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Sample records for active layer thaw

  1. Comparative Metagenomic Analysis Of Microbial Communities From Active Layer And Permafrost After Short-Term Thaw

    NASA Astrophysics Data System (ADS)

    Vishnivetskaya, T. A.; Chauhan, A.; Saarunya, G.; Murphy, J.; Williams, D.; Layton, A. C.; Pfiffner, S. M.; Stackhouse, B. T.; Sanders, R.; Lau, C. M.; myneni, S.; Phelps, T. J.; Fountain, A. G.; Onstott, T. C.

    2012-12-01

    .Permafrost areas occupy 20-25% of the Earth and extend of 1 km depths. The total number of prokaryotes and their biomass in cold regions are estimated to be 1 x 1030 cells and 140 x1015 g of C, respectively. Thus these environments serve as a reservoir of microbial and biogeochemical activity, which is likely to increase upon thawing. We are currently performing long-term thawing experiments at 4o C on 18, geochemically well-characterized, 1 meter long, intact cores consisting of active-layer (0-70 cm depth) and permafrost, collected from a 7 meter diameter ice-wedge polygon located at the McGill Arctic Research Station on Axel Heiberg Island, Nunavut, Canada. The organic carbon content of these cores averages ~1% at depth but increases to 5.4% in the top 10 cm. The cores were subdivided into four treatment groups: saturated cores (thawed while receiving artificial rain), drained cores (being thawed under natural hydrological conditions), dark cores (thawed under natural hydrological conditions with no light input) and control cores (maintain permafrost table at 70 cm depth). Over the course of 10 weeks the cores were progressively thawed from -4oC to 4oC from the top down to simulate spring thaw conditions in the Arctic. The temperatures at 5 cm, 35 cm, 65 cm, and below the permafrost table in the core were recorded continuously. Pore water and gas samples from 4 depths in each core were collected every two weeks and analyzed for pH, anions, cations, H2, CH4, CO, O2, N2, CO2 and δ13C of CO2. Headspace gas samples were collected weekly and analyzed for the same gases as the pore gases. Sediment sub-samples from the 4 depths were collected and total community genomic DNA (gDNA) was isolated using FastDNA SPIN kit followed by Qiagen column purification. The average yield of gDNA was ~3.5 μg/g of soil for the upper 5 cm active layers and decreased to ~1.5 μg/g of soil in the permafrost. The bacterial 16S copy numbers estimated by real-time quantitative PCR

  2. Active Layer Thawing and Freeze-Back in Svalbard using DC Resistivity Tomography

    NASA Astrophysics Data System (ADS)

    Oswald, A.; Juliussen, H.; Christiansen, H. H.

    2009-04-01

    The thawing of the active layer has an important impact on the permafrost below, since the state of the uppermost soil layers determines how large surface temperature fluctuations are translated to deeper ground. Latent heat and combined liquid water and energy transport during the thawing season influence the energy exchange between permafrost and atmosphere. A first step to a better understanding of these processes is to determine the depth of the active layer and its thermal state the best possible way. Borehole temperatures give a very accurate measure of the ground thermal state but are, like active layer depths from mechanical probing, single point measurements. Geophysical imaging methods, such as DC resistivity tomography, allow for a 2d-image of subsurface soil properties, but should be supplemented with point temperature measurements as the results might be ambiguous. In spring and late summer 2007 electrode arrays have been permanently installed in three different permafrost landforms in Svalbard (a gently sloping solifluction sheet, a valley bottom loess terrace and a vertical sandstone rockwall) as a part of the IPY-project - ‘Permafrost Observatory Project: A Contribution to the Thermal State of Permafrost in Norway and Svalbard' TSP Norway. With a spacing of 20cm and a total array length of 16m this allows for a maximum measurement depth of about 2.5m. During most parts of IPY measurements were carried on a more or less regular basis - ideally in a two weeks interval. While measurements in the rockwall suffered from permanent loosening of the electrodes in the brittle sandstone, the measurements on the loess terrace and the solifluction slope were only interrupted during the very cold spring conditions as grounding errors occurred. Hence field work focused on the loess terrace and the solifluction sheet - the former consisting of silt and fine clay; the latter characterized by its high water content and a rather heterogeneous grain size

  3. Soil Active Layer Freeze/Thaw Detection Using Combined L- and P-Band Radar Remote Sensing

    NASA Astrophysics Data System (ADS)

    Du, J.; Kimball, J. S.; Moghaddam, M.

    2014-12-01

    Monitoring of soil active layer freeze-thaw (FT) dynamics is critical for studying high-latitude ecosystem and environmental changes. We evaluated the potential of inferring FT state dynamics within a tundra soil profile using combined L- and P-band radar remote sensing and forward radiative transfer modeling of backscatter characteristics. A first-order two-layer soil scattering model (FTSS) was developed in this study to analyze soil multi-layer scattering effects. The FTSS was evaluated against other sophisticated modeling approaches and showed comparable performance. The FTSS was then applied to analyzing L- and P-band microwave responses to layered soil. We find that soil volume scattering is rather weak for the two frequencies for frozen or dry soil with mean particle size below 10mm diameter. Dielectric contrast between adjacent soil layers can contribute to total backscatter at both L- and P-band with more significant impact on P-band than L-band signals depending on the depth of soil profile. Combined L- and P-band radar data are shown to have greater utility than single channel observations in detecting soil FT dynamics and dielectric profile inhomogeneity. Further analysis using available airborne synthetic aperture radar (SAR) data and in-situ measurements also confirm that soil profile heterogeneity can be effectively detected using combined L- and P-band radar backscatter data. This study demonstrates the potential of lower frequency SARs from airborne missions, including UAV-SAR and AirMOSS, for Arctic and alpine assessment of soil active layer properties.

  4. Drivers and Estimates of Terrain Suitability for Active Layer Detachment Slides and Retrogressive Thaw Slumps in the Brooks Range and Foothills of Northwest Alaska, USA

    NASA Astrophysics Data System (ADS)

    Balser, A.; Jones, J.

    2015-12-01

    Active layer detachment sliding and retrogressive thaw slumping are important modes of upland permafrost degradation and disturbance in permafrost regions, and have been linked with climate warming trends, ecosystem impacts, and permafrost carbon release. In the Brooks Range and foothills of northwest Alaska, these features are widespread, with distribution linked to multiple landscape properties. Inter-related and co-varying terrain properties, including surficial geology, topography, geomorphology, vegetation and hydrology, are generally considered key drivers of permafrost landscape characteristics and responses to climate perturbation. However, these inter-relationships as collective drivers of terrain suitability for active layer detachment and retrogressive thaw slump processes are poorly understood in this region. We empirically tested and refined a hypothetical model of terrain factors driving active layer detachment and retrogressive thaw slump terrain suitability, and used final model results to generate synoptic terrain suitability estimates across the study region. Spatial data for terrain properties were examined against locations of 2,492 observed active layer detachments and 805 observed retrogressive thaw slumps using structural equation modelling and integrated terrain unit analysis. Factors significant to achieving model fit were found to substantially hone and constrain region-wide terrain suitability estimates, suggesting that omission of relevant factors leads to broad overestimation of terrain suitability. Resulting probabilistic maps of terrain suitability, and a threshold-delineated mask of suitable terrain, were used to quantify and describe landscape settings typical of these features. 51% of the study region is estimated suitable terrain for retrogressive thaw slumps, compared with 35% for active layer detachment slides, while 29% of the study region is estimated suitable for both. Results improve current understanding of arctic landscape

  5. Use of single-layer centrifugation with Androcoll-C to enhance sperm quality in frozen-thawed dog semen.

    PubMed

    Dorado, J; Gálvez, M J; Morrell, J M; Alcaráz, L; Hidalgo, M

    2013-11-01

    The aim of this study was to investigate whether single-layer centrifugation (SLC) with Androcoll-C could select good quality spermatozoa, including those with specific motility patterns, from doses of frozen dog semen. Semen from five dogs was collected and cryopreserved following a standard protocol. After thawing, the semen samples were divided in two aliquots, one of which was used as a control and the other one processed by SLC. Assessment of sperm motility (assessed by computer-assisted semen analysis), morphology (Diff-Quick staining), viability (dual staining with propidium iodine/acridine orange), and acrosome integrity (dual staining with propidium iodine/isothiocyanate-labeled peanut [Arachis hypogaea] agglutinin) were performed on aliquots of fresh semen, frozen-thawed control samples, and frozen-thawed SLC-treated preparations. A multivariate clustering procedure separated 57,577 motile spermatozoa into three subpopulations (sP): sP1 consisted of poorly active and nonprogressive spermatozoa (48.8%), sP2 consisted of moderately slow but progressive spermatozoa (13.3%), and sP3 consisted of highly active and/or progressive spermatozoa (37.8%). SLC with Androcoll-C yielded sperm suspensions with improved motility, viability, and acrosome integrity (P < 0.01). The frozen-thawed SLC-treated samples were enriched in sP3, representing 38.5% of the sperm population. Likewise, sP2 was more frequently observed after SLC, but not significantly so. From these results, we concluded that for dog semen samples selected by SLC with Androcoll-C after thawing, the sperm quality parameters, including motility patterns, are better than in frozen-thawed control samples.

  6. Single-layer centrifugation through PureSperm® 80 selects improved quality spermatozoa from frozen-thawed dog semen.

    PubMed

    Dorado, J; Alcaraz, L; Gálvez, M J; Acha, D; Ortiz, I; Urbano, M; Hidalgo, M

    2013-08-01

    The aim of this study was to investigate whether single-layer centrifugation (SLC) with PureSperm® 80 could select good quality spermatozoa, including those with specific motility patterns, from doses of frozen dog semen. Semen from 5 dogs was collected and cryopreserved following a standard protocol. After thawing, semen samples were divided into two aliquots: one of them was used as control and the other one processed by SLC. Assessment of sperm motility (assessed by computer-assisted semen analysis), morphology (Diff-Quick staining) and viability (triple fluorescent stain of propidium iodine/isothiocyanate-labeled peanut (Arachis hypogaea) agglutinin/Rhodamine 123), were performed on aliquots of fresh semen, frozen-thawed control and frozen-thawed SLC treated samples. A multivariate clustering procedure separated 26,051 motile spermatozoa into three subpopulations (sP): sP1 consisting of highly active but non-progressive spermatozoa (40.3%), sP2 consisting of spermatozoa with high velocity and progressive motility (30.0%), and sP3 consisting of poorly active and non-progressive spermatozoa (29.7%). SLC with PureSperm® 80 yielded sperm suspensions with improved motility, morphology, viability and acrosome integrity (P<0.001). The frozen-thawed SLC treated samples were enriched in sP2, reaching a proportion of 44.1% of the present spermatozoa. From these results, we concluded that SLC with PureSperm® 80 may be an alternative and successful method for improving the quality of frozen-thawed dog spermatozoa. Moreover, sP2 (high-speed and progressive spermatozoa) was more frequently observed after SLC. Finally, this study also demonstrated that the general motile sperm structure present in dogs remained constant despite the effect caused by either cryopreservation or separation by SLC through PureSperm® 80.

  7. Estimating Active Layer Thickness from Remotely Sensed Surface Deformation

    NASA Astrophysics Data System (ADS)

    Liu, L.; Schaefer, K. M.; Zhang, T.; Wahr, J. M.

    2010-12-01

    We estimate active layer thickness (ALT) from remotely sensed surface subsidence during thawing seasons derived from interferometric synthetic aperture radar (InSAR) measurements. Ground ice takes up more volume than ground water, so as the soil thaws in summer and the active layer deepens, the ground subsides. The volume of melted ground water during the summer thaw determines seasonal subsidence. ALT is defined as the maximum thaw depth at the end of a thawing season. By using InSAR to measure surface subsidence between the start and end of summer season, one can estimate the depth of thaw over a large area (typically 100 km by 100 km). We developed an ALT retrieval algorithm integrating InSAR-derived surface subsidence, observed soil texture, organic matter content, and moisture content. We validated this algorithm in the continuous permafrost area on the North Slope of Alaska. Based on InSAR measurements using ERS-1/2 SAR data, our estimated values match in situ measurements of ALT within 1--10 cm at Circumpolar Active Layer Monitoring (CALM) sites within the study area. The active layer plays a key role in land surface processes in cold regions. Current measurements of ALT using mechanical probing, frost/thaw tubes, or inferred from temperature measurements are of high quality, but limited in spatial coverage. Using InSAR to estimate ALT greatly expands the spatial coverage of ALT observations.

  8. Colloid single-layer centrifugation improves post-thaw donkey (Equus asinus) sperm quality and is related to ejaculate freezability.

    PubMed

    Ortiz, I; Dorado, J; Acha, D; Gálvez, M J; Urbano, M; Hidalgo, M

    2015-01-01

    The aim of this study was to determine whether colloid single-layer centrifugation (SLC) improves post-thaw donkey sperm quality and if this potential enhancement is related to ejaculate freezability. Semen from Andalusian donkeys was frozen following a standard protocol. SLC was performed on frozen-thawed semen and post-thaw sperm parameters were compared with uncentrifuged samples. Sperm quality was estimated by integrating in a single value sperm motility (assessed by computer-assisted sperm analysis), morphology and viability (evaluated under brightfield or fluorescence microscopy). Sperm freezability was calculated as the relationship between sperm quality obtained before freezing and after thawing. Ejaculates were classified into low, medium and high freezability groups using the 25th and 75th percentiles as thresholds. All sperm parameters were significantly (P<0.01) higher in SLC-selected samples in comparison to uncentrifuged frozen-thawed semen and several kinematic parameters were even higher than those obtained in fresh semen. The increment of sperm parameters after SLC selection was correlated with ejaculate freezability, obtaining the highest values after SLC in semen samples with low freezability. We concluded that, based on the sperm-quality parameters evaluated, SLC can be a suitable procedure to improve post-thaw sperm quality of cryopreserved donkey semen, in particular for those ejaculates with low freezability.

  9. Identifying active methane-oxidizers in thawed Arctic permafrost by proteomics

    NASA Astrophysics Data System (ADS)

    Lau, C. M.; Stackhouse, B. T.; Chourey, K.; Hettich, R. L.; Vishnivetskaya, T. A.; Pfiffner, S. M.; Layton, A. C.; Mykytczuk, N. C.; Whyte, L.; Onstott, T. C.

    2012-12-01

    The rate of CH4 release from thawing permafrost in the Arctic has been regarded as one of the determining factors on future global climate. It is uncertain how indigenous microorganisms would interact with such changing environmental conditions and hence their impact on the fate of carbon compounds that are sequestered in the cryosol. Multitudinous studies of pristine surface cryosol (top 5 cm) and microcosm experiments have provided growing evidence of effective methanotrophy. Cryosol samples corresponding to active layer were sampled from a sparsely vegetated, ice-wedge polygon at the McGill Arctic Research Station at Axel Heiberg Island, Nunavut, Canada (N79°24, W90°45) before the onset of annual thaw. Pyrosequencing of 16S rRNA gene indicated the occurrence of methanotroph-containing bacterial families as minor components (~5%) in pristine cryosol including Bradyrhizobiaceae, Methylobacteriaceae and Methylocystaceae within alpha-Proteobacteria, and Methylacidiphilaceae within Verrucomicrobia. The potential of methanotrophy is supported by preliminary analysis of metagenome data, which indicated putative methane monooxygenase gene sequences relating to Bradyrhizobium sp. and Pseudonocardia sp. are present. Proteome profiling in general yielded minute traces of proteins, which likely hints at dormant nature of the soil microbial consortia. The lack of specific protein database for permafrost posted additional challenge to protein identification. Only 35 proteins could be identified in the pristine cryosol and of which 60% belonged to Shewanella sp. Most of the identified proteins are known to be involved in energy metabolism or post-translational modification of proteins. Microcosms amended with sodium acetate exhibited a net methane consumption of ~65 ngC-CH4 per gram (fresh weight) of soil over 16 days of aerobic incubation at room temperature. The pH in microcosm materials remained acidic (decreased from initial 4.7 to 4.5). Protein extraction and

  10. Dynamics of active layer in wooded palsas of northern Quebec

    NASA Astrophysics Data System (ADS)

    Jean, Mélanie; Payette, Serge

    2014-02-01

    Palsas are organic or mineral soil mounds having a permafrost core. Palsas are widespread in the circumpolar discontinuous permafrost zone. The annual dynamics and evolution of the active layer, which is the uppermost layer over the permafrost table and subjected to the annual freeze-thaw cycle, are influenced by organic layer thickness, snow depth, vegetation type, topography and exposure. This study examines the influence of vegetation types, with an emphasis on forest cover, on active layer dynamics of palsas in the Boniface River watershed (57°45‧ N, 76°00‧ W). In this area, palsas are often colonized by black spruce trees (Picea mariana (Mill.) B.S.P.). Thaw depth and active layer thickness were monitored on 11 wooded or non-wooded mineral and organic palsas in 2009, 2010 and 2011. Snow depth, organic layer thickness, and vegetation types were assessed. The mapping of a palsa covered by various vegetation types and a large range of organic layer thickness were used to identify the factors influencing the spatial patterns of thaw depth and active layer. The active layer was thinner and the thaw rate slower in wooded palsas, whereas it was the opposite in more exposed sites such as forest openings, shrubs and bare ground. Thicker organic layers were associated with thinner active layers and slower thaw rates. Snow depth was not an important factor influencing active layer dynamics. The topography of the mapped palsa was uneven, and the environmental factors such as organic layer, snow depth, and vegetation types were heterogeneously distributed. These factors explain a part of the spatial variation of the active layer. Over the 3-year long study, the area of one studied palsa decreased by 70%. In a context of widespread permafrost decay, increasing our understanding of factors that influence the dynamics of wooded and non-wooded palsas and understanding of the role of vegetation cover will help to define the response of discontinuous permafrost landforms

  11. Application of Satellite SAR Imagery in Mapping the Active Layer of Arctic Permafrost

    NASA Technical Reports Server (NTRS)

    Zhang, Ting-Jun; Li, Shu-Sun

    2003-01-01

    The objective of this project is to map the spatial variation of the active layer over the arctic permafrost in terms of two parameters: (i) timing and duration of thaw period and (ii) differential frost heave and thaw settlement of the active layer. To achieve this goal, remote sensing, numerical modeling, and related field measurements are required. Tasks for the University of Colorado team are to: (i) determine the timing of snow disappearance in spring through changes in surface albedo (ii) simulate the freezing and thawing processes of the active layer and (iii) simulate the impact of snow cover on permafrost presence.

  12. Hydrothermal regimes of the dry active layer

    NASA Astrophysics Data System (ADS)

    Ishikawa, Mamoru; Zhang, Yinsheng; Kadota, Tsutomu; Ohata, Tetsuo

    2006-04-01

    Evaporation and condensation in the soil column clearly influence year-round nonconductive heat transfer dynamics in the dry active layer underlying semiarid permafrost regions. We deduced this from heat flux components quantified using state-of-the-art micrometeorological data sets obtained in dry and moist summers and in winters with various snow cover depths. Vapor moves easily through large pores, some of which connect to the atmosphere, allowing (1) considerable active layer warming driven by pipe-like snowmelt infiltration, and (2) direct vapor linkage between atmosphere and deeper soils. Because of strong adhesive forces, water in the dry active layer evaporates with great difficulty. The fraction of latent heat to total soil heat storage ranged from 26 to 45% in dry and moist summers, respectively. These values are not negligible, despite being smaller than those of arctic wet active layer, in which only freezing and thawing were considered.

  13. Landscape freeze/thaw retrievals from soil moisture active passive (SMAP) L-band radar measurements

    NASA Astrophysics Data System (ADS)

    Colliander, A.; Derksen, C.

    2015-12-01

    The NASA Soil Moisture Active Passive (SMAP) mission produces a daily landscape freeze/thaw product (L3_FT_A) which provides categorical (frozen, thawed, or [inverse] transitional) classification of the surface state (for land areas north of 45°N) derived from ascending and descending orbits of SMAP high-resolution L-band radar measurements. The FT retrievals are output to 3 km resolution polar and global grids with temporal revisit of 2 days or better north of ~55°N and 3 days or better north of 45°N. The algorithm classifies the land surface freeze/thaw state based on the time series of L-band radar backscatter compared to frozen and thawed reference states. This presentation will describe pre-launch L3_FT_A algorithm implementation and evaluation using NASA/SAC-D Aquarius L-band radar data, and provide an update on the current status of the SMAP L3_FT_A product. In advance of SMAP measurements, the L3_FT_A algorithm was configured and evaluated using Aquarius measurements. While the temporal (weekly) and spatial (~100 km) resolution is much coarser than SMAP, Aquarius provides L-band radar measurements at an incidence angle (normalized to 40 degrees) which is close to SMAP. Evaluation of FT retrievals derived using both Aquarius freeze/thaw references and backscatter time series as inputs identified good agreement during the fall freeze-up period with FT flag agreement (Aquarius versus in situ) exceeding the 80% SMAP mission requirement when summarized on a monthly basis. Disagreement was greater during the spring thaw transition due in part to uncertainty in characterizing the surface state from in situ measurements and backscatter sensitivity to the onset of snow melt, independent of the soil temperature beneath the snowpack. Initial challenges for SMAP derived FT retrievals include the scale difference between the Aquarius references (~100 km) and the SMAP measurements (3 km) which is particularly problematic in areas of complex topography and/or mixed

  14. Application of Satellite SAR Imagery in Mapping the Active Layer of Arctic Permafrost

    NASA Technical Reports Server (NTRS)

    Li, Shu-Sun; Romanovsky, V.; Lovick, Joe; Wang, Z.; Peterson, Rorik

    2003-01-01

    A method of mapping the active layer of Arctic permafrost using a combination of conventional synthetic aperture radar (SAR) backscatter and more sophisticated interferometric SAR (INSAR) techniques is proposed. The proposed research is based on the sensitivity of radar backscatter to the freeze and thaw status of the surface soil, and the sensitivity of INSAR techniques to centimeter- to sub-centimeter-level surface differential deformation. The former capability of SAR is investigated for deriving the timing and duration of the thaw period for surface soil of the active layer over permafrost. The latter is investigated for the feasibility of quantitative measurement of frost heaving and thaw settlement of the active layer during the freezing and thawing processes. The resulting knowledge contributes to remote sensing mapping of the active layer dynamics and Arctic land surface hydrology.

  15. Effect of single-layer centrifugation or washing on frozen-thawed donkey semen quality: Do they have the same effect regardless of the quality of the sample?

    PubMed

    Ortiz, I; Dorado, J; Morrell, J M; Crespo, F; Gosálvez, J; Gálvez, M J; Acha, D; Hidalgo, M

    2015-07-15

    The aims of this study were to determine the sperm quality of frozen-thawed donkey sperm samples after single-layer centrifugation (SLC) using Androcoll-E in comparison to sperm washing or no centrifugation and to determine if the effect on the sperm quality after SLC or sperm washing depends on the quality of the sample. Frozen-thawed sperm samples from Andalusian donkeys were divided into three aliquots, and they were processed using three different techniques after thawing: uncentrifuged diluted control (UDC), sperm washing (SW), and SLC. Afterward, sperm quality index was estimated by integrating all parameters (total and progressive sperm motility, membrane integrity, and DNA fragmentation) in a single value. The relationship between the sperm quality of thawed UDC samples and the effect on sperm parameters in SW and SLC-selected samples was assessed. Sperm quality index was significantly higher (P < 0.001) in SLC (0.8 ± 0.0) samples than that in UDC (0.6 ± 0.0) and SW (0.6 ± 0.0) samples, regardless of the sperm quality index after thawing of the sperm sample. In conclusion, SLC of frozen-thawed donkey spermatozoa using Androcoll-E-Small can be a suitable procedure for selecting frozen-thawed donkey sperm with better quality, in particular in those samples where an improvement in motility is needed.

  16. The effect of two pre-cryopreservation single layer colloidal centrifugation protocols in combination with different freezing extenders on the fragmentation dynamics of thawed equine sperm DNA

    PubMed Central

    2012-01-01

    Background Variability among stallions in terms of semen cryopreservation quality renders it difficult to arrive at a standardized cryopreservation method. Different extenders and processing techniques (such us colloidal centrifugation) are used in order to optimize post-thaw sperm quality. Sperm chromatin integrity analysis is an effective tool for assessing such quality. The aim of the present study was to compare the effect of two single layer colloidal centrifugation protocols (prior to cryopreservation) in combination with three commercial freezing extenders on the post-thaw chromatin integrity of equine sperm samples at different post-thaw incubation (37°C) times (i.e., their DNA fragmentation dynamics). Results Post-thaw DNA fragmentation levels in semen samples subjected to either of the colloidal centrifugation protocols were significantly lower (p<0.05) immediately after thawing and after 4 h of incubation at 37°C compared to samples that underwent standard (control) centrifugation. The use of InraFreeze® extender was associated with significantly less DNA fragmentation than the use of Botu-Crio® extender at 6 h of incubation, and than the use of either Botu-Crio® or Gent® extender at 24 h of incubation (p<0.05). Conclusions These results suggest that single layer colloidal centrifugation performed with extended or raw semen prior to cryopreservation reduces DNA fragmentation during the first four hours after thawing. Further studies are needed to determine the influence of freezing extenders on equine sperm DNA fragmentation dynamics. PMID:23217215

  17. Freeze-thaw stress: effects of temperature on hydraulic conductivity and ultrasonic activity in ten woody angiosperms.

    PubMed

    Charrier, Guillaume; Charra-Vaskou, Katline; Kasuga, Jun; Cochard, Hervé; Mayr, Stefan; Améglio, Thierry

    2014-02-01

    Freeze-thaw events can affect plant hydraulics by inducing embolism. This study analyzed the effect of temperature during the freezing process on hydraulic conductivity and ultrasonic emissions (UE). Stems of 10 angiosperms were dehydrated to a water potential at 12% percentage loss of hydraulic conductivity (PLC) and exposed to freeze-thaw cycles. The minimal temperature of the frost cycle correlated positively with induced PLC, whereby species with wider conduits (hydraulic diameter) showed higher freeze-thaw-induced PLC. Ultrasonic activity started with the onset of freezing and increased with decreasing subzero temperatures, whereas no UE were recorded during thawing. The temperature at which 50% of UE were reached varied between -9.1°C and -31.0°C across species. These findings indicate that temperatures during freezing are of relevance for bubble formation and air seeding. We suggest that species-specific cavitation thresholds are reached during freezing due to the temperature-dependent decrease of water potential in the ice, while bubble expansion and the resulting PLC occur during thawing. UE analysis can be used to monitor the cavitation process and estimate freeze-thaw-induced PLC.

  18. Acceleration of thaw slump activity in glaciated landscapes of the Western Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Segal, Rebecca A.; Lantz, Trevor C.; Kokelj, Steven V.

    2016-03-01

    Climate change is increasing the frequency and intensity of thermokarst, but the influences of regional climate and physiography remain poorly understood. Retrogressive thaw slumping is one of the most dynamic forms of thermokarst and affects many areas of glaciated terrain across northwestern Canada. In this study, we used airphotos and satellite imagery to investigate the influence of climate and landscape factors on thaw slump dynamics. We assessed slump size, density, and growth rates in four regions of ice-rich terrain with contrasting climate and physiographic conditions: the Jesse Moraine, the Tuktoyaktuk Coastlands, the Bluenose Moraine, and the Peel Plateau. Observed increases in: (1) the area impacted by slumps (+2 to +407%), (2) average slump sizes (+0.31 to +1.82 ha), and (3) slump growth rates (+169 to +465 m2 yr-1) showed that thermokarst activity is rapidly accelerating in ice-rich morainal landscapes in the western Canadian Arctic, where slumping has become a dominant driver of geomorphic change. Differences in slump characteristics among regions indicate that slump development is strongly influenced by topography, ground ice conditions, and Quaternary history. Observed increases in slump activity occurred in conjunction with increases in air temperature and precipitation, but variation in slump activity among the four regions suggests that increased precipitation has been an important driver of change. Our observation that the most rapid intensification of slump activity occurred in the coldest environment (the Jesse Moraine on Banks Island) indicates that ice-cored landscapes in cold permafrost environments are highly vulnerable to climate change.

  19. Assessing hazard risk, cost of adaptation and traditional land use activities in the context of permafrost thaw in communities in Yukon and the Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Benkert, B.; Perrin, A.; Calmels, F.

    2015-12-01

    Together with its partners, the Northern Climate ExChange (NCE, part of the Yukon Research Centre at Yukon College) has been mapping permafrost-related hazard risk in northern communities since 2010. By integrating geoscience and climate project data, we have developed a series of community-scale hazard risk maps. The maps depict hazard risk in stoplight colours for easy interpretation, and support community-based, future-focused adaptation planning. Communities, First Nations, consultants and local regulatory agencies have used the hazard risk maps to site small-scale infrastructure projects, guide land planning processes, and assess suitability of land development applications. However, we know that assessing risk is only one step in integrating the implications of permafrost degradation in societal responses to environmental change. To build on our permafrost hazard risk maps, we are integrating economic principles and traditional land use elements. To assess economic implications of adaptation to permafrost change, we are working with geotechnical engineers to identify adaptation options (e.g., modified building techniques, permafrost thaw mitigation approaches) that suit the risks captured by our existing hazard risk maps. We layer this with an economic analysis of the costs associated with identified adaptation options, providing end-users with a more comprehensive basis upon which to make decisions related to infrastructure. NCE researchers have also integrated traditional land use activities in assessments of permafrost thaw risk, in a project led by Jean Marie River First Nation in the Northwest Territories. Here, the implications of permafrost degradation on food security and land use priorities were assessed by layering key game and gathering areas on permafrost thaw vulnerability maps. Results indicated that close to one quarter of big and small game habitats, and close to twenty percent of key furbearer and gathering areas within the First Nation

  20. Seasonal thaw settlement at drained thermokarst lake basins, Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Liu, L.; Schaefer, K.; Gusmeroli, A.; Grosse, G.; Jones, B. M.; Zhang, T.; Parsekian, A. D.; Zebker, H. A.

    2013-12-01

    Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on arctic tundra lowlands, but their present-day dynamic states are seldom investigated. Here we report results based on high-resolution Interferometric Synthetic Aperture Radar (InSAR) measurements using space-borne data for a study area located near Prudhoe Bay, Alaska where we focus on the seasonal thaw settlement within DTLBs, averaged between 2006 and 2010. The majority (14) of the 18 DTLBs in the study area analyzed exhibited seasonal thaw settlement of 3-4 cm. However, four of the DTLBs analyzed exceeded 4 cm of thaw settlement, with one basin experiencing up to 12 cm. Combining the InSAR observations with the in situ active layer thickness measured using ground penetrating radar and mechanical probing, we calculated thaw strain, an index of thaw settlement strength along a transect across the basin that underwent large thaw settlement. We found thaw strains of 10-35% at the basin center, suggesting the seasonal melting of ground ice as a possible mechanism for the large settlement. These findings emphasize the dynamic nature of permafrost landforms, demonstrate the capability of the InSAR technique to remotely monitor surface deformation of individual DTLBs, and illustrate the combination of ground-based and remote sensing observations to estimate thaw strain. Our study highlights the need for better description of the spatial heterogeneity of landscape-scale processes for regional assessment of surface dynamics on arctic coastal lowlands.

  1. Multi-omics of permafrost, active layer and thermokarst bog soil microbiomes.

    PubMed

    Hultman, Jenni; Waldrop, Mark P; Mackelprang, Rachel; David, Maude M; McFarland, Jack; Blazewicz, Steven J; Harden, Jennifer; Turetsky, Merritt R; McGuire, A David; Shah, Manesh B; VerBerkmoes, Nathan C; Lee, Lang Ho; Mavrommatis, Kostas; Jansson, Janet K

    2015-05-14

    Over 20% of Earth's terrestrial surface is underlain by permafrost with vast stores of carbon that, once thawed, may represent the largest future transfer of carbon from the biosphere to the atmosphere. This process is largely dependent on microbial responses, but we know little about microbial activity in intact, let alone in thawing, permafrost. Molecular approaches have recently revealed the identities and functional gene composition of microorganisms in some permafrost soils and a rapid shift in functional gene composition during short-term thaw experiments. However, the fate of permafrost carbon depends on climatic, hydrological and microbial responses to thaw at decadal scales. Here we use the combination of several molecular 'omics' approaches to determine the phylogenetic composition of the microbial communities, including several draft genomes of novel species, their functional potential and activity in soils representing different states of thaw: intact permafrost, seasonally thawed active layer and thermokarst bog. The multi-omics strategy reveals a good correlation of process rates to omics data for dominant processes, such as methanogenesis in the bog, as well as novel survival strategies for potentially active microbes in permafrost. PMID:25739499

  2. Multi-omics of permafrost, active layer and thermokarst bog soil microbiomes

    NASA Astrophysics Data System (ADS)

    Hultman, Jenni; Waldrop, Mark P.; Mackelprang, Rachel; David, Maude M.; McFarland, Jack; Blazewicz, Steven J.; Harden, Jennifer; Turetsky, Merritt R.; McGuire, A. David; Shah, Manesh B.; Verberkmoes, Nathan C.; Lee, Lang Ho; Mavrommatis, Kostas; Jansson, Janet K.

    2015-05-01

    Over 20% of Earth's terrestrial surface is underlain by permafrost with vast stores of carbon that, once thawed, may represent the largest future transfer of carbon from the biosphere to the atmosphere. This process is largely dependent on microbial responses, but we know little about microbial activity in intact, let alone in thawing, permafrost. Molecular approaches have recently revealed the identities and functional gene composition of microorganisms in some permafrost soils and a rapid shift in functional gene composition during short-term thaw experiments. However, the fate of permafrost carbon depends on climatic, hydrological and microbial responses to thaw at decadal scales. Here we use the combination of several molecular `omics' approaches to determine the phylogenetic composition of the microbial communities, including several draft genomes of novel species, their functional potential and activity in soils representing different states of thaw: intact permafrost, seasonally thawed active layer and thermokarst bog. The multi-omics strategy reveals a good correlation of process rates to omics data for dominant processes, such as methanogenesis in the bog, as well as novel survival strategies for potentially active microbes in permafrost.

  3. Multi-omics of Permafrost, Active Layer and Thermokarst Bog Soil Microbiomes

    SciTech Connect

    Hultman, Jenni; Waldrop, Mark P.; Mackelprang, Rachel; David, Maude; McFarland, Jack; Blazewicz, Steven J.; Harden, Jennifer W.; Turetsky, Merritt; McGuire, A. David; Shah, Manesh B.; VerBerkmoes, Nathan C.; Lee, Lang Ho; Mavrommatis, Konstantinos; Jansson, Janet K.

    2015-03-04

    Over 20% of Earth’s terrestrial surface is underlain by permafrost with vast stores of carbon that, if thawed may represent the largest future transfer of C from the biosphere to the atmosphere 1. This process is largely dependent on microbial responses, but we know little about microbial activity in intact, let alone in thawing permafrost. Molecular approaches have recently revealed the identities and functional gene composition of microorganisms in some permafrost soils 2-4 and a rapid shift in functional gene composition during short-term thaw experiments 3. However, the fate of permafrost C depends on climatic, hydrologic, and microbial responses to thaw at decadal scales 5, 6. Here the combination of several molecular “omics” approaches enabled us to determine the phylogenetic composition of the microbial community, including several draft genomes of novel species, their functional potential and activity in soils representing different states of thaw: intact permafrost, seasonally thawed active layer and thermokarst bog. The multi-omics strategy revealed a good correlation of process rates to omics data for dominant processes, such as methanogenesis in the bog, as well as novel survival strategies for potentially active microbes in permafrost.

  4. Multi-omics of permafrost, active layer and thermokarst bog soil microbiomes.

    PubMed

    Hultman, Jenni; Waldrop, Mark P; Mackelprang, Rachel; David, Maude M; McFarland, Jack; Blazewicz, Steven J; Harden, Jennifer; Turetsky, Merritt R; McGuire, A David; Shah, Manesh B; VerBerkmoes, Nathan C; Lee, Lang Ho; Mavrommatis, Kostas; Jansson, Janet K

    2015-05-14

    Over 20% of Earth's terrestrial surface is underlain by permafrost with vast stores of carbon that, once thawed, may represent the largest future transfer of carbon from the biosphere to the atmosphere. This process is largely dependent on microbial responses, but we know little about microbial activity in intact, let alone in thawing, permafrost. Molecular approaches have recently revealed the identities and functional gene composition of microorganisms in some permafrost soils and a rapid shift in functional gene composition during short-term thaw experiments. However, the fate of permafrost carbon depends on climatic, hydrological and microbial responses to thaw at decadal scales. Here we use the combination of several molecular 'omics' approaches to determine the phylogenetic composition of the microbial communities, including several draft genomes of novel species, their functional potential and activity in soils representing different states of thaw: intact permafrost, seasonally thawed active layer and thermokarst bog. The multi-omics strategy reveals a good correlation of process rates to omics data for dominant processes, such as methanogenesis in the bog, as well as novel survival strategies for potentially active microbes in permafrost.

  5. Characterization of alkaline phosphatase activity in seminal plasma and in fresh and frozen-thawed stallion spermatozoa.

    PubMed

    Bucci, Diego; Giaretta, Elisa; Spinaci, Marcella; Rizzato, Giovanni; Isani, Gloria; Mislei, Beatrice; Mari, Gaetano; Tamanini, Carlo; Galeati, Giovanna

    2016-01-15

    Alkaline phosphatase (AP) has been studied in several situations to elucidate its role in reproductive biology of the male from different mammalian species; at present, its role in horse sperm physiology is not clear. The aim of the present work was to measure AP activity in seminal plasma and sperm extracts from freshly ejaculated as well as in frozen-thawed stallion spermatozoa and to verify whether relationship exists between AP activity and sperm quality parameters. Our data on 40 freshly ejaculated samples from 10 different stallions demonstrate that the main source of AP activity is seminal plasma, whereas sperm extracts contribution is very low. In addition, we found that AP activity at physiological pH (7.0) is significantly lower than that observed at pH 8.0, including the optimal AP pH (pH 10.0). Alkaline phosphatase did not exert any effect on sperm-oocyte interaction assessed by heterologous oocyte binding assay. Additionally, we observed a thermal stability of seminal plasma AP, concluding that it is similar to that of bone isoforms. Positive correlations were found between seminal plasma AP activity and sperm concentration, whereas a negative correlation was present between both spermatozoa extracts and seminal plasma AP activity and seminal plasma protein content. A significant decrease in sperm extract AP activity was found in frozen-thawed samples compared with freshly ejaculated ones (n = 21), concomitantly with the decrease in sperm quality parameters. The positive correlation between seminal plasma AP activity measured at pH 10 and viability of frozen-thawed spermatozoa suggests that seminal plasma AP activity could be used as an additional predictive parameter for stallion sperm freezability. In conclusion, we provide some insights into AP activity in both seminal plasma and sperm extracts and describe a decrease in AP after freezing and thawing.

  6. Estimating 3D variation in active-layer thickness beneath arctic streams using ground-penetrating radar

    USGS Publications Warehouse

    Brosten, T.R.; Bradford, J.H.; McNamara, J.P.; Gooseff, M.N.; Zarnetske, J.P.; Bowden, W.B.; Johnston, M.E.

    2009-01-01

    We acquired three-dimensional (3D) ground-penetrating radar (GPR) data across three stream sites on the North Slope, AK, in August 2005, to investigate the dependence of thaw depth on channel morphology. Data were migrated with mean velocities derived from multi-offset GPR profiles collected across a stream section within each of the 3D survey areas. GPR data interpretations from the alluvial-lined stream site illustrate greater thaw depths beneath riffle and gravel bar features relative to neighboring pool features. The peat-lined stream sites indicate the opposite; greater thaw depths beneath pools and shallower thaw beneath the connecting runs. Results provide detailed 3D geometry of active-layer thaw depths that can support hydrological studies seeking to quantify transport and biogeochemical processes that occur within the hyporheic zone.

  7. The Soil Moisture Active Passive (SMAP) Radar: Measurements at High Latitudes and of Surface Freeze/Thaw State

    NASA Technical Reports Server (NTRS)

    Spencer, Michael; Dunbar, Scott; Chen, Curtis

    2013-01-01

    The Soil Moisture Active/Passive (SMAP) mission is scheduled for a late 2014 launch date. The mission will use both active radar and passive radiometer instruments at L-Band in order to achieve the science objectives of measuring soil moisture and land surface freeze-thaw state. To achieve requirements for a wide swath at sufficiently high resolution for both active and passive channels, an instrument architecture that uses a large rotating reflector is employed. In this paper, focus will be placed on the radar design. The radar will employ synthetic-aperture processing to achieve a "moderate" resolution dual-pol product over a 1000 km swath. Because the radar is operating continuously, very frequent temporal coverage will be achieved at high latitudes. This data will be used to produce a surface freeze/thaw state data product.

  8. Permafrost thaw and intense thermokarst activity decreases abundance of stream benthic macroinvertebrates.

    PubMed

    Chin, Krista S; Lento, Jennifer; Culp, Joseph M; Lacelle, Denis; Kokelj, Steven V

    2016-08-01

    Intensification of permafrost thaw has increased the frequency and magnitude of large permafrost slope disturbances (mega slumps) in glaciated terrain of northwestern Canada. Individual thermokarst disturbances up to 40 ha in area have made large volumes of previously frozen sediments available for leaching and transport to adjacent streams, significantly increasing sediment and solute loads in these systems. To test the effects of this climate-sensitive disturbance regime on the ecology of Arctic streams, we explored the relationship between physical and chemical variables and benthic macroinvertebrate communities in disturbed and undisturbed stream reaches in the Peel Plateau, Northwest Territories, Canada. Highly disturbed and undisturbed stream reaches differed with respect to taxonomic composition and invertebrate abundance. Minimally disturbed reaches were not differentiated by these variables but rather were distributed along a disturbance gradient between highly disturbed and undisturbed sites. In particular, there was evidence of a strong negative relationship between macroinvertebrate abundance and total suspended solids, and a positive relationship between abundance and the distance from the disturbance. Increases in both sediments and nutrients appear to be the proximate cause of community differences in highly disturbed streams. Declines in macroinvertebrate abundance in response to slump activity have implications for the food webs of these systems, potentially leading to negative impacts on higher trophic levels, such as fish. Furthermore, the disturbance impacts on stream health can be expected to intensify as climate change increases the frequency and magnitude of thermokarst. PMID:26766394

  9. Permafrost thaw and intense thermokarst activity decreases abundance of stream benthic macroinvertebrates.

    PubMed

    Chin, Krista S; Lento, Jennifer; Culp, Joseph M; Lacelle, Denis; Kokelj, Steven V

    2016-08-01

    Intensification of permafrost thaw has increased the frequency and magnitude of large permafrost slope disturbances (mega slumps) in glaciated terrain of northwestern Canada. Individual thermokarst disturbances up to 40 ha in area have made large volumes of previously frozen sediments available for leaching and transport to adjacent streams, significantly increasing sediment and solute loads in these systems. To test the effects of this climate-sensitive disturbance regime on the ecology of Arctic streams, we explored the relationship between physical and chemical variables and benthic macroinvertebrate communities in disturbed and undisturbed stream reaches in the Peel Plateau, Northwest Territories, Canada. Highly disturbed and undisturbed stream reaches differed with respect to taxonomic composition and invertebrate abundance. Minimally disturbed reaches were not differentiated by these variables but rather were distributed along a disturbance gradient between highly disturbed and undisturbed sites. In particular, there was evidence of a strong negative relationship between macroinvertebrate abundance and total suspended solids, and a positive relationship between abundance and the distance from the disturbance. Increases in both sediments and nutrients appear to be the proximate cause of community differences in highly disturbed streams. Declines in macroinvertebrate abundance in response to slump activity have implications for the food webs of these systems, potentially leading to negative impacts on higher trophic levels, such as fish. Furthermore, the disturbance impacts on stream health can be expected to intensify as climate change increases the frequency and magnitude of thermokarst.

  10. The repeated drying-wetting and freezing-thawing cycles affect only the active pool of soil organic matter

    NASA Astrophysics Data System (ADS)

    Semenov, Vyacheslav; Zinyakova, Natalya; Tulina, Anastasiya

    2016-04-01

    The decrease in the content of soil organic carbon, particularly in active form, is one of the major problems of the 21st century, which is closely related to the disturbance of the biogeochemical carbon cycle and to the increase in the emission of carbon dioxide into the atmosphere. The main reasons for the SOM losses are the surplus of the SOM active pool losses due to mineralization, erosion, and infiltration over the input of fresh organic matter to the soil, as well as the changes in the soil conditions and processes due to natural and anthropogenic disturbing impacts. Experiments were carried out with mixed samples from the upper layers of soddy-podzolic soil, gray forest soil, and typical chernozems. Soil samples as controls were incubated after wetting for 150 days. The dynamics and cumulative production of C-CO2 under stable temperature (22°C) and moisture conditions were determined; the initial content of potentially mineralizable organic matter (C0) in the soil at the beginning of the incubation was then calculated to use these data as the control. Other soil samples were exposed in flasks to the following successive treatments: wetting →incubation → freezing → thawing → incubation →drying. Six repeated cycles of disturbing impacts were performed for 140 days of the experiment. After six cycles, the soil samples were incubated under stable temperature and moisture conditions for 150 days. The wetting of dried soils and the thawing of frozen soils are accompanied by the pulsed dynamics of the C-CO2 production with an abrupt increase in the rate of the C-CO2 emission within several days by 2.7-12.4 and 1.6-2.7 times, respectively, compared to the stable incubation conditions. The rate of the C-CO2 production pulses under each subsequent impact decreased compared to the preceding one similarly for all studied soils, which could be due to the depletion in potentially mineralizable soil organic matter (C0). The cumulative extra C-CO2 production by

  11. The Effect of Thawing Condition for Frozen Fish Meats

    NASA Astrophysics Data System (ADS)

    Abe, Shuji; Osako, Kazufumi; Watanabe, Manabu; Suzuki, Toru

    The influence of thawing speed on denaturation of muscle protein and quality of several kinds frozen fish meat was studied by measuring Ca-ATPase activity, drip loss, and microscopic observation. Frozen bigeye tuna, chub mackerel, alaska pollack and yellow tail meat thawed at 10°C by air (slow thawing) and water (rapid thawing). Ca-ATPase activity of slow thawed fishes meat decreased than it of rapid thawed fishes meat. On the other hand drip loss of slow thawed fishes meat increased than it of rapid thawed fishes meat. Decreasing of Ca-ATPase activity showed a good linear relation to increasing of drip loss. Further, from microscopic observation, it was confirmed that muscle cells of slow thawed fishes meat were disrupted than it of rapid thawed samples. Therefore,it was suggested that rapid warming on thawing process is better to inhibit protein denaturation and drip loss.

  12. Reviews and Syntheses: Effects of permafrost thaw on arctic aquatic ecosystems

    NASA Astrophysics Data System (ADS)

    Vonk, J. E.; Tank, S. E.; Bowden, W. B.; Laurion, I.; Vincent, W. F.; Alekseychik, P.; Amyot, M.; Billet, M. F.; Canário, J.; Cory, R. M.; Deshpande, B. N.; Helbig, M.; Jammet, M.; Karlsson, J.; Larouche, J.; MacMillan, G.; Rautio, M.; Anthony, K. M. Walter; Wickland, K. P.

    2015-07-01

    The Arctic is a water-rich region, with freshwater systems covering 16 % of the northern permafrost landscape. The thawing of this permafrost creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic and lotic systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas, vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying variables determine the degree to which permafrost thaw manifests as thermokarst, whether thermokarst leads to slumping or the formation of thermokarst lakes, and the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying variables determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted systems is also likely to change, with thaw-impacted lakes and streams having unique microbiological communities, and showing differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter and nutrient delivery. The degree to which thaw enables the delivery of

  13. Seasonal thaw settlement at drained thermokarst lake basins, Arctic Alaska

    USGS Publications Warehouse

    Liu, Lin; Schaefer, Kevin; Gusmeroli, Alessio; Grosse, Guido; Jones, Benjamin M.; Zhang, Tinjun; Parsekian, Andrew; Zebker, Howard

    2014-01-01

    Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on Arctic tundra lowland. Their dynamic states are seldom investigated, despite their importance for landscape stability, hydrology, nutrient fluxes, and carbon cycling. Here we report results based on high-resolution Interferometric Synthetic Aperture Radar (InSAR) measurements using space-borne data for a study area located on the North Slope of Alaska near Prudhoe Bay, where we focus on the seasonal thaw settlement within DTLBs, averaged between 2006 and 2010. The majority (14) of the 18 DTLBs in the study area exhibited seasonal thaw settlement of 3–4 cm. However, four of the DTLBs examined exceeded 4 cm of thaw settlement, with one basin experiencing up to 12 cm. Combining the InSAR observations with the in situ active layer thickness measured using ground penetrating radar and mechanical probing, we calculated thaw strain, an index of thaw settlement strength along a transect across the basin that underwent large thaw settlement. We found thaw strains of 10–35% at the basin center, suggesting the seasonal melting of ground ice as a possible mechanism for the large settlement. These findings emphasize the dynamic nature of permafrost landforms, demonstrate the capability of the InSAR technique to remotely monitor surface deformation of individual DTLBs, and illustrate the combination of ground-based and remote sensing observations to estimate thaw strain. Our study highlights the need for better description of the spatial heterogeneity of landscape-scale processes for regional assessment of surface dynamics on Arctic coastal lowlands.

  14. Seasonal thaw settlement at drained thermokarst lake basins, Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Liu, L.; Schaefer, K.; Gusmeroli, A.; Grosse, G.; Jones, B. M.; Zhang, T.; Parsekian, A. D.; Zebker, H. A.

    2014-05-01

    Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on Arctic tundra lowland. Their dynamic states are seldom investigated, despite their importance for landscape stability, hydrology, nutrient fluxes, and carbon cycling. Here we report results based on high-resolution Interferometric Synthetic Aperture Radar (InSAR) measurements using space-borne data for a study area located on the North Slope of Alaska near Prudhoe Bay, where we focus on the seasonal thaw settlement within DTLBs, averaged between 2006 and 2010. The majority (14) of the 18 DTLBs in the study area exhibited seasonal thaw settlement of 3-4 cm. However, four of the DTLBs examined exceeded 4 cm of thaw settlement, with one basin experiencing up to 12 cm. Combining the InSAR observations with the in situ active layer thickness measured using ground penetrating radar and mechanical probing, we calculated thaw strain, an index of thaw settlement strength along a transect across the basin that underwent large thaw settlement. We found thaw strains of 10-35% at the basin center, suggesting the seasonal melting of ground ice as a possible mechanism for the large settlement. These findings emphasize the dynamic nature of permafrost landforms, demonstrate the capability of the InSAR technique to remotely monitor surface deformation of individual DTLBs, and illustrate the combination of ground-based and remote sensing observations to estimate thaw strain. Our study highlights the need for better description of the spatial heterogeneity of landscape-scale processes for regional assessment of surface dynamics on Arctic coastal lowlands.

