions of Y and La with N2 in solid argon were studied using infrared spectroscopy. The reaction products YNN, (YN)2, LaNN, and (LaN)2 were formed in the present experiments and characterized on the basis of 14N/15N isotopic shifts, mixed isotope splitting patterns, stepwise annealing, change of reagent concentration and laser energy, and comparison with theoretical predictions. Some assignments were made based on a previous report. Density functional theory calculations were performed on these systems to identify possible reaction products. The agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts of the MNN and (MN)2 (M = Y and La) molecules supports the identification of these molecules from the matrix infrared spectra. Plausible reaction mechanisms were proposed for the formation of these molecules along with tentative identification of the Y3NN molecule.

Biomechanical evaluation of an integrated fixation cage during fatigue loading: a human cadaver study.

PubMed

Palepu, Vivek; Peck, Jonathan H; Simon, David D; Helgeson, Melvin D; Nagaraja, Srinidhi

2017-04-01

OBJECTIVE Lumbar cages with integrated fixation screws offer a low-profile alternative to a standard cage with anterior supplemental fixation. However, the mechanical stability of integrated fixation cages (IFCs) compared with a cage with anterior plate fixation under fatigue loading has not been investigated. The purpose of this study was to compare the biomechanical stability of a screw-based IFC with a standard cage coupled with that of an anterior plate under fatigue loading. METHODS Eighteen functional spinal units were implanted with either a 4-screw IFC or an anterior plate and cage (AP+C) without integrated fixation. Flexibility testing was conducted in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) on intact spines, immediately after device implantation, and post-fatigue up to 20,000 cycles of FE loading. Stability parameters such as range of motion (ROM) and lax zone (LZ) for each loading mode were compared between the 2 constructs at multiple stages of testing. In addition, construct loosening was quantified by subtracting post-instrumentation ROM from post-fatigue ROM. RESULTS IFC and AP+C configurations exhibited similar stability (ROM and LZ) at every stage of testing in FE (p ≥ 0.33) and LB (p ≥ 0.23) motions. In AR, however, IFCs had decreased ROM compared with AP+C constructs at pre-fatigue (p = 0.07) and at all post-fatigue time points (p ≤ 0.05). LZ followed a trend similar to that of ROM in AR. ROM increased toward intact motion during fatigue cycling for AP+C and IFC implants. IFC specimens remained significantly (p < 0.01) more rigid than specimens in the intact condition during fatigue for each loading mode, whereas AP+C construct motion did not differ significantly (p ≥ 0.37) in FE and LB and was significantly greater (p < 0.01) in AR motion compared with intact specimens after fatigue. Weak to moderate correlations (R 2 ≤ 56%) were observed between T-scores and construct loosening, with lower T-scores leading to decreased stability after fatigue testing. CONCLUSIONS These data indicate that a 4-screw IFC design provides fixation similar to that provided by an AP+C construct in FE and LB during fatigue testing and better stability in AR motion.

Quantifying denitrification losses from a sub-tropical pasture in Queensland/Australia - use of the 15N gas flux method

NASA Astrophysics Data System (ADS)

Friedl, Johannes; Scheer, Clemens; Warner, Daniel; Grace, Peter

2014-05-01

The microbial mediated production of nitrous oxide (N2O) and its reduction to dinitrogen (N2) via denitrification represents a loss of nitrogen (N) from fertilised agro ecosystems to the atmosphere. Although denitrification remains a major uncertainty in estimating N losses from soils, the magnitude of N2 losses and related N2:N2O ratios from soils are largely unknown due to difficulties measuring N2 against a high atmospheric background. In order to address this lack of data, this study investigated the influence of different soil moisture contents on N2 and N2O emissions from a sub-tropical pasture in Queensland/Australia using the 15N gas flux method. Intact soil cores were incubated over 14 days at 80% and 100% water filled pore space (WFPS). Gas samples were taken up to six times per day after application of 15N labelled nitrate, equivalent to 50 kg N ha-1 and analysed for N2 and N2O by isotope ratio mass spectrometry. Fluxes were calculated assuming non-random 15N distribution in the headspace according to Mulvaney and Kurtz (1984) using the labelled pool of nitrate estimated from N2O measurements (Stevens and Laughlin 2001). The main product of denitrification in both treatments was N2. N2 emissions exceeded N2O emissions by a factor of 1.3 ± 0.3 at 80% WFPS and a factor of 3 ± 0.8 at 100% WFPS. The total amount of N-N2 lost over the incubation period was 13.5±1.0 kg N ha-1 at 80% WFPS and 21.8±1.8 kg ha-1 at 100% WFPS respectively. Over the entire incubation period, N2 emissions remained elevated at 100% WFPS, showing high variation between soil cores, while related N2O emissions decreased. At 80% WFPS, N2 emissions increased constantly over time showing significantly higher values after day five. At the same time, N2O fluxes declined. Consequently, N2:N2O ratios rose over the incubation period in both treatments. Overall denitrification rates and related N2:N2O ratios were higher at 100% WFPS compared to 80% WFPS, confirming WFPS as a major driver of denitrification. This study highlights denitrification as a major pathway of N loss for sub-tropical pasture systems with a substantial amount of applied fertiliser lost as N2 at high WFPS. The 15N gas flux method proved an effective tool in assessing N losses from fertilised soils. However, its suitability to determine N2 fluxes from soils with lower denitrification rates needs to be confirmed in future studies. The high variation between soil cores emphasises the need for field measurements with a high spatial and temporal resolution in order to capture the dynamics of N2 emissions. Mulvaney, R. L. and L. T. Kurtz. 1984. "Evolution of Dinitrogen and Nitrous Oxide from Nitrogen-15 Fertilized Soil Cores Subjected to Wetting and Drying Cycles1." Soil Sci. Soc. Am. J. 48 (3): 596-602. https://www.soils.org/publications/sssaj/abstracts/48/3/596. doi: 10.2136/sssaj1984.03615995004800030026x. Stevens, R. J. and R. J. Laughlin. 2001. "Lowering the detection limit for dinitrogen using the enrichment of nitrous oxide." Soil Biology and Biochemistry 33 (9): 1287-1289. http://www.sciencedirect.com/science/article/pii/S0038071701000360. doi: http://dx.doi.org/10.1016/S0038-0717(01)00036-0.

N2-fixation dynamics during ecosystem recovery in longleaf pine savannas

NASA Astrophysics Data System (ADS)

Tierney, J. A.

2016-12-01

Biological nitrogen fixation (BNF) can alleviate nitrogen (N) deficiencies that inhibit ecosystem recovery. BNF may be particularly important in ecosystems recovering from land-use change and perturbations from fire, as these disturbances can exacerbate N limitation. Here, we investigated how BNF dynamics change throughout ecosystem development in restored longleaf pine savannas, and how BNF responds to fire. We conducted this study in 59 1-ha plots of longleaf pine distributed across gradients of stand age and fire frequency at two sites in the southeastern US. We determined BNF contributions by three functional groups of N2-fixers (herbaceous legumes, biological soil crusts, and asymbiotic N2-fixing bacteria) by quantifying their abundances, assessing nitrogenase activity, and scaling these estimates up to the plot-level. To determine aboveground N demands, we measured tree growth using diameter increments and allometric equations paired with tissue-specific N concentrations. We fit linear models to evaluate the effects of stand age and time since fire on BNF and N demands throughout stand development, and performed separate analyses on mature stands to determine how fire return interval affects BNF. We observed distinct temporal patterns of N2-fixation across stand development among the three groups of N2 fixers. N2-fixation by legumes and asymbiotic bacteria remained low until stands reached maturity, while N2-fixation by biological soil crusts (BSCs) was high in juvenile stands and decreased with stand age. These patterns suggest a compensatory shift in the importance of these functional groups throughout stand development such that contributions from BSCs are critical for meeting N demands when disturbances may hinder the establishment of legumes and asymbiotic bacteria. N2-fixation by BSCs and asymbiotic bacteria throughout stand development was not affected by time since fire, but legume abundance increased the year following fire, suggesting a recovery mechanism provided by this group. Our findings suggest that BSCs are the most important source of new N in the early phases of ecosystem restoration. In contrast, legumes appear to be critical in mature longleaf pine stands that burn frequently, and particularly for supplying new N in the year following a fire event.

Biomechanical comparison of a novel transoral atlantoaxial anchored cage with established fixation technique - a finite element analysis.

PubMed

Zhang, Bao-cheng; Liu, Hai-bo; Cai, Xian-hua; Wang, Zhi-hua; Xu, Feng; Kang, Hui; Ding, Ran; Luo, Xiao-qing

2015-09-22

The transoral atlantoaxial reduction plate (TARP) fixation has been introduced to achieve reduction, decompression, fixation and fusion of C1-C2 through a transoral-only approach. However, it may also be associated with potential disadvantages, including dysphagia and load shielding of the bone graft. To prevent potential disadvantages related to TARP fixation, a novel transoral atlantoaxial fusion cage with integrated plate (Cage + Plate) device for stabilization of the C1-C2 segment is designed. The aims of the present study were to compare the biomechanical differences between Cage + Plate device and Cage + TARP device for the treatment of basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD). A detailed, nonlinear finite element model (FEM) of the intact upper cervical spine had been developed and validated. Then a FEM of an unstable BI model treated with Cage + Plate fixation, was compared to that with Cage + TARP fixation. All models were subjected to vertical load with pure moments in flexion, extension, lateral bending and axial rotation. Range of motion (ROM) of C1-C2 segment and maximum von Mises Stress of the C2 endplate and bone graft were quantified for the two devices. Both devices significantly reduced ROM compared with the intact state. In comparison with the Cage + Plate model, the Cage + TARP model reduced the ROM by 82.5 %, 46.2 %, 10.0 % and 74.3 % in flexion, extension, lateral bending, and axial rotation. The Cage + Plate model showed a higher increase stresses on C2 endplate and bone graft than the Cage + TARP model in all motions. Our results indicate that the novel Cage + Plate device may provide lower biomechanical stability than the Cage + TARP device in flexion, extension, and axial rotation, however, it may reduce stress shielding of the bone graft for successful fusion and minimize the risk of postoperative dysphagia. Clinical trials are now required to validate the reproducibility and advantages of our findings using this anchored cage for the treatment of BI with IAAD.

Biomechanical Comparison of 3 Inferiorly Directed Versus 3 Superiorly Directed Locking Screws on Stability in a 3-Part Proximal Humerus Fracture Model.

PubMed

Donohue, David M; Santoni, Brandon G; Stoops, T Kyle; Tanner, Gregory; Diaz, Miguel A; Mighell, Mark

2018-06-01

To quantify the stability of 3 points of inferiorly directed versus 3 points of superiorly directed locking screw fixation compared with the full contingent of 6 points of locked screw fixation in the treatment of a 3-part proximal humerus fracture. A standardized 3-part fracture was created in 10 matched pairs (experimental groups) and 10 nonmatched humeri (control group). Osteosynthesis was performed using 3 locking screws in the superior hemisphere of the humeral head (suspension), 3 locking screws in the inferior hemisphere (buttress), or the full complement of 6 locking screws (control). Specimens were tested in varus cantilever bending (7.5 Nm) to 10,000 cycles or failure. Construct survival (%) and the cycles to failure were compared. Seven of 10 controls survived the 10,000-cycle runout (70%: 8193 average cycles to failure). No experimental constructs survived the 10,000-cycle runout. Suspension and buttress screw groups failed an average of 331 and 516 cycles, respectively (P = 1.00). The average number of cycles to failure and the number of humeri surviving the 10,000-cycle runout were greater in the control group than in the experimental groups (P ≤ 0.006). Data support the use of a full contingent of 6 points of locking screw fixation over 3 superior or 3 inferior points of fixation in the treatment of a 3-part proximal humerus fracture with a locking construct. No biomechanical advantage to the 3 buttress or 3 suspension screws used in isolation was observed.

Study of Synthesis of N-Nitroborazine Compounds. I. Nitryl Chloride as Nitrating Agent.

DTIC Science & Technology

dinitrogen tetroxide (N2O4) as the solid complexes of boron trifluoride (BF3). Nearly water-white nitryl chloride was obtained in this manner. A tinge of...yellow was attributed to the presence of chlorine . The reaction of nitryl chloride with a model compound, lithium dimethylamide, was found to yield

Denitrification by extremely halophilic bacteria

NASA Technical Reports Server (NTRS)

Hochstein, L. I.; Tomlinson, G. A.

1985-01-01

Extremely halophilic bacteria were isolated from widely separated sites by anaerobic enrichment in the presence of nitrate. The anaerobic growth of several of these isolates was accompanied by the production of nitrite, nitrous oxide, and dinitrogen. These results are a direct confirmation of the existence of extremely halophilic denitrifying bacteria, and suggest that such bacteria may be common inhabitants of hypersaline environments.

Cage Compounds as Potential Energetic Oxidizers: A Theoretical Study of a Cage Isomer of N2O3

DTIC Science & Technology

2014-07-01

Laboratory. References [1] P. W. M. Jacobs, H. M. Whitehead, Decomposition and Combustion of Ammonium Perchlorate, Chem. Rev., 1969, 69 551- 590 . [2...and Symmetric Dinitrogen Trioxide in Nitric-Oxide Matrices by Raman and Infrared- Spectroscopy, J. Phys. Chem. 1983, 87, 1113- 1120. [14] a) X. Wang

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, H. Diessel; Lubner, Carolyn E.; Tokmina-Lukaszewska, Monika

A newly-recognized third fundamental mechanism of energy conservation in biology, electron bifurcation, uses free energy from exergonic redox reactions to drive endergonic redox reactions. Flavin-based electron bifurcation furnishes low potential electrons to demanding chemical reactions such as reduction of dinitrogen to ammonia. We employed the heterodimeric flavoenzyme FixAB from the diazotrophic bacterium Rhodopseudomonas palustris to elucidate unique properties that underpin flavin-based electron bifurcation.

Characterization of the hupSL promoter activity in Nostoc punctiforme ATCC 29133

PubMed Central

2009-01-01

Background In cyanobacteria three enzymes are directly involved in the hydrogen metabolism; a nitrogenase that produces molecular hydrogen, H2, as a by-product of nitrogen fixation, an uptake hydrogenase that recaptures H2 and oxidize it, and a bidirectional hydrogenase that can both oxidize and produce H2.Nostoc punctiforme ATCC 29133 is a filamentous dinitrogen fixing cyanobacterium containing a nitrogenase and an uptake hydrogenase but no bidirectional hydrogenase. Generally, little is known about the transcriptional regulation of the cyanobacterial uptake hydrogenases. In this study gel shift assays showed that NtcA has a specific affinity to a region of the hupSL promoter containing a predicted NtcA binding site. The predicted NtcA binding site is centred at 258.5 bp upstream the transcription start point (tsp). To further investigate the hupSL promoter, truncated versions of the hupSL promoter were fused to either gfp or luxAB, encoding the reporter proteins Green Fluorescent Protein and Luciferase, respectively. Results Interestingly, all hupsSL promoter deletion constructs showed heterocyst specific expression. Unexpectedly the shortest promoter fragment, a fragment covering 57 bp upstream and 258 bp downstream the tsp, exhibited the highest promoter activity. Deletion of the NtcA binding site neither affected the expression to any larger extent nor the heterocyst specificity. Conclusion Obtained data suggest that the hupSL promoter in N. punctiforme is not strictly dependent on the upstream NtcA cis element and that the shortest promoter fragment (-57 to tsp) is enough for a high and heterocyst specific expression of hupSL. This is highly interesting because it indicates that the information that determines heterocyst specific gene expression might be confined to this short sequence or in the downstream untranslated leader sequence. PMID:19284581

The Holocene sedimentary record of cyanobacterial glycolipids in the Baltic Sea: an evaluation of their application as tracers of past nitrogen fixation

NASA Astrophysics Data System (ADS)

Sollai, Martina; Hopmans, Ellen C.; Bale, Nicole J.; Mets, Anchelique; Warden, Lisa; Moros, Matthias; Sinninghe Damsté, Jaap S.

2017-12-01

Heterocyst glycolipids (HGs) are lipids exclusively produced by heterocystous dinitrogen-fixing cyanobacteria. The Baltic Sea is an ideal environment to study the distribution of HGs and test their potential as biomarkers because of its recurring summer phytoplankton blooms, dominated by a few heterocystous cyanobacterial species of the genera Nodularia and Aphanizomenon. A multi-core and a gravity core from the Gotland Basin were analyzed to determine the abundance and distribution of a suite of selected HGs at a high resolution to investigate the changes in past cyanobacterial communities during the Holocene. The HG distribution of the sediments deposited during the Modern Warm Period (MoWP) was compared with those of cultivated heterocystous cyanobacteria, including those isolated from Baltic Sea waters, revealing high similarity. However, the abundance of HGs dropped substantially with depth, and this may be caused by either a decrease in the occurrence of the cyanobacterial blooms or diagenesis, resulting in partial destruction of the HGs. The record also shows that the HG distribution has remained stable since the Baltic turned into a brackish semi-enclosed basin ˜ 7200 cal. yr BP. This suggests that the heterocystous cyanobacterial species composition remained relatively stable as well. During the earlier freshwater phase of the Baltic (i.e., the Ancylus Lake and Yoldia Sea phases), the distribution of the HGs varied much more than in the subsequent brackish phase, and the absolute abundance of HGs was much lower than during the brackish phase. This suggests that the cyanobacterial community adjusted to the different environmental conditions in the basin. Our results confirm the potential of HGs as a specific biomarker of heterocystous cyanobacteria in paleo-environmental studies.

The Effect of Temperature on Key Aspects of the Nitrogen Cycle: Comparisons Across Systems

NASA Astrophysics Data System (ADS)

Warren, V.

2016-02-01

The nitrogen cycle sustains life by converting inert di-nitrogen gas (N2) into fixed bio-available forms (e.g. ammonium, nitrate), as well as returning it via gases such as N2 and nitrous oxide (N2O) back into the atmosphere. Recently, the effects of long term warming on key components of the carbon cycle, which is tightly coupled to the nitrogen cycle, have been highlighted but how global warming might systematically affect the balance of the nitrogen cycle is still largely unknown. The effect of long term warming on denitrification and nitrification were investigated using long-term, experimental mesocosm (2006 to present), allowing us to study the effect of warming on natural communities of bacteria involved in these processes. Denitrification activity responded to warming in the short-term in a predictable way, however, long-term moderate warming of 3-5oC (the predicted global increase by the end of the century) increased the specific activity of the sediment and had a pronounced effect on the ratio of N2O to N2. The latter suggesting that with sustained warming, denitrifying bacteria become more efficient at complete denitrification. Molecular analysis of denitrifying communities in our long-term mesocosm experiment also suggested a profound alteration of the communities underlying these differences in process. Similar short-term experiments were carried out on sediments and the water column of the North Eastern Tropical Pacific Oxygen minimum zone (NETP OMZ) including its effect on N2 fixation and here we contrast the findings from those markedly different settings. This research has indicated that we may see similar effects on the nitrogen cycle as we have previously determined in the carbon cycle, with the balance of N-species consumed and created becoming out of balance.

Morphological parameters for implantation of the screwless spring loop dynamic posterior spinous process stabilizing system.

PubMed

Song, Geun Soo; Lee, Yeon Soo

2015-07-01

This study aimed to quantify morphological characteristics of the posterior lumbar spinous process, which may affect stable implantation of screwless wire spring loops. Virtual implantations of a screwless wire spring loop onto pairs of lumbar spinous processes were performed for computed tomography (CT)-derived three-dimensional vertebral models of 40 Korean subjects. Morphological parameters of lumbar vertebrae 1 through 5 (L1-L5) were measured with regard to bone-implant interference. In males, the transspinous process fixation lengths decreased from 57.8±3.0mm to 48.8±3.2mm as the lumbar joints descend from L1-L2 to L4-L5, with those in females about 4.1±0.4mm shorter (p<0.05) than in males through all lumbar joints. The fixation angle on the sagittal plane varied from 105.0° to 101.3° relative to the transverse plane as the vertebrae descend. The clenched thickness in females was the least (6.7±1.2mm) for the L2 lower spinous process and the greatest (8.1±2.2mm) for the L4 upper spinous process; this was 1.0±10.3mm less than that for males at corresponding levels (p>0.05). The ratio of the spinous process clenched thickness to the transspinous fixation length increased from 0.133±0.016 to 0.196±0.076 for the upper spinous processes as the lumbar joints descend. The ratio of the spinous process clenched thickness to the transspinous fixation length varies, depending on gender and whether the clenched level is the upper or lower spinous process. These parameters related to the clenching fixation stability should be considered in development and implantations of the screwless wire spring loop. Copyright © 2015 Elsevier GmbH. All rights reserved.

Interannual Variations in Global Net Carbon Production in the Absence of Fixed Nitrogen: Implication of New Production Supported by Dinitrogen Fixing Microorganisms

NASA Astrophysics Data System (ADS)

Lee, K.; Ko, Y. H.

2016-12-01

In the ocean without the measurable levels of nitrate, new production, i.e. the amount of carbon transported from the sunlit upper water to deep water, was estimated by summing the seasonal reduction in the total dissolved inorganic carbon (NCT = CT x 35/S) concentration in the surface mixed layer. Total reduction in the mixed layer NCT inventory in each 4o latitude by 5o longitude was calculated using an annual cycle of NCT, which was deduced from global monthly records of partial pressure of CO2 (based on more than 6.5 million data) and total alkalinity fields using thermodynamic models. The estimation of total NCT reduction for each pixel was then corrected for small changes caused by atmospheric nitrogen deposition and net air-sea CO2 exchange. This novel method yields 0.8 ± 0.3 petagrams of global new production per year (Pg C yr, Pg = 1015 grams), which is likely to be mediated exclusively by dinitrogen (N2) fixing microorganisms. These organisms utilize the inexhaustible pool of dissolved N2 and thereby circumvent nitrate limitation, particularly in the oligotrophic tropical and subtropical ocean.

Effects of model structural uncertainty on carbon cycle projections: biological nitrogen fixation as a case study

NASA Astrophysics Data System (ADS)

Wieder, William R.; Cleveland, Cory C.; Lawrence, David M.; Bonan, Gordon B.

2015-04-01

Uncertainties in terrestrial carbon (C) cycle projections increase uncertainty of potential climate feedbacks. Efforts to improve model performance often include increased representation of biogeochemical processes, such as coupled carbon-nitrogen (N) cycles. In doing so, models are becoming more complex, generating structural uncertainties in model form that reflect incomplete knowledge of how to represent underlying processes. Here, we explore structural uncertainties associated with biological nitrogen fixation (BNF) and quantify their effects on C cycle projections. We find that alternative plausible structures to represent BNF result in nearly equivalent terrestrial C fluxes and pools through the twentieth century, but the strength of the terrestrial C sink varies by nearly a third (50 Pg C) by the end of the twenty-first century under a business-as-usual climate change scenario representative concentration pathway 8.5. These results indicate that actual uncertainty in future C cycle projections may be larger than previously estimated, and this uncertainty will limit C cycle projections until model structures can be evaluated and refined.

The mechanical and morphological properties of bone beneath internal fixation plates of differing rigidity.

PubMed

Claes, L

1989-01-01

The internal fixation of diaphyseal fractures by bone plates is a well recognized treatment. The normal physiological stress of bone is reduced by plates that cause a negative balance of bone-remodeling processes. Many investigators have shown that the degree of stress protection is dependent on the rigidity of the plates. It was the aim of this study to quantify mechanical and morphological changes at different locations in a plated diaphyseal bone as a function of differing plate rigidity. Two types of plates with the same size but different materials were used. The stainless steel plates had a modulus of elasticity and bending stiffness 3.2 times higher than the carbon fiber reinforced carbon plates. Both types of plates were applied to the intact right and left femora of six foxhounds for 6 months. The stiffer stainless steel plates led to a significantly higher bone loss and correspondingly greater loss of mechanical properties. These effects were greatest directly beneath the plate and less with increasing distance from the plate.

Immunofluorescence Analysis of Endogenous and Exogenous Centromere-kinetochore Proteins

PubMed Central

Niikura, Yohei; Kitagawa, Katsumi

2016-01-01

"Centromeres" and "kinetochores" refer to the site where chromosomes associate with the spindle during cell division. Direct visualization of centromere-kinetochore proteins during the cell cycle remains a fundamental tool in investigating the mechanism(s) of these proteins. Advanced imaging methods in fluorescence microscopy provide remarkable resolution of centromere-kinetochore components and allow direct observation of specific molecular components of the centromeres and kinetochores. In addition, methods of indirect immunofluorescent (IIF) staining using specific antibodies are crucial to these observations. However, despite numerous reports about IIF protocols, few discussed in detail problems of specific centromere-kinetochore proteins.1-4 Here we report optimized protocols to stain endogenous centromere-kinetochore proteins in human cells by using paraformaldehyde fixation and IIF staining. Furthermore, we report protocols to detect Flag-tagged exogenous CENP-A proteins in human cells subjected to acetone or methanol fixation. These methods are useful in detecting and quantifying endogenous centromere-kinetochore proteins and Flag-tagged CENP-A proteins, including those in human cells. PMID:26967065

Three-dimensional Fourier-domain optical coherence tomography of alveolar mechanics in stepwise inflated and deflated isolated and perfused rabbit lungs

NASA Astrophysics Data System (ADS)

Krueger, Alexander; Knels, Lilla; Meissner, Sven; Wendel, Martina; Heller, Axel R.; Lambeck, Thomas; Koch, Thea; Koch, Edmund

2007-07-01

Fourier domain optical coherence tomography (FD-OCT) was used to acquire three-dimensional image stacks of isolated and perfused rabbit lungs (n = 4) at different constant pulmonary airway pressures (CPAP) and during vascular fixation. After despeckling and applying a threshold, the images were segmented into air and tissue, and registered to each other to compensate for movement between CPAP steps. The air-filled cross-sectional areas were quantified using a semi-automatic algorithm. The cross-sectional area of alveolar structures taken at all three perpendicular planes increased with increasing CPAP. Between the minimal CPAP of 3 mbar and the maximum of 25 mbar the areas increased to about 140% of their initial value. There was no systematic dependency of inflation rate on initial size of the alveolar structure. During the perfusion fixation of the lungs with glutaraldehyde morphometric changes of the alveolar geometry measured with FD-OCT were negligible.

Nitrogen cycling in Sandusky Bay, Lake Erie: oscillations between strong and weak export and implications for harmful algal blooms

NASA Astrophysics Data System (ADS)

Salk, Kateri R.; Bullerjahn, George S.; McKay, Robert Michael L.; Chaffin, Justin D.; Ostrom, Nathaniel E.

2018-05-01

Recent global water quality crises point to an urgent need for greater understanding of cyanobacterial harmful algal blooms (cHABs) and their drivers. Nearshore areas of Lake Erie such as Sandusky Bay may become seasonally limited by nitrogen (N) and are characterized by distinct cHAB compositions (i.e., Planktothrix over Microcystis). This study investigated phytoplankton N uptake pathways, determined drivers of N depletion, and characterized the N budget in Sandusky Bay. Nitrate (NO3-) and ammonium (NH4+) uptake, N fixation, and N removal processes were quantified by stable isotopic approaches. Dissimilatory N reduction was a relatively modest N sink, with denitrification, anammox, and N2O production accounting for 84, 14, and 2 % of sediment N removal, respectively. Phytoplankton assimilation was the dominant N uptake mechanism, and NO3- uptake rates were higher than NH4+ uptake rates. Riverine N loading was sometimes insufficient to meet assimilatory and dissimilatory demands, but N fixation alleviated this deficit. N fixation made up 23.7-85.4 % of total phytoplankton N acquisition and indirectly supports Planktothrix blooms. However, N fixation rates were surprisingly uncorrelated with NO3- or NH4+ concentrations. Owing to temporal separation in sources and sinks of N to Lake Erie, Sandusky Bay oscillates between a conduit and a filter of downstream N loading to Lake Erie, delivering extensively recycled forms of N during periods of low export. Drowned river mouths such as Sandusky Bay are mediators of downstream N loading, but climate-change-induced increases in precipitation and N loading will likely intensify N export from these systems.

Symbiotic N fixation is not down-regulated in mature versus secondary tropical forests in Bahia, Brazil.

NASA Astrophysics Data System (ADS)

Winbourne, J. B.; Daniel, P.; Porder, S.

2016-12-01

Carbon accumulation in secondary tropical forests is substantial, and thought to be limited at least in part by nitrogen (N) availability. Slash and burn agriculture and grazing remove N from the system, however, the abundance of symbiotic N fixing trees in young tropical forests suggests rapid N accumulation as forests regrow. Here we use statistically robust spatial sampling to quantify symbiotic (SNF) and asymbiotic N fixation across a chronosequence of re-growing tropical forests in the Mata Atlântica of Bahia, Brasil. The Mata Atlântica once stretched 1500 km along the east coast of Brasil, is currently 85% deforested, and is a target of national and international restoration efforts that rely heavily on the planting of legume species to facilitate forest regrowth. As expected, we found the highest rates of SNF early in forest succession, but these rates were low compared with prior estimates (16-year-old forests fixed 5.75 ± 2.2 kg N ha-1 yr-1), and did not significantly decline in older stands. Mature forests (>100 years old) fixed 4.3 kg N ha-1 yr-1. This rate is similar to measurements using the same method in intact forests in Costa Rica, and both estimates are 5 times lower than previous estimates of SNF inputs into mature tropical forests. In our study, SNF accounted for > 99% of the total N inputs via biological N fixation. Several intriguing possibilities emerge from these data: 1) contrary to expectations, abundant legumes early in succession do not dramatically increase N inputs in these regrowing tropical forests and 2) the hypothesis that N fixation is down regulated by facultative fixers once forests reach maturity is not consistent with our observations.

Hip- and knee-strength assessments using a hand-held dynamometer with external belt-fixation are inter-tester reliable.

PubMed

Thorborg, Kristian; Bandholm, Thomas; Hölmich, Per

2013-03-01

In football, ice-hockey, and track and field, injuries have been predicted, and hip- and knee-strength deficits quantified using hand-held dynamometry (HHD). However, systematic bias exists when testers of different sex and strength perform the measurements. Belt-fixation of the dynamometer may resolve this. The aim of the present study was therefore to examine the inter-tester reliability concerning strength assessments of isometric hip abduction, adduction, flexion, extension and knee-flexion strength, using HHD with external belt-fixation. Twenty-one healthy athletes (6 women), 30 (8.6) (mean (SD)) years of age, were included. Two physiotherapy students (1 female and 1 male) performed all the measurements after careful instruction and procedure training. Isometric hip abduction, adduction, flexion, extension, and knee-flexion strength were tested. The tester-order and hip-action order were randomised. No systematic between-tester differences (bias) were observed for any of the hip or knee actions. The intra-class correlation coefficients (ICC 2.1) ranged from 0.76 to 0.95. Furthermore, standard errors of measurement in per cent (SEM %) ranged from 5 to 11 %, and minimal detectable change in per cent (MDC %) from 14 to 29 % for the different hip and knee actions. The present study shows that isometric hip- and knee-strength measurements have acceptable inter-tester reliability at the group level, when testing strong individuals, using HHD with belt-fixation. This procedure is therefore perfectly suited for the evaluation and monitoring of strong athletes with hip, groin and hamstring injuries, some of the most common and troublesome injuries in sports. Diagnostic, Level III.

Bone density and anisotropy affect periprosthetic cement and bone stresses after anatomical glenoid replacement: A micro finite element analysis.

PubMed

Chevalier, Yan; Santos, Inês; Müller, Peter E; Pietschmann, Matthias F

2016-06-14

Glenoid loosening is still a main complication for shoulder arthroplasty. We hypothesize that cement and bone stresses potentially leading to fixation failure are related not only to glenohumeral conformity, fixation design or eccentric loading, but also to bone volume fraction, cortical thickness and degree of anisotropy in the glenoid. In this study, periprosthetic bone and cement stresses were computed with micro finite element models of the replaced glenoid depicting realistic bone microstructure. These models were used to quantify potential effects of bone microstructural parameters under loading conditions simulating different levels of glenohumeral conformity and eccentric loading simulating glenohumeral instability. Results show that peak cement stresses were achieved near the cement-bone interface in all loading schemes. Higher stresses within trabecular bone tissue and cement mantle were obtained within specimens of lower bone volume fraction and in regions of low anisotropy, increasing with decreasing glenohumeral conformity and reaching their maxima below the keeled design when the load is shifted superiorly. Our analyses confirm the combined influences of eccentric load shifts with reduced bone volume fraction and anisotropy on increasing periprosthetic stresses. They finally suggest that improving fixation of glenoid replacements must reduce internal cement and bone tissue stresses, in particular in glenoids of low bone density and heterogeneity. Copyright © 2016 Elsevier Ltd. All rights reserved.

Postoperative complications associated with external skeletal fixators in cats.

PubMed

Beever, Lee; Giles, Kirsty; Meeson, Richard

2017-07-01

The objective of this study was to quantify complications associated with external skeletal fixators (ESFs) in cats and to identify potential risk factors. A retrospective review of medical records and radiographs following ESF placement was performed. Case records of 140 cats were reviewed; fixator-associated complications (FACs) occurred in 19% of cats. The region of ESF placement was significantly associated with complication development. Complications developed most frequently in the femur (50%), tarsus (35%) and radius/ulna (33%). Superficial pin tract infection (SPTI) and implant failure accounted for 45% and 41% of all FACs, respectively. SPTI occurred more frequently in the femur, humerus and tibia, with implant failure more frequent in the tarsus. No association between breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, degree of fracture load sharing, and the incidence or type of FAC was identified. No association between region of placement, breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, fracture load sharing and the time to complication development was identified. Complication development is not uncommon in cats following ESF placement. The higher complication rate in the femur, tarsus and radius/ulna should be considered when reviewing options for fracture management. However, cats appear to have a lower rate of pin tract infections than dogs.

[4 + 2] Cycloaddition reaction of C-aryl ketenimines with PTAD as a synthetic equivalent of dinitrogen. Synthesis of triazolocinnolines and cinnolines.

PubMed

Alajarin, Mateo; Bonillo, Baltasar; Marin-Luna, Marta; Vidal, Angel; Orenes, Raul-Angel

2009-05-01

C,C,N-Triaryl ketenimines and C-alkyl-C,N-diaryl ketenimines react with 2 equiv of PTAD to provide 1,2,4-triazolo[1,2-a]cinnolines with a pendant triazolidindione group by means of a Diels-Alder/ene sequence. The treatment of such adducts with potassium hydroxide affords 3-aminocinnolines.

Mechanism-based design of labile precursors for chromium(I) chemistry

DOE PAGES

Akturk, Eser S.; Yap, Glenn P. A.; Theopold, Klaus H.

2015-08-27

Here, we report that dinitrogen complexes of the type Tp R,RCr–N 2–CrTp R,R are not the most labile precursors for Cr(I) chemistry, as they are sterically protected from obligatory associative ligand substitution. A mononuclear alkyne complex – Tp tBu,MeCr(η 2-C 2(SiMe 3) 2) – proved to be much more reactive.

Dinitrogen emissions as an overlooked key component of the N balance of montane grasslands

NASA Astrophysics Data System (ADS)

Zistl-Schlingmann, Marcus; Feng, Jinchao; Kiese, Ralf; Stephan, Ruth; Dannenmann, Michael

2017-04-01

Numerous studies have been conducted on the emission dynamics and annual budget of the atmospheric pollutants and primary or secondary greenhouse gases NOx, NH3 and N2O, i.e. gaseous N losses which can play an important role in the N budget of ecosystems. Due to still existing methodical problems in their quantification, considerably less is known on soil dinitrogen (N2) emissions, an inert gas with no hazardous effects on the environment. Understanding of soil N2 emissions however may be important to better understand and manage the N balance of ecosystems and also to mitigate the emissions of the precursor and potent greenhouse gas N2O. Here we quantified soil N2 emissions from montane grasslands used for dairy farming as affected by climate change simulation (reduced annual precipitation, increased temperature). For this purpose, plant-soil-mesocosms were brought from field sites of different elevation to the laboratory for direct simultaneous quantification of soil N2 and N2O emissions by use of the Helium soil core method. Immediately after the measurements, the plant-soil mesocosms were reburied at the sites. Using this approach we found that under current climate conditions, soil N2 emissions exceeded soil N2O emissions by several orders of magnitude and increased from 25 kg N ha-1 year-1 (present climate) to 50 kg N ha-1 year-1 (climate change treatment). Because this approach based on monthly sampling cannot accurately consider N gas emission peaks after manure fertilization, measurements were supplemented by a laboratory incubation approach. In this experiment, the response of all N gas emissions (NH3, NO, N2O, N2) to manure fertilization (50 kg N ha-1) was monitored with subdaily temporal resolution until emissions had diminished. Total N gas losses amounted to roughly half of the supplied N by manure application. Surprisingly, we found that N2 but not NH3 dominated fertilizer-derived gaseous N losses, accounting for 78 to 85 % of total gaseous N losses. Ammonia losses amounted to only 13-18%, N2O losses to 1-3 % and NO losses to 1% of applied manure-N. In the context of the ecosystem total N budget, our results show that N2 losses are a so far overlooked key component of the N balance in montane grasslands. Understanding controls of N2 loss is therefore an indispensable prerequisite for the development of grassland management strategies targeted to improve N use efficiency.

The Assimilation of Diazotroph-Derived Nitrogen by Scleractinian Corals Depends on Their Metabolic Status.

PubMed

Bednarz, Vanessa N; Grover, Renaud; Maguer, Jean-François; Fine, Maoz; Ferrier-Pagès, Christine

2017-01-10

Tropical corals are associated with a diverse community of dinitrogen (N 2 )-fixing prokaryotes (diazotrophs) providing the coral an additional source of bioavailable nitrogen (N) in oligotrophic waters. The overall activity of these diazotrophs changes depending on the current environmental conditions, but to what extent it affects the assimilation of diazotroph-derived N (DDN) by corals is still unknown. Here, in a series of 15 N 2 tracer experiments, we directly quantified DDN assimilation by scleractinian corals from the Red Sea exposed to different environmental conditions. We show that DDN assimilation strongly varied with the corals' metabolic status or with phosphate availability in the water. The very autotrophic shallow-water (~5 m) corals showed low or no DDN assimilation, which significantly increased under elevated phosphate availability (3 µM). Corals that depended more on heterotrophy (i.e., bleached and deep-water [~45 m] corals) assimilated significantly more DDN, which contributed up to 15% of the corals' N demand (compared to 1% in shallow corals). Furthermore, we demonstrate that a substantial part of the DDN assimilated by deep corals was likely obtained from heterotrophic feeding on fixed N compounds and/or diazotrophic cells in the mucus. Conversely, in shallow corals, the net release of mucus, rich in organic carbon compounds, likely enhanced diazotroph abundance and activity and thereby the release of fixed N to the pelagic and benthic reef community. Overall, our results suggest that DDN assimilation by corals varies according to the environmental conditions and is likely linked to the capacity of the coral to acquire nutrients from seawater. Tropical corals are associated with specialized bacteria (i.e., diazotrophs) able to transform dinitrogen (N 2 ) gas into a bioavailable form of nitrogen, but how much of this diazotroph-derived nitrogen (DDN) is assimilated by corals under different environmental conditions is still unknown. Here, we used 15 N 2 labeling to trace the fate of DDN within the coral symbiosis. We show that DDN is assimilated by both the animal host and the endosymbiotic algae. In addition, the amount of assimilated DDN was significantly greater in mesophotic, bleached, or phosphorus-enriched corals than in surface corals, which almost did not take up this nitrogen form. DDN can thus be of particular importance for the nutrient budget of corals whenever they are limited by the availability of other forms of dissolved nutrients. Copyright © 2017 Bednarz et al.

Optical parameters of the tunable Bragg reflectors in squid.

PubMed

Ghoshal, Amitabh; Demartini, Daniel G; Eck, Elizabeth; Morse, Daniel E

2013-08-06

Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack-the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures.

Optical parameters of the tunable Bragg reflectors in squid

PubMed Central

Ghoshal, Amitabh; DeMartini, Daniel G.; Eck, Elizabeth; Morse, Daniel E.

2013-01-01

Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack—the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures. PMID:23740489

Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields

PubMed Central

Ariosa, Yoanna; Quesada, Antonio; Aburto, Juan; Carrasco, David; Carreres, Ramón; Leganés, Francisco; Fernández Valiente, Eduardo

2004-01-01

The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N2 fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N2 fixation rate associated with Chara was 27.53 kg of N ha−1 crop−1. The mean estimated N2 fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha−1 crop−1; submerged parts of rice plants, 3.93 kg of N ha−1 crop−1; and roots, 0.28 kg of N ha−1 crop−1. Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% ± 4.4% and 6.2% ± 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 ± 28.0 and 4.0 ± 3.8 μg mg [dry weight] of Chara−1 in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field ecosystem. PMID:15345425

Role of facial attractiveness in patients with slight-to-borderline treatment need according to the Aesthetic Component of the Index of Orthodontic Treatment Need as judged by eye tracking.

PubMed

Johnson, Elizabeth K; Fields, Henry W; Beck, F Michael; Firestone, Allen R; Rosenstiel, Stephen F

2017-02-01

Previous eye-tracking research has demonstrated that laypersons view the range of dental attractiveness levels differently depending on facial attractiveness levels. How the borderline levels of dental attractiveness are viewed has not been evaluated in the context of facial attractiveness and compared with those with near-ideal esthetics or those in definite need of orthodontic treatment according to the Aesthetic Component of the Index of Orthodontic Treatment Need scale. Our objective was to determine the level of viewers' visual attention in its treatment need categories levels 3 to 7 for persons considered "attractive," "average," or "unattractive." Facial images of persons at 3 facial attractiveness levels were combined with 5 levels of dental attractiveness (dentitions representing Aesthetic Component of the Index of Orthodontic Treatment Need levels 3-7) using imaging software to form 15 composite images. Each image was viewed twice by 66 lay participants using eye tracking. Both the fixation density (number of fixations per facial area) and the fixation duration (length of time for each facial area) were quantified for each image viewed. Repeated-measures analysis of variance was used to determine how fixation density and duration varied among the 6 facial interest areas (chin, ear, eye, mouth, nose, and other). Viewers demonstrated excellent to good reliability among the 6 interest areas (intraviewer reliability, 0.70-0.96; interviewer reliability, 0.56-0.93). Between Aesthetic Component of the Index of Orthodontic Treatment Need levels 3 and 7, viewers of all facial attractiveness levels showed an increase in attention to the mouth. However, only with the attractive models were significant differences in fixation density and duration found between borderline levels with female viewers. Female viewers paid attention to different areas of the face than did male viewers. The importance of dental attractiveness is amplified in facially attractive female models compared with average and unattractive female models between near-ideal and borderline-severe dentally unattractive levels. Copyright © 2017 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

Vascular risk reduction during anterior surgical approach sacroiliac joint plating.

PubMed

Alla, Sreenivasa R; Roberts, Craig S; Ojike, Nwakile I

2013-02-01

Open reduction and internal fixation of sacroiliac (SI) joint is often performed through an anterior approach. However, there were no studies to our knowledge which described the "at risk area" for injury to the nutrient artery as it relates to open reduction and internal fixation of the SI joint. The purpose of this study was to determine the "at risk area" for the nutrient artery during anterior surgical approaches to the SI joint and to define the safe location of the plate for SI joint fixation. Six right and five left hemipelvises (three male and three female cadavers) were dissected with a mean age of 72 years (range, 51-90 years). Three bony landmarks including the pelvic brim, anterior SI joint line, and the anterior superior iliac spine (ASIS) were identified to quantify the measurements. Three different measurements were taken: from the nutrient foramen to the anterior SI joint line; from the nutrient foramen to the nearest point on the pelvic brim; from the nutrient foramen to ASIS using a flexible ruler with a 1mm base. The nutrient artery courses across the SI joint to enter into the nutrient foramen. Whilst exposing the internal surface of the SI joint, the nutrient foramen was identified at a mean distance of 88.1mm medial to ASIS, 20.1mm above the pelvic brim, and 20.1mm lateral to SI joint. The variability of the location of the nutrient foramen was identified and was located from 80mm to 95mm medial to the ASIS, 12mm to 25mm lateral to the SI joint, and 16mm to 30mm above the pelvic brim. Familiarity of the vasculature of the internal pelvis is of utmost importance for the surgeon when considering operative fixation of the anterior SI joint. We were able to identify the relation of the nutrient artery to the anatomic landmarks of the internal pelvis and to define the "at risk area" for the nutrient artery. We believe increased understanding of the anatomy of the nutrient artery will aid in the avoidance of vascular complications during internal fixation of the anterior SI joint. Copyright © 2012 Elsevier Ltd. All rights reserved.

Characterization of Biogenic Gas and Mineral Formation Process by Denitrification in Porous Media

NASA Astrophysics Data System (ADS)

Hall, C. A.; Kim, D.; Mahabadi, N.; van Paassen, L. A.

2017-12-01

Biologically mediated processes have been regarded and developed as an alternative approach to traditional ground improvement techniques. Denitrification has been investigated as a potential ground improvement process towards liquefaction hazard mitigation. During denitrification, microorganisms reduce nitrate to dinitrogen gas and facilitate calcium carbonate precipitation as a by-product under adequate environmental conditions. The formation of dinitrogen gas desaturates soils and allows for potential pore pressure dampening during earthquake events. While, precipitation of calcium carbonate can improve the mechanical properties by filling the voids and cementing soil particles. As a result of small changes in gas and mineral phases, the mechanical properties of soils can be significantly affected. Prior research has primarily focused on quantitative analysis of overall residual calcium carbonate mineral and biogenic gas products in lab-scale porous media. However, the distribution of these products at the pore-scale has not been well-investigated. In this research, denitrification is activated in a microfluidic chip simulating a homogenous pore structure. The denitrification process is monitored by sequential image capture, where gas and mineral phase changes are evaluated by image processing. Analysis of these images correspond with previous findings, which demonstrate that biogenic gas behaviour at the pore scale is affected by the balance between reaction, diffusion, and convection rates.

Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle

PubMed Central

Smirnov, Alexander; Hausner, Douglas; Laffers, Richard; Strongin, Daniel R; Schoonen, Martin AA

2008-01-01

Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni80Fe20) and tetrataenite (Ni50Fe50). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm Ntot. While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts. PMID:18489746

Binding of dinitrogen to an iron-sulfur-carbon site

NASA Astrophysics Data System (ADS)

Čorić, Ilija; Mercado, Brandon Q.; Bill, Eckhard; Vinyard, David J.; Holland, Patrick L.

2015-10-01

Nitrogenases are the enzymes by which certain microorganisms convert atmospheric dinitrogen (N2) to ammonia, thereby providing essential nitrogen atoms for higher organisms. The most common nitrogenases reduce atmospheric N2 at the FeMo cofactor, a sulfur-rich iron-molybdenum cluster (FeMoco). The central iron sites that are coordinated to sulfur and carbon atoms in FeMoco have been proposed to be the substrate binding sites, on the basis of kinetic and spectroscopic studies. In the resting state, the central iron sites each have bonds to three sulfur atoms and one carbon atom. Addition of electrons to the resting state causes the FeMoco to react with N2, but the geometry and bonding environment of N2-bound species remain unknown. Here we describe a synthetic complex with a sulfur-rich coordination sphere that, upon reduction, breaks an Fe-S bond and binds N2. The product is the first synthetic Fe-N2 complex in which iron has bonds to sulfur and carbon atoms, providing a model for N2 coordination in the FeMoco. Our results demonstrate that breaking an Fe-S bond is a chemically reasonable route to N2 binding in the FeMoco, and show structural and spectroscopic details for weakened N2 on a sulfur-rich iron site.

Chemical formation of hybrid di-nitrogen calls fungal codenitrification into question

PubMed Central

Phillips, Rebecca L.; Song, Bongkeun; McMillan, Andrew M. S.; Grelet, Gwen; Weir, Bevan S.; Palmada, Thilak; Tobias, Craig

2016-01-01

Removal of excess nitrogen (N) can best be achieved through denitrification processes that transform N in water and terrestrial ecosystems to di-nitrogen (N2) gas. The greenhouse gas nitrous oxide (N2O) is considered an intermediate or end-product in denitrification pathways. Both abiotic and biotic denitrification processes use a single N source to form N2O. However, N2 can be formed from two distinct N sources (known as hybrid N2) through biologically mediated processes of anammox and codenitrification. We questioned if hybrid N2 produced during fungal incubation at neutral pH could be attributed to abiotic nitrosation and if N2O was consumed during N2 formation. Experiments with gas chromatography indicated N2 was formed in the presence of live and dead fungi and in the absence of fungi, while N2O steadily increased. We used isotope pairing techniques and confirmed abiotic production of hybrid N2 under both anoxic and 20% O2 atmosphere conditions. Our findings question the assumptions that (1) N2O is an intermediate required for N2 formation, (2) production of N2 and N2O requires anaerobiosis, and (3) hybrid N2 is evidence of codenitrification and/or anammox. The N cycle framework should include abiotic production of N2. PMID:27976694

Chemical formation of hybrid di-nitrogen calls fungal codenitrification into question.

PubMed

Phillips, Rebecca L; Song, Bongkeun; McMillan, Andrew M S; Grelet, Gwen; Weir, Bevan S; Palmada, Thilak; Tobias, Craig

2016-12-15

Removal of excess nitrogen (N) can best be achieved through denitrification processes that transform N in water and terrestrial ecosystems to di-nitrogen (N 2 ) gas. The greenhouse gas nitrous oxide (N 2 O) is considered an intermediate or end-product in denitrification pathways. Both abiotic and biotic denitrification processes use a single N source to form N 2 O. However, N 2 can be formed from two distinct N sources (known as hybrid N 2 ) through biologically mediated processes of anammox and codenitrification. We questioned if hybrid N 2 produced during fungal incubation at neutral pH could be attributed to abiotic nitrosation and if N 2 O was consumed during N 2 formation. Experiments with gas chromatography indicated N 2 was formed in the presence of live and dead fungi and in the absence of fungi, while N 2 O steadily increased. We used isotope pairing techniques and confirmed abiotic production of hybrid N 2 under both anoxic and 20% O 2 atmosphere conditions. Our findings question the assumptions that (1) N 2 O is an intermediate required for N 2 formation, (2) production of N 2 and N 2 O requires anaerobiosis, and (3) hybrid N 2 is evidence of codenitrification and/or anammox. The N cycle framework should include abiotic production of N 2 .

Modeling eye movements in visual agnosia with a saliency map approach: bottom-up guidance or top-down strategy?

PubMed

Foulsham, Tom; Barton, Jason J S; Kingstone, Alan; Dewhurst, Richard; Underwood, Geoffrey

2011-08-01

Two recent papers (Foulsham, Barton, Kingstone, Dewhurst, & Underwood, 2009; Mannan, Kennard, & Husain, 2009) report that neuropsychological patients with a profound object recognition problem (visual agnosic subjects) show differences from healthy observers in the way their eye movements are controlled when looking at images. The interpretation of these papers is that eye movements can be modeled as the selection of points on a saliency map, and that agnosic subjects show an increased reliance on visual saliency, i.e., brightness and contrast in low-level stimulus features. Here we review this approach and present new data from our own experiments with an agnosic patient that quantifies the relationship between saliency and fixation location. In addition, we consider whether the perceptual difficulties of individual patients might be modeled by selectively weighting the different features involved in a saliency map. Our data indicate that saliency is not always a good predictor of fixation in agnosia: even for our agnosic subject, as for normal observers, the saliency-fixation relationship varied as a function of the task. This means that top-down processes still have a significant effect on the earliest stages of scanning in the setting of visual agnosia, indicating severe limitations for the saliency map model. Top-down, active strategies-which are the hallmark of our human visual system-play a vital role in eye movement control, whether we know what we are looking at or not. Copyright © 2011 Elsevier Ltd. All rights reserved.

Structural biomechanics of the craniomaxillofacial skeleton under maximal masticatory loading: Inferences and critical analysis based on a validated computational model.

PubMed

Pakdel, Amir R; Whyne, Cari M; Fialkov, Jeffrey A

2017-06-01

The trend towards optimizing stabilization of the craniomaxillofacial skeleton (CMFS) with the minimum amount of fixation required to achieve union, and away from maximizing rigidity, requires a quantitative understanding of craniomaxillofacial biomechanics. This study uses computational modeling to quantify the structural biomechanics of the CMFS under maximal physiologic masticatory loading. Using an experimentally validated subject-specific finite element (FE) model of the CMFS, the patterns of stress and strain distribution as a result of physiological masticatory loading were calculated. The trajectories of the stresses were plotted to delineate compressive and tensile regimes over the entire CMFS volume. The lateral maxilla was found to be the primary vertical buttress under maximal bite force loading, with much smaller involvement of the naso-maxillary buttress. There was no evidence that the pterygo-maxillary region is a buttressing structure, counter to classical buttress theory. The stresses at the zygomatic sutures suggest that two-point fixation of zygomatic complex fractures may be sufficient for fixation under bite force loading. The current experimentally validated biomechanical FE model of the CMFS is a practical tool for in silico optimization of current practice techniques and may be used as a foundation for the development of design criteria for future technologies for the treatment of CMFS injury and disease. Copyright © 2017 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.

Convergence and stress analysis of the homogeneous structure of human femur bone during standing up condition

NASA Astrophysics Data System (ADS)

Izzawati, B.; Daud, R.; Afendi, M.; Majid, M. S. Abdul; Zain, N. A. M.

2017-09-01

Finite element models have been widely used to quantify the stress analysis and to predict the bone fractures of the human body. The present study highlights on the stress analysis of the homogeneous structure of human femur bone during standing up condition. The main objective of this study is to evaluate and understand the biomechanics for human femur bone and to prepare orthotropic homogeneous material models used for FE analysis of the global proximal femur. Thus, it is necessary to investigate critical stress on the human femur bone for future study on implantation of internal fixator and external fixator. The implication possibility to create a valid FE model by simply comparing the FE results with the actual biomechanics structures. Thus, a convergence test was performed by FE model of the femur and the stress analysis based on the actual biomechanics of the human femur bone. An increment of critical stress shows in the femur shaft as the increasing of load on the femoral head and decreasing the pulling force at greater trochanter.

The Nitrogenase in a Methanogenic Archaebacterium and Its Regulation.

DTIC Science & Technology

1987-08-31

strain 227. Initial studies centered on the growth physiology of M. barker! u’nder diazotrophic conditions. We have also demonstrated that crude...of a few minor control experiments. Among the highlights are that molybdate at levels as low as 10 nM stimulated diazotrophic growth while tungstate... diazotrophs . We showed that activity was only found in dinitrogen-grown cells, and that addition of ammonia or glutamine caused a switchoff of the

Derepression of nitrogenase activity in glutamine auxotrophs of Rhodopseudomonas capsulata.

PubMed Central

Wall, J D; Gest, H

1979-01-01

In contrast to wild-type cells, glutamine auxotrophs of the photosynthetic bacterium Rhodopseudomonas capsulata synthesize nitrogenase, produce H2 (catalyzed by nitrogenase), and continue to reduce dinitrogen to ammonia in the presence of exogenous NH4+. The glutamine synthetase activity of such mutants is less than 2% of that observed in the wild type. It appears that glutamine synthetase plays a significant role in regulation of nitrogenase synthesis in R. capsulata. PMID:35518

N2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

NASA Astrophysics Data System (ADS)

Caffin, Mathieu; Moutin, Thierry; Foster, Rachel Ann; Bouruet-Aubertot, Pascale; Michelangelo Doglioli, Andrea; Berthelot, Hugo; Guieu, Cécile; Grosso, Olivier; Helias-Nunige, Sandra; Leblond, Nathalie; Gimenez, Audrey; Petrenko, Anne Alexandra; de Verneil, Alain; Bonnet, Sophie

2018-05-01

We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February-March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m-2 d-1) and LD B (706 ± 302 µmol N m-2 d-1), and the diazotroph community was dominated by Trichodesmium. N2 fixation rates were lower (59 ± 16 µmol N m-2 d-1) at LD C, and the diazotroph community was dominated by unicellular N2-fixing cyanobacteria (UCYN). At all stations, N2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N2 fixation contributed circa 13-18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio = particulate carbon export / primary production) was maximum at LD A (9.7 %) and was higher than the e ratio in most studied oligotrophic regions (< 5 %), indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to 30.6 % of the PC export at LD A, while their contribution was 5 and < 0.1 % at LD B and LD C, respectively. At the three studied stations, the sum of all N input to the photic layer exceeded the N output through organic matter export. This disequilibrium leading to N accumulation in the upper layer appears as a characteristic of the WTSP during the summer season.

Ulnar collateral ligament reconstruction using bisuspensory fixation: a biomechanical comparison with the docking technique.

PubMed

Jackson, Timothy J; Adamson, Gregory J; Peterson, Alexander; Patton, John; McGarry, Michelle H; Lee, Thay Q

2013-05-01

Many ulnar collateral ligament (UCL) reconstruction techniques have been created and biomechanically tested. Single-bundle reconstructions aim to re-create the important anterior bundle of the UCL. To date, no technique has utilized suspensory fixation on the ulnar and humeral sides to create a single-bundle reconstruction. The bisuspensory technique will restore valgus laxity to its native state, with comparable load-to-failure characteristics to the docking technique. Controlled laboratory study. Six matched pairs of fresh-frozen cadaveric elbows were randomized to undergo UCL reconstruction using either the docking technique or a novel single-bundle bisuspensory technique. Valgus laxity and rotation measurements were quantified using a MicroScribe 3DLX digitizer at various flexion angles for the native ligament, transected ligament, and 1 of the 2 tested reconstructed ligaments. Laxity testing was performed from maximum extension to 120° of flexion. Each reconstruction was then tested to failure, and the method of failure was recorded. Valgus laxity was restored to the intact state at all degrees of elbow flexion for both the docking and bisuspensory techniques. In load-to-failure testing, there was no significant difference with regard to stiffness, ultimate torque, ultimate torque angle, energy absorbed, and applied moment to reach 10° of valgus. Yield torques for the bisuspensory and docking reconstructions were 18.7 ± 7.8 N·m and 18.6 ± 4.4 N·m, respectively (P = .95). The ultimate torque for the bisuspensory technique measured 26.5 ± 9.2 N·m and for the docking technique measured 25.1 ± 7.1 N·m (P = .78). The bisuspensory fixation technique, a reproducible single-bundle reconstruction, was able to restore valgus laxity to the native state, with similar load-to-failure characteristics as the docking technique. This reconstruction technique could be considered in a clinical setting as a primary method of UCL reconstruction or as a backup fixation method should intraoperative complications occur.

In search of rules behind environmental framing; the case of head pitch.

PubMed

Wilson, Gwendoline Ixia; Norman, Brad; Walker, James; Williams, Hannah J; Holton, M D; Clarke, D; Wilson, Rory P

2015-01-01

Whether, and how, animals move requires them to assess their environment to determine the most appropriate action and trajectory, although the precise way the environment is scanned has been little studied. We hypothesized that head attitude, which effectively frames the environment for the eyes, and the way it changes over time, would be modulated by the environment. To test this, we used a head-mounted device (Human-Interfaced Personal Observation platform - HIPOP) on people moving through three different environments; a botanical garden ('green' space), a reef ('blue' space), and a featureless corridor, to examine if head movement in the vertical axis differed between environments. Template matching was used to identify and quantify distinct behaviours. The data on head pitch from all subjects and environments over time showed essentially continuous clear waveforms with varying amplitude and wavelength. There were three stylised behaviours consisting of smooth, regular peaks and troughs in head pitch angle and variable length fixations during which the head pitch remained constant. These three behaviours accounted for ca. 40 % of the total time, with irregular head pitch changes accounting for the rest. There were differences in rates of manifestation of behaviour according to environment as well as environmentally different head pitch values of peaks, troughs and fixations. Finally, although there was considerable variation in head pitch angles, the peak and trough values bounded most of the variation in the fixation pitch values. It is suggested that the constant waveforms in head pitch serve to inform people about their environment, providing a scanning mechanism. Particular emphasis to certain sectors is manifest within the peak and trough limits and these appear modulated by the distribution of the points where fixation, interpreted as being due to objects of interest, occurs. This behaviour explains how animals allocate processing resources to the environment and shows promise for movement studies attempting to elucidate which parts of the environment affect movement trajectories.

Advanced Techniques for Assessment of Postural and Locomotor Ataxia, Spatial Orientation, and Gaze Stability

NASA Technical Reports Server (NTRS)

Wall, Conrad., III

1999-01-01

In addition to adapting to microgravity, major neurovestibular problems of space flight include postflight difficulties with standing, walking, turning corners, and other activities that require stable upright posture and gaze stability. These difficulties inhibit astronauts' ability to stand or escape from their vehicle during emergencies. The long-ter7n goal of the NSBRI is the development of countermeasures to ameliorate the effects of long duration space flight. These countermeasures must be tested with valid and reliable tools. This project aims to develop quantitative, parametric approaches for assessing gaze stability and spatial orientation during normal gait and when gait is perturbed. Two of this year's most important findings concern head fixation distance and ideal trajectory analysis. During a normal cycle of walking the head moves up and down linearly. A simultaneous angular pitching motion of the head keeps it aligned toward an imaginary point in space at a distance of about one meter in front of a subject and along the line of march. This distance is called the head fixation distance. Head fixation distance provides the fundamental framework necessary for understanding the functional significance of the vestibular reflexes that couple head motion to eye motion. This framework facilitates the intelligent design of counter-measures for the effects of exposure to microgravity upon the vestibular ocular reflexes. Ideal trajectory analysis is a simple candidate countermeasure based upon quantifying body sway during repeated up and down stair stepping. It provides one number that estimates the body sway deviation from an ideal sinusoidal body sway trajectory normalized on the subject's height. This concept has been developed with NSBRI funding in less than one year. These findings are explained in more detail below. Compared to assessments of the vestibuo-ocular reflex, analysis of vestibular effects on locomotor function is relatively less well developed and quantified. We are improving this situation by applying methodologies such as nonlinear orbital stability to quantify responses and by using multivariate statistical approaches to link together the responses across separate tests. In this way we can exploit the information available and increase the ability to discriminate between normal and pathological responses. Measures of stability and orientation are compared to measures such as dynamic visual acuity and with balance function tests. The responses of normal human subjects and of patients having well documented pathophysiologies are being characterized. When these studies are completed, we should have a clearer idea about normal and abnormal patterns of eye, head, and body movements during locomotion and their stability in a wide range of environments. We plan eventually to use this information to validate the efficacy of candidate neurovestibular and neuromuscular rehabilitative techniques. Some representative studies made during this year are summarized.

Does dinitrogen hydrogenation follow different mechanisms for [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) and {[PhP(CH2SiMe2NSiMe2CH2)PPh]Zr}2(mu2,eta2,eta2-N2) complexes? A computational study.

PubMed

Bobadova-Parvanova, Petia; Wang, Qingfang; Quinonero-Santiago, David; Morokuma, Keiji; Musaev, Djamaladdin G

2006-09-06

The mechanisms of dinitrogen hydrogenation by two different complexes--[(eta(5)-C(5)Me(4)H)(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)), synthesized by Chirik and co-workers [Nature 2004, 427, 527], and {[P(2)N(2)]Zr}(2)(mu(2),eta(2),eta(2)-N(2)), where P(2)N(2) = PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh, synthesized by Fryzuk and co-workers [Science 1997, 275, 1445]--are compared with density functional theory calculations. The former complex is experimentally known to be capable of adding more than one H(2) molecule to the side-on coordinated N(2) molecule, while the latter does not add more than one H(2). We have shown that the observed difference in the reactivity of these dizirconium complexes is caused by the fact that the former ligand environment is more rigid than the latter. As a result, the addition of the first H(2) molecule leads to two different products: a non-H-bridged intermediate for the Chirik-type complex and a H-bridged intermediate for the Fryzuk-type complex. The non-H-bridged intermediate requires a smaller energy barrier for the second H(2) addition than the H-bridged intermediate. We have also examined the effect of different numbers of methyl substituents in [(eta(5)-C(5)Me(n)H(5)(-)(n))(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) for n = 0, 4, and 5 (n = 5 is hypothetical) and [(eta(5)-C(5)H(2)-1,2,4-Me(3))(eta(5)-C(5)Me(5))(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) and have shown that all complexes of this type would follow a similar H(2) addition mechanism. We have also performed an extensive analysis on the factors (side-on coordination of N(2) to two Zr centers, availability of the frontier orbitals with appropriate symmetry, and inflexibility of the catalyst ligand environment) that are required for successful hydrogenation of the coordinated dinitrogen.

Synthesis and reactivity of bis(tetramethylcyclopentadienyl) yttrium metallocenes including the reduction of Me(3)SiN(3) to [(Me(3)Si)(2)N](-) with [(C(5)Me(4)H)(2)Y(THF)](2)(mu-eta(2):eta(2)-N(2)).

PubMed

Lorenz, Sara E; Schmiege, Benjamin M; Lee, David S; Ziller, Joseph W; Evans, William J

2010-07-19

The metallocene precursors needed to provide the tetramethylcyclopentadienyl yttrium complexes (C(5)Me(4)H)(3)Y, [(C(5)Me(4)H)(2)Y(THF)](2)(mu-eta(2):eta(2)-N(2)), and [(C(5)Me(4)H)(2)Y(mu-H)](2) for reactivity studies have been synthesized and fully characterized, and their reaction chemistry has led to an unexpected conversion of an azide to an amide. (C(5)Me(4)H)(2)Y(mu-Cl)(2)K(THF)(x), 1, synthesized from YCl(3) and KC(5)Me(4)H reacts with allylmagnesium chloride to make (C(5)Me(4)H)(2)Y(eta(3)-C(3)H(5)), 2, which is converted to [(C(5)Me(4)H)(2)Y][(mu-Ph)(2)BPh(2)], 3, with [Et(3)NH][BPh(4)]. Complex 3 reacts with KC(5)Me(4)H to form (C(5)Me(4)H)(3)Y, 4. The reduced dinitrogen complex, [(C(5)Me(4)H)(2)Y(THF)](2)(mu-eta(2):eta(2)-N(2)), 5, can be synthesized from either [(C(5)Me(4)H)(2)Y](2)[(mu-Ph)(2)BPh(2)], 3, or (C(5)Me(4)H)(3)Y, 4, with potassium graphite under a dinitrogen atmosphere. The (15)N labeled analogue, [(C(5)Me(4)H)(2)Y(THF)](2)(mu-eta(2):eta(2)-(15)N(2)), 5-(15)N, has also been prepared, and the (15)N NMR data have been compared to previously characterized reduced dinitrogen complexes. Complex 2 reacts with H(2) to form the corresponding hydride, [(C(5)Me(4)H)(2)Y(mu-H)](2), 6. Complex 5 displays similar reactivity to that of the analogous [(C(5)Me(4)H)(2)Ln(THF)](2)(mu-eta(2):eta(2)-N(2)) complexes (Ln = La, Lu), with substrates such as phenazine, anthracene, and CO(2). In addition, 5 reduces Me(3)SiN(3) to form (C(5)Me(4)H)(2)Y[N(SiMe(3))(2)], 7.

Sources of iron and phosphate affect the distribution of diazotrophs in the North Atlantic

NASA Astrophysics Data System (ADS)

Ratten, Jenni-Marie; LaRoche, Julie; Desai, Dhwani K.; Shelley, Rachel U.; Landing, William M.; Boyle, Ed; Cutter, Gregory A.; Langlois, Rebecca J.

2015-06-01

Biological nitrogen fixation (BNF) supplies nutrient-depleted oceanic surface waters with new biologically available fixed nitrogen. Diazotrophs are the only organisms that can fix dinitrogen, but the factors controlling their distribution patterns in the ocean are not well understood. In this study, the relative abundances of eight diazotrophic phylotypes in the subtropical North Atlantic Ocean were determined by quantitative PCR (qPCR) of the nifH gene using TaqMan probes. A total of 152 samples were collected at 27 stations during two GEOTRACES cruises; Lisbon, Portugal to Mindelo, Cape Verde Islands (USGT10) and Woods Hole, MA, USA via the Bermuda Time Series (BATS) to Praia, Cape Verde Islands (USGT11). Seven of the eight diazotrophic phylotypes tested were detected. These included free-living and symbiotic cyanobacteria (unicellular groups (UCYN) A, B and C, Trichodesmium, the diatom-associated cyanobacteria Rhizoselinia-Richelia and Hemiaulus-Richelia) and a γ-proteobacterium (Gamma A, AY896371). The nifH gene abundances were analyzed in the context of a large set of hydrographic parameters, macronutrient and trace metal concentrations measured in parallel with DNA samples using the PRIMER-E software. The environmental variables that most influenced the abundances and distribution of the diazotrophic phylotypes were determined. We observed a geographic segregation of diazotrophic phylotypes between east and west, with UCYN A, UCYN B and UCYN C and the Rhizosolenia-Richelia symbiont associated with the eastern North Atlantic (east of 40°W), and Trichodesmium and Gamma A detected across the basin. Hemiaulus-Richelia symbionts were primarily found in temperate waters near the North American coast. The highest diazotrophic phylotype abundance and diversity were associated with temperatures greater than 22 °C in the surface mixed layer, a high supply of iron from North African aeolian mineral dust deposition and from remineralized nutrients upwelled at the edge of the oxygen minimum zone off the northwestern coast of Africa.

Rocket propellant inhalation in the Apollo-Soyuz astronauts.

PubMed

DeJournette, R L

1977-10-01

Acute exposure to monomethylhydrazine and dinitrogen tetroxide, the principal toxic irritants in rocket fuels, is described with particular attention to the development of pulmonary edema as a herbinger of more severe central nervous system toxicity. An acute respiratory embarrassment is documented and possible means of therapy based on animal experimental models is suggested. Early clinical and radiographic examination as a baseline for further evaluation is essential, with follow-up radiographs recommended for assessment of possible developing chronic lung disease.

Distinct properties underlie flavin-based electron bifurcation in a novel electron transfer flavoprotein FixAB from Rhodopseudomonas palustris

DOE PAGES

Duan, H. Diessel; Lubner, Carolyn E.; Tokmina-Lukaszewska, Monika; ...

2018-02-09

A newly-recognized third fundamental mechanism of energy conservation in biology, electron bifurcation, uses free energy from exergonic redox reactions to drive endergonic redox reactions. Flavin-based electron bifurcation furnishes low potential electrons to demanding chemical reactions such as reduction of dinitrogen to ammonia. We employed the heterodimeric flavoenzyme FixAB from the diazotrophic bacterium Rhodopseudomonas palustris to elucidate unique properties that underpin flavin-based electron bifurcation.

Regioselective syntheses of 1,2-benzothiazines by rhodium-catalyzed annulation reactions.

PubMed

Cheng, Ying; Bolm, Carsten

2015-10-12

Rhodium-catalyzed directed carbene insertions into aromatic CH bonds of S-aryl sulfoximines lead to intermediates, which upon dehydration provide 1,2-benzothiazines in excellent yields. The domino-type process is regioselective and shows a high functional-group tolerance. It is scalable, and the only by-products are dinitrogen and water. Three illustrative transformations underscore the synthetic value of the products. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Relative importance of time, land use and lithology on determining aquifer-scale denitrification

NASA Astrophysics Data System (ADS)

Kolbe, Tamara; de Dreuzy, Jean-Raynald; Abbott, Benjamin W.; Marçais, Jean; Babey, Tristan; Thomas, Zahra; Peiffer, Stefan; Aquilina, Luc; Labasque, Thierry; Laverman, Anniet; Fleckenstein, Jan; Boulvais, Philippe; Pinay, Gilles

2017-04-01

Unconfined shallow aquifers are commonly contaminated by nitrate in agricultural regions, because of excess fertilizer application over the last decades. Watershed studies have indicated that 1) changes in agricultural practices have caused changes in nitrate input over time, 2) denitrification occurs in localized hotspots within the aquifer, and 3) heterogeneous groundwater flow circulation has led to strong nitrate gradients in aquifers that are not yet well understood. In this study we investigated the respective influence of land use, groundwater transit time distribution, and hotspot distribution on groundwater denitrification with a particular interest on how a detailed understanding of transit time distributions could be used to upscale the point denitrification measurements to the aquifer-scale. We measured CFC-based groundwater age, oxygen, nitrate, and dinitrogen gas excess in 16 agricultural wells of an unconfined crystalline aquifer in Brittany, France. Groundwater age data was used to calibrate a mechanistic groundwater flow model of the study site. Historical nitrate inputs were reconstructed by using measured nitrate concentrations, dinitrogen gas excess and transit time distributions of the wells. Field data showed large differences in denitrification activity among wells, strongly associated with differences in transit time distribution. This suggests that knowing groundwater flow dynamics and consequent transit time distributions at the catchment-scale could be used to estimate the overall denitrification capacity of agricultural aquifers.

Nitrogen turnover of three different agricultural soils determined by 15N triple labelling

NASA Astrophysics Data System (ADS)

Fiedler, Sebastian R.; Kleineidam, Kristina; Strasilla, Nicol; Schlüter, Steffen; Reent Köster, Jan; Well, Reinhard; Müller, Christoph; Wrage-Mönnig, Nicole

2017-04-01

To meet the demand for data to improve existing N turnover models and to evaluate the effect of different soil physical properties on gross nitrogen (N) transformation rates, we investigated two arable soils and a grassland soil after addition of ammonium nitrate (NH4NO3), where either ammonium (NH4+), or nitrate (NO3-), or both pools have been labelled with 15N at 60 atom% excess (triple 15N tracing method). Besides NH4+, NO3- and nitrite (NO2-) contents with their respective 15N enrichment, nitrous oxide (N2O) and dinitrogen (N2) fluxes have been determined. Each soil was adjusted to 60 % of maximum water holding capacity and pre-incubated at 20˚ C for two weeks. After application of the differently labelled N fertilizer, the soils were further incubated at 20˚ C under aerobic conditions in a He-N2-O2 atmosphere (21 % O2, 76 He, 2% N2) to increase the sensitivity of N2 rates via the 15N gas flux method. Over a 2 week period soil N pools were quantified by 2 M KCl extraction (adjusted to pH 7 to prevent nitrite losses) (Stevens and Laughlin, 1995) and N gas fluxes were measured by gas chromatography in combination with IRMS. Here, we present the pool sizes and fluxes as well as the 15N enrichments during the study. Results are discussed in light of the soil differences that were responsible for the difference in gross N dynamics quantified by the 15N tracing model Ntrace (Müller et al., 2007). References Müller, C., T. Rütting, J. Kattge, R.J. Laughlin, and R.J. Stevens, (2007) Estimation of parameters in complex 15N tracing models by Monte Carlo sampling. Soil Biology & Biochemistry. 39(3): p. 715-726. Stevens, R.J. and R.J. Laughlin, (1995) Nitrite transformations during soil extraction with potassium chloride. Soil Science Society of America Journal. 59(3): p. 933-938.

Abundance and Distribution of Diagnostic Carbon Fixation Genes in a Deep-Sea Hydrothermal Gradient Ecosystem

NASA Astrophysics Data System (ADS)

Blumenfeld, H. N.; Kelley, D. S.; Girguis, P. R.; Schrenk, M. O.

2010-12-01

The walls of deep-sea hydrothermal vent chimneys sustain steep thermal and chemical gradients resulting from the mixing of hot (350°C+) hydrothermal fluids with cold, oxygenated seawater. The chemical disequilibrium generated from this process has the potential to drive numerous chemolithoautotrophic metabolisms, many of which have been demonstrated to be operative in microbial pure cultures. In addition to the well-known Calvin Cycle, at least five additional pathways have been discovered including the Reverse Tricarboxylic Acid Cycle (rTCA), the Reductive Acetyl-CoA pathway, and the 3-hydroxyproprionate pathway. Most of the newly discovered pathways have been found in thermophilic and hyperthermophilic Bacteria and Archaea, which are the well represented in microbial diversity studies of hydrothermal chimney walls. However, to date, little is known about the environmental controls that impact various carbon fixation pathways. The overlap of limited microbial diversity with distinct habitat conditions in hydrothermal chimney walls provides an ideal setting to explore these relationships. Hydrothermal chimney walls from multiple structures recovered from the Juan de Fuca Ridge in the northeastern Pacific were sub-sampled and analyzed using PCR-based assays. Earlier work showed elevated microbial abundances in the outer portions of mature chimney walls, with varying ratios of Archaea to Bacteria from the outer to inner portions of the chimneys. Common phylotypes identified in these regions included Epsilonproteobacteria, Gammaproteobacteria, and Desulfurococcales. Total genomic DNA was extracted from mineralogically distinct niches within these structures and queried for genes coding key regulatory enzymes for each of the well studied carbon fixation pathways. Preliminary results show the occurrence of genes representing rTCA cycle (aclB) and methyl coenzyme A reductase (mcrA) - a proxy for the Reductive Acetyl-CoA Pathway within interior portion of mature hydrothermal chimneys. Ongoing analyses are aimed at quantifying the abundances of these diagnostic carbon fixation genes within the hydrothermal chimney gradients. These data are being compared to a broad array of contextual data to provide insight into the environmental and biological controls that may impact the distribution of the various carbon fixation pathways. Application of genomic approaches to the hydrothermal chimney ecosystem will provide insight into the microbial ecology of such structures and refine our ability to measure autotrophy in hydrothermal habitats sustained by chemical energy.

Fixation times in differentiation and evolution in the presence of bottlenecks, deserts, and oases.

PubMed

Chou, Tom; Wang, Yu

2015-05-07

Cellular differentiation and evolution are stochastic processes that can involve multiple types (or states) of particles moving on a complex, high-dimensional state-space or "fitness" landscape. Cells of each specific type can thus be quantified by their population at a corresponding node within a network of states. Their dynamics across the state-space network involve genotypic or phenotypic transitions that can occur upon cell division, such as during symmetric or asymmetric cell differentiation, or upon spontaneous mutation. Here, we use a general multi-type branching processes to study first passage time statistics for a single cell to appear in a specific state. Our approach readily allows for nonexponentially distributed waiting times between transitions, reflecting, e.g., the cell cycle. For simplicity, we restrict most of our detailed analysis to exponentially distributed waiting times (Poisson processes). We present results for a sequential evolutionary process in which L successive transitions propel a population from a "wild-type" state to a given "terminally differentiated," "resistant," or "cancerous" state. Analytic and numeric results are also found for first passage times across an evolutionary chain containing a node with increased death or proliferation rate, representing a desert/bottleneck or an oasis. Processes involving cell proliferation are shown to be "nonlinear" (even though mean-field equations for the expected particle numbers are linear) resulting in first passage time statistics that depend on the position of the bottleneck or oasis. Our results highlight the sensitivity of stochastic measures to cell division fate and quantify the limitations of using certain approximations (such as the fixed-population and mean-field assumptions) in evaluating fixation times. Published by Elsevier Ltd.

A Method to Quantify Visual Information Processing in Children Using Eye Tracking

PubMed Central

Kooiker, Marlou J.G.; Pel, Johan J.M.; van der Steen-Kant, Sanny P.; van der Steen, Johannes

2016-01-01

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational methods, it is difficult to make a quantitative assessment of a child's visual problems. This limits accurate diagnostics in children under the age of 4 years and in children with intellectual disabilities. Here we describe a quantitative method that overcomes these problems. The method uses a remote eye tracker and a four choice preferential looking paradigm to measure eye movement responses to different visual stimuli. The child sits without head support in front of a monitor with integrated infrared cameras. In one of four monitor quadrants a visual stimulus is presented. Each stimulus has a specific visual modality with respect to the background, e.g., form, motion, contrast or color. From the reflexive eye movement responses to these specific visual modalities, output parameters such as reaction times, fixation accuracy and fixation duration are calculated to quantify a child's viewing behavior. With this approach, the quality of visual information processing can be assessed without the use of communication. By comparing results with reference values obtained in typically developing children from 0-12 years, the method provides a characterization of visual information processing in visually impaired children. The quantitative information provided by this method can be advantageous for the field of clinical visual assessment and rehabilitation in multiple ways. The parameter values provide a good basis to: (i) characterize early visual capacities and consequently to enable early interventions; (ii) compare risk groups and follow visual development over time; and (iii), construct an individual visual profile for each child. PMID:27500922

Comparison of different hip prosthesis shapes considering micro-level bone remodeling and stress-shielding criteria using three-dimensional design space topology optimization.