  15. Genes Upregulated in Winter Wheat (Triticum aestivum L.) during Mild Freezing and Subsequent Thawing Suggest Sequential Activation of Multiple Response Mechanisms.

    PubMed

    Skinner, Daniel Z

    2015-01-01

    Exposing fully cold-acclimated wheat plants to a mild freeze-thaw cycle of -3 °C for 24h followed by +3 °C for 24 or 48 h results in dramatically improved tolerance of subsequent exposure to sub-freezing temperatures. Gene enrichment analysis of crown tissue from plants collected before or after the -3 °C freeze or after thawing at +3 °C for 24 or 48 h revealed that many biological processes and molecular functions were activated during the freeze-thaw cycle in an increasing cascade of responses such that over 150 processes or functions were significantly enhanced by the end of the 48 h, post-freeze thaw. Nearly 2,000 individual genes were upregulated more than 2-fold over the 72 h course of freezing and thawing, but more than 70% of these genes were upregulated during only one of the time periods examined, suggesting a series of genes and gene functions were involved in activation of the processes that led to enhanced freezing tolerance. This series of functions appeared to include extensive cell signaling, activation of stress response mechanisms and the phenylpropanoid biosynthetic pathway, extensive modification of secondary metabolites, and physical restructuring of cell membranes. By identifying plant lines that are especially able to activate these multiple mechanisms it may be possible to develop lines with enhanced winterhardiness.

  16. Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

    NASA Astrophysics Data System (ADS)

    Vonk, J. E.; Tank, S. E.; Bowden, W. B.; Laurion, I.; Vincent, W. F.; Alekseychik, P.; Amyot, M.; Billet, M. F.; Canário, J.; Cory, R. M.; Deshpande, B. N.; Helbig, M.; Jammet, M.; Karlsson, J.; Larouche, J.; MacMillan, G.; Rautio, M.; Anthony, K. M. Walter; Wickland, K. P.

    2015-12-01

    The Arctic is a water-rich region, with freshwater systems covering about 16 % of the northern permafrost landscape. Permafrost thaw creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic (still) and lotic (moving) systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying factors determine (i) the degree to which permafrost thaw manifests as thermokarst, (ii) whether thermokarst leads to slumping or the formation of thermokarst lakes, and (iii) the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying factors determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted lakes and streams is also likely to change; these systems have unique microbiological communities, and show differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter, and nutrient delivery. The degree to which thaw enables the delivery

  17. The Soil Moisture Active Passive (SMAP): Radar Measurements at High Latitudes and of Freeze/Thaw State

    NASA Technical Reports Server (NTRS)

    Spencer, Michael; Dunbar, Scott; Chen, Curtis

    2013-01-01

    The Soil Moisture Active/Passive (SMAP) mission is scheduled for a late 2014 launch date. The mission will use both active radar and passive radiometer instruments at L-Band. In order to achieve a wide swath at sufficiently high resolution for both active and passive channels, an instrument architecture that uses a large rotating reflector is employed. In this paper, a focus will be places on the radar design and associated data products at high latitudes. The radar will employ synthetic-aperture processing to achieve a "moderate" resolution dual-pol product over a 1000 km swath. Because the radar is operating continuously, very frequent temporal coverage will be achieved at high latitudes. This data will be used, among other things, to produce a surface freeze/thaw state data product.

  18. Mapping Microbial Carbon Substrate Utilization Across Permafrost Thaw

    NASA Astrophysics Data System (ADS)

    Anderson, D.; Rich, V. I.; Hodgkins, S. B.; Tfaily, M.; Chanton, J.

    2014-12-01

    Permafrost thaw is likely to create a substantial positive feedback to climate warming, as previously frozen carbon becomes bioavailable and is released to the atmosphere. Microbes mediate this release, while also consuming "new" carbon from plant inputs and middle-aged soil carbon pools in the seasonally-thawed active layer overlying permafrost. This carbon consumption releases carbon dioxide (CO2) and methane (CH4), both potent greenhouse gases. To investigate microbial carbon cycling in this changing habitat, we examined how microbial communities' carbon substrate degradation changes along a natural permafrost thaw gradient in Stordalen Mire (68.35°N, 19.05°E), northern Sweden. At this location, intermediate thaw creates Sphagnum moss-dominated bogs, while complete thaw results in Eriophorum sedge-dominated fens. The progression of thaw results in increasing organic matter lability (Hodgkins et al, 2014), shifting microbial community composition (Mondav & Woodcroft et al 2014), and changing carbon gas emissions (McCalley et al, in review). However, the inter-relationship of the first two in producing the third remains unclear. We analyzed microbial carbon substrate utilization in the intermediate-thaw and full-thaw sites by two incubation-based methods. We used Biolog EcoPlates, which contain 31 ecologically relevant carbon substrates and a colorimetric marker of their consumption, and into which we added a soil liquid suspension. In addition, we performed mason-jar incubations of peat with carbon substrate amendments and measured CH4 and CO2 emissions. Preliminary Biolog Ecoplate incubations showed that intermediate-thaw features responded faster and more strongly overall to a wide range of substrates relative to the full-thaw features. Preliminary mason jar incubations showed that acetate amendment elicited the greatest response increase in CH4 production and the second greatest increase in CO2 production relative to the controls, in samples from both

  19. Influences and interactions of inundation, peat, and snow on active layer thickness

    NASA Astrophysics Data System (ADS)

    Atchley, Adam L.; Coon, Ethan T.; Painter, Scott L.; Harp, Dylan R.; Wilson, Cathy J.

    2016-05-01

    Active layer thickness (ALT), the uppermost layer of soil that thaws on an annual basis, is a direct control on the amount of organic carbon potentially available for decomposition and release to the atmosphere as carbon-rich Arctic permafrost soils thaw in a warming climate. We investigate how key site characteristics affect ALT using an integrated surface/subsurface permafrost thermal hydrology model. ALT is most sensitive to organic layer thickness followed by snow depth but is relatively insensitive to the amount of water on the landscape with other conditions held fixed. The weak ALT sensitivity to subsurface saturation suggests that changes in Arctic landscape hydrology may only have a minor effect on future ALT. However, surface inundation amplifies the sensitivities to the other parameters and under large snowpacks can trigger the formation of near-surface taliks.

  20. Remote sensing of freeze-thaw transitions in Arctic soils using the complex resistivity method

    SciTech Connect

    Wu, Yuxin; Hubbard, Susan S; Ulrich, Craig; Wullschleger, Stan D

    2013-01-01

    Our ability to monitor freeze - thaw transitions is critical to developing a predictive understanding of biogeochemical transitions and carbon dynamics in high latitude environments. In this study, we conducted laboratory column experiments to explore the potential of the complex resistivity method for monitoring the freeze - thaw transitions of the arctic permafrost soils. Samples for the experiment were collected from the upper active layer of Gelisol soils at the Barrow Environmental Observatory, Barrow Alaska. Freeze - thaw transitions were induced through exposing the soil column to controlled temperature environments at 4 C and -20 C. Complex resistivity and temperature measurements were collected regularly during the freeze - thaw transitions using electrodes and temperature sensors installed along the column. During the experiments, over two orders of magnitude of resistivity variations were observed when the temperature was increased or decreased between -20 C and 0 C. Smaller resistivity variations were also observed during the isothermal thawing or freezing processes that occurred near 0 C. Single frequency electrical phase response and imaginary conductivity at 1 Hz were found to be exclusively related to the unfrozen water in the soil matrix, suggesting that these geophysical 24 attributes can be used as a proxy for the monitoring of the onset and progression of the freeze - thaw transitions. Spectral electrical responses and fitted Cole Cole parameters contained additional information about the freeze - thaw transition affected by the soil grain size distribution. Specifically, a shift of the observed spectral response to lower frequency was observed during isothermal thawing process, which we interpret to be due to sequential thawing, first from fine then to coarse particles within the soil matrix. Our study demonstrates the potential of the complex resistivity method for remote monitoring of freeze - thaw transitions in arctic soils. Although

  1. How Fast Can Permafrost Thaw? (Invited)

    NASA Astrophysics Data System (ADS)

    Romanovsky, V. E.; Nicolsky, D. J.

    2009-12-01

    Climate warming of the last half of a century resulted in many changes in all other components of the Earth’s system. One of the most impacted components was the Cryosphere. Permafrost, as an important part of the Cryosphere, has also been strongly affected. However, according to our data, a wide range of permafrost reaction has been observed. Typically, a much more significant warming has been observed in cold permafrost and much less in warm permafrost. At many sites where the permafrost temperatures are within 0.5 C from the freezing point of water, almost no measurable changes in permafrost temperature during the last 20 to 25 years were recorded. Also, while the warming of relatively cold permafrost was observed practically for the entire Northern Hemisphere permafrost domain, the permafrost thawing was much more restricted and mostly observed in mountain permafrost and at the sites where surface disturbances (natural or human-induced) have occurred and where isolative organic layer was reduced or removed from the ground surface. In our previous publications and in the publications of our colleagues, the lower rates of changes in relatively warm permafrost were correctly related to the unfrozen water presence in frozen fine-grained earth material. However, we believe that a more in-deep explanation of this phenomenon is warranted especially now when the changes in permafrost and specifically the rate of permafrost thawing were designated by the last IPPC report as one of the major uncertainties in future climate projections. The major driving force of permafrost warming and/or thawing is a long-term (one year or multi-years) imbalance in incoming and outgoing heat fluxes at the upper boundary of permafrost (permafrost table) integrated over a one-year time period. If more heat is coming in than going out, permafrost will be warming and eventually thawing. If the opposite is true, permafrost will be cooling and the active layer could be converting into

  2. Microbes in thawing permafrost: the unknown variable in the climate change equation

    SciTech Connect

    Graham, David E; Wallenstein, Matthew D; Vishnivetskaya, T.; Waldrop, Mark P.; Phelps, Tommy Joe; Pfiffner, Susan M.; Onstott, T. C.; Whyte, Lyle; Rivkina, Elizaveta; Gilichinsky, David A; Elias, Dwayne A; Mackelprang, Rachel; Verberkmoes, Nathan C; Hettich, Robert {Bob} L; Wagner, Dirk; Wullschleger, Stan D; Jansson, Janet

    2012-01-01

    Considering that 25% of Earth s terrestrial surface is underlain by permafrost (ground that has been continuously frozen for at least 2 years), our understanding of the diversity of microbial life in this extreme habitat is surprisingly limited. Taking into account the total mass of perennially frozen sediment (up to several hundred meters deep), permafrost contains a huge amount of buried, ancient organic carbon (Tarnocai et al., 2009). In addition, permafrost is warming rapidly in response to global climate change (Romanovsky et al., 2010), potentially leading to widespread thaw and a larger, seasonally thawed soil active layer. This concern has prompted the question: will permafrost thawing lead to the release of massive amounts of carbon dioxide (CO2) and methane (CH4) into the atmosphere? This question can only be answered by understanding how the microbes residing in permafrost will respond to thaw, through processes such as respiration, fermentation, methanogenesis and CH4 oxidation (Schuur et al., 2009). Predicting future carbon fluxes is complicated by the diversity of permafrost environments, ranging from high mountains, southern boreal forests, frozen peatlands and Pleistocene ice complexes (yedoma) up to several hundred meters deep, which vary widely in soil composition, soil organic matter (SOM) quality, hydrology and thermal regimes (Figure 1). Permafrost degradation can occur in many forms: thaw can progress downward from seasonally-thawed active layer soils in warming climates or laterally because of changes in surface or groundwater flow paths (Grosse et al., 2011). Permafrost degradation can sometimes lead to dramatic changes in ecosystem structure and function

  3. Environmental correlates of peatland carbon fluxes in a thawing landscape: do transitional thaw stages matter?

    NASA Astrophysics Data System (ADS)

    Malhotra, A.; Roulet, N. T.

    2015-01-01

    Peatlands in discontinuous permafrost regions occur as a mosaic of wetland types, each with variable sensitivity to climate change. Permafrost thaw further increases the spatial heterogeneity in ecosystem structure and function in peatlands. Carbon (C) fluxes are well characterized in end-member thaw stages such as fully intact or fully thawed permafrost but remain unconstrained for transitional stages that cover a significant area of thawing peatlands. Furthermore, changes in the environmental correlates of C fluxes, due to thaw are not well described: a requirement for modeling future changes to C storage of permafrost peatlands. We investigated C fluxes and their correlates in end-member and a number of transitional thaw stages in a sub-arctic peatland. Across peatland lumped CH4 and CO2 flux data had significant correlations with expected correlates such as water table depth, thaw depth, temperature, photosynthetically active radiation and vascular green area. Within individual thaw states, bivariate correlations as well as multiple regressions between C flux and environmental factors changed variably with increasing thaw. The variability in directions and magnitudes of correlates reflects the range of structural conditions that could be present along a thaw gradient. These structural changes correspond to changes in C flux controls, such as temperature and moisture, and their interactions. Temperature sensitivity of CH4 increased with increasing thaw in bivariate analyses, but lack of this trend in multiple regression analyses suggested cofounding effects of substrate or water limitation on the apparent temperature sensitivity. Our results emphasize the importance of incorporating transitional stages of thaw in landscape level C budgets and highlight that end-member or adjacent thaw stages do not adequately describe the variability in structure-function relationships present along a thaw gradient.

  4. Environmental correlates of peatland carbon fluxes in a thawing landscape: do transitional thaw stages matter?

    NASA Astrophysics Data System (ADS)

    Malhotra, A.; Roulet, N. T.

    2015-05-01

    Peatlands in discontinuous permafrost regions occur as a mosaic of wetland types, each with variable sensitivity to climate change. Permafrost thaw further increases the spatial heterogeneity in ecosystem structure and function in peatlands. Carbon (C) fluxes are well characterized in end-member thaw stages such as fully intact or fully thawed permafrost but remain unconstrained for transitional stages that cover a significant area of thawing peatlands. Furthermore, changes in the environmental correlates of C fluxes, due to thaw, are not well described - a requirement for modeling future changes to C storage of permafrost peatlands. We investigated C fluxes and their correlates in end-member and a number of transitional thaw stages in a sub-arctic peatland. Across peatland-lumped CH4 and CO2 flux data had significant correlations with expected correlates such as water table depth, thaw depth, temperature, photosynthetically active radiation and vascular green area. Within individual thaw states, bivariate correlations as well as multiple regressions between C flux and environmental factors changed variably with increasing thaw. The variability in directions and magnitudes of correlates reflects the range of structural conditions that could be present along a thaw gradient. These structural changes correspond to changes in C flux controls, such as temperature and moisture, and their interactions. Temperature sensitivity of CH4 increased with increasing thaw in bivariate analyses, but lack of this trend in multiple regression analyses suggested cofounding effects of substrate or water limitation on the apparent temperature sensitivity. Our results emphasize the importance of incorporating transitional stages of thaw in landscape level C budgets and highlight that end-member or adjacent thaw stages do not adequately describe the variability in structure-function relationships present along a thaw gradient.

  5. Active layer thermal monitoring at Fildes Peninsula, King George Island, Maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Michel, Roberto; Schaefer, Carlos; Simas, Felipe; Pregesbauer, Michael; Bockheim, James

    2013-04-01

    International attention on the climate change phenomena has grown in the last decade, intense modelling of climate scenarios were carried out by scientific investigations searching the sources and trends of these changes. The cryosphere and its energy flux became the focus of many investigations, being recognised as a key element for the understanding of future trends. The active layer and permafrost are key components of the terrestrial cryosphere due to their role in energy flux regulation and high sensitivity to climate change (Kane et al., 2001; Smith and Brown, 2009). Compared with other regions of the globe, our understanding of Antarctic permafrost is poor, especially in relation to its thermal state and evolution, its physical properties, links to pedogenesis, hydrology, geomorphic dynamics and response to global change (Bockheim, 1995, Bockheim et al., 2008). The active layer monitoring site was installed in the summer of 2008, and consist of thermistors (accuracy ± 0.2 °C) arranged in a vertical array (Turbic Eutric Cryosol 600 m asl, 10.5 cm, 32.5 cm, 67.5 cm and 83.5 cm). King George Island experiences a cold moist maritime climate characterized by mean annual air temperatures of -2°C and mean summer air temperatures above 0°C for up to four months (Rakusa-Suszczewski et al., 1993, Wen et al., 1994). Ferron et al., (2004) found great variability when analysing data from 1947 to1995 and identified cycles of 5.3 years of colder conditions followed by 9.6 years of warmer conditions. All probes were connected to a Campbell Scientific CR 1000 data logger recording data at hourly intervals from March 1st 2008 until November 30th 2012. Meteorological data for Fildes was obtained from the near by stations. We calculated the thawing days, freezing days; thawing degree days and freezing degree days; all according to Guglielmin et al. (2008). The active lawyer thickness was calculated as the 0 °C depth by extrapolating the thermal gradient from the two

  6. Impact of permafrost thaw on Arctic tundra pond geochemistry

    NASA Astrophysics Data System (ADS)

    Reyes, F.; Lougheed, V.

    2012-12-01

    Increasing evidence indicates the arctic tundra is changing physically, biologically, and chemically due to climate warming. With a warmer climate, permafrost is expected to thaw and influence the chemistry of arctic aquatic ecosystems. However, knowledge is limited on how geochemistry of arctic tundra pond ecosystems will respond. By re-sampling historical IBP ponds in Barrow, AK first sampled in the 1970s, previous studies have shown an increase in water temperature, nutrients and algal biomass through time. Results from this study indicate an increase of Ca, Mg, and Na in the water column, and a decrease in pH relative to the 1970s, suggesting an increased rate and magnitude of carbonate and Mg release. Seasonal trends were also examined to understand what processes, such as mineral weathering, peat decomposition and evaporation, were currently most influential in determining pond geochemistry. An increase in Ca/Na molar ratios, and carbonate and magnesium concentrations indicates that these tundra ponds are experiencing greater carbonate weathering compared to the 1970s and the rate of carbonate weathering increases in ponds as the summer progresses. However, increasing dissolved organic carbon (DOC) concentrations originating from peat decomposition are likely neutralizing additional inputs of carbonate, causing pond pH to decrease and exacerbating mineral weathering. A strong positive relationship between element concentrations and active layer pond thaw depth suggests that the origin of these additional solutes is likely from permafrost thaw. Active layer thaw depth has increased substantially over the past 40 years in the IBP ponds. Chloride/Bromide molar ratios and Deuterium/ 18-Oxygen isotope ratios will be used to determine the degree of evaporation occurring in tundra ponds. Ultimately, this study provides evidence for how geochemistry can identify the sources of chemical inputs to Arctic ponds affected by climate change and permafrost thaw.

  7. Bioavailability of soil organic matter and microbial community dynamics upon permafrost thaw.

    PubMed

    Coolen, Marco J L; van de Giessen, Jeroen; Zhu, Elizabeth Y; Wuchter, Cornelia

    2011-08-01

    Amplified Arctic warming could thaw 25% of the permafrost area by 2100, exposing vast amounts of currently fixed organic carbon to microbially mediated decomposition and release of greenhouse gasses through soil organic matter (SOM) respiration. We performed time-series incubation experiments with Holocene permafrost soils at 4°C for up to 11 days to determine changes in exoenzyme activities (EEAs) (i.e. phosphatase, β-glucosidase, aminopeptidase) as a measure for the bioavailability of SOM in response to permafrost thaw. We also profiled SSU rRNA transcripts to follow the qualitative and quantitative changes in viable prokaryotes and eukaryotes during incubation. EEA, amount of rRNA transcripts and microbial community structures differed substantially between the various soil intervals in response to thaw: after 11 days of incubation, the active layer became slightly depleted in C and P and harboured bacterial phyla indicative of more oligotrophic conditions (Acidobacteria). A fast response in phosphatase and β-glucosidase upon thaw, and a predominance of active copiotrophic Bacteroidetes, showed that the upper permafrost plate serves as storage of easily degradable carbon derived from the overlying thawed active layer during summer. EEA profiles and microbial community dynamics furthermore suggest that the deeper and older permafrost intervals mainly contain recalcitrant SOM, and that extracellular soil-bound exoenzymes play a role in the initial cleavage of biopolymers, which could kick-start microbial growth upon thaw. Basidiomycetous fungi and Candidate Subdivision OP5 bacteria were the first to respond in freshly thawed deeper permafrost intervals, and might play an important role in the decomposition of recalcitrant SOM to release more labile substrates to support the major bacterial phyla (β-Proteobacteria, Actinobacteria, Firmicutes), which predominated thereafter.

  8. Modeling Active Layer Depth Over Permafrost for the Arctic Drainage Basin and the Comparison to Measurements at CALM Field Sites

    NASA Astrophysics Data System (ADS)

    Oelke, C.; Zhang, T.; Serreze, M.; Armstrong, R.

    2002-12-01

    A finite difference model for one-dimensional heat conduction with phase change is applied to investigate soil freezing and thawing processes over the Arctic drainage basin. Calculations are performed on the 25~km~x~25~km resolution NSIDC EASE-Grid. NCEP re-analyzed sigma-0.995 surface temperature with a topography correction, and SSM/I-derived weekly snow height are used as forcing parameters. The importance of using an annual cycle of snow density for different snow classes is emphasized. Soil bulk density and the percentages of silt/clay and sand/gravel are from the SoilData System of the International Geosphere Biosphere Programme. In addition, we parameterize a spatially and vertically variable peat layer and modify soil bulk density and thermal conductivity accordingly. Climatological soil moisture content is from the Permafrost/Water Balance Model (P/WBM) at the University of New Hampshire. The model domain is divided into 3~layers with distinct thermal properties of frozen and thawed soil, respectively. Calculations are performed on 54~model nodes ranging from a thickness of 10~cm near the surface to 1~m at 15~m depth. Initial temperatures are chosen according to the grid cell's IPA permafrost classification on EASE grid. Active layer depths, simulated for the summers of 1999 and 2000, compare well to maximal thaw depths measured at about 60 Circumarctic Active Layer Monitoring Network (CALM) field sites. A remaining RMS-error between modeled and measured values is attributed mainly to scale discrepancies (100~m~x~100~m vs. 25~km~x~25~km) based on differences in the fields of air temperature, snow height, and soil bulk density. For the whole pan-Arctic land mass and the time period 1980 through 2001, this study shows the regionally highly variable active layer depth, frozen ground depth, lengths of freezing and thawing periods, and the day of year when the maxima are reached.

  9. [Lipoamide dehydrogenase, citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase in skeletal muscle. IX. The influence of the rate of thawing on activity and subcellular distribution in fast and slow frozen bovine muscle].

    PubMed

    Gottesmann, P; Hamm, R

    1985-10-01

    Samples of bovine muscle (post rigor) were frozen at -30 degrees C at two different rates (1.27 min/degrees C and 13.10 min/degrees C) and thawed at different rates between 1.6 (22 degrees C) and 430 min/degrees C (0 degrees C). The activities of the mitochondrial enzymes lipoamide dehydrogenase, citrate synthase, and beta-hydroxyacyl-CoA-dehydrogenase were determined in the supernatant of the tissue homogenate in phosphate buffer (total activity) and in the press juice of the intact tissue (activity in the sarcoplasma). The rate of thawing did not show a significant influence on total enzyme activities. In most cases, however, slow thawing caused a greater release of the enzymes from the mitochondria into the sarcoplasmic fluid than fast thawing, this effect being apparently independent of the rate of freezing. The greater damage to mitochondrial membranes upon slow thawing cannot be due to a longer exposure of the muscle cell to increased ionic strength in the non-freezable part of the cell water at the "critical" temperature around -3 degrees C because freezing of muscle samples at -3 degrees C and incubating them at -3 degrees C for five days resulted neither in changes of the total enzyme activities nor in a release of the three mitochondrial enzymes. From these results it is concluded that the influence of thawing rate on the damage to muscle mitochondria is probably not due to ionic effects or to recrystallization phenomena in the ice phase.

  10. Permafrost thaw in a nested groundwater-flow system

    USGS Publications Warehouse

    McKenzie, Jeffery M.; Voss, Clifford I.

    2013-01-01

    Groundwater flow in cold regions containing permafrost accelerates climate-warming-driven thaw and changes thaw patterns. Simulation analyses of groundwater flow and heat transport with freeze/thaw in typical cold-regions terrain with nested flow indicate that early thaw rate is particularly enhanced by flow, the time when adverse environmental impacts of climate-warming-induced permafrost loss may be severest. For the slowest climate-warming rate predicted by the Intergovernmental Panel on Climate Change (IPCC), once significant groundwater flow begins, thick permafrost layers can vanish in several hundred years, but survive over 1,000 years where flow is minimal. Large-scale thaw depends mostly on the balance of heat advection and conduction in the supra-permafrost zone. Surface-water bodies underlain by open taliks allow slow sub-permafrost flow, with lesser influence on regional thaw. Advection dominance over conduction depends on permeability and topography. Groundwater flow around permafrost and flow through permafrost impact thaw differently; the latter enhances early thaw rate. Air-temperature seasonality also increases early thaw. Hydrogeologic heterogeneity and topography strongly affect thaw rates/patterns. Permafrost controls the groundwater/surface-water-geomorphology system; hence, prediction and mitigation of impacts of thaw on ecology, chemical exports and infrastructure require improved hydrogeology/permafrost characterization and understanding

  11. Dynamics of the Thermal State of Active Layer at the Alaska North Slope and Northern Yakutia

    NASA Astrophysics Data System (ADS)

    Kholodov, A. L.; Romanovsky, V. E.; Marchenko, S.; Shiklomanov, N. I.; Fedorov-Davydov, D.

    2010-12-01

    Dynamics of the active layer is one of the most important indexes, reflecting permafrost response to the modern climate changes. Monitoring of active layer thickness dynamics is the main goal of CALM (Circumpolar Active Layer Monitoring) project. But, from different points of view, it is very important to know not only maximal depth of seasonal thawing but also dynamics of thermal field of active layer and duration of its staying in the unfrozen state. Current research was aimed on the analyzing data of temperature measurements have been done during the more then 10 years at the North Slope of Brooks Range (Alaska) and 2 years at the selected sites at the Northern Yakutia (Russia) and its comparison with the 17 to 10 years records of active layer thickness dynamics at the corresponding sites (http://www.udel.edu/Geography/calm/data/north.html). The area of investigation characterized by the typical tundra landscape and different kinds of micro topography. Reported observation sites located at the latitudinal range from 68.5 to 70.3N in Alaska and 70.5 to 71.75N in the Northern Yakutia. Observation have been done using the 1 meter long MRC probe with 11 sensors (every 10 cm) and single Campbell SCI A107 sensors in Alaska and 2-channel HOBO U23 data loggers with TMC-HD thermistors in the Northern Yakutia. Analyses of CALM data show what most observation sites in Alaska (except located near the Brooks Range and at the Arctic Ocean coast) do not subjected to the significant sustainable changes of active layer thickness over the last 10 years. At the same time active layer thickness at the Yakutian sites was increasing. Temperature observations show decreasing of the mean annual temperature at the average depth of active layer bottom at the Alaskan sites. But, because of general trend to increasing of period of thawing it does not lead to the decreasing of active layer thickness. Recent equipment deployment at the Tiksi and Allaikha sites (Northern Yakutia) does not

  12. An improved thaw-siphon method for the cryoprecipitate preparation.

    PubMed

    Kang, E P

    1980-01-01

    Cryoprecipitates were prepared by various techniques including slow-thaw, rapid-thaw, thaw-centrifuge and thaw-siphon methods. Recoveries of 42.3 +/- 9.5% for slow-thaw, 48.8 +/- 8.8% for rapid-thaw, 41.3 +/- 15.8% for thaw-centrifuge and 67.4 +/- 8.9% for thaw-siphon in factor VIII activity were obtained. These results indicated that cryoprecipitate prepared by the thaw-siphon method had the best recovery of the factor VIII procoagulant activity. However, the final volume of the plasma was rather difficult to control and there was a risk that some factor-VIII-containing materials were siphoned with the cryo-poor plasma, especially approaching the end of the process. A modified thaw-siphon method was developed which involved stopping the siphon after 60 min, centrifuging and expressing the remaining plasma to a final volume of less than 15 ml. A yield of 67.1 +/- 9.8% factor VIII activity was obtained. This product is similar to that produced by the original thaw-siphon method in yield but about half in volume.

  13. Climate Change and Thawing Permafrost in Two Iñupiaq Communities of Alaska's Arctic: Observations, Implications, and Resilience

    NASA Astrophysics Data System (ADS)

    Woodward, A.; Kofinas, G.

    2013-12-01

    For thousands of years the Iñupiat of northern Alaska have relied on ecosystems underlain by permafrost for material and cultural resources. As permafrost thaws across the Arctic, these social-ecological systems are changing rapidly. Community-based research and extensive local knowledge of Iñupiaq villagers offer unique and valuable contributions to understanding permafrost change and its implications for humans. We partnered with two Iñupiaq communities in Alaska's Arctic to investigate current and potential effects of thawing permafrost on social-ecological systems. Anaktuvuk Pass is situated on thaw-stable consolidated gravel in the Brooks Range, while Selawik rests on ice-rich permafrost in Beringia lowland tundra. Using the transdisciplinary approach of resilience theory and mixed geophysical and ethnographic methods, we measured active layer thaw depths and documented local knowledge about climate and permafrost change. Thaw depths were greater overall in Selawik. Residents of both communities reported a variety of changes in surface features, hydrology, weather, flora, and fauna that they attribute to thawing permafrost and / or climate change. Overall, Selawik residents described more numerous and extreme examples of such changes, expressed higher degrees of certainty that change is occurring, and anticipated more significant and negative implications for their way of life than did residents of Anaktuvuk Pass. Of the two villages, Selawik faces greater and more immediate challenges to the resilience of its social-ecological system as permafrost thaws.

  14. The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.

    PubMed

    Fisher, James P; Estop-Aragonés, Cristian; Thierry, Aaron; Charman, Dan J; Wolfe, Stephen A; Hartley, Iain P; Murton, Julian B; Williams, Mathew; Phoenix, Gareth K

    2016-09-01

    Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict

  15. The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.

    PubMed

    Fisher, James P; Estop-Aragonés, Cristian; Thierry, Aaron; Charman, Dan J; Wolfe, Stephen A; Hartley, Iain P; Murton, Julian B; Williams, Mathew; Phoenix, Gareth K

    2016-09-01

    Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict

  16. Active Layer Soil Carbon and Nutrient Mineralization, Barrow, Alaska, 2012

    DOE Data Explorer

    Stan D. Wullschleger; Holly M. Vander Stel; Colleen Iversen; Victoria L. Sloan; Richard J. Norby; Mallory P. Ladd; Jason K. Keller; Ariane Jong; Joanne Childs; Deanne J. Brice

    2015-10-29

    This data set consists of bulk soil characteristics as well as carbon and nutrient mineralization rates of active layer soils manually collected from the field in August, 2012, frozen, and then thawed and incubated across a range of temperatures in the laboratory for 28 day periods in 2013-2015. The soils were collected from four replicate polygons in each of the four Areas (A, B, C, and D) of Intensive Site 1 at the Next-Generation Ecosystem Experiments (NGEE) Arctic site near Barrow, Alaska. Soil samples were coincident with the established Vegetation Plots that are located in center, edge, and trough microtopography in each polygon. Data included are 1) bulk soil characteristics including carbon, nitrogen, gravimetric water content, bulk density, and pH in 5-cm depth increments and also by soil horizon, 2) carbon, nitrogen, and phosphorus mineralization rates for soil horizons incubated aerobically (and in one case both aerobically and anaerobically) for 28 days at temperatures that included 2, 4, 8, and 12 degrees C. Additional soil and incubation data are forthcoming. They will be available when published as part of another paper that includes additional replicate analyses.

  17. Correlations between the Heterogeneity of Permafrost Thaw Depth and Vegetation in Boreal Forests and Arctic Tundra in Alaska.

    NASA Astrophysics Data System (ADS)

    Uy, K. L. Q.; Natali, S.; Kholodov, A. L.; Loranty, M. M.

    2015-12-01

    Global climate change induces rapid large scale changes in the far Northern regions of the globe, which include the thickening of the active layer of arctic and subarctic soils. Active layer depth, in turn, drives many changes to the hydrology and geochemistry of the soil, making an understanding of this layer essential to boreal forest and arctic tundra ecology. Because the structure of plant communities can affect the thermal attributes of the soil, they may drive variations in active layer depth. For instance, trees and tussocks create shade, which reduces temperatures, but also hold snow, which increases temperature through insulation; these aspects of vegetation can increase or decrease summer thaw. The goal of this project is to investigate correlations between the degree of heterogeneity of active layer depths, organic layer thickness, and aboveground vegetation to determine how these facets of Northern ecosystems interact at the ecosystem scale. Permafrost thaw and organic layer depths were measured along 20m transects in twenty-four boreal forest and tundra sites in Alaska. Aboveground vegetation along these transects was characterized by measuring tree diameter at breast height (DBH), tussock dimensions, and understory biomass. Using the coefficient of variation as a measure of heterogeneity, we found a positive correlation between thaw depth variability and tussock volume variability, but little correlation between the former and tree DBH variability. Soil organic layer depth variability was also positively correlated with thaw depth variability, but weakly correlated with tree and tussock heterogeneity. These data suggest that low vegetation and organic layer control the degree of variability in permafrost thaw at the ecosystem scale. Vegetation can thus affect the microtopography of permafrost and future changes in the plant community that affect vegetation heterogeneity will drive corresponding changes in the variability of the soil.

  18. Active layer temperature in two Cryosols from King George Island, Maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Michel, Roberto F. M.; Schaefer, Carlos Ernesto G. R.; Poelking, Everton L.; Simas, Felipe N. B.; Fernandes Filho, Elpidio I.; Bockheim, James G.

    2012-06-01

    This study presents soil temperature and moisture regimes from March 2008 to January 2009 for two active layer monitoring (CALM-S) sites at King George Island, Maritime Antarctica. The monitoring sites were installed during the summer of 2008 and consist of thermistors (accuracy of ± 0.2 °C), arranged vertically with probes at different depths and one soil moisture probe placed at the bottommost layer at each site (accuracy of ± 2.5%), recording data at hourly intervals in a high capacity datalogger. The active layer thermal regime in the studied period for both soils was typical of periglacial environments, with extreme variation in surface temperature during summer resulting in frequent freeze and thaw cycles. The great majority of the soil temperature readings during the eleven month period was close to 0 °C, resulting in low values of freezing and thawing degree days. Both soils have poor thermal apparent diffusivity but values were higher for the soil from Fildes Peninsula. The different moisture regimes for the studied soils were attributed to soil texture, with the coarser soil presenting much lower water content during all seasons. Differences in water and ice contents may explain the contrasting patterns of freezing of the studied soils, being two-sided for the coarser soil and one-sided for the loamy soil. The temperature profile of the studied soils during the eleven month period indicates that the active layer reached a maximum depth of approximately 92 cm at Potter and 89 cm at Fildes. Longer data sets are needed for more conclusive analysis on active layer behaviour in this part of Antarctica.

  19. The impacts of recent permafrost thaw on land-atmosphere greenhouse gas exchange

    USGS Publications Warehouse

    Hayes, Daniel J.; Kicklighter, David W.; McGuire, Anthony; Chen, Min; Zhuang, Qianlai; Yuan, Fengming; Melillo, Jerry M.; Wullschleger, Stan D.

    2014-01-01

    Permafrost thaw and the subsequent mobilization of carbon (C) stored in previously frozen soil organic matter (SOM) have the potential to be a strong positive feedback to climate. As the northern permafrost region experiences as much as a doubling of the rate of warming as the rest of the Earth, the vast amount of C in permafrost soils is vulnerable to thaw, decomposition and release as atmospheric greenhouse gases. Diagnostic and predictive estimates of high-latitude terrestrial C fluxes vary widely among different models depending on how dynamics in permafrost, and the seasonally thawed 'active layer' above it, are represented. Here, we employ a process-based model simulation experiment to assess the net effect of active layer dynamics on this 'permafrost carbon feedback' in recent decades, from 1970 to 2006, over the circumpolar domain of continuous and discontinuous permafrost. Over this time period, the model estimates a mean increase of 6.8 cm in active layer thickness across the domain, which exposes a total of 11.6 Pg C of thawed SOM to decomposition. According to our simulation experiment, mobilization of this previously frozen C results in an estimated cumulative net source of 3.7 Pg C to the atmosphere since 1970 directly tied to active layer dynamics. Enhanced decomposition from the newly exposed SOM accounts for the release of both CO2 (4.0 Pg C) and CH4 (0.03 Pg C), but is partially compensated by CO2 uptake (0.3 Pg C) associated with enhanced net primary production of vegetation. This estimated net C transfer to the atmosphere from permafrost thaw represents a significant factor in the overall ecosystem carbon budget of the Pan-Arctic, and a non-trivial additional contribution on top of the combined fossil fuel emissions from the eight Arctic nations over this time period.

  20. Exploring Viral Mediated Carbon Cycling in Thawing Permafrost Microbial Communities

    NASA Astrophysics Data System (ADS)

    Trubl, G. G.; Solonenko, N.; Moreno, M.; Sullivan, M. B.; Rich, V. I.

    2014-12-01

    Viruses are the most abundant biological entities on Earth and their impact on carbon cycling in permafrost habitats is poorly understood. Arctic C cycling is particularly important to interpret due to the rapid climate change occurring and the large amount of C stockpiled there (~1/3 of global soil C is stored in permafrost). Viruses of microbes (i.e. phages) play central roles in C cycling in the oceans, through cellular lysis (phage drive the largest ocean C flux about 150 Gt yr-1, dwarfing all others by >5-fold), production of associated DOC, as well as transport and expression during infection (1029 transduction events day-1). C cycling in thawing permafrost systems is critical in understanding the climate trajectory and phages may be as important for C cycling here as they are in the ocean. The thawed C may become a food source for microbes, producing CO2 and potentially CH4, both potent greenhouse gases. To address the potential role of phage in C cycling in these dynamic systems, we are examining phage from an arctic permafrost thaw gradient in northern Sweden. We have developed a protocol for successfully extracting phage from peat soils and are quantifying phage in 15 peat and 2 lake sediment cores, with the goal of sequencing viromes. Preliminary data suggest that phage are present at 109 g-1 across the permafrost thaw gradient (compared to the typical marine count ~105 ml-1), implying a potentially robust phage-host interaction web in these changing environments. We are examining phage from 11 depth intervals (covering the active and permafrost layer) in the cores to assess phage-host community dynamics. Phage morphology and abundance for each layer and environment are being determined using qTEM and EFM. Understanding the phage that infect bacteria and archaea in these rapidly changing habitats will provide insight into the controls on current and future CH4 and CO2 emissions in permafrost habitats.

  1. Space-Borne Remote Sensing of Soil Moisture and Freeze/Thaw Dynamics at High Resolution Using a Combined Active and Passive Instrument Concept

    NASA Astrophysics Data System (ADS)

    Entekhabi, D.; Njoku, E. G.; Houser, P.; Gurney, R.; Jackson, T.; Kimball, J.; Koster, R.; McDonald, K.; ONeill, P.; Running, S.; VanZyl, J.; Wood, E. F.

    2001-05-01

    The design and expected characteristics of a space-borne system for high-resolution mapping of surface soil moisture and soil freeze/thaw dynamics is presented. This study represents the proposal for a comprehensive terrestrial hydrology monitoring mission. The mission objective is traced to the data requirements of research related to predictability, variations and change in the rate of the hydrologic cycle. The baseline mission builds on the heritage of ground-based and airborne passive and active low frequency microwave measurements that have demonstrated and validated the effectiveness of the measurements and associated algorithms for estimating the amount and phase of surface soil moisture. The satellite has both a radiometer and a radar on board. The radiometer provides polarized brightness temperature fields at 1.4 GHz across a wide swath (~ 900 km) at a resolution of 40 km. The radar operates at 1.2 GHz (VV, HH, and HV) and is capable of high-resolution mapping (less than 3 km) over 70 percent of the swath and low-resolution across the remainder. All terrestrial land regions are revisited within 2-3 days. The instrument uses a light-weight deployable mesh reflector antenna to make conical scans at a constant-incidence angle. The antenna scans at 6 rpm to generate the wide swath and mapping coverage. The algorithm design for producing 40 km and 10 km soil moisture and freeze/thaw data products and 3 km freeze/thaw and inundation extent products will be described. The strategy for estimating and correcting for wet biomass masking of the soil moisture and freeze/thaw signal by vegetation (with cover less than forest cover) will be presented. Finally we present a strategy for using data assimilation to use the synergy of measurements from other platforms, in situ data, and physical constraints on water and energy transports and balances to develop value-added data products that are continuous in time and provide estimates of soil water availability in the root

  2. Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

    SciTech Connect

    Newman, Brent D.; Throckmorton, Heather M.; Graham, David E.; Gu, Baohua; Hubbard, Susan S.; Liang, Liyuan; Wu, Yuxin; Heikoop, J. M.; Herndon, Elizabeth M.; Phelps, Tommy J.; Wilson, Cathy; Wullschleger, Stan D.

    2015-03-24

    Polygonal ground is a signature characteristic of Arctic lowlands, and carbon release from permafrost thaw can alter feedbacks to Arctic ecosystems and climate. This study describes the first comprehensive spatial examination of active layer biogeochemistry that extends across high- and low-centered, ice wedge polygons, their features, and with depth. Water chemistry measurements of 54 analytes were made on surface and active layer pore waters collected near Barrow, Alaska, USA. Significant differences were observed between high- and low-centered polygons suggesting that polygon types may be useful for landscape-scale geochemical classification. However, differences were found for polygon features (centers and troughs) for analytes that were not significant for polygon type, suggesting that finer-scale features affect biogeochemistry differently from polygon types. Depth variations were also significant, demonstrating important multidimensional aspects of polygonal ground biogeochemistry. These results have major implications for understanding how polygonal ground ecosystems function, and how they may respond to future change.

  3. Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

    NASA Astrophysics Data System (ADS)

    Newman, B. D.; Throckmorton, H. M.; Graham, D. E.; Gu, B.; Hubbard, S. S.; Liang, L.; Wu, Y.; Heikoop, J. M.; Herndon, E. M.; Phelps, T. J.; Wilson, C. J.; Wullschleger, S. D.

    2015-03-01

    Polygonal ground is a signature characteristic of Arctic lowlands, and carbon release from permafrost thaw can alter feedbacks to Arctic ecosystems and climate. This study describes the first comprehensive spatial examination of active layer biogeochemistry that extends across high- and low-centered, ice wedge polygons, their features, and with depth. Water chemistry measurements of 54 analytes were made on surface and active layer pore waters collected near Barrow, Alaska, USA. Significant differences were observed between high- and low-centered polygons suggesting that polygon types may be useful for landscape-scale geochemical classification. However, differences were found for polygon features (centers and troughs) for analytes that were not significant for polygon type, suggesting that finer-scale features affect biogeochemistry differently from polygon types. Depth variations were also significant, demonstrating important multidimensional aspects of polygonal ground biogeochemistry. These results have major implications for understanding how polygonal ground ecosystems function, and how they may respond to future change.

  4. Mapping Active-Layer Thickness in an Urbanized Environment: The Barrow Urban Heat Island Study

    NASA Astrophysics Data System (ADS)

    Klene, A. E.; Hinkel, K. M.; Nelson, F. E.; Shiklomanov, N. I.

    2003-12-01

    Local and global changes in the Arctic climate may have profound impacts on hydrology, soil stability, and infrastructure, such as roads, buildings, and water, gas, or oil pipelines. These changes will be manifested in large part through permafrost, which can influence virtually all physical, chemical, and biological processes occurring in the soil. The "Barrow Urban Heat Island Study" (BUHIS) is an ongoing project in northern Alaska that examines the effects of urbanization on air and soil temperatures in and around Barrow. At 4600 residents, Barrow is the largest native settlement in the circumarctic region and the northernmost urban area in the United States. Initiated in summer 2001, BUHIS is recording temperature and thaw depth at more than 60 locations throughout the village, the developing suburbs, and surrounding undisturbed tundra. This paper describes one part of study examining the active layer and anthropogenic influences on its thickness. Summer air and soil temperature data, together with digital vegetation and soil maps, are used as input to a modified Stefan solution to map depth of thaw over an area of 100 square kilometers that includes both the village of Barrow and the surrounding tundra. Maps representing end-of-summer conditions for 2001 provide the first spatial/temporal representation of active-layer variability within an urbanized area. Increasing urban development in Arctic regions is causing information about changes accompanying industrial development and urbanization to become more vital, particularly given the possibility of a warming climate.

  5. Determinants of carbon release from the active layer and permafrost deposits on the Tibetan Plateau

    PubMed Central

    Chen, Leiyi; Liang, Junyi; Qin, Shuqi; Liu, Li; Fang, Kai; Xu, Yunping; Ding, Jinzhi; Li, Fei; Luo, Yiqi; Yang, Yuanhe

    2016-01-01

    The sign and magnitude of permafrost carbon (C)-climate feedback are highly uncertain due to the limited understanding of the decomposability of thawing permafrost and relevant mechanistic controls over C release. Here, by combining aerobic incubation with biomarker analysis and a three-pool model, we reveal that C quality (represented by a higher amount of fast cycling C but a lower amount of recalcitrant C compounds) and normalized CO2–C release in permafrost deposits were similar or even higher than those in the active layer, demonstrating a high vulnerability of C in Tibetan upland permafrost. We also illustrate that C quality exerts the most control over CO2–C release from the active layer, whereas soil microbial abundance is more directly associated with CO2–C release after permafrost thaw. Taken together, our findings highlight the importance of incorporating microbial properties into Earth System Models when predicting permafrost C dynamics under a changing environment. PMID:27703168

  6. SLAPex Freeze/Thaw 2015: The First Dedicated Soil Freeze/Thaw Airborne Campaign

    NASA Technical Reports Server (NTRS)

    Kim, Edward; Wu, Albert; DeMarco, Eugenia; Powers, Jarrett; Berg, Aaron; Rowlandson, Tracy; Freeman, Jacqueline; Gottfried, Kurt; Toose, Peter; Roy, Alexandre; Derksen, Chris; Royer, Alain; Belair, Stephane; Houser, Paul; McDonald, Kyle; Entin, Jared; Lewis, Kristen

    2016-01-01

    Soil freezing and thawing is an important process in the terrestrial water, energy, and carbon cycles, marking the change between two very different hydraulic, thermal, and biological regimes. NASA's Soil Moisture Active/Passive (SMAP) mission includes a binary freeze/thaw data product. While there have been ground-based remote sensing field measurements observing soil freeze/thaw at the point scale, and airborne campaigns that observed some frozen soil areas (e.g., BOREAS), the recently-completed SLAPex Freeze/Thaw (F/T) campaign is the first airborne campaign dedicated solely to observing frozen/thawed soil with both passive and active microwave sensors and dedicated ground truth, in order to enable detailed process-level exploration of the remote sensing signatures and in situ soil conditions. SLAPex F/T utilized the Scanning L-band Active/Passive (SLAP) instrument, an airborne simulator of SMAP developed at NASA's Goddard Space Flight Center, and was conducted near Winnipeg, Manitoba, Canada, in October/November, 2015. Future soil moisture missions are also expected to include soil freeze/thaw products, and the loss of the radar on SMAP means that airborne radar-radiometer observations like those that SLAP provides are unique assets for freeze/thaw algorithm development. This paper will present an overview of SLAPex F/T, including descriptions of the site, airborne and ground-based remote sensing, ground truth, as well as preliminary results.

  7. Imaging depth-of-thaw beneath arctic streams using ground-penetrating radar

    NASA Astrophysics Data System (ADS)

    Bradford, J. H.; McNamara, J. P.; Bowden, W.; Gooseff, M. N.

    2003-12-01

    We are investigating the responses of arctic tundra stream geomorphology, hyporheic zone hydrology, and biogeochemical cycling to climate change. In particular, we expect that hyporheic exchange dynamics in tundra streams are controlled by 1) channel features (pools, riffles, etc.), and 2) depth-of-thaw beneath the stream channel. A key objective of this effort is monitoring sub-stream thaw through the thaw season using ground-penetrating radar (GPR). In general, GPR is a well established tool for imaging active layer thickness. However, sub-stream imaging presents a unique set of challenges. This is primarily related to strong frequency dependence and high levels of attenuation as the radar signal propagates through water. To test the effectiveness of GPR imaging of sub-stream permafrost we conducted a field investigation near the end of the thaw season when we expected the depth of thaw to be near its maximum. We investigated three sites located within the Kuparuk River and Toolik Lake basins, north of the Brooks Range, Alaska. The sites were characterized by low energy water flow, organic material lining the streambeds, and water depths ranging from 20 cm to 2 m. Water saturated peat with some pooled water was present along the stream banks. We acquired data using a pulsed radar system with high-power transmitter and 200 MHz antennas. We placed the radar antennas in the bottom of a small rubber boat, then pulled the boat across the bank and through the stream while triggering the radar at a constant rate. We verified depth to permafrost by pressing a metal probe through the active layer to the point of refusal. Although there is significant shift toward the low end of the frequency spectrum due to frequency dependent signal attenuation, we achieved excellent results at all three sites with a clear continuous image of the permafrost boundary both peripheral to, and beneath the stream. Depth migration was applied to the profiles to provide an accurate image of

  8. Seasonal variation of ecosystem respiration delta 13C in response to experimental permafrost thaw and vegetation removal in moist acidic tundra

    NASA Astrophysics Data System (ADS)

    Mauritz, M.; Pegoraro, E.; Salmon, V. G.; Natali, S.; Schuur, E.