PubMed

Boyle, Christopher; Kim, Il Yong

2011-06-03

Since the late 1980s, computational analysis of total hip arthroplasty (THA) prosthesis components has been completed using macro-level bone remodeling algorithms. The utilization of macro-sized elements requires apparent bone densities to predict cancellous bone strength, thereby, preventing visualization and analysis of realistic trabecular architecture. In this study, we utilized a recently developed structural optimization algorithm, design space optimization (DSO), to perform a micro-level three-dimensional finite element bone remodeling simulation on the human proximal femur pre- and post-THA. The computational simulation facilitated direct performance comparison between two commercially available prosthetic implant stems from Zimmer Inc.: the Alloclassic and the Mayo conservative. The novel micro-level approach allowed the unique ability to visualize the trabecular bone adaption post-operation and to quantify the changes in bone mineral content by region. Stress-shielding and strain energy distribution were also quantified for the immediate post-operation and the stably fixated, post-remodeling conditions. Stress-shielding was highest in the proximal region and remained unchanged post-remodeling; conversely, the mid and distal portions show large increases in stress, suggesting a distal shift in the loadpath. The Mayo design conserves bone mass, while simultaneously reducing the incidence of stress-shielding compared to the Alloclassic, revealing a key benefit of the distinctive geometry. Several important factors for stable fixation, determined in clinical evaluations from the literature, were evident in both designs: high levels of proximal bone loss and distal bone densification. The results suggest this novel computational framework can be utilized for comparative hip prosthesis shape, uniquely considering the post-operation bone remodeling as a design criterion. Copyright © 2011 Elsevier Ltd. All rights reserved.

A Method to Quantify Visual Information Processing in Children Using Eye Tracking.

PubMed

Kooiker, Marlou J G; Pel, Johan J M; van der Steen-Kant, Sanny P; van der Steen, Johannes

2016-07-09

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational methods, it is difficult to make a quantitative assessment of a child's visual problems. This limits accurate diagnostics in children under the age of 4 years and in children with intellectual disabilities. Here we describe a quantitative method that overcomes these problems. The method uses a remote eye tracker and a four choice preferential looking paradigm to measure eye movement responses to different visual stimuli. The child sits without head support in front of a monitor with integrated infrared cameras. In one of four monitor quadrants a visual stimulus is presented. Each stimulus has a specific visual modality with respect to the background, e.g., form, motion, contrast or color. From the reflexive eye movement responses to these specific visual modalities, output parameters such as reaction times, fixation accuracy and fixation duration are calculated to quantify a child's viewing behavior. With this approach, the quality of visual information processing can be assessed without the use of communication. By comparing results with reference values obtained in typically developing children from 0-12 years, the method provides a characterization of visual information processing in visually impaired children. The quantitative information provided by this method can be advantageous for the field of clinical visual assessment and rehabilitation in multiple ways. The parameter values provide a good basis to: (i) characterize early visual capacities and consequently to enable early interventions; (ii) compare risk groups and follow visual development over time; and (iii), construct an individual visual profile for each child.

Quantifying the contribution of single microbial cells to nitrogen assimilation in aquatic environments

NASA Astrophysics Data System (ADS)

Musat, N.; Kuypers, M. M. M.

2009-04-01

Nitrogen is a primary productivity-limiting nutrient in the ocean. The nitrogen limitation of productivity may be overcome by organisms capable of converting dissolved N2 into fixed nitrogen available to the ecosystem. In many oceanic regions, growth of phytoplankton is nitrogen limited because fixation of N2 cannot make up for the removal of fixed inorganic nitrogen (NH4+, NO2-, NO3-) by anaerobic microbial processes. The amount of available fixed nitrogen in the ocean can be changed by the biological processes of heterotrophic denitrification, anaerobic ammonium oxidation and nitrogen fixation. For a complete understanding of nitrogen cycling in the ocean a link between the microbial and biogeochemical processes at the single cell level and their role in global biogeochemical cycles is essential. Here we report a recently developed method, Halogen In Situ Hybridization-Secondary Ion Mass Spectroscopy (HISH-SIMS) and its potential application to study the nitrogen-cycle processes in the ocean. The method allows simultaneous phylogenetic identification and quantitation of metabolic activities of single microbial cells in the environment. It uses horseradish-peroxidase-labeled oligonucleotide probes and fluorine-containing tyramides for the identification of microorganisms in combination with stable-isotope-labeling experiments for analyzing the metabolic function of single microbial cells. HISH-SIMS was successfully used to study nitrogen assimilation and nitrogen fixation by anaerobic phototrophs in a meromictic alpine lake. The HISH-SIMS method enables studies of the ecophysiology of individual, phylogenetically identified microorganisms involved in the N-cycle and allows us to track the flow of nitrogen within microbial communities.

Modeling guidance and recognition in categorical search: bridging human and computer object detection.

PubMed

Zelinsky, Gregory J; Peng, Yifan; Berg, Alexander C; Samaras, Dimitris

2013-10-08

Search is commonly described as a repeating cycle of guidance to target-like objects, followed by the recognition of these objects as targets or distractors. Are these indeed separate processes using different visual features? We addressed this question by comparing observer behavior to that of support vector machine (SVM) models trained on guidance and recognition tasks. Observers searched for a categorically defined teddy bear target in four-object arrays. Target-absent trials consisted of random category distractors rated in their visual similarity to teddy bears. Guidance, quantified as first-fixated objects during search, was strongest for targets, followed by target-similar, medium-similarity, and target-dissimilar distractors. False positive errors to first-fixated distractors also decreased with increasing dissimilarity to the target category. To model guidance, nine teddy bear detectors, using features ranging in biological plausibility, were trained on unblurred bears then tested on blurred versions of the same objects appearing in each search display. Guidance estimates were based on target probabilities obtained from these detectors. To model recognition, nine bear/nonbear classifiers, trained and tested on unblurred objects, were used to classify the object that would be fixated first (based on the detector estimates) as a teddy bear or a distractor. Patterns of categorical guidance and recognition accuracy were modeled almost perfectly by an HMAX model in combination with a color histogram feature. We conclude that guidance and recognition in the context of search are not separate processes mediated by different features, and that what the literature knows as guidance is really recognition performed on blurred objects viewed in the visual periphery.

Modeling guidance and recognition in categorical search: Bridging human and computer object detection

PubMed Central

Zelinsky, Gregory J.; Peng, Yifan; Berg, Alexander C.; Samaras, Dimitris

2013-01-01

Search is commonly described as a repeating cycle of guidance to target-like objects, followed by the recognition of these objects as targets or distractors. Are these indeed separate processes using different visual features? We addressed this question by comparing observer behavior to that of support vector machine (SVM) models trained on guidance and recognition tasks. Observers searched for a categorically defined teddy bear target in four-object arrays. Target-absent trials consisted of random category distractors rated in their visual similarity to teddy bears. Guidance, quantified as first-fixated objects during search, was strongest for targets, followed by target-similar, medium-similarity, and target-dissimilar distractors. False positive errors to first-fixated distractors also decreased with increasing dissimilarity to the target category. To model guidance, nine teddy bear detectors, using features ranging in biological plausibility, were trained on unblurred bears then tested on blurred versions of the same objects appearing in each search display. Guidance estimates were based on target probabilities obtained from these detectors. To model recognition, nine bear/nonbear classifiers, trained and tested on unblurred objects, were used to classify the object that would be fixated first (based on the detector estimates) as a teddy bear or a distractor. Patterns of categorical guidance and recognition accuracy were modeled almost perfectly by an HMAX model in combination with a color histogram feature. We conclude that guidance and recognition in the context of search are not separate processes mediated by different features, and that what the literature knows as guidance is really recognition performed on blurred objects viewed in the visual periphery. PMID:24105460

Establishing a New Screening System for Mild Cognitive Impairment and Alzheimer's Disease with Mental Rotation Tasks that Evaluate Visuospatial Function.

PubMed

Suzuki, Ayuko; Shinozaki, Jun; Yazawa, Shogo; Ueki, Yoshino; Matsukawa, Noriyuki; Shimohama, Shun; Nagamine, Takashi

2018-01-01

The mental rotation task is well-known for the assessment of visuospatial function; however, it has not been used for screening of dementia patients. The aim of this study was to create a simple screening test for patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD) by focusing on non-amnestic symptoms. Age-matched healthy controls (age 75.3±6.8), patients with MCI (76.5±5.5), and AD (78.2±5.0) participated in this study. They carried out mental rotation tasks targeting geometric graphics or alphabetical characters with three rotating angles (0°, 90°, and 180°) and indicated the correct answer. Response accuracy and reaction time were recorded along with their eye movements using an eye tracker. To quantify their visual processing strategy, the run count ratio (RC ratio) was calculated by dividing the mean number of fixations in incorrect answers by that in correct answers. AD patients showed lower accuracy and longer reaction time than controls. They also showed a significantly greater number of fixation and smaller saccade amplitude than controls, while fixation duration did not differ significantly. The RC ratio was higher for AD, followed by MCI and control groups. By setting the cut-off value to 0.47 in the 180° rotating angle task, we could differentiate MCI patients from controls with a probability of 80.0%. We established a new screening system for dementia patients by evaluating visuospatial function. The RC ratio during a mental rotation task is useful for discriminating MCI patients from controls.

Biomechanical stability of a supra-acetabular pedicle screw internal fixation device (INFIX) vs external fixation and plates for vertically unstable pelvic fractures.

PubMed

Vigdorchik, Jonathan M; Esquivel, Amanda O; Jin, Xin; Yang, King H; Onwudiwe, Ndidi A; Vaidya, Rahul

2012-09-27

We have recently developed a subcutaneous anterior pelvic fixation technique (INFIX). This internal fixator permits patients to sit, roll over in bed and lie on their sides without the cumbersome external appliances or their complications. The purpose of this study was to evaluate the biomechanical stability of this novel supraacetabular pedicle screw internal fixation construct (INFIX) and compare it to standard internal fixation and external fixation techniques in a single stance pelvic fracture model. Nine synthetic pelves with a simulated anterior posterior compression type III injury were placed into three groups (External Fixator, INFIX and Internal Fixation). Displacement, total axial stiffness, and the stiffness at the pubic symphysis and SI joint were calculated. Displacement and stiffness were compared by ANOVA with a Bonferroni adjustment for multiple comparisons The mean displacement at the pubic symphysis was 20, 9 and 0.8 mm for external fixation, INFIX and internal fixation, respectively. Plate fixation was significantly stiffer than the INFIX and external Fixator (P = 0.01) at the symphysis pubis. The INFIX device was significantly stiffer than external fixation (P = 0.017) at the symphysis pubis. There was no significant difference in SI joint displacement between any of the groups. Anterior plate fixation is stiffer than both the INFIX and external fixation in single stance pelvic fracture model. The INFIX was stiffer than external fixation for both overall axial stiffness, and stiffness at the pubic symphysis. Combined with the presumed benefit of minimizing the complications associated with external fixation, the INFIX may be a more preferable option for temporary anterior pelvic fixation in situations where external fixation may have otherwise been used.

Biomechanical Evaluation of All-Polyethylene Pegged Bony Ingrowth Glenoid Fixation Techniques on Implant Micromotion.

PubMed

Wiater, Brett P; Moravek, James E; Kurdziel, Michael D; Baker, Kevin C; Wiater, J Michael

2016-01-01

Newer glenoid components that allow for hybrid cement fixation via traditional cementation of peripheral pegs and bony ingrowth into an interference-fit central peg introduce the possibility of long-term biological fixation. However, little biomechanical work has been done on the initial stability of these components and the various fixation options. We conducted a study in which all-polyethylene glenoid components with a centrally fluted peg were implanted in polyurethane blocks with interference-fit, hybrid cement, and fully cemented fixation (5 per fixation group). Biomechanical evaluation of glenoid loosening, according to ASTM Standard F-2028-12, subjected the glenoids to 50,000 cycles of rim loading, and glenoid component motion was recorded with 2 differential variable reluctance transducers fixed to each glenoid prosthesis. Fully cemented fixation exhibited significantly less mean distraction in comparison with interference-fit fixation (P < .001) and hybrid cement fixation (P < .001). Hybrid cement fixation exhibited significantly less distraction (P < .001), more compression (P < .001), and no significant difference in glenoid translation (P = .793) in comparison with interference-fit fixation. Fully cemented fixation exhibited the most resistance to glenoid motion in comparison with hybrid cement fixation and interference-fit fixation. However, hybrid cement fixation and interference-fit fixation exhibited equivocal motion. Given these results, cementation of peripheral pegs may confer no additional initial stability over that provided by uncemented interference-fit fixation.

Stress Corrosion Cracking Behavior of LD10 Aluminum Alloy in UDMH and N2O4 propellant

NASA Astrophysics Data System (ADS)

Zhang, Youhong; Chang, Xinlong; Liu, Wanlei

2018-03-01

The LD10 aluminum alloy double cantilever beam specimens were corroded under the conditions of Unsymmetric Uimethyl Hydrazine (UDMH), Dinitrogen Tetroxide (N2O4), and 3.5% NaCl environment. The crack propagation behavior of the aluminum alloy in different corrosion environment was analyzed. The stress corrosion cracking behavior of aluminum alloy in N2O4 is relatively slight and there are not evident stress corrosion phenomenons founded in UDMH.

Isolation of ntrA-like mutants of Azotobacter vinelandii.

PubMed Central

Santero, E; Luque, F; Medina, J R; Tortolero, M

1986-01-01

A number of chlorate-resistant mutants of Azotobacter vinelandii affected in a general control of nitrogen metabolism were isolated. These mutants could not utilize dinitrogen, nitrate, or nitrite as a nitrogen source. The reason for this inability is that they were simultaneously deficient in nitrogenase and nitrate and nitrite reductase activities. They were complemented by a cosmid carrying a DNA fragment of A. vinelandii able to complement ntrA mutants of Escherichia coli, so they seemed to be ntrA-like mutants. PMID:3009406

Ru(II)-Catalyzed Cross-Coupling of Cyclopropenes with Diazo Compounds: Formation of Olefins from Two Different Carbene Precursors.

PubMed

Wang, Bo; Yi, Heng; Zhang, Hang; Sun, Tong; Zhang, Yan; Wang, Jianbo

2018-01-19

Formal carbene dimerization is a convergent method for the synthesis of alkenes. Herein, we report a Ru(II)-catalyzed carbene dimerization of cyclopropenes and diazo compounds. The yields are up to 97% and the stereoselectivity are up to >20:1. Mechanistically, it has been experimentally demonstrated that the catalyst reacts with cyclopropene first to generate a Ru(II)-carbene species, which is attacked by nucleophilic diazo substrate, followed by dinitrogen extrusion to form the double bond.

Nitrogen cycling during secondary succession in Atlantic Forest of Bahia, Brazil.

PubMed

Winbourne, Joy B; Feng, Aida; Reynolds, Lovinia; Piotto, Daniel; Hastings, Meredith G; Porder, Stephen

2018-01-22

Carbon accumulation in tropical secondary forests may be limited in part by nitrogen (N) availability, but changes in N during tropical forest succession have rarely been quantified. We explored N cycle dynamics across a chronosequence of secondary tropical forests in the Mata Atlântica of Bahia, Brazil in order to understand how quickly the N cycle recuperates. We hypothesized that N fixation would decline over the course of succession as N availability and N gaseous losses increased. We measured N fixation, KCl-extractable N, net mineralization and nitrification, resin-strip sorbed N, gaseous N emissions and the soil δ 15 N in stands that were 20, 35, 50, and > 50 years old. Contrary to our initial hypothesis, we found no significant differences between stand ages in any measured variable. Our findings suggest that secondary forests in this region of the Atlantic forest reached pre-disturbance N cycling dynamics after just 20 years of succession. This result contrasts with previous study in the Amazon, where the N cycle recovered slowly after abandonment from pasture reaching pre-disturbance N cycling levels after ~50 years of succession. Our results suggest the pace of the N cycle, and perhaps tropical secondary forest, recovery, may vary regionally.

Biomechanical characteristics of fixation methods for floating pubic symphysis.

PubMed

Song, Wenhao; Zhou, Dongsheng; He, Yu

2017-03-07

Floating pubic symphysis (FPS) is a relatively rare injury caused by high-energy mechanisms. There are several fixation methods used to treat FPS, including external fixation, subcutaneous fixation, internal fixation, and percutaneous cannulated screw fixation. To choose the appropriate fixation, it is necessary to study the biomechanical performance of these different methods. The goal of this study was to compare the biomechanical characteristics of six methods by finite element analysis. A three-dimensional finite element model of FPS was simulated. Six methods were used in the FPS model, including external fixation (Ext), subcutaneous rod fixation (Sub-rod), subcutaneous plate fixation (Sub-plate), superior pectineal plate fixation (Int-sup), infrapectineal plate fixation (Int-ifa), and cannulated screw fixation (Int-scr). Compressive and rotational loads were then applied in all models. Biomechanical characteristics that were recorded and analyzed included construct stiffness, micromotion of the fracture gaps, von Mises stress, and stress distribution. The construct stiffness of the anterior pelvic ring was decreased dramatically when FPS occurred. Compressive stiffness was restored by the three internal fixation and Sub-rod methods. Unfortunately, rotational stiffness was not restored satisfactorily by the six methods. For micromotion of the fracture gaps, the displacement was reduced significantly by the Int-sup and Int-ifa methods under compression. The internal fixation methods and Sub-plate method performed well under rotation. The maximum von Mises stress of the implants was not large. For the plate-screw system, the maximum von Mises stress occurred over the region of the fracture and plate-screw joints. The maximum von Mises stress appeared on the rod-screw and screw-bone interfaces for the rod-screw system. The present study showed the biomechanical advantages of internal fixation methods for FPS from a finite element view. Superior stabilization of the anterior pelvic ring and fracture gaps was obtained by internal fixation. Subcutaneous fixation had satisfactory outcomes as well. Sub-rod fixation offered good anti-compression, while the Sub-plate fixation provided favorable anti-rotational capacity.

Comparison of Tibiofemoral Contact Mechanics After Various Transtibial and All-Inside Fixation Techniques for Medial Meniscus Posterior Root Radial Tears in a Porcine Model.

PubMed

Chung, Kyu Sung; Choi, Choong Hyeok; Bae, Tae Soo; Ha, Jeong Ku; Jun, Dal Jae; Wang, Joon Ho; Kim, Jin Goo

2018-04-01

To compare tibiofemoral contact mechanics after fixation for medial meniscus posterior root radial tears (MMPRTs). Seven fresh knees from mature pigs were used. Each knee was tested under 5 conditions: normal knee, MMPRT, pullout fixation with simple sutures, fixation with modified Mason-Allen sutures, and all-inside fixation using Fastfix 360. The peak contact pressure and contact surface area were evaluated using a capacitive sensor positioned between the meniscus and tibial plateau, under a 1,000-N compression force, at different flexion angles (0°, 30°, 60°, and 90°). The peak contact pressure was significantly higher in MMPRTs than in normal knees (P = .018). Although the peak contact pressure decreased significantly after fixation at all flexion angles (P = .031), it never recovered to the values noted in the normal meniscus. No difference was observed among fixation groups (P = .054). The contact surface area was significantly lower in MMPRTs than in the normal meniscus (P = .018) and increased significantly after fixation at all flexion angles (P = .018) but did not recover to within normal limits. For all flexion angles except 60°, the contact surface area was significantly higher for fixation with Mason-Allen sutures than for fixation with simple sutures or all-inside fixation (P = .027). At 90° of flexion, the contact surface area was significantly better for fixation with simple sutures than for all-inside fixation (P = .031). The peak contact pressure and contact surface area improved significantly after fixation, regardless of the fixation method, but did not recover to the levels noted in the normal meniscus after any type of fixation. Among the fixation methods evaluated in this time 0 study, fixation using modified Mason-Allen sutures provided a superior contact surface area compared with that noted after fixation using simple sutures or all-inside fixation, except at 60° of flexion. However, this study had insufficient power to accurately detect the differences between the outcomes of various fixation methods. Our results in a porcine model suggest that fixation can restore tibiofemoral contact mechanics in MMPRT and that fixation with a locking mechanism leads to superior biomechanical properties. Copyright © 2017 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Denitrification and anammox in tropical aquaculture settlement ponds: an isotope tracer approach for evaluating N2 production.

PubMed

Castine, Sarah A; Erler, Dirk V; Trott, Lindsay A; Paul, Nicholas A; de Nys, Rocky; Eyre, Bradley D

2012-01-01

Settlement ponds are used to treat aquaculture discharge water by removing nutrients through physical (settling) and biological (microbial transformation) processes. Nutrient removal through settling has been quantified, however, the occurrence of, and potential for microbial nitrogen (N) removal is largely unknown in these systems. Therefore, isotope tracer techniques were used to measure potential rates of denitrification and anaerobic ammonium oxidation (anammox) in the sediment of settlement ponds in tropical aquaculture systems. Dinitrogen gas (N(2)) was produced in all ponds, although potential rates were low (0-7.07 nmol N cm(-3) h(-1)) relative to other aquatic systems. Denitrification was the main driver of N(2) production, with anammox only detected in two of the four ponds. No correlations were detected between the measured sediment variables (total organic carbon, total nitrogen, iron, manganese, sulphur and phosphorous) and denitrification or anammox. Furthermore, denitrification was not carbon limited as the addition of particulate organic matter (paired t-Test; P = 0.350, n = 3) or methanol (paired t-Test; P = 0.744, n = 3) did not stimulate production of N(2). A simple mass balance model showed that only 2.5% of added fixed N was removed in the studied settlement ponds through the denitrification and anammox processes. It is recommended that settlement ponds be used in conjunction with additional technologies (i.e. constructed wetlands or biological reactors) to enhance N(2) production and N removal from aquaculture wastewater.

Denitrification and Anammox in Tropical Aquaculture Settlement Ponds: An Isotope Tracer Approach for Evaluating N2 Production

PubMed Central

Castine, Sarah A.; Erler, Dirk V.; Trott, Lindsay A.; Paul, Nicholas A.; de Nys, Rocky; Eyre, Bradley D.

2012-01-01

Settlement ponds are used to treat aquaculture discharge water by removing nutrients through physical (settling) and biological (microbial transformation) processes. Nutrient removal through settling has been quantified, however, the occurrence of, and potential for microbial nitrogen (N) removal is largely unknown in these systems. Therefore, isotope tracer techniques were used to measure potential rates of denitrification and anaerobic ammonium oxidation (anammox) in the sediment of settlement ponds in tropical aquaculture systems. Dinitrogen gas (N2) was produced in all ponds, although potential rates were low (0–7.07 nmol N cm−3 h−1) relative to other aquatic systems. Denitrification was the main driver of N2 production, with anammox only detected in two of the four ponds. No correlations were detected between the measured sediment variables (total organic carbon, total nitrogen, iron, manganese, sulphur and phosphorous) and denitrification or anammox. Furthermore, denitrification was not carbon limited as the addition of particulate organic matter (paired t-Test; P = 0.350, n = 3) or methanol (paired t-Test; P = 0.744, n = 3) did not stimulate production of N2. A simple mass balance model showed that only 2.5% of added fixed N was removed in the studied settlement ponds through the denitrification and anammox processes. It is recommended that settlement ponds be used in conjunction with additional technologies (i.e. constructed wetlands or biological reactors) to enhance N2 production and N removal from aquaculture wastewater. PMID:22962581

Eighth international congress on nitrogen fixation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-01-01

This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

Eighth international congress on nitrogen fixation. Final program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-12-31

This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

Comparison of clinical outcomes of iris fixation and scleral fixation as treatment for intraocular lens dislocation.

PubMed

Kim, Kyeong Hwan; Kim, Wan Soo

2015-09-01

To compare the efficacy and safety of iris fixation with scleral fixation in surgical repositioning of dislocated intraocular lenses (IOLs). Retrospective, consecutive, comparative interventional case series. setting: Referral hospital. Seventy-eight consecutive patients who underwent surgical repositioning of dislocated intraocular lenses using suturing to the sclera or iris. Forty-four eyes of 44 patients underwent scleral fixation and 35 eyes of 34 patients underwent iris fixation of dislocated intraocular lenses. Visual acuity, refractive stability, operation time, and perioperative complications, including recurrence of IOL dislocation. Corrected distance visual acuity (CDVA) improved significantly 1 month postoperatively in both groups (P < .01 each), and remained stable for 12 months. One week postoperatively, however, CDVA improved significantly in the scleral fixation (P = .040) but not in the iris fixation (P = .058) group. The amount of refractive error significantly diminished 1 day after surgery (P = .028 in the scleral fixation and P = .046 in the iris fixation group). For the astigmatic components, Jackson crossed cylinders equivalent to conventional cylinders of positive power at axes of 0 degrees (J0) and 45 degrees (J45), J45 differed significantly in the scleral fixation and iris fixation groups (P = .009), whereas J0 was similar (P > .05). Operation time was significantly shorter (P = .0007), while immediate postoperative inflammation was significantly more severe (P = .001), in the iris fixation than in the scleral fixation group. Recurrence rates were similar (P > .05), but the mean time to recurrence was significantly shorter in the iris fixation than in the scleral fixation group (P = .031). Iris fixation and scleral fixation techniques had similar efficacy in the repositioning of dislocated intraocular lenses. Although operation time was shorter for iris fixation, it had several disadvantages, including induced astigmatism, immediate postoperative inflammation, earlier recurrence, and less stable refraction. Copyright © 2015 Elsevier Inc. All rights reserved.

Reverse Anterior Cruciate Ligament Reconstruction Fixation: A Biomechanical Comparison Study of Tibial Cross-Pin and Femoral Interference Screw Fixation.

PubMed

Lawley, Richard J; Klein, Samuel E; Chudik, Steven C

2017-03-01

To evaluate the biomechanical performance of tibial cross-pin (TCP) fixation relative to femoral cross-pin (FCP), femoral interference screw (FIS), and tibial interference screw (TIS) fixation. We randomized 40 porcine specimens (20 tibias and 20 femurs) to TIS fixation (group 1, n = 10), FIS fixation (group 2, n = 10), TCP fixation (group 3, n = 10), or FCP fixation (group 4, n = 10) and performed biomechanical testing to compare ultimate load, stiffness, yield load, cyclic displacement, and load at 5-mm displacement. We performed cross-pin fixation of the looped end and interference screw fixation of the free ends of 9-mm-diameter bovine extensor digitorum communis tendon grafts. Graft fixation constructs were cyclically loaded and then loaded to failure in line with the tunnels. Regarding yield load, FIS was superior to TIS (704 ± 125 N vs 504 ± 118 N, P = .002), TCP was superior to TIS (1,449 ± 265 N vs 504 ± 118 N, P < .001), and TCP was superior to FCP (1,449 ± 265 N vs 792 ± 397 N, P < .001). Cyclic displacement for FCP was superior to TCP. Cyclic displacement for TIS versus FIS showed no statistically significant difference (2.5 ± 1.0 mm vs 2.2 ± 0.6 mm, P = .298). Interference screw fixation consistently failed by graft slippage, whereas TCP fixation failed by tibial bone failure. FCP fixation failed by either femoral bone failure or failure elsewhere in the testing apparatus. Regarding yield load, TCP fixation performed biomechanically superior to the clinically proven FCP at time zero. Because TIS fixation shows the lowest yield strength, it represents the weak link, and combined TCP-FIS fixation theoretically would be biomechanically superior relative to combined FCP-TIS fixation with regard to yield load. Cyclic displacement showed a small difference in favor of FCP over TCP fixation and no difference between TIS and FIS. Time-zero biomechanics of TCP fixation paired with FIS fixation show that this method of fixation can be considered a potential alternative to current practice and may pose clinical benefits in different clinical scenarios of anterior cruciate ligament reconstruction. Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Comparison of Risk of Carpal Tunnel Syndrome in Patients with Distal Radius Fractures After 7 Treatments

PubMed Central

Zhao, Huan-Li; Wang, Gui-Bin; Jia, Yue-Qing; Zhu, Shi-Cai; Zhang, Feng-Fang; Liu, Hong-Mei

2015-01-01

Background To compare risk of carpal tunnel syndrome (CTS) in distal radius fracture (DRF) patients after 7 treatments using bridging external fixation (BrEF), non-bridging external fixation (non-BrEF), plaster fixation, K-wire fixation, dorsal plating fixation, volar plating fixation, and dorsal and volar plating by performing a network meta-analysis. Material/Methods An exhaustive search of electronic databases identified randomized controlled trails (RCTs) closely related to our study topic. The published articles were screened, based on predefined inclusion and exclusion criteria, to select high-quality studies for the present network meta-analysis. Data extracted from the selected studies were analyzed using STATA version 12.0 software. Results The literature search and selection process identified 12 eligible RCTs that contained a total of 1370 DRF patients (394 patients with BrEF, 377 patients with non-BrEF, 89 patients with K-wire fixation, 192 patients with plaster fixation, 42 patients with dorsal plating fixation, 152 patients with volar plating fixation, and 124 patients with dorsal and volar plating fixation). Our network meta-analysis results demonstrated no significant differences in CTS risk among the 7 treatments (P>0.05). The value of surface under the cumulative ranking curve (SUCRA), however, suggested that dorsal plating fixation is the optimal treatment, with the lowest risk of CTS in DRF patients (dorsal plating fixation: 89.2%; dorsal and volar plating: 57.8%; plaster fixation: 50.9%; non-BrEF: 50.6%; volar plating fixation: 39.6%; BrEF: 38.4%; K-wire fixation: 23.6%). Conclusions Our network meta-analysis provides evidence that dorsal plating fixation significantly decreases the risk of CTS and could be the method of choice in DRF patients. PMID:26391617

Single-screw Fixation of Adolescent Salter-II Proximal Humeral Fractures: Biomechanical Analysis of the "One Pass Door Lock" Technique.

PubMed

Miller, Mark Carl; Redman, Christopher N; Mistovich, R Justin; Muriuki, Muturi; Sangimino, Mark J

2017-09-01

Pin fixation of Salter-II proximal humeral fractures in adolescents approaching skeletal maturity has potential complications that can be avoided with single-screw fixation. However, the strength of screw fixation relative to parallel and diverging pin fixation is unknown. To compare the biomechanical fixation strength between these fixation modalities, we used synthetic composite humeri, and then compared these results in composite bone with cadaveric humeri specimens. Parallel pinning, divergent pinning, and single-screw fixation repairs were performed on synthetic composite humeri with simulated fractures. Six specimens of each type were tested in axial loading and other 6 were tested in torsion. Five pair of cadaveric humeri were tested with diverging pins and single screws for comparison. Single-screw fixation was statistically stronger than pin fixation in axial and torsional loading in both composite and actual bone. There was no statistical difference between composite and cadaveric bone specimens. Single-screw fixation can offer greater stability to adolescent Salter-II fractures than traditional pinning. Single-screw fixation should be considered as a viable alternative to percutaneous pin fixation in transitional patients with little expected remaining growth.

The inner workings of the hydrazine synthase multiprotein complex.

PubMed

Dietl, Andreas; Ferousi, Christina; Maalcke, Wouter J; Menzel, Andreas; de Vries, Simon; Keltjens, Jan T; Jetten, Mike S M; Kartal, Boran; Barends, Thomas R M

2015-11-19

Anaerobic ammonium oxidation (anammox) has a major role in the Earth's nitrogen cycle and is used in energy-efficient wastewater treatment. This bacterial process combines nitrite and ammonium to form dinitrogen (N2) gas, and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans. Strikingly, the anammox process relies on the highly unusual, extremely reactive intermediate hydrazine, a compound also used as a rocket fuel because of its high reducing power. So far, the enzymatic mechanism by which hydrazine is synthesized is unknown. Here we report the 2.7 Å resolution crystal structure, as well as biophysical and spectroscopic studies, of a hydrazine synthase multiprotein complex isolated from the anammox organism Kuenenia stuttgartiensis. The structure shows an elongated dimer of heterotrimers, each of which has two unique c-type haem-containing active sites, as well as an interaction point for a redox partner. Furthermore, a system of tunnels connects these active sites. The crystal structure implies a two-step mechanism for hydrazine synthesis: a three-electron reduction of nitric oxide to hydroxylamine at the active site of the γ-subunit and its subsequent condensation with ammonia, yielding hydrazine in the active centre of the α-subunit. Our results provide the first, to our knowledge, detailed structural insight into the mechanism of biological hydrazine synthesis, which is of major significance for our understanding of the conversion of nitrogenous compounds in nature.

Concise Synthesis of (-)-Hodgkinsine, (-)-Calycosidine, (-)-Hodgkinsine B, (-)-Quadrigemine C, and (-)-Psycholeine via Convergent and Directed Modular Assembly of Cyclotryptamines.

PubMed

Lindovska, Petra; Movassaghi, Mohammad

2017-12-06

The enantioselective total synthesis of (-)-hodgkinsine, (-)-calycosidine, (-)-hodgkinsine B, (-)-quadrigemine C, and (-)-psycholeine through a diazene-directed assembly of cyclotryptamine fragments is described. Our synthetic strategy enables multiple and directed assembly of intact cyclotryptamine subunits for convergent synthesis of highly complex bis- and tris-diazene intermediates. Photoextrusion of dinitrogen from these intermediates enables completely stereoselective formation of all C3a-C3a' and C3a-C7' carbon-carbon bonds and all the associated quaternary stereogenic centers. In a representative example, photoextrusion of three dinitrogen molecules from an advanced intermediate in a single-step led to completely controlled introduction of four quaternary stereogenic centers and guided the assembly of four cyclotryptamine monomers en route to (-)-quadrigemine C. The synthesis of these complex diazenes was made possible through a new methodology for synthesis of aryl-alkyl diazenes using electronically attenuated hydrazine-nucleophiles for a silver-promoted addition to C3a-bromocyclotryptamines. The application of Rh- and Ir-catalyzed C-H amination reactions in complex settings were used to gain rapid access to C3a- and C7-functionalized cyclotryptamine monomers, respectively, used for diazene synthesis. This convergent and modular assembly of intact cyclotryptamines offers the first solution to access these alkaloids through completely stereoselective union of monomers at challenging linkages and the associated quaternary stereocenters as illustrated in our synthesis of five members of the oligocyclotryptamine family of alkaloids.

Landscape-scale estimation of denitrification rates and nitrous oxide to dinitrogen ratio at Georgia and Pennsylvania LTAR sites

NASA Astrophysics Data System (ADS)

Dell, C. J.; Groffman, P. M.; Strickland, T.; Kleinman, P. J. A.; Bosch, D. D.; Bryant, R.

2015-12-01

Denitrification results in a significant loss of plant-available nitrogen from agricultural systems and contributes to climate change, due to the emissions of both the potent greenhouse gas nitrous oxide (N2O) and environmentally benign dinitrogen (N2). However total quantities of the gases emitted and the ratio of N2:N2O are often not clearly understood, because N2 emissions cannot be directly measured in the field because of the high background level of N2 in the atmosphere. While variability in soil conditions across landscapes, especially water content and aeration, is believed to greatly impact both total denitrification rates and N2:N2O, the measurement limitations have prevented a clear understanding of landscape-scale emissions of denitrification products. The Cary Institute has developed an approach where soil core are maintained in a sealed system with an N2-free airstream, allowing emitted N2 and N2O emissions to be measured without interference from atmospheric N2. Emissions of the gases are measured under a range of oxygen concentrations and soil water contents. Laboratory responses can then be correlated with measured field conditions at the sampling points and resulting emission estimates extrapolated to the field-scale. Measurements are currently being conducted on peanut/cotton rotations, dairy forage rotations (silage corn/alfalfa), and bioenergy crops (switchgrass and miscanthus) at Long Term Agricultural Research (LTAR) sites at Tifton, GA and University Park, PA.

Utility of Lithium in Rare-Earth Metal Reduction Reactions to Form Nontraditional Ln2+ Complexes and Unusual [Li(2.2.2-cryptand)]1+ Cations.

PubMed

Huh, Daniel N; Darago, Lucy E; Ziller, Joseph W; Evans, William J

2018-02-19

The utility of lithium compared to other alkali metals in generating Ln 2+ rare-earth metal complexes via reduction of Ln 3+ precursors in reactions abbreviated as LnA 3 /M (Ln = rare-earth metal; A = anionic ligand; M = alkali metal) is described. Lithium reduction of Cp' 3 Ln (Cp' = C 5 H 4 SiMe 3 ; Ln = Y, Tb, Dy, Ho) under Ar in the presence of 2.2.2-cryptand (crypt) forms new examples of crystallographically characterizable Ln 2+ complexes of these metals, [Li(crypt)][Cp' 3 Ln]. In each complex, lithium is found in an N 2 O 4 donor atom coordination geometry that is unusual for the cryptand ligand. Magnetic susceptibility data on these new examples of nontraditional divalent lanthanide complexes are consistent with 4f n 5d 1 electronic configurations. The Dy and Ho complexes have exceptionally high single-ion magnetic moments, 11.35 and 11.67 μ B , respectively. Lithium reduction of Cp' 3 Y under N 2 at -35 °C forms the Y 2+ complex (Cp' 3 Y) 1- , which reduces dinitrogen upon warming to room temperature to generate the (N 2 ) 2- complex [Cp' 2 Y(THF)] 2 (μ-η 2 :η 2 -N 2 ). These results provide insight on the factors that lead to reduced dinitrogen complexes and/or stable divalent lanthanide complexes as a function of the specific reducing agent and conditions.

Ozone and dinitrogen monoxide production in atmospheric pressure air dielectric barrier discharge plasma effluent generated by nanosecond pulse superimposed alternating current voltage

NASA Astrophysics Data System (ADS)

Takashima, Keisuke; Kaneko, Toshiro

2017-06-01

The effects of nanosecond pulse superposition to alternating current voltage (NS + AC) on the generation of an air dielectric barrier discharge (DBD) plasma and reactive species are experimentally studied, along with measurements of ozone (O3) and dinitrogen monoxide (N2O) in the exhausted gas through the air DBD plasma (air plasma effluent). The charge-voltage cycle measurement indicates that the role of nanosecond pulse superposition is to induce electrical charge transport and excess charge accumulation on the dielectric surface following the nanosecond pulses. The densities of O3 and N2O in NS + AC DBD are found to be significantly increased in the plasma effluent, compared to the sum of those densities generated in NS DBD and AC DBD operated individually. The production of O3 and N2O is modulated significantly by the phase in which the nanosecond pulse is superimposed. The density increase and modulation effects by the nanosecond pulse are found to correspond with the electrical charge transport and the excess electrical charge accumulation induced by the nanosecond pulse. It is suggested that the electrical charge transport by the nanosecond pulse might result in the enhancement of the nanosecond pulse current, which may lead to more efficient molecular dissociation, and the excess electrical charge accumulation induced by the nanosecond pulse increases the discharge coupling power which would enhance molecular dissociation.

Open reduction and internal fixation compared to closed reduction and external fixation in distal radial fractures

PubMed Central

Kopylov, Philippe; Geijer, Mats; Tägil, Magnus

2009-01-01

Background and purpose In unstable distal radial fractures that are impossible to reduce or to maintain in reduced position, the treatment of choice is operation. The type of operation and the choice of implant, however, is a matter of discussion. Our aim was to investigate whether open reduction and internal fixation would produce a better result than traditional external fixation. Methods 50 patients with an unstable or comminute distal radius fracture were randomized to either closed reduction and bridging external fixation, or open reduction and internal fixation using the TriMed system. The primary outcome parameter was grip strength, but the patients were followed for 1 year with objective clinical assessment, subjective outcome using DASH, and radiographic examination. Results At 1 year postoperatively, grip strength was 90% (SD 16) of the uninjured side in the internal fixation group and 78% (17) in the external fixation group. Pronation/supination was 150° (15) in the internal fixation group and 136° (20) in the external fixation group at 1 year. There were no differences in DASH scores or in radiographic parameters. 5 patients in the external fixation group were reoperated due to malunion, as compared to 1 in the internal fixation group. 7 other cases were classified as radiographic malunion: 5 in the external fixation group and 2 in the internal fixation group. Interpretation Internal fixation gave better grip strength and a better range of motion at 1 year, and tended to have less malunions than external fixation. No difference could be found regarding subjective outcome. PMID:19857180

[Comparison of external fixation with or without limited internal fixation for open knee fractures].

PubMed

Li, K N; Lan, H; He, Z Y; Wang, X J; Yuan, J; Zhao, P; Mu, J S

2018-03-01

Objective: To explore the characteristics and methods of different fixation methods and prevention of open knee joint fracture. Methods: The data of 86 cases of open knee joint fracture admitted from January 2002 to December 2015 in Department of Orthopaedics, Affiliated Hospital of Chengdu University were analyzed retrospectively.There were 65 males and 21 females aged of 38.6 years. There were 38 cases treated with trans articular external fixation alone, 48 cases were in the trans articular external fixation plus auxiliary limited internal fixation group. All the patients were treated according to the same three stages except for different fixation methods. Observation of external fixation and fracture fixation, fracture healing, wound healing and treatment, treatment and related factors of infection control and knee function recovery. χ(2) test was used to analyze data. Results: Eleven patients had primary wound healing, accounting for 12.8%. Seventy-five patients had two wounds healed, accounting for 87.2%. Only 38 cases of trans articular external fixator group had 31 cases of articular surface reduction, accounting for 81.6%; Five cases of trans articular external fixator assisted limited internal fixation group had 5 cases of poor reduction, accounting for 10.4%; There was significant difference between the two groups (χ(2)=44.132, P <0.05). Take a single cross joint external fixation group, a total of 23 cases of patients with infection, accounted for 60.5% of external fixation group; trans articular external fixation assisted limited internal fixation group there were 30 cases of patients with infection, accounting for the assistance of external fixator and limited internal fixation group 62.5%; There was significant difference between the two groups(χ(2)=0.035, P >0.05). Five cases of fracture nonunion cases of serious infection, patients voluntarily underwent amputation. The Lysholm Knee Scale: In the external fixation group, 23 cases were less than 50 points, accounting for 60.5%, 15 cases were more than 50 points, accounting for 39.5%, external fixation and limited internal fixation group 20 cases were less than 50 points, accounting for 41.7%, 28 cases were more than 50 points, accounting for 58.3%; There was significant difference between the two groups(χ(2)=1.279, P >0.05). Conclusions: Prevention and control of infection is a central link in the treatment of open fracture of the knee. Trans articular external fixator plus limited internal fixation is an important measure to treat open fracture of the knee-joint.

Analysis of usage and associated cost of external fixators at an urban level 1 trauma centre.

PubMed

Chaus, George W; Dukes, Chase; Hak, David J; Mauffrey, Cyril; Mark Hammerberg, E

2014-10-01

To determine the usage, indication, duration, and cost associated with external fixation usage. Additionally, to show the significant cost associated with external fixator use and reinvigorate discussions on external fixator reuse. A retrospective review of a prospectively gathered trauma database was undertaken to identify all patients treated with external fixation frames for pelvic and lower extremity injuries between September 2007 and July 2010. We noted the indications for frame use, and we determined the average duration of external fixation for each indication. The cost of each frame was calculated from implant records. 341 lower extremity and pelvic fractures were treated with external fixation frames during the study period. Of these, 92% were used as temporary external fixation. The average duration of temporary external fixation was 10.5 days. The cost of external fixation frame components was $670,805 per year. The average cost per external fixation frame was $5900. The majority of external fixators are intended as temporary frames, in place for a limited period of time prior to definitive fixation of skeletal injuries. As such, most frames are not intended to withstand physiologic loads, nor are they expected provide a precise maintenance of reduction. Given the considerable expense associated with external fixation frame components, the practice of purchasing external fixation frame components as disposable "single-use" items appears to be somewhat wasteful. Level II. Copyright © 2014 Elsevier Ltd. All rights reserved.

Fixation distance and fixation duration to vertical road signs.

PubMed

Costa, Marco; Simone, Andrea; Vignali, Valeria; Lantieri, Claudio; Palena, Nicola

2018-05-01

The distance of first-fixation to vertical road signs was assessed in 22 participants while driving a route of 8.34 km. Fixations to road signs were recorded by a mobile eye-movement-tracking device synchronized to GPS and kinematic data. The route included 75 road signs. First-fixation distance and fixation duration distributions were positively skewed. Median distance of first-fixation was 51 m. Median fixation duration was 137 ms with a modal value of 66 ms. First-fixation distance was linearly related to speed and fixation duration. Road signs were gazed at a much closer distance than their visibility distance. In a second study a staircase procedure was used to test the presentation-time threshold that lead to a 75% accuracy in road sign identification. The threshold was 35 ms, showing that short fixations to a road signs could lead to a correct identification. Copyright © 2018 Elsevier Ltd. All rights reserved.

An in-vitro biomechanical study of different fixation techniques for the extended trochanteric osteotomy in revision THA.

PubMed

Zhu, Zhonglin; Ding, Hui; Shao, Hongyi; Zhou, Yixin; Wang, Guangzhi

2013-04-09

The wire fixation and the cable grip fixation have been developed for the extended trochanteric osteotomy (ETO) in the revision of total hip arthroplasty (THA). Many studies reported the postoperative performance of the patients, but with little quantitative biomechanical comparison of the two fixation systems. An in-vitro testing approach was designed to record the loosening between the femoral bed and the greater trochanter after fixations. Ten cadaveric femurs were chosen in this study. Each femur underwent the THA, revision by ETO and fixations. The tension to the greater trochanter was from 0 to 500N in vertical and lateral direction, respectively. The translation and rotation of the greater trochanter with respect to the bony bed were captured by an optical tracking system. In the vertical tension tests, the overall translation of the greater trochanter was observed 0.4 mm in the cable fixations and 7.0 mm in the wire fixations. In the lateral tension tests, the overall motion of the greater trochanter was 2.0 mm and 1.2° in the cable fixations, while it was 6.2 mm and 5.3° in the wire fixations. The result was significantly different between the two fixation systems. The stability of the proximal femur after ETO using different fixations in the revision THA was investigated. The cable grip fixation was significantly more stable than the wire fixation.

Prism under cover test in alternate fixation horizontal strabismus.

PubMed

Tejedor, Jaime; Gutiérrez-Carmona, Francisco José

2018-02-01

To evaluate the applicability of the prism under cover test (PUCT) to quantify manifest deviation in horizontal strabismus with alternate fixation when simultaneous prism and cover test (SPCT) is not feasible. Children aged 4-11 years, with alternate fixation horizontal strabismus and alternate prism and cover test (APCT) distance deviation (DD) up to 25 PD were eligible. In group 1 of the study, SPCT was not feasible (n = 18), whereas in group 2, it was feasible (n = 24). Refraction, PUCT, APCT, central/peripheral fusion, and stereoacuity were measured. Repeatability of PUCT, agreement between PUCT and SPCT, and Pearson correlations between variables were studied. In group 1, mean DD was 15.6 and 9.5 PD using APCT and PUCT, respectively (intraclass correlation, ICC: 0.90). Mean stereoacuity was 201.1 arc seconds. PUCT was better correlated with stereoacuity than APCT, but not significantly (p = 0.12). Coefficient of repeatability for PUCT was 3.4 PD. In group 2, mean DD was 17.6, 14.1, and 12.5 PD using APCT, PUCT, and SPCT, respectively. Mean stereoacuity was 285.9 arc seconds. Correlations APCT-PUCT (0.87), APCT-SPCT (0.82), and SPCT-PUCT (0.95) were significant. APCT did not show as good correlation with stereoacuity (0.58) as SPCT and PUCT (0.74 and 0.78, respectively). Concordance correlation coefficient between SPCT and PUCT was 0.91, and Bland Altman agreement between the two variables was also good. PUCT is a procedure with good repeatability, of interest in children to estimate manifest deviation when SPCT is not feasible, and in support of the diagnosis of monofixation syndrome.

γH2AX assay in ex vivo irradiated tumour specimens: A novel method to determine tumour radiation sensitivity in patient-derived material.

PubMed

Menegakis, Apostolos; von Neubeck, Cläre; Yaromina, Ala; Thames, Howard; Hering, Sandra; Hennenlotter, Joerg; Scharpf, Marcus; Noell, Susan; Krause, Mechthild; Zips, Daniel; Baumann, Michael

2015-09-01

To establish a clinically applicable protocol for quantification of residual γH2AX foci in ex vivo irradiated tumour samples and to apply this method in a proof-of-concept feasibility study to patient-derived tumour specimens. Evaluation of γH2AX foci formation and disappearance in excised FaDu tumour specimens after (a) different incubation times in culture medium, 4Gy irradiation and fixation after 24h (cell recovery), (b) 10h medium incubation, 4Gy irradiation and fixation after various time points (double strand break repair kinetics), and (c) 10h medium incubation, irradiation with graded single radiation doses and fixation after 24h (dose-response). The optimised protocol was applied to patient-derived samples of seminoma, prostate cancer and glioblastoma multiforme. Post excision or biopsy, tumour tissues showed stable radiation-induced γH2AX foci values in oxic cells after >6h of recovery in medium. Kinetics of foci disappearance indicated a plateau of residual foci after >12h following ex vivo irradiation. Fitting the dose-response of residual γH2AX foci yielded slopes comparable with in situ irradiation of FaDu tumours. Significant differences in the slopes of ex vivo irradiated patient-derived tumour samples were found. A novel clinically applicable method to quantify residual γH2AX foci in ex vivo irradiated tumour samples was established. The first clinical results suggest that this method allows to distinguish between radiosensitive and radioresistant tumour types. These findings support further translational evaluation of this assay to individualise radiation therapy. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

The Effect of Land-use Change and Management on Free-living N2 fixation in the Brazilian Atlantic Forest

NASA Astrophysics Data System (ADS)

De Oliveira Bomfim, B.; Silva, L. C. R.; Horwath, W. R.; Hello, J.; Doane, T. A.

2016-12-01

Globally, primary tropical forests are increasingly disturbed by deforestation, urbanization, agriculture, and cattle ranching. It has been recognized that the resulting (secondary) forests now play a key role in global biogeochemical cycles; however, little is known about alterations in forest function caused by the combination of disturbance and land use change. Fire, deforestation, and forest-to-monocrop conversion are all likely to affect biotic N inputs, yet our understanding of how free-living N2 fixation influences ecosystem response after disturbance remains poorly understood. Our research is assessing the role of asymbiotic (free-living) biological nitrogen fixation (BNF), a microbially-mediated process responsible for providing N inputs across terrestrial ecosystems and modulating the effect of fire and land cover in secondary forest succession. Free-living BNF is being quantified through incubations using stable isotope (15N2 labeling experiment) in different substrates (soil and leaf litter) under contrasting land use and management in the Brazilian Atlantic Forest, the most deforested Biome in Brazil with only 7% of its original cover. Soil and litter samples were collected in primary forests, 12-year secondary forests, Eucalyptus spp. plantations and 10-year Brachiaria brizantha pastures. Preliminary results indicate that free-living BNF rates did not vary significantly between either secondary land use (0.02 to 0.46 µg N2 fixed gDW-1 h-1), but rates were significantly higher in the litter layer (0.32 to 3.8 µg N2 fixed gDW-1 h-1) than in the surface soil (0 - 10 cm and 10 - 30 cm). Free-living BNF in this stretch of the Brazilian Atlantic Forest seems not to be significantly affected by contrasting land use and management.

Tendon transfer fixation: comparing a tendon to tendon technique vs. bioabsorbable interference-fit screw fixation.

PubMed

Sabonghy, Eric Peter; Wood, Robert Michael; Ambrose, Catherine Glauber; McGarvey, William Christopher; Clanton, Thomas Oscar

2003-03-01

Tendon transfer techniques in the foot and ankle are used for tendon ruptures, deformities, and instabilities. This fresh cadaver study compares the tendon fixation strength in 10 paired specimens by performing a tendon to tendon fixation technique or using 7 x 20-25 mm bioabsorbable interference-fit screw tendon fixation technique. Load at failure of the tendon to tendon fixation method averaged 279N (Standard Deviation 81N) and the bioabsorbable screw 148N (Standard Deviation 72N) [p = 0.0008]. Bioabsorbable interference-fit screws in these specimens show decreased fixation strength relative to the traditional fixation technique. However, the mean bioabsorbable screw fixation strength of 148N provides physiologic strength at the tendon-bone interface.

A Novel Fixation System for Acetabular Quadrilateral Plate Fracture: A Comparative Biomechanical Study

PubMed Central

Zha, Guo-Chun; Sun, Jun-Ying; Dong, Sheng-Jie; Zhang, Wen; Luo, Zong-Ping

2015-01-01

This study aims to assess the biomechanical properties of a novel fixation system (named AFRIF) and to compare it with other five different fixation techniques for quadrilateral plate fractures. This in vitro biomechanical experiment has shown that the multidirectional titanium fixation (MTF) and pelvic brim long screws fixation (PBSF) provided the strongest fixation for quadrilateral plate fracture; the better biomechanical performance of the AFRIF compared with the T-shaped plate fixation (TPF), L-shaped plate fixation (LPF), and H-shaped plate fixation (HPF); AFRIF gives reasonable stability of treatment for quadrilateral plate fracture and may offer a better solution for comminuted quadrilateral plate fractures or free floating medial wall fracture and be reliable in preventing protrusion of femoral head. PMID:25802849

Calibration and standardization of microwave ovens for fixation of brain and peripheral nerve tissue.

PubMed

Login, G R; Leonard, J B; Dvorak, A M

1998-06-01

Rapid and reproducible fixation of brain and peripheral nerve tissue for light and electron microscopy studies can be done in a microwave oven. In this review we report a standardized nomenclature for diverse fixation techniques that use microwave heating: (1) microwave stabilization, (2) fast and ultrafast primary microwave-chemical fixation, (3) microwave irradiation followed by chemical fixation, (4) primary chemical fixation followed by microwave irradiation, and (5) microwave fixation used in various combinations with freeze fixation. All of these methods are well suited to fix brain tissue for light microscopy. Fast primary microwave-chemical fixation is best for immunoelectron microscopy studies. We also review how the physical characteristics of the microwave frequency and the dimensions of microwave oven cavities can compromise microwave fixation results. A microwave oven can be calibrated for fixation when the following parameters are standardized: irradiation time; water load volume, initial temperature, and placement within the oven; fixative composition, volume, and initial temperature; and specimen container shape and placement within the oven. Using two recently developed calibration tools, the neon bulb array and the agar-saline-Giemsa tissue phantom, we report a simple calibration protocol that identifies regions within a microwave oven for uniform microwave fixation. Copyright 1998 Academic Press.

Application of alternative fixatives to formalin in diagnostic pathology

PubMed Central

Gatta, L. Benerini; Cadei, M.; Balzarini, P.; Castriciano, S.; Paroni, R.; Verzeletti, A.; Cortellini, V.; De Ferrari, F.; Grigolato, P.

2012-01-01

Fixation is a critical step in the preparation of tissues for histopathology. The aim of this study was to investigate the effects of different fixatives vs formalin on proteins and DNA, and to evaluate alternative fixation for morphological diagnosis and nucleic acid preservation for molecular methods. Forty tissues were fixed for 24 h with six different fixatives: the gold standard fixative formalin, the historical fixatives Bouin and Hollande, and the alternative fixatives Greenfix, UPM and CyMol. Tissues were stained (Haematoxylin-Eosin, Periodic Acid Schiff, Trichromic, Alcian-blue, High Iron Diamine stainings), and their antigenicity was determined by immunohistochemistry (performed with PAN-CK, CD31, Ki-67, S100, CD68, AML antibodies). DNA extraction, KRAS sequencing, FISH for CEP-17, and flow cytometry analysis of nuclear DNA content were applied. For cell morphology the alternative fixatives (Greenfix, UPM, CyMol) were equivalent to formalin. As expected, Hollande proved to be the best fixative for morphology. The morphology obtained with Bouin was comparable to the one with formalin. Hollande was the best fixative for histochemistry. Bouin proved to be equivalent to formalin. The alternative fixatives were equivalent to formalin, although with greater variability in haematoxylin-eosin staining. It proved the possibility to obtain immunohistochemical staining largely equivalent to that following formalin-fixation with the following fixatives: Greenfix, Hollande, UPM and CyMol. The tissues fixed in Bouin did not provide results comparable to those obtained with formalin. The DNA extracted from samples fixed with alternative fixatives was found to be suitable for molecular analysis. PMID:22688293

[Tibial press-fit fixation of flexor tendons for reconstruction of the anterior cruciate ligament].

PubMed

Ettinger, M; Liodakis, E; Haasper, C; Hurschler, C; Breitmeier, D; Krettek, C; Jagodzinski, M

2012-09-01

Press-fit fixation of hamstring tendon autografts for anterior cruciate ligament reconstruction is an interesting technique because no hardware is necessary. This study compares the biomechanical properties of press-fit fixations to an interference screw fixation. Twenty-eight human cadaveric knees were used for hamstring tendon explantation. An additional bone block was harvested from the tibia. We used 28 porcine femora for graft fixation. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclic loading were investigated. The maximum load to failure was 970±83 N for the press-fit tape fixation (T), 572±151 N for the bone bridge fixation (TS), 544±109 N for the interference screw fixation (I), 402±77 N for the press-fit suture fixation (S) and 290±74 N for the bone block fixation technique (F). The T fixation had a significantly better maximum load to failure compared to all other techniques (p<0.001). This study demonstrates that a tibial press-fit technique which uses an additional bone block has better maximum load to failure results compared to a simple interference screw fixation.

Porcine Intestinal Mast Cells. Evaluation of Different Fixatives for Histochemical Staining Techniques Considering Tissue Shrinkage

PubMed Central

Rieger, J.; Twardziok, S.; Huenigen, H.; Hirschberg, R.M.; Plendl, J.

2013-01-01

Staining of mast cells (MCs), including porcine ones, is critically dependent upon the fixation and staining technique. In the pig, mucosal and submucosal MCs do not stain or stain only faintly after formalin fixation. Some fixation methods are particularly recommended for MC staining, for example the fixation with Carnoy or lead salts. Zinc salt fixation (ZSF) has been reported to work excellently for the preservation of fixation-sensitive antigens. The aim of this study was to establish a reliable histological method for counting of MCs in the porcine intestinum. For this purpose, different tissue fixation and staining methods that also allow potential subsequent immunohistochemical investigations were evaluated in the porcine mucosa, as well as submucosa of small and large intestine. Tissues were fixed in Carnoy, lead acetate, lead nitrate, Zamboni and ZSF and stained subsequently with either polychromatic methylene blue, alcian blue or toluidine blue. For the first time our study reveals that ZSF, a heavy metal fixative, preserves metachromatic staining of porcine MCs. Zamboni fixation was not suitable for histochemical visualization of MCs in the pig intestine. All other tested fixatives were suitable. Alcian blue and toluidine blue co-stained intestinal goblet cells which made a prima facie identification of MCs difficult. The polychromatic methylene blue proved to be the optimal staining. In order to compare MC counting results of the different fixation methods, tissue shrinkage was taken into account. As even the same fixation caused shrinkagedifferences between tissue from small and large intestine, different factors for each single fixation and intestinal localization had to be calculated. Tissue shrinkage varied between 19% and 57%, the highest tissue shrinkage was found after fixation with ZSF in the large intestine, the lowest one in the small intestine after lead acetate fixation. Our study emphasizes that MC counting results from data using different fixation techniques can only be compared if the respective studyimmanent shrinkage factor has been determined and quantification results are adjusted accordingly. PMID:24085270

[Effectiveness comparison of flexible fixation and rigid fixation in treatment of ankle pronation-external rotation fractures with distal tibiofibular syndesmosis].

PubMed

Li, Yuewei; Zhang, Minghui; Li, Xiaorong; Chen, Xiaoyong; Deng, Jianlong

2017-07-01

To compare the effectiveness of flexible fixation and rigid fixation in the treatment of ankle pronation-external rotation fractures with distal tibiofibular syndesmosis. A retrospective analysis was made on the clinical data of 50 patients with ankle pronation-external rotation fractures and distal tibiofibular syndesmosis treated between January 2013 and December 2015. Suture-button fixation was used in 23 patients (flexible fixation group) and cortical screw fixation in 27 patients (rigid fixation group). There was no significant difference in age, gender, weight, side, fracture type, and time from trauma to surgery between 2 groups ( P >0.05). The operation time, medial clear space (MCS), tibiofibular clear space (TFCS), tibiofibular overlap (TFO), American Orthopaedic Foot and Ankle Society (AOFAS) score, and Foot and Ankle Disability Index (FADI) score were compared between 2 groups. The operation time was (83.0±9.1) minutes in the flexible fixation group and was (79.6±13.1) minutes in the rigid fixation group, showing no significant difference ( t =1.052, P =0.265). All patients achieved healing of incision by first intention. The patients were followed up 12-20 months (mean, 14 months). The X-ray films showed good healing of fracture in 2 groups. There was no screw fracture, delayed union or nounion. The fracture healing time was (12.1±2.5) months in the flexible fixation group and was (11.3±3.2) months in the rigid fixation group, showing no significant difference between 2 groups ( t =1.024, P =0.192). Reduction loss occurred after removal of screw in 2 cases of the rigid fixation group. At last follow-up, there was no significant difference in MCS, TFCS, TFO, AOFAS score and FADI score between 2 groups ( P >0.05). Suture-button fixation has similar effectiveness to screw fixation in ankle function and imaging findings, and flexible fixation has lower risk of reduction loss of distal tibiofibular syndesmosis than rigid fixation.

Comparison of Monolateral External Fixation and Internal Fixation for Skeletal Stabilisation in the Management of Small Tibial Bone Defects following Successful Treatment of Chronic Osteomyelitis.

PubMed

Wang, Yicun; Jiang, Hui; Deng, Zhantao; Jin, Jiewen; Meng, Jia; Wang, Jun; Zhao, Jianning; Sun, Guojing; Qian, Hongbo

2017-01-01

To compare the salvage rate and complication between internal fixation and external fixation in patients with small bone defects caused by chronic infectious osteomyelitis debridement. 125 patients with chronic infectious osteomyelitis of tibia fracture who underwent multiple irrigation, debridement procedure, and local/systemic antibiotics were enrolled. Bone defects, which were less than 4 cm, were treated with bone grafting using either internal fixation or monolateral external fixation. 12-month follow-up was conducted with an interval of 3 months to evaluate union of bone defect. Patients who underwent monolateral external fixation had higher body mass index and fasting blood glucose, longer time since injury, and larger bone defect compared with internal fixation. No significant difference was observed in incidence of complications (23.5% versus 19.3%), surgery time (156 ± 23 minutes versus 162 ± 21 minutes), and time to union (11.1 ± 3.0 months versus 10.9 ± 3.1 months) between external fixation and internal fixation. Internal fixation had no significant influence on the occurrence of postoperation complications after multivariate adjustment when compared with external fixation. Furthermore, patients who underwent internal fixation experienced higher level of daily living scales and lower level of anxiety. It was relatively safe to use internal fixation for stabilization in osteomyelitis patients whose bone defects were less than 4 cm and infection was well controlled.

Comparison of Monolateral External Fixation and Internal Fixation for Skeletal Stabilisation in the Management of Small Tibial Bone Defects following Successful Treatment of Chronic Osteomyelitis

PubMed Central

Wang, Yicun; Jiang, Hui; Deng, Zhantao; Meng, Jia; Wang, Jun

2017-01-01

Background To compare the salvage rate and complication between internal fixation and external fixation in patients with small bone defects caused by chronic infectious osteomyelitis debridement. Methods 125 patients with chronic infectious osteomyelitis of tibia fracture who underwent multiple irrigation, debridement procedure, and local/systemic antibiotics were enrolled. Bone defects, which were less than 4 cm, were treated with bone grafting using either internal fixation or monolateral external fixation. 12-month follow-up was conducted with an interval of 3 months to evaluate union of bone defect. Results Patients who underwent monolateral external fixation had higher body mass index and fasting blood glucose, longer time since injury, and larger bone defect compared with internal fixation. No significant difference was observed in incidence of complications (23.5% versus 19.3%), surgery time (156 ± 23 minutes versus 162 ± 21 minutes), and time to union (11.1 ± 3.0 months versus 10.9 ± 3.1 months) between external fixation and internal fixation. Internal fixation had no significant influence on the occurrence of postoperation complications after multivariate adjustment when compared with external fixation. Furthermore, patients who underwent internal fixation experienced higher level of daily living scales and lower level of anxiety. Conclusions It was relatively safe to use internal fixation for stabilization in osteomyelitis patients whose bone defects were less than 4 cm and infection was well controlled. PMID:29333448

Comparison of screw fixation with elastic fixation methods in the treatment of syndesmosis injuries in ankle fractures.

PubMed

Seyhan, Mustafa; Donmez, Ferdi; Mahirogullari, Mahir; Cakmak, Selami; Mutlu, Serhat; Guler, Olcay

2015-07-01

17 patients with ankle syndesmosic injury were treated with a 4.5mm single cortical screw fixation (passage of screw 4 cortices) and 15 patients were treated with single-level elastic fixation material. All patients were evaluated according to the AOFAS ankle and posterior foot scale at the third, sixth and twelfth months after the fixation. The ankle range of movement was recorded together with the healthy side. The Student's t test was used for statistical comparisons. No statistical significant difference was observed between the AOFAS scores (p>0.05). The range of dorsiflexion and plantar flexion motion of the elastic fixation group at the 6th and 12th months were significantly better compared to the screw fixation group (p<0.01). Elastic fixation is as functional as screw fixation in the treatment of ankle syndesmosis injuries. The unnecessary need of a second surgical intervention for removal of the fixation material is another advantageous aspect of this method of fixation. Copyright © 2015. Published by Elsevier Ltd.

A Subconscious Interaction between Fixation and Anticipatory Pursuit

PubMed Central

Bal, Japjot; Heinen, Stephen J.

2017-01-01

Ocular smooth pursuit and fixation are typically viewed as separate systems, yet there is evidence that the brainstem fixation system inhibits pursuit. Here we present behavioral evidence that the fixation system modulates pursuit behavior outside of conscious awareness. Human observers (male and female) either pursued a small spot that translated across a screen, or fixated it as it remained stationary. As shown previously, pursuit trials potentiated the oculomotor system, producing anticipatory eye velocity on the next trial before the target moved that mimicked the stimulus-driven velocity. Randomly interleaving fixation trials reduced anticipatory pursuit, suggesting that a potentiated fixation system interacted with pursuit to suppress eye velocity in upcoming pursuit trials. The reduction was not due to passive decay of the potentiated pursuit signal because interleaving “blank” trials in which no target appeared did not reduce anticipatory pursuit. Interspersed short fixation trials reduced anticipation on long pursuit trials, suggesting that fixation potentiation was stronger than pursuit potentiation. Furthermore, adding more pursuit trials to a block did not restore anticipatory pursuit, suggesting that fixation potentiation was not overridden by certainty of an imminent pursuit trial but rather was immune to conscious intervention. To directly test whether cognition can override fixation suppression, we alternated pursuit and fixation trials to perfectly specify trial identity. Still, anticipatory pursuit did not rise above that observed with an equal number of random fixation trials. The results suggest that potentiated fixation circuitry interacts with pursuit circuitry at a subconscious level to inhibit pursuit. SIGNIFICANCE STATEMENT When an object moves, we view it with smooth pursuit eye movements. When an object is stationary, we view it with fixational eye movements. Pursuit and fixation are historically regarded as controlled by different neural circuitry, and alternating between invoking them is thought to be guided by a conscious decision. However, our results show that pursuit is actively suppressed by prior fixation of a stationary object. This suppression is involuntary, and cannot be avoided even if observers are certain that the object will move. The results suggest that the neural fixation circuitry is potentiated by engaging stationary objects, and interacts with pursuit outside of conscious awareness. PMID:29061701

A Subconscious Interaction between Fixation and Anticipatory Pursuit.

PubMed

Watamaniuk, Scott N J; Bal, Japjot; Heinen, Stephen J

2017-11-22

Ocular smooth pursuit and fixation are typically viewed as separate systems, yet there is evidence that the brainstem fixation system inhibits pursuit. Here we present behavioral evidence that the fixation system modulates pursuit behavior outside of conscious awareness. Human observers (male and female) either pursued a small spot that translated across a screen, or fixated it as it remained stationary. As shown previously, pursuit trials potentiated the oculomotor system, producing anticipatory eye velocity on the next trial before the target moved that mimicked the stimulus-driven velocity. Randomly interleaving fixation trials reduced anticipatory pursuit, suggesting that a potentiated fixation system interacted with pursuit to suppress eye velocity in upcoming pursuit trials. The reduction was not due to passive decay of the potentiated pursuit signal because interleaving "blank" trials in which no target appeared did not reduce anticipatory pursuit. Interspersed short fixation trials reduced anticipation on long pursuit trials, suggesting that fixation potentiation was stronger than pursuit potentiation. Furthermore, adding more pursuit trials to a block did not restore anticipatory pursuit, suggesting that fixation potentiation was not overridden by certainty of an imminent pursuit trial but rather was immune to conscious intervention. To directly test whether cognition can override fixation suppression, we alternated pursuit and fixation trials to perfectly specify trial identity. Still, anticipatory pursuit did not rise above that observed with an equal number of random fixation trials. The results suggest that potentiated fixation circuitry interacts with pursuit circuitry at a subconscious level to inhibit pursuit. SIGNIFICANCE STATEMENT When an object moves, we view it with smooth pursuit eye movements. When an object is stationary, we view it with fixational eye movements. Pursuit and fixation are historically regarded as controlled by different neural circuitry, and alternating between invoking them is thought to be guided by a conscious decision. However, our results show that pursuit is actively suppressed by prior fixation of a stationary object. This suppression is involuntary, and cannot be avoided even if observers are certain that the object will move. The results suggest that the neural fixation circuitry is potentiated by engaging stationary objects, and interacts with pursuit outside of conscious awareness. Copyright © 2017 the authors 0270-6474/17/3711424-07$15.00/0.

Stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture: a comparative finite element study.

PubMed

Huang, Xiaowei; Zhi, Zhongzheng; Yu, Baoqing; Chen, Fancheng

2015-11-25

The purpose of this study is to compare the stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture. A three-dimensional (3D) finite element model of the medial tibial plateau fracture (Schatzker type IV fracture) was created. An axial force of 2500 N with a distribution of 60% to the medial compartment was applied to simulate the axial compressive load on an adult knee during single-limb stance. The equivalent von Mises stress, displacement of the model relative to the distal tibia, and displacement of the implants were used as the output measures. The mean stress value of the plate-screw fixation system was 18.78 MPa, which was significantly (P < 0.001) smaller than that of the screw fixation system. The maximal value of displacement (sum) in the plate-screw fixation system was 2.46 mm, which was lower than that in the screw fixation system (3.91 mm). The peak stress value of the triangular fragment in the plate-screw fixation system model was 42.04 MPa, which was higher than that in the screw fixation model (24.18 MPa). But the mean stress of the triangular fractured fragment in the screw fixation model was significantly higher in terms of equivalent von Mises stress (EVMS), x-axis, and z-axis (P < 0.001). This study demonstrated that the load transmission mechanism between plate-screw fixation system and screw fixation system was different and the stability provided by the plate-screw fixation system was superior to the screw fixation system.

Comparison of effects of seven treatment methods for distal radius fracture on minimizing complex regional pain syndrome

PubMed Central

Sun, Tao

2016-01-01

Introduction Using network meta-analysis, we evaluated the adverse effects of the seven most common treatment methods, i.e., bridging external fixation, non-bridging external fixation, K-wire fixation, plaster fixation, dorsal plating, volar plating, and dorsal and volar plating, by their associated risk of developing complex regional pain syndrome (CRPS) in distal radius fracture (DRF) patients. Material and methods Following an exhaustive search of scientific literature databases for high quality studies, randomized controlled trials (RCTs) related to our study topic were screened and selected based on stringent predefined inclusion and exclusion criteria. Data extracted from the selected studies were used for statistical analyses using Stata 12.0 software. Results A total of 17 RCTs, including 1658 DRF patients, were enrolled in this network meta-analysis. Among the 1658 DRF patients, 452 received bridging external fixation, 525 received non-bridging external fixation, 154 received K-wire fixation, 84 received plaster fixation, 132 received dorsal plating, 123 received volar plating, and 188 received dorsal and volar plating. When compared to bridging external fixation patients, there was no marked difference in the CRPS risk in DRF patients receiving different treatments (all p > 0.05). However, the surface under the cumulative ranking curves (SUCRA) for plaster fixation (77.0%) and non-bridging external fixation (71.3%) were significantly higher compared with the other five methods. Conclusions Our findings suggest that compared with bridging external fixation, K-wire fixation, dorsal plating, volar plating, dorsal and volar plating, plaster fixation and non-bridging external fixation might be the better treatment methods to reduce the risk of CRPS in DRF patients. PMID:28144268

Measurements of stratospheric NO, NO2, and N2O5 by ISAMS: Preliminary observations and data validation

NASA Technical Reports Server (NTRS)

Kerridge, Brian J.; Ballard, J.; Knight, R. J.; Stevens, A. D.; Reburn, J.; Morris, P.; Remedios, John J.; Taylor, Fredric W.

1994-01-01

The Improved Stratospheric and Mesospheric Sounder (ISAMS) is a multichannel radiometer and forms part of the science payload of the Upper Atmosphere Research Satellite (UARS). ISAMS measures infrared emissions from the Earth's atmosphere in several wavelength bands. Three such bands include emission from nitric oxide, nitrogen dioxide, and dinitrogen pentoxide. In this paper, we briefly discuss how the ISAMS instrument measures NO, NO2, and N2O5. We also present preliminary data from these channels and describe preliminary validation work.

A New Method for the Production of Tetranitroglycoluril From Imidazo-[4,5-d]-Imidazoles With the Loss of Dinitrogen Oxide

DTIC Science & Technology

2014-02-01

reactions over time. ............................................8 List of Tables Table 1. Performance predictions from Cheetah 7.0...making it a highly desirable target (table 1). 3 Table 1. Performance predictions from Cheetah 7.0 (4). Substance ρa ∆Hf (kJ/mol) Pcjd (GPa) Dv e (km...HMXc 1.90 75.02 37.19 9.246 11.00 –21.61 aDensity. bPredicted using the methods of Rice (10–14). c∆Hf and density numbers obtained from Cheetah 7.0

Comment on “Observations of ammonia, nitric acid, and fine particles in a rural gas production region” by Yi Li, Florian M. Schwandnera, H. James Sewell, Angela Zivkovich, Mark Tigges, Suresh Raja, Stephen Holcomb, John V. Molenar, Lincoln Sherman, Cassie Archuleta, Taehyoung Lee and Jeffrey L. Collett Jr. Atmospheric Environment (in press)

NASA Astrophysics Data System (ADS)

Phillips, Gavin J.

2014-05-01

An artefact of the detection of nitric acid (HNO3) by denuder methods is discussed. This artefact arises from the likely reaction of dinitrogen pentoxide (N2O5) on the denuder train resulting in the report of some fraction of N2O5 as HNO3.

Potential role of the nitroacidium ion on HONO emissions from the snowpack.

PubMed

Hellebust, Stig; Roddis, Tristan; Sodeau, John R

2007-02-22

The effects of photolysis on frozen, thin films of water-ice containing nitrogen dioxide (as its dimer dinitrogen tetroxide) have been investigated using a combination of Fourier transform reflection-absorption infrared (FT-RAIR) spectroscopy and mass spectrometry. The release of HONO is ascribed to a mechanism in which nitrosonium nitrate (NO+NO3-) is formed. Subsequent solvation of the cation leads to the nitroacidium ion, H2ONO+, i.e., protonated nitrous acid. The pathway proposed explains why the field measurement of HONO at different polar sites is often contradictory.

Nitric Oxide--Some Old and New Perspectives

NASA Astrophysics Data System (ADS)

Ainscough, Eric W.; Brodie, Andrew M.

1995-08-01

The discovery and early use of NO is recalled followed by some of its chemical reactions to give useful products such as nitric acid and fertilizers. However NO produced from the internal combustion engine results in photochemical smog production and ozone depletion. A rebirth of interest in NO has occurred because of its unexpected roles in physiology and neurobiology. Its production can lead to biological responses such as vasodilation, cell adhesion, neurotransmission and immune regulation. Finally the ways denitrifying bacteria convert NO and other oxides of nitrogen to dinitrogen are discussed.

Recent advances in fixation of the craniomaxillofacial skeleton.

PubMed

Meslemani, Danny; Kellman, Robert M

2012-08-01

Fixation of the craniomaxillofacial skeleton is an evolving aspect for facial plastic, oral and maxillofacial, and plastic surgery. This review looks at the recent advances that aid in reduction and fixation of the craniomaxillofacial skeleton. More surgeons are using resorbable plates for craniomaxillofacial fixation. A single miniplate on the inferior border of the mandible may be sufficient to reduce and fixate an angle fracture. Percutaneous K-wires may assist in plating angle fractures. Intraoperative computed tomography (CT) may prove to be useful for assessing reduction and fixation. Resorbable plates are becoming increasingly popular in orthognathic surgery and facial trauma surgery. There are newer operative techniques for fixating the angle of the mandible. Also, the utilization of the intraoperative CT provides immediate feedback for accurate reduction and fixation. Prebent surgical plates save operative time, decrease errors, and provide more accurate fixation.

Time Savings and Surgery Task Load Reduction in Open Intraperitoneal Onlay Mesh Fixation Procedure.

PubMed

Roy, Sanjoy; Hammond, Jeffrey; Panish, Jessica; Shnoda, Pullen; Savidge, Sandy; Wilson, Mark

2015-01-01

This study assessed the reduction in surgeon stress associated with savings in procedure time for mechanical fixation of an intraperitoneal onlay mesh (IPOM) compared to a traditional suture fixation in open ventral hernia repair. Nine general surgeons performed 36 open IPOM fixation procedures in porcine model. Each surgeon conducted two mechanical (using ETHICON SECURESTRAP ™ Open) and two suture fixation procedures. Fixation time was measured using a stopwatch, and related surgeon stress was assessed using the validated SURG-TLX questionnaire. T-tests were used to compare between-group differences, and a two-sided 95% confidence interval for the difference in stress levels was established using nonparametric methodology. The mechanical fixation group demonstrated an 89.1% mean reduction in fixation time, as compared to the suture group (p < 0.00001). Surgeon stress scores measured using SURG-TLX were 55.5% lower in the mechanical compared to the suture fixation group (p < 0.001). Scores in five of the six sources of stress were significantly lower for mechanical fixation. Mechanical fixation with ETHICON SECURESTRAP ™ Open demonstrated a significant reduction in fixation time and surgeon stress, which may translate into improved operating efficiency, improved performance, improved surgeon quality of life, and reduced overall costs of the procedure.

Time Savings and Surgery Task Load Reduction in Open Intraperitoneal Onlay Mesh Fixation Procedure

PubMed Central

Roy, Sanjoy; Hammond, Jeffrey; Panish, Jessica; Shnoda, Pullen; Savidge, Sandy; Wilson, Mark

2015-01-01

Background. This study assessed the reduction in surgeon stress associated with savings in procedure time for mechanical fixation of an intraperitoneal onlay mesh (IPOM) compared to a traditional suture fixation in open ventral hernia repair. Study Design. Nine general surgeons performed 36 open IPOM fixation procedures in porcine model. Each surgeon conducted two mechanical (using ETHICON SECURESTRAPTM Open) and two suture fixation procedures. Fixation time was measured using a stopwatch, and related surgeon stress was assessed using the validated SURG-TLX questionnaire. T-tests were used to compare between-group differences, and a two-sided 95% confidence interval for the difference in stress levels was established using nonparametric methodology. Results. The mechanical fixation group demonstrated an 89.1% mean reduction in fixation time, as compared to the suture group (p < 0.00001). Surgeon stress scores measured using SURG-TLX were 55.5% lower in the mechanical compared to the suture fixation group (p < 0.001). Scores in five of the six sources of stress were significantly lower for mechanical fixation. Conclusions. Mechanical fixation with ETHICON SECURESTRAPTM Open demonstrated a significant reduction in fixation time and surgeon stress, which may translate into improved operating efficiency, improved performance, improved surgeon quality of life, and reduced overall costs of the procedure. PMID:26240834

Salient in space, salient in time: Fixation probability predicts fixation duration during natural scene viewing.

PubMed

Einhäuser, Wolfgang; Nuthmann, Antje

2016-09-01

During natural scene viewing, humans typically attend and fixate selected locations for about 200-400 ms. Two variables characterize such "overt" attention: the probability of a location being fixated, and the fixation's duration. Both variables have been widely researched, but little is known about their relation. We use a two-step approach to investigate the relation between fixation probability and duration. In the first step, we use a large corpus of fixation data. We demonstrate that fixation probability (empirical salience) predicts fixation duration across different observers and tasks. Linear mixed-effects modeling shows that this relation is explained neither by joint dependencies on simple image features (luminance, contrast, edge density) nor by spatial biases (central bias). In the second step, we experimentally manipulate some of these features. We find that fixation probability from the corpus data still predicts fixation duration for this new set of experimental data. This holds even if stimuli are deprived of low-level images features, as long as higher level scene structure remains intact. Together, this shows a robust relation between fixation duration and probability, which does not depend on simple image features. Moreover, the study exemplifies the combination of empirical research on a large corpus of data with targeted experimental manipulations.