    2015-12-01

    Permafrost soils store twice as much carbon (C) as is contained in the atmosphere and about one-third of global soil C. Under a warmer future climate, permafrost is expected to thaw and decompose, releasing C to the atmosphere, further amplifying global warming. However, studies show that warmer arctic temperatures promote plant growth, in addition to stimulating losses from the soil C pool. Using delta 13C of ecosystem respiration (Reco) during the seasonal cycle of active layer thaw, we seek to understand the effect of permafrost thaw on the relative contributions from microbial decomposition of soil C and more recently fixed, plant-dominated C. We measured weekly CO2 flux rates and delta 13C of Reco from experimentally warmed plots with rapid permafrost thaw and control thaw. Vegetation removal plots, in un-warmed tundra, were monitored to isolate the seasonal contributions from soil alone. We expected delta 13C to be dominated by plant activity in vegetated plots, particularly in areas with greater permafrost thaw because they have highest plant biomass. In vegetation removal plots we expected to see greater contribution from deep soil as seasonal thaw progressed. From May to July delta 13C was extremely variable early in the growing season, but became more uniform as vegetation greened and thaw deepened. In vegetated plots CO2 fluxes doubled, but remained constant in vegetation removal plots. This indicates that, with thaw, microbes had access to a more spatially uniform C substrate, but this had little effect on the magnitude of CO2 flux. Overall delta 13C in rapidly thawed plots was least enriched (-29.4 ‰), control plots intermediate (-28.9 ‰), and vegetation removal plots were most enriched (-28.5 ‰). This suggests that in vegetation removal plots microbes used more decomposed soil C as substrate, and much of the increase in CO2 flux in vegetated plots was the result of C recently fixed and contributed by plants.

  9. Decomposition of old organic matter as a result of deeper active layers in a snow depth manipulation experiment

    PubMed Central

    Taneva, Lina; Trumbore, Susan E.; Welker, Jeffrey M.

    2010-01-01

    A snow addition experiment in moist acidic tussock tundra at Toolik Lake, Alaska, increased winter snow depths 2–3 m, and resulted in a doubling of the summer active layer depth. We used radiocarbon (∆14C) to (1) determine the age of C respired in the deep soils under control and deepened active layer conditions (deep snow drifts), and (2) to determine the impact of increased snow and permafrost thawing on surface CO2 efflux by partitioning respiration into autotrophic and heterotrophic components. ∆14C signatures of surface respiration were higher in the deep snow areas, reflecting a decrease in the proportion of autotrophic respiration. The radiocarbon age of soil pore CO2 sampled near the maximum mid-July thaw depth was approximately 1,000 years in deep snow treatment plots (45–55 cm thaw depth), while CO2 from the ambient snow areas was ~100 years old (30-cm thaw depth). Heterotrophic respiration ∆14C signatures from incubations were similar between the two snow depths for the organic horizon and were extremely variable in the mineral horizon, resulting in no significant differences between treatments in either month. Radiocarbon ages of heterotrophically respired C ranged from <50 to 235 years BP in July mineral soil samples and from 1,525 to 8,300 years BP in August samples, suggesting that old soil C in permafrost soils may be metabolized upon thawing. In the surface fluxes, this old C signal is obscured by the organic horizon fluxes, which are significantly higher. Our results indicate that, as permafrost in tussock tundra ecosystems of arctic Alaska thaws, carbon buried up to several thousands of years ago will become an active component of the carbon cycle, potentially accelerating the rise of CO2 in the atmosphere. Electronic supplementary material The online version of this article (doi:10.1007/s00442-009-1556-x) contains supplementary material, which is available to authorized users. PMID:20084398

  10. Bioassay for follicle stimulating activity of equine gonadotropic hormone in mare serum using frozen/thawed transiently transfected reporter cells.

    PubMed

    Sahmi, F; Nicola, E; Price, C A

    2012-09-01

    The objective was to establish a cell line-based bioassay for FSH in horse serum for screening samples with high eCG bioactivity. A cell line (HEK293) was transiently cotransfected with an FSH reporter expression plasmid and a cAMP-responsive β-galactosidase reporter plasmid. Cells were bulk frozen, and thawed for assay purposes. This assay was specific for FSH, with no cross-reaction with LH or insulin-like growth factor-1. Standard curves (eCG) and serum samples from pregnant mares passed parallel line bioassay validity tests (linearity and parallelism). Estimates of bioactivity with this bioassay were highly correlated with estimates obtained with the Steelman-Pohley hCG augmentation assay. The colorimetric end point permitted the use of this assay as a rapid screen for FSH bioactivity without the need for animal use or complex cell culture facilities. PMID:22578627

  11. The impacts of recent permafrost thaw on land-atmosphere greenhouse gas exchange

    NASA Astrophysics Data System (ADS)

    Hayes, Daniel J.; Kicklighter, David W.; McGuire, A. David; Chen, Min; Zhuang, Qianlai; Yuan, Fengming; Melillo, Jerry M.; Wullschleger, Stan D.

    2014-04-01

    Permafrost thaw and the subsequent mobilization of carbon (C) stored in previously frozen soil organic matter (SOM) have the potential to be a strong positive feedback to climate. As the northern permafrost region experiences as much as a doubling of the rate of warming as the rest of the Earth, the vast amount of C in permafrost soils is vulnerable to thaw, decomposition and release as atmospheric greenhouse gases. Diagnostic and predictive estimates of high-latitude terrestrial C fluxes vary widely among different models depending on how dynamics in permafrost, and the seasonally thawedactive layer’ above it, are represented. Here, we employ a process-based model simulation experiment to assess the net effect of active layer dynamics on this ‘permafrost carbon feedback’ in recent decades, from 1970 to 2006, over the circumpolar domain of continuous and discontinuous permafrost. Over this time period, the model estimates a mean increase of 6.8 cm in active layer thickness across the domain, which exposes a total of 11.6 Pg C of thawed SOM to decomposition. According to our simulation experiment, mobilization of this previously frozen C results in an estimated cumulative net source of 3.7 Pg C to the atmosphere since 1970 directly tied to active layer dynamics. Enhanced decomposition from the newly exposed SOM accounts for the release of both CO2 (4.0 Pg C) and CH4 (0.03 Pg C), but is partially compensated by CO2 uptake (0.3 Pg C) associated with enhanced net primary production of vegetation. This estimated net C transfer to the atmosphere from permafrost thaw represents a significant factor in the overall ecosystem carbon budget of the Pan-Arctic, and a non-trivial additional contribution on top of the combined fossil fuel emissions from the eight Arctic nations over this time period.

  12. Field information links permafrost carbon to physical vulnerabilities of thawing

    USGS Publications Warehouse

    Harden, Jennifer W.; Koven, Charles; Ping, Chien-Lu; Hugelius, Gustaf; McGuire, A. David; Camill, P.; Jorgenson, Torre; Kuhry, Peter; Michaelson, Gary; O'Donnell, Jonathan A.; Schuur, Edward A.G.; Tamocai, Charles; Johnson, K.; Grosse, G.

    2012-01-01

    Deep soil profiles containing permafrost (Gelisols) were characterized for organic carbon (C) and total nitrogen (N) stocks to 3m depths. Using the Community Climate System Model (CCSM4) we calculate cumulative probability functions (PDFs) for active layer depths under current and future climates. The difference in PDFs over time was multiplied by C and N contents of soil horizons in Gelisol suborders to calculate newly thawed C and N, Thawing ranged from 147 PgC with 10 PgN by 2050 (representative concentration pathway RCP scenario 4.5) to 436 PgC with 29 PgN by 2100 (RCP 8.5). Organic horizons that thaw are vulnerable to combustion, and all horizon types are vulnerable to shifts in hydrology and decomposition. The rates and extent of such losses are unknown and can be further constrained by linking field and modelling approaches. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems.

  13. Field information links permafrost carbon to physical vulnerabilities of thawing

    NASA Astrophysics Data System (ADS)

    Harden, Jennifer W.; Koven, Charles D.; Ping, Chien-Lu; Hugelius, Gustaf; David McGuire, A.; Camill, Phillip; Jorgenson, Torre; Kuhry, Peter; Michaelson, Gary J.; O'Donnell, Jonathan A.; Schuur, Edward A. G.; Tarnocai, Charles; Johnson, Kristopher; Grosse, Guido

    2012-08-01

    Deep soil profiles containing permafrost (Gelisols) were characterized for organic carbon (C) and total nitrogen (N) stocks to 3 m depths. Using the Community Climate System Model (CCSM4) we calculate cumulative distributions of active layer thickness (ALT) under current and future climates. The difference in cumulative ALT distributions over time was multiplied by C and N contents of soil horizons in Gelisol suborders to calculate newly thawed C and N. Thawing ranged from 147 PgC with 10 PgN by 2050 (representative concentration pathway RCP scenario 4.5) to 436 PgC with 29 PgN by 2100 (RCP 8.5). Organic horizons that thaw are vulnerable to combustion, and all horizon types are vulnerable to shifts in hydrology and decomposition. The rates and extent of such losses are unknown and can be further constrained by linking field and modelling approaches. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems.

  14. Permafrost Active Layer Seismic Interferometry Experiment (PALSIE).

    SciTech Connect

    Abbott, Robert; Knox, Hunter Anne; James, Stephanie; Lee, Rebekah; Cole, Chris

    2016-01-01

    We present findings from a novel field experiment conducted at Poker Flat Research Range in Fairbanks, Alaska that was designed to monitor changes in active layer thickness in real time. Results are derived primarily from seismic data streaming from seven Nanometric Trillium Posthole seismometers directly buried in the upper section of the permafrost. The data were evaluated using two analysis methods: Horizontal to Vertical Spectral Ratio (HVSR) and ambient noise seismic interferometry. Results from the HVSR conclusively illustrated the method's effectiveness at determining the active layer's thickness with a single station. Investigations with the multi-station method (ambient noise seismic interferometry) are continuing at the University of Florida and have not yet conclusively determined active layer thickness changes. Further work continues with the Bureau of Land Management (BLM) to determine if the ground based measurements can constrain satellite imagery, which provide measurements on a much larger spatial scale.

  15. Layer-by-layer nanoencapsulation of camptothecin with improved activity.

    PubMed

    Parekh, Gaurav; Pattekari, Pravin; Joshi, Chaitanya; Shutava, Tatsiana; DeCoster, Mark; Levchenko, Tatyana; Torchilin, Vladimir; Lvov, Yuri

    2014-04-25

    160 nm nanocapsules containing up to 60% of camptothecin in the core and 7-8 polyelectrolyte bilayers in the shell were produced by washless layer-by-layer assembly of heparin and block-copolymer of poly-l-lysine and polyethylene glycol. The outer surface of the nanocapsules was additionally modified with polyethylene glycol of 5 kDa or 20 kDa molecular weight to attain protein resistant properties, colloidal stability in serum and prolonged release of the drug from the capsules. An advantage of the LbL coated capsules is the preservation of camptothecin lactone form with the shell assembly starting at acidic pH and improved chemical stability of encapsulated drug at neutral and basic pH, especially in the presence of albumin that makes such formulation more active than free camptothecin. LbL nanocapsules preserve the camptothecin lactone form at pH 7.4 resulting in triple activity of the drug toward CRL2303 glioblastoma cell. PMID:24508806

  16. Layer-by-layer nanoencapsulation of camptothecin with improved activity

    PubMed Central

    Parekh, Gaurav; Pattekari, Pravin; Joshi, Chaitanya; Shutava, Tatsiana; DeCoster, Mark; Levchenko, Tatyana; Torchilin, Vladimir; Lvov, Yuri

    2014-01-01

    160 nm nanocapsules containing up to 60% of camptothecin in the core and 7–8 polyelectrolyte bilayers in the shell were produced by washless layer-by-layer assembly of heparin and block-copolymer of poly-L-lysine and polyethylene glycol. The outer surface of the nanocapsules was additionally modified with polyethylene glycol of 5 kDa or 20 kDa molecular weight to attain protein resistant properties, colloidal stability in serum and prolonged release of the drug from the capsules. An advantage of the LbL coated capsules is the preservation of camptothecin lactone form with the shell assembly starting at acidic pH and improved chemical stability of encapsulated drug at neutral and basic pH, especially in the presence of albumin that makes such formulation more active than free camptothecin. LbL nanocapsules preserve the camptothecin lactone form at pH 7.4 resulting in triple activity of the drug toward CRL2303 glioblastoma cell. PMID:24508806

  17. A comparison between modelling for spatial distribution of thaw depths using MODIS datasets and observational data of permafrost in Mongolia

    NASA Astrophysics Data System (ADS)

    Zorigt, Munkhtsetseg; Alexander, Orkhonselenge; Kwadijk, Jaap; van Beek, Eelco

    2016-04-01

    Thaw and freezing depth and the related variation in the top of the active layer of the permafrost are important variables for studying runoff production in permafrost regions. In this study we provide data on spatially distributed thawing depths in Mongolia based on Kudryavtsev approach. This approach requires land surface temperature (LSTs) and soil physical characteristics for estimating thaw depths. Measured data of ground land surface temperatures is lacking in Mongolia. Therefore, we estimated the LST based on satellite images of surface temperatures. Monthly values of the LSTs were obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) data. Soil physical characteristics are defined by reference values from previous studies (Tumurbaatar, 2004; Anarmaa, 2006). We validated the results by comparing them with the observational data of permafrost boreholes in Mongolia in 2002-2009 CALM, 2009. The results indicate that thaw depths range between 0-14.5 m from southern to northern parts of Mongolia. This study shows that distribution of thaw depths using the MODIS LSTs can indicate a general overview of thaw depths distribution throughout the country.

  18. Effect of the permafrost thawing on the organic carbon and microbial activity in thermokarst lakes of Western Siberia: important source of carbon dioxide in the atmosphere

    NASA Astrophysics Data System (ADS)

    Shirokova, L. S.; Pokrovsky, O. S.; Kirpotin, S. N.; Dupre, B.

    2008-12-01

    Ongoing processes of the permafrost thawing in Western Siberia are likely to increase the surface of water reservoirs via forming so-called thermokarst lakes, mobilizing the organic carbon (OC) from the soil pool to the rivers and, finally, to the ocean, and thus modifying the fluxes of methane and CO2 to the atmosphere. In order to understand the mechanisms of carbon mobilization and biodegradation during permafrost thawing and to establish the link between the OC and microbial activity in forming thermokarstic lakes, we performed a comparative multidisciplinary study on the biogeochemistry of OC and metals in lakes located in the northern part of Western Siberia. About 10 lakes and small ponds of various size and age were sampled for dissolved and colloidal organic carbon and metals and total bacterial cell number. There is a systematic evolution of DOC, pH, trace elements and biological activity during successions of thermokarst lakes encountered in the present study. At the beginning of permafrost thawing at the scale of several meter size ponds, fast lixiviation of unaltered peat yields significant amount of OC, major and trace elements; the pH of these waters is between 3.5 and 4.0 and the conductivity is 20-30 μS. The intermediate stage of lake formation still preserve low pHs, high DOC and conductivity, even in relatively large, up to 1 km diameter but fast growing lakes. At these stages, there is no any productivity as phytoplankton cannot live in these acidic waters and bacterial mineralization intensity is around 0.3 mg C/L/day both in the surface and bottom horizons. Once the lake border is stabilized, there are no new "unaltered peat" sources and the biological processes start to consume the OC and nutrients. At this stage, there is still no production in the water column (< 0.01 mg C/L/day) but the bacterial mineralization intensity remains high, up to 0.3 mg C/L/day. At this final stage, the remaining part of the lake located in the centre of the

  19. Genes upregulated in winter wheat (Triticum aestivum L) during mild freezing and subsequent thawing suggest sequential activation of multiple response mechanisms

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Exposing fully cold-acclimated wheat plants to a freeze-thaw cycle of -3°C for 24h followed by +3°C for 24 or 48h resulted in dramatically improved freezing tolerance. To assess the transcriptomic changes that occur during the -3°C freeze, and the subsequent +3°C thaw, microarray analysis was applie...

  20. Groundwater hydrochemistry in the active layer of the proglacial zone, Finsterwalderbreen, Svalbard

    USGS Publications Warehouse

    Cooper, R.J.; Wadham, J.L.; Tranter, M.; Hodgkins, R.; Peters, N.E.

    2002-01-01

    Glacial bulk meltwaters and active-layer groundwaters were sampled from the proglacial zone of Finsterwalderbreen during a single melt season in 1999, in order to determine the geochemical processes that maintain high chemical weathering rates in the proglacial zone of this glacier. Results demonstrate that the principle means of solute acquisition is the weathering of highly reactive moraine and fluvial active-layer sediments by supra-permafrost groundwaters. Active-layer groundwater derives from the thaw of the proglacial snowpack, buried ice and glacial bulk meltwaters. Groundwater evolves by sulphide oxidation and carbonate dissolution. Evaporation- and freeze-concentration of groundwater in summer and winter, respectively produce Mg-Ca-sulphate salts on the proglacial surface. Re-dissolution of these salts in early summer produces groundwaters that are supersaturated with respect to calcite. There is a pronounced spatial pattern to the geochemical evolution of groundwater. Close to the main proglacial channel, active layer sediments are flushed diurnally by bulk meltwaters. Here, Mg-Ca-sulphate deposits become exhausted in the early season and geochemical evolution proceeds by a combination of sulphide oxidation and carbonate dissolution. At greater distances from the channel, the dissolution of Mg-Ca-sulphate salts is a major influence and dilution by the bulk meltwaters is relatively minor. The influence of sulphate salt dissolution decreases during the sampling season, as these salts are exhausted and waters become increasingly routed by subsurface flowpaths. ?? 2002 Elsevier Science B.V. All rights reserved.

  1. Estimating 1992-2000 average active layer thickness on the Alaskan North Slope from remotely sensed surface subsidence

    NASA Astrophysics Data System (ADS)

    Liu, Lin; Schaefer, Kevin; Zhang, Tingjun; Wahr, John

    2012-01-01

    The measurement of temporal changes in active layer thickness (ALT) is crucial to monitoring permafrost degradation in the Arctic. We develop a retrieval algorithm to estimate long-term average ALT using thaw-season surface subsidence derived from spaceborne interferometric synthetic aperture radar (InSAR) measurements. Our algorithm uses a model of vertical distribution of water content within the active layer accounting for soil texture, organic matter, and moisture. We determine the 1992-2000 average ALT for an 80 × 100 km study area of continuous permafrost on the North Slope of Alaska near Prudhoe Bay. We obtain an ALT of 30-50 cm over moist tundra areas, and a larger ALT of 50-80 cm over wet tundra areas. Our estimated ALT values match in situ measurements at Circumpolar Active Layer Monitoring (CALM) sites within uncertainties. Our results demonstrate that InSAR can provide ALT estimates over large areas at high spatial resolution.

  2. Remotely Sensed Active Layer Thickness (ReSALT) from InSAR data near Toolik Lake in Northern Alaska

    NASA Astrophysics Data System (ADS)

    Chen, A. C.; Liu, L.; Schaefer, K. M.; Parsekian, A.; Jafarov, E. E.; Zebker, H. A.; Zhang, T.

    2014-12-01

    Toolik Field Station is built on spatially continuous permafrost on the north slope of Alaska. Seasonal surface subsidence and uplift occurs in permafrost regions due to thaw settlement and frost heave as the active layer thaws and refreezes. Using L-band (23.6 cm wavelength) InSAR data from ALOS-PALSAR acquired between 2006 and 2010, we use a small-baseline subset (SBAS) method to estimate seasonal surface subsidence and retrieve fine-resolution maps of active layer thickness (ALT) for a ~25x25 km area surrounding Toolik Field Station (located at 68.63°N, -149.60°E). We compare these remotely sensed ALT (ReSALT) results with in situ data from: 1) the Circumpolar Active Layer Monitoring (CALM) network showing mean ALT of ~40-50 cm in the region surrounding Toolik Field Station, corresponding to seasonal subsidence of 1 to 2 cm, and 2) mechanical probing measurements of ALT, obtained during field work in the study area in August 2014. We also solve for secular subsidence trends from the InSAR data. The trends are close to zero in most places, but larger subsidence trends in some isolated areas could be due to thermokarst processes (long-term thawing of ice-rich permafrost). We note, however, that downslope motion due to gelifluction cannot be separated from vertical thermokarst-related deformation without incorporating InSAR measurements from multiple look angles. Two key limitations to our method are the spatial variability of volumetric soil moisture content and the accuracy of the DEM needed to correct for topographic effects. We investigate the use of bulk volumetric water content inferred from ground-penetrating radar (GPR) data to improve the ReSALT retrieval algorithm. We also quantify the effect of DEM accuracy on ReSALT uncertainties, leads to requirements for DEM accuracy in InSAR-based ALT retrieval.

  3. Active layer thermal monitoring at Fildes Peninsula, King George Island, Maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Michel, R. F. M.; Schaefer, C. E. G. R.; Simas, F. N. B.; Francelino M., R.; Fernandes-Filho, E. I.; Lyra, G. B.; Bockheim, J. G.

    2014-07-01

    International attention to the climate change phenomena has grown in the last decade; the active layer and permafrost are of great importance in understanding processes and future trends due to their role in energy flux regulation. The objective of the this paper is to present active layer temperature data for one CALM-S site located at Fildes Peninsula, King George Island, Maritime Antarctica over an fifth seven month period (2008-2012). The monitoring site was installed during the summer of 2008 and consists of thermistors (accuracy of ± 0.2 °C), arranged vertically with probes at different depths, recording data at hourly intervals in a~high capacity data logger. A series of statistical analysis were performed to describe the soil temperature time series, including a linear fit in order to identify global trend and a series of autoregressive integrated moving average (ARIMA) models were tested in order to define the best fit for the data. The controls of weather on the thermal regime of the active layer have been identified, providing insights about the influence of climate chance over the permafrost. The active layer thermal regime in the studied period was typical of periglacial environment, with extreme variation at the surface during summer resulting in frequent freeze and thaw cycles. The active layer thickness (ALT) over the studied period showed variability related to different annual weather conditions, reaching a maximum of 117.5 cm in 2009. The ARIMA model was considered appropriate to treat the dataset, enabling more conclusive analysis and predictions when longer data sets are available. Despite the variability when comparing temperature readings and active layer thickness over the studied period, no warming trend was detected.

  4. Active-layer thermal monitoring on the Fildes Peninsula, King George Island, maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Michel, R. F. M.; Schaefer, C. E. G. R.; Simas, F. M. B.; Francelino, M. R.; Fernandes-Filho, E. I.; Lyra, G. B.; Bockheim, J. G.

    2014-12-01

    International attention to climate change phenomena has grown in the last decade; the active layer and permafrost are of great importance in understanding processes and future trends due to their role in energy flux regulation. The objective of this paper is to present active-layer temperature data for one Circumpolar Active Layer Monitoring South hemisphere (CALM-S) site located on the Fildes Peninsula, King George Island, maritime Antarctica over an 57-month period (2008-2012). The monitoring site was installed during the summer of 2008 and consists of thermistors (accuracy of ±0.2 °C), arranged vertically with probes at different depths, recording data at hourly intervals in a high-capacity data logger. A series of statistical analyses was performed to describe the soil temperature time series, including a linear fit in order to identify global trends, and a series of autoregressive integrated moving average (ARIMA) models was tested in order to define the best fit for the data. The affects of weather on the thermal regime of the active layer have been identified, providing insights into the influence of climate change on permafrost. The active-layer thermal regime in the studied period was typical of periglacial environments, with extreme variation in surface during the summer resulting in frequent freeze and thaw cycles. The active-layer thickness (ALT) over the studied period shows a degree of variability related to different annual weather conditions, reaching a maximum of 117.5 cm in 2009. The ARIMA model could describe the data adequately and is an important tool for more conclusive analysis and predictions when longer data sets are available. Despite the variability when comparing temperature readings and ACT over the studied period, no trend can be identified.

  5. Bioavailable Carbon and the Relative Degradation State of Organic Matter in Active Layer and Permafrost Soils

    NASA Astrophysics Data System (ADS)

    Jastrow, J. D.; Burke, V. J.; Vugteveen, T. W.; Fan, Z.; Hofmann, S. M.; Lederhouse, J. S.; Matamala, R.; Michaelson, G. J.; Mishra, U.; Ping, C. L.

    2015-12-01

    The decomposability of soil organic carbon (SOC) in permafrost regions is a key uncertainty in efforts to predict carbon release from thawing permafrost and its impacts. The cold and often wet environment is the dominant factor limiting decomposer activity, and soil organic matter is often preserved in a relatively undecomposed and uncomplexed state. Thus, the impacts of soil warming and permafrost thaw are likely to depend at least initially on the genesis and past history of organic matter degradation before its stabilization in permafrost. We compared the bioavailability and relative degradation state of SOC in active layer and permafrost soils from Arctic tundra in Alaska. To assess readily bioavailable SOC, we quantified salt (0.5 M K2SO4) extractable organic matter (SEOM), which correlates well with carbon mineralization rates in short-term soil incubations. To assess the relative degradation state of SOC, we used particle size fractionation to isolate fibric (coarse) from more degraded (fine) particulate organic matter (POM) and separated mineral-associated organic matter into silt- and clay-sized fractions. On average, bulk SOC concentrations in permafrost were lower than in comparable active layer horizons. Although SEOM represented a very small proportion of the bulk SOC, this proportion was greater in permafrost than in comparable active layer soils. A large proportion of bulk SOC was found in POM for all horizons. Even for mineral soils, about 40% of bulk SOC was in POM pools, indicating that organic matter in both active layer and permafrost mineral soils was relatively undecomposed compared to typical temperate soils. Not surprisingly, organic soils had a greater proportion of POM and mineral soils had greater silt- and clay-sized carbon pools, while cryoturbated soils were intermediate. For organic horizons, permafrost organic matter was generally more degraded than in comparable active layer horizons. However, in mineral and cryoturbated horizons

  6. An Integrated Observational and Model Synthesis Approach to Examine Dominant Environmental Controls on Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Atchley, A. L.; Coon, E.; Painter, S. L.; Harp, D. R.; Wilson, C. J.

    2015-12-01

    The active layer thickness (ALT) - the annual maximum depth of soil with above 0°C temperatures - in part determines the volume of carbon-rich stores available for decomposition and therefore potential greenhouse gas release into the atmosphere from Arctic tundra. However, understanding and predicting ALT in polygonal tundra landscapes is difficult due to the complex nature of hydrothermal atmospheric-surface-subsurface interactions in freezing/thawing soil. Simply deconvolving effects of single environmental controls on ALT is not possible with measurements alone as processes act in concert to drive thaw depth formation. Process-rich models of thermal hydrological dynamics, conversely, are a valuable tool for understanding the dominant controls and uncertainties in predicting permafrost conditions. By integrating observational data with known physical relationships to form process-rich models, synthetic experiments can then be used to explore a breadth of environmental conditions encountered and the effect of each environmental attribute may be assessed. Here a process rich thermal hydrology model, The Advanced Terrestrial Simulator, has been created and calibrated using observed data from Barrow, AK. An ensemble of 1D thermal hydrologic models were simulated that span a range of three environmental factors 1) thickness of organic rich soil, 2) snow depth, and 3) soil moisture content, to investigate the role of each factor on ALT. Results show that organic layer thickness acts as a strong insulator and is the dominant control of ALT, but the strength of the effect of organic layer thickness is also dependent on the saturation state. Using the ensemble results, the effect of peat thickness on ALT was then examined on a 2D domain. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and

  7. Influences and interactions of inundation, peat, and snow on active layer thickness: Modeling Archive

    DOE Data Explorer

    Scott Painter; Ethan Coon; Cathy Wilson; Dylan Harp; Adam Atchley

    2016-04-21

    This Modeling Archive is in support of an NGEE Arctic publication currently in review [4/2016]. The Advanced Terrestrial Simulator (ATS) was used to simulate thermal hydrological conditions across varied environmental conditions for an ensemble of 1D models of Arctic permafrost. The thickness of organic soil is varied from 2 to 40cm, snow depth is varied from approximately 0 to 1.2 meters, water table depth was varied from -51cm below the soil surface to 31 cm above the soil surface. A total of 15,960 ensemble members are included. Data produced includes the third and fourth simulation year: active layer thickness, time of deepest thaw depth, temperature of the unfrozen soil, and unfrozen liquid saturation, for each ensemble member. Input files used to run the ensemble are also included.

  8. Influence of Plant Communities on Active Layer Depth in Boreal Forest

    NASA Astrophysics Data System (ADS)

    Phoenix, G. K.; Fisher, J. P.; Estop-Aragones, C.; Thierry, A.; Hartley, I. P.; Murton, J.; Charman, D.; Williams, M.

    2014-12-01

    Vegetation plays a crucial role in determining active layer depth (ALD) and hence also the extent that permafrost may thaw under climate change. Such influences are multifaceted and include, for example, promotion of shallow ALD by insulation from moss or shading by plant canopies in summer, or trapping of snow in evergreen tree canopies that reduces snow insulation of soil in winter. However, while the role of different vegetation components are understood at a conceptual level, quantitative understanding of the relative importance of different vegetation components and how they interact to determine active layer depth is lacking. In addition, major abiotic factors such as fire and soil hydrological properties will considerably influence the role of vegetation in mediating ALD, though again this is not well understood. To address this we surveyed multiple plots across 4 sites of contrasting vegetation and fire status, including a range of soil moisture and organic matter thickness, in the discontinuous permafrost zone near Yellowknife, NT, Canada. In each plot we measured ALD and a range of vegetation and soil parameters to understand how key characteristics of the understory and canopy vegetation, and soil properties influence ALD. Measurements included moss depth, tree canopy LAI, understory LAI, understory height, vegetation composition, soil organic matter depth, slope and soil moisture. By undertaking these surveys in sites with contrasting hydrological conditions in both burned and unburned areas we have also been able to determine which characteristics of the vegetation and soil are important for protecting permafrost, which characteristics emerge as the most important factors across sites (i.e. irrespective of site conditions) and which factors have site (ecosystem) specific influences. This work provides a major insight into how ecosystem properties influence ALD and therefore also how changes in ecosystems properties arising from climate change may

  9. Microwave thawing apparatus and method

    DOEpatents

    Fathi, Zakaryae; Lauf, Robert J.; McMillan, April D.

    2004-06-01

    An apparatus for thawing a frozen material includes: a microwave energy source; a microwave applicator which defines a cavity for applying microwave energy from the microwave source to a material to be thawed; and a shielded region which is shielded from the microwave source, the shielded region in fluid communication with the cavity so that thawed material may flow from the cavity into the shielded region.

  10. Microwave thawing package and method

    DOEpatents

    Fathi, Zakaryae; Lauf, Robert J.

    2004-03-16

    A package for containing frozen liquids during an electromagnetic thawing process includes: a first section adapted for containing a frozen material and exposing the frozen material to electromagnetic energy; a second section adapted for receiving thawed liquid material and shielding the thawed liquid material from further exposure to electromagnetic energy; and a fluid communication means for allowing fluid flow between the first section and the second section.

  11. Using dissolved organic matter (DOM) composition to detect permafrost thaw in arctic and boreal watersheds

    NASA Astrophysics Data System (ADS)

    ODonnell, J. A.; Aiken, G.; Walvoord, M. A.; Butler, K.

    2013-12-01

    Permafrost thaw can profoundly alter hydrology and carbon dynamics in northern high-latitude regions. Thawing of permafrost has been detected through monitoring of borehole temperatures and active layer thickness (ALT), but these measurements have limited spatial inference and primarily reflect local conditions. Remote sensing analyses have been useful for detecting thermokarst features, yet have limited application in upland forests or in ice-poor regions not susceptible to ground subsidence. Analysis of stream discharge time-series (e.g. recession flow analysis) can be a powerful tool for detecting watershed-scale changes in ALT, but long-term hydrologic data is sparse in many northern regions. Given the large pool of organic carbon (C) in permafrost soils, most research has focused on how permafrost thaw impacts C released to the atmosphere. However, permafrost thaw may also modify the lateral flux of C from terrestrial to aquatic systems, often through increasing groundwater discharge to stream flow. Here, we present data from arctic (n=36) and boreal rivers (n=60) of Alaska to address the question: can DOM character in rivers be used as a tool for detecting permafrost thaw in high-latitude watersheds? We hypothesize that the chemical composition of DOM is sensitive to permafrost configuration as a control on (1) groundwater transit times, (2) microbial processing, and (3) stabilization in mineral soils. Using measurements of DOM optical properties, chemical fractionation, and 14C-DOC, we distinguished DOM character between supra- and sub-permafrost aquifers. DOM transported from supra-permafrost soils to rivers is subject to seasonal thawing and re-freezing of the active layer. DOC concentrations peaked during spring snowmelt (7.5 to 41.7 mgC L-1), when frozen soils confine subsurface flow to organic-soil horizons, and declined during summer (2.6 to 27.3 mgC L-1), when soils of the active layer thaw. Δ14C-DOC in three boreal rivers also declined seasonally

  12. Microbial activity and diversity during extreme freeze-thaw cycles in periglacial soils, 5400 m elevation, Cordillera Vilcanota, Perú.

    PubMed

    Schmidt, S K; Nemergut, D R; Miller, A E; Freeman, K R; King, A J; Seimon, A

    2009-09-01

    High-elevation periglacial soils are among the most extreme soil systems on Earth and may be good analogs for the polar regions of Mars where oligotrophic mineral soils abut with polar ice caps. Here we report on preliminary studies carried out during an expedition to an area where recent glacial retreat has exposed porous mineral soils to extreme, daily freeze-thaw cycles and high UV fluxes. We used in situ methods to show that inorganic nitrogen (NO(3) (-) and NH(4) (+)) was being actively cycled even during a period when diurnal soil temperatures (5 cm depth) ranged from -12 to 27 degrees C and when sub-zero, soil cooling rates reached 1.8 degrees C h(-1) (the most rapid soil cooling rates recorded to date). Furthermore, phylogenetic analyses of microbial phylotypes present at our highest sites (5410 m above sea level) showed the presence of nitrifying bacteria of the genus Nitrospira and newly discovered nitrite-oxidizing Betaproteobacteria. These soils were overwhelmingly dominated (>70% of phylotypes) by photosynthetic bacteria that were related to novel cyanobacteria previously found almost exclusively in other plant-free, high-elevation soils. We also demonstrated that soils from our highest sites had higher potential for mineralizing glutamate and higher microbial biomass than lower elevation soils that had been more recently covered by ice. Overall, our findings indicate that a diverse and robustly functioning microbial ecosystem is present in these previously unstudied high-elevation soils.

  13. Microbial activity and diversity during extreme freeze-thaw cycles in periglacial soils, 5400 m elevation, Cordillera Vilcanota, Perú.

    PubMed

    Schmidt, S K; Nemergut, D R; Miller, A E; Freeman, K R; King, A J; Seimon, A

    2009-09-01

    High-elevation periglacial soils are among the most extreme soil systems on Earth and may be good analogs for the polar regions of Mars where oligotrophic mineral soils abut with polar ice caps. Here we report on preliminary studies carried out during an expedition to an area where recent glacial retreat has exposed porous mineral soils to extreme, daily freeze-thaw cycles and high UV fluxes. We used in situ methods to show that inorganic nitrogen (NO(3) (-) and NH(4) (+)) was being actively cycled even during a period when diurnal soil temperatures (5 cm depth) ranged from -12 to 27 degrees C and when sub-zero, soil cooling rates reached 1.8 degrees C h(-1) (the most rapid soil cooling rates recorded to date). Furthermore, phylogenetic analyses of microbial phylotypes present at our highest sites (5410 m above sea level) showed the presence of nitrifying bacteria of the genus Nitrospira and newly discovered nitrite-oxidizing Betaproteobacteria. These soils were overwhelmingly dominated (>70% of phylotypes) by photosynthetic bacteria that were related to novel cyanobacteria previously found almost exclusively in other plant-free, high-elevation soils. We also demonstrated that soils from our highest sites had higher potential for mineralizing glutamate and higher microbial biomass than lower elevation soils that had been more recently covered by ice. Overall, our findings indicate that a diverse and robustly functioning microbial ecosystem is present in these previously unstudied high-elevation soils. PMID:19597697

  14. Characterization and Modeling Of Microbial Carbon Metabolism In Thawing Permafrost

    NASA Astrophysics Data System (ADS)

    Graham, D. E.; Phelps, T. J.; Xu, X.; Carroll, S.; Jagadamma, S.; Shakya, M.; Thornton, P. E.; Elias, D. A.

    2012-12-01

    Increased annual temperatures in the Arctic are warming the surface and subsurface, resulting in thawing permafrost. Thawing exposes large pools of buried organic carbon to microbial degradation, increasing greenhouse gas generation and emission. Most global-scale land-surface models lack depth-dependent representations of carbon conversion and GHG transport; therefore they do not adequately describe permafrost thawing or microbial mineralization processes. The current work was performed to determine how permafrost thawing at moderately elevated temperatures and anoxic conditions would affect CO2 and CH4 generation, while parameterizing depth-dependent GHG production processes with respect to temperature and pH in biogeochemical models. These enhancements will improve the accuracy of GHG emission predictions and identify key biochemical and geochemical processes for further refinement. Three core samples were obtained from discontinuous permafrost terrain in Fairbanks, AK with a mean annual temperature of -3.3 °C. Each core was sectioned into surface/near surface (0-0.8 m), active layer (0.8-1.6 m), and permafrost (1.6-2.2 m) horizons, which were homogenized for physico-chemical characterization and microcosm construction. Surface samples had low pH values (6.0), low water content (18% by weight), low organic carbon (0.8%), and high C:N ratio (43). Active layer samples had higher pH values (6.4), higher water content (34%), more organic carbon (1.4%) and a lower C:N ratio (24). Permafrost samples had the highest pH (6.5), highest water content (46%), high organic carbon (2.5%) and the lowest C:N ratio (19). Most organic carbon was quantified as labile or intermediate pool versus stable pool in each sample, and all samples had low amounts of carbonate. Surface layer microcosms, containing 20 g sediment in septum-sealed vials, were incubated under oxic conditions, while similar active and permafrost layer samples were anoxic. These microcosms were incubated at -2

  15. Bacterial production in subarctic peatland lakes enriched by thawing permafrost

    NASA Astrophysics Data System (ADS)

    Deshpande, Bethany N.; Crevecoeur, Sophie; Matveev, Alex; Vincent, Warwick F.

    2016-08-01

    Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, carbon and nutrient regime of a set of thermokarst (thaw) lakes and their adjacent peatland permafrost soils in a rapidly degrading landscape in subarctic Québec, Canada, and by way of fluorescence microscopy, flow cytometry, production measurements and an in situ enrichment experiment, determine the bacterial characteristics of these waters relative to other thaw lakes and rock-basin lakes in the region. The soil active layer in a degrading palsa (peatland permafrost mound) adjacent to one of the lakes contained an elevated carbon content (51 % of dry weight), high C : N ratios (17 : 1 by mass), and large stocks of other elements including N (3 % of dry weight), Fe (0.6 %), S (0.5 %), Ca (0.5 %) and P (0.05 %). Two permafrost cores were obtained to a depth of 2.77 m in the palsa, and computerized tomography scans of the cores confirmed that they contained high concentrations (> 80 %) of ice. Upon thawing, the cores released nitrate and dissolved organic carbon (from all core depths sampled), and soluble reactive phosphorus (from bottom depths), at concentrations well above those in the adjacent lake waters. The active layer soil showed a range of particle sizes with a peak at 229 µm, and this was similar to the distribution of particles in the upper permafrost cores. The particle spectrum for the lake water overlapped with those for the soil, but extended to larger (surface water) or finer (bottom water) particles. On average, more than 50 % of the bacterial cells and bacterial production was associated with particles > 3 µm. This relatively low contribution of free-living cells (operationally defined as the < 1 µm fraction) to bacterial production was a general

  16. Realizing the full potential of Remotely Sensed Active Layer Thickness (ReSALT) Products

    NASA Astrophysics Data System (ADS)

    Schaefer, K. M.; Chen, A.; Liu, L.; Parsekian, A.; Jafarov, E. E.; Panda, S. K.; Zebker, H. A.

    2015-12-01

    The Remotely Sensed Active Layer Thickness (ReSALT) product uses the Interferometric Synthetic Aperture Radar (InSAR) technique to measure ground subsidence, active layer thickness (ALT), and thermokarst activity in permafrost regions. ReSALT supports research for the Arctic-Boreal Vulnerability Experiment (ABoVE) field campaign in Alaska and northwest Canada and is a precursor for a potential Nasa-Isro Synthetic Aperture Radar (NISAR) product. ALT is a critical parameter for monitoring the status of permafrost and thermokarst activity is one of the key drivers of change in permafrost regions. The ReSALT product currently includes 1) long-term subsidence trends resulting from the melting and subsequent drainage of excess ground ice in permafrost-affected soils, 2) seasonal subsidence resulting from the expansion of soil water into ice as the active layer freezes and thaws, and 3) ALT estimated from the seasonal subsidence assuming a vertical profile of water within the soil column. ReSALT includes uncertainties for all parameters and is validated against in situ measurements from the Circumpolar Active Layer Monitoring (CALM) network, Ground Penetrating Radar and mechanical probe measurements. We present high resolution ReSALT products on the North Slope of Alaska: Prudhoe Bay, Barrow, Toolik Lake, Happy Valley, and the Anaktuvuk fire zone. We believe that the ReSALT product could be expanded to include maps of individual thermokarst features identified as spatial anomalies in the subsidence trends, with quantified expansion rates. We illustrate the technique with multiple examples of thermokarst features on the North Slope of Alaska. Knowing the locations and expansion rates for individual features allows us to evaluate risks to human infrastructure. Our results highlight the untapped potential of the InSAR technique to remotely sense ALT and thermokarst dynamics over large areas of the Arctic.

  17. Effects of permafrost thaw on carbon emissions under aerobic and anaerobic environments in the Great Hing'an Mountains, China.

    PubMed

    Song, Changchun; Wang, Xianwei; Miao, Yuqing; Wang, Jiaoyue; Mao, Rong; Song, Yanyu

    2014-07-15

    The carbon (C) pool of permafrost peatland is very important for the global C cycle. Little is known about how permafrost thaw could influence C emissions in the Great Hing'an Mountains of China. Through aerobic and anaerobic incubation experiments, we studied the effects of permafrost thaw on CH4 and CO2 emissions. The rates of CH4 and CO2 emissions were measured at -10, 0 and 10°C. Although there were still C emissions below 0°C, rates of CH4 and CO2 emissions significantly increased with permafrost thaw under aerobic and anaerobic conditions. The C release under aerobic conditions was greater than under anaerobic conditions, suggesting that permafrost thaw and resulting soil environment change should be important influences on C emissions. However, CH4 stored in permafrost soils could affect accurate estimation of CH4 emissions from microbial degradation. Calculated Q10 values in the permafrost soils were significantly higher than values in active-layer soils under aerobic conditions. Our results highlight that permafrost soils have greater potential decomposability than soils of the active layer, and such carbon decomposition would be more responsive to the aerobic environment.

  18. DC resistivity tomography applied to monitoring active layer environments below patterned ground in Svalbard

    NASA Astrophysics Data System (ADS)

    Watanabe, Tatsuya; Juliussen, Hâvard; Matsuoka, Norikazu; Christiansen, Hanne H.

    2010-05-01

    Patterned ground is one of the most characteristic features in arctic periglacial landscapes that originated from various periglacial processes. On flat tundra surfaces composed of fine-grained soils, ice-wedge polygons are dominant, but mud boils and hummocks are also developed. Their distribution is constrained by local ground material, hydrology, snow cover, vegetation and freeze/thaw regimes. Whereas there have been a large number of studies on patterned ground phenomena, environmental factors distinguishing the types of patterned ground are not well understood. We applied DC resistivity tomography to understanding hydrological characteristics and freeze/thaw dynamics at adjoining ice-wedge and mud-boil sites in Adventdalen, Svalbard, where comprehensive periglacial process monitoring has been undertaken. Electrode arrays consisting of 81 nails spaced at 20 cm intervals were fixed at each site early in June 2009 immediately after the snow cover disappeared. The nails were stuck within the top 5 cm to resolve the top layer of the ground. Measurements were carried out repeatedly at approximately two week intervals. Spring results from both sites are characterized by an increase in resistivity near surface due to drying up. This tendency is prominent in the ice-wedge polygon centre where standing water remains until late spring. Time-lapse analyses indicate a distinct decrease in resistivity in seasonal frozen layer at both sites probably due to an increase in unfrozen water content by downward heat transfer. Summer profiles from both sites display a distinct resistivity boundary propagating downward with time, corresponding well with the thaw depth measured by mechanical probing. These data also show near-surface high resistivity spots indicating the location of desiccation cracks. Profiles from the mud-boil site show higher resistivity in the thaw layer than those of ice-wedge site, implying different drainage condition between them. After seasonal freezing

  19. Geochemical drivers of organic matter decomposition in the active layer of Arctic tundra

    NASA Astrophysics Data System (ADS)

    Herndon, E.; Roy Chowdhury, T.; Mann, B.; Graham, D. E.; Wullschleger, S. D.; Gu, B.; Liang, L.

    2014-12-01

    Arctic tundra soils store large quantities of organic carbon that are susceptible to decomposition and release to the atmosphere as CO2 and CH4. Decomposition rates are limited by cold temperatures and widespread anoxia; however, ongoing changes in soil temperature, thaw depth, and water saturation are expected to influence rates and pathways of organic matter decomposition. In order to predict greenhouse gas releases from high-latitude ecosystems, it is necessary to identify how geochemical factors (e.g. terminal electron acceptors, carbon substrates) influence CO2 and CH4 production in tundra soils. This study evaluates spatial patterns of aqueous geochemistry in the active layer of low- to high-centered polygons located at the Barrow Environmental Observatory in northern Alaska. Pore waters from saturated soils were low in sulfate and nitrate but contained abundant Fe which may serve a major terminal electron acceptor for anaerobic microbial metabolism. Relatively high concentrations of soluble Fe accumulated in the middle of the active layer near the boundary between the organic and mineral horizon, and we infer that Fe-oxide reduction and dissolution in the mineral horizon produced soluble Fe that diffused upwards and was stabilized by complexation with dissolved organic matter. Fe concentrations in the bulk soil were higher in organic than mineral horizons due to the presence of these organic-Fe complexes and Fe-oxide precipitates. Dissolved CH4 increased with increasing proportions of dissolved Fe(III) in saturated soils from transitional and low-centered polygons. The opposite trend was observed in drier soils from flat- and high-centered polygons where deeper oxidation fronts may inhibit methanogenesis. Using multiple spectroscopic and molecular methods (e.g. UV-Vis, Fourier transform infrared, ultrahigh resolution mass spectrometry), we also observed that pore waters from the middle of the active layer contained more aromatic organics than in mineral

  20. Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

    DOE PAGES

    Newman, Brent D.; Throckmorton, Heather M.; Graham, David E.; Gu, Baohua; Hubbard, Susan S.; Liang, Liyuan; Wu, Yuxin; Heikoop, J. M.; Herndon, Elizabeth M.; Phelps, Tommy J.; et al

    2015-03-24

    Polygonal ground is a signature characteristic of Arctic lowlands, and carbon release from permafrost thaw can alter feedbacks to Arctic ecosystems and climate. This study describes the first comprehensive spatial examination of active layer biogeochemistry that extends across high- and low-centered, ice wedge polygons, their features, and with depth. Water chemistry measurements of 54 analytes were made on surface and active layer pore waters collected near Barrow, Alaska, USA. Significant differences were observed between high- and low-centered polygons suggesting that polygon types may be useful for landscape-scale geochemical classification. However, differences were found for polygon features (centers and troughs) formore » analytes that were not significant for polygon type, suggesting that finer-scale features affect biogeochemistry differently from polygon types. Depth variations were also significant, demonstrating important multidimensional aspects of polygonal ground biogeochemistry. These results have major implications for understanding how polygonal ground ecosystems function, and how they may respond to future change.« less

  1. Thermal regime of active layer at two lithologically contrasting sites on James Ross Island, Antarctic Peninsula.

    NASA Astrophysics Data System (ADS)

    Hrbáček, Filip; Nývlt, Daniel; Láska, Kamil

    2016-04-01

    Antarctic Peninsula region (AP) represents one of the most rapidly warming parts of our planet in the last 50 years. Despite increasing research activities along both western and eastern sides of AP in last decades, there is still a lot of gaps in our knowledge relating to permafrost, active layer and its thermal and physical properties. This study brings new results of active layer monitoring on James Ross Island, which is the largest island in northern AP. Its northern part, Ulu Peninsula, is the largest ice-free area (more than 200 km2) in the region. Due its large area, we focused this study on sites located in different lithologies, which would affect local thermal regime of active layer. Study site (1) at Abernethy Flats area (41 m a.s.l.) lies ~7 km from northern coast. Lithologically is formed by disintegrated Cretaceous calcareous sandstones and siltstones of the Santa Marta Formation. Study site (2) is located at the northern slopes of Berry Hill (56 m a.s.l.), about 0.4 km from northern coastline. Lithology is composed of muddy to intermediate diamictites, tuffaceous siltstones to fine grained sandstones of the Mendel Formation. Data of air temperature at 2 meters above ground and the active layer temperatures at 75 cm deep profiles were obtained from both sites in period 1 January 2012 to 31 December 2014. Small differences were found when comparing mean air temperatures and active temperatures at 5 and 75 cm depth in the period 2012-2014. While the mean air temperatures varied between -7.7 °C and -7.0 °C, the mean ground temperatures fluctuated between -6.6 °C and -6.1 °C at 5 cm and -6.9 °C and -6.0 °C at 75 cm at Abernethy Flats and Berry Hill slopes respectively. Even though ground temperature differences along the profiles weren't pronounced during thawing seasons, the maximum active layer thickness was significantly larger at Berry Hill slopes (80 to 82 cm) than at Abernethy Flats (52 to 64 cm). We assume this differences are affected by

  2. Melanin as an active layer in biosensors

    SciTech Connect

    Piacenti da Silva, Marina Congiu, Mirko Oliveira Graeff, Carlos Frederico de; Fernandes, Jéssica Colnaghi Biziak de Figueiredo, Natália Mulato, Marcelo

    2014-03-15

    The development of pH sensors is of great interest due to its extensive application in several areas such as industrial processes, biochemistry and particularly medical diagnostics. In this study, the pH sensing properties of an extended gate field effect transistor (EGFET) based on melanin thin films as active layer are investigated and the physical mechanisms related to the device operation are discussed. Thin films were produced from different melanin precursors on indium tin oxide (ITO) and gold substrates and were investigated by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy. Experiments were performed in the pH range from 2 to 12. EGFETs with melanin deposited on ITO and on gold substrates showed sensitivities ranging from 31.3 mV/pH to 48.9 mV/pH, depending on the melanin precursor and the substrate used. The pH detection is associated with specific binding sites in its structure, hydroxyl groups and quinone imine.

  3. Effects of stratified active layers on high-altitude permafrost warming: a case study on the Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    Pan, Xicai; Li, Yanping; Yu, Qihao; Shi, Xiaogang; Yang, Daqing; Roth, Kurt

    2016-07-01

    Seasonally variable thermal conductivity in active layers is one important factor that controls the thermal state of permafrost. The common assumption is that this conductivity is considerably lower in the thawed than in the frozen state, λt/λf < 1. Using a 9-year dataset from the Qinghai-Tibet Plateau (QTP) in conjunction with the GEOtop model, we demonstrate that the ratio λt/λf may approach or even exceed 1. This can happen in thick (> 1.5 m) active layers with strong seasonal total water content changes in the regions with summer-monsoon-dominated precipitation pattern. The conductivity ratio can be further increased by typical soil architectures that may lead to a dry interlayer. The unique pattern of soil hydraulic and thermal dynamics in the active layer can be one important contributor for the rapid permafrost warming at the study site. These findings suggest that, given the increase in air temperature and precipitation, soil hydraulic properties, particularly soil architecture in those thick active layers must be properly taken into account in permafrost models.

  4. Soil thawing and warming in the High Arctic and the potential breakdown of previously frozen

    NASA Astrophysics Data System (ADS)

    Sletten, R. S.; Hagedorn, B.

    2012-12-01

    The Arctic has accumulated substantial stores of carbon within permanently frozen soils during the Holocene. Recent, unprecedented warming in the Arctic may release considerable carbon within this region. Record high temperatures and melting of the Greenland Ice Sheet occurred this past summer and we have recorded significant thawing of the permafrost in the High Arctic of Greenland. Our decade long soil temperature record at our High Arctic sites at Thule, Greenland reveals a significant increase in the thawed depth and soil temperature. The rate of breakdown of soil organics depends on soil temperature as well as moisture content. The balance between wet, anaerobic soils versus dry soils is recognized but not often studied. Our data on soil temperature, moisture, and microclimate provide insights into the covariance of these parameters and relative estimates of how soil organic carbon decomposition can vary under the changing conditions. Our previous work has shown that soil organic carbon in the High Arctic was underestimated by over an order of magnitude, particularly in the most barren sites. The primary source of the previously missed carbon was carbon at depth that is nearly always or continuously frozen. The deepening of the thawed layer is documented at our Thule sites. We present a conceptual model of the potential carbon release. These soils continue to undergo freeze-thaw cycles that may also mix the soils by cryoturbation and bring more carbon to the upper, better drained portion of the active layer. As the soil warms, it may allow greater development of vegetation; however this will also depend on the soil stability and the potential for a stable substrate for vegetation. Some arctic studies indicate a greater rate of carbon mineralization while others indicate increased vegetation biomass. The complex interplay will ultimately determine the rate of carbon release. Clearly the arctic system is unique in storing substantial carbon below the ground

  5. Impact of dry-wet and freeze-thaw events on pesticide mineralizing populations and their activity in wetland ecosystems: A microcosm study.

    PubMed

    Vandermeeren, Pieter; Baken, Stijn; Vanderstukken, Ruben; Diels, Jan; Springael, Dirk

    2016-03-01

    Riparian wetlands are proposed to mitigate diffuse pollution of surface water by pesticides in agricultural landscapes. Wetland ecosystems though are highly dynamic environments and seasonal disturbances such as freezing and drying can affect microbial population sizes in the sediment and their functionality including pesticide biodegradation, which has hardly been studied. This study examined the effect of artificially induced dry-wet or freeze-thaw events on the mineralization of the pesticides isoproturon (IPU) and 2-methoxy-4-chlorophenoxy acetic acid (MCPA) in wetland microcosms, either without or with prior enrichment of IPU/MCPA degrading populations. Without prior enrichment, mineralization of IPU and MCPA was significantly reduced after exposure to especially freeze-thaw events, as evidenced by lower mineralization rates and longer lag times compared to non-exposed microcosms. However, herbicide mineralization kinetics correlated poorly with cell numbers of herbicide mineralizers as estimated by a most probable number (MPN) approach and the number of IPU and MCPA mineralizers was unexpectedly higher in freeze-thaw and dry-wet cycle exposed setups compared to the control setups. This suggested that the observed effects of season-bound disturbances were due to other mechanisms than decay of pesticide mineralizers. In addition, in systems in which the growth of pesticide mineralizing bacteria was stimulated by amendment of IPU and MCPA, exposure to a freeze-thaw or dry-wet event only marginally affected the herbicide mineralization kinetics. Our results show that season bound environmental disturbances can affect pesticide mineralization kinetics in wetlands but that this effect can depend on the history of pesticide applications. PMID:26714290

  6. Post-thaw viability of cryopreserved peripheral blood stem cells (PBSC) does not guarantee functional activity: important implications for quality assurance of stem cell transplant programmes.

    PubMed

    Morgenstern, Daniel A; Ahsan, Gulrukh; Brocklesby, Margaret; Ings, Stuart; Balsa, Carmen; Veys, Paul; Brock, Penelope; Anderson, John; Amrolia, Persis; Goulden, Nicholas; Cale, Catherine M; Watts, Michael J

    2016-09-01

    Standard quality assurance (QA) of cryopreserved peripheral blood stem cells (PBSC) uses post-thaw viable CD34(+) cell counts. In 2013, concerns arose at Great Ormond Street Hospital (GOSH) about 8 patients with delayed engraftment following myeloablative chemotherapy with cryopreserved cell rescue, despite adequate post-thaw viable cell counts in all cases. Root cause analysis was undertaken; investigations suggested the freeze process itself was a contributing factor to suboptimal engraftment. Experiments were undertaken in which a single PBSC product was divided into three and cryopreserved in parallel using a control-rate freezer (CRF) or passive freezing method (-80°C freezer) at GOSH, or the same passive freezing at another laboratory. Viable CD34(+) counts were equivalent and adequate in each. Granulocyte-monocyte colony-forming unit assays demonstrated colonies from the products cryopreserved using passive freezing (both laboratories), but no colonies from products cryopreserved using the CRF. The CRF was shown to be operating within manufacturer's specifications with freeze-profile within acceptable limits. This experience has important implications for quality assurance for all transplant programmes, particularly those using cryopreserved products. The failure of post-thaw viable CD34(+) counts, the most widely used routine QA test available, to ensure PBSC function is of great concern and should prompt reassessment of protocols and QA procedures. PMID:27291859

  7. Post-thaw viability of cryopreserved peripheral blood stem cells (PBSC) does not guarantee functional activity: important implications for quality assurance of stem cell transplant programmes.

    PubMed

    Morgenstern, Daniel A; Ahsan, Gulrukh; Brocklesby, Margaret; Ings, Stuart; Balsa, Carmen; Veys, Paul; Brock, Penelope; Anderson, John; Amrolia, Persis; Goulden, Nicholas; Cale, Catherine M; Watts, Michael J

    2016-09-01

    Standard quality assurance (QA) of cryopreserved peripheral blood stem cells (PBSC) uses post-thaw viable CD34(+) cell counts. In 2013, concerns arose at Great Ormond Street Hospital (GOSH) about 8 patients with delayed engraftment following myeloablative chemotherapy with cryopreserved cell rescue, despite adequate post-thaw viable cell counts in all cases. Root cause analysis was undertaken; investigations suggested the freeze process itself was a contributing factor to suboptimal engraftment. Experiments were undertaken in which a single PBSC product was divided into three and cryopreserved in parallel using a control-rate freezer (CRF) or passive freezing method (-80°C freezer) at GOSH, or the same passive freezing at another laboratory. Viable CD34(+) counts were equivalent and adequate in each. Granulocyte-monocyte colony-forming unit assays demonstrated colonies from the products cryopreserved using passive freezing (both laboratories), but no colonies from products cryopreserved using the CRF. The CRF was shown to be operating within manufacturer's specifications with freeze-profile within acceptable limits. This experience has important implications for quality assurance for all transplant programmes, particularly those using cryopreserved products. The failure of post-thaw viable CD34(+) counts, the most widely used routine QA test available, to ensure PBSC function is of great concern and should prompt reassessment of protocols and QA procedures.

  8. Urban Geocryology: Mapping Urban-Rural Contrasts in Active-Layer Thickness, Barrow Penninsula, Northern Alaska

    NASA Astrophysics Data System (ADS)

    Klene, A. E.; Nelson, F. E.

    2014-12-01

    As development proceeds in the high latitudes, information about interactions between urban influences and the thickness of the active layer above permafrost becomes vital, particularly given the possibility of increasing temperatures accompanying climate change. Permafrost characteristics are often mapped at small geographical scales (i.e., over large areas), at low resolution, and without extensive field validation. Although maps of active-layer thickness (ALT) have been created for areas of relatively undisturbed terrain, this has rarely been done within urbanized areas, even though ALT is a critical factor in the design of roads, buildings, pipelines, and other elements of infrastructure. The need for detailed maps of ALT is emphasized in work on potential hazards in permafrost regions associated with global warming scenarios. Northern Alaska is a region considered to be at moderate to high risk for thaw-induced damage under climatic warming. The Native Village of Barrow (71°17'44"N; 156°45' 59"W), the economic, transportation, and administrative hub of the North Slope Borough, is the northernmost community in the USA, and the largest native settlement in the circum-Arctic. A winter urban heat island in Barrow, earlier snowmelt in the village, and dust deposition downwind of gravel pads and roads are all urban effects that could increase ALT. A recent empirical study documented a 17 to 41 cm difference in ALT between locations in the village of Barrow and surrounding undeveloped tundra, even in similar land-cover classes. We mapped ALT in the Barrow Peninsula, with particular attention to contrasts between the urbanized village and relatively undisturbed tundra in the nearby Barrow Environmental Observatory. The modified Berggren solution, an advanced analytic solution to the general Stefan problem of calculating frost and thaw depth, was used in a geographic context to map ALT over the 150 km² area investigated in the Barrow Urban Heat Island Study. The

  9. Thermokarst and thaw-related landscape dynamics -- an annotated bibliography with an emphasis on potential effects on habitat and wildlife

    USGS Publications Warehouse

    Jones, Benjamin M.; Amundson, Courtney L.; Koch, Joshua C.; Grosse, Guido

    2013-01-01

    Permafrost has warmed throughout much of the Northern Hemisphere since the 1980s, with colder permafrost sites warming more rapidly (Romanovsky and others, 2010; Smith and others, 2010). Warming of the near-surface permafrost may lead to widespread terrain instability in ice-rich permafrost in the Arctic and the Subarctic, and may result in thermokarst development and other thaw-related landscape features (Jorgenson and others, 2006; Gooseff and others, 2009). Thermokarst and other thaw-related landscape features result from varying modes and scales of permafrost thaw, subsidence, and removal of material. An increase in active-layer depth, water accumulation on the soil surface, permafrost degradation and associated retreat of the permafrost table, and changes to lake shores and coastal bluffs act and interact to create thermokarst and other thaw-related landscape features (Shur and Osterkamp, 2007). There is increasing interest in the spatial and temporal dynamics of thermokarst and other thaw-related features from diverse disciplines including landscape ecology, hydrology, engineering, and biogeochemistry. Therefore, there is a need to synthesize and disseminate knowledge on the current state of near-surface permafrost terrain. The term "thermokarst" originated in the Russian literature, and its scientific use has varied substantially over time (Shur and Osterkamp, 2007). The modern definition of thermokarst refers to the process by which characteristic landforms result from the thawing of ice-rich permafrost or the melting of massive ice (van Everdingen, 1998), or, more specifically, the thawing of ice-rich permafrost and (or) melting of massive ice that result in consolidation and deformation of the soil surface and formation of specific forms of relief (Shur, 1988). Jorgenson (2013) identifies 23 distinct thermokarst and other thaw-related features in the Arctic, Subarctic, and Antarctic based primarily on differences in terrain condition, ground-ice volume

  10. Thin-Layer Chromatography: Four Simple Activities for Undergraduate Students.

    ERIC Educational Resources Information Center

    Anwar, Jamil; And Others

    1996-01-01

    Presents activities that can be used to introduce thin-layer chromatography at the undergraduate level in relatively less developed countries and that can be performed with very simple and commonly available apparati in high schools and colleges. Activities include thin-layer chromatography with a test-tube, capillary feeder, burette, and rotating…

  11. Sporadic E-Layers and Meteor Activity

    NASA Astrophysics Data System (ADS)

    Alimov, Obid

    2016-07-01

    In average width it is difficult to explain variety of particularities of the behavior sporadic layer Es ionospheres without attraction long-lived metallic ion of the meteoric origin. Mass spectrometric measurements of ion composition using rockets indicate the presence of metal ions Fe+, Mg+, Si+, Na+, Ca+, K+, Al+ and others in the E-region of the ionosphere. The most common are the ions Fe+, Mg+, Si+, which are primarily concentrated in the narrow sporadic layers of the ionosphere at altitudes of 90-130 km. The entry of meteoric matter into the Earth's atmosphere is a source of meteor atoms (M) and ions (M +) that later, together with wind shear, produce midlatitude sporadic Es layer of the ionosphere. To establish the link between sporadic Es layer and meteoroid streams, we proceeded from the dependence of the ionization coefficient of meteors b on the velocity of meteor particles in different meteoroid streams. We investigated the dependence of the critical frequency f0Es of sporadic E on the particle velocity V of meteor streams and associations. It was established that the average values of f0Es are directly proportional to the velocity V of meteor streams and associations, with the correlation coefficient of 0.53 < R < 0.74. Thus, the critical frequency of the sporadic layer Es increases with the increase of particle velocity V in meteor streams, which indicates the direct influence of meteor particles on ionization of the lower ionosphere and formation of long-lived metal atoms M and ions M+ of meteoric origin.

  12. Thawed and liquid plasma--what do we know?

    PubMed

    Cardigan, R; Green, L

    2015-07-01

    There is increasing interest in the use of liquid or frozen plasma thawed and stored for extended periods (>24 h) to reduce wastage and to improve rapid availability of plasma in massive transfusion protocols advocating the early use of plasma in trauma by some centres. There is now a body of studies that have assessed individual coagulation factors during storage of thawed plasma. These show that factor VIII (FVIII) is the worst affected factor and that its activity is mainly lost during the first 24 h following thawing. However, for most factors studied, there is a continual decline during further storage. The few studies that have assessed thrombin generation in thawed plasma have shown variable results. Extended storage of plasma is associated with an increase in levels of DEHP in the component and could theoretically increase the risk of bacterial contamination, although the latter does not appear to have been an issue in countries that have adopted the use of thawed plasma. There are no clinical studies relating to the efficacy of extended-thawed plasma, and therefore, the potential reduction in its efficacy must be balanced with the clinical need for the component.

  13. Thawed and liquid plasma--what do we know?

    PubMed

    Cardigan, R; Green, L

    2015-07-01

    There is increasing interest in the use of liquid or frozen plasma thawed and stored for extended periods (>24 h) to reduce wastage and to improve rapid availability of plasma in massive transfusion protocols advocating the early use of plasma in trauma by some centres. There is now a body of studies that have assessed individual coagulation factors during storage of thawed plasma. These show that factor VIII (FVIII) is the worst affected factor and that its activity is mainly lost during the first 24 h following thawing. However, for most factors studied, there is a continual decline during further storage. The few studies that have assessed thrombin generation in thawed plasma have shown variable results. Extended storage of plasma is associated with an increase in levels of DEHP in the component and could theoretically increase the risk of bacterial contamination, although the latter does not appear to have been an issue in countries that have adopted the use of thawed plasma. There are no clinical studies relating to the efficacy of extended-thawed plasma, and therefore, the potential reduction in its efficacy must be balanced with the clinical need for the component. PMID:25833464

  14. Effects of temperature, moisture, and permafrost thaw on ecosystem carbon exchange in Alaskan tundra.

    NASA Astrophysics Data System (ADS)

    Natali, S.; Schuur, E. A.; Webb, E.

    2012-12-01

    Carbon has been accumulating in northern high latitude ecosystems for thousands of years because cold and moist conditions have protected soil organic matter from microbial decomposition. Over the past several decades, warming surface air temperatures have been accompanied by thawing of the perennially frozen permafrost layer where much of the accumulated carbon is stored. In addition to its role in carbon storage, permafrost regulates surface hydrology by restricting vertical water flow, thereby maintaining a water table that remains close to the ground surface. In the absence of the permafrost layer, enhanced water drainage will result in increased water table depth and decreased soil moisture. The biological availability of permafrost carbon may increase in a warmer and drier soil environment, as is expected for the region of this study. To determine the effects of warming temperatures and changes in soil moisture on ecosystem carbon exchange, we established a water table drawdown experiment within the footprint of the Carbon in Permafrost Experimental Heating Research (CiPEHR) project, an ecosystem warming experiment in Interior Alaska that warms air and soil temperatures and degrades permafrost. Here we present ecosystem carbon balance results from combined warming and moisture manipulation treatments at the CiPEHR project. Soil warming increased soil temperature by 2-3o C and resulted in a 10% increase in growing season thaw depth. Surprisingly, the additional 2 kg of thawed soil C m-2 in the warmed plots did not increase net growing season CO2 loss from this ecosystem. In contrast, soil warming and permafrost thaw increased growing season CO2 uptake, which was a result of both higher net primary productivity and an inhibition of microbial decomposition by soil saturation at the base of the active layer. The drying treatment (i.e., water table drawdown) decreased soil moisture by 25%, which led to an increase in ecosystem respiration and decrease in net

  15. InSAR detects possible thaw settlement in the Alaskan Arctic Coastal Plain

    USGS Publications Warehouse

    Rykhus, R.P.; Lu, Zhiming

    2008-01-01

    Satellite interferometric synthetic aperture radar (InSAR) has proven to be an effective tool for monitoring surface deformation from volcanoes, earthquakes, landslides, and groundwater withdrawal. This paper seeks to expand the list of applications of InSAR data to include monitoring subsidence possibly associated with thaw settlement over the Alaskan Arctic Coastal Plain. To test our hypothesis that InSAR data are sufficiently sensitive to detect subsidence associated with thaw settlement, we acquired all Japanese Earth Resources Satellite-1 (JERS-1) L-band data available for the summers of 1996, 1997, and 1998 over two sites on the Alaska North Slope. The least amount of subsidence for both study sites was detected in the interferograms covering the summer of 1996 (2-3 cm), interferograms from 1997 and 1998 revealed that about 3 cm of subsidence occurred at the northern Cache One Lake site, and about 5 cm of subsidence was detected at the southern Kaparuk River site. These preliminary results illustrate the capacity of the L-band (24 cm) wavelength JERS-1 radar data to penetrate the short Arctic vegetation to monitor subsidence possibly associated with thaw settlement of the active layer and (or) other hydrologic changes over relatively large areas. ?? 2008 CASI.

  16. Active unjamming of confluent cell layers

    NASA Astrophysics Data System (ADS)

    Marchetti, M. Cristina

    Cell motion inside dense tissues governs many biological processes, including embryonic development and cancer metastasis, and recent experiments suggest that these tissues exhibit collective glassy behavior. Motivated by these observations, we have studied a model of dense tissues that combines self-propelled particle models and vertex models of confluent cell layers. In this model, referred to as self-propelled Voronoi (SPV), cells are described as polygons in a Voronoi tessellation with directed noisy cell motility and interactions governed by a shape energy that incorporates the effects of cell volume incompressibility, contractility and cell-cell adhesion. Using this model, we have demonstrated a new density-independent solid-liquid transition in confluent tissues controlled by cell motility and a cell-shape parameter measuring the interplay of cortical tension and cell-cell adhesion. An important insight of this work is that the rigidity and dynamics of cell layers depends sensitively on cell shape. We have also used the SPV model to test a new method developed by our group to determine cellular forces and tissue stresses from experimentally accessible cell shapes and traction forces, hence providing the spatio-temporal distribution of stresses in motile dense tissues. This work was done with Dapeng Bi, Lisa Manning and Xingbo Yang. MCM was supported by NSF-DMR-1305184 and by the Simons Foundation.

  17. Method for Differentiation between Fresh and Frozen-thawed Fish

    NASA Astrophysics Data System (ADS)

    Kitamikado, Manabu; Yoshioka, Keiko

    In Japan fresh fish has a much higher market price than that for frozen-thawed fish. However, a large number of frozen-thawed fish are sold without being differentiated from fresh fish. We discuss here the differentiation methods described in literatures and our works in the search for such a method. We used the opacity of crystalline lens and the destruction of red blood cells as the index for the differentiation, in addition to the activity of neutral β-N-acetylglucosaminidase in blood. Thus, a fluorometric method and a rapid paper test method were developed based on measurement of the activity of this enzyme. This enzyme, found in fish red blood cells, was inactive in intact cells but was activated when cells were disrupted by freezing, and thawing. Both methods were applicable for testing most commom edible fish prior to filleting and required about 20 min using a UV-lamp.

  18. Use of Androcoll-S after thawing improves the quality of electroejaculated and epididymal sperm samples from red deer.

    PubMed

    Anel-López, L; Martínez-Rodríguez, C; Soler, A J; Fernández-Santos, M R; Garde, J J; Morrell, J M

    2015-07-01

    Single Layer Centrifugation is a useful technique to select sperm with good quality. The use of selection methods such as Androcoll could become an important tool to improve the quality of sperm samples and therefore to improve other artificial reproductive techniques such as sperm sex sorting, in vitro fertilization or AI. The aim of this study was to evaluate the effect of a Single Layer Centrifugation with Androcoll-S on the sperm quality of red deer sperm samples of two different origins, electroejaculated samples and epididymal samples obtained post-mortem, after thawing and after an incubation for 2h at 37°C. Sperm motility, viability, membrane permeability, mitochondrial activity, acrosomal status and DNA fragmentation were determined for all samples. The samples selected by Androcoll-S showed an improvement in sperm kinematics compared to unselected samples after thawing and after incubation. The same effect was observed in parameters such as viability, mitochondrial activity or acrosomal status which were improved after the selection. In contrast, no difference was found in DNA fragmentation between selected and unselected samples within the same sperm type. We conclude that sperm selection by SLC with Androcoll-S after thawing for red deer sperm of both types is a suitable technique that allows sperm quality in both types of sperm samples to be improved, thereby improving other assisted reproductive techniques. Further studies (IVF and in vivo fertilization) are required to determine whether this improvement can increase fertility, as has been shown for other species. PMID:26002696

  19. Greenhouse Gas Exchange in Small Arctic Thaw Ponds

    NASA Astrophysics Data System (ADS)

    Laurion, I.; Bégin, P. N.; Bouchard, F.; Preskienis, V.

    2014-12-01

    Arctic lakes and ponds can represent up to one quarter of the land surface in permafrost landscapes, particularly in lowland tundra landscapes characterized by ice wedge organic polygons. Thaw ponds can be defined as the aquatic ecosystems associated to thawing of organic soils, either resulting from active layer processes and located above low-center peat polygons (hereafter low-center polygonal or LCP ponds), or resulting from thermokarst slumping above melting ice wedges linked to the accelerated degradation of permafrost (hereafter ice-wedge trough or IWT ponds). These ponds can merge together forming larger water bodies, but with relatively stable shores (hereafter merged polygonal or MPG ponds), and with limnological characteristics similar to LCP ponds. These aquatic systems are very small and shallow, and present a different physical structure than the larger thermokarst lakes, generated after years of development and land subsidence. In a glacier valley on Bylot Island, Nunavut, Canada, thermokarst and kettle lakes together represent 29% of the aquatic area, with a thermal profile resembling those of more standard arctic lakes (mixed epilimnion). The IWT ponds (44% of the area) are stratified for a large fraction of the summer despite their shallowness, while LCP and MPG ponds (27% of the area) show a more homogeneous water column. This will affect gas exchange in these diverse aquatic systems, in addition to their unique microbiota and organic carbon lability that control the production and consumption rates of greenhouse gases. The stratification in IWT ponds generates hypoxic conditions at the bottom, and together with the larger availability of organic carbon, stimulates methanogenesis and limits the mitigating action of methanotrophs. Overall, thaw ponds are largely supersaturated in methane, with IWT ponds dominating the emissions in this landscape (92% of total aquatic emissions estimated for the same valley), and they present large variations in

  20. Kinetics of Ion Transport in Perovskite Active Layers and Its Implications for Active Layer Stability.

    PubMed

    Bag, Monojit; Renna, Lawrence A; Adhikari, Ramesh Y; Karak, Supravat; Liu, Feng; Lahti, Paul M; Russell, Thomas P; Tuominen, Mark T; Venkataraman, D

    2015-10-14

    Solar cells fabricated using alkyl ammonium metal halides as light absorbers have the right combination of high power conversion efficiency and ease of fabrication to realize inexpensive but efficient thin film solar cells. However, they degrade under prolonged exposure to sunlight. Herein, we show that this degradation is quasi-reversible, and that it can be greatly lessened by simple modifications of the solar cell operating conditions. We studied perovskite devices using electrochemical impedance spectroscopy (EIS) with methylammonium (MA)-, formamidinium (FA)-, and MA(x)FA(1-x) lead triiodide as active layers. From variable temperature EIS studies, we found that the diffusion coefficient using MA ions was greater than when using FA ions. Structural studies using powder X-ray diffraction (PXRD) show that for MAPbI3 a structural change and lattice expansion occurs at device operating temperatures. On the basis of EIS and PXRD studies, we postulate that in MAPbI3 the predominant mechanism of accelerated device degradation under sunlight involves thermally activated fast ion transport coupled with a lattice-expanding phase transition, both of which are facilitated by absorption of the infrared component of the solar spectrum. Using these findings, we show that the devices show greatly improved operation lifetimes and stability under white-light emitting diodes, or under a solar simulator with an infrared cutoff filter or with cooling. PMID:26414066

  1. Influence of Plant Communities on Active Layer Depth in Boreal Forest

    NASA Astrophysics Data System (ADS)

    Fisher, James; Estop Aragones, Cristian; Thierry, Aaron; Hartley, Iain; Murton, Julian; Charman, Dan; Williams, Mathew; Phoenix, Gareth

    2015-04-01

    Vegetation plays a crucial role in determining active layer depth (ALD) and hence the extent to which permafrost may thaw under climate change. Such influences are multifaceted and include, for example, promotion of shallow ALD by insulation from moss or shading by plant canopies in summer, or trapping of snow in evergreen tree canopies that reduces snow insulation of soil in winter. However, while the role of different vegetation components are understood at a conceptual level, quantitative understanding of the relative importance of different vegetation components and how they interact to determine active layer depth is lacking. In addition, major abiotic factors such as fire and soil hydrological properties will considerably influence the role of vegetation in mediating ALD, though again this is not well understood. To address this we surveyed 60 plots across 4 sites of contrasting vegetation and fire status, encompassing a range of soil moisture and organic matter thickness, in the discontinuous permafrost zone near Yellowknife, NT, Canada. In each plot we measured ALD and a range of vegetation and soil parameters to understand how key characteristics of the understory and canopy vegetation, and soil properties influence ALD. Measurements included moss depth, tree canopy LAI, understory LAI, understory height, vegetation composition, soil organic matter depth, slope and soil moisture. By undertaking these surveys in sites with contrasting hydrological conditions in both burned and unburned areas we have also been able to determine which characteristics of the vegetation and soil are important for protecting permafrost, which characteristics emerge as the most important factors across sites (i.e. irrespective of site conditions) and which factors have site (ecosystem) specific influences. This work provides a major insight into how ecosystem properties influence ALD and therefore also how changes in ecosystems properties arising from climate change may influence

  2. Effect of thaw depth on fluxes of CO₂ and CH₄ in manipulated Arctic coastal tundra of Barrow, Alaska.

    PubMed

    Kim, Yongwon

    2015-02-01

    Changes in CO₂ and CH₄ emissions represent one of the most significant consequences of drastic climate change in the Arctic, by way of thawing permafrost, a deepened active layer, and decline of thermokarst lakes in the Arctic. This study conducted flux-measurements of CO₂ and CH₄, as well as environmental factors such as temperature, moisture, and thaw depth, as part of a water table manipulation experiment in the Arctic coastal plain tundra of Barrow, Alaska during autumn. The manipulation treatment consisted of draining, controlling, and flooding treated sections by adjusting standing water. Inundation increased CH₄ emission by a factor of 4.3 compared to non-flooded sections. This may be due to the decomposition of organic matter under a limited oxygen environment by saturated standing water. On the other hand, CO₂ emission in the dry section was 3.9-fold higher than in others. CH₄ emission tends to increase with deeper thaw depth, which strongly depends on the water table; however, CO₂ emission is not related to thaw depth. Quotients of global warming potential (GWPCO₂) (dry/control) and GWPCH₄ (wet/control) increased by 464 and 148%, respectively, and GWPCH₄ (dry/control) declined by 66%. This suggests that CO₂ emission in a drained section is enhanced by soil and ecosystem respiration, and CH₄ emission in a flooded area is likely stimulated under an anoxic environment by inundated standing water. The findings of this manipulation experiment during the autumn period demonstrate the different production processes of CO₂ and CH₄, as well as different global warming potentials, coupled with change in thaw depth. Thus the outcomes imply that the expansion of tundra lakes leads the enhancement of CH₄ release, and the disappearance of the lakes causes the stimulated CO₂ production in response to the Arctic climate change. PMID:25461040

  3. Effect of thaw depth on fluxes of CO₂ and CH₄ in manipulated Arctic coastal tundra of Barrow, Alaska.

    PubMed

    Kim, Yongwon

    2015-02-01

    Changes in CO₂ and CH₄ emissions represent one of the most significant consequences of drastic climate change in the Arctic, by way of thawing permafrost, a deepened active layer, and decline of thermokarst lakes in the Arctic. This study conducted flux-measurements of CO₂ and CH₄, as well as environmental factors such as temperature, moisture, and thaw depth, as part of a water table manipulation experiment in the Arctic coastal plain tundra of Barrow, Alaska during autumn. The manipulation treatment consisted of draining, controlling, and flooding treated sections by adjusting standing water. Inundation increased CH₄ emission by a factor of 4.3 compared to non-flooded sections. This may be due to the decomposition of organic matter under a limited oxygen environment by saturated standing water. On the other hand, CO₂ emission in the dry section was 3.9-fold higher than in others. CH₄ emission tends to increase with deeper thaw depth, which strongly depends on the water table; however, CO₂ emission is not related to thaw depth. Quotients of global warming potential (GWPCO₂) (dry/control) and GWPCH₄ (wet/control) increased by 464 and 148%, respectively, and GWPCH₄ (dry/control) declined by 66%. This suggests that CO₂ emission in a drained section is enhanced by soil and ecosystem respiration, and CH₄ emission in a flooded area is likely stimulated under an anoxic environment by inundated standing water. The findings of this manipulation experiment during the autumn period demonstrate the different production processes of CO₂ and CH₄, as well as different global warming potentials, coupled with change in thaw depth. Thus the outcomes imply that the expansion of tundra lakes leads the enhancement of CH₄ release, and the disappearance of the lakes causes the stimulated CO₂ production in response to the Arctic climate change.

  4. Activity recognition from video using layered approach

    NASA Astrophysics Data System (ADS)

    McPherson, Charles A.; Irvine, John M.; Young, Mon; Stefanidis, Anthony

    2012-01-01

    The adversary in current threat situations can no longer be identified by what they are, but by what they are doing. This has lead to a large increase in the use of video surveillance systems for security and defense applications. With the quantity of video surveillance at the disposal of organizations responsible for protecting military and civilian lives comes issues regarding the storage and screening the data for events and activities of interest. Activity recognition from video for such applications seeks to develop automated screening of video based upon the recognition of activities of interest rather than merely the presence of specific persons or vehicle classes developed for the Cold War problem of "Find the T72 Tank". This paper explores numerous approaches to activity recognition, all of which examine heuristic, semantic, and syntactic methods based upon tokens derived from the video. The proposed architecture discussed herein uses a multi-level approach that divides the problem into three or more tiers of recognition, each employing different techniques according to their appropriateness to strengths at each tier using heuristics, syntactic recognition, and HMM's of token strings to form higher level interpretations.

  5. Mesoporous layer-by-layer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability.

    PubMed

    Gunjakar, Jayavant L; Kim, Tae Woo; Kim, Hyo Na; Kim, In Young; Hwang, Seong-Ju

    2011-09-28

    Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical

  6. Sporadic Layer es and Siesmic Activity

    NASA Astrophysics Data System (ADS)

    Alimov, Obid; Blokhin, Alexandr; Kalashnikova, Tatyana

    2016-07-01

    To determine the influence of seismogenic disturbances on the calm state of the iono-sphere and assess the impact of turbulence development in sporadic-E during earthquake prepa-ration period we calculated the variation in the range of semitransparency ∆fES = f0ES - fbES. The study was based primarily on the ionograms obtained by vertical sounding of the ionosphere at Dushanbe at nighttime station from 15 to 29 August 1986. In this time period four successive earthquakes took place, which serves the purpose of this study of the impact of seis-mogenic processes on the intensity of the continuous generation of ionospheric turbulence. Analysis of the results obtained for seismic-ionospheric effects of 1986 earthquakes at station Dushanbe has shown that disturbance of ionospheric parameters during earthquake prepa-ration period displays a pronounced maximum with a duration of t = 1-6 hours. Ionospheric effects associated with the processes of earthquake preparation emerge quite predictably, which verifies seismogenic disturbances in the ionosphere. During the preparation of strong earthquakes, ionograms of vertical sounding produced at station Dushanbe - near the epicenter area - often shown the phenomenon of spreading traces of sporadic Es. It is assumed that the duration of manifestation of seismic ionospheric precursors in Du-shanbe τ = 1 - 6 hours may be associated with deformation processes in the Earth's crust and var-ious faults, as well as dissimilar properties of the environment of the epicentral area. It has been shown that for earthquakes with 4.5 ≤ M ≤ 5.5 1-2 days prior to the event iono-spheric perturbations in the parameters of the sporadic layer Es and an increase in the value of the range of semitransparency Es - ΔfEs were observed, which could lead to turbulence at altitudes of 100-130 km.

  7. Modeling the effect of active layer deepening on stocks of soil organic carbon in the Pechora River Basin

    NASA Astrophysics Data System (ADS)

    Eriksson, P.; Hugelius, G.; Marchenko, S. S.

    2012-12-01

    This study investigates how much of the estimated mass of surface permafrost (1 m deep) soil organic carbon stored in soils of the northern Pechora River Basin (Russian Arctic) could be affected due to active layer deepening for the time period 1980 to 2099. The study estimates how much of the upper permafrost soil organic carbon (1-100 cm depth range) will be affected by active layer deepening due to climate warming, on what timescale the deepening will take place and if the estimated changes differ depending on the extent of permafrost in the region. A model developed in a Geographic Information System combines datasets from The Northern Circumpolar Soil Carbon Database (Hugelius, in press), field data of soil organic carbon content (SOCC) in different permafrost soil horizons in the Usa basin (Hugelius et al., 2011) and data of recent (observed) and future (projected) active layer depth from a spatially distributed permafrost dynamics model in the Pechora River Basin (GIPL2 model; Marchenko et al., 2008). For the simulation of permafrost dynamics we used output from the regional climate model HIRHAM5 with the physical parameterization of ECHAM5 with a doubling gradual increase of atmospheric CO2 concentration by the end of the current century (Stendel et al., 2010). According to this specific climate scenario, projections of future changes in permafrost suggest that by the end of the 21st century, permafrost in the Russian North may be actively thawing at many locations of the Pechora River watershed. The results show that in 1980, 75% of the available 0-100 cm Gelisol SOCC is affected by seasonal thawing (Figure 1). In 2050 the proportion is increased to 86% and by 2090 almost the whole study area has an active layer deeper than 1 meter (98%). This indicates an increase from approximately 0.64% to 0.84% of the total 1-100 cm soil organic carbon mass in the northern permafrost region. The change is more gradual in the isolated and the sporadic permafrost zones

  8. Effect of soil property uncertainties on permafrost thaw projections: A calibration-constrained analysis

    DOE PAGES

    Harp, Dylan R.; Atchley, Adam L.; Painter, Scott L.; Coon, Ethan T.; Wilson, Cathy J.; Romanovsky, Vladimir E.; Rowland, Joel C.

    2016-02-11

    Here, the effect of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The Null-Space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21more » $$^{st}$$ century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows for the evaluation of intra-annual uncertainty due to soil properties and the inter-annual variability due to year to year differences in CESM climate forcings. After calibrating to borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant intra-annual uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Intra-annual uncertainties in projected soil moisture content and Stefan number are small. A volume and time integrated Stefan number decreases significantly in the future climate, indicating that latent heat of phase change becomes more important than heat conduction in future climates. Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we show that the effect of calibration-constrained uncertainty in soil properties

  9. Effect of soil property uncertainties on permafrost thaw projections: A calibration-constrained analysis

    DOE PAGES

    Harp, D. R.; Atchley, A. L.; Painter, S. L.; Coon, E. T.; Wilson, C. J.; Romanovsky, V. E.; Rowland, J. C.

    2015-06-29

    The effect of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The Null-Space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21st century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows formore » the evaluation of intra-annual uncertainty due to soil properties and the inter-annual variability due to year to year differences in CESM climate forcings. After calibrating to borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant intra-annual uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Intra-annual uncertainties in projected soil moisture content and Stefan number are small. A volume and time integrated Stefan number decreases significantly in the future climate, indicating that latent heat of phase change becomes more important than heat conduction in future climates. Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we show that the effect of calibration-constrained uncertainty in soil properties, although

  10. Effect of soil property uncertainties on permafrost thaw projections: A calibration-constrained analysis

    SciTech Connect

    Harp, D. R.; Atchley, A. L.; Painter, S. L.; Coon, E. T.; Wilson, C. J.; Romanovsky, V. E.; Rowland, J. C.

    2015-06-29

    The effect of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The Null-Space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21st century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows for the evaluation of intra-annual uncertainty due to soil properties and the inter-annual variability due to year to year differences in CESM climate forcings. After calibrating to borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant intra-annual uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Intra-annual uncertainties in projected soil moisture content and Stefan number are small. A volume and time integrated Stefan number decreases significantly in the future climate, indicating that latent heat of phase change becomes more important than heat conduction in future climates. Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we show that the effect of calibration-constrained uncertainty in soil properties, although significant, is

  11. Effect of soil property uncertainties on permafrost thaw projections: a calibration-constrained analysis

    NASA Astrophysics Data System (ADS)

    Harp, D. R.; Atchley, A. L.; Painter, S. L.; Coon, E. T.; Wilson, C. J.; Romanovsky, V. E.; Rowland, J. C.

    2015-06-01

    The effect of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The Null-Space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21st century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows for the evaluation of intra-annual uncertainty due to soil properties and the inter-annual variability due to year to year differences in CESM climate forcings. After calibrating to borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant intra-annual uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Intra-annual uncertainties in projected soil moisture content and Stefan number are small. A volume and time integrated Stefan number decreases significantly in the future climate, indicating that latent heat of phase change becomes more important than heat conduction in future climates. Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we show that the effect of calibration-constrained uncertainty in soil properties, although significant, is

  12. The potential influence of thaw slumps and sea-level rise on the Arctic carbon cycle (Invited)

    NASA Astrophysics Data System (ADS)

    Rowland, J. C.; Crosby, B. T.; Travis, B. J.

    2010-12-01

    Potential soil carbon stores in the Arctic are estimated to be second only in size to that of the oceans. The majority of this carbon lies within permafrost dominated regions and is presently stored in frozen soils in the shallow subsurface (the upper 3 meters). Considerable attention and research is presently focused on how climate warming-induced thawing of permafrost and deepening of the seasonally thawed upper layer of the permafrost may alter the carbon cycle across the Arctic and globally. Less studied, however, many natural hazards have the potential to influence the Arctic carbon cycle due to their alteration of the landsurface. The temperature dependence and the influence of hydrology on Arctic landsurface processes make the occurrence of many natural hazards in the Arctic critically dependent on interactions between the landsurface, atmosphere, and oceans. Here we explore the potential role of two natural hazards in the Arctic carbon cycle: deep, retrogressive thaw slumps; and sea-level rise. Retrogressive thaw slumps are deep landslide features hypothesized to be initially triggered by the melting of bodies of ice contained within frozen sediments. Once triggered continued thawing of frozen soils and melting of buried ice along the failure face of the slide drives retreat of the slump headwall. Along the Selawik River in northwest Alaska a thaw slump triggered in 2004 has retreated approximately 300 m into a high river bluff and liberated more than a half million cubic meters of ice and sediment. The slump failure has mobilized both shallow soil carbon and much older carbon previously buried within the glacial deposits but now exposed in the actively retreating slump face. An unknown fraction of the carbon contained within slump sediments may be released directly to the atmosphere by oxidation or microbially mediated transformations. The remaining carbon is physically transported first onto the slump floor and then into the Selawik River. Once in the

  13. Effects of freeze-thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat.

    PubMed

    Sawicka, Joanna E; Robador, Alberto; Hubert, Casey; Jørgensen, Bo Barker; Brüchert, Volker

    2010-04-01

    Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring (35)S sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.

  14. Slow-roll thawing quintessence

    SciTech Connect

    Chiba, Takeshi

    2009-04-15

    We derive slow-roll conditions for thawing quintessence. We solve the equation of motion of {phi} for a Taylor expanded potential (up to the quadratic order) in the limit where the equation of state w is close to -1 to derive the equation of state as a function of the scale factor. We find that the evolution of {phi} and hence w are described by only two parameters. The expression for w(a), which can be applied to general thawing models, coincides precisely with that derived recently by Dutta and Scherrer for hilltop quintessence. The consistency conditions of |w+1|<<1 are derived. The slow-roll conditions for freezing quintessence are also derived.

  15. [Lipoamide dehydrogenase, citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase in skeletal muscle. VIII. The influence of temperature and rate of freezing of bovine muscle on the activity and subcellular distribution of the enzymes in the thawed tissue].

    PubMed

    Hamm, R; Gottesmann, P

    1985-09-01

    Samples of bovine muscle (post rigor) were frozen at different temperatures between -5 degrees and -196 degrees C at different freezing rates, and thawed at room temperature. The activities of the mitochondrial enzymes lipoamide dehydrogenase, citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase were determined in the supernatant of the tissue homogenates in phosphate buffer (total enzyme activity), as well as in the press juice of the intact tissue (enzyme activity in the sarcoplasma). Neither the temperature nor the rate of freezing (varying from 25.5 to 0.01 min/degrees C) showed a significant influence on the total enzyme activities. Freezing at -5 degrees and -10 degrees C (at different rates but without intracellular freezing) and thawing did not result in an appreciable release of enzymes. Below -10 degrees C the release of the three enzymes from their binding to the inner membrane of the mitochondrion into the sarcoplasmic fluid increased upon rapid freezing with decreasing temperature i.e. with increasing intracellular ice formation, whereas at slow freezing (with extracellular ice formation only) freezing below -20 degrees C did not cause further enzyme release. At freezing temperatures below -20 degrees C rapid freezing resulted in a significantly stronger release of the three enzymes than slow freezing. From these results it was concluded that the damage to mitochondrial membranes upon fast freezing is primarily a result of intracellular (and perhaps also intramitochondrial) ice formation, whereas the membrane damage during slow freezing is primarily due to dehydration caused by the migration of water from the muscle fibers into the extracellular space as a result of osmotic effects. Ion concentration in the nonfreezing fraction of tissue water seems to be only of minor importance for the disintegration of mitochondrial membranes.

  16. High risk of permafrost thaw

    SciTech Connect

    Schuur, E.A.G.; Abbott, B.; Koven, C.D,; Riley, W.J.; Subin, Z.M.; al, et

    2011-11-01

    In the Arctic, temperatures are rising fast, and permafrost is thawing. Carbon released to the atmosphere from permafrost soils could accelerate climate change, but the likely magnitude of this effect is still highly uncertain. A collective estimate made by a group of permafrost experts, including myself, is that carbon could be released more quickly than models currently suggest, and at levels that are cause for serious concern. While our models of carbon emission from permafrost thaw are lacking, experts intimately familiar with these landscapes and processes have accumulated knowledge about what they expect to happen, based on both quantitative data and qualitative understanding of these systems. We (the authors of this piece) attempted to quantify this expertise through a survey developed over several years, starting in 2009. Our survey asked experts what percentage of surface permafrost they thought was likely to thaw, how much carbon would be released, and how much of that would be methane, for three time periods and under four warming scenarios that are part of the new IPCC Fifth Assessment Report.

  17. Structural complexities in the active layers of organic electronics.

    PubMed

    Lee, Stephanie S; Loo, Yueh-Lin

    2010-01-01

    The field of organic electronics has progressed rapidly in recent years. However, understanding the direct structure-function relationships between the morphology in electrically active layers and the performance of devices composed of these materials has proven difficult. The morphology of active layers in organic electronics is inherently complex, with heterogeneities existing across multiple length scales, from subnanometer to micron and millimeter range. A major challenge still facing the organic electronics community is understanding how the morphology across all of the length scales in active layers collectively determines the device performance of organic electronics. In this review we highlight experiments that have contributed to the elucidation of structure-function relationships in organic electronics and also point to areas in which knowledge of such relationships is still lacking. Such knowledge will lead to the ability to select active materials on the basis of their inherent properties for the fabrication of devices with prespecified characteristics.

  18. Modeling soil freezing and thawing fronts in a land surface-atmosphere interaction scheme

    NASA Astrophysics Data System (ADS)

    Yi, Shuhua

    This dissertation presents development, testing and applications of an algorithm for the simulation of soil freezing and thawing fronts (FTFs) in land surface models. A Two-direction Stefans Algorithm (TDSA), derived from the solution of the Stefan Problem, was developed to predict the position of FTFs in soil. TDSA was tested using observed soil temperature and moisture data from several sites across a north-south transect in North America. TDSA performed well for both permafrost and seasonal frost regions. TDSA was then implemented in the Community Land Model 3 (CLM3), used in a global climate model, to predict FTFs. Several modifications, including incorporation of peat layer, canopy heat capacity, and unfrozen soil water, were also made to make CLM3 compatible to northern cold regions. Coupled CLM3-TDSA Model testing in a boreal forest site in Saskatchewan for multiple years indicated significant improvements in the thermal response of the model, and TDSA provided better simulations of FTFs than the zero-isothermal method. Defining the start and end of the growing season using FTFs significantly improved the simulation of photosynthetic uptake. Projected warming may cause an earlier start of growing season and a higher photosynthesis during spring. Warmer temperatures would increase ecosystem respiration, causing annual net ecosystem productivity to decline. The coupled CLM3-TDSA model was also applied to study the development of ALD (active layer depth) in permafrost regions. The roles of climate warming, soil texture and vegetation were investigated. Results showed that warming caused deeper and earlier thaw of permafrost, soil texture had a significant effect on the development of ALD, and vegetation cover affected the ALD development through its effect on ground surface energy, and the start and length of thawing season. These results showed that TDSA can be applied to study the long term changes in ALD in permafrost regions under projected climate change.

  19. Thaw Characteristics of Soil around Buried Pipeline in Permafrost Regions Based on Numerical Simulation of Temperature Fields

    NASA Astrophysics Data System (ADS)

    Fu, Zaiguo; Yu, Bo; Zhu, Jie; Li, Wang

    The freezing-thawing processes of the soil around the buried oil and gas pipelines in permafrost regions due to the effect of the pipe and atmospheric environment may bring about dangers to the pipelines as frost heave and thaw settlement occur and go on, and then the buried pipes may face huge challenges for safe operation. To analyze the thermal effect of the buried pipe on the surrounding soil, a two-dimensional computational model of the soil temperature fields was established based on the process of the heat transfer with phase change in the soil. The temperature fields and the thaw characteristics of the soil around the operating pipeline in permafrost regions were studied using numerical methods via the software FLUENT in this paper. The developments of the maximum thawed cylinders and corresponding thaw depths under the pipeline within operation life cycle were predicted and analyzed for various medium temperatures, water contents of soils, insulation layer thicknesses and imposed boundary conditions by climatic warming. In addition, the maximum thaw settlement of the soil under the pipeline in 5 typical permafrost areas along the Russia — China oil pipeline (the section in China) within operation life cycle was calculated. The medium temperatures were assumed to be constant and sinusoidal. The results indicated that the maximum thaw depths and thawed cylinders around the pipeline in permafrost regions enlarged with time elapse and the decrease in water content of the soils under the same boundary conditions. The maximum thaw depths and thawed cylinders increased with the increase of medium temperatures after the same operation time. The insulation layer weakened heat exchange between the pipeline and the surrounding soils and thus reduced the development of the thawed cylinders effectively during the early operation period. This research may provide an effective method for engineering application, and the results may provide references for predicting the

  20. The Effects of Permafrost Thaw on Organic Matter Quality and Availability Along a Hill Slope in Northeastern Siberia

    NASA Astrophysics Data System (ADS)

    Connolly, C. T.; Spawn, S.; Ludwig, S.; Schade, J. D.; Natali, S.

    2014-12-01

    Climate warming and permafrost thaw in northeastern Siberia are expected to change the quantity and quality of organic matter (OM) transported through watersheds, releasing previously frozen carbon (C) to biologically available pool. Hill slopes have shown to influence the distribution of OM, resulting in a downhill accumulation of available C and nutrients relative to uphill. Here we examine how future permafrost thaw will change OM quality and availability along a hill slope in a larch-dominated watershed. We collected soils from the thawed organic and mineral layers, and 1m deep permafrost cores for dissolved organic C (DOC) and total dissolved N (TDN), C composition from measures of colored dissolved organic matter (CDOM), DOC lability from biodegradable DOC (BDOC) incubations, C and nutrient availability from extracellular-enzyme assays (EEA's), and microbial respiration from aerobic soil incubations. Here we show that organic soils (O), in comparison to mineral soils (M) and permafrost (P) are the most abundant source of C (avg O DOC: 51.6mg/L), exhibiting low molecular complexity (avg O SUVA254: 4.05) and high quality. Evidence suggests permafrost OM may be an equally abundant, and more labile source of C than mineral soils (highest P DOC: 16.1 mg/L, lowest P SUVA254: 6.32; median M DOC: 18.5 mg/L, median M SUVA254: 24.0). Furthermore, we demonstrate that there may be a positive relationship in the rate of C mineralization and distance downhill, showing 15-30% greater CO2 production/gC downhill relative to uphill. Evidence also supports a similar relationship in permafrost DOC content and molecular complexity, showing more DOC of a lower complexity further downhill. This indicates DOC transport may have been occurring through the active layer and downhill during ice-rich permafrost formation, and may supply a labile source of carbon to lowland areas and adjacent stream networks upon thaw.