The comparative risk of developing postoperative complications in patients with distal radius fractures following different treatment modalities

PubMed Central

Qiu, Wen-Jun; Li, Yi-Fan; Ji, Yun-Han; Xu, Wei; Zhu, Xiao-Dong; Tang, Xian-Zhong; Zhao, Huan-Li; Wang, Gui-Bin; Jia, Yue-Qing; Zhu, Shi-Cai; Zhang, Feng-Fang; Liu, Hong-Mei

2015-01-01

In this study, we performed a network meta-analysis to compare the outcomes of seven most common surgical procedures to fix DRF, including bridging external fixation, non-bridging external fixation, K-wire fixation, plaster fixation, dorsal plating, volar plating, and dorsal and volar plating. Published studies were retrieved through PubMed, Embase and Cochrane Library databases. The database search terms used were the following keywords and MeSH terms: DRF, bridging external fixation, non-bridging external fixation, K-wire fixation, plaster fixation, dorsal plating, volar plating, and dorsal and volar plating. The network meta-analysis was performed to rank the probabilities of postoperative complication risks for the seven surgical modalities in DRF patients. This network meta-analysis included data obtained from a total of 19 RCTs. Our results revealed that compared to DRF patients treated with bridging external fixation, marked differences in pin-track infection (PTI) rate were found in patients treated with plaster fixation, volar plating, and dorsal and volar plating. Cluster analysis showed that plaster fixation is associated with the lowest probability of postoperative complication in DRF patients. Plaster fixation is associated with the lowest risk for postoperative complications in DRF patients, when compared to six other common DRF surgical methods examined. PMID:26549312

When do anterior external or internal fixators provide additional stability in an unstable (Tile C) pelvic fracture? A biomechanical study.

PubMed

Mcdonald, E; Theologis, A A; Horst, P; Kandemir, U; Pekmezci, M

2015-12-01

This study aimed at evaluating the additional stability that is provided by anterior external and internal fixators in an unstable pelvic fracture model (OTA 61-C). An unstable pelvic fracture (OTA 61-C) was created in 27 synthetic pelves by making a 5-mm gap through the sacral foramina (posterior injury) and an ipsilateral pubic rami fracture (anterior injury). The posterior injury was fixed with either a single iliosacral (IS) screw, a single trans-iliac, trans-sacral (TS) screw, or two iliosacral screws (S1S2). Two anterior fixation techniques were utilized: external fixation (Ex-Fix) and supra-acetabular external fixation and internal fixation (In-Fix); supra-acetabular pedicle screws connected with a single subcutaneous spinal rod. The specimens were tested using a nondestructive single-leg stance model. Peak-to-peak (P2P) displacement and rotation and conditioning displacement (CD) were calculated. The Ex-Fix group failed in 83.3 % of specimens with concomitant single-level posterior fixation (Total: 15/18-7 of 9 IS fixation, 8 of 9 TS fixation), and 0 % (0/9) of specimens with concomitant two-level (S1S2) posterior fixation. All specimens with the In-Fix survived testing except for two specimens treated with In-Fix combined with IS fixation. Trans-sacral fixation had higher pubic rotation and greater sacral and pubic displacement than S1S2 (p < 0.05). Rotation of the pubis and sacrum was not different between In-Fix constructs combined with single-level IS and TS fixation. In this model of an unstable pelvic fracture (OTA 61-C), anterior fixation with an In-Fix was biomechanically superior to an anterior Ex-Fix in the setting of single-level posterior fixation. There was no biomechanical difference between the In-Fix and Ex-Fix when each was combined with two levels of posterior sacral fixation.

Comparison of stability of different types of external fixation.

PubMed

Grubor, Predrag; Grubor, Milan; Asotic, Mithat

2011-01-01

Stabilization of fractures by external fixator is based on the mechanical connecting of the pins, screwed into the proximal and distal bone fragment. Site of fracture is left without any foreign materials, which is essential for prevention of infections. Aim of this work is to compare stability of constructs bone model-external fixators of different types (Ortofix, Mitković, Charneley and Ilizarov). Stability is estimated under compression and bending (vertical and horizontal forces of 100 kg magnitudes, with distances between pins of4 cm). The mathematical-computer software (Tower, Planet and Planet Pro) was used in the laboratory for accurate measurements of MDP "Jelsingrad" company, Banjaluka. Interfragmental motions in millimeters at the appliance of vertical and horizontal forces were 2.80/2.56 at Ortofix (uniplanar fixator), 1.57/1.56 and fixator by Mitković-M20 (uniplanar fixator with convergent oriented pins), 0.16/0.28 at Charnely's external fixator (biplanar fixator), and 4.49/0.114 mm at Ilizarov's external fixator (fixator with two proximal and two distal rings, each attached on the 6 Kirschner wires). It has confirmed that uniplanar fixation is easier and provides sufficient biomechanics circumstances in the site of fracture for bone healing, especially if the pins are oriented convergently. Ilizarov's fixator is multiplanar fixator, but its stability is dependent of tightness of wires, and provides adequate stability only in transversal plane. By other words, each fixator has its indications; selection of the fixator should be based on theirs mechanic characteristics, fracture geometry, and potential of bone healing, with permanent simplification of treatment, which has to be safe and acceptable for the patient. The main advantage of this study is Sits nature-the comparison of four most used external fixators, by the only one possible way-on the bone model. Each other way of comparison would result with much more questions than answers, due to unacceptable high bias of other parameters, which significantly influences on the results of the study.

Ocular Fixation Abnormality in Patients with Autism Spectrum Disorder

ERIC Educational Resources Information Center

Shirama, Aya; Kanai, Chieko; Kato, Nobumasa; Kashino, Makio

2016-01-01

We examined the factors that influence ocular fixation control in adults with autism spectrum disorder (ASD) including sensory information, individuals' motor characteristics, and inhibitory control. The ASD group showed difficulty in maintaining fixation especially when there was no fixation target. The fixational eye movement characteristics of…

Hot topics and controversies in arthroplasty: cementless femoral fixation in elderly patients.

PubMed

Dutton, Andrew; Rubash, Harry E

2008-01-01

Cementless femoral fixation has been established as the gold standard for hip arthroplasty in young patients because of its exceptional longevity. Because older Americans are living longer and staying active, cementless femoral fixation for hip arthroplasty should be considered in all patients who have good bone quality. Numerous studies have shown excellent results using cementless fixation for hip arthroplasty in elderly patients. Histologic analysis, radiographic review, and dual-energy x-ray absorptiometry have shown solid osseointegration for biologic fixation and minimal bone loss. Cementless fixation provides superb functional outcomes with results comparable to those achieved using cemented fixation for hip arthroplasty. Additional advantages of cementless femoral fixation include shorter surgical times and substantial savings in health care costs.

Fixation Characteristics of Severe Amblyopia Subtypes: Which One is Worse?

PubMed

Koylu, Mehmet Talay; Ozge, Gokhan; Kucukevcilioglu, Murat; Mutlu, Fatih Mehmet; Ceylan, Osman Melih; Akıncıoglu, Dorukcan; Ayyıldız, Onder

2017-01-01

To determine differences in macular sensitivity and fixation patterns in different subtypes of severe amblyopia. This case-control study enrolled a total of 73 male adults, including 18 with pure strabismic severe amblyopia, 19 with pure anisometropic severe amblyopia, 18 with mixed (strabismic plus anizometropic) severe amblyopia, and 18 healthy controls. MP-1 microperimetry was used to evaluate macular sensitivity, location of fixation, and stability of fixation. Mean macular sensitivity, stability of fixation, and location of fixation were significantly worse in all amblyopia subtypes when compared with healthy controls. Intergroup comparisons between amblyopia subtypes revealed that mean macular sensitivity, stability of fixation, and location of fixation were significantly worse in pure strabismic and mixed amblyopic eyes when compared with pure anisometropic amblyopic eyes. Strabismus seems to be a worse prognostic factor in severe amblyopia than anisometropia in terms of fixation characteristics and retinal sensitivity.

An oculomotor continuum from exploration to fixation

PubMed Central

Otero-Millan, Jorge; Macknik, Stephen L.; Langston, Rachel E.; Martinez-Conde, Susana

2013-01-01

During visual exploration, saccadic eye movements scan the scene for objects of interest. During attempted fixation, the eyes are relatively still but often produce microsaccades. Saccadic rates during exploration are higher than those of microsaccades during fixation, reinforcing the classic view that exploration and fixation are two distinct oculomotor behaviors. An alternative model is that fixation and exploration are not dichotomous, but are instead two extremes of a functional continuum. Here, we measured the eye movements of human observers as they either fixed their gaze on a small spot or scanned natural scenes of varying sizes. As scene size diminished, so did saccade rates, until they were continuous with microsaccadic rates during fixation. Other saccadic properties varied as function of image size as well, forming a continuum with microsaccadic parameters during fixation. This saccadic continuum extended to nonrestrictive, ecological viewing conditions that allowed all types of saccades and fixation positions. Eye movement simulations moreover showed that a single model of oculomotor behavior can explain the saccadic continuum from exploration to fixation, for images of all sizes. These findings challenge the view that exploration and fixation are dichotomous, suggesting instead that visual fixation is functionally equivalent to visual exploration on a spatially focused scale. PMID:23533278

Effectiveness of external fixator combined with T-plate internal fixation for the treatment of comminuted distal radius fractures.

PubMed

Han, L R; Jin, C X; Yan, J; Han, S Z; He, X B; Yang, X F

2015-03-31

This study compared the efficacy between external fixator combined with palmar T-plate internal fixation and simple plate internal fixation for the treatment of comminuted distal radius fractures. A total of 61 patients classified as type C according to the AO/ASIF classification underwent surgery for comminuted distal radius fractures. There were 54 and 7 cases of closed and open fractures, respectively. Moreover, 19 patients received an external fixator combined with T-plate internal fixation, and 42 received simple plate internal fixation. All patients were treated successfully during 12-month postoperative follow-up. The follow-up results show that the palmar flexion and dorsiflexion of the wrist, radial height, and palmar angle were significantly better in those treated with the external fixator combined with T-plate compared to those treated with the simple plate only (P < 0.05); however, there were no significant differences in radial-ulnar deviation, wrist range of motion, or wrist function score between groups (P > 0.05). Hence, the effectiveness of external fixator combined with T-plate internal fixation for the treatment of comminuted distal radius fractures was satisfactory. Patients sufficiently recovered wrist, forearm, and hand function. In conclusion, compared to the simple T-plate, the external fixator combined with T-plate internal fixation can reduce the possibility of the postoperative re-shifting of broken bones and keep the distraction of fractures to maintain radial height and prevent radial shortening.

[Complications of open reduction and internal fixation versus external fixation for unstable distal radius fractures: a meta-analysis].

PubMed

Yang, Z; Yuan, Z Z; Ma, J X; Ma, X L

2016-12-20

Objective: To make a systematic assessment of the complications of open reduction and internal fixation versus external fixation for unstable distal radius fractures. Method: A computer-based online search of PubMed, ScienceDirect, EMBASE, BIOSIS, Springer and Cochrane Library were performed.The randomized and controlled trials of open reduction and internal fixation versus external fixation for unstable distal radius fractures were collected.The included trials were screened out strictly based on the criterion of inclusion and exclusion.The quality of included trials was evaluated.RevMan 5.0 was used for data analysis. Result: A total of 17 studies involving 1 402 patients were included.There were 687 patients with open reduction and internal fixation and 715 with external fixation.The results of Meta-analysis indicated that there were statistically significant differences with regard to the postoperatively total complications, infection, malunion, tendon rupture ( I 2 =8%, RR =0.77(95% CI 0.65-0.91, Z =3.10, P <0.05). There were no statistically significant differences observed between two approaches with respect to nounion, re-operation, complex regional pain syndrome, carpal tunnel syndrome, neurapraxia, tendonitis, painful hardware, scar( P >0.05). Conclusion: Postoperative complications are present in both open reduction and internal fixation and external fixation.Compared with external fixation, open reduction and internal fixation is lower in total complications postoperatively, infection and malunion, but external fixation has lower tendon rupture incidence.

An ex vivo mechanical evaluation of single versus double semitubular plate fixation of a transverse distal-third scapular osteotomy in the dog.

PubMed

Mair, Jacqueline J; Belkoff, Stephen M; Boudrieau, Randy J

2003-01-01

To compare single versus double semitubular plate fixation for scapular body fractures. Ex vivo mechanical study. Eighteen paired cadaveric canine scapulae. Transverse scapular body osteotomies were created in the distal third of 18 pairs of scapulae. One scapula of each pair was repaired with a single plate, whereas the contralateral scapula was repaired with 2 plates. Initial strength and stiffness of the constructs were measured in 10 pairs of scapulae. Eight pairs of scapulae underwent cyclic loading and then were subjected to failure testing. Double-plate fixation was significantly stronger (3,899 +/- 632 N) but not stiffer (614 +/- 130 N/mm) than the single-plate fixation (3,238 +/- 935 N and 537 +/- 202 N/mm, respectively). Cyclic loading variables were not significantly different between the 2 methods of fixation. After cyclic loading, double-plate fixation was significantly stronger (2,916 +/- 618 N) than single-plate fixation (2,347 +/- 495 N). There was no significant difference (P =.11) in stiffness between double- versus single-plate fixations: 734 +/- 247 N/mm and 595 +/- 139 N/mm, respectively. Double-plate fixation was generally stronger and stiffer than single-plate fixation. Because all constructs failed at loads that greatly exceeded those estimated to occur clinically, any difference between the 2 methods of fixation probably is not clinically relevant. Single-plate fixation may be of sufficient strength for fixation of scapular body fractures. Copyright 2003 by The American College of Veterinary Surgeons

Screw fixation versus arthroplasty versus plate fixation for 3-part radial head fractures.

PubMed

Wu, P H; Shen, L; Chee, Y H

2016-04-01

To compare the outcome following headless compression screw fixation versus radial head arthroplasty versus plate fixation for 3-part Mason types III or IV radial head fracture. Records of 25 men and 16 women aged 21 to 80 (mean, 43.3) years who underwent fixation using 2 to 3 2-mm cannulated headless compression screws (n=16), radial head arthroplasty (n=13), or fixation with a 2-mm Synthes plate (n=12) for 3-part Mason types III or IV radial head and neck fracture were reviewed. Treatment option was decided by the surgeon based on the presence of associated injury, neurovascular deficit, and the Mason classification. Bone union, callus formation, and complications (such as heterotopic ossification, malunion, and nonunion) were assessed by an independent registrar or consultant using radiographs. The Mayo Elbow Performance Score and range of motion were assessed by an independent physiotherapist. The median age of the 3 groups were comparable. Associated injuries were most common in patients with arthroplasty, followed by screw fixation and plate fixation (61.5% vs. 50% vs. 33%, p=0.54). The median time to bone union was shorter after screw fixation than plate fixation (55 vs. 86 days, p=0.05). No patient with screw fixation had nonunion, but 4 patients with plate fixation had nonunion. The 3 groups were comparable in terms of the mean Mayo Elbow Performance Score (p=0.56) and the mean range of motion (p=0.45). The complication rate was highest after plate fixation, followed by screw fixation and arthroplasty (50% vs. 18.8% vs. 15.4%, p=0.048). Excluding 20 patients with associated injuries (8 in screw fixation, 8 in arthroplasty, and 4 in plate fixation), the 3 groups were comparable in terms of the median time to bone union (p=0.109), mean Mayo Elbow Performance Score (p=0.260), mean range of motion (p=0.162), and complication rate (p=0.096). Headless compression screw fixation is a viable option for 3-part radial head fracture. It achieves earlier bone union with fewer complications.

Plate versus intramedullary fixation of two-part and multifragmentary displaced midshaft clavicle fractures - a long-term analysis.

PubMed

Chan, Gareth; Korac, Zelimir; Miletic, Matija; Vidovic, Dinko; Phadnis, Joideep; Bakota, Bore

2017-11-01

Surgical fixation of displaced midshaft clavicle fractures is predominantly achieved with intramedullary (IM) or plate fixation. Both techniques have potential pitfalls: plate fixation involves greater periosteal stripping and protuberance of the implant, whereas IM fixation may be associated with implant-related complications, such as migration or skin irritation, which may lead to further surgery for implant removal. The aim of this study was to compare these two methods in simple (Robinson 2b.1) and multifragmentary (Robinson 2b.2) displaced midshaft clavicle fractures. A total of 133 consecutive patients who underwent surgical fixation for a displaced midshaft clavicle fracture with either IM fixation using a 2.5-mm Kirschner wire or plate fixation using an 8-hole Dynamic Compression Plate (DCP) were retrospectively reviewed. Follow-up was a minimum of 1 year. The patients were allocated into two injury groups: displaced simple 2-part fractures (64 IM vs. 16 DCP) and displaced multifragmentary fractures (27 IM vs. 26 DCP). The major observed outcome measures were: infection rate, non-union rate, reoperation rate and postoperative range of motion (ROM). Rates of non-union for displaced 2-part fractures were 2/64 (3.13%) with IM fixation and 0/16 (0.00%) with plate fixation (p = 0.477). For displaced multifragmentary fractures, rates of non-union were 2/27 (7.41%) with IM fixation and 0/26 (0.00%) with plate fixation (p = 0.161). No significant difference was observed between the two fixation modalities in patient-reported time to regain ROM on the injured side for displaced 2-part fractures (p = 0.129) and displaced multifragmentary fractures (p = 0.070). Deep infection rate was zero (p = 1.000) overall in the study, and reoperation rate for IM and plate fixation, respectively, was 3.13% and 6.25% in the Robinson 2b.1 group (p = 0.559) and 7.41% and 7.69% in the Robinson 2b.2 group (p = 0.969). IM fixation of displaced midshaft clavicle fractures (Robinson 2b.1) has an equivalent non-union rate to plate fixation and similarly low complication and reoperation rates. For displaced midshaft multifragmentary clavicle fractures (Robinson 2b.2), the higher non-union rates observed with IM fixation leads us to recommend consideration of plate fixation for Robinson 2b.2 fractures. © 2017 Elsevier Ltd. All rights reserved.

Elevated temperature alters proteomic responses of individual organisms within a biofilm community

DOE PAGES

Mosier, Annika C.; Li, Zhou; Thomas, Brian C.; ...

2014-07-22

Microbial communities that underpin global biogeochemical cycles will likely be influenced by elevated temperature associated with environmental change. In this paper, we test an approach to measure how elevated temperature impacts the physiology of individual microbial groups in a community context, using a model microbial-based ecosystem. The study is the first application of tandem mass tag (TMT)-based proteomics to a microbial community. We accurately, precisely and reproducibly quantified thousands of proteins in biofilms growing at 40, 43 and 46 °C. Elevated temperature led to upregulation of proteins involved in amino-acid metabolism at the level of individual organisms and the entiremore » community. Proteins from related organisms differed in their relative abundance and functional responses to temperature. Elevated temperature repressed carbon fixation proteins from two Leptospirillum genotypes, whereas carbon fixation proteins were significantly upregulated at higher temperature by a third member of this genus. Leptospirillum group III bacteria may have been subject to viral stress at elevated temperature, which could lead to greater carbon turnover in the microbial food web through the release of viral lysate. Finally, overall, these findings highlight the utility of proteomics-enabled community-based physiology studies, and provide a methodological framework for possible extension to additional mixed culture and environmental sample analyses.« less

Whole blood staining in suspension for nonspecific esterase and alkaline phosphatase analyzed with a Technicon H-1.

PubMed

Ross, D W; Bishop, C; Henderson, A; Kaplow, L

1990-01-01

We adapted previously published methods for nonspecific esterase and alkaline phosphatase staining of white blood cells in suspension for use on a Technicon H-1 hematology analyzer. The objective was to develop a semiautomated method using whole blood that could be employed on a large scale for hematology laboratory applications, including toxicology studies, measurement of neutrophil left shift, and cytochemical classification of myeloid leukemias. The nonspecific esterase method uses the pararosaniline stain, generating the unstable substrate from two stable precursors. Whole blood is added to the substrate plus dye mix. Next, acid lysis and fixation steps destroy red cells and stabilize the monocyte staining. The alkaline phosphatase stain employs a stable naphthyl phosphate substrate and fast blue B coupling dye. The red cells are lysed with a pH 10.3 propanediol buffer, and the white blood cells are then stabilized with formalin fixation. For both methods the staining is performed off-line, and the sample is then diluted with propanediol to match the refractive index of the sheath on the H-1 analyzer, before aspiration into the direct cytometry port. A cytogram of scattered versus absorbed light is obtained. The number of cells staining and the intensity of the stain can be quantified from the cytogram.

Accuracy and safety verification of ovarian reserve assessment technique for ovarian tissue transplantation using optical coherence tomography in mice ovary

NASA Astrophysics Data System (ADS)

Takae, Seido; Tsukada, Kosuke; Sato, Yorino; Okamoto, Naoki; Kawahara, Tai; Suzuki, Nao

2017-03-01

Except for histological study, there are currently no suitable techniques available for the detection and identification of primordial follicles in ovary of primary ovarian insufficiency patients who have undetectable AMH levels. Also, the ability to locate and quantify follicles on ovarian cortex strips, without fixation, is valuable for patients who could undergo subsequent successful ovarian tissue transplantation. Although optical coherence tomography (OCT) is a well-established high resolution imaging technique without fixation commonly applied in biomedicine, few reports are available on ovarian tissue imaging. In present study, we established standard OCT follicle images at each developmental stage, including the primordial follicle, and demonstrated the efficacy of OCT to estimate IVF outcome in transplanted mice ovary like ovarian reserve tests. Unfortunately, the current commercial OCT could not be used to accurate follicle count the number of follicles for whole ovary, because the maximum depth of examination was 100 μm. And we demonstrated the safety of OCT examination, it did not affect IVF outcome and birth defect rate, and reproductive ability. Although there is room for improvement, these findings will be first step to bring OCT examination a step closer to clinical application for measuring true ovarian reserve and localizing follicles.

A comparative analysis of the effectiveness of active versus passive atrial lead fixation in Chinese patients with cardiac implantable electrical devices: a long term, retrospective, observational, single-center study.

PubMed

Hao, Yinglu; Li, Yanping; Liao, Derong; Yang, Ling; Liu, Fangyan

2017-03-01

Data comparing active atrial lead fixation with passive atrial lead fixation in Chinese patients with cardiovascular implantable electronic devices (CIEDs) for atrial pacing is limited. Our study evaluated the effectiveness of active fixation versus passive fixation of atrial leads by observing the lead performance parameters. This retrospective, long-term, single-center study included a cohort of Chinese patients who underwent CIED implantation at the Department of Cardiology of People's Hospital of Yuxi City, China, from 1 March 2010 to 1 March 2015. Efficacy was determined by comparing implantation time, threshold values, incidence of lead dislocation/failure, and lead-related complications between the two groups. Of the 1217 patients, active and passive atrial lead fixation were performed in 530 (mean age, 69.37 ± 11.44 years) and 497 (mean age, 68.33 ± 10.96 years). The active fixation group reported significantly lower mean atrial implantation times (P = .0001) and threshold values (P = .044) compared with the passive atrial lead fixation group. In addition, threshold values in the active atrial lead fixation group were stable throughout the observation period. No instances of myocardial perforation, cardiac tamponade, implantation failure, or electrode dislocation/re-fixation were reported in the active atrial lead fixation group. A favorable decrease in patient comfort parameters such as bed rest time (P = .027) and duration of hospital stay (P = .038) were also observed in the active lead fixation group. Active atrial lead fixation demonstrated greater stability, steady long-term thresholds and minimal lead-related complications compared to passive lead fixation in Chinese patients with CIEDs.

Relocatable fixation systems in intracranial stereotactic radiotherapy. Accuracy of serial CT scans and patient acceptance in a randomized design.

PubMed

Theelen, A; Martens, J; Bosmans, G; Houben, R; Jager, J J; Rutten, I; Lambin, P; Minken, A W; Baumert, B G

2012-01-01

The goal was to provide a quantitative evaluation of the accuracy of three different fixation systems for stereotactic radiotherapy and to evaluate patients' acceptance for all fixations. A total of 16 consecutive patients with brain tumours undergoing fractionated stereotactic radiotherapy (SCRT) were enrolled after informed consent (Clinical trials.gov: NCT00181350). Fixation systems evaluated were the BrainLAB® mask, with and without custom made bite-block (fixations S and A) and a homemade neck support with bite-block (fixation B) based on the BrainLAB® frame. The sequence of measurements was evaluated in a randomized manner with a cross-over design and patients' acceptance by a questionnaire. The mean three-dimensional (3D) displacement and standard deviations were 1.16 ± 0.68 mm for fixation S, 1.92 ± 1.28 and 1.70 ± 0.83 mm for fixations A and B, respectively. There was a significant improvement of the overall alignment (3D vector) when using the standard fixation instead of fixation A or B in the craniocaudal direction (p = 0.037). Rotational deviations were significantly less for the standard fixation S in relation to fixations A (p = 0.005) and B (p = 0.03). EPI imaging with off-line correction further improved reproducibility. Five out of 8 patients preferred the neck support with the bite-block. The mask fixation system in conjunction with a bite-block is the most accurate fixation for SCRT reducing craniocaudal and rotational movements. Patients favoured the more comfortable but less accurate neck support. To optimize the accuracy of SCRT, additional regular portal imaging is warranted.

Nutrient feedbacks to soil heterotrophic nitrogen fixation in forests

USGS Publications Warehouse

Perakis, Steven; Pett-Ridge, Julie C.; Catricala, Christina E.

2017-01-01

Multiple nutrient cycles regulate biological nitrogen (N) fixation in forests, yet long-term feedbacks between N-fixation and coupled element cycles remain largely unexplored. We examined soil nutrients and heterotrophic N-fixation across a gradient of 24 temperate conifer forests shaped by legacies of symbiotic N-fixing trees. We observed positive relationships among mineral soil pools of N, carbon (C), organic molybdenum (Mo), and organic phosphorus (P) across sites, evidence that legacies of symbiotic N-fixing trees can increase the abundance of multiple elements important to heterotrophic N-fixation. Soil N accumulation lowered rates of heterotrophic N-fixation in organic horizons due to both N inhibition of nitrogenase enzymes and declines in soil organic matter quality. Experimental fertilization of organic horizon soil revealed widespread Mo limitation of heterotrophic N-fixation, especially at sites where soil Mo was scarce relative to C. Fertilization also revealed widespread absence of P limitation, consistent with high soil P:Mo ratios. Responses of heterotrophic N-fixation to added Mo (positive) and N (negative) were correlated across sites, evidence that multiple nutrient controls of heterotrophic N-fixation were more common than single-nutrient effects. We propose a conceptual model where symbiotic N-fixation promotes coupled N, C, P, and Mo accumulation in soil, leading to positive feedback that relaxes nutrient limitation of overall N-fixation, though heterotrophic N-fixation is primarily suppressed by strong negative feedback from long-term soil N accumulation.

21 CFR 888.3040 - Smooth or threaded metallic bone fixation fastener.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Smooth or threaded metallic bone fixation fastener... metallic bone fixation fastener. (a) Identification. A smooth or threaded metallic bone fixation fastener..., slotted head on the end. It may be used for fixation of bone fractures, for bone reconstructions, as a...

21 CFR 888.3040 - Smooth or threaded metallic bone fixation fastener.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Smooth or threaded metallic bone fixation fastener... metallic bone fixation fastener. (a) Identification. A smooth or threaded metallic bone fixation fastener..., slotted head on the end. It may be used for fixation of bone fractures, for bone reconstructions, as a...

21 CFR 888.3040 - Smooth or threaded metallic bone fixation fastener.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Smooth or threaded metallic bone fixation fastener... metallic bone fixation fastener. (a) Identification. A smooth or threaded metallic bone fixation fastener..., slotted head on the end. It may be used for fixation of bone fractures, for bone reconstructions, as a...

21 CFR 888.3040 - Smooth or threaded metallic bone fixation fastener.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Smooth or threaded metallic bone fixation fastener... metallic bone fixation fastener. (a) Identification. A smooth or threaded metallic bone fixation fastener..., slotted head on the end. It may be used for fixation of bone fractures, for bone reconstructions, as a...

21 CFR 888.3040 - Smooth or threaded metallic bone fixation fastener.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Smooth or threaded metallic bone fixation fastener... metallic bone fixation fastener. (a) Identification. A smooth or threaded metallic bone fixation fastener..., slotted head on the end. It may be used for fixation of bone fractures, for bone reconstructions, as a...

Complement fixation test to C burnetii

MedlinePlus

... complement fixation test; Coxiella burnetii - complement fixation test; C burnetii - complement fixation test ... a specific foreign substance ( antigen ), in this case, C burnetii . Antibodies defend the body against bacteria, viruses, ...

Fixation Patterns and Reading Rates in Eyes with Central Scotomas from Advanced Atrophic Age-related Macular Degeneration and Stargardt Disease

PubMed Central

Sunness, Janet S.; Applegate, Carol A.; Haselwood, David; Rubin, Gary S.

2009-01-01

Purpose To study fixation patterns and reading rates in eyes with central scotomas from geographic atrophy (GA) of age-related macular degeneration and to compare fixation patterns with those of patients with Stargardt disease. Methods Scanning laser ophthalmoscope analysis of fixation patterns in eyes with 20/80 to 20/200 visual acuity. Included were 41 eyes of 35 patients with GA and 10 eyes of 5 patients with Stargardt disease. The patients with GA also were tested for maximum reading rate, and the size of the areas of atrophy were measured by fundus photograph analysis. Results Sixty-three percent of GA eyes fixating outside the atrophy placed the scotoma to the right of fixation in visual field space, 22% placed the scotoma above fixation, and 15% placed it to the left, regardless of the laterality of the GA eye. Fixation was stable in subsequent years of testing for scotoma placement to the right of or above fixation. All GA eyes fixated immediately adjacent to the atrophy. In contrast, seven of ten eyes with Stargardt disease fixated at a considerable distance from the scotoma border, with the dense scotoma far above the fixation site in visual field space. For the patients with GA, the maximum reading rate was highly correlated with size of the atrophic area, but not with age or visual acuity within the limited visual acuity range tested. There was a trend to more rapid reading with the scotoma above fixation and slower reading with the scotoma to the left. Conclusion There is a preference for fixation with the scotoma to the right in eyes with GA. Patients with Stargardt disease use different strategies for fixation, perhaps due to subclinical pathology adjacent to the atrophic regions. The size of the atrophic area in GA plays the predominant role in reading rate for eyes that have already lost foveal vision. PMID:8841306

Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws.

PubMed

Lapsiwala, Samir B; Anderson, Paul A; Oza, Ashish; Resnick, Daniel K

2006-03-01

We performed a biomechanical comparison of several C1 to C2 fixation techniques including crossed laminar (intralaminar) screw fixation, anterior C1 to C2 transarticular screw fixation, C1 to 2 pedicle screw fixation, and posterior C1 to C2 transarticular screw fixation. Eight cadaveric cervical spines were tested intact and after dens fracture. Four different C1 to C2 screw fixation techniques were tested. Posterior transarticular and pedicle screw constructs were tested twice, once with supplemental sublaminar cables and once without cables. The specimens were tested in three modes of loading: flexion-extension, lateral bending, and axial rotation. All tests were performed in load and torque control. Pure bending moments of 2 nm were applied in flexion-extension and lateral bending, whereas a 1 nm moment was applied in axial rotation. Linear displacements were recorded from extensometers rigidly affixed to the C1 and C2 vertebrae. Linear displacements were reduced to angular displacements using trigonometry. Adding cable fixation results in a stiffer construct for posterior transarticular screws. The addition of cables did not affect the stiffness of C1 to C2 pedicle screw constructs. There were no significant differences in stiffness between anterior and posterior transarticular screw techniques, unless cable fixation was added to the posterior construct. All three posterior screw constructs with supplemental cable fixation provide equal stiffness with regard to flexion-extension and axial rotation. C1 lateral mass-C2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as the other screw fixation techniques. All four screw fixation techniques limit motion at the C1 to 2 articulation. The addition of cable fixation improves resistance to flexion and extension for posterior transarticular screw fixation.

Differential vergence movements in reading Chinese and English: Greater fixation-initial binocular disparity is advantageous in reading the denser orthography.

PubMed

Hsiao, Yi-Ting; Shillcock, Richard; Obregón, Mateo; Kreiner, Hamutal; Roberts, Matthew A J; McDonald, Scott

2017-07-11

We explore two aspects of exovergence: we test whether smaller binocular fixation disparities accompany the shorter saccades and longer fixations observed in reading Chinese; we test whether potentially advantageous psychophysical effects of exovergence (cf. Arnold & Schindel, 2010; Kersten & Murray, 2010) transfer to text reading. We report differential exovergence in reading Chinese and English: Chinese readers begin fixations with more binocular disparity, but end fixations with a disparity closely similar to that of the English readers. We conclude that greater fixation-initial binocular fixation disparity can be adaptive in the reading of visually and cognitively denser text.

Contributions of retinal input and phenomenal representation of a fixation object to the saccadic gap effect.

PubMed

Ueda, Hiroshi; Takahashi, Kohske; Watanabe, Katsumi

2013-04-19

The saccadic "gap effect" refers to a phenomenon whereby saccadic reaction times (SRTs) are shortened by the removal of a visual fixation stimulus prior to target presentation. In the current study, we investigated whether the gap effect was influenced by retinal input of a fixation stimulus, as well as phenomenal permanence and/or expectation of the re-emergence of a fixation stimulus. In Experiment 1, we used an occluded fixation stimulus that was gradually hidden by a moving plate prior to the target presentation, which produced the impression that the fixation stimulus still remained and would reappear from behind the plate. We found that the gap effect was significantly weakened with the occluded fixation stimulus. However, the SRT with the occluded fixation stimulus was still shorter in comparison to when the fixation stimulus physically remained on the screen. In Experiment 2, we investigated whether this effect was due to phenomenal maintenance or expectation of the reappearance of the fixation stimulus; this was achieved by using occluding plates that were an identical color to the background screen, giving the impression of reappearance of the fixation stimulus but not of its maintenance. The result showed that the gap effect was still weakened by the same degree even without phenomenal maintenance of the fixation stimulus. These results suggest that the saccadic gap effect is modulated by both retinal input and subjective expectation of re-emergence of the fixation stimulus. In addition to oculomotor mechanisms, other components, such as attentional mechanisms, likely contribute to facilitation of the subsequent action. Copyright © 2013 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ledbetter, Rhesa N.; Garcia Costas, Amaya M.; Lubner, Carolyn E.

The biological reduction of dinitrogen (N 2) to ammonia (NH 3) by nitrogenase is an energetically demanding reaction that requires low-potential electrons and ATP; however, pathways used to deliver the electrons from central metabolism to the reductants of nitrogenase, ferredoxin or flavodoxin, remain unknown for many diazotrophic microbes. The FixABCX protein complex has been proposed to reduce flavodoxin or ferredoxin using NADH as the electron donor in a process known as electron bifurcation. Herein, the FixABCX complex from Azotobacter vinelandii was purified and demonstrated to catalyze an electron bifurcation reaction: oxidation of NADH (E m = -320 mV) coupled tomore » reduction of flavodoxin semiquinone (E m = -460 mV) and reduction of coenzyme Q (E m = 10 mV). Knocking out fix genes rendered ..delta..rnf A. vinelandii cells unable to fix dinitrogen, confirming that the FixABCX system provides another route for delivery of electrons to nitrogenase. Characterization of the purified FixABCX complex revealed the presence of flavin and iron-sulfur cofactors confirmed by native mass spectrometry, electron paramagnetic resonance spectroscopy, and transient absorption spectroscopy. Transient absorption spectroscopy further established the presence of a short-lived flavin semiquinone radical, suggesting that a thermodynamically unstable flavin semiquinone may participate as an intermediate in the transfer of an electron to flavodoxin. A structural model of FixABCX, generated using chemical cross-linking in conjunction with homology modeling, revealed plausible electron transfer pathways to both high- and low-potential acceptors. Altogether, this study informs a mechanism for electron bifurcation, offering insight into a unique method for delivery of low-potential electrons required for energy-intensive biochemical conversions.« less

Synthesis of benzo-fused 1-azabicyclo[m.n.0]alkanes via the Schmidt reaction: a formal synthesis of gephyrotoxin.

PubMed

Pearson, W H; Fang, W

2000-10-20

The intramolecular capture of benzocyclobutyl, benzocyclopentyl, and benzocyclohexyl carbocations 7 by azides produces spirocyclic aminodiazonium ions 8, which undergo 1,2-C-to-N rearrangement with loss of dinitrogen to produce benzo-fused iminium ions resulting from either aryl (9) or alkyl (10) migration to the electron-deficient nitrogen atom. Reduction of the iminium ions affords regioisomeric benzo-fused 1-azabicyclo[m.n.0]alkanes, e.g., benzopyrrolizidines, benzoindolizidines, benzoquinolizidines, or perhydrobenzo[f]pyrrolo[1,2-a]azepines in two regioisomeric versions, anilines (e.g., 11-14) and benzylic amines (e.g., 15-18), the result of aryl and alkyl migrations, respectively. Generally, aryl migration is preferred, despite modeling that shows that the lowest energy aminodiazonium ions are those where the departing dinitrogen is preferentially antiperiplanar to the migrating alkyl group rather than the aryl group. The utility of this methodology was illustrated by a formal synthesis of the alkaloid gephyrotoxin 4. A dependence on the efficiency and regioselectivity of the Schmidt reaction upon subtle changes in the structure of the cation precursor was observed, necessitating the exploration of a variety of substrates. Fortunately, these materials were easily made. Ultimately, the azido-alkene 81 bearing a 2-bromoethyl side-chain was useful for the Schmidt reaction, producing the known benzo-fused indolizidine 49, which had been transformed by Ito et al. into gephyrotoxin 4. The synthesis of 49 required nine steps (five purifications) from commercially available 4-methoxy-1-indanone 60 and proceeded in 22% overall yield.

The Role of Personality and Team-Based Product Dissection on Fixation Effects

ERIC Educational Resources Information Center

Toh, Christine; Miller, Scarlett; Kremer, Gül E. Okudan

2013-01-01

Design fixation has been found to be complex in its definition and expression, but it plays an important role in design idea generation. Identifying the factors that influence fixation is crucial in understanding how to enhance the design process and reduce the negative effects of fixation. One way to potentially mitigate fixation is through…

In Situ Denitrification and Biological Nitrogen Fixation Under Enhanced Atmospheric Reactive Nitrogen Deposition in UK Peatlands

NASA Astrophysics Data System (ADS)

Ullah, Sami; Saiz Val, Ernesto; Sgouridis, Fotis; Peichl, Matthias; Nilsson, Mats

2017-04-01

Dinitrogen (N2) and nitrous oxide (N2O) losses due to denitrification and biological N2 fixation (BNF) are the most uncertain components of the nitrogen (N) cycle in peatlands under enhanced atmospheric reactive nitrogen (Nr) deposition. This uncertainty hampers our ability to assess the contribution of denitrification to the removal of biologically fixed and/or atmospherically deposited Nr in peatlands. This uncertainty emanates from the difficulty in measuring in situ soil N2 and N2O production and consumption in peatlands. In situ denitrification and its contribution to total N2O flux was measured monthly between April 2013 and October 2014 in peatlands in two UK catchments. An adapted 15N-Gas Flux method1 with low level addition of 15N tracer (0.03 ± 0.005 kg 15N ha-1) was used to measure denitrification and its contribution to net N2O production (DN2O/TN2O). BNF was measured in situ through incubation of selected sphagnum species under 15N2 gas tracer. Denitrification2 varied temporally and averaged 8 kg N-N2 ha-1 y-1. The contribution of denitrification was about 48% to total N2O flux3 of 0.05 kg N ha-1 y-1. Soil moisture, temperature, ecosystem respiration, pH and mineral N content mainly regulated the flux of N2 and N2O. Preliminary results showed suppression of BNF, which was 1.8 to 7 times lower in peatland mosses exposed to ˜15 to 20 kg N ha-1 y-1 Nr deposition in the UK than in peatland mosses in northern Sweden with background Nr deposition. Overall, the contribution of denitrification to Nr removal in the selected peatlands was ˜50% of the annual Nr deposition rates, making these ecosystems vulnerable to chronic N saturation. These results point to a need for a more comprehensive annual BNF measurement to more accurately account for total Nr input into peatlands and its atmospheric loss due to denitrification. References Sgouridis F, Stott A & Ullah S, 2016. Application of the 15N-Gas Flux method for measuring in situ N2 and N2O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique. Biogeosciences, 13, 1821-1835. Sgouridis F and Ullah S. 2015. Relative magnitude and controls of in situ N2 and N2O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems using 15N tracers. Environmental Science & Technology, vol. 49(24), 14110-14119. Sgouridis F and Ullah S. 2017. Environmental controls on soil greenhouse gas (CO2, CH4, N2O) fluxes and the partitioning of N2O sources in natural and semi-natural land use types in the UK. JGR-B (under review)

A Prospective Randomized Trial to Assess Fixation Strategies for Severe Open Tibia Fractures: Modern Ring External Fixators Versus Internal Fixation (FIXIT Study).