  1. Effects of Freezing and Thawing on Consolidation Behavior of Clayey Soils

    NASA Astrophysics Data System (ADS)

    Binal, Adil; Adeli, Parisa

    2015-04-01

    An apprehending of freezing and thawing effects on cohesive soil is considerable for many construction and environmental subjects. This paper relates the effects of freezing and thawing on consolidation behaviour of clayey soils. The Capital of Ankara settled on a sequence of lacustrine sediments. These sediments include fine grain soils, locally. Collected samples were undisturbed grey clay and clayey sand that were obtained from the bottom of a construction zone at about 1m depth below the ground surface. Total of 32 moulded samples were prepared with constant water content to reflect the moisture condition in the active surface layer. Gray clay and clayey sand were analysed in the laboratory, and found to have the plastic limits (PL) of 33.01% and 22.56%, the liquid limits (LL) of 75.05% and 36.97%, and the plasticity indexes (PI) of 42.04% and 14.41%. The soil samples were classified as "CH" and "SC" in accordance with the unified soil classification system. Soil samples for all tests were placed in a freezer that has -18°C temperature. Samples have been waited in it for twenty-four hours. Then, they have been removed from the freezer and allowed to stand for twenty-four hours at a constant room temperature (21°C) and humidity (80% RH). As a result, one freezing and thawing cycle was achieved between -18°C (24 hours) and 21°C (24 hours), and it took two days. Freezing and thawing (FT) sequences were selected as 1, 3, 7, 14 and 21. After each FT sequence, Atterberg limits and consolidation tests were carried out in accordance with ASTM standards. Liquid and plastic limits of soil samples, suddenly, were decreased after first FT cycle. That state is a sign of the clay mineral orientation due to freezing and thawing process. The soil classification of clayey sand was changed from "SC" to "SM" after first FT cycle. Furthermore, the coefficient of consolidation and permeability of grey clay had been increased by rising in FT cycles up to 7 and then continue to

  2. Evaluation of Spaceborne L-band Radiometer Measurements for Terrestrial Freeze/Thaw Retrievals in Canada

    NASA Technical Reports Server (NTRS)

    Roy, A.; Royer, A.; Derksen, C.; Brucker, L.; Langlois, A.; Mailon, A.; Kerr, Y.

    2015-01-01

    The landscape freeze/thaw (FT) state has an important impact on the surface energy balance, carbon fluxes, and hydrologic processes; the timing of spring melt is linked to active layer dynamics in permafrost areas. L-band (1.4 GHz) microwave emission could allow the monitoring of surface state dynamics due to its sensitivity to the pronounced permittivity difference between frozen and thawed soil. The aim of this paper is to evaluate the performance of both Aquarius and Soil Moisture and Ocean Salinity (SMOS) L-band passive microwave measurements using a polarization ratio-based algorithm for landscape FT monitoring. Weekly L-band satellite observations are compared with a large set of reference data at 48 sites across Canada spanning three environments: tundra, boreal forest, and prairies. The reference data include in situ measurements of soil temperature (Tsoil) and air temperature (Tair), and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and snow cover area (SCA) products. Results show generally good agreement between Lband FT detection and the surface state estimated from four reference datasets. The best apparent accuracies for all seasons are obtained using Tair as the reference. Aquarius radiometer 2 (incidence angle of 39.6) data gives the best accuracies (90.8), while for SMOS the best results (87.8 of accuracy) are obtained at higher incidence angles (55- 60). The FT algorithm identifies both freeze onset and end with a delay of about one week in tundra and two weeks in forest and prairies, when compared to Tair. The analysis shows a stronger FT signal at tundra sites due to the typically clean transitions between consistently frozen and thawed conditions (and vice versa) and the absence of surface vegetation. Results in the prairies were poorer because of the influence of vegetation growth in summer (which decreases the polarization ratio) and the high frequency of ephemeral thaw events during winter. Freeze onset

  3. Microbial community response to permafrost thaw after wildfire in an Alaskan upland boreal forest

    NASA Astrophysics Data System (ADS)

    Tas, N.; Jorgenson, M. T.; Wang, S.; Berhe, A. A.; Wickland, K. P.; Waldrop, M. P.; Jansson, J. K.

    2012-12-01

    Fire is a major factor controlling the long-term dynamics of soil carbon in Alaskan boreal forests. Wildfire not only contributes to a significant global emission of greenhouse gasses but also can indirectly result in the deepening of the active layer and thawing of near-surface permafrost due to reductions in organic layer depth and increases in heat flux through soil. Although boreal ecosystems are fire-adapted, increased fire frequency and rising global temperatures may result in warmer soils and therefore increase the metabolic rates of decomposer microbes and result in accelerated permafrost decomposition and greenhouse gas fluxes. In addition to fire-mediated changes in soil and vegetation structure, changes in the soil microbial community structure are likely to have consequences for rates of soil carbon cycling. In this study we aimed to define the impact of fire on soil microbial communities in an upland black spruce forest and to assess microbial metabolic potential for soil respiration, methanogenesis, and nitrous oxide (N2O) flux. Soil samples from two fire impacted and three control (unburned) locations were collected near Nome Creek, AK, an upland moderately drained black spruce forest. This location was within the Boundary fire that burned between mid-June and the end of August 2004. Soil temperature measurements from before and after the fire showed that soils were warmer after the fire event and the permafrost thawed below 1m. At each sampling location, soil and permafrost samples were collected every 10 cm to a depth of 1 m. Besides biochemical characterization, CO2, CH4, N2O fluxes and potential activities of enzymes involved in extracellular decomposition of complex organic molecules (hemicellulose, chitin and lignin) were measured. The microbial community composition in the samples was determined by sequencing of 16S rRNA genes and microbial metabolic potential was assessed via sequencing of total genomic DNA (metagenomics) in selected active

  4. Effect of freezing and thawing rates on denaturation of proteins in aqueous solutions.

    PubMed

    Cao, Enhong; Chen, Yahuei; Cui, Zhanfeng; Foster, Peter R

    2003-06-20

    The freeze denaturation of model proteins, LDH, ADH, and catalase, was investigated in absence of cryoprotectants using a microcryostage under well-controlled freezing and thawing rates. Most of the experimental data were obtained from a study using a dilute solution with an enzyme concentration of 0.025 g/l. The dependence of activity recovery of proteins on the freezing and thawing rates showed a reciprocal and independent effect, that is, slow freezing (at a freezing rate about 1 degrees C/min) and fast thawing (at a thawing rate >10 degrees C/min) produced higher activity recovery, whereas fast freezing with slow thawing resulted in more severe damage to proteins. With minimizing the freezing concentration and pH change of buffer solution by using a potassium phosphate buffer, this phenomenon could be ascribed to surface-induced denaturation during freezing and thawing process. Upon the fast freezing (e.g., when the freezing rate >20 degrees C/min), small ice crystals and a relatively large surface area of ice-liquid interface are formed, which increases the exposure of protein molecules to the ice-liquid interface and hence increases the damage to the proteins. During thawing, additional damage to proteins is caused by recrystallization process. Recrystallization exerts additional interfacial tension or shear on the entrapped proteins and hence causes additional damage to the latter. When buffer solutes participated during freezing, the activity recovery of proteins after freezing and thawing decreased due to the change of buffer solution pH during freezing. However, the patterns of the dependence on freezing and thawing rates of activity recovery did not change except for that at extreme low freezing rates (<0.5 degrees C/min). The results exhibited that the freezing damage of protein in aqueous solutions could be reduced by changing the buffer type and composition and by optimizing the freezing-thawing protocol.

  5. Monodisperse, polymeric microspheres produced by irradiation of slowly thawing frozen drops

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu (Inventor); Hyson, Michael T. (Inventor); Chung, Sang-Kun (Inventor); Colvin, Michael S. (Inventor); Chang, Manchium (Inventor)

    1991-01-01

    Monodisperse, polymeric microspheres are formed by injecting uniformly shaped droplets of radiation polymerizable monomers, preferably a biocompatible monomer, having covalent binding sites such as hydroxyethylmethacrylate, into a zone, impressing a like charge on the droplet so that they mutually repel each other, spheroidizing the droplets within the zone and collecting the droplets in a pool of cryogenic liquid. As the droplets enter the liquid, they freeze into solid, glassy microspheres, which vaporizes a portion of the cryogenic liquid to form a layer. The like-charged microspheres, suspended within the layer, move to the edge of the vessel holding the pool, are discharged, fall and are collected. The collected microspheres are irradiated while frozen in the cryogenic liquid to form latent free radicals. The frozen microspheres are then slowly thawed to activate the free radicals which polymerize the monomer to form evenly-sized, evenly-shaped, monodisperse polymeric microspheres.

  6. Preservation of labile organic matter in soils of drained thaw lakes in Northern Alaska

    NASA Astrophysics Data System (ADS)

    Mueller, Carsten W.; Rethemeyer, Janet; Kao-Kniffin, Jenny; Löppmann, Sebastian; Hinkel, Kenneth; Bockheim, James

    2014-05-01

    A large number of studies predict changing organic matter (OM) dynamics in arctic soils due to global warming. In contrast to rather slowly altering bulk soil properties, single soil organic matter (SOM) fractions can provide a more detailed picture of the dynamics of differently preserved SOM pools in climate sensitive arctic regions. By the study of the chemical composition of such distinctive SOM fractions using nuclear magnetic resonance spectroscopy (NMR) together with radiocarbon analyses it is possible to evaluate the stability of the major OM pools. Approximately 50-75% of Alaska's Arctic Coastal Plain is covered with thaw lakes and drained thaw lakes that follow a 5,000 yr cycle of development (between creation and final drainage), thus forming a natural soil chronosequence. The drained thaw lakes offer the possibility to study SOM dynamics affected by permafrost processes over millennial timescales. In April 2010 we sampled 16 soil cores (including the active and permanent layer) reaching from young drained lakes (0-50 years since drainage) to ancient drained lakes (3000-5500 years since drainage). Air dried soil samples from soil horizons of the active and permanent layer were subjected to density fractionation in order to differentiate particulate OM and mineral associated OM. The chemical composition of the SOM fractions was analyzed by 13C CPMAS NMR spectroscopy. For a soil core of a young and an ancient drained thaw lake basin we also analyzed the 14C content. For the studied soils we can show that up to over 25 kg OC per square meter are stored mostly as labile, easily degradable organic matter rich in carbohydrates. In contrast only 10 kg OC per square meter were sequestered as presumably more stable mineral associated OC dominated by aliphatic compounds. Comparable to soils of temperate regions, we found small POM (< 20 µm) occluded in aggregated soil structures which differed in the chemical composition from larger organic particles. This was

  7. Temperature-activated layer-breathing vibrations in few-layer graphene.

    PubMed

    Lui, Chun Hung; Ye, Zhipeng; Keiser, Courtney; Xiao, Xun; He, Rui

    2014-08-13

    We investigated the low-frequency Raman spectra of freestanding few-layer graphene (FLG) at varying temperatures (400-900 K) controlled by laser heating. At high temperature, we observed the fundamental Raman mode for the lowest-frequency branch of rigid-plane layer-breathing mode (LBM) vibration. The mode frequency redshifts dramatically from 81 cm(-1) for bilayer to 23 cm(-1) for 8-layer. The thickness dependence is well described by a simple model of coupled oscillators. Notably, the LBM Raman response is unobservable at room temperature, and it is turned on at higher temperature (>600 K) with a steep increase of Raman intensity. The observation suggests that the LBM vibration is strongly suppressed by molecules adsorbed on the graphene surface but is activated as desorption occurs at high temperature.

  8. Passive and active control of boundary layer transition

    NASA Astrophysics Data System (ADS)

    Nosenchuck, Daniel Mark

    It is well known that laminar-turbulent boundary layer transition is initiated by the formation of Tollmien-Schlichting laminar instability waves. The amplification rates of these waves are strongly dependent on the shape of the boundary layer velocity profile. Consequently, the transition process can be controlled by modifying the velocity profile. This can be accomplished by controlling the pressure gradient (dp/dx), using boundary layer suction, installing surface roughness elements, or by surface heating or cooling. Methods used to modify the transition process through changes in the mean velocity profile are called "passive" in this paper. There exists a large set of experiments and theory on the application of passive methods for boundary layer control. In the present work only surface heating will be addressed.Transition measurements were made on a heated flat plate in water. Results are presented for several plate wall temperature distributions. An increase by a factor of 2.5 in transition Reynolds number was observed for a 5°C isothermal wall overheat. Buoyancy effects on transition were minimal due to the small Richardson and Grashof numbers encountered in the experiments.The amplification of laminar instability waves is comparatively to process, taking place over many boundary layer thicknesses. After the slow amplification of the laminar instability waves, transition occurs by a strong three dimensional dynamic instability. It appears possible to attenuate (or reinforce) the instability waves by introducing amplitude-and phase-controlled perturbations into the laminar boundary layer using feedback control system. This method is called "active" control and forms the larger part of the research reported in this thesis.A combination of sensors, activators and feedback control electronics is required for active control. The sensors used in the experiments are flush-mounted hot film wall shear robes. A new type of activator was developed using thin, flush

  9. The high resolution topographic evolution of an active retrogressive thaw slump compiled from a decade of photography, ground surveys, laser scans and satellite imagery

    NASA Astrophysics Data System (ADS)

    Crosby, B. T.; Barnhart, T. B.; Rowland, J. C.

    2015-12-01

    Remote sensing imagery has enables the temporal reconstruction of thermal erosion features including lakes, shorelines and hillslope failures in remote Arctic locations, yet these planar data limit analysis to lines and areas. This study explores the application of varying techniques to reconstruct the three dimensional evolution of a single thermal erosion feature using a mixture of opportunistic oblique photos, ground surveys and satellite imagery. At the Selawik River retrogressive thaw slump in northwest Alaska, a bush plane collected oblique aerial photos when the feature was first discovered in 2004 and in subsequent years. These images were recently processed via Structure from Motion to generate georeferenced point clouds for the years prior to the initiation of our research. High resolution ground surveys in 2007, 2009 and 2010 were completed using robotic total station. Terrestrial laser scans (TLS) were collected in the summers of 2011 and 2012. Analysis of stereo satellite imagery from 2012 and 2015 enable continued monitoring of the feature after ground campaigns ended. As accurate coregistraion between point clouds is vital to topographic change detection, all prior and subsequent datasets were georeferenced to stable features observed in the 2012 TLS scan. Though this coregistration introduces uncertainty into each image, the magnitudes of uncertainty are significantly smaller than the topographic changes detected. Upslope retreat of the slump headwall generally decreases over time as the slump floor progresses from a highly dissected gully topography to a low relief, earthflow dominated depositional plane. The decreasing slope of the slump floor diminishes transport capacity, resulting in the progressive burial of the slump headwall, thus decreasing headwall retreat rates. This self-regulation of slump size based on feature relief and transport capacity suggests a capacity to predict the maximum size a given feature can expand to before

  10. Active layer thermal monitoring of a Dry Valley of the Ellsworth Mountains, Continental Antarctica

    NASA Astrophysics Data System (ADS)

    Schaefer, Carlos Ernesto; Michel, Roberto; Souza, Karoline; Senra, Eduardo; Bremer, Ulisses

    2015-04-01

    The Ellsworth Mountains occur along the southern edge of the Ronne-Filchner Ice Shelf and are subdivided by the Minnesota Glacier into the Heritage Range to the east and the Sentinel Range to the West. The climate of the Ellsworth Mountains is strongly controlled by proximity to the Ronne-Filchner Ice Shelf and elevation. The mean annual air temperature at the 1,000 m level is estimated to be -25°C, and the average annual accumulation of water-equivalent precipitation likely ranges from 150 to 175 mm yr-1 (Weyant, 1966). The entire area is underlain by continuous permafrost of unknown thickness. Based on data collected from 22 pits, 41% of the sites contained dry permafrost below 70 cm, 27% had ice-cemented permafrost within 70 cm of the surface, 27% had bedrock within 70 cm, and 5% contained an ice-core (Bockheim, unpublished; Schaefer et al., 2015). Dry-frozen permafrost, which may be unique to Antarctica, appears to form from sublimation of moisture in ice-cemented permafrost over time. Active-layer depths in drift sheets of the Ellsworth Mountains range from 15 to 50 cm (Bockheim, unpublished); our understanding of Antarctic permafrost is poor, especially at the continent. The active layer monitoring sites were installed at Edson Hills, Ellsworth_Mountains, in the summer of 2012, and consist of thermistors (accuracy ± 0.2 °C) installed at 1 m above ground for air temperature measurements at two soil profiles on quartzite drift deposits, arranged in a vertical array (Lithic Haplorthel 886 m asl, 5 cm, 10 cm, 30 cm and Lithic Anyorthel 850 m asl, 5 cm, 10 cm, 30 cm). All probes were connected to a Campbell Scientific CR 1000 data logger recording data at hourly intervals from January 2nd 2012 until December 29th 2013. We calculated the thawing days (TD), freezing days (FD); isothermal days (ID), freeze thaw days (FTD), thawing degree days (TDD) and freezing degree days (FDD); all according to Guglielmin et al. (2008). Temperature at 5 cm reaches a maximum

  11. Study of the Northern Qinghai-Tibetan Plateau Permafrost Active Layer Depth Rate Using Satellite Geodetic Observations

    NASA Astrophysics Data System (ADS)

    Jia, Y.; Su, X.; Shum, C. K.; Kim, J. W.; Kuo, C. Y.

    2015-12-01

    The Tibetan Plateau is the world's largest and the highest plateau with distinct and competing surface and subsurface processes. It is the Third Pole and the World Water Tower, owing to its vast ice reservoir with the largest number of glaciers in the world, and covered by a large (1.3 to 1.6 million km2) layer of discontinuous and sporadic alpine permafrost. The thawing over Tibetan Plateau permafrost regions is thought to be more severe compared with other high latitude permafrost regions by the fact that the permafrost is warm. During the past few decades, 82% of Tibetan Plateau glaciers have retreated and 10% permafrost has degraded. The overall mean active layer depth (ALD) rate increase over the Plateau is 1.4 cm yr-1, 1980-2001, based on model studies and comparison with in situ borehole data. Here we report on the work in progress to quantify ALD rate increase in the northern Tibetan Plateau near the Tibetan national highway, using multi-band SAR/InSAR for improved the thermokarst surface classification, Envisat radar altimetry and ALOS-1 InSAR observed land subsidence, ALD modeling for the various thermokarst surface to relate to subsidence measurements, and the associated validations using available in situ borehole subsidence measurements.

  12. Active microwave remote sensing of an anisotropic random medium layer

    NASA Technical Reports Server (NTRS)

    Lee, J. K.; Kong, J. A.

    1985-01-01

    A two-layer anisotropic random medium model has been developed to study the active remote sensing of the earth. The dyadic Green's function for a two-layer anisotropic medium is developed and used in conjunction with the first-order Born approximation to calculate the backscattering coefficients. It is shown that strong cross-polarization occurs in the single scattering process and is indispensable in the interpretation of radar measurements of sea ice at different frequencies, polarizations, and viewing angles. The effects of anisotropy on the angular responses of backscattering coefficients are also illustrated.

  13. The Canadian Experiment for Freeze/Thaw in 2012 or 2013 CanEx-FT12 or FT13

    NASA Technical Reports Server (NTRS)

    Belair, Stephane; Bernier, Monique; Colliander, Andreas; Jackson, Thomas; McDonald, Kyle; Walker, Anne

    2011-01-01

    General objectives of the experiment are: Pre-launch Calibration/Validation of SMAP Freeze/Thaw products and retrieval algorithms and rehearsal for Soil Moisture Active-Passive (SMAP) post launch validation. The basis of the radar freeze-thaw measurement is the large shift in dielectric constant and backscatter (dB) between predominantly frozen & thawed conditions. The Dielectric constant of liquid water varies with frequency, whereas that of pure ice is constant

  14. Last Decade of Changes in Ground Temperature and Active Layer Thickness in the High Canadian Arctic and in Barrow

    NASA Astrophysics Data System (ADS)

    Romanovsky, V. E.; Cable, W.; Walker, D. A.; Yoshikawa, K.; Marchenko, S. S.

    2013-12-01

    The impact of climate warming on permafrost and the potential of climate feedbacks resulting from permafrost thawing have recently received a great deal of attention. Most of the permafrost observatories in the Northern Hemisphere show substantial warming of permafrost since circa 1980-1990. The magnitude of warming has varied with location, but was typically from 0.5 to 2°C. Permafrost is already thawing within the southern part of the permafrost domain. However, recent observations documented propagation of this process northward into the continuous permafrost zone. The close proximity of the exceptionally icy soil horizons to the ground surface, which is typical for the arctic tundra biome, makes tundra surfaces extremely sensitive to the natural and human-made changes that may resulted in development of processes such as thermokarst, thermal erosion, and retrogressive thaw slumps that strongly affect the stability of ecosystems and infrastructure. In 2003-2005, three Ecological Permafrost Observatories where established in the High Canadian Arctic (Green Cabin on the Banks Island, Mould Bay on the Prince Patrick Island, and Isachsen on the Ellef Ringnes Island) as a part of the University of Alaska Fairbanks NSF funded Biocomplexity Project. These observatories represent the northern part of the North American Arctic Transect (NAAT) established as a result of this project. The climatic and ground temperature data collected at these observatories show a general warming trend similar to what has been observed at the other locations in the North American Arctic. An important result of this resent warming is a significant increase in the active layer thickness (ALT) during the last decade. For example, ALT at the Isachsen observatory increased from 0.4-0.42 m in 2005 to 0.54 m in 2012. The maximum ALT of 0.58 m was recorded in 2008. In a shallow excavation across an ice wedge at the Isachsen site, we estimated that the top of the ice wedge ice was located at 42

  15. The effect of vegetation type and fire on permafrost thaw: An empirical test of a process based model

    NASA Astrophysics Data System (ADS)

    Thierry, Aaron; Estop-Aragones, Cristian; Fisher, James; Hartley, Iain; Murton, Julian; Phoenix, Gareth; Street, Lorna; Williams, Mathew

    2015-04-01

    As conditions become more favourable for plant growth in the high latitudes, most models predict that these areas will take up more carbon during the 21st century. However, vast stores of carbon are frozen in boreal and arctic permafrost, and warming may result in some of this carbon being released to the atmosphere. The recent inclusion of permafrost thaw in large-scale model simulations has suggested that the permafrost feedback could potentially substantially reduce the predicted global net uptake of carbon by terrestrial ecosystems, with major implications for the rate of climate change. However, large uncertainties remain in predicting rates of permafrost thaw and in determining the impacts of thaw in contrasting ecosystems, with many of the key processes missing from carbon-climate models. The role that different plant communities play in insulating soils and protecting permafrost is poorly quantified, with key groups such as mosses absent in many models. But it is thought that they may play a key role in determining permafrost resilience. In order to test the importance of these ecological processes we use a new specially acquired dataset from sites in the Canadian arctic to develop, parameterise and evaluate a detailed process-based model of vegetation-soil-permafrost interactions which includes an insulating moss understory. We tested the sensitivity of modelled active layer depth to a series of factors linked to fire disturbance, which is common in boreal permafrost areas. We show how simulations of active layer depth (ALD) respond to removals of (i) vascular vegetation, (ii) moss cover, and (iii) organic soil layers. We compare model responses to observed patterns from Canada. We also describe the sensitivity of our modelled ALD to changes in temperature and precipitation. We found that four parameters controlled most of the sensitivity in the modelled ALD, linked to conductivity of organic soils and mosses.

  16. Thaw bulb dimensions determined using electrical imaging across thermokarst lakes, Seward Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    Nolan, J. T.; Slater, L. D.; Parsekian, A.; Plug, L. J.; Grosse, G.; Walter Anthony, K. M.

    2009-12-01

    Geophysical imaging of thaw bulb dimensions underlying thermokarst lakes may provide data required to validate models for thaw bulb evolution and to quantify availability of previously frozen soil carbon to atmospheric emission. Direct measurements by drilling are costly in remote arctic regions and are limited by poor spatial resolution. We report the results of an experiment to test the use of electrical resistivity imaging for determining thaw bulb dimensions of thermokarst lakes on the Seward Peninsula, Alaska. Continuous resistivity measurements were collected using a floating array of electrodes pulled by a motorized inflatable boat. The inversion of the resistivity data was conducted using a one dimensional laterally constrained inversion routine that solves for thickness and resistivity based on three layer model. Since the water layer is partly constrained in terms of thickness (from depth sounder measurements) and resistivity (from measurements made with a conductance probe), and the thaw bulb and permafrost resistivity are known from coring, the only totally unconstrained parameter is the thickness of the thaw bulb sediments. This overdetermined inverse problem yields a high degree of confidence in the resulting model, as evident from low model residuals and parameter covariance analysis. Results from this experiment show that electrical resistivity imaging is a relatively low cost method for determining the thaw bulb dimensions along a laterally continuous survey line.

  17. Fate and Transport of Methane Formed in the Active Layer of Alaskan Permafrost

    NASA Astrophysics Data System (ADS)

    Conrad, M. E.; Curtis, J. B.; Smith, L. J.; Bill, M.; Torn, M. S.

    2015-12-01

    Over the past 2 years a series of tracer tests designed to estimate rates of methane formation via acetoclastic methanogenesis in the active layer of permafrost soils were conducted at the Barrow Environmental Observatory (BEO) in northernmost Alaska. The tracer tests consisted of extracting 0.5 to 1.0 liters of soil water in gas-tight bags from different features of polygons at the BEO, followed by addition of a tracer cocktail including acetate with a 13C-labeled methyl group and D2O (as a conservative tracer) into the soil water and injection of the mixture back into the original extraction site. Samples were then taken at depths of 30 cm (just above the bottom of the active layer), 20 cm, 10 cm and surface flux to determine the fate of the 13C-labeled acetate. During 2014 (2015 results are pending) water, soil gas, and flux gas were sampled for 60 days following injection of the tracer solution. Those samples were analyzed for concentrations and isotopic compositions of CH4, DIC/CO2 and water. At one site (the trough of a low-centered polygon) the 13C acetate was completely converted to 13CH4 within the first 2 days. The signal persisted for throughout the entire monitoring period at the injection depth with little evidence of transport or oxidation in any of the other sampling depths. In the saturated center of the same polygon, the acetate was also rapidly converted to 13CH4, but water turnover caused the signal to rapidly dissipate. High δ13C CO2 in flux samples from the polygon center indicate oxidation of the 13CH4 in near-surface waters. Conversely, CH4 production in the center of an unsaturated, flat-centered polygon was relatively small 13CH4 and dissipated rapidly without any evidence of either 13CH4 transport to shallower levels or oxidation. At another site in the edge of that polygon no 13CH4 was produced, but significant 13CO2/DIC was observed indicating direct aerobic oxidation of the acetate was occurring at this site. These results suggest that

  18. The impacts of permafrost thaw on land-atmosphere greenhouse gas exchange

    SciTech Connect

    Hayes, Daniel J; Kicklighter, David W.; McGuire, A. David; Chen, Min; Zhuang, Qianlai; Yuan, Fengming; Melillo, Jerry; Wullschleger, Stan

    2014-01-01

    Permafrost thaw and the subsequent mobilization of carbon stored in previously frozen soil organic matter (SOM) would be a strong positive feedback to climate1. As the northern permafrost region experiences double the rate of warming as the rest of the Earth2, the vast amount of carbon in permafrost soils3 is vulnerable to thaw, decomposition and release as atmospheric greenhouse gases (GHG). Here, we employ a process-based model simulation experiment to assess the net effect of this so-called permafrost carbon feedback (PCF) in recent decades. Results show a wide-spread increase in the depth to permafrost between 1990 and 2006, with simulated active layer thickness (ALT) capturing the mean and spatial variability of the observational data. Analysis of the simulation experiment provides an estimate of a 2.8 mm/yr increase in permafrost depth, which translates to 281 TgC/yr thawed from previously frozen SOM. Overall, we estimate a net GHG forcing of 534 MtCO2eq/yr directly tied to ALT dynamics, while accounting for CO2 (562 MtCO2eq/yr) and CH4 (52 MtCO2eq/yr) release as well as CO2 uptake by vegetation (-80 MtCO2eq/yr). This net forcing represents a significant factor in the estimated 640 MtCO2eq/yr pan-arctic GHG source4, and an additional 6.9% contribution on top of the combined 7792 MtCO2eq/yr fossil fuel emissions from the eight Arctic nations over this time period5.

  19. Changes in Soil Nitrogen Availability Associated with Permafrost Thaw

    NASA Astrophysics Data System (ADS)

    Salmon, V. G.; Natali, S.; Crummer, K. G.; Mack, M. C.; Schuur, E. A.

    2013-12-01

    The globally significant size of the permafrost carbon (C) pool reflects the balance between soil decomposition and plant growth in high latitude ecosystems. Projected increases in mean annual temperatures in these cold systems are expected to increase rates of both of these processes. As the nutrient limiting plant productivity in high latitude ecosystems, nitrogen (N) is expected to play a key role in determining the future balance between permafrost C losses and increased C sequestration by plants. In this experiment a tundra ecosystem in interior Alaska was subjected to soil and air warming treatments for five years. Soil warming was executed using an insulating snow pack that was removed prior to spring thaw while air warming was achieved using open top chambers deployed during the growing season. Soil warming treatments increased growing season thaw depth by 9 cm and increased soil temperature by 4°C. Air warming treatments raised air temperatures by 0.5°C. To assess N availability across treatments, anion and cation binding resins were deployed during the fourth and fifth years of warming manipulations at a depth of 10cm. Analysis of resin extracts indicated that inorganic N availability of surface soils increased significantly with soil warming but did not significantly change from control levels when soil and air warming treatments were combined. Resins from control plots had 5.2 μg N per g dry resin in the form of ammonium and nitrate while resins from soil warmed plots had 10.7 μg N per g dry resin. Resins from combined soil and air warming plots had 7.3 μg N per g dry resin. Changes in inorganic N availability were partially explained by changes in environmental variables (active layer depth, soil temperature, and soil moisture). Nondestructive methods were used to survey aboveground plant biomass and are combined with %N analysis of live and senesced plant tissues. The resulting estimates of aboveground plant N pools and fluxes of litter N into

  20. Mechanism of freeze-thaw instability of aluminum hydroxycarbonate and magnesium hydroxide gels.

    PubMed

    Zapata, M I; Feldkamp, J R; Peck, G E; White, J L; Hem, S L

    1984-01-01

    The effect of freeze-thaw cycles on the physical stability of aluminum hydroxycarbonate and magnesium hydroxide gels was studied. Coagulation following a freeze-thaw cycle, leading to the formation of visible aggregates, affected the content uniformity of both gels. The freeze-thaw cycles did not affect the crystal form or surface characteristics of the gels as determined by X-ray powder diffraction and point of zero charge, but caused a slight reduction in the rate of acid neutralization and a large increase in the rate of sedimentation. The greatest effect was observed after the first freeze-thaw cycle. While the duration of freezing was not a factor, the rate of freezing was important and was inversely related to the aggregate size. The aggregates which formed following a freeze-thaw cycle were not redispersed by shaking, but were reversed by ultrasonic treatment or homogenization. The adsorption of polymers or surface-active agents prior to freezing reduced and, in some cases, prevented the formation of aggregates. The physical instability produced by a freeze-thaw cycle was explained by the modified DLVO theory. The force exerted on the particles by the growing ice crystals forced the particles into the primary minimum, producing strong interparticle attraction. On thawing, simple agitation did not provide enough force to overcome the attractive force of the primary minimum. Adsorption of polymers or surface-active agents increased the steric repulsive force and prevented the particles from reaching the primary minimum. PMID:6694078

  1. Active layer hydrology for Imnavait Creek, Toolik, Alaska

    SciTech Connect

    Kane, D.L.

    1986-01-01

    In the annual hydrologic cycle, snowmelt is the most significant event at Imnavait Creek located near Toolik Lake, Alaska. Precipitation that has accumulated for more than 6 months on the surface melts in a relatively short period of 7 to 10 days once sustained melting occurs. During the ablation period, runoff dominates the hydrologic cycle. Some meltwater goes to rewetting the organic soils in the active layer. The remainder is lost primarily because of evaporation, since transpiration is not a very active process at this time. Following the snowmelt period, evapotranspiration becomes the dominate process, with base flow contributing the other watershed losses. It is important to note that the water initally lost by evapotranspiration entered the organic layer during melt. This water from the snowpack ensures that each year the various plant communities will have sufficient water to start a new summer of growth.

  2. Layered shielding design for an active neutron interrogation system

    NASA Astrophysics Data System (ADS)

    Whetstone, Zachary D.; Kearfott, Kimberlee J.

    2016-08-01

    The use of source and detector shields in active neutron interrogation can improve detector signal. In simulations, a shielded detector with a source rotated π/3 rad relative to the opening decreased neutron flux roughly three orders of magnitude. Several realistic source and detector shield configurations were simulated. A layered design reduced neutron and secondary photon flux in the detector by approximately one order of magnitude for a deuterium-tritium source. The shield arrangement can be adapted for a portable, modular design.

  3. The Role of Snow Cover in Affecting Pan-Arctic Soil Freeze/Thaw and Carbon Dynamics

    NASA Astrophysics Data System (ADS)

    Yi, Y.; Kimball, J. S.; Rawlins, M. A.; Moghaddam, M.; Euskirchen, E. S.

    2015-12-01

    Satellite data records spanning the past 3 decades indicate widespread reductions (~0.8-1.3 days decade-1) in mean annual snow cover and frozen season duration across the pan-Arctic domain, coincident with regional climate warming. How the northern soil carbon pool responds to these changes will have a large impact on projected regional and global climate trends. The objective of this study was to assess how northern soil thermal and carbon dynamics respond to changes in surface snow cover and freeze/thaw (F/T) cycles indicated from satellite observations. We developed a coupled permafrost, hydrology and carbon model framework to investigate the sensitivity of soil organic carbon stocks and soil decomposition to recent climate variations across the pan-Arctic region from 1982 to 2010. The model simulations were also evaluated against satellite observation records on snow cover and F/T processes. Our results indicate that surface warming promotes wide-spread soil thawing and active layer deepening due to strong control of surface air temperature on upper (<0.5 m) soil temperatures during the warm season. Earlier spring snowmelt and shorter seasonal snow cover duration with regional warming will mostly likely enhance soil warming in warmer climate zones (mean annual Tair>-5°C) and promote permafrost degradation in these areas. Our results also show that seasonal snow cover has a large impact on soil temperatures, whereby increases in snow cover promote deeper (≥0.5 m) soil layer warming and soil respiration, while inhibiting soil decomposition from surface (≤0.2 m) soil layers, especially in colder climate zones (mean annual Tair≤-10 °C). This non-linear relationship between snow cover and soil decomposition is particularly important in permafrost areas, where a large amount of soil carbon is stored in deep perennial frozen soils that are potentially vulnerable to thawing, with resulting mobilization and accelerated carbon losses from near-term climate change.

  4. Mobilization of stable organic carbon in thawing permafrost by fresh organic matter from recent vegetation

    NASA Astrophysics Data System (ADS)

    Knoblauch, C.; Beer, C.; Pfeiffer, E. M.

    2015-12-01

    Permafrost affected soils contain 1,300 Pg organic carbon which is about twice the amount of the global vegetation. Most of this carbon (C) is locked in the perennially frozen ground (permafrost) and only a minor part is stored in the seasonal surface thaw layer (active layer). Rising arctic temperatures will cause deeper active layer thaw and permafrost degradation, which liberates additional soil organic matter (SOM) for microbial mineralization. After thaw, old permafrost C will be mixed with fresh organic matter from plant residues, e.g. by cryoturbation or leaching. Recent incubation studies have increased our understanding on how fast permafrost SOM may be mineralized to the greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4). After initial maximum GHG production from labile SOM components (labile C pool) mineralization rates slow down since the remaining SOM is more recalcitrant (stable C pool). The current study investigates if this stabile C pool may be mobilized by fresh organic matter from recent vegetation ("priming effect"). Therefore, permafrost samples (14C ages 0.1 - 17 ka BP) from the Siberian tundra were spiked with a 13C-labeled sedge (Carex aquatilis) after the samples were pre-incubated for 4 years. The amount of C released from permafrost SOM was calculated from the δ13C-values of produced GHG using a mixing model. Under aerobic conditions, all samples showed an accelerated mineralization of SOM after the addition of C. aquatilis (positive priming). After 4 months, which is about one vegetation period, the measured CO2 production exceeded the estimated CO2 release without labile plant material by 60 ± 28%. Under anaerobic conditions, priming was more pronounced increasing CO2 production by 100 ± 67% and CH4 production by 33 ± 32%. The CO2/CH4 ratio increased from 0.9 before priming to 1.3 after priming. The total mineralization of SOM over 4 months was significantly higher under aerobic (14.2 ± 6.1 μmol CO2-C gdw-1) than under

  5. Moisture drives surface decomposition in thawing tundra

    NASA Astrophysics Data System (ADS)

    Hicks Pries, Caitlin E.; Schuur, E. A. G.; Vogel, Jason G.; Natali, Susan M.

    2013-07-01

    Permafrost thaw can affect decomposition rates by changing environmental conditions and litter quality. As permafrost thaws, soils warm and thermokarst (ground subsidence) features form, causing some areas to become wetter while other areas become drier. We used a common substrate to measure how permafrost thaw affects decomposition rates in the surface soil in a natural permafrost thaw gradient and a warming experiment in Healy, Alaska. Permafrost thaw also changes plant community composition. We decomposed 12 plant litters in a common garden to test how changing plant litter inputs would affect decomposition. We combined species' tissue-specific decomposition rates with species and tissue-level estimates of aboveground net primary productivity to calculate community-weighted decomposition constants at both the thaw gradient and warming experiment. Moisture, specifically growing season precipitation and water table depth, was the most significant driver of decomposition. At the gradient, an increase in growing season precipitation from 200 to 300 mm increased mass loss of the common substrate by 100%. At the warming experiment, a decrease in the depth to the water table from 30 to 15 cm increased mass loss by 100%. At the gradient, community-weighted decomposition was 21% faster in extensive than in minimal thaw, but was similar when moss production was included. Overall, the effect of climate change and permafrost thaw on surface soil decomposition are driven more by precipitation and soil environment than by changes to plant communities. Increasing soil moisture is thereby another mechanism by which permafrost thaw can become a positive feedback to climate change.

  6. Surface activation of CNT Webs towards layer by layer assembly of biosensors.

    PubMed

    Musameh, Mustafa; Huynh, Chi P; Hickey, Mark; Kyratzis, Ilias Louis

    2016-04-25

    Several surface activation methods such as chemical, electrochemical and plasma have been used for enhancing the electrochemical performance of carbon based electrodes for various applications. However, some of these surface activation methods may not be useful depending on the chemical and physical properties of the activated surface. Herein we investigate the surface activation of carbon nanotube (CNT) webs by electrochemical and plasma techniques to enhance their electrochemical performance and enable the fabrication of a biosensor using the layer-by-layer (LBL) approach. The pretreated CNT webs were characterized by SEM, TEM, Raman, XPS and electrochemical methods. TEM images and Raman analysis showed an increase in the level of surface defects upon pretreatment with higher number of defects after electrochemical pretreatment. XPS analysis showed an increase in the level of oxygen functional groups after pretreatment (4 to 5 times increase) which resulted in enhanced water wettability especially for plasma pretreated CNT webs. The pretreated CNT web electrodes also showed an enhanced electrochemical activity towards the oxidation and reduction of different redox probes with higher sensitivity for the electrochemically pretreated CNT web electrode that was accompanied by a higher level of noise in amperometric measurements. A highly linear response was obtained for the untreated and the electrochemically pretreated CNT web electrodes towards the amperometric detection of NADH (R(2) of 0.9996 and 0.9986 respectively) while a non-linear response was observed for the plasma pretreated CNT web electrode (R(2) of 0.8538). The pretreated CNT web electrodes enabled the fabrication of a LBL biosensor for alcohol detection with highest operational stability obtained for the plasma pretreated CNT web surface.

  7. [Dynamic change of dissolved iron in wetland soil solutions responding to freeze-thaw cycles].

    PubMed

    Yu, Xiao-fei; Wang, Guo-ping; Lü, Xian-guo; Zou, Yuan-chun; Jiang, Ming

    2010-05-01

    The effects of five freeze-thaw cycles on the dynamic change of dissolved iron in three typical wetland soils (humus marsh soil in Carex lasiocarpa community, meadow marsh soil in Cares meyeriarna community, and meadow albic soil in Calamagrostis angustifolia community)of Sanjiang Plain, Northeast China, was analyzed through in-situ soil column simulation. One freeze-thaw cycle was conducted as freezing at -10 degrees C for 1 d and then thawing at 5 degrees C for 7 d. The thermostatically incubated soils at 5 degrees C were controls. The results showed that most pH and Eh values increased after the first freeze-thaw cycle, and then decreased after the subsequent cycles. 84.4% of the pH values of freeze-thaw treated soils were smaller than that of control, while 82.2% of the Eh values of freeze-thaw treated soils were greater than that of control. Most of the dissolved iron in all soil solutions were Fe3+ ions and colloids, and the reduction of these Fe3+ species were inhibited. The concentrations of Fe2, Fe3+, and total dissolved iron (TFe) of the freeze-thaw treated soils were all smaller than that of controls, with the means of (0.62 +/- 0.08) mg x L(-1) and (1.25 +/- 0.16) mg x L(-1), respectively. The variation trends of pH, Eh, and dissolved iron in the humus marsh soil were significantly different from that in the meadow albic soil. The trends in the meadow marsh soil, as the transitional soil type, were more similar to the meadow albic soil for pH, while more similar to the humus marsh soil for Eh and dissolved iron. Among the three soils, the difference between freeze-thaw treated columns and controls of the second layer were all smaller than that of the third and fourth layer, which indicated that the effect of freeze-thaw cycles were more significant for the upper annular wetland soil layers than the lower layers.

  8. Experiments on the active control of transitional boundary layers

    NASA Astrophysics Data System (ADS)

    Nelson, P. A.; Rioual, J.-L.; Fisher, M. J.

    Experimental results are presented which demonstrate that the streamwise position of the transition region of a flat plate boundary layer can be actively controlled. The means of control is through the application of suction through the surface of the plate, a progressive increase in suction rate being capable of producing transition at progressively larger distances downstream from the plate leading edge. A simple digital feedback regulator based on an integral control law is shown to be most effective in regulating the position of transition, an error signal being derived from measurements of pressure fluctuations on the surface of the plate.

  9. Effect of soil property uncertainties on permafrost thaw projections: a calibration-constrained analysis

    NASA Astrophysics Data System (ADS)

    Harp, D. R.; Atchley, A. L.; Painter, S. L.; Coon, E. T.; Wilson, C. J.; Romanovsky, V. E.; Rowland, J. C.

    2016-02-01

    The effects of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The null-space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21st century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows for the evaluation of predictive uncertainty (due to soil property (parametric) uncertainty) and the inter-annual climate variability due to year to year differences in CESM climate forcings. After calibrating to measured borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant predictive uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Inter-annual climate variability in projected soil moisture content and Stefan number are small. A volume- and time-integrated Stefan number decreases significantly, indicating a shift in subsurface energy utilization in the future climate (latent heat of phase change becomes more important than heat conduction). Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we quantify the relative magnitude of soil

  10. Optical activity of transparent polymer layers characterized by spectral means

    NASA Astrophysics Data System (ADS)

    Cosutchi, Andreea Irina; Dimitriu, Dan Gheorghe; Zelinschi, Carmen Beatrice; Breaban, Iuliana; Dorohoi, Dana Ortansa

    2015-06-01

    The method based on the channeled spectrum, validated for inorganic optical active layers, is used now to determine the optical activity of some transparent polymer solutions in different solvents. The circular birefringence, the dispersion parameter and the specific rotation were estimated in the visible range by using the measurements of wavelengths in the channeled spectra of Hydroxypropyl cellulose in water, methanol and acetic acid. The experiments showed the specific rotation dependence on the polymer concentration and also on the solvent nature. The decrease of the specific rotation in the visible range with the increase in wavelength was evidenced. The method has some advantages as the rapidity of the experiments and the large spectral range in which it can be applied. One disadvantage is the fact that the channeled spectrum does not allow to establish the rotation sense of the electric field intensity.

  11. Impact of Climate and Fires on Abrupt Permafrost Thaw in Alaskan Tundra

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Reents, C.; Greenberg, J. A.; Hu, F.

    2015-12-01

    Thermo-erosion from abrupt permafrost thaw is a key pulse disturbance in the Arctic that may impact the global carbon cycle. Abrupt thaw can occur when the permafrost active layer expands in response to climate warming and/or increased wildfire activity. Understanding these drivers of thermo-erosion is necessary to anticipate feedbacks in the Arctic, where summer temperature and fire frequency are predicted to increase. We examine modern and late-Holocene thermo-erosion in high-fire (Noatak) and low-fire (North Slope) tundra ecoregions of Alaska using a combination of remote-sensing and paleo-records. Lakes with active thaw features were identified through Landsat-7 image classification and time-series analysis based on observed 0.52-0.60 μm reflectance peaks following slump formation. We identified 1067 and 1705 lakes with active features between CE 2000-2012 in the Noatak and North Slope ecoregions, respectively. The density of features was higher in the highly flammable Noatak (0.04 versus 0.01 features km-2, respectively), suggesting that warmer climate and/or fires likely promote high thermo-erosional activity at present. To assess modern signals of thermo-erosion and identify past events, we analyzed soil profiles and lake-sediment cores from both ecoregions using X-ray fluorescence. The ratios of Ca:K and Ca:Sr increased with depth in permafrost soils, were higher in soils from younger versus older slump surfaces, and were significantly correlated with the ratio of carbonate to feldspar and clay minerals in lake sediments (r=0.96 and 0.93, P<0.0001, n=15). We interpret past increases in Ca:K, Ca:Sr, and δ13C as enhanced weathering of carbonate-rich permafrost soils associated with thermo-erosion. At the North Slope site, we identified ten episodes of thermoerosion over the past 6000 years and found strong correspondence to summer temperature trends. Events were more frequent at the Noatak site, where 15 thermo-erosional episodes and 26 fires occurred over

  12. Assessment of Climate Driven Dynamics of Active Layer, Hydrological and Vegetation Status at the Qinghai-Tibet Plateau Using Dynamic Global Vegetation Model

    NASA Astrophysics Data System (ADS)

    Yang, Y.

    2014-12-01

    Extensive permafrost degradation starting from 1970s is observed at the Qinghai-Tibet Plateau , China. Degradation is attributed to an increase in mean annual ground temperature 0.1◦-0.5◦ C with mainly winter warming. The construction of Qinghai-Tibet Railway also influenced a state of permafrost in the area Permafrost degradation caused negative environmental consequences in the area. The areas covered by sand are expanding steadily making large concern of accelerating desertification. The general pathway of future joint dynamics of permafrost, vegetation and hydrological status at the Qinghai-Tibet Plateau is still poorly understood and foreseeable. Hydrology in the area is determined by heat-moisture dynamics of active layer. This dynamics is highly non-linear and depends as on external climatic variables temperature and precipitation, so on soil and rock properties (amount of sand against aeolian deposits in the Plateau) as well as vegetation cover, which determine thaw and freeze processes in the active layer and evaporation and run-off. SEVER DGVM was modified to include heat-moisture dynamics of active layer in the Qinghai-Tibet Plateau. SEVER DGVM imitates processes in 10 plant functional types at coarse resolution of 0.5 degrees. This model imitates behavior of average individual of each plant type in each grid cell through simulation years. Each of those grid cells processed independently. First, this model starts from "bare soil", placing a bit of each plant type and giving them some time to grow and achieve equilibrium. Then, including active layer thickness and soil moisture dynamics into this layer, it allows assessment of potential environmental dynamics in this area. Simulations demonstrate further degradation of pastureland and accelerating desertification processes in this vitally important water feed area for many Asian rivers. Negative environmental problems related to operation of Qinghai-Tibet are also assessed.

  13. Insufficiency of copper ion homeostasis causes freeze-thaw injury of yeast cells as revealed by indirect gene expression analysis.

    PubMed

    Takahashi, Shunsuke; Ando, Akira; Takagi, Hiroshi; Shima, Jun

    2009-11-01

    Saccharomyces cerevisiae is exposed to freeze-thaw stress in commercial processes, including frozen dough baking. Cell viability and fermentation activity after a freeze-thaw cycle were dramatically decreased due to freeze-thaw injury. Because this type of injury involves complex phenomena, the injury mechanisms are not fully understood. We examined freeze-thaw injury by indirect gene expression analysis during postthaw incubation after freeze-thaw treatment using DNA microarray profiling. The results showed that genes involved in the homeostasis of metal ions were frequently contained in genes that were upregulated, depending on the freezing period. We assessed the phenotype of deletion mutants of the metal ion homeostasis genes that exhibited freezing period-dependent upregulation and found that the strains with deletion of the MAC1 and CTR1 genes involved in copper ion homeostasis exhibited freeze-thaw sensitivity, suggesting that copper ion homeostasis is required for freeze-thaw tolerance. We found that supplementation with copper ions during postthaw incubation increased intracellular superoxide dismutase activity and intracellular levels of reactive oxygen species were decreased. Moreover, cell viability was increased by supplementation with copper ions. These results suggest that insufficiency of copper ion homeostasis may be one of the causes of freeze-thaw injury. PMID:19749072

  14. The transcriptional response of microbial communities in thawing Alaskan permafrost soils

    PubMed Central

    Coolen, Marco J. L.; Orsi, William D.