PubMed

OʼToole, Robert V; Gary, Joshua L; Reider, Lisa; Bosse, Michael J; Gordon, Wade T; Hutson, James; Quinnan, Stephen M; Castillo, Renan C; Scharfstein, Daniel O; MacKenzie, Ellen J

2017-04-01

The treatment of high-energy open tibia fractures is challenging in both the military and civilian environments. Treatment with modern ring external fixation may reduce complications common in these patients. However, no study has rigorously compared outcomes of modern ring external fixation with commonly used internal fixation approaches. The FIXIT study is a prospective, multicenter randomized trial comparing 1-year outcomes after treatment of severe open tibial shaft fractures with modern external ring fixation versus internal fixation among men and women of ages 18-64. The primary outcome is rehospitalization for major limb complications. Secondary outcomes include infection, fracture healing, limb function, and patient-reported outcomes including physical function and pain. One-year treatment costs and patient satisfaction will be compared between the 2 groups, and the percentage of Gustilo IIIB fractures that can be salvaged without soft tissue flap among patients receiving external fixation will be estimated.

SU-E-T-235: Monte Carlo Analysis of the Dose Enhancement in the Scalp of Patients Due to Titanium Plate Backscatter During Post-Operative Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardin, M; Elson, H; Lamba, M

2014-06-01

Purpose: To quantify the clinically observed dose enhancement adjacent to cranial titanium fixation plates during post-operative radiotherapy. Methods: Irradiation of a titanium burr hole cover was simulated using Monte Carlo code MCNPX for a 6 MV photon spectrum to investigate backscatter dose enhancement due to increased production of secondary electrons within the titanium plate. The simulated plate was placed 3 mm deep in a water phantom, and dose deposition was tallied for 0.2 mm thick cells adjacent to the entrance and exit sides of the plate. These results were compared to a simulation excluding the presence of the titanium tomore » calculate relative dose enhancement on the entrance and exit sides of the plate. To verify simulated results, two titanium burr hole covers (Synthes, Inc. and Biomet, Inc.) were irradiated with 6 MV photons in a solid water phantom containing GafChromic MD-55 film. The phantom was irradiated on a Varian 21EX linear accelerator at multiple gantry angles (0–180 degrees) to analyze the angular dependence of the backscattered radiation. Relative dose enhancement was quantified using computer software. Results: Monte Carlo simulations indicate a relative difference of 26.4% and 7.1% on the entrance and exit sides of the plate respectively. Film dosimetry results using a similar geometry indicate a relative difference of 13% and -10% on the entrance and exit sides of the plate respectively. Relative dose enhancement on the entrance side of the plate decreased with increasing gantry angle from 0 to 180 degrees. Conclusion: Film and simulation results demonstrate an increase in dose to structures immediately adjacent to cranial titanium fixation plates. Increased beam obliquity has shown to alleviate dose enhancement to some extent. These results are consistent with clinically observed effects.« less

[Domestic external fixator application in the treatment of limb deformities: 7 289 cases application report].

PubMed

Qin, S H; Guo, B F; Zheng, X J; Jiao, S F; Xia, H T; Peng, A M; Pan, Q; Zang, J C; Wang, Z J

2017-09-01

Objective: To discuss the clinical application and effects of domestic external fixator in the treatment of patients with malformations of limbs. Methods: A total of 7 289 patients with malformation of limbs who had been operated in Qin Sihe orthopedic surgery team from January 1989 to June 2016 were retrospective analyzed. The patients were treated with domestic external fixator, including 4 033 males and 3 256 females, aging from 2 to 82 years with a mean age of 23.4 years. There were 2 732 patients using Ilizarov external fixator, 4 713 patients using hybrid external fixator, 57 patients using monobrachial external fixator, 232 patients using Ilizarov external fixator and hybrid external fixator. The Ilizarov, hybrid and monobrachial external fixator were used in 67, 65 and 0 patients on the upper limbs and in 2 665, 4 616 and 57 patients on the lower limbs. There were 3 028 patients operated on the left limbs, 3 260 patients operated on the right limbs and 1 001 patients operated on the bilateral limbs. The top three types of diseases were sequelae of poliomyelitis, cerebral palsy and post-traumatic stress disorder peromely. Deformity types inclued talipes equinovarus, knee flexion deformity, cavus foot and so on. Results: All the patients were followed up for a period of 2.5 months to 22.4 years, with an average follow-up time of 5.4 years. All of the external fixators were used for single once, and there was no substitute for external fixator quality problem. All the patients were completed surgery goal until removing external fixation except 1 patient gave up treatment and 1 removed the fixator because of metal allergy. The common complications included wire or pin infection and joint movement limitation and so on. Conclusions: The domestic external fixator developed and produced based on the characteristics of Chinese limb deformity disability. The domestic external fixator can be used to treat kinds of limb deformities with the advantages of practical, economical, adjustable, universal and portable. The domestic external fixator could meet the clinical demand for fixation of the osteotomy end of the limbs, the correction of the deformity, the repair of the defects and the limb lengthening.

Fixation strength analysis of cup to bone material using finite element simulation

NASA Astrophysics Data System (ADS)

Anwar, Iwan Budiwan; Saputra, Eko; Ismail, Rifky; Jamari, J.; van der Heide, Emile

2016-04-01

Fixation of acetabular cup to bone material is an important initial stability for artificial hip joint. In general, the fixation in cement less-type acetabular cup uses press-fit and screw methods. These methods can be applied alone or together. Based on literature survey, the additional screw inside of cup is effective; however, it has little effect in whole fixation. Therefore, an acetabular cup with good fixation, easy manufacture and easy installation is required. This paper is aiming at evaluating and proposing a new cup fixation design. To prove the strength of the present cup fixation design, the finite element simulation of three dimensional cup with new fixation design was performed. The present cup design was examined with twist axial and radial rotation. Results showed that the proposed cup design was better than the general version.

Formaldehyde substitute fixatives: effects on nucleic acid preservation.

PubMed

Moelans, Cathy B; Oostenrijk, Daphne; Moons, Michiel J; van Diest, Paul J

2011-11-01

In surgical pathology, formalin-fixed paraffin-embedded tissues are increasingly being used as a source of DNA and RNA for molecular assays in addition to histopathological evaluation. However, the commonly used formalin fixative is carcinogenic, and its crosslinking impairs DNA and RNA quality. The suitability of three new presumably less toxic, crosslinking (F-Solv) and non-crosslinking (FineFIX, RCL2) alcohol-based fixatives was tested for routine molecular pathology in comparison with neutral buffered formalin (NBF) as gold standard. Size ladder PCR, epidermal growth factor receptor sequence analysis, microsatellite instability (MSI), chromogenic (CISH), fluorescence in situ hybridisation (FISH) and qPCR were performed. The alcohol-based non-crosslinking fixatives (FineFIX and RCL2) resulted in a higher DNA yield and quality compared with crosslinking fixatives (NBF and F-Solv). Size ladder PCR resulted in a shorter amplicon size (300 bp) for both crosslinking fixatives compared with the non-crosslinking fixatives (400 bp). All four fixatives were directly applicable for MSI and epidermal growth factor receptor sequence analysis. All fixatives except F-Solv showed clear signals in CISH and FISH. RNA yield and quality were superior after non-crosslinking fixation. qPCR resulted in lower Ct values for RCL2 and FineFIX. The alcohol-based non-crosslinking fixatives performed better than crosslinking fixatives with regard to DNA and RNA yield, quality and applicability in molecular diagnostics. Given the higher yield, less starting material may be necessary, thereby increasing the applicability of biopsies for molecular studies.

Elevated temperature increases carbon and nitrogen fluxes between phytoplankton and heterotrophic bacteria through physical attachment

DOE PAGES

Arandia-Gorostidi, Nestor; Weber, Peter K.; Alonso-Sáez, Laura; ...

2016-12-06

Quantifying the contribution of marine microorganisms to carbon and nitrogen cycles and their response to predicted ocean warming is one of the main challenges of microbial oceanography. Here we present a single-cell NanoSIMS isotope analysis to quantify C and N uptake by free-living and attached phytoplankton and heterotrophic bacteria, and their response to short-term experimental warming of 4 °C. Elevated temperature increased total C fixation by over 50%, a small but significant fraction of which was transferred to heterotrophs within 12 h. Cell-to-cell attachment doubled the secondary C uptake by heterotrophic bacteria and increased secondary N incorporation by autotrophs bymore » 68%. Warming also increased the abundance of phytoplankton with attached heterotrophs by 80%, and promoted C transfer from phytoplankton to bacteria by 17% and N transfer from bacteria to phytoplankton by 50%. Lastly, our results indicate that phytoplankton-bacteria attachment provides an ecological advantage for nutrient incorporation, suggesting a mutualistic relationship that appears to be enhanced by temperature increases.« less

Elevated temperature increases carbon and nitrogen fluxes between phytoplankton and heterotrophic bacteria through physical attachment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arandia-Gorostidi, Nestor; Weber, Peter K.; Alonso-Sáez, Laura

Quantifying the contribution of marine microorganisms to carbon and nitrogen cycles and their response to predicted ocean warming is one of the main challenges of microbial oceanography. Here we present a single-cell NanoSIMS isotope analysis to quantify C and N uptake by free-living and attached phytoplankton and heterotrophic bacteria, and their response to short-term experimental warming of 4 °C. Elevated temperature increased total C fixation by over 50%, a small but significant fraction of which was transferred to heterotrophs within 12 h. Cell-to-cell attachment doubled the secondary C uptake by heterotrophic bacteria and increased secondary N incorporation by autotrophs bymore » 68%. Warming also increased the abundance of phytoplankton with attached heterotrophs by 80%, and promoted C transfer from phytoplankton to bacteria by 17% and N transfer from bacteria to phytoplankton by 50%. Lastly, our results indicate that phytoplankton-bacteria attachment provides an ecological advantage for nutrient incorporation, suggesting a mutualistic relationship that appears to be enhanced by temperature increases.« less

Feature integration, attention, and fixations during visual search.

PubMed

Khani, Abbas; Ordikhani-Seyedlar, Mehdi

2017-01-01

We argue that mechanistic premises of "item-based" theories are not invalidated by the fixation-based approach. We use item-based theories to propose an account that does not advocate strict serial item processing and integrates fixations. The main focus of this account is feature integration within fixations. We also suggest that perceptual load determines the size of the fixations.

Modeling fixation locations using spatial point processes.

PubMed

Barthelmé, Simon; Trukenbrod, Hans; Engbert, Ralf; Wichmann, Felix

2013-10-01

Whenever eye movements are measured, a central part of the analysis has to do with where subjects fixate and why they fixated where they fixated. To a first approximation, a set of fixations can be viewed as a set of points in space; this implies that fixations are spatial data and that the analysis of fixation locations can be beneficially thought of as a spatial statistics problem. We argue that thinking of fixation locations as arising from point processes is a very fruitful framework for eye-movement data, helping turn qualitative questions into quantitative ones. We provide a tutorial introduction to some of the main ideas of the field of spatial statistics, focusing especially on spatial Poisson processes. We show how point processes help relate image properties to fixation locations. In particular we show how point processes naturally express the idea that image features' predictability for fixations may vary from one image to another. We review other methods of analysis used in the literature, show how they relate to point process theory, and argue that thinking in terms of point processes substantially extends the range of analyses that can be performed and clarify their interpretation.

Individual Objective and Subjective Fixation Disparity in Near Vision

PubMed Central

Jaschinski, Wolfgang

2017-01-01

Binocular vision refers to the integration of images in the two eyes for improved visual performance and depth perception. One aspect of binocular vision is the fixation disparity, which is a suboptimal condition in individuals with respect to binocular eye movement control and subsequent neural processing. The objective fixation disparity refers to the vergence angle between the visual axes, which is measured with eye trackers. Subjective fixation disparity is tested with two monocular nonius lines which indicate the physical nonius separation required for perceived alignment. Subjective and objective fixation disparity represent the different physiological mechanisms of motor and sensory fusion, but the precise relation between these two is still unclear. This study measures both types of fixation disparity at viewing distances of 40, 30, and 24 cm while observers fixated a central stationary fusion target. 20 young adult subjects with normal binocular vision were tested repeatedly to investigate individual differences. For heterophoria and subjective fixation disparity, this study replicated that the binocular system does not properly adjust to near targets: outward (exo) deviations typically increase as the viewing distance is shortened. This exo proximity effect—however—was not found for objective fixation disparity, which–on the average–was zero. But individuals can have reliable outward (exo) or inward (eso) vergence errors. Cases with eso objective fixation disparity tend to have less exo states of subjective fixation disparity and heterophoria. In summary, the two types of fixation disparity seem to respond in a different way when the viewing distance is shortened. Motor and sensory fusion–as reflected by objective and subjective fixation disparity–exhibit complex interactions that may differ between individuals (eso versus exo) and vary with viewing distance (far versus near vision). PMID:28135308

[Results of femoral lengthening over an intramedullary nail and external fixator].

PubMed

Jasiewicz, Barbara; Kacki, Wojciech; Tesiorowski, Maciej; Potaczek, Tomasz

2008-01-01

Current techniques of operative limb lengthening usually are based on distraction osteogenesis. One of the techniques is limb lengthening over an intramedullary nail. The goal of this study is to evaluate the results of femoral lengthening over an intramedullary nail. Between 1999 and 200619 femoral "over nail" lengthenings were performed. There were 7 males and 12 females. Mean patients' age at surgery was 15.8 years, and mean initial femoral shortening was 5.1 cm. Operative technique consisted of one-stage implantation of intramedullary nail and external fixator. Ilizarov apparatus was used in 9 patients, monolateral fixator in 10 cases--ORTHOFIX in 9 patients, Wagner fixator--in 1 patient. Intramedullary nail was locked proximally with screws or Schanz pins from external fixator. After distraction phase, external fixator was removed and distal locking screws were applied. Evaluation criteria: obtained lengthening, time of external fixator, treatment time, healing index, external fixation index, range of motion in hip and knee joints and complications according to Paley. The mean lengthening was 4.6 cm, and mean distraction time was 66.6 days. Mean time of external fixation was 115.5 days, and external fixation index was 26.2 days for centimeter. Healing index was 36.9 days for centimeter. In cases with monolateral fixator, healing index did not differ with the whole group. During treatment 18 complications occurred, for a rate of 0.9 complication per segment. Lengthening over an intramedullary nail reduces the time of external fixator. Over nail femoral lengthening can prevent axis deviation following regenerate bending. Complication rate is similar to lengthenings with the classic Ilizarov technique. There are no differences in the treatment time in relation to the type of external fixator.

The Assimilation of Diazotroph-Derived Nitrogen by Scleractinian Corals Depends on Their Metabolic Status

PubMed Central

Grover, Renaud; Maguer, Jean-François; Fine, Maoz; Ferrier-Pagès, Christine

2017-01-01

ABSTRACT Tropical corals are associated with a diverse community of dinitrogen (N2)-fixing prokaryotes (diazotrophs) providing the coral an additional source of bioavailable nitrogen (N) in oligotrophic waters. The overall activity of these diazotrophs changes depending on the current environmental conditions, but to what extent it affects the assimilation of diazotroph-derived N (DDN) by corals is still unknown. Here, in a series of 15N2 tracer experiments, we directly quantified DDN assimilation by scleractinian corals from the Red Sea exposed to different environmental conditions. We show that DDN assimilation strongly varied with the corals’ metabolic status or with phosphate availability in the water. The very autotrophic shallow-water (~5 m) corals showed low or no DDN assimilation, which significantly increased under elevated phosphate availability (3 µM). Corals that depended more on heterotrophy (i.e., bleached and deep-water [~45 m] corals) assimilated significantly more DDN, which contributed up to 15% of the corals’ N demand (compared to 1% in shallow corals). Furthermore, we demonstrate that a substantial part of the DDN assimilated by deep corals was likely obtained from heterotrophic feeding on fixed N compounds and/or diazotrophic cells in the mucus. Conversely, in shallow corals, the net release of mucus, rich in organic carbon compounds, likely enhanced diazotroph abundance and activity and thereby the release of fixed N to the pelagic and benthic reef community. Overall, our results suggest that DDN assimilation by corals varies according to the environmental conditions and is likely linked to the capacity of the coral to acquire nutrients from seawater. PMID:28074021

Levels of daily light doses under changed day-night cycles regulate temporal segregation of photosynthesis and N2 Fixation in the cyanobacterium Trichodesmium erythraeum IMS101.

PubMed

Cai, Xiaoni; Gao, Kunshan

2015-01-01

While the diazotrophic cyanobacterium Trichodesmium is known to display inverse diurnal performances of photosynthesis and N2 fixation, such a phenomenon has not been well documented under different day-night (L-D) cycles and different levels of light dose exposed to the cells. Here, we show differences in growth, N2 fixation and photosynthetic carbon fixation as well as photochemical performances of Trichodesmium IMS101 grown under 12L:12D, 8L:16D and 16L:8D L-D cycles at 70 μmol photons m-2 s-1 PAR (LL) and 350 μmol photons m-2 s-1 PAR (HL). The specific growth rate was the highest under LL and the lowest under HL under 16L:8D, and it increased under LL and decreased under HL with increased levels of daytime light doses exposed under the different light regimes, respectively. N2 fixation and photosynthetic carbon fixation were affected differentially by changes in the day-night regimes, with the former increasing directly under LL with increased daytime light doses and decreased under HL over growth-saturating light levels. Temporal segregation of N2 fixation from photosynthetic carbon fixation was evidenced under all day-night regimes, showing a time lag between the peak in N2 fixation and dip in carbon fixation. Elongation of light period led to higher N2 fixation rate under LL than under HL, while shortening the light exposure to 8 h delayed the N2 fixation peaking time (at the end of light period) and extended it to night period. Photosynthetic carbon fixation rates and transfer of light photons were always higher under HL than LL, regardless of the day-night cycles. Conclusively, diel performance of N2 fixation possesses functional plasticity, which was regulated by levels of light energy supplies either via changing light levels or length of light exposure.

Start Position Strongly Influences Fixation Patterns during Face Processing: Difficulties with Eye Movements as a Measure of Information Use

PubMed Central

Arizpe, Joseph; Kravitz, Dwight J.; Yovel, Galit; Baker, Chris I.

2012-01-01

Fixation patterns are thought to reflect cognitive processing and, thus, index the most informative stimulus features for task performance. During face recognition, initial fixations to the center of the nose have been taken to indicate this location is optimal for information extraction. However, the use of fixations as a marker for information use rests on the assumption that fixation patterns are predominantly determined by stimulus and task, despite the fact that fixations are also influenced by visuo-motor factors. Here, we tested the effect of starting position on fixation patterns during a face recognition task with upright and inverted faces. While we observed differences in fixations between upright and inverted faces, likely reflecting differences in cognitive processing, there was also a strong effect of start position. Over the first five saccades, fixation patterns across start positions were only coarsely similar, with most fixations around the eyes. Importantly, however, the precise fixation pattern was highly dependent on start position with a strong tendency toward facial features furthest from the start position. For example, the often-reported tendency toward the left over right eye was reversed for the left starting position. Further, delayed initial saccades for central versus peripheral start positions suggest greater information processing prior to the initial saccade, highlighting the experimental bias introduced by the commonly used center start position. Finally, the precise effect of face inversion on fixation patterns was also dependent on start position. These results demonstrate the importance of a non-stimulus, non-task factor in determining fixation patterns. The patterns observed likely reflect a complex combination of visuo-motor effects and simple sampling strategies as well as cognitive factors. These different factors are very difficult to tease apart and therefore great caution must be applied when interpreting absolute fixation locations as indicative of information use, particularly at a fine spatial scale. PMID:22319606

Medial malleolar fractures: a biomechanical study of fixation techniques.

PubMed

Fowler, T Ty; Pugh, Kevin J; Litsky, Alan S; Taylor, Benjamin C; French, Bruce G

2011-08-08

Fracture fixation of the medial malleolus in rotationally unstable ankle fractures typically results in healing with current fixation methods. However, when failure occurs, pullout of the screws from tension, compression, and rotational forces is predictable. We sought to biomechanically test a relatively new technique of bicortical screw fixation for medial malleoli fractures. Also, the AO group recommends tension-band fixation of small avulsion type fractures of the medial malleolus that are unacceptable for screw fixation. A well-documented complication of this technique is prominent symptomatic implants and secondary surgery for implant removal. Replacing stainless steel 18-gauge wire with FiberWire suture could theoretically decrease symptomatic implants. Therefore, a second goal was to biomechanically compare these 2 tension-band constructs. Using a tibial Sawbones model, 2 bicortical screws were compared with 2 unicortical cancellous screws on a servohydraulic test frame in offset axial, transverse, and tension loading. Second, tension-band fixation using stainless steel wire was compared with FiberWire under tensile loads. Bicortical screw fixation was statistically the stiffest construct under tension loading conditions compared to unicortical screw fixation and tension-band techniques with FiberWire or stainless steel wire. In fact, unicortical screw fixation had only 10% of the stiffness as demonstrated in the bicortical technique. In a direct comparison, tension-band fixation using stainless steel wire was statistically stiffer than the FiberWire construct. Copyright 2011, SLACK Incorporated.

Does the Watson-Jones or Modified Smith-Petersen Approach Provide Superior Exposure for Femoral Neck Fracture Fixation?

PubMed

Lichstein, Paul M; Kleimeyer, John P; Githens, Michael; Vorhies, John S; Gardner, Michael J; Bellino, Michael; Bishop, Julius

2018-07-01

A well-reduced femoral neck fracture is more likely to heal than a poorly reduced one, and increasing the quality of the surgical exposure makes it easier to achieve anatomic fracture reduction. Two open approaches are in common use for femoral neck fractures, the modified Smith-Petersen and Watson-Jones; however, to our knowledge, the quality of exposure of the femoral neck exposure provided by each approach has not been investigated. (1) What is the respective area of exposed femoral neck afforded by the Watson-Jones and modified Smith-Petersen approaches? (2) Is there a difference in the ability to visualize and/or palpate important anatomic landmarks provided by the Watson-Jones and modified Smith-Petersen approaches? Ten fresh-frozen human pelvi underwent both modified Smith-Petersen (utilizing the caudal extent of the standard Smith-Petersen interval distal to the anterosuperior iliac spine and parallel to the palpable interval between the tensor fascia lata and the sartorius) and Watson-Jones approaches. Dissections were performed by three fellowship-trained orthopaedic traumatologists with extensive experience in both approaches. Exposure (in cm) was quantified with calibrated digital photographs and specialized software. Modified Smith-Petersen approaches were analyzed before and after rectus femoris tenotomy. The ability to visualize and palpate seven clinically relevant anatomic structures (the labrum, femoral head, subcapital femoral neck, basicervical femoral neck, greater trochanter, lesser trochanter, and medial femoral neck) was also recorded. The quantified area of the exposed proximal femur was utilized to compare which approach afforded the largest field of view of the femoral neck and articular surface for assessment of femoral neck fracture and associated femoral head injury. The ability to visualize and palpate surrounding structures was assessed so that we could better understand which approach afforded the ability to assess structures that are relevant to femoral neck fracture reduction and fixation. After controlling for age, body mass index, height, and sex, we found the modified Smith-Petersen approach provided a mean of 2.36 cm (95% confidence interval [CI], 0.45-4.28 cm; p = 0.015) additional exposure without rectus femoris tenotomy (p = 0.015) and 3.33 cm (95% CI, 1.42-5.24 cm; p = 0.001) additional exposure with a tenotomy compared with the Watson-Jones approach. The labrum, femoral head, subcapital femoral neck, basicervical femoral neck, and greater trochanter were reliably visible and palpable in both approaches. The lesser trochanter was palpable in all of the modified Smith-Petersen and none of the Watson-Jones approaches (p < 0.001). All modified Smith-Petersen approaches (10 of 10) provided visualization and palpation of the medial femoral neck, whereas visualization of the medial femoral neck was only possible in one of 10 Watson-Jones approaches (p < 0.001) and palpation was possible in eight of 10 Watson-Jones versus all 10 modified Smith-Petersen approaches (p = 0.470). In the hands of surgeons experienced with both surgical approaches to the femoral neck, the modified Smith-Petersen approach, with or without rectus femoris tenotomy, provides superior exposure of the femoral neck and articular surface as well as visualization and palpation of clinically relevant proximal femoral anatomic landmarks compared with the Watson-Jones approach. Open reduction and internal fixation of a femoral neck fracture is typically performed in a young patient (< 60 years old) with the objective of obtaining anatomic reduction that would not be possible by closed manipulation, thus enhancing healing potential. In the hands of surgeons experienced in both approaches, the modified Smith-Petersen approach offers improved direct access for reduction and fixation. Higher quality reductions and fixation are expected to translate to improved healing potential and outcomes. Although our experimental results are promising, further clinical studies are needed to verify if this larger exposure area imparts increased quality of reduction, healing, and improved outcomes compared with other approaches. The learning curve for the exposure is unclear, but the approach has broad applications and is frequently used in other subspecialties such as for direct anterior THA and pediatric septic hip drainage. Surgeons treating femoral neck fractures with open reduction and fixation should familiarize themselves with the modified Smith-Petersen approach.

Gaze Control in One Versus One Defensive Situations in Soccer Players With Various Levels of Expertise.

PubMed

Krzepota, Justyna; Stępiński, Miłosz; Zwierko, Teresa

2016-12-01

Experienced and less experienced soccer players were compared in terms of their gaze behavior (number of fixations, fixation duration, number of fixation regions, and distribution of fixations across specific regions) during frontal 1 vs. 1 defensive situations. Twenty-four men (eight experienced soccer players, eight less experienced players and eight non-players) watched 20 video clips. Gaze behavior was registered with an Eye Tracking System. The video scenes were analyzed frame-by-frame. Significant main effect of the group (experience) was observed for the number of fixation regions. Experienced soccer players had a lower number of fixation regions than the non-soccer players. Moreover, the former group presented with significantly larger percentage of fixations in the ball/foot region. These findings suggest that experienced players may use a more efficient search strategy than novices, involving fixation on a lesser number of areas in specific locations. © The Author(s) 2016.

An effective fixative for glucocorticoid receptors in fetal tissues

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koga, T.; Kurisu, K.

1982-01-01

As a preliminary study in an autoradiographic study of glucocorticoid (GC) receptor localization in orofacial tissues of mouse fetuses, a search was made to determine the most effective fixative for preservation of the GC-receptor complex. Twelve-day-old mouse fetuses were administered tritiated triamcinolone acetonide (/sup 3/H-TAC) intraamniotically and subsequently processed by one of the following three procedures: freeze-drying, prefixation with Karnovsky's fixative, or the catechin fixative (Karnovsky's fixative containing 1% D-catechin) and postfixation with osmium tetroxide. Light microscopic autoradiography and liquid scintillation counting of the specimens revealed that the catechin fixative gave the best results for fixation of the steroid-receptor complexmore » and preservation of tissue structure. Light and electron microscopic autoradiographic studies of the time course of the localization of /sup 3/H-TAC in palatal shelves supported the catechin fixative as being the most effective in preservation of GC-receptor or ligand complexes.« less

Intramedullary nail fixation of non-traditional fractures: Clavicle, forearm, fibula.

PubMed

Dehghan, Niloofar; Schemitsch, Emil H

2017-06-01

Locked intramedullary fixation is a well-established technique for managing long-bone fractures. While intramedullary nail fixation of diaphyseal fractures in the femur, tibia, and humerus is well established, the same is not true for other fractures. Surgical fixations of clavicle, forearm and ankle are traditionally treated with plate and screw fixation. In some cases, fixation with an intramedullary device is possible, and may be advantageous. However, there is however a concern regarding a lack of rotational stability and fracture shortening. While new generation of locked intramedullary devices for fractures of clavicle, forearm and fibula are recently available, the outcomes are not as reliable as fixation with plates and screws. Further research in this area is warranted with high quality comparative studies, to investigate the outcomes and indication of these fractures treated with intramedullary nail devices compared to intramedullary nail fixation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Neural correlates of fixation duration in natural reading: Evidence from fixation-related fMRI.

PubMed

Henderson, John M; Choi, Wonil; Luke, Steven G; Desai, Rutvik H

2015-10-01

A key assumption of current theories of natural reading is that fixation duration reflects underlying attentional, language, and cognitive processes associated with text comprehension. The neurocognitive correlates of this relationship are currently unknown. To investigate this relationship, we compared neural activation associated with fixation duration in passage reading and a pseudo-reading control condition. The results showed that fixation duration was associated with activation in oculomotor and language areas during text reading. Fixation duration during pseudo-reading, on the other hand, showed greater involvement of frontal control regions, suggesting flexibility and task dependency of the eye movement network. Consistent with current models, these results provide support for the hypothesis that fixation duration in reading reflects attentional engagement and language processing. The results also demonstrate that fixation-related fMRI provides a method for investigating the neurocognitive bases of natural reading. Copyright © 2015 Elsevier Inc. All rights reserved.

[Case-control study on effects of external fixation combined with limited internal fixation for the treatment of Pilon fractures of Rüedi-Allgower type III].

PubMed

Duan, Da-Peng; You, Wu-Lin; Ji, Le; Zhang, Yong-Tao; Dang, Xiao-Qian; Wang, Kun-Zheng

2014-01-01

To analyze the effects of three surgical operations in the treatment of Pilon fracture of Rüedi-Allgower type III, and put forward the best therapeutic method. The clinical data of 33 patients with Pilon fracture who received surgical operations (plaster immobilization group, 10 cases; distal tibia anatomical plate group, 11 cases; external fixation with limited internal fixation group, 12 cases) from October 2009 to January 2012 were analyzed. There were 5 males and 5 females, ranging in age from 24 to 61 years in the plaster immobilization group. There were 7 males and 4 females, ranging in age from 21 to 64 years in the distal tibia anatomical plate group. There were 7 males and 5 females, ranging in age from 23 to 67 years in the external fixation with limited internal fixation group. The Ankle X-ray of Pilon fracture after operation, ankle score, early and late complications were collected. Bourne system was used to evaluate ankle joint function. After 8 months to 3 years follow-up, it was found that three kinds of treatment had significant differences in the outcomes and complications (P < 0.05): the external fixation with limited internal fixation group got the best results. The number of anatomic reduction cases in the external fixation with limited internal fixation group (7 cases) and the distal tibia anatomical plate group (8 cases) was more than the plaster immobilization group (2 cases). According to the ankle score, 8 patients got an excellent result, 3 good and 1 poor in the limited internal fixation group ,which was better than those of distal tibia anatomical plate group (5 excellent, 4 good and 2 poor) and the plaster immobilization group (3 excellent, 4 good and 3 poor). The number of early and late complications in the external fixation with limited internal fixation group was more than those in the plaster immobilization group and the distal tibia anatomical plate group (P< 0.05). Treatment of external fixation with limited internal fixation in the treatment of Pilon fracture of Rüedi-Allgower type III is effective and safe.

Reconstruction of the lateral tibia plateau fracture with a third triangular support screw: A biomechanical study.

PubMed

Moran, Eduardo; Zderic, Ivan; Klos, Kajetan; Simons, Paul; Triana, Miguel; Richards, R Geoff; Gueorguiev, Boyko; Lenz, Mark

2017-10-01

Split fractures of the lateral tibia plateau in young patients with good bone quality are commonly treated using two minimally invasive percutaneous lag screws, followed by unloading of the knee joint. Improved stability could be achieved with the use of a third screw inserted either in the jail-technique fashion or with a triangular support screw configuration. The aim of this study was to investigate under cyclic loading the compliance and endurance of the triangular support fixation in comparison with the standard two lag-screw fixation and the jail technique. Lateral split fractures of type AO/OTA 41-B1 were created on 21 synthetic tibiae and subsequently fixed with one of the following three techniques for seven specimens: standard fixation by inserting two partially threaded 6.5 mm cannulated lag screws parallel to each other and orthogonal to the fracture plane; triangular support fixation-standard fixation with one additional support screw at the distal end of the fracture at 30° proximal inclination; and jail fixation-standard fixation with one additional orthogonal support screw inserted in the medial nonfractured part of the bone. Mechanical testing was performed under progressively increasing cyclic compression loading. Fragment displacement was registered via triggered radiographic imaging. Mean construct compliance was 3.847 × 10 -3  mm/N [standard deviation (SD) 0.784] for standard fixation, 3.838 × 10 -3  mm/N (SD 0.242) for triangular fixation, and 3.563 × 10 -3  mm/N (SD 0.383) for jail fixation, with no significant differences between the groups ( p  = 0.525). The mean numbers of cycles to 2 mm fragment dislocation, defined as a failure criterion, were 12,384 (SD 2267) for standard fixation, 17,708 (SD 2193) for triangular fixation, and 14,629 (SD 5194) for jail fixation. Triangular fixation revealed significantly longer endurance than the standard one ( p  = 0.047). Triangular support fixation enhanced interfragmentary stability at the ultimate stage of dynamic loading. However, the level of improvement seems to be limited and may not legitimate the intervention with an additional third screw.

Mechanical comparison between lengthened and short sacroiliac screws in sacral fracture fixation: a finite element analysis.

PubMed

Zhao, Y; Zhang, S; Sun, T; Wang, D; Lian, W; Tan, J; Zou, D; Zhao, Y

2013-09-01

To compare the stability of lengthened sacroiliac screw and standard sacroiliac screw for the treatment of unilateral vertical sacral fractures; to provide reference for clinical applications. A finite element model of Tile type C pelvic ring injury (unilateral Denis type II fracture of the sacrum) was produced. The unilateral sacral fractures were fixed with lengthened sacroiliac screw and sacroiliac screw in six different types of models respectively. The translation and angle displacement of the superior surface of the sacrum (in standing position on both feet) were measured and compared. The stability of one lengthened sacroiliac screw fixation in S1 or S2 segment is superior to that of one sacroiliac screw fixation in the same sacral segment. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one sacroiliac screw fixation in S1 and S2 segments respectively. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one lengthened sacroiliac screw fixation in S1 or S2 segment. The stability of one sacroiliac screw fixation in S1 and S2 segments respectively is markedly superior to that of one sacroiliac screw fixation in S1 or S2 segment. The vertical and rotational stability of lengthened sacroiliac screw fixation and sacroiliac screw fixation in S2 is superior to that of S1. In a finite element model of type C pelvic ring disruption, S1 and S2 lengthened sacroiliac screws should be utilized for the fixation as regularly as possible and the most stable fixation is the combination of the lengthened sacroiliac screws of S1 and S2 segments. Even if lengthened sacroiliac screws cannot be systematically used due to specific conditions, one sacroiliac screw fixation in S1 and S2 segments respectively is recommended. No matter which kind of sacroiliac screw is used, if only one screw can be implanted, the fixation in S2 segment is more recommended than that in S1. Experimental study Level III. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

A further look at postview effects in reading: An eye-movements study of influences from the left of fixation.

PubMed

Jordan, Timothy R; McGowan, Victoria A; Kurtev, Stoyan; Paterson, Kevin B

2016-02-01

When reading from left to right, useful information acquired during each fixational pause is widely assumed to extend 14 to 15 characters to the right of fixation but just 3 to 4 characters to the left, and certainly no further than the beginning of the fixated word. However, this leftward extent is strikingly small and seems inconsistent with other aspects of reading performance and with the general horizontal symmetry of visual input. Accordingly, 2 experiments were conducted to examine the influence of text located to the left of fixation during each fixational pause using an eye-tracking paradigm in which invisible boundaries were created in sentence displays. Each boundary corresponded to the leftmost edge of each word so that, as each sentence was read, the normal letter content of text to the left of each fixated word was corrupted by letter replacements that were either visually similar or visually dissimilar to the originals. The proximity of corrupted text to the left of fixation was maintained at 1, 2, 3, or 4 words from the left boundary of each fixated word. In both experiments, relative to completely normal text, reading performance was impaired when each type of letter replacement was up to 2 words to the left of fixated words but letter replacements further from fixation produced no impairment. These findings suggest that key aspects of reading are influenced by information acquired during each fixational pause from much further leftward than is usually assumed. Some of the implications of these findings for reading are discussed. (c) 2016 APA, all rights reserved).

Ball-joint versus single monolateral external fixators for definitive treatment of tibial shaft fractures.

PubMed

Beltsios, Michail; Mavrogenis, Andreas F; Savvidou, Olga D; Karamanis, Eirineos; Kokkalis, Zinon T; Papagelopoulos, Panayiotis J

2014-07-01

To compare modular monolateral external fixators with single monolateral external fixators for the treatment of open and complex tibial shaft fractures, to determine the optimal construct for fracture union. A total of 223 tibial shaft fractures in 212 patients were treated with a monolateral external fixator from 2005 to 2011; 112 fractures were treated with a modular external fixator with ball-joints (group A), and 111 fractures were treated with a single external fixator without ball-joints (group B). The mean follow-up was 2.9 years. We retrospectively evaluated the operative time for fracture reduction with the external fixator, pain and range of motion of the knee and ankle joints, time to union, rate of malunion, reoperations and revisions of the external fixators, and complications. The time for fracture reduction was statistically higher in group B; the rate of union was statistically higher in group B; the rate of nonunion was statistically higher in group A; the mean time to union was statistically higher in group A; the rate of reoperations was statistically higher in group A; and the rate of revision of the external fixator was statistically higher in group A. Pain, range of motion of the knee and ankle joints, rates of delayed union, malunion and complications were similar. Although modular external fixators are associated with faster intraoperative fracture reduction with the external fixator, single external fixators are associated with significantly better rates of union and reoperations; the rates of delayed union, malunion and complications are similar.

Acrylic Resin Molding Based Head Fixation Technique in Rodents.

PubMed

Roh, Mootaek; Lee, Kyungmin; Jang, Il-Sung; Suk, Kyoungho; Lee, Maan-Gee

2016-01-12

Head fixation is a technique of immobilizing animal's head by attaching a head-post on the skull for rigid clamping. Traditional head fixation requires surgical attachment of metallic frames on the skull. The attached frames are then clamped to a stationary platform resulting in immobilization of the head. However, metallic frames for head fixation have been technically difficult to design and implement in general laboratory environment. In this study, we provide a novel head fixation method. Using a custom-made head fixation bar, head mounter is constructed during implantation surgery. After the application of acrylic resin for affixing implants such as electrodes and cannula on the skull, additional resins applied on top of that to build a mold matching to the port of the fixation bar. The molded head mounter serves as a guide rails, investigators conveniently fixate the animal's head by inserting the head mounter into the port of the fixation bar. This method could be easily applicable if implantation surgery using dental acrylics is necessary and might be useful for laboratories that cannot easily fabricate CNC machined metal head-posts.

New insights into ambient and focal visual fixations using an automatic classification algorithm

PubMed Central

Follet, Brice; Le Meur, Olivier; Baccino, Thierry

2011-01-01

Overt visual attention is the act of directing the eyes toward a given area. These eye movements are characterised by saccades and fixations. A debate currently surrounds the role of visual fixations. Do they all have the same role in the free viewing of natural scenes? Recent studies suggest that at least two types of visual fixations exist: focal and ambient. The former is believed to be used to inspect local areas accurately, whereas the latter is used to obtain the context of the scene. We investigated the use of an automated system to cluster visual fixations in two groups using four types of natural scene images. We found new evidence to support a focal–ambient dichotomy. Our data indicate that the determining factor is the saccade amplitude. The dependence on the low-level visual features and the time course of these two kinds of visual fixations were examined. Our results demonstrate that there is an interplay between both fixation populations and that focal fixations are more dependent on low-level visual features than are ambient fixations. PMID:23145248

Influence of removal of invisible fixation on the saccadic and manual gap effect.

PubMed

Ueda, Hiroshi; Takahashi, Kohske; Watanabe, Katsumi

2014-01-01

Saccadic and manual reactions to a peripherally presented target are facilitated by removing a central fixation stimulus shortly before a target onset (the gap effect). The present study examined the effects of removal of a visible and invisible fixation point on the saccadic gap effect and the manual gap effect. Participants were required to fixate a central fixation point and respond to a peripherally presented target as quickly and accurately as possible by making a saccade (Experiment 1) or pressing a corresponding key (Experiment 2). The fixation point was dichoptically presented, and visibility was manipulated by using binocular rivalry and continuous flash suppression technique. In both saccade and key-press tasks, removing the visible fixation strongly quickened the responses. Furthermore, the invisible fixation, which remained on the display but suppressed, significantly delayed the saccadic response. Contrarily, the invisible fixation had no effect on the manual task. These results indicate that partially different processes mediate the saccadic gap effect and the manual gap effect. In particular, unconscious processes might modulate an oculomotor-specific component of the saccadic gap effect, presumably via subcortical mechanisms.

The Role of Oxygen in the Evolution of Molybdenum Nitrogenase

NASA Astrophysics Data System (ADS)

Peters, J.; Boyd, E. S.; Hamilton, T. L.

2012-12-01

Since early in Earth's history, the supply of nitrogen (N) into the biosphere has been controlled by the activity of nitrogenase, an oxygen sensitive enzyme that catalyzes the reduction of dinitrogen gas (N2) to bioavailable ammonia. The most common form of nitrogenase harbors a complex molybdenum (Mo) cofactor at its active site [Mo-nitrogenase (Nif)], although other phylogenetically related (alternative) forms of nitrogenase that differ in their active-site metal composition also likely contribute NH3 in environments that are limiting in Mo. The solubility of Mo is significantly influenced by redox and this fact has been used to argue that that the iron (Fe)-dependent nitrogenase (Anf) was predominant prior to ~ 2.5 Ga because oceans were depleted in Mo and rich in Fe. This hypothesis, however, is inconsistent with recent phylogenetic data which strongly suggest that Anf is derived from Nif. Here, we examine the evolutionary history of the Nif enzyme complex in reference to the physiological, biochemical, and morphological strategies for reducing damage by molecular oxygen. A total of 189 nif operons were characterized and quantitatively mapped on a NifHDK concatenated phylogenetic tree. An overlay of the primary mode of metabolism, as defined as either anaerobic (AN) or aerobic/facultative aerobic (AFA), on the NifHDK tree indicates that Nif originated in an anoxic environment and was first acquired in an AFA lineage within the actinobacteria. The complexity of nif operons increased during the evolutionary history of Nif, with a pronounced increase observed during the transition from AN to AFA modes of metabolism. This increase in operon complexity is accompanied by a number of gene loss (nifI1 and nifI2) and gene acquisition (nifW, nifT, nifZ, nifQ) events, with variation in the overall composition of nif operons attributable to adaptations that mediated the toxicity of O2. Collectively, these results underscore the role of O2 in shaping the evolutionary history of Nif, presumably through selection to evolve regulatory and/or protective mechanisms to temporally or spatially decouple N2 fixation from aerobic metabolism.

21st Century Carbon-Climate Change as Simulated by the Canadian Earth System Model CanESM1

NASA Astrophysics Data System (ADS)

Curry, C.; Christian, J. R.; Arora, V.; Boer, G. J.; Denman, K. L.; Flato, G. M.; Scinocca, J. F.; Merryfield, W. J.; Lee, W. G.; Yang, D.

2009-12-01

The Canadian Earth System Model CanESM1 is a fully coupled climate/carbon-cycle model with prognostic ocean and terrestrial components. The model has been used to simulate the 1850-2000 climate using historical greenhouse gas emissions, and future climates using IPCC emission scenarios. Modelled globally averaged CO2 concentration, land and ocean carbon uptake compare well with observation-based values at year 2000, as do the annual cycle and latitudinal distribution of CO2, instilling confidence that the model is suitable for future projections of carbon cycle behaviour in a changing climate. Land use change emissions are calculated explicitly using an observation-based time series of fractional coverage of different plant functional types. A more complete description of the model may be found in Arora et al. (2009). Differences in the land-atmosphere CO2 flux from the present to the future period under the SRES A2 emissions scenario show an increase in land sinks by a factor of 7.5 globally, mostly the result of CO2 fertilization. By contrast, the magnitude of the global ocean CO2 sink increases by a factor of only 2.3 by 2100. Expressed as a fraction of total emissions, ocean carbon uptake decreases throughout the 2000-2100 period, while land carbon uptake increases until around 2050, then declines. The result is an increase in airborne CO2 fraction after the mid-21st century, reaching a value of 0.55 by 2100. The simulated decline in ocean carbon uptake over the 21st century occurs despite steadily rising atmospheric CO2. This behaviour is usually attributed to climate-induced changes in surface temperature and salinity that reduce CO2 solubility, and increasing ocean stratification that weakens the biological pump. However, ocean biological processes such as dinitrogen fixation and calcification may also play an important role. Although not well understood at present, improved parameterizations of these processes will increase confidence in projections of future trends in CO2 uptake.

Cell biology and molecular basis of denitrification.

PubMed Central

Zumft, W G

1997-01-01

Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary transport, protein translocation, cytochrome c biogenesis, anaerobic gene regulation, metalloprotein assembly, and the biosynthesis of the cofactors molybdopterin and heme D1. An important class of regulators for the anaerobic expression of the denitrification apparatus are transcription factors of the greater FNR family. Nitrate and nitric oxide, in addition to being respiratory substrates, have been identified as signaling molecules for the induction of distinct N oxide-metabolizing enzymes. PMID:9409151

Hinged external fixation of the elbow.

PubMed

Chen, Neal C; Julka, Abhishek

2010-08-01

Hinged external fixation of the elbow provides the advantages of static fixation with the benefits of continued motion through the joint. Indications for the use of this method of fixation include traumatic instability, distraction interposition arthroplasty, instability after contracture release, and instability after excision of heterotopic ossification. Orthopedic surgeons should be familiar with hinged fixators and their application when faced with an unstable ulnohumeral joint. 2010 Elsevier Inc. All rights reserved.

Biomechanical comparison of straight DCP and helical plates for fixation of transverse and oblique bone fractures.

PubMed

Aksakal, Bunyamin; Gurger, Murat; Say, Yakup; Yilmaz, Erhan

2014-01-01

Biomechanical comparison of straight DCP and helical plates for fixation of transversal and oblique tibial bone fractures were analyzed and compared to each other by axial compression, bending and torsion tests. An in vitro osteosynthesis of transverse (TF) and oblique bone fracture (OF) fixations have been analysed on fresh sheep tibias by using the DCP and helical compression plates (HP). Statistically significant differences were found for both DCP and helical plate fixations under axial compression, bending and torsional loads. The strength of fixation systems was in favor of DC plating with exception of the TF-HP fixation group under compression loads and torsional moments. The transvers fracture (TF) stability was found to be higher than that found in oblique fracture (OF) fixed by helical plates (HP). However, under torsional testing, compared to conventional plating, the helical plate fixations provided a higher torsional resistance and strength. The maximum stiffness at axial compression loading and maximum torsional strength was achieved in torsional testing for the TF-HP fixations. From in vitro biomechanical analysis, fracture type and plate fixation system groups showed different responses under different loadings. Consequently, current biomechanical analyses may encourage the usage of helical HP fixations in near future during clinical practice for transverse bone fractures.

Neural Correlates of Fixation Duration during Real-world Scene Viewing: Evidence from Fixation-related (FIRE) fMRI.

PubMed

Henderson, John M; Choi, Wonil

2015-06-01

During active scene perception, our eyes move from one location to another via saccadic eye movements, with the eyes fixating objects and scene elements for varying amounts of time. Much of the variability in fixation duration is accounted for by attentional, perceptual, and cognitive processes associated with scene analysis and comprehension. For this reason, current theories of active scene viewing attempt to account for the influence of attention and cognition on fixation duration. Yet almost nothing is known about the neurocognitive systems associated with variation in fixation duration during scene viewing. We addressed this topic using fixation-related fMRI, which involves coregistering high-resolution eye tracking and magnetic resonance scanning to conduct event-related fMRI analysis based on characteristics of eye movements. We observed that activation in visual and prefrontal executive control areas was positively correlated with fixation duration, whereas activation in ventral areas associated with scene encoding and medial superior frontal and paracentral regions associated with changing action plans was negatively correlated with fixation duration. The results suggest that fixation duration in scene viewing is controlled by cognitive processes associated with real-time scene analysis interacting with motor planning, consistent with current computational models of active vision for scene perception.

Respiratory Nitrate Ammonification by Shewanella oneidensis MR-1▿

PubMed Central

Cruz-García, Claribel; Murray, Alison E.; Klappenbach, Joel A.; Stewart, Valley; Tiedje, James M.

2007-01-01

Anaerobic cultures of Shewanella oneidensis MR-1 grown with nitrate as the sole electron acceptor exhibited sequential reduction of nitrate to nitrite and then to ammonium. Little dinitrogen and nitrous oxide were detected, and no growth occurred on nitrous oxide. A mutant with the napA gene encoding periplasmic nitrate reductase deleted could not respire or assimilate nitrate and did not express nitrate reductase activity, confirming that the NapA enzyme is the sole nitrate reductase. Hence, S. oneidensis MR-1 conducts respiratory nitrate ammonification, also termed dissimilatory nitrate reduction to ammonium, but not respiratory denitrification. PMID:17098906

The microbial nitrogen-cycling network.

PubMed

Kuypers, Marcel M M; Marchant, Hannah K; Kartal, Boran

2018-05-01

Nitrogen is an essential component of all living organisms and the main nutrient limiting life on our planet. By far, the largest inventory of freely accessible nitrogen is atmospheric dinitrogen, but most organisms rely on more bioavailable forms of nitrogen, such as ammonium and nitrate, for growth. The availability of these substrates depends on diverse nitrogen-transforming reactions that are carried out by complex networks of metabolically versatile microorganisms. In this Review, we summarize our current understanding of the microbial nitrogen-cycling network, including novel processes, their underlying biochemical pathways, the involved microorganisms, their environmental importance and industrial applications.

Halobacterium denitrificans sp. nov. - An extremely halophilic denitrifying bacterium

NASA Technical Reports Server (NTRS)

Tomlinson, G. A.; Jahnke, L. L.; Hochstein, L. I.

1986-01-01

Halobacterium denitrificans was one of several carbohydrate-utilizing, denitrifying, extremely halophilic bacteria isolated by anaerobic enrichment in the presence of nitrate. Anaerobic growth took place only when nitrate (or nitrite) was present and was accompanied by the production of dinitrogen. In the presence of high concentrations of nitrate (i.e., 0.5 percent), nitrous oxide and nitrite were also detected. When grown aerobically in a mineral-salts medium containing 0.005 percent yeast extract, H. denitrificans utilized a variety of carbohydrates as sources of carbon and energy. In every case, carbohydrate utilization was accompanied by acid production.

Halobacterium denitrificans sp. nov., an extremely halophilic denitrifying bacterium

NASA Technical Reports Server (NTRS)

Tomlinson, G. A.; Jahnke, L. L.; Hochstein, L. I.

1986-01-01

Halobacterium denitrificans was one of several carbohydrate-utilizing, denitrifying, extremely halophilic bacteria isolated by anaerobic enrichment in the presence of nitrate. Anaerobic growth took place only when nitrate (or nitrite) was present and was accompanied by the production of dinitrogen. In the presence of high concentrations of nitrate (i.e., 0.5 percent), nitrous oxide and nitrite were also detected. When grown aerobically in a mineral-salts medium containing 0.005 percent yeast extract, H. denitrificans utilized a variety of carbohydrates as sources of carbon and energy. In every case, carbohydrate utilization was accompanied by acid production.

Changes in biomolecular profile in a single nucleolus during cell fixation.

PubMed

Kuzmin, Andrey N; Pliss, Artem; Prasad, Paras N

2014-11-04

Fixation of biological sample is an essential technique applied in order to "freeze" in time the intracellular molecular content. However, fixation induces changes of the cellular molecular structure, which mask physiological distribution of biomolecules and bias interpretation of results. Accurate, sensitive, and comprehensive characterization of changes in biomolecular composition, occurring during fixation, is crucial for proper analysis of experimental data. Here we apply biomolecular component analysis for Raman spectra measured in the same nucleoli of HeLa cells before and after fixation by either formaldehyde solution or by chilled ethanol. It is found that fixation in formaldehyde does not strongly affect the Raman spectra of nucleolar biomolecular components, but may significantly decrease the nucleolar RNA concentration. At the same time, ethanol fixation leads to a proportional increase (up to 40%) in concentrations of nucleolar proteins and RNA, most likely due to cell shrinkage occurring in the presence of coagulant fixative. Ethanol fixation also triggers changes in composition of nucleolar proteome, as indicated by an overall reduction of the α-helical structure of proteins and increase in the concentration of proteins containing the β-sheet conformation. We conclude that cross-linking fixation is a more appropriate protocol for mapping of proteins in situ. At the same time, ethanol fixation is preferential for studies of RNA-containing macromolecules. We supplemented our quantitative Raman spectroscopic measurements with mapping of the protein and lipid macromolecular groups in live and fixed cells using coherent anti-Stokes Raman scattering nonlinear optical imaging.

A model based on temporal dynamics of fixations for distinguishing expert radiologists' scanpaths

NASA Astrophysics Data System (ADS)

Gandomkar, Ziba; Tay, Kevin; Brennan, Patrick C.; Mello-Thoms, Claudia

2017-03-01

This study investigated a model which distinguishes expert radiologists from less experienced radiologists based on features describing spatio-temporal dynamics of their eye movement during interpretation of digital mammograms. Eye movements of four expert and four less experienced radiologists were recorded during interpretation of 120 two-view digital mammograms of which 59 had biopsy proven cancers. For each scanpath, a two-dimensional recurrence plot, which represents the radiologist's refixation pattern, was generated. From each plot, six features indicating the spatio-temporal dynamics of fixations were extracted. The first feature measured the percentage of recurrent fixations; the second indicated the percentage of recurrent fixations which was fixated later in several consecutive fixations; the third measured the percentage of recurrent fixations that form a repeated sequence of fixations and the fourth assessed whether the recurrent fixations were occurring sequentially close together. The number of switches between the two mammographic views was also measured, as was the average number of consecutive fixations in each view before switching. These six features along with total time on case and average fixation duration were fed into a support vector machine whose performance was evaluated using 10-fold cross validation. The model achieved a sensitivity of 86.3% and a specificity of 85.2% for distinguishing experts' scanpaths. The obtained result suggests that spatio-temporal dynamics of eye movements can characterize expertise level and has potential applications for monitoring the development of expertise among radiologists as a result of different training regimes and continuing education schemes.

Correction of complex equino cavo varus foot deformity in skeletally mature patients by Ilizarov external fixation versus staged external-internal fixation.

PubMed

Emara, Khaled; El Moatasem, El Hussein; El Shazly, Ossama

2011-12-01

Complex foot deformity is a multi-planar foot deformity with many etiologic factors. Different corrective procedures using Ilizarov external fixation have been described which include, soft tissue release, V-osteotomy, multiple osteotomies and triple fusion. In this study we compare the results of two groups of skeletally mature patients with complex foot deformity who were treated by two different protocols. The first group (27 patients, 29 feet) was treated by triple fusion fixed by Ilizarov external fixator until union. The second group (29 patients, 30 feet), was treated by triple fusion with initial fixation by Ilizarov external fixation until correction of the deformity was achieved clinically, and then the Ilizarov fixation was replaced by internal fixation using percutaneous screws. Both groups were compared as regard the surgical outcome and the incidence of complications. There was statistically significant difference between the two groups regarding duration of external fixation and duration of casting with shorter duration in the group 2. Also there was statistically significant difference between both groups regarding pin tract infection with less incidence in group 2. Early removal of Ilizarov external fixation after correction of the deformity and percutaneous internal fixation using 6.5 cannulated screws can shorten the duration of treatment and be more comfortable for the patient with a low risk of recurrence or infection. Copyright © 2010 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

Biomechanical Evaluation of Standard Versus Extended Proximal Fixation Olecranon Plates for Fixation of Olecranon Fractures.

PubMed

Boden, Allison L; Daly, Charles A; Dalwadi, Poonam P; Boden, Stephanie A; Hutton, William C; Muppavarapu, Raghuveer C; Gottschalk, Michael B

2018-01-01

Small olecranon fractures present a significant challenge for fixation, which has resulted in development of plates with proximal extension. Olecranon-specific plates with proximal extensions are widely thought to offer superior fixation of small proximal fragments but have distinct disadvantages: larger dissection, increased hardware prominence, and the increased possibility of impingement. Previous biomechanical studies of olecranon fracture fixation have compared methods of fracture fixation, but to date there have been no studies defining olecranon plate fixation strength for standard versus extended olecranon plates. The purpose of this study is to evaluate the biomechanical utility of the extended plate for treatment of olecranon fractures. Sixteen matched pairs of fresh-frozen human cadaveric elbows were used. Of the 16, 8 matched pairs received a transverse osteotomy including 25% and 8 including 50% of the articular surface on the proximal fragment. One elbow from each pair was randomly assigned to a standard-length plate, and the other elbow in the pair received the extended-length plate, for fixation of the fracture. The ulnae were cyclically loaded and subsequently loaded to failure, with ultimate load, number of cycles, and gap formation recorded. There was no statistically significant difference between the standard and extended fixation plates in simple transverse fractures at either 25% or 50% from the proximal most portion of the articular surface of the olecranon. Standard fixation plates are sufficient for the fixation of small transverse fractures, but caution should be utilized particularly with comminution and nontransverse fracture patterns.

Use of dissolved and vapor‐phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the subsurface

USGS Publications Warehouse

Amos, Richard T.; Mayer, K. Ulrich; Bekins, Barbara A.; Delin, Geoffrey N.; Williams, Randi L.

2005-01-01

At many sites contaminated with petroleum hydrocarbons, methanogenesis is a significant degradation pathway. Techniques to estimate CH4 production, consumption, and transport processes are needed to understand the geochemical system, provide a complete carbon mass balance, and quantify the hydrocarbon degradation rate. Dissolved and vapor‐phase gas data collected at a petroleum hydrocarbon contaminated site near Bemidji, Minnesota, demonstrate that naturally occurring nonreactive or relatively inert gases such as Ar and N2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity in the subsurface. In the vadose zone, regions of Ar and N2 depletion and enrichment are indicative of methanogenic and methanotrophic zones, and concentration gradients between the regions suggest that reaction‐induced advection can be an important gas transport process. In the saturated zone, dissolved Ar and N2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along the flow path, into the downgradient aquifer, is largely controlled by physical processes. Slight but discernable preferential depletion of N2 over Ar, in both the saturated and unsaturated zones near the free‐phase oil, suggests reactivity of N2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site.

Flow cytometry for receptor analysis from ex-vivo brain tissue in adult rat.

PubMed

Benoit, A; Guillamin, M; Aitken, P; Smith, P F; Philoxene, B; Sola, B; Poulain, L; Coquerel, A; Besnard, S

2018-07-01

Flow cytometry allows single-cell analysis of peripheral biological samples and is useful in many fields of research and clinical applications, mainly in hematology, immunology, and oncology. In the neurosciences, the flow cytometry separation method was first applied to stem cell extraction from healthy or cerebral tumour tissue and was more recently tested in order to phenotype brain cells, hippocampal neurogenesis, and to detect prion proteins. However, it remains sparsely applied in quantifying membrane receptors in relation to synaptic plasticity. We aimed to optimize a flow cytometric procedure for receptor quantification in neurons and non-neurons. A neural dissociation process, myelin separation, fixation, and membrane permeability procedures were optimized to maximize cell survival and analysis in hippocampal tissue obtained from adult rodents. We then aimed to quantify membrane muscarinic acetylcholine receptors (mAChRs) in rats with and without bilateral vestibular loss (BVL). mAChR's were quantified for neuronal and non-neuronal cells in the hippocampus and striatum following BVL. At day 30 but not at day 7 following BVL, there was a significant increase (P ≤ 0.05) in the percentage of neurons expressing M 2/4 mAChRs in both the hippocampus and the striatum. Here, we showed that flow cytometry appears to be a reliable method of membrane receptor quantification in ex-vivo brain tissue. Copyright © 2018 Elsevier B.V. All rights reserved.

When the mean is not enough: Calculating fixation time distributions in birth-death processes.

PubMed

Ashcroft, Peter; Traulsen, Arne; Galla, Tobias

2015-10-01

Studies of fixation dynamics in Markov processes predominantly focus on the mean time to absorption. This may be inadequate if the distribution is broad and skewed. We compute the distribution of fixation times in one-step birth-death processes with two absorbing states. These are expressed in terms of the spectrum of the process, and we provide different representations as forward-only processes in eigenspace. These allow efficient sampling of fixation time distributions. As an application we study evolutionary game dynamics, where invading mutants can reach fixation or go extinct. We also highlight the median fixation time as a possible analog of mixing times in systems with small mutation rates and no absorbing states, whereas the mean fixation time has no such interpretation.

The role of eye fixation in memory enhancement under stress - An eye tracking study.

PubMed

Herten, Nadja; Otto, Tobias; Wolf, Oliver T

2017-04-01

In a stressful situation, attention is shifted to potentially relevant stimuli. Recent studies from our laboratory revealed that participants stressed perform superior in a recognition task involving objects of the stressful episode. In order to characterize the role of a stress induced alteration in visual exploration, the present study investigated whether participants experiencing a laboratory social stress situation differ in their fixation from participants of a control group. Further, we aimed at shedding light on the relation of fixation behaviour with obtained memory measures. We randomly assigned 32 male and 31 female participants to a control or a stress condition consisting of the Trier Social Stress Test (TSST), a public speaking paradigm causing social evaluative threat. In an established 'friendly' control condition (f-TSST) participants talk to a friendly committee. During both conditions, the committee members used ten office items (central objects) while another ten objects were present without being used (peripheral objects). Participants wore eye tracking glasses recording their fixations. On the next day, participants performed free recall and recognition tasks involving the objects present the day before. Stressed participants showed enhanced memory for central objects, accompanied by longer fixation times and larger fixation amounts on these objects. Contrasting this, fixation towards the committee faces showed the reversed pattern; here, control participants exhibited longer fixations. Fixation indices and memory measures were, however, not correlated with each other. Psychosocial stress is associated with altered fixation behaviour. Longer fixation on objects related to the stressful situation may reflect enhanced encoding, whereas diminished face fixation suggests gaze avoidance of aversive, socially threatening stimuli. Modified visual exploration should be considered in future stress research, in particular when focussing on memory for a stressful episode. Copyright © 2017 Elsevier Inc. All rights reserved.

The importance of nodule CO2 fixation for the efficiency of symbiotic nitrogen fixation in pea at vegetative growth and during pod formation.

PubMed

Fischinger, Stephanie Anastasia; Schulze, Joachim

2010-05-01

Nodule CO2 fixation is of pivotal importance for N2 fixation. The process provides malate for bacteroids and oxaloacetate for nitrogen assimilation. The hypothesis of the present paper was that grain legume nodules would adapt to higher plant N demand and more restricted carbon availability at pod formation through increased nodule CO2 fixation and a more efficient N2 fixation. Growth, N2 fixation, and nodule composition during vegetative growth and at pod formation were studied in pea plants (Pisum sativum L.). In parallel experiments, 15N2 and 13CO2 uptake, as well as nodule hydrogen and CO2 release, was measured. Plants at pod formation showed higher growth rates and N2 fixation per plant when compared with vegetative growth. The specific activity of active nodules was about 25% higher at pod formation. The higher nodule activity was accompanied by higher amino acid concentration in nodules and xylem sap with a higher share of asparagine. Nodule 13CO2 fixation was increased at pod formation, both per plant and per 15N2 fixed unit. However, malate concentration in nodules was only 40% of that during vegetative growth and succinate was no longer detectable. The data indicate that increased N2 fixation at pod formation is connected with strongly increased nodule CO2 fixation. While the sugar concentration in nodules at pod formation was not altered, the concentration of organic acids, namely malate and succinate, was significantly lower. It is concluded that strategies to improve the capability of nodules to fix CO2 and form organic acids might prolong intensive N2 fixation into the later stages of pod formation and pod filling in grain legumes.

Internal Versus External Fixation of Charcot Midfoot Deformity Realignment.

PubMed

Lee, Daniel J; Schaffer, Joseph; Chen, Tien; Oh, Irvin

2016-07-01

Internal and external fixation techniques have been described for realignment and arthrodesis of Charcot midfoot deformity. There currently is no consensus on the optimal method of surgical reconstruction. This systematic review compared the clinical results of surgical realignment with internal and external fixation, specifically in regard to return to functional ambulation, ulcer occurrence, nonunion, extremity amputation, unplanned further surgery, deep infection, wound healing problems, peri- or intraoperative fractures, and total cases with any complication. A search of multiple databases for all relevant articles published from January 1, 1990, to March 22, 2014, was performed. A logistic regression model evaluated each of the outcomes and its association with the type of fixation method. The odds of returning to functional ambulation were 25% higher for internal fixation (odds ratio [OR], 1.259). Internal fixation had a 42% reduced rate of ulcer occurrence (OR, 0.578). External fixation was 8 times more likely to develop radiographic nonunion than internal fixation (OR, 8.2). Internal fixation resulted in a 1.5-fold increase in extremity amputation (OR, 1.488), a 2-fold increase in deep infection (OR, 2.068), a 3.4-fold increase in wound healing complications (OR, 3.405), and a 1.5-fold increase in the total number of cases experiencing any complication (OR, 1.525). This was associated with a 20% increase in the need for unplanned further surgery with internal fixation (OR, 1.221). Although internal fixation may decrease the risk of nonunion and increase return to functional ambulation, it had a higher rate of overall complications than external fixation for realignment and arthrodesis of Charcot midfoot deformity. [Orthopedics. 2016; 39(4):e595-e601.]. Copyright 2016, SLACK Incorporated.

Comparing Different Surgical Techniques for Addressing the Posterior Malleolus in Supination External Rotation Ankle Fractures and the Need for Syndesmotic Screw Fixation.

PubMed

Li, Mengnai; Collier, Rachel C; Hill, Brian W; Slinkard, Nathaniel; Ly, Thuan V

Trimalleolar ankle fractures are unstable injuries with possible syndesmotic disruption. Recent data have described inherent morbidity associated with screw fixation of the syndesmosis, including the potential for malreduction, hardware irritation, and post-traumatic arthritis. The posterior malleolus is an important soft tissue attachment for the posterior inferior syndesmosis ligament. We hypothesized that fixation of a sizable posterior malleolar (PM) fracture in supination external rotation type IV (SER IV) ankle fractures would act to stabilize the syndesmosis and minimize or eliminate the need for trans-syndesmotic fixation. A retrospective review of trimalleolar ankle fractures surgically treated from October 2006 to April of 2011 was performed. A total of 143 trimalleolar ankle fractures were identified, and 97 were classified as SER IV. Of the 97 patients, 74 (76.3%) had a sizable PM fragment. Syndesmotic fixation was required in 7 of 34 (20%) and 27 of 40 (68%), respectively, when the PM was fixed versus not fixed (p = .0002). When the PM was indirectly reduced using an anterior to posterior screw, 7 of 15 patients (46.7%) required syndesmotic fixation compared with none of 19 patients when the PM fragment was fixated with direct posterior lateral plate fixation (p = .0012). Fixation of the PM fracture in SER IV ankle fractures can restore syndesmotic stability and, thus, lower the rate of syndesmotic fixation. We found that fixation of a sizable PM fragment in SER IV or equivalent injuries through posterolateral plating can eliminate the need for syndesmotic screw fixation. Copyright © 2017 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Low rates of nitrogen fixation in eastern tropical South Pacific surface waters

PubMed Central

Knapp, Angela N.; Casciotti, Karen L.; Berelson, William M.; Prokopenko, Maria G.; Capone, Douglas G.

2016-01-01

An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2 fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2 fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2 fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m−2 d−1 based on sediment trap fluxes. Whereas the fractional importance of N2 fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2 fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m−2 d−1, and detected N2 fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2 fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2 fixation in the ETSP. PMID:26976587

Comminuted olecranon fracture fixation with pre-contoured plate: Comparison of composite and cadaver bones

PubMed Central

Hamilton Jr, David A; Reilly, Danielle; Wipf, Felix; Kamineni, Srinath

2015-01-01

AIM: To determine whether use of a precontoured olecranon plate provides adequate fixation to withstand supraphysiologic force in a comminuted olecranon fracture model. METHODS: Five samples of fourth generation composite bones and five samples of fresh frozen human cadaveric left ulnae were utilized for this study. The cadaveric specimens underwent dual-energy X-ray absorptiometry (DEXA) scanning to quantify the bone quality. The composite and cadaveric bones were prepared by creating a comminuted olecranon fracture and fixed with a pre-contoured olecranon plate with locking screws. Construct stiffness and failure load were measured by subjecting specimens to cantilever bending moments until failure. Fracture site motion was measured with differential variable resistance transducer spanning the fracture. Statistical analysis was performed with two-tailed Mann-Whitney-U test with Monte Carlo Exact test. RESULTS: There was a significant difference in fixation stiffness and strength between the composite bones and human cadaver bones. Failure modes differed in cadaveric and composite specimens. The load to failure for the composite bones (n = 5) and human cadaver bones (n = 5) specimens were 10.67 nm (range 9.40-11.91 nm) and 13.05 nm (range 12.59-15.38 nm) respectively. This difference was statistically significant (P ˂ 0.007, 97% power). Median stiffness for composite bones and human cadaver bones specimens were 5.69 nm/mm (range 4.69-6.80 nm/mm) and 7.55 nm/mm (range 6.31-7.72 nm/mm). There was a significant difference for stiffness (P ˂ 0.033, 79% power) between composite bones and cadaveric bones. No correlation was found between the DEXA results and stiffness. All cadaveric specimens withstood the physiologic load anticipated postoperatively. Catastrophic failure occurred in all composite specimens. All failures resulted from composite bone failure at the distal screw site and not hardware failure. There were no catastrophic fracture failures in the cadaveric specimens. Failure of 4/5 cadaveric specimens was defined when a fracture gap of 2 mm was observed, but 1/5 cadaveric specimens failed due to a failure of the triceps mechanism. All failures occurred at forces greater than that expected in postoperative period prior to healing. CONCLUSION: The pre-contoured olecranon plate provides adequate fixation to withstand physiologic force in a composite bone and cadaveric comminuted olecranon fracture model. PMID:26495247

Distributions and Abundances of Sublineages of the N2-Fixing Cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN-A) in the New Caledonian Coral Lagoon

PubMed Central

Henke, Britt A.; Turk-Kubo, Kendra A.; Bonnet, Sophie; Zehr, Jonathan P.

2018-01-01

Nitrogen (N2) fixation is a major source of nitrogen that supports primary production in the vast oligotrophic areas of the world’s oceans. The Western Tropical South Pacific has recently been identified as a hotspot for N2 fixation. In the Noumea lagoon (New Caledonia), high abundances of the unicellular N2-fixing cyanobacteria group A (UCYN-A), coupled with daytime N2 fixation rates associated with the <10 μm size fraction, suggest UCYN-A may be an important diazotroph (N2-fixer) in this region. However, little is known about the seasonal variability and diversity of UCYN-A there. To assess this, surface waters from a 12 km transect from the mouth of the Dumbea River to the Dumbea Pass were sampled monthly between July 2012 and March 2014. UCYN-A abundances for two of the defined sublineages, UCYN-A1 and UCYN-A2, were quantified using qPCR targeting the nifH gene, and the nifH-based diversity of UCYN-A was characterized by identifying oligotypes, alternative taxonomic units defined by nucleotide positions with high variability. UCYN-A abundances were dominated by the UCYN-A1 sublineage, peaked in September and October and could be predicted by a suite of nine environmental parameters. At the sublineage level, UCYN-A1 abundances could be predicted based on lower temperatures (<23°C), nitrate concentrations, precipitation, wind speed, while UCYN-A2 abundances could be predicted based on silica, and chlorophyll a concentrations, wind direction, precipitation, and wind speed. Using UCYN-A nifH oligotyping, similar environmental variables explained the relative abundances of sublineages and their associated oligotypes, with the notable exception of the UCYN-A2 oligotype (oligo43) which had relative abundance patterns distinct from the dominant UCYN-A2 oligotype (oligo3). The results support an emerging pattern that UCYN-A is comprised of a diverse group of strains, with sublineages that may have different ecological niches. By identifying environmental factors that influence the composition and abundance of UCYN-A sublineages, this study helps to explain global UCYN-A abundance patterns, and is important for understanding the significance of N2 fixation at local and global scales. PMID:29674998

Rapid Prototyping Amphiphilic Polymer/Hydroxyapatite Composite Scaffolds with Hydration-Induced Self-Fixation Behavior

PubMed Central

Kutikov, Artem B.; Gurijala, Anvesh

2015-01-01

Two major factors hampering the broad use of rapid prototyped biomaterials for tissue engineering applications are the requirement for custom-designed or expensive research-grade three-dimensional (3D) printers and the limited selection of suitable thermoplastic biomaterials exhibiting physical characteristics desired for facile surgical handling and biological properties encouraging tissue integration. Properly designed thermoplastic biodegradable amphiphilic polymers can exhibit hydration-dependent hydrophilicity changes and stiffening behavior, which may be exploited to facilitate the surgical delivery/self-fixation of the scaffold within a physiological tissue environment. Compared to conventional hydrophobic polyesters, they also present significant advantages in blending with hydrophilic osteoconductive minerals with improved interfacial adhesion for bone tissue engineering applications. Here, we demonstrated the excellent blending of biodegradable, amphiphilic poly(D,L-lactic acid)-poly(ethylene glycol)-poly(D,L-lactic acid) (PLA-PEG-PLA) (PELA) triblock co-polymer with hydroxyapatite (HA) and the fabrication of high-quality rapid prototyped 3D macroporous composite scaffolds using an unmodified consumer-grade 3D printer. The rapid prototyped HA-PELA composite scaffolds and the PELA control (without HA) swelled (66% and 44% volume increases, respectively) and stiffened (1.38-fold and 4-fold increases in compressive modulus, respectively) in water. To test the hypothesis that the hydration-induced physical changes can translate into self-fixation properties of the scaffolds within a confined defect, a straightforward in vitro pull-out test was designed to quantify the peak force required to dislodge these scaffolds from a simulated cylindrical defect at dry versus wet states. Consistent with our hypothesis, the peak fixation force measured for the PELA and HA-PELA scaffolds increased 6-fold and 15-fold upon hydration, respectively. Furthermore, we showed that the low-fouling 3D PELA inhibited the attachment of NIH3T3 fibroblasts or bone marrow stromal cells while the HA-PELA readily supported cellular attachment and osteogenic differentiation. Finally, we demonstrated the feasibility of rapid prototyping biphasic PELA/HA-PELA scaffolds for potential guided bone regeneration where an osteoconductive scaffold interior encouraging osteointegration and a nonadhesive surface discouraging fibrous tissue encapsulation is desired. This work demonstrated that by combining facile and readily translatable rapid prototyping approaches with unique biomaterial designs, biodegradable composite scaffolds with well-controlled macroporosities, spatially defined biological microenvironment, and useful handling characteristics can be developed. PMID:25025950

[Surgical strategy for upper cervical vertebrae instability through the anterior approach].

PubMed

Huang, Wei-bing; Cai, Xian-hua; Chen, Zhuang-hong; Huang, Ji-feng; Liu, Xi-ming; Wei, Shi-jun

2013-07-01

To explore the choice and effect of internal fixation in treating upper cervical vertebrae instability through anterior approach. From March 2000 to September 2010,83 patients with upper cervical vertebrae instability were treated with internal fixation through anterior approach. There were 59 males and 24 females with a mean age of 42 years old (ranged, 20 to 68). Among these patients, 36 patients were treated with odontoid screw fixation, 16 patients with C1,2 transarticular screw fixation, 23 patients with C2,3 steel plate fixation, 5 patients with odontoid screw and transarticular screw fixation,2 patients with odontoid screw and C2.3 steel plate fixation, 1 patient with C1,2 transarticular screw and C2,3 steel plate fixation. One patient with completely cervical vertebrae cord injury died of pulmonary infection after C1,2 transarticular screw fixation. Other patients were followed up from 8 to 36 months with an average of 15 months. Upper cervical vertebrae stability were restored without vertebral artery and spinal cord injury. Thirty-six patients were treated with odontoid screw fixation and 5 patients were treated with screw combined with transarticular screw fixation obtained bone union in the dentations without bone graft. Among the 16 patients treated with C1,2 transarticular screw fixation, 13 patients obtained bone union after bone graft; 1 patient died of pulmonary infection after surgery; 1 patient with comminuted odontoid fracture of type II C and atlantoaxial anterior dislocation did not obtain bone union after bone graft,but the fibrous healing was strong enough to maintain the atlantoaixal joint stability; 1 patient with obsolete atlantoaxial anterior dislocation were re-treated with Brooks stainless steel wire fixation and bone graft through posterior approach, and finally obtained bone union. It could obtain satisfactory effects depending on the difference of cervical vertebrae instability to choose the correctly surgical method.

Paraformaldehyde fixation of neutrophils for immunolabeling of granule antigens in cryoultrasections.

PubMed

Elliott, E; Dennison, C; Fortgens, P H; Travis, J

1995-10-01

Paraformaldehyde (PFA) fixation was optimized to facilitate the immobilization and labeling of multiple granule antigens, using short fixation regimens and cryoultramicrotomy of unembedded neutrophils (PMNs). In the optimal protocol, extraction of azurophil granule antigens (especially of the abundant elastase) was obviated by manipulating the polymeric state of PFA, and hence its rate of cross-linking, by altering its concentration and pH in a multistep process. Primary fixation conditions used (4% PFA, pH 8.0, 5 min) favor fixative penetration and rapid cross-linking. Stable cross-linking of the antigen was achieved in a secondary fixation step using conditions that favor larger, more cross-linking polymeric forms of PFA (8% PFA, pH 7.2, 15 min). Immobilization of granule antigens was enhanced by flotation of cut sections on fixative (8% PFA, pH 8.0) before labeling and by using post-labeling fixation with 1% glutaraldehyde. The optimized protocol facilitated immobilization and immunolabeling of elastase, myeloperoxidase, lactoferrin, and cathepsin D in highly hydrated, unembedded PMNs.

Perception of Object-Context Relations: Eye-Movement Analyses in Infants and Adults

PubMed Central

Bornstein, Marc H.; Mash, Clay; Arterberry, Martha E.

2011-01-01

Twenty-eight 4-month-olds’ and 22 20-year-olds’ attention to object-context relations was investigated using a common eye-movement paradigm. Infants and adults scanned both objects and contexts. Infants showed equivalent preferences for animals and vehicles and for congruent and incongruent object-context relations overall, more fixations of objects in congruent object-context relations, more fixations of contexts in incongruent object-context relations, more fixations of objects than contexts in vehicle scenes, and more fixation shifts in incongruent than congruent vehicle scenes. Adults showed more fixations of congruent than incongruent scenes, vehicles than animals, and objects than contexts, equal fixations of animals and their contexts but more fixations of vehicles than their contexts, and more shifts of fixation when inspecting animals in context than vehicles in context. These findings for location, number, and order of eye movements indicate that object-context relations play a dynamic role in the development and allocation of attention. PMID:21244146

Reevaluating split-fovea processing in word recognition: hemispheric dominance, retinal location, and the word-nonword effect.

PubMed

Jordan, Timothy R; Paterson, Kevin B; Kurtev, Stoyan

2009-03-01

Many studies have claimed that hemispheric projections are split precisely at the foveal midline and so hemispheric asymmetry affects word recognition right up to the point of fixation. To investigate this claim, four-letter words and nonwords were presented to the left or right of fixation, either close to fixation in foveal vision or farther from fixation in extrafoveal vision. Presentation accuracy was controlled using an eyetracker linked to a fixation-contingent display. Words presented foveally produced identical performance on each side of fixation, but words presented extrafoveally showed a clear left-hemisphere (LH) advantage. Nonwords produced no evidence of hemispheric asymmetry in any location. Foveal stimuli also produced an identical word-nonword effect on each side of fixation, whereas extrafoveal stimuli produced a word-nonword effect only for LH (not right-hemisphere) displays. These findings indicate that functional unilateral projections to contralateral hemispheres exist in extrafoveal locations but provide no evidence of a functional division in hemispheric processing at fixation.

Diluted povidone-iodine versus saline for dressing metal-skin interfaces in external fixation.

PubMed

Chan, C K; Saw, A; Kwan, M K; Karina, R

2009-04-01

To compare infection rates associated with 2 dressing solutions for metal-skin interfaces. 60 patients who underwent distraction osteogenesis with external fixators were equally randomised into 2 dressing solution groups (diluted povidone-iodine vs. saline). Fixations were attained using either rigid stainless steel 5-mm diameter half pins or smooth stainless steel 1.8-mm diameter wires. Half-pin fixation had one metal-skin interface, whereas wire fixation had 2 interfaces. Patients were followed up every 2 weeks for 6 months. Of all 788 metal-skin interfaces, 143 (18%) were infected: 72 (19%) of 371 in the diluted povidone-iodine group and 71 (17%) of 417 in the saline group. Dressing solution and patient age did not significantly affect infection rates. Half-pin fixation was more likely to become infected than wire fixation (25% vs 15%). Saline is as effective as diluted povidone-iodine as a dressing solution for metal-skin interfaces of external fixators. Saline is recommended in view of its easy availability and lower costs.