    2015-01-01

    Thawing of permafrost soils is expected to stimulate microbial decomposition and respiration of sequestered carbon. This could, in turn, increase atmospheric concentrations of greenhouse gasses, such as carbon dioxide and methane, and create a positive feedback to climate warming. Recent metagenomic studies suggest that permafrost has a large metabolic potential for carbon processing, including pathways for fermentation and methanogenesis. Here, we performed a pilot study using ultrahigh throughput Illumina HiSeq sequencing of reverse transcribed messenger RNA to obtain a detailed overview of active metabolic pathways and responsible organisms in up to 70 cm deep permafrost soils at a moist acidic tundra location in Arctic Alaska. The transcriptional response of the permafrost microbial community was compared before and after 11 days of thaw. In general, the transcriptional profile under frozen conditions suggests a dominance of stress responses, survival strategies, and maintenance processes, whereas upon thaw a rapid enzymatic response to decomposing soil organic matter (SOM) was observed. Bacteroidetes, Firmicutes, ascomycete fungi, and methanogens were responsible for largest transcriptional response upon thaw. Transcripts indicative of heterotrophic methanogenic pathways utilizing acetate, methanol, and methylamine were found predominantly in the permafrost table after thaw. Furthermore, transcripts involved in acetogenesis were expressed exclusively after thaw suggesting that acetogenic bacteria are a potential source of acetate for acetoclastic methanogenesis in freshly thawed permafrost. Metatranscriptomics is shown here to be a useful approach for inferring the activity of permafrost microbes that has potential to improve our understanding of permafrost SOM bioavailability and biogeochemical mechanisms contributing to greenhouse gas emissions as a result of permafrost thaw. PMID:25852660

  15. The transcriptional response of microbial communities in thawing Alaskan permafrost soils.

    PubMed

    Coolen, Marco J L; Orsi, William D

    2015-01-01

    Thawing of permafrost soils is expected to stimulate microbial decomposition and respiration of sequestered carbon. This could, in turn, increase atmospheric concentrations of greenhouse gasses, such as carbon dioxide and methane, and create a positive feedback to climate warming. Recent metagenomic studies suggest that permafrost has a large metabolic potential for carbon processing, including pathways for fermentation and methanogenesis. Here, we performed a pilot study using ultrahigh throughput Illumina HiSeq sequencing of reverse transcribed messenger RNA to obtain a detailed overview of active metabolic pathways and responsible organisms in up to 70 cm deep permafrost soils at a moist acidic tundra location in Arctic Alaska. The transcriptional response of the permafrost microbial community was compared before and after 11 days of thaw. In general, the transcriptional profile under frozen conditions suggests a dominance of stress responses, survival strategies, and maintenance processes, whereas upon thaw a rapid enzymatic response to decomposing soil organic matter (SOM) was observed. Bacteroidetes, Firmicutes, ascomycete fungi, and methanogens were responsible for largest transcriptional response upon thaw. Transcripts indicative of heterotrophic methanogenic pathways utilizing acetate, methanol, and methylamine were found predominantly in the permafrost table after thaw. Furthermore, transcripts involved in acetogenesis were expressed exclusively after thaw suggesting that acetogenic bacteria are a potential source of acetate for acetoclastic methanogenesis in freshly thawed permafrost. Metatranscriptomics is shown here to be a useful approach for inferring the activity of permafrost microbes that has potential to improve our understanding of permafrost SOM bioavailability and biogeochemical mechanisms contributing to greenhouse gas emissions as a result of permafrost thaw.

  16. Bacterial community structure across environmental gradients in permafrost thaw ponds: methanotroph-rich ecosystems

    PubMed Central

    Crevecoeur, Sophie; Vincent, Warwick F.; Comte, Jérôme; Lovejoy, Connie

    2015-01-01

    Permafrost thawing leads to the formation of thermokarst ponds that potentially emit CO2 and CH4 to the atmosphere. In the Nunavik subarctic region (northern Québec, Canada), these numerous, shallow ponds become well-stratified during summer. This creates a physico-chemical gradient of temperature and oxygen, with an upper oxic layer and a bottom low oxygen or anoxic layer. Our objective was to determine the influence of stratification and related limnological and landscape properties on the community structure of potentially active bacteria in these waters. Samples for RNA analysis were taken from ponds in three contrasting valleys across a gradient of permafrost degradation. A total of 1296 operational taxonomic units were identified by high throughput amplicon sequencing, targeting bacterial 16S rRNA that was reverse transcribed to cDNA. β-proteobacteria were the dominant group in all ponds, with highest representation by the genera Variovorax and Polynucleobacter. Methanotrophs were also among the most abundant sequences at most sites. They accounted for up to 27% of the total sequences (median of 4.9% for all samples), indicating the importance of methane as a bacterial energy source in these waters. Both oxygenic (cyanobacteria) and anoxygenic (Chlorobi) phototrophs were also well-represented, the latter in the low oxygen bottom waters. Ordination analyses showed that the communities clustered according to valley and depth, with significant effects attributed to dissolved oxygen, pH, dissolved organic carbon, and total suspended solids. These results indicate that the bacterial assemblages of permafrost thaw ponds are filtered by environmental gradients, and are complex consortia of functionally diverse taxa that likely affect the composition as well as magnitude of greenhouse gas emissions from these abundant waters. PMID:25926816

  17. Bacterial community structure across environmental gradients in permafrost thaw ponds: methanotroph-rich ecosystems.

    PubMed

    Crevecoeur, Sophie; Vincent, Warwick F; Comte, Jérôme; Lovejoy, Connie

    2015-01-01

    Permafrost thawing leads to the formation of thermokarst ponds that potentially emit CO2 and CH4 to the atmosphere. In the Nunavik subarctic region (northern Québec, Canada), these numerous, shallow ponds become well-stratified during summer. This creates a physico-chemical gradient of temperature and oxygen, with an upper oxic layer and a bottom low oxygen or anoxic layer. Our objective was to determine the influence of stratification and related limnological and landscape properties on the community structure of potentially active bacteria in these waters. Samples for RNA analysis were taken from ponds in three contrasting valleys across a gradient of permafrost degradation. A total of 1296 operational taxonomic units were identified by high throughput amplicon sequencing, targeting bacterial 16S rRNA that was reverse transcribed to cDNA. β-proteobacteria were the dominant group in all ponds, with highest representation by the genera Variovorax and Polynucleobacter. Methanotrophs were also among the most abundant sequences at most sites. They accounted for up to 27% of the total sequences (median of 4.9% for all samples), indicating the importance of methane as a bacterial energy source in these waters. Both oxygenic (cyanobacteria) and anoxygenic (Chlorobi) phototrophs were also well-represented, the latter in the low oxygen bottom waters. Ordination analyses showed that the communities clustered according to valley and depth, with significant effects attributed to dissolved oxygen, pH, dissolved organic carbon, and total suspended solids. These results indicate that the bacterial assemblages of permafrost thaw ponds are filtered by environmental gradients, and are complex consortia of functionally diverse taxa that likely affect the composition as well as magnitude of greenhouse gas emissions from these abundant waters.

  18. Active Flow Control on a Boundary-Layer-Ingesting Inlet

    NASA Technical Reports Server (NTRS)

    Gorton, Susan Althoff; Owens, Lewis R.; Jenkins, Luther N.; Allan, Brian G.; Schuster, Ernest P.

    2004-01-01

    Boundary layer ingestion (BLI) is explored as means to improve overall system performance for Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides framework within which to assess the benefits of an integrated BLI inlet and lays the groundwork for higher-fidelity systems studies. The results of the system study show that BLI provides a significant improvement in vehicle performance if the inlet distortion can be controlled, thus encouraging the pursuit of active flow control (AFC) as a BLI enabling technology. The effectiveness of active flow control in reducing engine inlet distortion was assessed using a 6% scale model of a 30% BLI offset, diffusing inlet. The experiment was conducted in the NASA Langley Basic Aerodynamics Research Tunnel with a model inlet designed specifically for this type of testing. High mass flow pulsing actuators provided the active flow control. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion was determined by 120 total pressure measurements located at the aerodynamic interface plane. The test matrix was limited to a maximum freestream Mach number of 0.15 with scaled mass flows through the inlet for that condition. The data show that the pulsed actuation can reduce distortion from 29% to 4.6% as measured by the circumferential distortion descriptor DC60 using less than 1% of inlet mass flow. Closed loop control of the actuation was also demonstrated using a sidewall surface static pressure as the response sensor.

  19. Modeling the effects of fire severity and climate warming on active layer and soil carbon dynamics of black spruce forests across the landscape in interior Alaska

    USGS Publications Warehouse

    Genet, H.; McGuire, Anthony David; Barrett, K.; Breen, A.; Euskirchen, E.S.; Johnstone, J.F.; Kasischke, E.S.; Melvin, A.M.; Bennett, A.; Mack, M.C.; Rupp, T.S.; Schuur, A.E.G.; Turetsky, M.R.; Yuan, F.

    2013-01-01

    There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layer caused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness

  20. Modeling the effects of fire severity and climate warming on active layer thickness and soil carbon storage of black spruce forests across the landscape in interior Alaska

    NASA Astrophysics Data System (ADS)

    Genet, H.; McGuire, A. D.; Barrett, K.; Breen, A.; Euskirchen, E. S.; Johnstone, J. F.; Kasischke, E. S.; Melvin, A. M.; Bennett, A.; Mack, M. C.; Rupp, T. S.; Schuur, A. E. G.; Turetsky, M. R.; Yuan, F.

    2013-12-01

    There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layer caused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness

  1. Environmental selection of planktonic methanogens in permafrost thaw ponds

    PubMed Central

    Crevecoeur, Sophie; Vincent, Warwick F.; Lovejoy, Connie

    2016-01-01

    The warming and thermal erosion of ice-containing permafrost results in thaw ponds that are strong emitters of methane to the atmosphere. Here we examined methanogens and other Archaea, in two types of thaw ponds that are formed by the collapse of either permafrost peat mounds (palsas) or mineral soil mounds (lithalsas) in subarctic Quebec, Canada. Using high-throughput sequencing of a hypervariable region of 16S rRNA, we determined the taxonomic structure and diversity of archaeal communities in near-bottom water samples, and analyzed the mcrA gene transcripts from two sites. The ponds at all sites were well stratified, with hypoxic or anoxic bottom waters. Their archaeal communities were dominated by Euryarchaeota, specifically taxa in the methanogenic orders Methanomicrobiales and Methanosarcinales, indicating a potentially active community of planktonic methanogens. The order Methanomicrobiales accounted for most of the mcrA transcripts in the two ponds. The Archaeal communities differed significantly between the lithalsa and palsa ponds, with higher alpha diversity in the organic-rich palsa ponds, and pronounced differences in community structure. These results indicate the widespread occurrence of planktonic, methane-producing Archaea in thaw ponds, with environmental selection of taxa according to permafrost landscape type. PMID:27501855

  2. Environmental selection of planktonic methanogens in permafrost thaw ponds.

    PubMed

    Crevecoeur, Sophie; Vincent, Warwick F; Lovejoy, Connie

    2016-01-01

    The warming and thermal erosion of ice-containing permafrost results in thaw ponds that are strong emitters of methane to the atmosphere. Here we examined methanogens and other Archaea, in two types of thaw ponds that are formed by the collapse of either permafrost peat mounds (palsas) or mineral soil mounds (lithalsas) in subarctic Quebec, Canada. Using high-throughput sequencing of a hypervariable region of 16S rRNA, we determined the taxonomic structure and diversity of archaeal communities in near-bottom water samples, and analyzed the mcrA gene transcripts from two sites. The ponds at all sites were well stratified, with hypoxic or anoxic bottom waters. Their archaeal communities were dominated by Euryarchaeota, specifically taxa in the methanogenic orders Methanomicrobiales and Methanosarcinales, indicating a potentially active community of planktonic methanogens. The order Methanomicrobiales accounted for most of the mcrA transcripts in the two ponds. The Archaeal communities differed significantly between the lithalsa and palsa ponds, with higher alpha diversity in the organic-rich palsa ponds, and pronounced differences in community structure. These results indicate the widespread occurrence of planktonic, methane-producing Archaea in thaw ponds, with environmental selection of taxa according to permafrost landscape type. PMID:27501855

  3. Environmental selection of planktonic methanogens in permafrost thaw ponds

    NASA Astrophysics Data System (ADS)

    Crevecoeur, Sophie; Vincent, Warwick F.; Lovejoy, Connie

    2016-08-01

    The warming and thermal erosion of ice-containing permafrost results in thaw ponds that are strong emitters of methane to the atmosphere. Here we examined methanogens and other Archaea, in two types of thaw ponds that are formed by the collapse of either permafrost peat mounds (palsas) or mineral soil mounds (lithalsas) in subarctic Quebec, Canada. Using high-throughput sequencing of a hypervariable region of 16S rRNA, we determined the taxonomic structure and diversity of archaeal communities in near-bottom water samples, and analyzed the mcrA gene transcripts from two sites. The ponds at all sites were well stratified, with hypoxic or anoxic bottom waters. Their archaeal communities were dominated by Euryarchaeota, specifically taxa in the methanogenic orders Methanomicrobiales and Methanosarcinales, indicating a potentially active community of planktonic methanogens. The order Methanomicrobiales accounted for most of the mcrA transcripts in the two ponds. The Archaeal communities differed significantly between the lithalsa and palsa ponds, with higher alpha diversity in the organic-rich palsa ponds, and pronounced differences in community structure. These results indicate the widespread occurrence of planktonic, methane-producing Archaea in thaw ponds, with environmental selection of taxa according to permafrost landscape type.

  4. Environmental selection of planktonic methanogens in permafrost thaw ponds.

    PubMed

    Crevecoeur, Sophie; Vincent, Warwick F; Lovejoy, Connie

    2016-01-01

    The warming and thermal erosion of ice-containing permafrost results in thaw ponds that are strong emitters of methane to the atmosphere. Here we examined methanogens and other Archaea, in two types of thaw ponds that are formed by the collapse of either permafrost peat mounds (palsas) or mineral soil mounds (lithalsas) in subarctic Quebec, Canada. Using high-throughput sequencing of a hypervariable region of 16S rRNA, we determined the taxonomic structure and diversity of archaeal communities in near-bottom water samples, and analyzed the mcrA gene transcripts from two sites. The ponds at all sites were well stratified, with hypoxic or anoxic bottom waters. Their archaeal communities were dominated by Euryarchaeota, specifically taxa in the methanogenic orders Methanomicrobiales and Methanosarcinales, indicating a potentially active community of planktonic methanogens. The order Methanomicrobiales accounted for most of the mcrA transcripts in the two ponds. The Archaeal communities differed significantly between the lithalsa and palsa ponds, with higher alpha diversity in the organic-rich palsa ponds, and pronounced differences in community structure. These results indicate the widespread occurrence of planktonic, methane-producing Archaea in thaw ponds, with environmental selection of taxa according to permafrost landscape type.

  5. Quality changes during frozen storage and thawing of mixed bread.

    PubMed

    Fik, M; Macura, R

    2001-04-01

    In the present work investigations of the dependence between frozen storage time, the method of thawing (air blast at 50 degrees C and microwave), organoleptic and physico-chemical changes in bread are reported. The quality of the thawed product was analysed directly after thawing and after two days of storage at room temperature. It was found that changes in quality of bread are more affected by frozen storage than by the employed thawing method. The thawing methods had a significant (p < or = 0.01) effect on the investigated physico-chemical parameters of the product, however, their statistically significant (p < or = 0.01) effect on the sensory quality could only be revealed after two days of storage of the previously thawed bread at room temperature rather than directly after thawing. The results obtained in the present study suggest that bread which underwent microwave thawing had generally better quality in comparison with air blast thawing.

  6. Nitrogen availability increases in a tundra ecosystem during five years of experimental permafrost thaw.

    PubMed

    Salmon, Verity G; Soucy, Patrick; Mauritz, Marguerite; Celis, Gerardo; Natali, Susan M; Mack, Michelle C; Schuur, Edward A G

    2016-05-01

    Perennially frozen soil in high latitude ecosystems (permafrost) currently stores 1330-1580 Pg of carbon (C). As these ecosystems warm, the thaw and decomposition of permafrost is expected to release large amounts of C to the atmosphere. Fortunately, losses from the permafrost C pool will be partially offset by increased plant productivity. The degree to which plants are able to sequester C, however, will be determined by changing nitrogen (N) availability in these thawing soil profiles. N availability currently limits plant productivity in tundra ecosystems but plant access to N is expected improve as decomposition increases in speed and extends to deeper soil horizons. To evaluate the relationship between permafrost thaw and N availability, we monitored N cycling during 5 years of experimentally induced permafrost thaw at the Carbon in Permafrost Experimental Heating Research (CiPEHR) project. Inorganic N availability increased significantly in response to deeper thaw and greater soil moisture induced by Soil warming. This treatment also prompted a 23% increase in aboveground biomass and a 49% increase in foliar N pools. The sedge Eriophorum vaginatum responded most strongly to warming: this species explained 91% of the change in aboveground biomass during the 5 year period. Air warming had little impact when applied alone, but when applied in combination with Soil warming, growing season soil inorganic N availability was significantly reduced. These results demonstrate that there is a strong positive relationship between the depth of permafrost thaw and N availability in tundra ecosystems but that this relationship can be diminished by interactions between increased thaw, warmer air temperatures, and higher levels of soil moisture. Within 5 years of permafrost thaw, plants actively incorporate newly available N into biomass but C storage in live vascular plant biomass is unlikely to be greater than losses from deep soil C pools.

  7. Characterization of cathode keeper wear by surface layer activation

    NASA Technical Reports Server (NTRS)

    Polk, James E.

    2003-01-01

    In this study, the erosion rates of the discharge cathode keeper in a 30 cm NSTAR configuration ion thruster were measured using a technique known as Surface Layer Activation (SLA). This diagnostic technique involves producing a radioactive tracer in a given surface by bombardment with high energy ions. The decrease in activity of the tracer material may be monitored as the surface is subjected to wear processes and correlated to a depth calibration curve, yielding the eroded depth. Analysis of the activities was achieved through a gamma spectroscopy system. The primary objectives of this investigation were to reproduce erosion data observed in previous wear studies in order to validate the technique, and to determine the effect of different engine operating parameters on erosion rate. The erosion profile at the TH 15 (23 kw) setting observed during the 8200 hour Life Demonstration Test (LDT) was reproduced. The maximum keeper erosion rate at this setting was determined to be 0.085 pm/hr. Testing at the TH 8 (1.4 kw) setting demonstrated lower erosion rates than TH 15, along with a different wear profile. Varying the keeper voltage was shown to have a significant effect on the erosion, with a positive bias with respect to cathode potential decreasing the erosion rate significantly. Accurate measurements were achieved after operating times of only 40 to 70 hours, a significant improvement over other erosion diagnostic methods.

  8. Superplasticizer effect on cement paste structure and concrete freeze-thaw resistance

    NASA Astrophysics Data System (ADS)

    Shuldyakov, Kirill; Kramar, Lyudmila; Trofimov, Boris; Ivanov, Ilya

    2016-01-01

    Article presents the results of studies of various types of superplasticizer additives and their influence on concrete structure and resistance under cyclic freezing-thawing. Glenium ACE 430 was taken as a polycarboxylate superplasticizer, and SP-1 - as a naphthalene-formaldehyde superplasticizer. It is revealed that at identical structure, W/C and fluidity of concrete mix, application of the polycarboxylate superplasticizer, Glenium AC 430, in comparison to the naphthalene-formaldehyde one SP-1, facilitates the increase of the concrete grade in freeze and thaw resistance from F2300 to F2400, concrete freeze and thaw resistance can be possible even higher if the gravel with higher freeze and thaw resistance is applied. To assess the superplasticizers influence on cement paste structure tests of the phase composition of the cement paste of the studied concrete were conducted. It is established that the use of polycarboxylate superplasticizer together with silica fume facilitates formation of cement plaster structure from tobermorite gel. This gel has increased basicity and is resistant to crystallization due to cyclic freezing. It is shown that in the presence of SP-1+SF in the cement paste of concrete during hydration the structure of hydrosilicate phases preferably comprises of C-S-H(I) and C-S-H(II) phases which actively crystallize while cyclic freezing and thawing and reduce freeze-thaw resistance of concrete.

  9. The effect of fire and permafrost interactions on soil carbon accumulation in an upland black spruce ecosystem of interior Alaska: Implications for post-thaw carbon loss

    USGS Publications Warehouse

    O'Donnell, J. A.; Harden, J.W.; McGuire, A.D.; Kanevskiy, M.Z.; Jorgenson, M.T.; Xu, X.

    2011-01-01

    High-latitude regions store large amounts of organic carbon (OC) in active-layer soils and permafrost, accounting for nearly half of the global belowground OC pool. In the boreal region, recent warming has promoted changes in the fire regime, which may exacerbate rates of permafrost thaw and alter soil OC dynamics in both organic and mineral soil. We examined how interactions between fire and permafrost govern rates of soil OC accumulation in organic horizons, mineral soil of the active layer, and near-surface permafrost in a black spruce ecosystem of interior Alaska. To estimate OC accumulation rates, we used chronosequence, radiocarbon, and modeling approaches. We also developed a simple model to track long-term changes in soil OC stocks over past fire cycles and to evaluate the response of OC stocks to future changes in the fire regime. Our chronosequence and radiocarbon data indicate that OC turnover varies with soil depth, with fastest turnover occurring in shallow organic horizons (~60 years) and slowest turnover in near-surface permafrost (>3000 years). Modeling analysis indicates that OC accumulation in organic horizons was strongly governed by carbon losses via combustion and burial of charred remains in deep organic horizons. OC accumulation in mineral soil was influenced by active layer depth, which determined the proportion of mineral OC in a thawed or frozen state and thus, determined loss rates via decomposition. Our model results suggest that future changes in fire regime will result in substantial reductions in OC stocks, largely from the deep organic horizon. Additional OC losses will result from fire-induced thawing of near-surface permafrost. From these findings, we conclude that the vulnerability of deep OC stocks to future warming is closely linked to the sensitivity of permafrost to wildfire disturbance. ?? 2010 Blackwell Publishing Ltd.

  10. Modeling the effects of fire severity and climate warming on active layer thickness and soil carbon storage of black spruce forests across the landscape in interior Alaska

    SciTech Connect

    Genet, Helene; McGuire, A. David; Barrett, K.; Breen, Amy; Euskirchen, Eugenie S; Johnstone, J. F.; Kasischke, Eric S.; Melvin, A. M.; Bennett, A.; Mack, M. C.; Rupp, Scott T.; Schuur, Edward; Turetsky, M. R.; Yuan, Fengming

    2013-01-01

    There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layercaused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness

  11. Permafrost distribution and active layer thickness in the Aksu catchment, Central Tian Shan (P.R. China)

    NASA Astrophysics Data System (ADS)

    Imbery, S.; Gao, Q.; Sun, Z.; Duishonakunov, M.; King, L.

    2012-04-01

    Climate change actually leads to an accelerated ablation and retreat of high mountain glaciers in most parts of the world, and to a runoff increase of the related rivers in the short to middle term. Whereas this is a well-known fact, the additional runoff supplied by slowly melting ground-ice and perennial snow fields is almost unknown. However, this periglacial contribution is significant in extremely arid mountain areas as e.g. the Central Tian Shan. Here, the rivers form the vital source for the development of the Taklamakan basin, rich in natural resources, and strongly suffering from water shortage. Main scientific tasks in our subproject hence include an improvement of knowledge on permafrost distribution and active layer thickness, and their role for water discharge in the Aksu catchment. A dense network of 46 high resolution thermistor strings and mini data loggers were installed in the Gukur catchment (130 km2), a tributary of the Aksu river. Hourly temperatures are recorded at the ground surface and at various depths of up to 150 cm. First results indicate that the depth of the active layer and the propagation of the diurnal temperature signal depend - besides altitude, slope and aspect - largely on snow thickness/-distribution and substratum. The detailed identification of parameters determining the active layer thickness and thaw dynamics is fundamental for the large scale modelling of the state of the permafrost in the Central Tian Shan. The field studies will contribute to a better understanding of the thermal effects of substantial debris cover of subsurface ice-rich material or ground-ice, and of the temperature regime of rock glaciers and ice-cored moraines. These features store large amounts of ice in a permafrost environment over long time periods. In addition to the generally ice-rich top of the permafrost in the fine grained silty sediments in valleys and lee positions, they might have considerable influence on the amount and annual

  12. Characterizing Thawing Permafrost Carbon Emissions: An Integrated Pilot Study in Support of Satellite Evaluation/Design and Earth System Modeling Capabilities

    NASA Astrophysics Data System (ADS)

    Wilson, E. L.; Ott, L. E.; DiGregorio, A.; Duncan, B. N.; Euskirchen, E. S.; Carter, L. M.; Tucker, C. J.; Miller, J. H. H.; Liang, Q.; Elshorbany, Y. F.; Edgar, C.; Melocik, K. A.; Ramanathan, A. K.; Mao, J.; Bailey, D. M.; Adkins, E. M.; Melroy, H.

    2015-12-01

    We present a multi-disciplinary, multi-scaled study to measure methane (CH4) and carbon dioxide (CO2) above thawing permafrost at three sites, each representing a different ecosystem, near Fairbanks, AK. We have designed a unique and comprehensive array of ground experiments at these sites that will record permafrost depth and subsurface structure, meteorological data, and concentrations of key GHGs during seasonal ground thaw of the active layer in the summer. This is the first time that these types of measurements have been combined to provide a holistic view of the evolution of, and the atmospheric response to permafrost thaw. These data will allow us to estimate emission fluxes of carbon from the thawing permafrosts. To estimate a global source of GHG emissions from thawing permafrosts, we will use MODIS and Landsat-8 Operational Land Imager and Thermal Infrared Sensor data to "scale up" the data collected at the three sites on the basis of land surface type information. We refer to this effort as a pilot study as we will collect observations near Fairbanks, AK with the intent to expand our observational network in the future to other sites in North America, which will aid in the monitoring of changes in GHG emissions in the Arctic as well as complement and help interpret data collected by space-borne instruments, such as GOSAT, IASI, and AIRS. Based on the data collected at the three sites and a variety of existing satellite data sets, we will develop a computationally-efficient parameterization of emissions from thawing permafrosts for use in the NASA GEOS-5 Atmospheric General Circulation Model (AGCM), thus benefiting ongoing efforts in the NASA Global Modeling and Assimilation Office (GMAO) to build an Earth System Model which is used for both retrospective and predictive simulations of important GHGs. We will use the AGCM to interpret the data collected by tracking methane and CO2 plumes from various sources that impact the three sites. In addition, we

  13. Long-term geoelectrical monitoring of laboratory freeze-thaw experiments on bedrock samples

    NASA Astrophysics Data System (ADS)

    Kuras, Oliver; Uhlemann, Sebastian; Murton, Julian; Krautblatter, Michael

    2014-05-01

    Much attention has recently focussed on the continuous and near-real-time geophysical monitoring of permafrost-affected bedrock with permanently installed sensor arrays. It is hoped that such efforts will enhance process understanding in such environments (permafrost degradation, weathering mechanisms) and augment our capability to predict future instabilities of rock walls and slopes. With regard to electrical methods for example, recent work has demonstrated that temperature-calibrated electrical resistivity tomography (ERT) is capable of imaging recession and re-advance of rock permafrost in response to the ambient temperature regime. However, field experience also shows that several fundamental improvements to ERT methodology are still required to achieve the desired sensitivity, spatial-temporal resolution and long-term robustness that must underpin continuous geophysical measurements. We have applied 4D geoelectrical tomography to monitoring laboratory experiments simulating permafrost growth, persistence and thaw in bedrock over a period of 26 months. Six water-saturated samples of limestone and chalk of varying porosity represented lithologies commonly affected by permafrost-related instability. Time-lapse imaging of the samples was undertaken during multiple successive freeze-thaw cycles, emulating annual seasonal change over several decades. Further experimental control was provided by simultaneous measurements of vertical profiles of temperature and moisture content within the bedrock samples. These experiments have helped develop an alternative methodology for the volumetric imaging of permafrost bedrock and tracking active layer dynamics. Capacitive resistivity imaging (CRI), a technique based upon low-frequency, capacitively-coupled measurements emulates ERT methodology, but without the need for galvanic contact on frozen rock. The latter is perceived as a key potential weakness, which could lead to significant limitations as a result of the variable

  14. Using dissolved organic matter age and composition to detect permafrost thaw in boreal watersheds of interior Alaska

    USGS Publications Warehouse

    O'Donnell, Jonathan A.; Aiken, George R.; Walvoord, Michelle Ann; Raymond, Peter A.; Butler, Kenna; Dornblaser, Mark M.; Heckman, Katherine

    2014-01-01

    Recent warming at high latitudes has accelerated permafrost thaw, which can modify soil carbon dynamics and watershed hydrology. The flux and composition of dissolved organic matter (DOM) from soils to rivers are sensitive to permafrost configuration and its impact on subsurface hydrology and groundwater discharge. Here, we evaluate the utility of DOM composition and age as a tool for detecting permafrost thaw in three rivers (Beaver, Birch, and Hess Creeks) within the discontinuous permafrost zone of interior Alaska. We observed strong temporal controls on Δ14C content of hydrophobic acid isolates (Δ14C-HPOA) across all rivers, with the most enriched values occurring during spring snowmelt (75 ± 8‰) and most depleted during winter flow (−21 ± 8‰). Radiocarbon ages of winter flow samples ranged from 35 to 445 yr BP, closely tracking estimated median base flow travel times for this region (335 years). During spring snowmelt, young DOM was composed of highly aromatic, high molecular-weight compounds, whereas older DOM of winter flow had lower aromaticity and molecular weight. We observed a significant correlation between Δ14C-HPOA and UV absorbance coefficient at 254 nm (α254) across all study rivers. Usingα254 as an optical indicator for Δ14C-HPOA, we also observed a long-term decline in α254 during maximum annual thaw depth over the last decade at the Hess Creek study site. These findings suggest a shift in watershed hydrology associated with increasing active layer thickness. Further development of DOM optical indicators may serve as a novel and inexpensive tool for detecting permafrost degradation in northern watersheds.

  15. The relationship between species and functional diversity for permafrost and active layer Arctic microorganisms: implications for decomposition in response to warming

    NASA Astrophysics Data System (ADS)

    Ernakovich, J. G.; Wallenstein, M. D.

    2012-12-01

    For higher organisms, decades of research has examined the relationship between species diversity and ecosystem function. In contrast, we know little about this relationship in bacterial communities. Recently, molecular techniques have been used to explore the impact of microbial community composition on ecosystem function, but results have been mixed when the response variable is an ecosystem flux rate, such as CO2 production. Despite the ambiguity of the link between ecosystem flux rate and microbial community composition, it is becoming clear that different consortia of bacterial taxa utilize different substrates. Thus, the relative rate at which various constituents of soil organic matter are decomposed may be affected by the particular taxa that are present and active. In permafrost soils, there is an added layer of complexity, because the community may composed of microorganisms selected for survival of extreme cold rather than those suited to decompose available carbon. Understanding the relationship between the species and functional diversity of the permafrost microbial community will inform our predictions of the fate of permafrost carbon as it thaws under a warmer climate. Permafrost and seasonally thawed ("active layer") soils were collected from Sagwon Hills, Alaska in August of 2009. The functional diversity of microbial communities was explored using Ecolog plates (Biolog, Inc) incubated at 1°C, 10°C, and 20°C. Bacterial species diversity was investigated with 454 pyrosequencing of the 16S rRNA. The functional diversity of the permafrost microbial community was temperature dependent with diversity increasing with temperature (p<0.001), whereas the active layer utilized similar numbers of substrates at all temperatures. At 1°C, the permafrost community was only able to utilize 1.6 + 0.11 substrates on average, but the active layer was able to utilize an order of magnitude more substrates (21.3 + 0.33). Initial analysis of the 454 pyrosequencing

  16. Biogeochemistry: Long-term effects of permafrost thaw

    NASA Astrophysics Data System (ADS)

    Zona, Donatella

    2016-09-01

    Carbon emissions from the Arctic tundra could increase drastically as global warming thaws permafrost. Clues now obtained about the long-term effects of such thawing on carbon dioxide emissions highlight the need for more data.

  17. Towards NOAA Forecasts of Permafrost Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Livezey, M. M.; Jonassen, R. G.; Horsfall, F. M. C.; Jafarov, E. E.; Schaefer, K. M.

    2014-12-01

    NOAA's implementation of its 2014 Arctic Action Plan (AAP) lacks services related to permafrost change yet the Interagency Working Group on Coordination of Domestic Energy Development and Permitting in Alaska noted that warming permafrost challenges land-based development and calls for agencies to provide focused information needed by decision-makers. To address this we propose to link NOAA's existing seasonal forecasts of temperature and precipitation with a high-resolution model of the thermal state of permafrost (Jafarov et al., 2012) to provide near-term (one year ahead) forecasts of active layer thickness (ALT). Such forecasts would be an official NOAA statement of the expected thermal state of permafrost ALT in Alaska and would require: (1) long-term climate outlooks, (2) a permafrost model, (3) detailed specification of local spatial and vertical controls upon soil thermal state, (4) high-resolution vertical measurements of that thermal state, and (5) demonstration of forecast skill in pilot studies. Pilot efforts should focus on oil pipelines where the cost can be justified. With skillful forecasts, engineers could reduce costs of monitoring and repair as well as ecosystem damage by positioning equipment to more rapidly respond to predicted disruptions.

  18. Active millimeter wave detection of concealed layers of dielectric material

    NASA Astrophysics Data System (ADS)

    Bowring, N. J.; Baker, J. G.; Rezgui, N. D.; Southgate, M.; Alder, J. F.

    2007-04-01

    Extensive work has been published on millimetre wave active and passive detection and imaging of metallic objects concealed under clothing. We propose and demonstrate a technique for revealing the depth as well as the outline of partially transparent objects, which is especially suited to imaging layer materials such as explosives and drugs. The technique uses a focussed and scanned FMCW source, swept through many GHz to reveal this structure. The principle involved is that a parallel sided dielectric slab produces reflections at both its upper and lower surfaces, acting as a Fabry-Perot interferometer. This produces a pattern of alternating reflected peaks and troughs in frequency space. Fourier or Burg transforming this pattern into z-space generates a peak at the thickness of the irradiated sample. It could be argued that though such a technique may work for single uniform slabs of dielectric material, it will give results of little or no significance when the sample both scatters the incident radiation and gives erratic reflectivities due to its non-uniform thickness and permittivity . We show results for a variety of materials such as explosive simulants, powder and drugs, both alone and concealed under clothing or in a rucksack, which display strongly directional reflectivities at millimeter wavelengths, and whose location is well displayed by a varying thickness parameter as the millimetre beam is scanned across the target. With this system we find that samples can easily be detected at standoff distances of at least 4.6m.

  19. Active layer hydrology for Imnavait Creek, Toolik, Alaska

    SciTech Connect

    Hinzman, L.D.; Kane, D.L.

    1987-04-01

    The hydrology of the active layer of a watershed is described. In the annual hydrologic cycle, snowmelt is the most significant event at Imnavait Creek located near Toolik Lake, Alaska. Precipitation that has accumulated for more than 6 months on the surface melts in a relatively short period of 7 to 10 days once sustained melting occurs. Significant runoff events are few. Convective storms covering relatively small areas on the North Slope of Alaska can produce significant small-scale events in a small watershed scale,but these events are rapidly attenuated outside the basin. Data collection began in August 1984. We have continuously monitored the hydrologic, the meteorologic, and the soil`s physical conditions. Information was collected through implementation of four snowmelt runoff plots and measurements of essential microclimate parameters. Soil moisture and temperature profiles were measured adjacent to each snowmelt runoff plot, and heat flux is collected adjacent to one of these plots. Meteorological parameters were measured locally. The water content of the snowpack prior to snowmelt was measured throughout the watershed and measured daily adjacent to each plot during snowmelt. The stream draining the basin was measured regularly during the spring melt event to provide information on watershed runoff rates and the volume of snowmelt.

  20. Active layer hydrology for Imnavait Creek, Toolik, Alaska

    SciTech Connect

    Hinzman, L.D.; Kane, D.L.

    1987-04-01

    The hydrology of the active layer of a watershed is described. In the annual hydrologic cycle, snowmelt is the most significant event at Imnavait Creek located near Toolik Lake, Alaska. Precipitation that has accumulated for more than 6 months on the surface melts in a relatively short period of 7 to 10 days once sustained melting occurs. Significant runoff events are few. Convective storms covering relatively small areas on the North Slope of Alaska can produce significant small-scale events in a small watershed scale,but these events are rapidly attenuated outside the basin. Data collection began in August 1984. We have continuously monitored the hydrologic, the meteorologic, and the soil's physical conditions. Information was collected through implementation of four snowmelt runoff plots and measurements of essential microclimate parameters. Soil moisture and temperature profiles were measured adjacent to each snowmelt runoff plot, and heat flux is collected adjacent to one of these plots. Meteorological parameters were measured locally. The water content of the snowpack prior to snowmelt was measured throughout the watershed and measured daily adjacent to each plot during snowmelt. The stream draining the basin was measured regularly during the spring melt event to provide information on watershed runoff rates and the volume of snowmelt.

  1. Effects of Soil Property Uncertainty on Projected Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Harp, D. R.; Atchley, A. L.; Coon, E.; Painter, S. L.; Wilson, C. J.; Romanovsky, V. E.; Liljedahl, A.

    2014-12-01

    Uncertainty in future climate is often assumed to contribute the largest uncertainty to active layer thickness (ALT) projections. However, the impact of soil property uncertainty on these projections may be significant. In this research, we evaluate the contribution of soil property uncertainty on ALT projections at the Barrow Environmental Observatory, Alaska. The effect of variations in porosity, thermal conductivity, saturation, and water retention properties of peat and mineral soil are evaluated. The micro-topography of ice wedge polygons present at the site is included in the analysis using three 1D column models to represent polygon center, rim and trough features. The Arctic Terrestrial Simulator (ATS) is used to model multiphase thermal and hydrological processes in the subsurface. We apply the Null-Space Monte Carlo (NSMC) algorithm to identify an ensemble of soil property combinations that produce simulated temperature profiles that are consistent with temperature measurements available from the site. ALT is simulated for the ensemble of soil property combinations for four climate scenarios. The uncertainty in ALT due to soil properties within and across climate scenarios is evaluated. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.

  2. Phototrophic pigment diversity and picophytoplankton in permafrost thaw lakes

    NASA Astrophysics Data System (ADS)

    Przytulska, A.; Comte, J.; Crevecoeur, S.; Lovejoy, C.; Laurion, I.; Vincent, W. F.

    2016-01-01

    Permafrost thaw lakes (thermokarst lakes) are widely distributed across the northern landscape, and are known to be biogeochemically active sites that emit large amounts of carbon to the atmosphere as CH4 and CO2. However, the abundance and composition of the photosynthetic communities that fix CO2 have been little explored in this ecosystem type. In order to identify the major groups of phototrophic organisms and their controlling variables, we sampled 12 permafrost thaw lakes along a permafrost degradation gradient in northern Québec, Canada. Additional samples were taken from five rock-basin reference lakes in the region to determine if the thaw lakes differed in limnological properties and phototrophs. Phytoplankton community structure was determined by high-performance liquid chromatography analysis of their photoprotective and photosynthetic pigments, and autotrophic picoplankton concentrations were assessed by flow cytometry. One of the black-colored lakes located in a landscape of rapidly degrading palsas (permafrost mounds) was selected for high-throughput 18S rRNA sequencing to complement conclusions based on the pigment and cytometry analyses. The results showed that the limnological properties of the thaw lakes differed significantly from the reference lakes, and were more highly stratified. However, both waterbody types contained similarly diverse phytoplankton groups, with dominance of the pigment assemblages by fucoxanthin-containing taxa, as well as chlorophytes, cryptophytes and cyanobacteria. Chlorophyll a concentrations (Chl a) were correlated with total phosphorus (TP), and both were significantly higher in the thaw lakes (overall means of 3.3 µg Chl a L-1 and 34 µg TP L-1) relative to the reference lakes (2.0 µg Chl a L-1 and 8.2 µg TP L-1). Stepwise multiple regression of Chl a against the other algal pigments showed that it was largely a function of alloxanthin, fucoxanthin and Chl b (R2 = 0.85). The bottom waters of two of the thaw

  3. Thawing in a coupled quintessence model

    NASA Astrophysics Data System (ADS)

    Honardoost, M.; Sadjadi, H. Mohseni; Sepangi, H. R.

    2016-10-01

    We consider the thawing model in the framework of coupled quintessence model. The effective potential has Z_2 symmetry which is broken spontaneously when the dark matter density becomes less than a critical value leading the quintessence equation of state parameter to deviate from -1. Conditions required for this procedure are obtained and analytical solution for the equation of state parameter is derived.

  4. Freeze-thaw induced gelation of alginates.

    PubMed

    Zhao, Ying; Shen, Wei; Chen, Zhigang; Wu, Tao

    2016-09-01

    Adding divalent ions or lowering pH below the pKa values of alginate monomers are common ways in preparing alginate gels. Herein a new way of preparing alginate gels using freeze-thaw technique is described. Solvent crystallization during freezing drove the polymers to associate into certain structures that became the junction zones of hydrogels after thawing. It enabled the preparation of alginate gels at pH 4.0 and 3.5, two pH at which the gel could not be formed previously. At pH 3.0 where alginate gel could be formed initially, applying freeze-thaw treatment increased the gel storage modulus almost 100 times. The formation of hydrogels and the resulting gel properties, such as dynamic moduli and gel syneresis were influenced by the pH values, number of freeze-thaw cycles, alginate concentrations, and ionic strengths. The obtained hydrogels were soft and demonstrated a melting behavior upon storage, which may find novel applications in the biomedical industry.

  5. Time lapse imaging of thaw-bulb development beneath arctic streams using ground-penetrating radar

    NASA Astrophysics Data System (ADS)

    Brosten, T. R.; Bradford, J. H.; McNamara, J. P.; Bowden, W.; Gooseff, M. N.

    2004-12-01

    We are investigating the responses of arctic tundra stream geomorphology, hyporheic zone hydrology, and biogeochemical cycling to climate change. Field results from summer, 2003, demonstrate that GPR is an effective tool for imaging the depth to sub-stream permafrost. The results presented here are the next step in the use of ground-penetrating radar (GPR) data for measuring sub-stream thaw over the summer season. We acquired a series of GPR profiles at seven sites from May - September, 2004, using 100, 200, and 400 MHz antennas. We selected sites with the objective of including stream reaches spanning a range of geomorphologic conditions in rivers and streams on Alaska's North Slope. Generally the streams can be placed into two categories: 1) as low-energy water flow with organic material lining the streambeds (peat streams) or 2) as high-energy water flow with cobble to gravel material lining the streambeds (alluvial streams). We acquired data using a pulsed radar system with high-power transmitter. Early in the field season we used the 400 and 200 MHz antennas to maximize resolution potential, then gradually shifted to the lower frequency 100 MHz antennas later in the season to increase depth of penetration. We placed the radar antennas in the bottom of a small rubber boat, then pulled the boat across the bank and through the stream while triggering at a constant interval via a string odometer system. Depth to permafrost was verified by pressing a metal probe through the active layer to the point of refusal. In addition, we recorded temperature data using thermocouples placed at varying substream depths along two of the seven GPR profiles. We used the temperature profiles to constrain and verify the GPR interpretation. At several sites we obtained excellent results and have produced images of thaw-bulb growth through the summer season in both alluvial and peat stream morphologies.

  6. Characteristics of sugar surfactants in stabilizing proteins during freeze-thawing and freeze-drying.

    PubMed

    Imamura, Koreyoshi; Murai, Katsuyuki; Korehisa, Tamayo; Shimizu, Noriyuki; Yamahira, Ryo; Matsuura, Tsutashi; Tada, Hiroko; Imanaka, Hiroyuki; Ishida, Naoyuki; Nakanishi, Kazuhiro

    2014-06-01

    Sugar surfactants with different alkyl chain lengths and sugar head groups were compared for their protein-stabilizing effect during freeze-thawing and freeze-drying. Six enzymes, different in terms of tolerance against inactivation because of freeze-thawing and freeze-drying, were used as model proteins. The enzyme activities that remained after freeze-thawing and freeze-drying in the presence of a sugar surfactant were measured for different types and concentrations of sugar surfactants. Sugar surfactants stabilized all of the tested enzymes both during freeze-thawing and freeze-drying, and a one or two order higher amount of added sugar surfactant was required for achieving protein stabilization during freeze-drying than for the cryoprotection. The comprehensive comparison showed that the C10-C12 esters of sucrose or trehalose were the most effective through the freeze-drying process: the remaining enzyme activities after freeze-thawing and freeze-drying increased at the sugar ester concentrations of 1-10 and 10-100 μM, respectively, and increased to a greater extent than for the other surfactants at higher concentrations. Results also indicate that, when a decent amount of sugar was also added, the protein-stabilizing effect of a small amount of sugar ester through the freeze-drying process could be enhanced.

  7. Gas flux dynamics in high arctic permafrost polygon and ice wedge active layer soil; microbial feedback implications

    NASA Astrophysics Data System (ADS)

    Mykytczuk, N. C.; Stackhouse, B. T.; Bennett, P.; Lamarche-Gagnon, G.; Hettich, R. L.; Phelps, T. J.; Layton, A.; Pfiffner, S. M.; Allan, J.; Vishnivetskaya, T. A.; Chourey, K.; Whyte, L.; Onstott, T. C.

    2011-12-01

    Temperatures in the Arctic may increase 4-8°C over the next 100 years, thereby increasing the depth of the active layer (AL) and thawing the underlying permafrost, with ice wedges in particular acting as an early indicator, a bellwether, for changing permafrost. Although data on CO2 and CH4 fluxes have been studied along with microbial diversity of AL and permafrost environments, the relationship between methanogenic, methanotrophic and heterotrophic in situ activities within the AL and CO2 and CH4 fluxes as a function of temperature has not been delineated. Defining these relationships is critical for accurately modeling the extent and rate of + / - feedback in global climate models. Initial field investigations of diurnal CO2 and CH4 flux from permafrost and ice-wedge AL soils were conducted during July on Axel Heiberg Island in the Canadian high arctic. The AL soils (68-69 cm depth) were completely thawed while ambient air temperatures were between 9 and 27°C. The AL soils above the ice wedges had a higher water content and finer texture than the polygon AL soils. Diurnal patterns using in situ flux chambers and a Picarro C-13 CO2 cavity ring-down spectrometer recorded net outward flux of CO2 (3.2 to 8.8 g/m2/day) and consumption of atmospheric CH4 (-2.2 mg/m2/day) from the AL surfaces. Gas flux from the ice wedge soil surface were in a similar range as the polygon soil surface, having slightly higher maximal flux of CO2 (10.4 g/m2/day) and net efflux of CH4 (-2.2 to 14 mg/m2/day). Using a vertical probe, gas flux below the surface measured higher amounts of CO2 with increasing depth ranging from 10.4 to 21.4 g/m2/day in the polygon soils vs. 10 to 28.5 g/m2/day in the ice wedge soils. Through the same profile, the CH4 concentration decreased from 0.59 ppmv to < 0.1 ppmv within 30 cm of the surface in the ice wedge and from 1.1 to 0.54 ppmv at the base of the polygon AL. The δ13C of the CO2 efflux from the surface were consistent with microbial activity

  8. Layers

    NASA Astrophysics Data System (ADS)

    Hong, K. J.; Jeong, T. S.; Youn, C. J.

    2014-09-01

    The temperature-dependent photoresponse characteristics of MnAl2S4 layers have been investigated, for the first time, by use of photocurrent (PC) spectroscopy. Three peaks were observed at all temperatures. The electronic origin of these peaks was associated with band-to-band transitions from the valence-band states Γ4( z), Γ5( x), and Γ5( y) to the conduction-band state Γ1( s). On the basis of the relationship between PC-peak energy and temperature, the optical band gap could be well expressed by the expression E g( T) = E g(0) - 2.80 × 10-4 T 2/(287 + T), where E g(0) was estimated to be 3.7920 eV, 3.7955 eV, and 3.8354 eV for the valence-band states Γ4( z), Γ5( x), and Γ5( y), respectively. Results from PC spectroscopy revealed the crystal-field and spin-orbit splitting were 3.5 meV and 39.9 meV. The gradual decrease of PC intensity with decreasing temperature can be explained on the basis of trapping centers associated with native defects in the MnAl2S4 layers. Plots of log J ph, the PC current density, against 1/ T, revealed a dominant trap level in the high-temperature region. By comparing PC and the Hall effect results, we confirmed that this trap level is a shallow donor 18.9 meV below the conduction band.

  9. Freeze-thaw and high-voltage discharge allow macromolecule uptake into ileal brush-border vesicles

    SciTech Connect

    Donowitz, M.; Emmer, E.; McCullen, J.; Reinlib, L.; Cohen, M.E.; Rood, R.P.; Madara, J.; Sharp, G.W.G.; Murer, H.; Malmstrom, K.

    1987-06-01

    High-voltage discharge or one cycle of freeze-thawing are shown to transiently permeabilize rabbit ileal brush-border membrane vesicles to macromolecules. Uptake of the radiolabeled macromolecule dextran, mol wt 70,000, used as a marker for vesicle permeability, was determined by a rapid filtration technique, with uptake defined as substrate associated with the vesicle and releasable after incubation of vesicles with 0.1% saponin. Dextran added immediately after electric shock (2000 V) or at the beginning of one cycle of freeze-thawing was taken up approximately eightfold compared with control. ATP also was taken up into freeze-thawed vesicles, whereas there was no significant uptake into control vesicles. The increase in vesicle permeability was reversible, based on Na-dependent D-glucose uptake being decreased when studied 5 but not 15 min after electric shock, and was not significantly decreased after completion of one cycle of freeze-thawing. In addition, adenosine 3',5'-cyclic monophosphate and Ca/sup 2 +/-calmodulin-dependent protein kinase activity were similar in control vesicles and vesicles exposed to high-voltage discharge or freeze-thawing. Also, vesicles freeze-thawed with (/sup 32/P)ATP demonstrated increased phosphorylation compared with nonfrozen vesicles, while freeze-thawing did not alter vesicle protein as judged by Coomassie blue staining. These techniques should allow intestinal membrane vesicles to be used for studies of intracellular control of transport processes, for instance, studies of protein kinase regulation of transport.

  10. Effects of permafrost thaw on nitrogen availability and plant nitrogen acquisition in Interior Alaska

    NASA Astrophysics Data System (ADS)

    Finger, R.; Euskirchen, E. S.; Turetsky, M.