Distal tibial pilon fractures (AO/OTA type B, and C) treated with the external skeletal and minimal internal fixation method.

PubMed

Milenković, Sasa; Mitković, Milorad; Micić, Ivan; Mladenović, Desimir; Najman, Stevo; Trajanović, Miroslav; Manić, Miodrag; Mitković, Milan

2013-09-01

Distal tibial pilon fractures include extra-articular fractures of the tibial metaphysis and the more severe intra-articular tibial pilon fractures. There is no universal method for treating distal tibial pilon fractures. These fractures are treated by means of open reduction, internal fixation (ORIF) and external skeletal fixation. The high rate of soft-tissue complications associated with primary ORIF of pilon fractures led to the use of external skeletal fixation, with limited internal fixation as an alternative technique for definitive management. The aim of this study was to estimate efficacy of distal tibial pilon fratures treatment using the external skeletal and minimal internal fixation method. We presented a series of 31 operated patients with tibial pilon fractures. The patients were operated on using the method of external skeletal fixation with a minimal internal fixation. According to the AO/OTA classification, 17 patients had type B fracture and 14 patients type C fractures. The rigid external skeletal fixation was transformed into a dynamic external skeletal fixation 6 weeks post-surgery. This retrospective study involved 31 patients with tibial pilon fractures, average age 41.81 (from 21 to 60) years. The average follow-up was 21.86 (from 12 to 48) months. The percentage of union was 90.32%, nonunion 3.22% and malunion 6.45%. The mean to fracture union was 14 (range 12-20) weeks. There were 4 (12.19%) infections around the pins of the external skeletal fixator and one (3.22%) deep infections. The ankle joint arthrosis as a late complication appeared in 4 (12.90%) patients. All arthroses appeared in patients who had type C fractures. The final functional results based on the AOFAS score were excellent in 51.61%, good in 32.25%, average in 12.90% and bad in 3.22% of the patients. External skeletal fixation and minimal internal fixation of distal tibial pilon fractures is a good method for treating all types of inta-articular pilon fractures. In fractures types B and C dynamic external skeletal fixation allows early mobility in the ankle joint.

[Do prisms according to Hans-Joachim Haase improve stereoacuity?].

PubMed

Kromeier, Miriam; Schmitt, Christina; Bach, Michael; Kommerell, Guntram

2002-06-01

The "Measuring and Correcting Methodology" after H.-J. Haase (MKH) aims at converting "fixation disparity" into bicentral fixation, using prismatic spectacles. In the context of the MKH, fixation disparity is diagnosed by a series of subjective tests. According to H.-J. Haase, a long-standing fixation disparity can lead to "disparate correspondence" between the central areas of both retinae, which consolidates the fixation disparity and gradually converts a "young" into an "old fixation disparity". In "old fixation disparity" it is thought that bicentral fixation does not occur anymore, so that stereoacuity is impaired. However, prismatic spectacles can, according to H.-J. Haase, restitute bicentral fixation and consequently improve stereoacuity, even in some cases of "old fixation disparity". Ten non-strabismic subjects with a visual acuity of >/= 1.0 in both eyes were examined. It turned out that all ten had, according to MKH, a "disparate correspondence", 5 subjects with a "young" and 5 with an "old fixation disparity". According to the MKH, a correcting prism was determined. All 10 subjects underwent the automatic Freiburg Stereoacuity Test, without and with the MKH-prism. Without the MKH-prism, the stereoscopic threshold ranged between 1.5 and 14.5 arcsec. With the MKH-prism, the values were not significantly different. Stereoacuity ranged between good and excellent in the 5 subjects with "young" as well as in the 5 subjects with "old fixation disparity". The MKH-prism did not improve the stereoacuity in any of the subjects. These results cast doubt on Haase's assertion that an "old fixation disparity" implies a reduced stereoacuity. Hence, the premise for a benefit of the MKH-prism with respect of stereoacuity is not substantiated. In the 5 subjects with a "young fixation disparity", the good stereoacuity is consistent with Haase's theory, so that a benefit of the MKH-prism for stereoacuity was not expected. In previous studies, stereoacuity was found to be better with the MKH-prism than without it. These studies are questionable since learning with repeated testing was not taken into account. We conclude that there is no sound evidence for the assumption that the MKH-prism can improve stereoacuity.

Memory for the search path: evidence for a high-capacity representation of search history.

PubMed

Dickinson, Christopher A; Zelinsky, Gregory J

2007-06-01

Using a gaze-contingent paradigm, we directly measured observers' memory capacity for fixated distractor locations during search. After approximately half of the search objects had been fixated, they were masked and a spatial probe appeared at either a previously fixated location or a non-fixated location; observers then rated their confidence that the target had appeared at the probed location. Observers were able to differentiate the 12 most recently fixated distractor locations from non-fixated locations, but analyses revealed that these locations were represented fairly coarsely. We conclude that there exists a high-capacity, but low-resolution, memory for a search path.

Fixation of a human rib by an intramedullary telescoping splint anchored by bone cement.

PubMed

Liovic, Petar; Šutalo, Ilija D; Marasco, Silvana F

2016-09-01

A novel concept for rib fixation is presented that involves the use of a bioresorbable polymer intramedullary telescoping splint. Bone cement is used to anchor each end of the splint inside the medullary canal on each side of the fracture site. In this manner, rib fixation is achieved without fixation device protrusion from the rib, making the splint completely intramedullary. Finite element analysis is used to demonstrate that such a splint/cement composite can preserve rib fixation subjected to cough-intensity force loadings. Computational fluid dynamics and porcine rib experiments were used to study the anchor formation process required to complete the fixation.

Fractures of the capitellum--a comparison of two fixation methods.

PubMed

Poynton, A R; Kelly, I P; O'Rourke, S K

1998-06-01

Isolated capitellar fractures are rare, accounting for only 1 per cent of all elbow fractures (Bryan and Morrey, The Elbow and its Disorders, 1985). Many different fixation methods have been described but no series has compared these treatment modalities because of the rarity of these fractures. This paper compares the outcome of two types of fixation of type I capitellar fractures. Group one (n = 6) had open reduction and Kirschner wire fixation while group two (n = 6) had open reduction and Herbert screw fixation. Both groups were compared clinically, functionally and radiographically. We found that Herbert screw fixation enabled earlier mobilization and a better functional outcome.

A theoretical analysis and finite element simulation of fixator-bone system stiffness on healing progression.

PubMed

Li, Jianfeng; Zhao, Xia; Hu, Xiaojie; Tao, Chunjing; Ji, Run

2018-03-01

The unilateral external fixator has become a quick and easy application for fracture stabilization of the extremities; the main value for evaluation of mechanical stability of the external fixator is stiffness. The stiffness property of the external fixator affects the local biomechanical environment of fractured bone. In this study, a theoretical model with changing Young's modulus of the callus is established by using the Castigliano's theory, investigating compression stiffness, torsional stiffness and bending stiffness of the fixator-bone system during the healing process. The effects of pin deviation angle on three stiffness methods are also investigated. In addition, finite element simulation is discussed regarding the stress distribution between the fixator and bone. The results reveal the three stiffness evaluation methods are similar for the fixator-bone system. Finite element simulation shows that with increased healing time, the transmission of the load between the fixator and bone are different. In addition, the finite element analyses verify the conclusions obtained from the theoretical model. This work helps orthopedic doctors to monitor the progression of fracture healing and determine the appropriate time for removal of a fixation device and provide important theoretical methodology.

Use of Resorbable Fixation System in Pediatric Facial Fractures.

PubMed

Wong, Frankie K; Adams, Saleigh; Hudson, Donald A; Ozaki, Wayne

2017-05-01

Resorbable fixation system (RFS) is an alternative to titanium in open reduction and internal fixation of pediatric facial fractures. This study retrospectively reviewed all medical records in a major metropolitan pediatric hospital in Cape Town, South Africa from September 2010 through May 2014. Inclusion criteria were children under the age of 13 with facial fractures who have undergone open reduction and internal fixation using RFS. Intraoperative and postoperative complications were reviewed. A total of 21 patients were included in this study. Twelve were males and 9 were females. Good dental occlusion was achieved in all patients and there were no complications intraoperatively. Three patients developed postoperative implanted-related complications: all 3 patients developed malocclusions and 1 developed an additional sterile abscess over the right zygomatic bone. For the latter, incision and drainage was performed and the problem resolved without additional operations. Resorbable fixation system is an alternative to titanium products in the setting of pediatric facial fractures without complications involving delayed union or malunion. The combination of intermaxillary fixation and RFS is not needed postoperatively for adequate fixation of mandible fractures. Resorbable fixation system is able to provide adequate internal fixation when both low-stress and high-stress craniofacial fractures occur simultaneously.

Heterophoria and fixation disparity: a review.

PubMed

Kommerell, G; Gerling, J; Ball, M; de Paz, H; Bach, M

2000-06-01

Heterophoria does not provide a reliable clue for ordering prisms in an asthenopic patient. The same reservation applies to associated phoria, as determined by prism correction of fixation disparity. Subjective tests for fixation disparity, even those with a fusionable fixation target, do not correctly indicate the vergence position of the eyes under natural viewing conditions. Attempts to measure fixation disparity on the basis of stereo disparity, using the "Measuring and Correction Methods of H.-J. Haase", have failed.

The Use of Mouse Models of Breast Cancer and Quantitative Image Analysis to Evaluate Hormone Receptor Antigenicity after Microwave-assisted Formalin Fixation

PubMed Central

Engelberg, Jesse A.; Giberson, Richard T.; Young, Lawrence J.T.; Hubbard, Neil E.

2014-01-01

Microwave methods of fixation can dramatically shorten fixation times while preserving tissue structure; however, it remains unclear if adequate tissue antigenicity is preserved. To assess and validate antigenicity, robust quantitative methods and animal disease models are needed. We used two mouse mammary models of human breast cancer to evaluate microwave-assisted and standard 24-hr formalin fixation. The mouse models expressed four antigens prognostic for breast cancer outcome: estrogen receptor, progesterone receptor, Ki67, and human epidermal growth factor receptor 2. Using pathologist evaluation and novel methods of quantitative image analysis, we measured and compared the quality of antigen preservation, percentage of positive cells, and line plots of cell intensity. Visual evaluations by pathologists established that the amounts and patterns of staining were similar in tissues fixed by the different methods. The results of the quantitative image analysis provided a fine-grained evaluation, demonstrating that tissue antigenicity is preserved in tissues fixed using microwave methods. Evaluation of the results demonstrated that a 1-hr, 150-W fixation is better than a 45-min, 150-W fixation followed by a 15-min, 650-W fixation. The results demonstrated that microwave-assisted formalin fixation can standardize fixation times to 1 hr and produce immunohistochemistry that is in every way commensurate with longer conventional fixation methods. PMID:24682322

Microwave-Assisted Tissue Preparation for Rapid Fixation, Decalcification, Antigen Retrieval, Cryosectioning, and Immunostaining

PubMed Central

2016-01-01

Microwave irradiation of tissue during fixation and subsequent histochemical staining procedures significantly reduces the time required for incubation in fixation and staining solutions. Minimizing the incubation time in fixative reduces disruption of tissue morphology, and reducing the incubation time in staining solution or antibody solution decreases nonspecific labeling. Reduction of incubation time in staining solution also decreases the level of background noise. Microwave-assisted tissue preparation is applicable for tissue fixation, decalcification of bone tissues, treatment of adipose tissues, antigen retrieval, and other special staining of tissues. Microwave-assisted tissue fixation and staining are useful tools for histological analyses. This review describes the protocols using microwave irradiation for several essential procedures in histochemical studies, and these techniques are applicable to other protocols for tissue fixation and immunostaining in the field of cell biology. PMID:27840640

Strength of surgical wire fixation. A laboratory study.

PubMed

Guadagni, J R; Drummond, D S

1986-08-01

Because of the frequent use of stainless steel wire in spinal surgery and to augment fracture fixation, several methods of securing wire fixation were tested in the laboratory to determine the relative strength of fixation. Any method of fixation stronger than the yield strength of the wire is sufficient. Square knots, knot twists, symmetric twists, and the AO loop-tuck techniques afforded acceptable resistance against tension loads, but the wire wrap and AO loop technique were unacceptable. The double symmetric twist, which is frequently used for tension banding, was barely acceptable. The symmetric twist technique was the most practical because it is strong enough, efficient in maintaining tension applied during fixation, and least likely to cause damage to the wire. To optimize the fixation strength of the symmetrical twist, at least two twists are required at a reasonably tight pitch.

Biomechanical principles and mechanobiologic aspects of flexible and locked plating.

PubMed

Claes, Lutz

2011-02-01

The goal of minimally invasive surgery in extramedullary internal fixation has led to the development of flexible plates, bridging plates, and locked internal fixators. The change from conventional compression plates to these new implants, however, resulted in different biomechanics of fixation and different mechanobiologic processes for fracture healing. The aim of a flexible fixation is the stimulation of fracture healing by callus formation. Fracture healing follows mechanobiologic rules based mainly on interfragmentary strain, which is dependent on the stability of the fixation construct and the type of fracture. Knowledge of the mechanobiologic processes and the factors influencing the stability of fracture fixation are necessary for the surgeon to choose the correct technique for fracture fixation. Problems in the selection of the correct technique and limitations with the available implants as well as possible future developments are discussed.

A California Nitrogen Mass Balance: Uncertainties and information needs

NASA Astrophysics Data System (ADS)

Liptzin, D.; Dahlgren, R. A.

2011-12-01

The goal of the California Nitrogen (N) Assessment (CNA) is to evaluate the current state of N science, practice, and policy in the state of California. One component is to develop a N mass balance for the state. Because the CNA is an assessment, evaluating the data quality and quantifying uncertainty are also part of the mass balance . We estimate that a total of 1500 Gg of new reactive N is added to California every year. Of this new N, only about half of the N leaves the state while the rest is retained. The main inputs of new reactive N to California are, in order of importance: synthetic N fertilizer, fossil fuel combustion, and biological N fixation. The three largest N outputs from the state are, in order of importance, atmospheric advection, wastewater discharge to the ocean, and riverine discharge to the ocean. Approximately half of the stored N leaches to groundwater, with the other half divided between soils and vegetation, reservoirs, and urban landscapes. These N flows vary not just in magnitude, but also in the uncertainty associated with them. There was no trend in the tonnage of fertilizer sold from 1981-2001, but the 2002-2007 average has remained higher (760 Gg N) than the long-term average (520 Gg N). Bottom up calculations based on crop acreage and fertilization rates are more consistent with the 1980-2001 average suggesting a problem with the sales data. The emission of NOx from fossil fuel burning is one of the most well established flows of N. The production of ammonia and nitrous oxide from fossil fuel combustion is significantly lower than NOx, but there is less evidence to support the emissions inventories. Rates of biological N fixation are speculative with evidence more limited in natural lands than croplands. For most crops it appears that N fixation rates are strongly related to plant production, suggesting that using a single rate across large regions may be inappropriate. In addition, many studies either only measure aboveground N fixation or do not explicitly specify whether the measured rates are total N fixation or only aboveground fixation. There is medium evidence to estimate how much of the emitted NOx and ammonia is redeposited within California. The Community Multiscale Air Quality model is the standard for modeling atmospheric deposition, but is dependent on the quality of the emissions inventory used. There is less agreement among sources on ammonia emissions which will be increasingly problematic as reduced N emissions will soon outpace oxidized N emissions. There is high evidence for wastewater discharge and riverine discharge. Most wastewater facilities are required monitor their N discharge although they often only measure the N species with the highest concentration (either ammonia or nitrate) depending on the level of treatment. Riverine N concentrations and flow in large watersheds are monitored by the US Geological Survey and there are relatively small uncertainties in the model calculating N discharge from these parameters. We suggest that while the best estimate of a mass balance is important, an evaluation of the major uncertainties can be just as important.

[Effectiveness comparison of suspension fixation plus hinged external fixator and double plate internal fixation in treatment of type C humeral intercondylar fractures].

PubMed

Zhang, Jian; Lin, Xu; Zhong, Zeli; Wu, Chao; Tan, Lun

2017-07-01

To compare the effectiveness of suspension fixation plus hinged external fixator with double plate internal fixation in the treatment of type C humeral intercondylar fractures. Between January 2014 and April 2016, 30 patients with type C (Association for the Study of Internal Fixation, AO/ASIF) humeral intercondylar fractures were treated. Kirschner wire suspension fixation plus hinged external fixator was used in 14 cases (group A), and double plate internal fixation in 16 cases (group B). There was no significant difference in gender, age, injury cause, disease duration, injury side, and type of fracture between 2 groups ( P >0.05). There was no significant difference in operation time and hospitalization stay between 2 groups ( P >0.05). But the intraoperative blood loss in group A was significantly less than that in group B ( P <0.05); the visual analogue scale (VAS) score at 1 day and 3 days after operation in group A were significantly less than those in group B ( P <0.05). Primary healing of incision was obtained in all patients of 2 groups, and no surgery-related complications occurred. The patients were followed up 6-24 months (mean, 12.3 months) in group A and 6-24 months (mean, 12.8 months) in group B. The self-evaluation satisfaction rate was 85.7% (12/14) in group A and was 81.2% (13/16) in group B at 3 months after operation, showing no significant difference ( χ 2 =0.055, P =0.990). Based on the improved Gassebaum elbow performance score at 6 months after operation, excellent and good rate of the elbow function was 78.6% (excellent in 5 cases, good in 6 cases, fair in 2 cases, and poor in 1 case) in group A and was 81.2% (excellent in 6 cases, good in 7 cases, fair in 2 cases, and poor in 1 case) in group B, showing no significant difference between 2 groups ( χ 2 =0.056, P =0.990). Heterotopic ossification occurred at 3 months after operation in 1 case of each group respectively. The X-ray films showed bony union in all cases; no loosening or breakage of screw was observed. The bone union time showed no significant difference between 2 groups ( t =-0.028, P =0.978). The time of internal fixation removal, the intraoperative blood loss, and VAS score at 1 day and 3 days after operation in group A were significant better than those in group B ( P <0.05). The suspension fixation plus hinged external fixator and double plate internal fixation for the treatment of type C humeral intercondylar fractures have ideal outcome in elbow function. But the suspension fixation plus hinged external fixator is better than double plate internal fixation in intraoperative blood loss, postoperative VAS score, and time of internal fixation removal.

Suture Button Fixation Versus Syndesmotic Screws in Supination-External Rotation Type 4 Injuries: A Cost-Effectiveness Analysis.

PubMed

Neary, Kaitlin C; Mormino, Matthew A; Wang, Hongmei

2017-01-01

In stress-positive, unstable supination-external rotation type 4 (SER IV) ankle fractures, implant selection for syndesmotic fixation is a debated topic. Among the available syndesmotic fixation methods, the metallic screw and the suture button have been routinely compared in the literature. In addition to strength of fixation and ability to anatomically restore the syndesmosis, costs associated with implant use have recently been called into question. This study aimed to examine the cost-effectiveness of the suture button and determine whether suture button fixation is more cost-effective than two 3.5-mm syndesmotic screws not removed on a routine postoperative basis. Economic and decision analysis; Level of evidence, 2. Studies with the highest evidence levels in the available literature were used to estimate the hardware removal and failure rates for syndesmotic screws and suture button fixation. Costs were determined by examining the average costs for patients who underwent surgery for unstable SER IV ankle fractures at a single level-1 trauma institution. A decision analysis model that allowed comparison of the 2 fixation methods was developed. Using a 20% screw hardware removal rate and a 4% suture button hardware removal rate, the total cost for 2 syndesmotic screws was US$20,836 and the total effectiveness was 5.846. This yielded a total cost of $3564 per quality-adjusted life-year (QALY) over an 8-year time period. The total cost for suture button fixation was $19,354 and the total effectiveness was 5.904, resulting in a total cost of $3294 per QALY over the same time period. A sensitivity analysis was then conducted to assess suture button fixation costs as well as screw and suture button hardware removal rates. Other possible treatment scenarios were also examined, including 1 screw and 2 suture buttons for operative fixation of the syndesmosis. To become more cost-effective, the screw hardware removal rate would have to be reduced to less than 10%. Furthermore, fixation with a single suture button continued to be the dominant treatment strategy compared with 2 suture buttons, 1 screw, and 2 screws for syndesmotic fixation. This cost-effectiveness analysis suggests that for unstable SER IV ankle fractures, suture button fixation is more cost-effective than syndesmotic screws not removed on a routine basis. Suture button fixation was a dominant treatment strategy, because patients spent on average $1482 less and had a higher quality of life by 0.058 QALYs compared with patients who received fixation with 2 syndesmotic screws. Assuming that functional outcomes and failure rates were equivalent, screw fixation only became more cost-effective when the screw hardware removal rate was reduced to less than 10% or when the suture button cost exceeded $2000. In addition, fixation with a single suture button device proved more cost-effective than fixation with either 1 or 2 syndesmotic screws.

In vivo implant fixation of carbon fiber-reinforced PEEK hip prostheses in an ovine model.

PubMed

Nakahara, Ichiro; Takao, Masaki; Bandoh, Shunichi; Bertollo, Nicky; Walsh, William R; Sugano, Nobuhiko

2013-03-01

Carbon fiber-reinforced polyetheretherketone (CFR/PEEK) is theoretically suitable as a material for use in hip prostheses, offering excellent biocompatibility, mechanical properties, and the absence of metal ions. To evaluate in vivo fixation methods of CFR/PEEK hip prostheses in bone, we examined radiographic and histological results for cementless or cemented CFR/PEEK hip prostheses in an ovine model with implantation up to 52 weeks. CFR/PEEK cups and stems with rough-textured surfaces plus hydroxyapatite (HA) coatings for cementless fixation and CFR/PEEK cups and stems without HA coating for cement fixation were manufactured based on ovine computed tomography (CT) data. Unilateral total hip arthroplasty was performed using cementless or cemented CFR/PEEK hip prostheses. Five cementless cups and stems and six cemented cups and stems were evaluated. On the femoral side, all cementless stems demonstrated bony ongrowth fixation and all cemented stems demonstrated stable fixation without any gaps at both the bone-cement and cement-stem interfaces. All cementless cases and four of the six cemented cases showed minimal stress shielding. On the acetabular side, two of the five cementless cups demonstrated bony ongrowth fixation. Our results suggest that both cementless and cemented CFR/PEEK stems work well for fixation. Cup fixation may be difficult for both cementless and cemented types in this ovine model, but bone ongrowth fixation on the cup was first seen in two cementless cases. Cementless fixation can be achieved using HA-coated CFR/PEEK implants, even under load-bearing conditions. Copyright © 2012 Orthopaedic Research Society.

[Biomechanical performance of different wires and cable fixation devices in posterior instrumentation for atlantoaxial instability].

PubMed

Liu, Tie-long; Yan, Wang-jun; Han, Yu; Ye, Xiao-jian; Jia, Lian-shun; Li, Jia-shun; Yuan, Wen

2010-05-01

To compare the biomechanical performances of different wires and cable fixation devices in posterior instrumentation for atlantoaxial instability, and test the effect of different fixation strengths and fixation approaches on the surgical outcomes. Six specimens of the atlantoaxial complex (C0-C3) were used to establish models of the normal complex, unstable complex (type II odontoid fracture) and fixed complex. On the wd-5 mechanical testing machine, the parameters including the strength and rigidity of anti-rotation, change and strength of stress, and stability were measured for the normal complex, atlantoaxial instability complex, the new type titanium cable fixation system, Atlas titanium cable, Songer titanium cable, and stainless wire. The strength and rigidity of anti-rotation, change and strength of stress, stability of flexion, extension and lateral bending of the unstable atlantoaxial complex fixed by the new double locking titanium cable fixation system were superior to those of the Songer or Atlas titanium cable (P<0.05) and medical stainless wire (P<0.05). Simultaneous cable fastening on both sides resulted in better fixation effect than successive cable fastening (P<0.05). Better fixation effect was achieved by fastening the specimen following a rest (P<0.05). The fixation effects can be enhanced by increased fastening strengths. The new type double locking titanium cable fixation system has better biomechanical performance than the conventional Songer and Atlas titanium cables. Fastening the unstable specimens after a rest following simultaneous fastening of the specimen on both sides produces better fixation effect.

The Role of Minimally Invasive Plate Osteosynthesis in Rib Fixation: A Review

PubMed Central

Bemelman, Michael; van Baal, Mark; Yuan, Jian Zhang; Leenen, Luke

2016-01-01

More than a century ago, the first scientific report was published about fracture fixation with plates. During the 1950’s, open reduction and plate fixation for fractures were standardized by the founders of Arbeitsgemeinschaft für osteosynthesefragen/Association for the Study of Internal Fixation. Since the introduction of plate fixation for fractures, several plates and screws have been developed, all with their own characteristics. To accomplice more fracture stability, it was thought the bigger the plate, the better. The counter side was a compromised blood supply of the bone, often resulting in bone necrosis and ultimately delayed or non-union. With the search and development of new materials and techniques for fracture fixation, less invasive procedures have become increasingly popular. This resulted in the minimally invasive plate osteosynthesis (MIPO) technique for fracture fixation. With the MIPO technique, procedures could be performed with smaller incisions and thus with less soft tissue damage and a better preserved blood supply. The last 5 years rib fixation has become increasingly popular, rising evidence has become available suggesting that surgical rib fixation improves outcome of patients with a flail chest or isolated rib fractures. Many surgical approaches for rib fixation have been described in the old literature, however, most of these techniques are obscure nowadays. Currently mostly large incisions with considerable surgical insult are used to stabilize rib fractures. We think that MIPO deserves a place in the surgical treatment of rib fractures. We present the aspects of diagnosis, preoperative planning and operative techniques in regard to MIPO rib fixation. PMID:26889439

Measuring the effect of multiple eye fixations on memory for visual attributes.

PubMed

Palmer, J; Ames, C T

1992-09-01

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.

Response of Carbon Dioxide Fixation to Water Stress

PubMed Central

Plaut, Z.; Bravdo, B.

1973-01-01

Application of water stress to isolated spinach (Spinacia oleracea) chloroplasts by redutcion of the osmotic potentials of CO2 fixation media below −6 to −8 bars resulted in decreased rates of fixation regardless of solute composition. A decrease in CO2 fixation rate of isolated chloroplasts was also found when leaves were dehydrated in air prior to chloroplast isolation. An inverse response of CO2 fixation to osmotic potential of the fixation medium was found with chloroplasts isolated from dehydrated leaves—namely, fixation rate was inhibited at −8 bars, compared with −16 or −24 bars. Low leaf water potentials were found to inhibit CO2 fixation of intact leaf discs to almost the same degree as they did CO2 fixation by chloroplasts isolated from those leaves. CO2 fixation by intact leaves was decreased by 50 and 80% when water potentials were reduced from −7.1 to −9.6 and from −7.1 to −17.6 bars, respectively. Transpiration was decreased by only 40 and 60%, under the same conditions. However, correction for the increase in leaf temperature indicated transpiration decreases of 57 and 80%, similar to the relative decreases in CO2 fixation. Despite the 4-fold increase in leaf resistance to CO2 diffusion in the gas phase when the water potential of leaves was reduced from −6.5 to −14.0 bars, an additional increase of about 50% in mesophyll resistance was obtained. CO2 concentration at compensation also increased when leaf water potential was reduced. PMID:16658493

21 CFR 888.3030 - Single/multiple component metallic bone fixation appliances and accessories.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Single/multiple component metallic bone fixation....3030 Single/multiple component metallic bone fixation appliances and accessories. (a) Identification. Single/multiple component metallic bone fixation appliances and accessories are devices intended to be...

21 CFR 888.3010 - Bone fixation cerclage.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Bone fixation cerclage. 888.3010 Section 888.3010...) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3010 Bone fixation cerclage. (a) Identification. A bone fixation cerclage is a device intended to be implanted that is made of alloys, such as...

21 CFR 888.3030 - Single/multiple component metallic bone fixation appliances and accessories.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Single/multiple component metallic bone fixation....3030 Single/multiple component metallic bone fixation appliances and accessories. (a) Identification. Single/multiple component metallic bone fixation appliances and accessories are devices intended to be...

21 CFR 888.3030 - Single/multiple component metallic bone fixation appliances and accessories.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Single/multiple component metallic bone fixation....3030 Single/multiple component metallic bone fixation appliances and accessories. (a) Identification. Single/multiple component metallic bone fixation appliances and accessories are devices intended to be...

21 CFR 888.3010 - Bone fixation cerclage.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Bone fixation cerclage. 888.3010 Section 888.3010...) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3010 Bone fixation cerclage. (a) Identification. A bone fixation cerclage is a device intended to be implanted that is made of alloys, such as...

21 CFR 888.3010 - Bone fixation cerclage.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Bone fixation cerclage. 888.3010 Section 888.3010...) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3010 Bone fixation cerclage. (a) Identification. A bone fixation cerclage is a device intended to be implanted that is made of alloys, such as...

21 CFR 888.3010 - Bone fixation cerclage.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Bone fixation cerclage. 888.3010 Section 888.3010...) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3010 Bone fixation cerclage. (a) Identification. A bone fixation cerclage is a device intended to be implanted that is made of alloys, such as...

21 CFR 888.3030 - Single/multiple component metallic bone fixation appliances and accessories.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Single/multiple component metallic bone fixation....3030 Single/multiple component metallic bone fixation appliances and accessories. (a) Identification. Single/multiple component metallic bone fixation appliances and accessories are devices intended to be...

21 CFR 888.3010 - Bone fixation cerclage.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Bone fixation cerclage. 888.3010 Section 888.3010...) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3010 Bone fixation cerclage. (a) Identification. A bone fixation cerclage is a device intended to be implanted that is made of alloys, such as...

21 CFR 888.3030 - Single/multiple component metallic bone fixation appliances and accessories.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Single/multiple component metallic bone fixation....3030 Single/multiple component metallic bone fixation appliances and accessories. (a) Identification. Single/multiple component metallic bone fixation appliances and accessories are devices intended to be...

21 CFR 872.4880 - Intraosseous fixation screw or wire.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Intraosseous fixation screw or wire. 872.4880... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4880 Intraosseous fixation screw or wire. (a) Identification. An intraosseous fixation screw or wire is a metal device intended to be inserted...

21 CFR 872.4880 - Intraosseous fixation screw or wire.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Intraosseous fixation screw or wire. 872.4880... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4880 Intraosseous fixation screw or wire. (a) Identification. An intraosseous fixation screw or wire is a metal device intended to be inserted...

Heterotrophic Carbon Dioxide Fixation Products of Euglena

PubMed Central

Peak, Jennifer G.; Peak, Meyrick J.; Ting, Irwin P.

1980-01-01

The metabolic products of heterotrophic (dark) CO2 fixation by Euglena gracilis Klebs strain Z Pringsheim were separated and identified. They consisted of amino acids, phosphorylated compounds, tricarboxylic acid cycle intermediates, and nucleotides. Exposure of the cells to NH4+ after a period of NH4+ deprivation stimulated heterotrophic CO2 fixation almost 4-fold, modifying the spectrum of the fixation products. In particular, the NH4+ treatment stimulated fixation of CO2 into glutamine, glycine, alanine, and serine. PMID:16661238

The contribution of changes in P release and CO2 consumption by chemical weathering to the historical trend in land carbon uptake

NASA Astrophysics Data System (ADS)

Goodale, C. L.; Fredriksen, G.; McCalley, C. K.; Sparks, J. P.; Thomas, S. A.

2011-12-01

The atmospheric carbon dioxide (CO2) concentration has increased to a level unprecedented in the last 2 million years, and the concentration is projected to increase further with a rate unseen in geological past. The increase in CO2 cause a rise in surface temperatures and changes in the hydrological cycle through the redistribution of rainfall patterns. All of these changes will impact the weathering of rocks, which in turn affect atmospheric CO2 concentrations via two different pathways. On the one hand, CO2 is consumed by the dissolution reaction of the exposed minerals. And on the other hand, biological CO2 fixation is affected due to changes in phosphorus release from minerals, as biological activity is constrained by phosphorus availability at large scales. The traditional view is that both effects are negligible on a centennial time scale, but recent work on catchment scale challenge this view in favor of a potential high sensitivity of weathering to ongoing climate and land use changes. To globally quantify the contribution of CO2 fixation associated with weathering on the historical trend in terrestrial CO2 uptake, we applied a model of chemical weathering and phosphorus release under climate reconstructions from four Earth System Models. The simulations indicate that changes in weathering could have contributed considerably to the trend in terrestrial CO2 uptake since the pre-industrial revolution, with warming being the main driver of change. The increase in biological CO2 fixation is of comparable magnitude as the increase in CO2 consumption by chemical weathering. Our simulations support the previous findings on catchment scale that weathering can change significantly on a centennial time scale. This finding has implications for 21st century climate projections, which ignore changes in weathering, as well as for long-term airborne fraction of CO2 emissions, whose calculation usually neglects changes in phosphorus availability.

The contribution of changes in P release and CO2 consumption by chemical weathering to the historical trend in land carbon uptake

NASA Astrophysics Data System (ADS)

Goll, D. S.; Moosdorf, N.; Brovkin, V.; Hartmann, J.

2013-12-01

The atmospheric carbon dioxide (CO2) concentration has increased to a level unprecedented in the last 2 million years, and the concentration is projected to increase further with a rate unseen in geological past. The increase in CO2 cause a rise in surface temperatures and changes in the hydrological cycle through the redistribution of rainfall patterns. All of these changes will impact the weathering of rocks, which in turn affect atmospheric CO2 concentrations via two different pathways. On the one hand, CO2 is consumed by the dissolution reaction of the exposed minerals. And on the other hand, biological CO2 fixation is affected due to changes in phosphorus release from minerals, as biological activity is constrained by phosphorus availability at large scales. The traditional view is that both effects are negligible on a centennial time scale, but recent work on catchment scale challenge this view in favor of a potential high sensitivity of weathering to ongoing climate and land use changes. To globally quantify the contribution of CO2 fixation associated with weathering on the historical trend in terrestrial CO2 uptake, we applied a model of chemical weathering and phosphorus release under climate reconstructions from four Earth System Models. The simulations indicate that changes in weathering could have contributed considerably to the trend in terrestrial CO2 uptake since the pre-industrial revolution, with warming being the main driver of change. The increase in biological CO2 fixation is of comparable magnitude as the increase in CO2 consumption by chemical weathering. Our simulations support the previous findings on catchment scale that weathering can change significantly on a centennial time scale. This finding has implications for 21st century climate projections, which ignore changes in weathering, as well as for long-term airborne fraction of CO2 emissions, whose calculation usually neglects changes in phosphorus availability.

Quantitative assessment of effect of preanalytic cold ischemic time on protein expression in breast cancer tissues.

PubMed

Neumeister, Veronique M; Anagnostou, Valsamo; Siddiqui, Summar; England, Allison Michal; Zarrella, Elizabeth R; Vassilakopoulou, Maria; Parisi, Fabio; Kluger, Yuval; Hicks, David G; Rimm, David L

2012-12-05

Companion diagnostic tests can depend on accurate measurement of protein expression in tissues. Preanalytic variables, especially cold ischemic time (time from tissue removal to fixation in formalin) can affect the measurement and may cause false-negative results. We examined 23 proteins, including four commonly used breast cancer biomarker proteins, to quantify their sensitivity to cold ischemia in breast cancer tissues. A series of 93 breast cancer specimens with known time-to-fixation represented in a tissue microarray and a second series of 25 matched pairs of core needle biopsies and breast cancer resections were used to evaluate changes in antigenicity as a function of cold ischemic time. Estrogen receptor (ER), progesterone receptor (PgR), HER2 or Ki67, and 19 other antigens were tested. Each antigen was measured using the AQUA method of quantitative immunofluorescence on at least one series. All statistical tests were two-sided. We found no evidence for loss of antigenicity with time-to-fixation for ER, PgR, HER2, or Ki67 in a 4-hour time window. However, with a bootstrapping analysis, we observed a trend toward loss for ER and PgR, a statistically significant loss of antigenicity for phosphorylated tyrosine (P = .0048), and trends toward loss for other proteins. There was evidence of increased antigenicity in acetylated lysine, AKAP13 (P = .009), and HIF1A (P = .046), which are proteins known to be expressed in conditions of hypoxia. The loss of antigenicity for phosphorylated tyrosine and increase in expression of AKAP13, and HIF1A were confirmed in the biopsy/resection series. Key breast cancer biomarkers show no evidence of loss of antigenicity, although this dataset assesses the relatively short time beyond the 1-hour limit in recent guidelines. Other proteins show changes in antigenicity in both directions. Future studies that extend the time range and normalize for heterogeneity will provide more comprehensive information on preanalytic variation due to cold ischemic time.

Interactions between nitrogen cycling and methane oxidation in the pelagic waters of the Gulf of Mexico.

NASA Astrophysics Data System (ADS)

Joye, S. B.; Weber, S.; Battles, J.; Montoya, J. P.

2014-12-01

Methane is an important greenhouse gas that plays a critical role in climate variation. Although a variety of marine methane sources and sinks have been identified, key aspects of the fate of methane in the ocean remain poorly constrained. At cold seeps in the Gulf of Mexico and elsewhere, methane is introduced into the overlying water column via fluid escape from the seabed. We quantified the fate of methane in the water column overlying seafloor cold seeps, in a brine basin, and at several control sites. Our goals were to determine the factors that regulated methane consumption and assimilation and to explore how these controlling factors varied among and between sites. In particular, we examined the impact of nitrogen availability on methane oxidation and studied the ability of methane oxidizing bacteria to fix molecular nitrogen. Methane oxidation rates were highest in the methane rich bottom waters of natural hydrocabron seeps. At these sites, inorganic nitrogen addition stimulated methane oxidation in laboratory experiments. In vitro shipboard experiments revealed that rates of methane oxidation and nitrogen fixation were correlated strongly, suggesting that nitrogen fixation may have been mediated by methanotrophic bacteria. The highest rates of methane oxidation and nitrogen fixation were observed in the deepwater above at natural hydrocarbon seeps. Rates of methane oxidation were substantial along the chemocline of a brine basin but in these ammonium-rich brines, addition of inorganic nitrogen had little impact on methane oxidation suggesting that methanotrophy in these waters were not nitrogen limited. Control sites exhibited the lowest methane concentrations and methane oxidation rates but even these waters exhibited substantial potential for methane oxidation when methane and inorganic nitrogen concentrations were increased. Together, these data suggest that the availability of inorganic nitrogen plays a critical role in regulating methane oxidation in pelagic ocean waters. Some methanotrophs may obtain a competitive advantage in nitrogen-limited oceanic environments by fixing molecular nitrogen. The importance of such "methano-diazotrophy" on a global scale warrants further investigation.

Nitrous oxide emissions from crop rotations including wheat, oilseed rape and dry peas

NASA Astrophysics Data System (ADS)

Jeuffroy, M. H.; Baranger, E.; Carrouée, B.; de Chezelles, E.; Gosme, M.; Hénault, C.; Schneider, A.; Cellier, P.

2013-03-01

Approximately 65% of anthropogenic emissions of N2O, a potent greenhouse gas (GHG), originate from soils at a global scale, and particularly after N fertilisation of the main crops in Europe. Thanks to their capacity to fix atmospheric N2 through biological fixation, legumes can reduce N fertilizer use, and possibly N2O emissions. Nevertheless, the decomposition of crop organic matter during the crop cycle and residue decomposition, and possibly the N fixation process itself, could lead to N2O emissions. The objective of this study was to quantify N2O emissions from a dry pea crop (Pisum sativum, harvested at maturity) and from the subsequent crops in comparison with N2O emissions from wheat and oilseed rape crops, fertilized or not, in various rotations. A field experiment was conducted over 4 consecutive years to compare the emissions during the pea crop, in comparison with those during the wheat (fertilized or not) or oilseed rape crops, and after the pea crop, in comparison with other preceding crops. N2O fluxes were measured using static chambers. In spite of low N2O fluxes, mainly due to the site's soil characteristics, fluxes during the crop were significantly lower for pea and unfertilized wheat than for fertilized wheat and oilseed rape. The effect of the preceding crop was not significant, while soil mineral N at harvest was higher after the pea crop. These results should be confirmed over a wider range of soil types. Nevertheless, they demonstrate the absence of N2O emissions linked to the symbiotic N fixation process, and allow us to estimate the decrease in N2O emissions by 20-25% through including one pea crop in a three-year rotation. On a larger scale, this reduction of GHG emissions at field level has to be added to the decrease due to the reduced production and transport of the N fertilizer not applied to the pea crop.