    2013-12-01

    The degradation of ice-rich permafrost, which covers a large portion of Interior Alaska, typically leads to thermokarst and increases in soil saturation. As a result, conifer peat plateaus degrade and are often replaced by wet collapse scar bogs. This state change results in profound changes in regional hydrology, biogeochemical cycling, and plant community composition. Preliminary data suggest that permafrost thaw can increase surface soil inorganic nitrogen (IN) concentrations but it is still unknown whether these changes in nutrient availability are short-lived (pulse releases) and whether or not they impact collapse scar vegetation composition or productivity, particularly as collapse scars undergo succession with time-after-thaw. Therefore we are currently examining changes in plant community composition, N availability and plant N acquisition along three thermokarst gradients in Interior Alaska. Each gradient is comprised of a forested permafrost peat plateau, adjacent ecotones experiencing active permafrost degradation (including a collapsing forest canopy and a saturated moat), and a collapse scar bog where permafrost has completely degraded. We predicted that IN concentrations would be highest along the active thaw margin, and lowest in the peat plateau. We also predicted that IN concentrations would be positively related to shifts in vegetation community composition, nutrient use efficiency (NUE) and tissue 15N concentrations. Preliminary results have shown that IN concentrations increase in newer collapse scar features as well as with thaw depth. Our data also show a shift from feather moss and ericaceous shrub-dominate understories in the permafrost plateau to Sphagnum and sedge dominated thaw ecotone and bog communities. Further successional development of the collapse scar bog results in the reintroduction of small evergreen and deciduous shrubs as the peat mat develops. Over time, collapse scar succession and peat accumulation appears to lead to

  11. Grain sorting in the morphological active layer of a braided river physical model

    NASA Astrophysics Data System (ADS)

    Leduc, P.; Ashmore, P.; Gardner, J. T.

    2015-07-01

    A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the river. This vertical sorting is important for analyzing braided river sedimentology, for numerical modeling of braided river morpho-dynamics and for measuring and predicting bed load transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to re-work the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs of the model river bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morphological active layer and variation in grain size in three-dimensions. Normalizing active layer thickness and dividing into 10 sub-layers we show that all grain sizes occur with almost equal frequency in all sub-layers. Occurrence of patches and strings of coarser (or finer) material relates to preservation of particular morpho-textural features within the active layer. For numerical modeling and bed load prediction a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.

  12. Proteomic changes associated with freeze-thaw injury and post-thaw recovery in onion (Allium cepa L.) scales.

    PubMed

    Chen, Keting; Renaut, Jenny; Sergeant, Kjell; Wei, Hui; Arora, Rajeev

    2013-04-01

    The ability of plants to recover from freeze-thaw injury is a critical component of freeze-thaw stress tolerance. To investigate the molecular basis of freeze-thaw recovery, here we compared the proteomes of onion scales from unfrozen control (UFC), freeze-thaw injured (INJ), and post-thaw recovered (REC) treatments. Injury-related proteins (IRPs) and recovery-related proteins (RRPs) were differentiated according to their accumulation patterns. Many IRPs decreased right after thaw without any significant re-accumulation during post-thaw recovery, while others were exclusively induced in INJ tissues. Most IRPs are antioxidants, stress proteins, molecular chaperones, those induced by physical injury or proteins involved in energy metabolism. Taken together, these observations suggest that while freeze-thaw compromises the constitutive stress protection and energy supply in onion scales, it might also recruit 'first-responders' (IRPs that were induced) to mitigate such injury. RRPs, on the other hand, are involved in the injury-repair program during post-thaw environment conducive for recovery. Some RRPs were restored in REC tissues after their first reduction right after thaw, while others exhibit higher abundance than their 'constitutive' levels. RRPs might facilitate new cellular homeostasis, potentially by re-establishing ion homeostasis and proteostasis, cell-wall remodelling, reactive oxygen species (ROS) scavenging, defence against possible post-thaw infection, and regulating the energy budget to sustain these processes.

  13. [Effect freezing and thawing cycles on fluorescence characterization of black soil dissolved organic matter].

    PubMed

    Wang, Tai-Ming; Wang, Ye-Yao; Xiang, Bao; Hu, Yu

    2011-08-01

    Fluorescence characterization of soil dissolved organic matter (DOM), which is one of the most important indexes concerning study on soil organic matter, can be effected by freezing and thawing cycles. In this paper, the fluorescence characterization of black soil DOM under the effect of freezing and thawing cycles was studied, using three-dimensional excitation-emission-matrix fluorescence spectroscopic (EEM). Based on the transformation of fluorescence characterization, the influences of humification degree and active humus in black soil were analysed. The result showed, compared with untreated by freezing and thawing cycles, (1) The phenomena red-shift of UV fulvic-like was found in soil DOM. It meant that the aromatization and humification degree increased. (2) Protein-like fluorescence peak was observed in some soil samples, which meant microbial activity was enhanced. (3) Active humus and humification degree are the indexs of soil fertility. The content of TOC in the active humus rose, just the same as the value of humification degree. It meant that soil fertility was improved. (4) Compared with the ratio of UV: visible humic-like fluorescence (r(a,c)), there were positive correlations with the active humus and humification degree. It meant that r(a, c) of soil DOM was one of the indexs on active humus, humification degree and soil fertility effected by freezing and thawing cycles.

  14. Mercury export pathways in thawing Peatlands: Insights from Stordalen, Sweden

    NASA Astrophysics Data System (ADS)

    Prado, M. F.; Varner, R. K.; Bryce, J. G.; McCalley, C. K.; Erickson, L. M.; Crill, P. M.

    2013-12-01

    Recent studies have shown that climate change in northern high latitudes plays a significant role in enhancing the mobilization of previously sequestered mercury (Hg) in peatlands to the atmosphere and hydrosphere. The magnitude and mechanics of Hg mobilization, however, remain poorly constrained. To investigate the coupling of different export pathways and the major fate and transport of Hg in a subarctic ecosystem, we measured atmospheric Hg fluxes across a permafrost thaw gradient and compared these fluxes with exchangeable Hg from peat cores collected in July 2012 and July 2013 at the Stordalen Mire, Abisko, Sweden (68°21'N). Mercury flux measurements were estimated using a Tekran 2537 ambient air mercury analyzer integrated into a dynamic chamber system. The nine chamber array is divided into three sites, three chambers per site: (1) palsa site: dwarf-shrub dominated hummocks overlying permafrost, (2) Sphagnum : semi-wet hollows with 100% sphagnum cover with minor Eriophorum vaginatum, and (3) Eriophorum: wet hollows dominated by Carex rostrata and Eriophorum angustifolium. Continuous ambient air Hg measurements were made for multiple days at each site prior to flux chamber measurements. All three sites show a diel pattern characterized by Hg deposition during lows of photosynthetically active radiation (PAR) and ground temperature and a release of Hg during the peak PAR and ground temperature periods (13:00-15:00h). The palsa site yielded the highest Hg flux accompanied with the least amount of Hg deposition in the evening. The Eriophorum releases the least amount of Hg and is associated with the highest Hg deposition. The Sphagnum shows the most variability of the three sites, at times releasing as much as the palsa site but absorbing more than the Eriophorum in one instance. Consideration of the Hg flux measurements together with exchangeable Hg concentrations of the peat suggests that the palsa has the highest amount of stored Hg and given the aerobic

  15. Long-Term Hydrological Changes of Coastal Arctic Tundra Ponds in Drained Thaw Lake Basins

    NASA Astrophysics Data System (ADS)

    Andresen, C. G.; Lougheed, V.

    2013-12-01

    Given the dominance of these ponds in the tundra landscape, documenting long-term changes in these aquatic systems is essential to understand carbon and energy balance, trophic energy flow, and biodiversity for the Arctic. The combination of remote sensing using historical imagery, as well as rare historical data from the International Biological Program, provides a unique opportunity for understanding long-term changes in hydrology, chemistry and biology of these significant freshwater environments. To assess the changes in pond area and abundance in 22 drained thaw-lake basins (DTLB) across the Barrow Peninsula over the past 60 years, we utilized historic aerial imagery from USGS archives (1948) and modern high-resolution Quickbird (2002, 2008, 2010). Age classification of DTLB was based on Hinkel et al 2003. We compared water temperature, active layer thickness, and aboveground biomass of these systems to historical datasets compiled in the Limnology of Tundra Ponds' by Hobbie et al 1975. We observed an overall decrease of 28% in pond area and 19% decrease in pond number, where smaller ponds (<100m2) had the highest change. These losses were coincident with significantly higher air and water temperature and reduced annual rainfall, which has decreased by 2.5 cm over the past 62 years (-0.4mm/yr). Active layer in ponds increased on average by 15cm. Aquatic grasses increased in density and cover in ponds over the past 40 years. Area and number of ponds loss was independent of DTLB age; however, medium-age DTLBs had significantly higher number of new ponds over old and ancient-age basins. While we observe new ponds due to thaw lake processes, climate seems to be having a stronger effect on these systems by reducing the overall inundated area and pond number in these basins. Increased evaporation due to warmer and longer summers, permafrost degradation, transpiration from encroaching aquatic grasses and changes in precipitation patterns are likely the current major

  16. Effects of spatial variation of skull and cerebrospinal fluid layers on optical mapping of brain activities

    NASA Astrophysics Data System (ADS)

    Wang, Shuping; Shibahara, Nanae; Kuramashi, Daishi; Okawa, Shinpei; Kakuta, Naoto; Okada, Eiji; Maki, Atsushi; Yamada, Yukio

    2010-07-01

    In order to investigate the effects of anatomical variation in human heads on the optical mapping of brain activity, we perform simulations of optical mapping by solving the photon diffusion equation for layered-models simulating human heads using the finite element method (FEM). Particularly, the effects of the spatial variations in the thicknesses of the skull and cerebrospinal fluid (CSF) layers on mapping images are investigated. Mapping images of single active regions in the gray matter layer are affected by the spatial variations in the skull and CSF layer thicknesses, although the effects are smaller than those of the positions of the active region relative to the data points. The increase in the skull thickness decreases the sensitivity of the images to active regions, while the increase in the CSF layer thickness increases the sensitivity in general. The images of multiple active regions are also influenced by their positions relative to the data points and by their depths from the skin surface.

  17. CO2, CH4, and DOC Flux During Long Term Thaw of High Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Stackhouse, B. T.; Vishnivetskaya, T. A.; Layton, A.; Bennett, P.; Mykytczuk, N.; Lau, C. M.; Whyte, L.; Onstott, T. C.

    2013-12-01

    Arctic regions are expected to experience temperature increases of >4° C by the end of this century. This warming is projected to cause a drastic reduction in the extent of permafrost at high northern latitudes, affecting an estimated 1000 Pg of SOC in the top 3 m. Determining the effects of this temperature change on CO2 and CH4 emissions is critical for defining source constraints to global climate models. To investigate this problem, 18 cores of 1 m length were collected in late spring 2011 before the thawing of the seasonal active layer from an ice-wedge polygon near the McGill Arctic Research Station (MARS) on Axel Heiberg Island, Nunavut, Canada (N79°24, W90°45). Cores were collected from acidic soil (pH 5.5) with low SOC (~1%), summertime active layer depth between 40-70 cm (2010-2013), and sparse vegetation consisting primarily of small shrubs and sedges. Cores were progressively thawed from the surface over the course of 14 weeks to a final temperature of 4.5° C and held at that temperature for 15 months under the following conditions: in situ water saturation conditions versus fully water saturated conditions using artificial rain fall, surface light versus no surface light, cores from the polygon edge, and control cores with a permafrost table maintained at 70 cm depth. Core headspaces were measured weekly for CO2, CH4, H2, CO, and O2 flux during the 18 month thaw experiment. After ~20 weeks of thawing maximum, CO2 flux for the polygon edge and dark treatment cores were 3.0×0.7 and 1.7×0.4 mmol CO2 m-2 hr-1, respectively. The CO2 flux for the control, saturated, and in situ saturation cores reached maximums of 0.6×0.2, 0.9×0.5, and 0.9×0.1 mmol CO2 m-2 hr-1, respectively. Field measurements of CO2 flux from an adjacent polygon during the mid-summer of 2011 to 2013 ranged from 0.3 to 3.7 mmol CO2 m-2 hr-1. Cores from all treatments except water saturated were found to consistently oxidize CH4 at ~atmospheric concentrations (2 ppmv) with a maximum

  18. Layer-by-layer engineered nanocapsules of curcumin with improved cell activity.

    PubMed

    Kittitheeranun, Paveenuch; Sajomsang, Warayuth; Phanpee, Sarunya; Treetong, Alongkot; Wutikhun, Tuksadon; Suktham, Kunat; Puttipipatkhachorn, Satit; Ruktanonchai, Uracha Rungsardthong

    2015-08-15

    Nanocarriers based on electrostatic Layer-by-layer (LbL) assembly of CaCO3 nanoparticles (CaCO3 NPs) was investigated. These inorganic nanoparticles was used as templates to construct nanocapsules made from films based on two oppositely charged polyelectrolytes, poly(diallyldimethylammonium chloride), and poly (sodium 4-styrene-sulfonate sodium salt), followed by core dissolution. The naked CaCO3 NPs, CaCO3 NPs coated with the polyelectrolytes and hollow nanocapsules were found with hexagonal shape with average sizes of 350-400 nm. A reversal of the surface charge between positive to negative zeta potential values was found, confirming the adsorption of polyelectrolytes. The loading efficiency and release of curcumin were controlled by the hydrophobic interactions between the drug and the polyelectrolyte matrix of the hollow nanocapsules. The quantity of curcumin released from hollow nanocapsules was found to increase under acidic environments, which is a desirable for anti-cancer drug delivery. The hollow nanocapsules were found to localize in the cytoplasm and nucleus compartment of Hela cancer cells after 24 h of incubation. Hollow nanocapsules were non-toxic to human fibroblast cells. Furthermore, curcumin loaded hollow nanocapsules exhibited higher in vitro cell inhibition against Hela cells than that of free curcumin, suggesting that polyelectrolyte based-hollow nanocapsules can be utilized as new carriers for drug delivery. PMID:26143232

  19. Effects of trehalose supplementation on cell viability and oxidative stress variables in frozen-thawed bovine calf testicular tissue.

    PubMed

    Zhang, Xiao-Gang; Wang, Yan-Hua; Han, Cong; Hu, Shan; Wang, Li-Qiang; Hu, Jian-Hong

    2015-06-01

    Trehalose is widely used for cryopreservation of various cells and tissues. Until now, the effect of trehalose supplementation on cell viability and antioxidant enzyme activity in frozen-thawed bovine calf testicular tissue remains unexplored. The objective of the present study was to compare the effect of varying doses of trehalose in cryomedia on cell viability and key antioxidant enzymes activities in frozen-thawed bovine calf testicular tissue. Bovine calf testicular tissue samples were collected and cryopreserved in the cryomedias containing varying doses (0, 5, 10, 15, 20 and 25%; v/v) of trehalose, respectively. Cell viability, total antioxidant capacity (T-AOC) activity, catalase (CAT) activity, superoxide dismutase (SOD) activity, glutathione (GSH) content and malondialdehyde (MDA) content were measured and analyzed. The results showed that cell viability, T-AOC activity, SOD activity, CAT activity and GSH content of frozen-thawed bovine calf testicular tissue was decreased compared with that of fresh group (P<0.05). MDA content in frozen-thawed bovine calf testicular tissue was significantly increased compared with that of fresh group (P<0.05). The cryomedia added 15% trehalose exhibited the greatest percentage of cell viability and antioxidant enzyme activity (SOD and CAT) among frozen-thawed groups (P<0.05). Meanwhile, GSH content was the lowest among frozen-thawed groups (P<0.05). However, there were no significance differences in MDA content among the groups added 10, 15 and 20% trehalose (P>0.05). In conclusion, the cryomedia added 15% trehalose reduced the oxidative stress and improved the cryoprotective effect of bovine calf testicular tissue. Further studies are required to obtain more concrete results on the determination of antioxidant capacity of trehalose in frozen-thawed bovine calf testicular tissue. PMID:25818604

  20. Silver ions/ovalbumin films layer-by-layer self-assembled polyacrylonitrile nanofibrous mats and their antibacterial activity.

    PubMed

    Song, Rukun; Yan, Jinjiao; Xu, Shasha; Wang, Yuntao; Ye, Ting; Chang, Jing; Deng, Hongbing; Li, Bin

    2013-08-01

    The CN groups of polyacrylonitrile (PAN) can strongly adsorb silver ions. The possibility of using this attraction as a layer-by-layer (LBL) self-assembly driving force was investigated. Firstly, the surface of the PAN nanofibrous mats was modified by silver ions to make sure it was positively charged. Then oppositely charged ovalbumin (OVA) and silver ions in aqueous media were alternatively deposited onto the surface of the obtained composite mats by layer-by-layer self-assembly technique. The morphology of the LBL films coating mats was observed by field emission scanning electron microscope (FE-SEM). The deposition of silver ions and OVA was confirmed by X-ray photoelectron spectroscopy (XPS) and wide-angle X-ray diffraction (XRD). The thermal degradation properties were investigated by thermo-gravimetric analysis (TGA). Besides these, the cytotoxicity and antibacterial activity of the prepared mats were studied via flow cytometry (FCM) and inhibition zone test, respectively. The results showed that the composite mats after LBL self-assembly processing exhibited improved thermal stability, slightly decreased cytotoxicity, and excellent antibacterial activity against Escherichia coil and Staphylococcus aureus. PMID:23563300

  1. Estimation of Mercury Storage in Permafrost and Potential Release to the Environment by Thaw

    NASA Astrophysics Data System (ADS)

    Schuster, P. F.; Kamark, B. L.; Striegl, R. G.; Aiken, G.

    2011-12-01

    northern hemisphere suggest the potential range of THg sequestered in permafrost is 35,000 to 17 million metric tons. Using the mean THg value for all three cores and assuming an average 1 meter permafrost depth with a soil density of 0.75 g cm-3, we estimate sequestered THg to be about 1.5 million metric tons. The current estimate of annual natural and anthropogenic Hg inputs to the global atmospheric pool is about 7500 metric tons. These data suggest that permafrost contain a substantial reservoir of Hg. Efforts are under way to measure THg in up to seven more permafrost cores and associated active layers recently collected in interior Alaska to further refine the estimate of THg stocks in permafrost. In a warming northern climate, the pool of Hg currently residing in permafrost could become mobilized and undergo transformation reactions such as methylation, the main pathway by which Hg enters the food web as a toxic agent. Areas that are conducive to the methylation of Hg, typically wetlands and riparian zones, are often referred to as hot spots. If the northern climate continues to warm and permafrost continues to thaw there may be an increase in wetlands, riparian areas and sources of previously sequestered Hg that could lead to an increased number of hot spots in the northern regions of the world.

  2. Reversible Photoinhibition in Antarctic Moss during Freezing and Thawing.

    PubMed Central

    Lovelock, C. E.; Jackson, A. E.; Melick, D. R.; Seppelt, R. D.

    1995-01-01

    Tolerance of antarctic moss to freezing and thawing stress was investigated using chlorophyll a fluorescence. Freezing in darkness caused reductions in Fv/Fm (ratio of variable to maximum fluorescence) and Fo (initial fluorescence) that were reversible upon thawing. Reductions in Fv/Fm and Fo during freezing in darkness indicate a reduction in the potential efficiency of photosystem II that may be due to conformational changes in pigment-protein complexes due to desiccation associated with freezing. The absorption of light during freezing further reduced Fv/Fm and Fo but was also reversible. Using dithiothreitol (DTT), which inhibits the formation of the carotenoid zeaxanthin, we found reduced flurorescence quenching during freezing and reduced concentrations of zeaxanthin and antheraxanthin after freezing in DTT-treated moss. Reduced concentrations of zeaxanthin and antheraxanthin in DTT-treated moss were partially associated with reductions in nonphotochemical fluorescence quenching. The reversible photoinhibition observed in antarctic moss during freezing indicates the existence of processes that protect from photoinhibitory damage in environments where freezing temperatures occur in conjunction with high solar radiation levels. These processes may limit the need for repair cycles that require temperatures favorable for enzyme activity. PMID:12228644

  3. Permafrost Thaw Induces Methane Oxidation in Transitional Thaw Stages in a Subarctic Peatland

    NASA Astrophysics Data System (ADS)

    Perryman, C. R.; Kashi, N. N.; Malhotra, A.; McCalley, C. K.; Varner, R. K.

    2015-12-01

    Rising temperatures in the subarctic are accelerating permafrost thaw and increasing methane (CH4) emissions from subarctic peatlands. Methanotrophs in these peatlands can consume/oxidize CH4, potentially mitigating CH4 emissions in these peatlands. Oxidation rates can exceed 90% of CH4 production in some settings, depending on O2 and CH4 availability and environmental conditions. Malhotra and Roulet identified 10 thaw stages in Stordalen Mire near Abisko, Sweden (68°21'N,18°49'E ) with variable vegetation, environmental conditions, and associated CH4 emissions. We investigated potential methane oxidation rates across these thaw stages. Peat cores were extracted from two depths at each stage and incubated in 350ml glass jars at in situ temperatures and CH4 concentrations. Headspace samples were collected from each incubation jar over a 48-hour period and analyzed for CH4 concentration using flame ionization detection gas chromatography (GC-FID). Oxidation rates ranged from <0.1 to 17 μg of CH4 per gram of dry biomass per day. Water table depth and pore water pH were the strongest environmental correlates of oxidation (sample size = 56, p < 0.001). The highest potential oxidation rates were observed in collapsing palsa sites and recently collapsed sedge-dominated open water sites near palsa mounds. Our results suggest that permafrost thaw induces high CH4 oxidation rates by creating conditions ideal for both methanogenic and methanotrophic microbial communities. Our results also reinforce the importance of incorporating transitional thaw stages in landscape level carbon budgets of thawing peatlands emphasized by Malhotra and Roulet. Forthcoming microbial analysis and stable isotope analysis will further elucidate the factors controlling methane oxidation rates at Stordalen Mire.

  4. Experimental System for Simulating a Natural Soil Temperature Profile during Freeze-thaw Cycles

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In order to better assess the effects of freeze-thaw cycles on soil physical properties, water and contaminant transport, and microbial activity, a simple experimental soil thermal cycling system was developed. The system consisted of an insulated bin containing four cylindrical PVC lysimeters encas...

  5. Seminal plasma applied post-thawing affects boar sperm physiology: a flow cytometry study.

    PubMed

    Fernández-Gago, Rocío; Domínguez, Juan Carlos; Martínez-Pastor, Felipe

    2013-09-01

    Cryopreservation induces extensive biophysical and biochemical changes in the sperm. In the present study, we used flow cytometry to assess the capacitation-like status of frozen-thawed boar spermatozoa and its relationship with intracellular calcium, assessment of membrane fluidity, modification of thiol groups in plasma membrane proteins, reactive oxygen species (ROS) levels, viability, acrosomal status, and mitochondrial activity. This experiment was performed to verify the effect of adding seminal plasma on post-thaw sperm functions. To determine these effects after cryopreservation, frozen-thawed semen from seven boars was examined after supplementation with different concentrations of pooled seminal plasma (0%, 10%, and 50%) at various times of incubation from 0 to 4 hours. Incubation caused a decrease in membrane integrity and an increase in acrosomal damage, with small changes in other parameters (P > 0.05). Although 10% seminal plasma showed few differences with 0% (ROS increase at 4 hours, P < 0.05), 50% seminal plasma caused important changes. Membrane fluidity increased considerably from the beginning of the experiment, and ROS and free thiols in the cell surface increased by 2 hours of incubation. By the end of the experiment, viability decreased and acrosomal damage increased in the 50% seminal plasma samples. The addition of 50% of seminal plasma seems to modify the physiology of thawed boar spermatozoa, possibly through membrane changes and ROS increase. Although some effects were detrimental, the stimulatory effect of 50% seminal plasma could favor the performance of post-thawed boar semen, as showed in the field (García JC, Domínguez JC, Peña FJ, Alegre B, Gonzalez R, Castro MJ, Habing GG, Kirkwood RN. Thawing boar semen in the presence of seminal plasma: effects on sperm quality and fertility. Anim Reprod Sci 2010;119:160-5). PMID:23756043

  6. High temperature microbial activity in upper soil layers.

    PubMed

    Santana, M M; Gonzalez, J M

    2015-11-01

    Biomineralization at high temperatures in upper soil layers has been largely ignored, although desertification and global warming have led to increasing areas of soils exposed to high temperatures. Recent publications evidenced thermophilic bacteria ubiquity in soils as viable cells, and their role in nutrient cycling and seedling development. High temperature events, frequently observed at medium and low latitudes, locate temporal niches for thermophiles to grow in soils. There, at temperatures inhibitory for common mesophiles, thermophilic bacteria could perform biogeochemical reactions important to the soil food web. Nutrient cycling analyses in soils at medium and low latitudes would benefit from considering the potential role of thermophiles.

  7. Grain sorting in the morphological active layer of a braided river physical model

    NASA Astrophysics Data System (ADS)

    Leduc, P.; Ashmore, P.; Gardner, J. T.

    2015-12-01

    A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the river. This vertical sorting is important for analyzing braided river sedimentology, for numerical modeling of braided river morphodynamics, and for measuring and predicting bedload transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to rework the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs (digital elevation models) of the model river bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morphological active layer and variation in grain size in three dimensions. By normalizing active layer thickness and dividing into 10 sublayers, we show that all grain sizes occur with almost equal frequency in all sublayers. Occurrence of patches and strings of coarser (or finer) material relates to preservation of particular morpho-textural features within the active layer. For numerical modeling and bedload prediction, a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.

  8. FEM assessment of large-strain thaw consolidation

    SciTech Connect

    Foriero, A.; Ladanyi, B.

    1995-02-01

    Finite-element simulations using a large-strain thaw-consolidation model, formulated by the writers, are presented and compared with the data obtained from a warm-oil test pipeline at Inuvik, Northwest Territory, Canada. Nondimensional design charts generated by the method are used to predict thaw-consolidation settlements. A good agreement is found between observed and predicted settlement values giving encouragement for future thaw-settlement predictions, based on finite-element-generated nondimensional charts.

  9. Thaw flow control for liquid heat transport systems

    DOEpatents

    Kirpich, Aaron S.

    1989-01-01

    In a liquid metal heat transport system including a source of thaw heat for use in a space reactor power system, the thaw flow throttle or control comprises a fluid passage having forward and reverse flow sections and a partition having a plurality of bleed holes therein to enable fluid flow between the forward and reverse sections. The flow throttle is positioned in the system relatively far from the source of thaw heat.

  10. The Impact of Enhanced Summer Thaw, Hillslope Disturbances, and Late Season Rainfall on Solute Fluxes from High Arctic Headwater Catchments

    NASA Astrophysics Data System (ADS)

    Lafreniere, M. J.; Lamoureux, S. F.

    2011-12-01

    This study examines variations in the composition and total seasonal fluxes of dissolved solutes in several small High Arctic headwater catchments at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut (74°54'N, 109°35'W) over multiple snowmelt seasons (2007, 2008, 2009) with contrasting climate and permafrost active layer conditions. Climate warming in the High Arctic will affect a number processes that will alter the hydrological and biogeochemical exports from the landscape. Climate change is projected to alter precipitation regimes, resulting in increases in both winter and summer precipitation in the High Arctic, thereby altering hydrological regimes. Warming will result in thickening of the seasonal active layer, which will alter hydrological flow paths and water and solute sources. Additionally, active layer thickening and permafrost warming is also project to enhance the development of thermokarst features, including hillslope disturbances, such as active layer detachment slides and retrogressive thaw slumps. This research compares the flux of inorganic and organic solutes emanating from a group of catchments that were subject to a range hillslope disturbances, or active layer detachment slides (ALDs), at the end of summer 2007. One of the catchments, Goose, was not subject to any disturbance, while active layer slides covered between 6% and 46% of the catchment area in the disturbed catchments. It was hypothesised that solute fluxes would increase primarily with increasing extent and degree of disturbance. This however, was not observed. Rather, comparing five sites with varying degrees of disturbance in 2009 illustrates that on a specific area and specific volume of runoff basis, solute fluxes were unrelated to disturbance extent. Comparing two catchments that were monitored from 2007 (pre-disturbance) through to 2009 (2 yrs post disturbance), shows that both catchments were subject to solute flux increases, however the solute

  11. Quality Evaluation of Pork with Various Freezing and Thawing Methods.

    PubMed

    Ku, Su Kyung; Jeong, Ji Yun; Park, Jong Dae; Jeon, Ki Hong; Kim, Eun Mi; Kim, Young Boong

    2014-01-01

    In this study, the physicochemical and sensory quality characteristics due to the influence of various thawing methods on electro-magnetic and air blast frozen pork were examined. The packaged pork samples, which were frozen by air blast freezing at -45℃ or electro-magnetic freezing at -55℃, were thawed using 4 different methods: refrigeration (4±1℃), room temperature (RT, 25℃), cold water (15℃), and microwave (2450 MHz). Analyses were carried out to determine the drip and cooking loss, water holding capacity (WHC), moisture content and sensory evaluation. Frozen pork thawed in a microwave indicated relatively less thawing loss (0.63-1.24%) than the other thawing methods (0.68-1.38%). The cooking loss after electro-magnetic freezing indicated 37.4% by microwave thawing, compared with 32.9% by refrigeration, 36.5% by RT, and 37.2% by cold water in ham. The thawing of samples frozen by electro-magnetic freezing showed no significant differences between the methods used, while the moisture content was higher in belly thawed by microwave (62.0%) after electro-magnetic freezing than refrigeration (54.8%), RT (61.3%), and cold water (61.1%). The highest overall acceptability was shown for microwave thawing after electro-magnetic freezing but there were no significant differences compared to that of the other samples.

  12. The impact of soil compaction and freezing-thawing cycles on soil structure and yield in Mollisol region of China

    NASA Astrophysics Data System (ADS)

    Wang, Enheng; Zhao, Yusen; Chen, Xiangwei

    2015-04-01

    Agricultural machinery tillage and alternating freezing and thawing are two critical factors associated with soil structure change and accelerates soil erosion in the black soil region of Northeast China. Combining practical machinery operation and natural freeze-thaw cycles with artificial machinery compaction in the field and artificial freeze-thaw cycles in the lab, the plus and minus benefits of machinery tillage, characterization of seasonal freeze-thaw cycles, and their effects on soil structure and yield were studied. Firstly,the effects of machinery type and antecedent water content on soil structure and soil available nutrient were investigated by measuring soil bulk density, soil strength, soil porosity, soil aggregate distribution and stability, and three soil phases. The results showed that: Machinery tillage had positive and negative influence on soil structure, soil in top cultivated layer can be loosened and ameliorated however the subsoil accumulation of compaction was resulted. For heavy and medium machinery, subsoil compaction formed in the soil depth of 41~60cm and 31~40cm, respectively; however during the soil depth of 17.5~30cm under medium machinery operation there was a new plow pan produced because of the depth difference between harvesting and subsoiling. Antecedent water content had a significant effect on soil structure under machinery operations. Higher water antecedent resulted in deeper subsoil compaction at 40cm,which was deeper by 10cm than lower water content and soil compaction accumulation occurred at the first pass under higher water content condition. Besides water content and bulk density, soil organic matter is another key factor for affecting compressive-resilient performance of tillage soil. Secondly, based on the soils sampled from fields of the black soil region, the effects of freeze-thaw cycles on soil structure at different soil depths (0 -- 40 cm, 40 -- 80 cm, 120 -- 160 cm) and size scales (field core sampling

  13. Response of Soil Biogeochemistry to Freeze-thaw Cycles: Impacts on Greenhouse Gas Emission and Nutrient Fluxes

    NASA Astrophysics Data System (ADS)

    Rezanezhad, F.; Parsons, C. T.; Smeaton, C. M.; Van Cappellen, P.

    2014-12-01

    Freeze-thaw is an abiotic stress applied to soils and is a natural process at medium to high latitudes. Freezing and thawing processes influence not only the physical properties of soil, but also the metabolic activity of soil microorganisms. Fungi and bacteria play a crucial role in soil organic matter degradation and the production of greenhouse gases (GHG) such as CO2, CH4 and N2O. Production and consumption of these atmospheric trace gases are the result of biological processes such as photosynthesis, aerobic respiration (CO2), methanogenesis, methanotrophy (CH4), nitrification and denitrification (N2O). To enhance our understanding of the effects of freeze-thaw cycles on soil biogeochemical transformations and fluxes, a highly instrumented soil column experiment was designed to realistically simulate freeze-thaw dynamics under controlled conditions. Pore waters collected periodically from different depths of the column and solid-phase analyses on core material obtained at the initial and end of the experiment highlighted striking geochemical cycling. CO2, CH4 and N2O production at different depths within the column were quantified from dissolved gas concentrations in pore water. Subsequent emissions from the soil surface were determined by direct measurement in the head space. Pulsed CO2 emission to the headspace was observed at the onset of thawing, however, the magnitude of the pulse decreased with each subsequent freeze-thaw cycle indicating depletion of a "freeze-thaw accessible" carbon pool. Pulsed CO2 emission was due to a combination of physical release of gases dissolved in porewater and entrapped below the frozen zone and changing microbial respiration in response to electron acceptor variability (O2, NO3-, SO42-). In this presentation, we focus on soil-specific physical, chemical, microbial factors (e.g. redox conditions, respiration, fermentation) and the mechanisms that drive GHG emission and nutrient cycling in soils under freeze-thaw cycles.

  14. Recent low-latitude freeze thaw on Mars

    NASA Astrophysics Data System (ADS)

    Page, David P.

    2007-07-01

    Outside polar latitudes, features corresponding to surface thaw have yet to be identified on Mars. The youthful gully landforms observed at mid-high latitude [Malin, M., Edgett, K., 2000. Science 288, 2330-2335] are the nearest candidate, but the source (and nature) of the gully carving agent remains controversial [e.g., Musselwhite, D.S., Swindle, T.D., Lunine, J.I., 2001. Geophys. Res. Lett. 28, 1283-1285; Mellon, M.T., Phillips, R.J., 2001. J. Geophys. Res. 106, 1-15; Knauth, L.P., Burt, D.M., 2002. Icarus 158, 267-271; Costard, F., Forget, F., Mangold, N., Peulvast, J.P., 2002. Science 295, 110-113; Christensen, P.R., 2003. Nature 422, 45-48; Treiman, A.H., 2003. J. Geophys. Res. 108]. At higher obliquity than the present epoch, near-surface ground ice should be present globally [Mellon, M.T., Jakosky, B.M., 1995. J. Geophys. Res. 100 (E6), 11781-11799], populated by condensation of atmospheric water vapour in the top few metres of the regolith, or emplaced as dusty ice sheets reaching down towards the equator. The latitudinal restriction of these gullies to regions poleward of ±30° appears to argue against a thaw component to their formation—since ground ice is present and stable at all latitudes at high obliquity, the current (low) obliquity regime should result in ground ice thaw at low latitudes, where insolation and daytime temperatures are currently greatest, and this is not observed. A previously undescribed meltwater sequence in the Cerberus plains, at 20° N/187° E, shows that comparable, but much more continuous, and mappable melting and surface runoff have occurred in the geologically recent past at near-equatorial latitudes on Mars. Polygonal ground in the Cerberus plains is seen by the Mars Global Surveyor Mars Orbiter Camera (MOC) to suffer sequential, regional-scale volatile-loss consistent with thaw of near-surface ground ice under periglacial conditions. This degradation is continuously sampled by a single MOC strip, showing an icy

  15. Orexin-dependent activation of layer VIb enhances cortical network activity and integration of non-specific thalamocortical inputs.

    PubMed

    Hay, Y Audrey; Andjelic, Sofija; Badr, Sammy; Lambolez, Bertrand

    2015-11-01

    Neocortical layer VI is critically involved in thalamocortical activity changes during the sleep/wake cycle. It receives dense projections from thalamic nuclei sensitive to the wake-promoting neuropeptides orexins, and its deepest part, layer VIb, is the only cortical lamina reactive to orexins. This convergence of wake-promoting inputs prompted us to investigate how layer VIb can modulate cortical arousal, using patch-clamp recordings and optogenetics in rat brain slices. We found that the majority of layer VIb neurons were excited by nicotinic agonists and orexin through the activation of nicotinic receptors containing α4-α5-β2 subunits and OX2 receptor, respectively. Specific effects of orexin on layer VIb neurons were potentiated by low nicotine concentrations and we used this paradigm to explore their intracortical projections. Co-application of nicotine and orexin increased the frequency of excitatory post-synaptic currents in the ipsilateral cortex, with maximal effect in infragranular layers and minimal effect in layer IV, as well as in the contralateral cortex. The ability of layer VIb to relay thalamocortical inputs was tested using photostimulation of channelrhodopsin-expressing fibers from the orexin-sensitive rhomboid nucleus in the parietal cortex. Photostimulation induced robust excitatory currents in layer VIa neurons that were not pre-synaptically modulated by orexin, but exhibited a delayed, orexin-dependent, component. Activation of layer VIb by orexin enhanced the reliability and spike-timing precision of layer VIa responses to rhomboid inputs. These results indicate that layer VIb acts as an orexin-gated excitatory feedforward loop that potentiates thalamocortical arousal.

  16. Extending airborne electromagnetic surveys for regional active layer and permafrost mapping with remote sensing and ancillary data, Yukon Flats ecoregion, central Alaska

    USGS Publications Warehouse

    Pastick, Neal J.; Jorgenson, M. Torre; Wylie, Bruce K.; Minsley, Burke J.; Ji, Lei; Walvoord, Michelle A.; Smith, Bruce D.; Abraham, Jared D.; Rose, Joshua R.

    2013-01-01

    Machine-learning regression tree models were used to extrapolate airborne electromagnetic resistivity data collected along flight lines in the Yukon Flats Ecoregion, central Alaska, for regional mapping of permafrost. This method of extrapolation (r = 0.86) used subsurface resistivity, Landsat Thematic Mapper (TM) at-sensor reflectance, thermal, TM-derived spectral indices, digital elevation models and other relevant spatial data to estimate near-surface (0–2.6-m depth) resistivity at 30-m resolution. A piecewise regression model (r = 0.82) and a presence/absence decision tree classification (accuracy of 87%) were used to estimate active-layer thickness (ALT) (< 101 cm) and the probability of near-surface (up to 123-cm depth) permafrost occurrence from field data, modelled near-surface (0–2.6 m) resistivity, and other relevant remote sensing and map data. At site scale, the predicted ALTs were similar to those previously observed for different vegetation types. At the landscape scale, the predicted ALTs tended to be thinner on higher-elevation loess deposits than on low-lying alluvial and sand sheet deposits of the Yukon Flats. The ALT and permafrost maps provide a baseline for future permafrost monitoring, serve as inputs for modelling hydrological and carbon cycles at local to regional scales, and offer insight into the ALT response to fire and thaw processes.

  17. Possible Future Changes in Permafrost and Active Layer Thickness in Northern Eurasia and their Relation to Permafrost Carbon Pool

    NASA Astrophysics Data System (ADS)

    Marchenko, S. S.; Romanovsky, V. E.; Chapman, W. L.; Walsh, J. E.

    2012-12-01

    Recent observations indicate a warming of permafrost in many northern regions with the resulting degradation of ice-rich and carbon-rich permafrost. Permafrost temperature has increased by 1 to 3 deg C in northern Eurasia during the last 30 years. To assess possible changes in the permafrost thermal state and the active layer thickness we implemented the GIPL2 (Geophysical Institute Permafrost Lab) transient model for the entire Northern Eurasia for the 1981-2100 time period. Input parameters to the model are spatial datasets of mean monthly air temperature, snow properties or SWE, prescribed vegetation and thermal properties of the multilayered soil column, and water content. The climate scenario was derived from an ensemble of five IPCC Global Circulation Models (GCM) ECHAM5, GFDL21, CCSM, HADcm and CCCMA. The outputs from these five models have been scaled down to 25 km spatial resolution with monthly temporal resolution, based on the composite (mean) output of the five models, using the IPCC SRES A1B CO2 emission scenario through the end of current century. Historic ground temperature measurements in shallow boreholes (3.2 m in depth) from more than 120 weather stations located within the continuous, discontinuous, and sporadic permafrost zones were available for the initial model validation and calibration. To prescribe the thermal properties we used the map of soil characteristics for whole of Russia (Stolbovoi & Savin, 2002) and the map of Soil Carbon Pools, CO2 and CH4 emissions (Tarnocai et al., 2009) and also the soil structure descriptions available for some locations. We estimated dynamics of the seasonally thawed volume of soils within the two upper meters for the entire North Eurasia. The model results indicate 1,200 km3 of seasonally unfrozen soils within the two upper meters within 10,800,000 km2 of northern Eurasian permafrost domain during the last two decades of the 20th century. Our projections have shown that unfrozen volume of soil within two

  18. Freezing and thawing or freezing, thawing, and aging effects on beef tenderness.

    PubMed

    Grayson, A L; King, D A; Shackelford, S D; Koohmaraie, M; Wheeler, T L

    2014-06-01

    The objective of this study was to determine the effect of freezing and thawing or freezing and thawing with an additional aging period after frozen storage on the tenderness of longissimus lumborum (LL) and semitendinosus (ST) steaks relative to aged, fresh steaks. Left-side LL and ST (n = 35 each) were obtained from U.S. Select carcasses classified at the grading stand by the U.S. Meat Animal Research Center visible and near-infrared spectroscopy tenderness system to have predicted slice shear force greater than 16.5 kg at 14 d postmortem. At 2 d postmortem, 2.54 cm thick steaks were cut from each muscle and assigned to 1 of the following treatments: 2 d fresh (2FRESH), 2 d freeze + thaw (2FREEZE), 2 d freeze + thaw + 12 d age (2FREEZE+12AGE), 14 d fresh (14FRESH), 14 d freeze + thaw (14FREEZE), 14 d freeze + thaw + 14 d age (14FREEZE+14AGE), and 28 d fresh (28FRESH). Steaks assigned to a freezing treatment were frozen at -26°C for 30 d before thawing/cooking or thawing with an additional aging period at 2°C. Slice shear force for LL and ST was lower (P < 0.01) for 2FREEZE (27.4 and 24.5 kg) and 14FREEZE (22.4 and 22.4 kg) compared to 2FRESH (33.0 and 29.2 kg) and 14FRESH (25.3 and 25.5 kg), respectively. Slice shear force for LL and ST was lower (P < 0.01) for 2FREEZE+12AGE (17.8 and 20.8 kg) and 14FREEZE+14AGE (14.6 and 19.0 kg) compared to 14FRESH (25.3 and 25.5 kg) and 28FRESH (18.7 and 21.7 kg), respectively. Desmin degradation for LL was not different (P > 0.05) between 2FREEZE (21.0%) and 2FRESH (14.6%) or between 14FREEZE (40.4%) and 14FRESH (38.4%); however, desmin degradation was higher (P < 0.06) in 2FREEZE+12AGE (46.7%) and 14FREEZE+14AGE (71.1%) when compared to 14FRESH (38.4%) and 28FRESH (60.5%), respectively. Cooking loss for LL was higher (P < 0.01) in 2FREEZE+12AGE (15.2%) compared to 14FRESH (14.0%) but was not different (P > 0.05) between 14FREEZE+14AGE (15.0%) and 28FRESH (14.3%). Freezing and thawing or a combination of freezing, thawing

  19. Permafrost vulnerability and active layer thickness increases over the high northern latitudes inferred from satellite remote sensing and process model assessments

    NASA Astrophysics Data System (ADS)

    Park, Hotaek; Kim, Youngwook

    2016-04-01

    Permafrost extent (PE) and active layer thickness (ALT) are important for assessing high northern latitude (HNL) ecological and hydrological processes, and potential land-atmosphere carbon and climate feedbacks. We developed a new approach to infer PE from satellite microwave remote sensing of daily landscape freeze-thaw (FT) status. Our results document, for the first time, the use of satellite microwave FT observations for monitoring permafrost extent and condition. The FT observations define near-surface thermal status used to determine permafrost extent and stability over a 30-year (1980-2009) satellite record. The PE results showed similar performance against independent inventory and process model (CHANGE) estimates, but with larger differences over heterogeneous permafrost subzones. A consistent decline in the ensemble mean of permafrost areas (‑0.33 million km2 decade‑1; p < 0.05) coincides with regional warming (0.4 °C decade‑1; p < 0.01), while more than 40% (9.6 million km2) of permafrost areas are vulnerable to degradation based on the 30-year PE record. ALT estimates determined from satellite (MODIS) and ERA-Interim temperatures, and CHANGE simulations, compared favorably with independent field observations and indicate deepening ALT trends consistent with widespread permafrost degradation under recent climate change. The integration of remote sensing and modeling of permafrost and active layer conditions developed from this study may facilitate regular and effective regional monitoring of these parameters, and expand applications of remote sensing for examining permafrost-related feedbacks and consequences for biogeochemical and hydrological cycling in the Arctic.

  20. Effect of alpha-lipoic acid on boar spermatozoa quality during freezing-thawing.

    PubMed

    Shen, Tao; Jiang, Zhong-Liang; Li, Cong-Jun; Hu, Xiao-Chen; Li, Qing-Wang

    2016-04-01

    Alpha-lipoic acid (ALA) is known to be a natural antioxidant. The aim of the present study was to evaluate the cryoprotective effect of ALA on the motility of boar spermatozoa and its antioxidant effect on boar spermatozoa during freezing-thawing. Different concentrations (2.0, 4.0, 6.0, 8.0 or 10.0 mg/ml) of ALA were added to the extender used to freeze boar semen, and the effects on the quality and endogenous antioxidant enzyme activities of frozen-thawed spermatozoa were assessed. The results indicated that the addition of ALA to the extender resulted in a higher percentage of motile spermatozoa post-thaw (P < 0.05). The activities of superoxide dismutase, lactate dehydrogenase, glutamic-oxaloacetic transaminase and catalase improved after adding ALA to the extender (P < 0.05). Artificial insemination results showed that pregnancy rate and litter size were significantly higher at 6.0 mg/ml in the ALA group than in the control group (P < 0.05). In conclusion, ALA conferred a cryoprotective capacity to the extender used for boar semen during the process of freezing-thawing, and the optimal concentration of ALA for the frozen extender was 6.0 mg/ml.

  1. The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

    SciTech Connect

    Park, Jeong Y.; Aliaga, Cesar; Renzas, J. Russell; Lee, Hyunjoo; Somorjai, Gabor A.

    2008-12-17

    We report the catalytic activity of colloid platinum nanoparticles synthesized with different organic capping layers. On the molecular scale, the porous organic layers have open spaces that permit the reactant and product molecules to reach the metal surface. We carried out CO oxidation on several platinum nanoparticle systems capped with various organic molecules to investigate the role of the capping agent on catalytic activity. Platinum colloid nanoparticles with four types of capping layer have been used: TTAB (Tetradecyltrimethylammonium Bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). The reactivity of the Pt nanoparticles varied by 30%, with higher activity on TTAB coated nanoparticles and lower activity on HDT, while the activation energy remained between 27-28 kcal/mol. In separate experiments, the organic capping layers were partially removed using ultraviolet light-ozone generation techniques, which resulted in increased catalytic activity due to the removal of some of the organic layers. These results indicate that the nature of chemical bonding between organic capping layers and nanoparticle surfaces plays a role in determining the catalytic activity of platinum colloid nanoparticles for carbon monoxide oxidation.

  2. Evaluation of human sperm function after repeated freezing and thawing.

    PubMed

    Bandularatne, Enoka; Bongso, Ariff

    2002-01-01

    Sperm storage via freezing has been useful for men who have difficulty masturbating during assisted reproductive technology (ART) programs and before impotency caused by chemotherapy, vasectomy, and other procedures. Studies were undertaken to evaluate the extent of cryoinjury to sperm after repeated freezing and thawing. The results showed that normozoospermic and oligozoospermic sperm survived after 3 repeated freeze-thaw cycles. The inclusion of seminal plasma did not seem to protect human sperm during freezing and thawing. There were no significant differences in recovery percentages for motile, vital, and morphologically normal sperm between slow and rapid freezing methods in thaws 1, 2, and 3 of normozoospermic and oligozoospermic unwashed (u), washed (w), and washed + seminal plasma (ws) samples. However, there were significant percentage drops in the recovery of motile and vital sperm between each thaw (ie, first to second thaw, and second to third thaw) using both slow and rapid freezing for u, w, and ws samples (P < .01). There were also no significant differences in percentage recovery of motile, vital, and morphologically normal sperm between u, w, and ws samples during thaws 1 to 3 in the normozoospermic and oligozoospermic groups. Sperm were capable of fertilizing hamster oocytes microinjected with single sperms after 3 freeze-thaw cycles as evidenced by the formation of 2 distinct pronuclei and 2 polar bodies in 22.2% and 17.2% of normozoospermic and oligozoospermic samples, respectively. The numbers of normal vital motile sperm after 3 serial freeze-thaw cycles are adequate for bringing about fertilization via intracytoplasmic sperm injection in ART programs. Thus, leftover washed sperm in laboratories that perform in vitro fertilization can be frozen, thawed, and refrozen several times without loss of the sperms' ability to fertilize. This approach has tremendous benefits for men who have difficulty producing sperm and for those with low and

  3. Improving ice nucleation activity of zein film through layer-by-layer deposition of extracellular ice nucleators.

    PubMed

    Shi, Ke; Yu, Hailong; Lee, Tung-Ching; Huang, Qingrong

    2013-11-13

    Zein protein has been of scientific interest in the development of biodegradable functional food packaging. This study aimed at developing a novel zein-based biopolymer film with ice nucleation activity through layer-by-layer deposition of biogenic ice nucleators, that is, extracellular ice nucleators (ECINs) isolated from Erwinia herbicola , onto zein film surface. The adsorption behaviors and mechanisms were investigated using quartz crystal microbalance with dissipation monitoring (QCM-D). On unmodified zein surface, the highest ECINs adsorption occurred at pH 5.0; on UV/ozone treated zein surface followed by deposition of poly(diallyldimethylammonium chloride) (PDADMAC) layer, the optimum condition for ECINs adsorption occurred at pH 7.0 and I 0.05 M, where the amount of ECINs adsorbed was also higher than that on unmodified zein surface. QCM-D analyses further revealed a two-step adsorption process on unmodified zein surfaces, compared to a one-step adsorption process on PDADMAC-modified zein surface. Also, significantly, in order to quantify the ice nucleation activity of ECINs-coated zein films, an empirical method was developed to correlate the number of ice nucleators with the ice nucleation temperature measured by differential scanning calorimetry. Calculated using this empirical method, the highest ice nucleation activity of ECINs on ECINs-modified zein film reached 64.1 units/mm(2), which was able to elevate the ice nucleation temperature of distilled water from -15.5 °C to -7.3 °C.

  4. Freeze-thaw cycles as drivers of complex ribozyme assembly

    PubMed Central

    Mutschler, Hannes; Wochner, Aniela; Holliger, Philipp

    2015-01-01

    The emergence of an RNA catalyst capable of self-replication is considered a key transition in the origin of life. However, how such replicase ribozymes emerged from the pools of short RNA oligomers arising from prebiotic chemistry and non-enzymatic replication is unclear. Here we show that RNA polymerase ribozymes can assemble from simple catalytic networks of RNA oligomers no longer than 30 nucleotides. The entropically disfavoured assembly reaction is driven by iterative freeze-thaw cycles even in the absence of external activation chemistry. The steep temperature and concentration gradients of such cycles result in an RNA chaperone effect that enhances the otherwise only partially realized catalytic potential of the RNA oligomer pool by an order of magnitude. Our work outlines how cyclic physicochemical processes could have driven an expansion of RNA compositional and phenotypic complexity from simple oligomer pools. PMID:25991529

  5. Depth heterogeneity of fully aromatic polyamide active layers in reverse osmosis and nanofiltration membranes.

    PubMed

    Coronell, Orlando; Mariñas, Benito J; Cahill, David G

    2011-05-15

    We studied the depth heterogeneity of fully aromatic polyamide (PA) active layers in commercial reverse osmosis (RO) and nanofiltration (NF) membranes by quantifying near-surface (i.e., top 6 nm) and volume-averaged properties of the active layers using X-ray photoelectron spectrometry (XPS) and Rutherford backscattering spectrometry (RBS), respectively. Some membranes (e.g., ESPA3 RO) had active layers that were depth homogeneous with respect to the concentration and pK(a) distribution of carboxylic groups, degree of polymer cross-linking, concentration of barium ion probe that associated with ionized carboxylic groups, and steric effects experienced by barium ion. Other membranes (e.g., NF90 NF) had active layers that were depth heterogeneous with respect to the same properties. Our results therefore support the existence of both depth-homogeneous and depth-heterogeneous active layers. It remains to be assessed whether the depth heterogeneity consists of gradually changing properties throughout the active layer depth or of distinct sublayers with different properties.

  6. Activity of lactoperoxidase when adsorbed on protein layers.

    PubMed

    Haberska, Karolina; Svensson, Olof; Shleev, Sergey; Lindh, Liselott; Arnebrant, Thomas; Ruzgas, Tautgirdas

    2008-09-15

    Lactoperoxidase (LPO) is an enzyme, which is used as an antimicrobial agent in a number of applications, e.g., food technology. In the majority of applications LPO is added to a homogeneous product phase or immobilised on product surface. In the latter case, however, the measurements of LPO activity are seldom reported. In this paper we have assessed LPO enzymatic activity on bare and protein modified gold surfaces by means of electrochemistry. It was found that LPO rapidly adsorbs to bare gold surfaces resulting in an amount of LPO adsorbed of 2.9mg/m(2). A lower amount of adsorbed LPO is obtained if the gold surface is exposed to bovine serum albumin, bovine or human mucin prior to LPO adsorption. The enzymatic activity of the adsorbed enzyme is in general preserved at the experimental conditions and varies only moderately when comparing bare gold and gold surface pretreated with the selected proteins. The measurement of LPO specific activity, however, indicate that it is about 1.5 times higher if LPO is adsorbed on gold surfaces containing a small amount of preadsorbed mucin in comparison to the LPO directly adsorbed on bare gold.

  7. Crystallinity Modulation of Layered Carbon Nitride for Enhanced Photocatalytic Activities.

    PubMed

    Wang, Jianhai; Shen, Yanfei; Li, Ying; Liu, Songqin; Zhang, Yuanjian

    2016-08-22

    As an emerging metal-free semiconductor, covalently bonded carbon nitride (CN) has attracted much attention in photocatalysis. However, drawbacks such as a high recombination rate of excited electrons and holes hinder its potential applications. Tailoring the crystallinity of semiconductors is an important way to suppress unwanted charge recombination, but has rarely been applied to CN so far. Herein, a simple method to synthesize CN of high crystallinity by protonation of specific intermediate species during conventional polymerization is reported. Interestingly, the as-obtained CN exhibited improved photocatalytic activities of up to seven times those of the conventional bulk CN. This approach, with only a slight change to the conventional method, provides a facile way to effectively regulate the crystallinity of bulk CN to improve its photocatalytic activities and sheds light on large-scale industrial applications of CN with high efficiency for sustainable energy. PMID:27436164

  8. Crystallinity Modulation of Layered Carbon Nitride for Enhanced Photocatalytic Activities.

    PubMed

    Wang, Jianhai; Shen, Yanfei; Li, Ying; Liu, Songqin; Zhang, Yuanjian

    2016-08-22

    As an emerging metal-free semiconductor, covalently bonded carbon nitride (CN) has attracted much attention in photocatalysis. However, drawbacks such as a high recombination rate of excited electrons and holes hinder its potential applications. Tailoring the crystallinity of semiconductors is an important way to suppress unwanted charge recombination, but has rarely been applied to CN so far. Herein, a simple method to synthesize CN of high crystallinity by protonation of specific intermediate species during conventional polymerization is reported. Interestingly, the as-obtained CN exhibited improved photocatalytic activities of up to seven times those of the conventional bulk CN. This approach, with only a slight change to the conventional method, provides a facile way to effectively regulate the crystallinity of bulk CN to improve its photocatalytic activities and sheds light on large-scale industrial applications of CN with high efficiency for sustainable energy.

  9. Ancient Yedoma carbon loss: primed by ice wedge thaw?

    NASA Astrophysics Data System (ADS)

    Dowdy, K. L.; Vonk, J. E.; Mann, P. J.; Zimov, N.; Bulygina, E. B.; Davydova, A.; Spencer, R. G.; Holmes, R. M.

    2012-12-01

    Northeast Siberian permafrost is dominated by frozen Yedoma deposits containing ca. 500 Gt of carbon, nearly a quarter of northern permafrost organic carbon (OC). Yedoma deposits are Pleistocene-age alluvial and/or aeolian accumulations characterized by high ice wedge content (~50%), making them particularly vulnerable to a warming climate and to surface collapse upon thaw. Dissolved OC in streams originating primarily from Yedoma has been shown to be highly biolabile, relative to waters containing more modern OC. The cause of this biolability, however, remains speculative. Here we investigate the influence of ice wedge input upon the bioavailability of Yedoma within streams from as a potential cause of Yedoma carbon biolability upon release into the Kolyma River from the thaw-eroding river exposures of Duvannyi Yar, NE Siberia. We measured biolability on (1) ice wedge, Kolyma, and Yedoma leachate controls; (2) ice wedge and Kolyma plus Yedoma OC (8 g/L); and (3) varying ratios of ice wedge water to Kolyma river water. Biolability assays were conducted using both 5-day BOD (biological oxygen demand) and 11-day BDOC (biodegradable dissolved organic carbon) incubations. We found that ancient DOC in Yedoma soil leachate alone was highly biolabile with losses of 52±0.1% C over a 5-day BOD incubation. Similarly, DOC contained in pure ice wedge water was found to be biolabile, losing 21±0% C during a 5-day BOD incubation. Increased ice wedge contributions led to higher overall C losses in identical Yedoma soil leachates, with 8.9±0.6% losses of Yedoma C with 100% ice wedge water, 7.1±1% (50% ice wedge/ 50% Kolyma) and 5±0.3% with 100% Kolyma River water. We discuss potential mechanisms for the increased loss of ancient C using associated measurements of nutrient availability, carbon quality (CDOM/FDOM) and extracellular enzyme activity rates. Our initial results indicate that ice wedge meltwater forming Yedoma streams makes Yedoma OC more bioavailable than it would

  10. Cross-tolerance between osmotic and freeze-thaw stress in microbial assemblages from temperate lakes.

    PubMed

    Wilson, Sandra L; Frazer, Corey; Cumming, Brian F; Nuin, Paulo A S; Walker, Virginia K

    2012-11-01

    Osmotic stress can accompany increases in solute concentrations because of freezing or high-salt environments. Consequently, microorganisms from environments with a high-osmotic potential may exhibit cross-tolerance to freeze stress. To test this hypothesis, enrichments derived from the sediment and water of temperate lakes with a range of salt concentrations were subjected to multiple freeze-thaw cycles. Surviving isolates were identified and metagenomes were sampled prior to and following selection. Enrichments from alkali lakes were typically the most freeze-thaw resistant with only 100-fold losses in cell viability, and those from freshwater lakes were most susceptible, with cell numbers reduced at least 100,000-fold. Metagenomic analysis suggested that selection reduced assemblage diversity more in freshwater samples than in those from saline lakes. Survivors included known psychro-, halo- and alkali-tolerant bacteria. Characterization of freeze-thaw-resistant isolates from brine and alkali lakes showed that few isolates had ice-associating activities such as antifreeze or ice nucleation properties. However, all brine- and alkali-derived isolates had high intracellular levels of osmolytes and/or appeared more likely to form biofilms. Conversely, these phenotypes were infrequent amongst the freshwater-derived isolates. These observations are consistent with microbial cross-tolerance between osmotic and freeze-thaw stresses. PMID:22551442

  11. Effect of prostatic fluid on the quality of fresh and frozen-thawed canine epididymal spermatozoa.

    PubMed

    Korochkina, E; Johannisson, A; Goodla, Lavanya; Morrell, J M; Axner, E

    2014-12-01

    Canine epididymal spermatozoa have a low freeze-tolerance ability compared with ejaculated spermatozoa, which could arise from the absence of prostatic fluid (PF). Therefore, the purpose of this work was to elucidate the influence of PF on the quality of canine epididymal sperm before and after freezing. Caudae epididymides were retrieved from eight dogs after routine castration. Spermatozoa were released by slicing the tissue and were extended in either Tris solution or PF before freezing. Frozen sperm samples were thawed at 70 °C for 8 seconds in a waterbath. Sperm concentration, motility using computer-assisted sperm analysis, morphology, plasma membrane, acrosome and chromatin integrity were assessed in the fresh sperm samples (after 20 minutes incubation) and at 0 and 4 hours after thawing. Progressive motility, distance straight line, distance average path, average path velocity, curvilinear velocity, straight line velocity, straightness, linearity, wobble, and beat cross frequency were significantly increased after extraction into PF. There was a higher proportion of spermatozoa with DNA damage in the PF treatment group at 4 hours after thawing than in the Tris treatment group (15.8% vs. 6.7%, P < 0.05). These results suggest that the addition of PF to canine spermatozoa activates sperm motility in fresh spermatozoa but has a negative effect on chromatin integrity after freezing-thawing.

  12. Disappearing Arctic tundra ponds: Fine-scale analysis of surface hydrology in drained thaw lake basins over a 65 year period (1948-2013)

    NASA Astrophysics Data System (ADS)

    Andresen, Christian G.; Lougheed, Vanessa L.

    2015-03-01

    Long-term fine-scale dynamics of surface hydrology in Arctic tundra ponds (less than 1 ha) are largely unknown; however, these small water bodies may contribute substantially to carbon fluxes, energy balance, and biodiversity in the Arctic system. Change in pond area and abundance across the upper Barrow Peninsula, Alaska, was assessed by comparing historic aerial imagery (1948) and modern submeter resolution satellite imagery (2002, 2008, and 2010). This was complemented by photogrammetric analysis of low-altitude kite-borne imagery in combination with field observations (2010-2013) of pond water and thaw depth transects in seven ponds of the International Biological Program historic research site. Over 2800 ponds in 22 drained thaw lake basins (DTLB) with different geological ages were analyzed. We observed a net decrease of 30.3% in area and 17.1% in number of ponds over the 62 year period. The inclusion of field observations of pond areas in 1972 from a historic research site confirms the linear downward trend in area. Pond area and number were dependent on the age of DTLB; however, changes through time were independent of DTLB age, with potential long-term implications for the hypothesized geomorphologic landscape succession of the thaw lake cycle. These losses were coincident with increases in air temperature, active layer, and density and cover of aquatic emergent plants in ponds. Increased evaporation due to warmer and longer summers, permafrost degradation, and transpiration from encroaching aquatic emergent macrophytes are likely the factors contributing to the decline in surface area and number of ponds.

  13. Influence of increasing active-layer depth and continued permafrost degradation on carbon, water and energy fluxes over two forested permafrost landscapes in the Taiga Plains, NWT, Canada

    NASA Astrophysics Data System (ADS)

    Sonnentag, O.; Baltzer, J.; Chasmer, L. E.; Detto, M.; Marsh, P.; Quinton, W. L.

    2012-12-01

    Recent research suggests an increase in active-layer depth (ALD) in the continuous permafrost zone and degradation of the discontinuous permafrost zone into seasonally frozen. Increasing ALD and continued permafrost degradation will have far-reaching consequences for northern ecosystems including altered regional hydrology and the exposure of additional soil organic carbon (C) to microbial decomposition. These changes might cause positive or negative net feedbacks to the climate system by altering important land surface properties and/or by releasing stored soil organic C to the atmosphere as CO2 and/or CH4. Knowledge gaps exist regarding the links between increasing ALD and/or permafrost degradation, regional hydrology, vegetation composition and structure, land surface properties, and CO2 and CH4 sink-source strengths. The goal of our interdisciplinary project is to shed light on these links by providing a mechanistic understanding of permafrost-thawing consequences for hydrological, ecophysiological and biogeochemical processes at two forested permafrost landscapes in the Taiga Plains, NWT, Canada: Scotty Creek and Havikpak Creek in the discontinuous and in the continuous permafrost zones, respectively (Fig.). The sites will be equipped with identical sets of instrumentation (start: 2013), to measure landscape-scale net exchanges of CO2, CH4, water and energy with the eddy covariance technique. These measurements will be complemented by repeated surveys of surface and frost table topography and vegetation, by land cover-type specific fluxes of CO2 and CH4 measured with a static chamber technique, and by remote sensing-based footprint analysis. With this research we will address the following questions: What is the net effect of permafrost thawing-induced biophysical and biogeochemical feedbacks to the climate system? How do these two different types of feedback differ between the discontinuous and continuous permafrost zones? Is the decrease (increase) in net CO

  14. Contribution of S-Layer Proteins to the Mosquitocidal Activity of Lysinibacillus sphaericus

    PubMed Central

    Allievi, Mariana Claudia; Palomino, María Mercedes; Prado Acosta, Mariano; Lanati, Leonardo; Ruzal, Sandra Mónica; Sánchez-Rivas, Carmen

    2014-01-01

    Lysinibacillus sphaericus strains belonging the antigenic group H5a5b produce spores with larvicidal activity against larvae of Culex mosquitoes. C7, a new isolated strain, which presents similar biochemical characteristics and Bin toxins in their spores as the reference strain 2362, was, however, more active against larvae of Culex mosquitoes. The contribution of the surface layer protein (S-layer) to this behaviour was envisaged since this envelope protein has been implicated in the pathogenicity of several bacilli, and we had previously reported its association to spores. Microscopic observation by immunofluorescence detection with anti S-layer antibody in the spores confirms their attachment. S-layers and BinA and BinB toxins formed high molecular weight multimers in spores as shown by SDS-PAGE and western blot detection. Purified S-layer from both L. sphaericus C7 and 2362 strain cultures was by itself toxic against Culex sp larvae, however, that from C7 strain was also toxic against Aedes aegypti. Synergistic effect between purified S-layer and spore-crystal preparations was observed against Culex sp. and Aedes aegypti larvae. This effect was more evident with the C7 strain. In silico analyses of the S-layer sequence suggest the presence of chitin-binding and hemolytic domains. Both biochemical characteristics were detected for both S-layers strains that must justify their contribution to pathogenicity. PMID:25354162

  15. Discovery of a novel methanogen prevalent in thawing permafrost.

    PubMed

    Mondav, Rhiannon; Woodcroft, Ben J; Kim, Eun-Hae; McCalley, Carmody K; Hodgkins, Suzanne B; Crill, Patrick M; Chanton, Jeffrey; Hurst, Gregory B; VerBerkmoes, Nathan C; Saleska, Scott R; Hugenholtz, Philip; Rich, Virginia I; Tyson, Gene W

    2014-01-01

    Thawing permafrost promotes microbial degradation of cryo-sequestered and new carbon leading to the biogenic production of methane, creating a positive feedback to climate change. Here we determine microbial community composition along a permafrost thaw gradient in northern Sweden. Partially thawed sites were frequently dominated by a single archaeal phylotype, Candidatus 'Methanoflorens stordalenmirensis' gen. nov. sp. nov., belonging to the uncultivated lineage 'Rice Cluster II' (Candidatus 'Methanoflorentaceae' fam. nov.). Metagenomic sequencing led to the recovery of its near-complete genome, revealing the genes necessary for hydrogenotrophic methanogenesis. These genes are highly expressed and methane carbon isotope data are consistent with hydrogenotrophic production of methane in the partially thawed site. In addition to permafrost wetlands, 'Methanoflorentaceae' are widespread in high methane-flux habitats suggesting that this lineage is both prevalent and a major contributor to global methane production. In thawing permafrost, Candidatus 'M. stordalenmirensis' appears to be a key mediator of methane-based positive feedback to climate warming.

  16. Thawing of Frozen Dressed Tuna by Microwave Heating

    NASA Astrophysics Data System (ADS)

    Tanaka, Takeo; Nagasaki, Tasuku; Takahashi, Kenji

    Large sized frozen yellowfin tuna and southern bluefin tuna in dressed form (decapitated and gutted) were thawed by microwave (915 MHz) irradiation. Temperature rise of the tuna during thawing was measured. Quality of the tuna meat before and after thawing was compared with each other using objective quality index such as degree of discoloration (met-myoglobin ratio), freshness (K1 value) and taste cornponent (K2 value). Results are as follows : (1) Both frozen tunas were thawed fairly well within as short time as 30 min without any partial over heating. (2) No changes in met-myoglobin ratio, K1 and K2 values were observed in the cases of yellow fin tuna. Slight discoloration, however, occurred in southern bluefin tuna meat during microwave thawing. This problem has been left unsolved.

  17. Is Thawing Permafrost as a Result of Global Warming a Possible Significant Source of Degradable Carbon for Microbiota Residing In Situ and in Arctic Rivers?

    NASA Astrophysics Data System (ADS)

    Zhu, E. Y.; Coolen, M. J.

    2008-12-01

    Northern high-latitude ecosystems contain about half of the world's soil carbon, most of which is stored in permanently frozen soil (permafrost). Global warming through the 21st century is expected to induce permafrost thaw, which will increase microbial organic matter (OM) decomposition and release large amounts of the greenhouse gasses methane and carbon dioxide into the atmosphere. In addition, Arctic rivers are a globally important source of terrestrial organic carbon to the ocean and further permafrost melting will impact surface runoff, directly affecting groundwater storage and river discharge. Up to now, it remains largely unknown to what extent the ancient OM stored in newly thawing permafrost can be consumed by microbes in situ or by microbes residing in Arctic rivers which become exposed to newly discharged permafrost OM. In addition, we know little about which microbes are capable of degrading permafrost OM. During a field trip to the Toolik Lake Arctic Long Term Ecological Research (LTER) field station in northern Alaska in August 2008, we cored permafrost located near the Kuparuk River down to 110 cm below the active layer (i.e. the top layer which melts each summer) and analyzed the initial microbial enzymatic cleavage of particulate OM (POM) stored in permafrost. Alkaline phosphatase activity remained fairly constant throughout the permafrost and was only one order of magnitude lower than in the active layer. The latter enzyme cleaves organic phosphoesters into phosphate, which could cause eutrophication of lakes and rivers via ground water discharge. Similar results were found for β-glucosidase, which cleaves cellobiose into glucose. This process could fuel heterotrophic bacteria to produce carbon dioxide which, in return, could be converted to the stronger greenhouse gas methane by methanogenic archaea. Leucine aminopeptidase activities, on the other hand, were highest in the top Sphagnum root layer and quickly dropped to below detection limit

  18. Impact of Freezing and Thawing on Soil Oxygen Dynamics and Nutrient Fluxes

    NASA Astrophysics Data System (ADS)

    Milojevic, T.; Rezanezhad, F.; Van Cappellen, P.; Smeaton, C. M.; Parsons, C. T.

    2015-12-01

    Freeze-thaw cycles (FTCs) influence the physical properties, microbial activity, biogeochemistry, nutrient and carbon cycling in soils, and regulate subsurface oxygen (O2) availability, affecting greenhouse gas exchanges between soils and the atmosphere. The ability to monitor changes in O2 levels, which are indicative of aerobic and anaerobic conditions, is key to understanding how changes in the frequency and amplitude of freeze-thaw cycles affect a soil's geochemical conditions and microbial activity. In this study, a highly instrumented soil column experiment was designed to accurately simulate freeze-thaw dynamics under controlled conditions. This design allowed us to reproduce realistic, time- and depth-dependent temperature gradients in the soil column. Continuous O2 levels throughout the soil column were monitored using high-resolution, luminescence-based, Multi Fiber Optode (MuFO) microsensors. Image-processing techniques were used to convert light intensity of high-resolution digital images of the sensor-emitted light into O2 concentrations. Water samples from various depths in the column were collected to monitor pore water composition changes. Headspace gas measurements were used to derive the effluxes of CO2 and CH4 during the experiment. The results indicate that the pulse of oxygen introduced by thawing caused partial and temporal oxidation of previously reduced sulfur and nitrogen species, leading to concomitant changes in pore water SO42- and NO3- concentrations. Pulsed CO2 emission to the headspace was observed at the onset of thawing, indicating that a physical ice barrier had formed during frozen conditions and prevented gas exchange between the soil and atmosphere. CO2 emission was due to a combination of the physical release of gases dissolved in pore water and entrapped below the frozen zone and changing microbial respiration in response to electron acceptor variability (O2, NO3-, SO42-).

  19. Mercury Content of Vegetation across a Subarctic Mire Thaw Gradient

    NASA Astrophysics Data System (ADS)

    Mayedo, A. L.; Remiszewski, K.; Prado, M. F.; McCalley, C. K.; Bryce, J. G.; Varner, R. K.

    2014-12-01

    Mercury deposition from natural and anthropogenic sources is known to accumulate in subarctic environments, particularly peatlands, due to their abundant organic matter that effectively sequester mercury and other heavy metals. Given direct links between mercury mobilization and aquatic and terrestrial ecosystem health, it is vital to understand the degree to which thawing peatlands serve as sinks or sources of mercury to the environment. In a peat mire underlain by permafrost in subarctic Sweden (Stordalen Mire, lat. 68°21' N, lon. 19°03' E), the onset of climate-driven permafrost thaw influences regional hydrology and therefore the composition of plant communities. The purpose of this work is to assess mercury content of vegetation and underlying peat across a thaw gradient. The study was conducted on two transects that transition from an unthawed dwarf shrub-dominated hummock community to a fully thawed graminoid-dominated wet depression community. Drained hummock sites at initial stages of the thaw sequence are characterized by a diverse graminoid and shrub community, including Eriophorum, Andromeda, and Empetrum populations underlain by Sphagnum litter. Semi-wet sites are characterized by moist Sphagnum mats with sparse populations of Eriophorum and Empetrum. Wet sites are characterized by tall graminoid Eriophorum underlain by submerged Sphagnum mats. Total mercury abundances in vegetation was analyzed via thermal decomposition. Generally, mercury contents in plant tissues exhibit decreasing concentrations of mercury with increasing thaw. Higher concentration of mercury in vegetation in drained sites versus that in wet sites supports the notion that mercury in the dry mire is exported into the local water and peat column. Changing mercury concentration profiles in peat core afford a means to assess that mercury is mobilized during the thaw but not fully exported from the thawed wetlands. Our results, coupled with earlier findings of mobilization and

  20. Nanofibrous mats layer-by-layer assembled by HTCC/layered silicate composites with in vitro antitumor activity against SMMC-7721 cells.

    PubMed

    Huang, Rong; Zhou, Xue; Liu, Xinqin; Zhang, Qi; Jin, Huan'guang; Shi, Xiaowen; Luo, Wenjing; Deng, Hongbing

    2014-03-01

    Organic rectorite (OREC) was used to prepare the intercalated nanocomposites with N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC), and then the immobilization of the positively charged HTCC-OREC nanocomposites and the negatively charged sodium alginate (ALG) on cellulose nanofibrous mats was performed through layer-by-layer (LBL) technique. Fiber diameter distribution results from Field Emission Scanning Electron Microscopy (FE-SEM) images showed that the average fiber diameter of (HTCC-OREC/ALG)(n) films coating obviously increased from 433 to 608 nm. Moreover, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results further confirmed the interaction between HTCC and OREC and their successful immobilization on cellulose template. MTT assay indicated that the prepared nanofibrous mats exhibited strong inhibitory activity against human hepatocellular carcinoma cells (SMMC-7721) but a little cytotoxic effect on human Chang liver (CCL-13) cells. Furthermore, the experimental results from FE-SEM and Inverted Fluorescence Microscope of SMMC-7721 cells cultured on LBL structured nanofibrous mats demonstrated the significant antitumor activity of prepared samples. The developed approach to immobilize nanocomposites onto polymer nanofibers with controllable thickness may also be utilized to tumor therapy. PMID:24730244

  1. Use of fluorescence-activated flow cytometry to determine membrane lipid peroxidation during hypothermic liquid storage and freeze-thawing of viable boar sperm loaded with 4, 4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid.

    PubMed

    Guthrie, H D; Welch, G R

    2007-06-01

    Part of the reduction in boar sperm motility and fertility associated with hypothermic liquid storage and cryopreservation may be due to membrane lipid peroxidation. Lipid peroxidation was monitored by the shift from red to green fluorescence emission of the lipophilic probe 4, 4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid, C(11)BODIPY(581/591) (BODIPY), as measured by fluorescence-activated flow cytometry in live sperm (negative for propidium iodide). Experiments were conducted with Percoll-washed sperm to determine the specificity of BODIPY oxidation in the presence of different reactive oxygen species generators and metal chelators. Compared with no FeSO(4) and Na ascorbate, the combination of FeSO(4) and Na ascorbate (FeAc) increased (P < 0.01) the percentage of sperm containing oxidized BODIPY from 70% and increased (P < 0.05) BOD-IPY fluorescence intensity/cell by 5- to 10-fold after a 30-min incubation. Motility was depressed (P < 0.05) after exposure to FeAc, but viability was not affected. Of the reactive oxygen species generators tested, BODIPY oxidation was specific for FeAc, because menadione and H(2)O(2) had little or no effect. The oxidization of hydroethidine to ethidium was specific for menadione and H(2)O(2); FeAc had no effect. The presence of the metal chelators EDTA or deferoxamine mesylate at 3 and 9 muM inhibited FeAc-induced BODIPY oxidation and maintained motility. Experiments were conducted to determine the effect of liquid storage at 17 degrees C for 1 and 5 d and the effect of freeze-thawing on basal and FeAc-induced BODIPY oxidation. Basal BODIPY oxidation (no FeAc) was low in liquid stored and thawed viable sperm (1.3 and 3.4%, respectively). Although the incidence of basal or spontaneous membrane lipid peroxidation was low during liquid storage and after freeze-thawing, viable boar sperm were susceptible to FeAc-induced lipid peroxidation. PMID:17296775

  2. Permafrost and Active Layer Monitoring in the Maritime Antarctic: A Contribution to TSP and ANTPAS projects

    NASA Astrophysics Data System (ADS)

    Vieira, G.; Ramos, M.; Batista, V.; Caselli, A.; Correia, A.; Fragoso, M.; Gruber, S.; Hauck, C.; Kenderova, R.; Lopez-Martinez, J.; Melo, R.; Mendes-Victor, L. A.; Miranda, P.; Mora, C.; Neves, M.; Pimpirev, C.; Rocha, M.; Santos, F.; Blanco, J. J.; Serrano, E.; Trigo, I.; Tome, D.; Trindade, A.

    2008-12-01

    Permafrost and active layer monitoring in the Maritime Antarctic (PERMANTAR) is a Portuguese funded International Project that, in cooperation with the Spanish project PERMAMODEL, will assure the installation and the maintenance of a network of boreholes and active layer monitoring sites, in order to characterize the spatial distribution of the physical and thermal properties of permafrost, as well as the periglacial processes in Livingston and Deception Islands (South Shetlands). The project is part of the International Permafrost Association IPY projects Thermal State of Permafrost (TSP) and Antarctic and Sub-Antarctic Permafrost, Soils and Periglacial Environments (ANTPAS). It contributes to GTN-P and CALM-S networks. The PERMANTAR-PERMAMODEL permafrost and active layer monitoring network includes several boreholes: Reina Sofia hill (since 2000, 1.1m), Incinerador (2000, 2.3m), Ohridski 1 (2008, 5m), Ohridski 2 (2008, 6m), Gulbenkian-Permamodel 1 (2008, 25m) and Gulbenkian- Permamodel 2 (2008, 15m). For active layer monitoring, several CALM-S sites have been installed: Crater Lake (2006), Collado Ramos (2007), Reina Sofia (2007) and Ohridski (2007). The monitoring activities are accompanied by detailed geomorphological mapping in order to identify and map the geomorphic processes related to permafrost or active layer dynamics. Sites will be installed in early 2009 for monitoring rates of geomorphological activity in relation to climate change (e.g. solifluction, rockglaciers, thermokarst). In order to analyse the spatial distribution of permafrost and its ice content, electrical resistivity tomography (ERT), and seismic refraction surveys have been performed and, in early 2009, continuous ERT surveying instrumentation will be installed for monitoring active layer evolution. The paper presents a synthesis of the activities, as well as the results obtained up to the present, mainly relating to ground temperature monitoring and from permafrost characteristics and

  3. Effects of antioxidants and duration of pre-freezing equilibration on frozen-thawed ram semen.

    PubMed

    Câmara, D R; Silva, S V; Almeida, F C; Nunes, J F; Guerra, M M P

    2011-07-15

    The objective was to evaluate the effects of various antioxidants and duration of pre-freezing equilibration on cryopreservation of ram semen. Semen samples from four rams were pooled, diluted with Tris-egg yolk extender without antioxidants (control), or supplemented with reduced glutathione (GSH: 0.5, 1.0, and 2.0 mM), superoxide dismutase (SOD: 5, 10, and 20 U/mL), or catalase (CAT: 5, 10, and 20 U/mL), and cryopreserved, immediately after thermal equilibrium was reached at 5 °C (0 h), or 12 or 24 h after equilibration. Total antioxidant capacity was determined in the in natura extenders and after addition of semen samples for various durations of processing (fresh/dilute, throughout refrigeration, and post-thaw). Plasma membrane (PI-CFDA), acrosome integrity (FITC-PNA), and mitochondrial membrane potential (JC-1) were determined in fresh/diluted, refrigerated, and post-thaw samples. Post-thaw sperm motility was assessed with a computerized analysis system (CASA). There were no significant differences in acrosome damage or mitochondrial membrane potential after refrigeration and freeze-thaw, regardless of antioxidant addition. Sperm plasma membrane integrity was worse (P < 0.05) with cryopreservation immediately after equilibration (average 20.1 ± 8.3; mean ± SD) than after 12 h of equilibration (average 42.5 ± 10.9); however, the addition of SOD and CAT (10 and 20 U/mL) resulted in no significant difference between post-equilibration intervals of 0 and 12 h. Total antioxidant activity was not different (P > 0.05) among treatments after sperm addition or throughout the refrigeration and post-thaw. In conclusion, adding GSH, SOD or CAT did not increase the total antioxidant capacity of semen, nor did it enhance the quality of the post-thaw sperm. However, maintenance of ram semen at 5 °C for 12 h prior to cryopreservation reduced membrane damage of frozen-thawed sperm. PMID:21529917

  4. Layer-by-layer carbon nanotube bio-templates for in situ monitoring of the metabolic activity of nitrifying bacteria

    NASA Astrophysics Data System (ADS)

    Loh, Kenneth J.; Guest, Jeremy S.; Ho, Genevieve; Lynch, Jerome P.; Love, Nancy G.

    2009-03-01

    Despite the wide variety of effective disinfection and wastewater treatment techniques for removing organic and inorganic wastes, pollutants such as nitrogen remain in wastewater effluents. If left untreated, these nitrogenous wastes can adversely impact the environment by promoting the overgrowth of aquatic plants, depleting dissolved oxygen, and causing eutrophication. Although nitrification/denitrification processes are employed during advanced wastewater treatment, effective and efficient operation of these facilities require information of the pH, dissolved oxygen content, among many other parameters, of the wastewater effluent. In this preliminary study, a biocompatible CNT-based nanocomposite is proposed and validated for monitoring the biological metabolic activity of nitrifying bacteria in wastewater effluent environments (i.e., to monitor the nitrification process). Using carbon nanotubes and a pH-sensitive conductive polymer (i.e., poly(aniline) emeraldine base), a layer-by-layer fabrication technique is employed to fabricate a novel thin film pH sensor that changes its electrical properties in response to variations in ambient pH environments. Laboratory studies are conducted to evaluate the proposed nanocomposite's biocompatibility with wastewater effluent environments and its pH sensing performance.

  5. Rapid electrostatics-assisted layer-by-layer assembly of near-infrared-active colloidal photonic crystals.

    PubMed

    Askar, Khalid; Leo, Sin-Yen; Xu, Can; Liu, Danielle; Jiang, Peng

    2016-11-15

    Here we report a rapid and scalable bottom-up technique for layer-by-layer (LBL) assembling near-infrared-active colloidal photonic crystals consisting of large (⩾1μm) silica microspheres. By combining a new electrostatics-assisted colloidal transferring approach with spontaneous colloidal crystallization at an air/water interface, we have demonstrated that the crystal transfer speed of traditional Langmuir-Blodgett-based colloidal assembly technologies can be enhanced by nearly 2 orders of magnitude. Importantly, the crystalline quality of the resultant photonic crystals is not compromised by this rapid colloidal assembly approach. They exhibit thickness-dependent near-infrared stop bands and well-defined Fabry-Perot fringes in the specular transmission and reflection spectra, which match well with the theoretical calculations using a scalar-wave approximation model and Fabry-Perot analysis. This simple yet scalable bottom-up technology can significantly improve the throughput in assembling large-area, multilayer colloidal crystals, which are of great technological importance in a variety of optical and non-optical applications ranging from all-optical integrated circuits to tissue engineering. PMID:27494632

  6. Transfection activity of layer-by-layer plasmid DNA/poly(ethylenimine) films deposited on PLGA microparticles

    PubMed Central

    Kakade, Sandeep; Manickam, Devika Soundara; Handa, Hitesh; Mao, Guangzhao; Oupický, David

    2009-01-01

    Layer-by-layer (LbL) assemblies of DNA and polycations on the surface of colloidal templates can be used for gene delivery. Plasmid DNA encoding for secreted alkaline phosphatase (SEAP) was used to deposit LbL films with poly(ethylenimine) (PEI) on the surface of polystyrene and poly(lactide-co-glycolide) microparticles. The formation of LBL films was confirmed by zeta potential analysis and fluorescence and atomic force microscopy techniques. The LbL particles were rapidly internalized in a dose-dependent manner by J774.1 murine macrophages. Transfection activity of the LbL particles was evaluated in J774.1 cells using three different doses (5, 10, 25 particle per cell). The levels of SEAP expression increased with increasing dose but were lower than transfection levels mediated by control PEI/DNA polyplexes at corresponding DNA doses. The LbL particles reported here present a promising platform for delivery of DNA to phagocytic cells. PMID:18786622

  7. Rapid electrostatics-assisted layer-by-layer assembly of near-infrared-active colloidal photonic crystals.

    PubMed

    Askar, Khalid; Leo, Sin-Yen; Xu, Can; Liu, Danielle; Jiang, Peng

    2016-11-15

    Here we report a rapid and scalable bottom-up technique for layer-by-layer (LBL) assembling near-infrared-active colloidal photonic crystals consisting of large (⩾1μm) silica microspheres. By combining a new electrostatics-assisted colloidal transferring approach with spontaneous colloidal crystallization at an air/water interface, we have demonstrated that the crystal transfer speed of traditional Langmuir-Blodgett-based colloidal assembly technologies can be enhanced by nearly 2 orders of magnitude. Importantly, the crystalline quality of the resultant photonic crystals is not compromised by this rapid colloidal assembly approach. They exhibit thickness-dependent near-infrared stop bands and well-defined Fabry-Perot fringes in the specular transmission and reflection spectra, which match well with the theoretical calculations using a scalar-wave approximation model and Fabry-Perot analysis. This simple yet scalable bottom-up technology can significantly improve the throughput in assembling large-area, multilayer colloidal crystals, which are of great technological importance in a variety of optical and non-optical applications ranging from all-optical integrated circuits to tissue engineering.

  8. Carbon nanotubes supported cerium dioxide and platinum nanohybrids: Layer-by-layer synthesis and enhanced electrocatalytic activity for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Lou, Xinyuan; Chen, Jiayi; Wang, Mengdi; Gu, Jialei; Wu, Ping; Sun, Dongmei; Tang, Yawen

    2015-08-01

    We successfully synthesize carbon nanotubes (CNTs) supported cerium dioxide and platinum (Pt/CeO2/CNTs) nanohybrids via layer-by-layer assembly. The composition, morphology and structure of the as-prepared Pt/CeO2/CNTs nanohybrids are characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDX), selected-area electron diffraction (SAED), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and inductively coupled plasma atomic emission spectrometry (ICP-AES). By comparison of the electrocatalytic properties of the Pt/CeO2/CNTs with the Pt/CNTs, we systematically investigate the promotion effect of CeO2 on the Pt/CeO2/CNTs catalysts towards methanol oxidation. It is found that the introduction of CeO2 not only enhances the electrocatalytic activity and stability of the Pt/CeO2/CNTs catalyst for methanol oxidation but also minimizes the CO poisoning, probably accounting for the good oxygen carrying capacity of CeO2 and its high stability in acidic solution.

  9. Enhanced photocurrent density in graphene/Si based solar cell (GSSC) by optimizing active layer thickness

    SciTech Connect

    Rosikhin, Ahmad Hidayat, Aulia Fikri; Syuhada, Ibnu; Winata, Toto

    2015-12-29

    Thickness dependent photocurrent density in active layer of graphene/Si based solar cell has been investigated via analytical – simulation study. This report is a preliminary comparison of experimental and analytical investigation of graphene/Si based solar cell. Graphene sheet was interfaced with Si thin film forming heterojunction solar cell that was treated as a device model for photocurrent generator. Such current can be enhanced by optimizing active layer thickness and involving metal oxide as supporting layer to shift photons absorption. In this case there are two type of devices model with and without TiO{sub 2} in which the silicon thickness varied at 20 – 100 nm. All of them have examined and also compared with each other to obtain an optimum value. From this calculation it found that generated currents almost linear with thickness but there are saturated conditions that no more enhancements will be achieved. Furthermore TiO{sub 2} layer is effectively increases photon absorption but reducing device stability, maximum current is fluctuates enough. This may caused by the disturbance of excitons diffusion and resistivity inside each layer. Finally by controlling active layer thickness, it is quite useful to estimate optimization in order to develop the next solar cell devices.

  10. [Comparison of thawing of plasma by microwave or water bath: preliminary longitudinal biological study of hemostatic parameters].

    PubMed

    Gris, J C; Joussemet, M; Bourin, P; Fabre, G; Schved, J F

    1988-10-01

    Exploration of haemostasis was performed on plasmas thawed in an experimental microwave oven comparatively to a 37 degrees C water bath. Factor VIII:R:Ag, procoagulant and antigenic fibrinogen, and Fg:C/Fg:Ag ratio were found to be significantly, slightly decreased with microwave thawing. Factor VIII:C and VIII:C/VIII:R:Ag ratio were found to be increased with microwaves. Antigenic fractions were decreased because of partial precipitation. In addition, Fibrinogen slightly lost its activity; on the contrary, factor VIIIC was activated by micro-waves. All this allows to select parameters for new experimental microwave ovens development.

  11. Discrete-Layer Piezoelectric Plate and Shell Models for Active Tip-Clearance Control

    NASA Technical Reports Server (NTRS)

    Heyliger, P. R.; Ramirez, G.; Pei, K. C.

    1994-01-01

    The objectives of this work were to develop computational tools for the analysis of active-sensory composite structures with added or embedded piezoelectric layers. The targeted application for this class of smart composite laminates and the analytical development is the accomplishment of active tip-clearance control in turbomachinery components. Two distinct theories and analytical models were developed and explored under this contract: (1) a discrete-layer plate theory and corresponding computational models, and (2) a three dimensional general discrete-layer element generated in curvilinear coordinates for modeling laminated composite piezoelectric shells. Both models were developed from the complete electromechanical constitutive relations of piezoelectric materials, and incorporate both displacements and potentials as state variables. This report describes the development and results of these models. The discrete-layer theories imply that the displacement field and electrostatic potential through-the-thickness of the laminate are described over an individual layer rather than as a smeared function over the thickness of the entire plate or shell thickness. This is especially crucial for composites with embedded piezoelectric layers, as the actuating and sensing elements within these layers are poorly represented by effective or smeared properties. Linear Lagrange interpolation polynomials were used to describe the through-thickness laminate behavior. Both analytic and finite element approximations were used in the plane or surface of the structure. In this context, theoretical developments are presented for the discrete-layer plate theory, the discrete-layer shell theory, and the formulation of an exact solution for simply-supported piezoelectric plates. Finally, evaluations and results from a number of separate examples are presented for the static and dynamic analysis of the plate geometry. Comparisons between the different approaches are provided when

  12. Inversion of dispersive GPR data recorded across precipitation and thawing induced waveguides

    NASA Astrophysics Data System (ADS)

    van der Kruk, J.; Jacob, R. W.; Steelman, C.; Endres, A. L.; Vereecken, H.

    2009-05-01

    High frequency GPR is particularly well suited for monitoring the shallow subsurface due to its non-invasive nature and ability to measure the soil water content. In case of precipitation or thawing, a low velocity waveguide can be induced due to the strong influence of the change in water content on the radar velocity. In this way, the lower substrate medium has a lower permittivity than the middle waveguide layer and causes total internal reflection when the angle of incidence at both interfaces is larger than the critical angle which enables the signal to propagate over relatively large distances. Low-velocity waveguides are induced by thawing of frozen sand and by precipitation events. In both cases, the waveguide properties can be obtained by calculating phase-velocity spectra, followed by picking dispersion curves from the maxima in the spectra. The picked dispersion curve is then inverted for a single- or multi-layer subsurface model; inversion involves adjusting the model parameters until the difference between the picked dispersion curve and the model-predicted dispersion curve is minimized. Here, we show that a waveguide develops after a significant precipitation event soaks a dry surface layer on a test site in New England. The newly wet surface layer has a higher relative permittivity and associated lower velocity than the immediately underlying dry material. TE and TM data collected after the rainfall show clear dispersion. A joint inversion of the TE and TM fundamental modes provides more reliable estimates of the medium parameters than separate inversions. Analysis of another GPR data set collected after the soaking of an existing wet layer show the presence of 4 TE and 4 TM modes. Including higher order modes in the joint TE- TM inversion resulted in better constrained models than fundamental mode inversion. Common mid-point gathers using high-frequency 900 MHz antennas were collected on a test site in Waterloo. Surveys were conducted during the

  13. Active/Passive Control of Sound Radiation from Panels using Constrained Layer Damping

    NASA Technical Reports Server (NTRS)

    Gibbs, Gary P.; Cabell, Randolph H.

    2003-01-01

    A hybrid passive/active noise control system utilizing constrained layer damping and model predictive feedback control is presented. This system is used to control the sound radiation of panels due to broadband disturbances. To facilitate the hybrid system design, a methodology for placement of constrained layer damping which targets selected modes based on their relative radiated sound power is developed. The placement methodology is utilized to determine two constrained layer damping configurations for experimental evaluation of a hybrid system. The first configuration targets the (4,1) panel mode which is not controllable by the piezoelectric control actuator, and the (2,3) and (5,2) panel modes. The second configuration targets the (1,1) and (3,1) modes. The experimental results demonstrate the improved reduction of radiated sound power using the hybrid passive/active control system as compared to the active control system alone.

  14. Increase in sedge biomass across a permafrost thaw gradient correlates to changes in the magnitude and isotopic composition of methane emissions

    NASA Astrophysics Data System (ADS)

    Werner, S. L.; Malhotra, A.; McCalley, C. K.; Varner, R. K.; Roulet, N. T.; Crill, P. M.

    2013-12-01

    Species transitions have been observed in northern latitudes in response to a warming climate. Sedge species in particular are becoming more abundant as permafrost thaws. These species are closely linked to increases in methane (CH4) emission, which has 23 times the global warming potential of carbon dioxide (CO2) and wetlands are a major natural source of emissions. Understanding how CH4emissions are associated with species changes during thaw is essential for estimating CH4 fluxes from discontinuous permafrost regions and for predicting the trajectory of CH4 emissions under future climate change. To understand the relationship between sedges and methane emissions, we measured methane fluxes and the isotopic composition of pore water CH4 and CO2 along a permafrost thaw gradient in Stordalen Mire, Abisko, Sweden. To determine the controls on CH4emission, we measured vegetation biomass, pH, soil temperature, active layer depth and species composition. Significant differences were found between different vegetation classes, with lowest fluxes of CH4 observed in the frozen palsa (0.73 × 4.41 mg m-2d-1), mid-range fluxes in Sphagnum sites (14.2 1 × 15.8 mg m-2d-1) and highest fluxes in the wet graminoid (165.4 × 136.6 mg m-2d-1). The best indicator of CH4 flux was biomass of sedge vegetation (e.g Eriophorum vaginatum and Carex spp.) (R2= 0.86 p= 0.001). In general, pore water CH4 increased with depth and was on average highest and most variable in the Carex spp. dominated sites compared to the mixed vegetation, Sphagnum and E. vaginatum dominated sites. The best predictor of below ground CH4 concentration was also sedge biomass (R2= 0.86 p= 0.01 at 30 cm). The variability and abundance of CH4 indicates differences in methane production rates depending on the presence of sedges. Patterns in del13C-CH4 suggest a shift from hydrogenotrophic production in Sphagnum dominated sites to increasing contributions from acetate fermentation in sedge-dominated sites. These

  15. Aerobic Conditions are Required for Rapid Carbon Losses following Permafrost Thaw

    NASA Astrophysics Data System (ADS)

    Cooper, M. D. A.; Estop-Aragones, C.

    2015-12-01

    Permafrost soils store between 1,330-1,580 billion tonnes of carbon (C), which may start to be released to the atmosphere if warming promotes widespread thaw. Considerable uncertainty remains regarding how rapidly this C may be released and what proportion will be released as the more powerful greenhouse gas, methane (CH4), rather than carbon dioxide (CO2). Central to answering these questions, is quantifying in situ rates of old, previously-frozen C release under aerobic conditions versus anaerobic conditions. To meet this aim, we investigated the amount and form (CH4 versus CO2) of previously-frozen C released in response to 1) forest fire-induced permafrost thaw (aerobic soil conditions) and 2) permafrost plateau collapse in peatlands which results in waterlogging (anaerobic conditions), in the Yukon and Northwest Territories of Canada. We quantified in situ rates of CO2 and CH4 release, using a novel collar design to either include or exclude C released from deep soil layers, and collected samples for 14CO2 and 14CH4 analysis. Our 14CO2 results identified substantial rates of old C release from burnt forests where the organic horizon was thick and deep thaw was observed. In contrast, in the wetlands old C release was barely detectable as CO2 (<1%), and, although high CH4 fluxes were measured, a maximum of 1.5-2g m-2 yr-1 was derived from previously-frozen C. Furthermore, because peat accumulation increased substantially (>4 times), , thaw resulted in net C gain in the wetland. However, the high rate of CH4 release, albeit derived mainly from contemporary sources, means that permafrost plateau collapse can still represent a positive feedback to climate change in terms of global warming potential. Overall, our results indicate a much greater release of permafrost C under aerobic conditions, with little release of previously-frozen C as either CO2 or CH4 under anaerobic conditions.

  16. Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

    SciTech Connect

    Gregory A. Mulhollan

    2010-11-16

    Specific activation recipes for bulk, 100 nm thick MBE grown and high polarization III-V photocathode material have been developed which mitigate the effects of exposure to background gasses. Lifetime data using four representative gasses were acquired for bulk GaAs, 100 nm unstrained GaAs and strained superlattice GaAs/GaAsP, all activated both with Cs and then Cs and Li (bi-alkali). Each photoemitter showed marked resilience improvement when activated using the bi-alkali recipe compared to the standard single alkali recipe. A dual alkali activation system at SLAC was constructed, baked and commissioned with the purpose of performing spin-polarization measurements on electrons emitted from the bi-alkali activated surfaces. An end station at SSRL was configured with the required sources for energy resolved photoemission measurements on the bi-alkali activated and CO2 dosed surfaces. The bi-alkali recipes were successfully implemented at SLAC/SSRL. Measurements at SLAC of the photoelectron spin-polarization from the modified activation surface showed no sign of a change in value compared to the standard activated material, i.e., no ill effects. Analysis of photoemission data indicates that the addition of Li to the activation layer results in a multi-layer structure. The presence of Li in the activation layer also acts as an inhibitor to CO2 absorption, hence better lifetimes in worse vacuum were achieved. The bi-alkali activation has been tested on O2 activated GaAs for comparison with NF3 activated surfaces. Comparable resilience to CO2 exposure was achieved for the O2 activated surface. An RF PECVD amorphous silicon growth system was modified to allow high temperature heat cleaning of GaAs substrates prior to film deposition. Growth versus thickness data were collected. Very thin amorphous silicon germanium layers were optimized to exhibit good behavior as an electron emitter. Growth of the amorphous silicon germanium films on the above substrates was fine tuned

  17. MAPLE prepared heterostructures with arylene based polymer active layer for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Stanculescu, F.; Rasoga, O.; Catargiu, A. M.; Vacareanu, L.; Socol, M.; Breazu, C.; Preda, N.; Socol, G.; Stanculescu, A.

    2015-05-01

    This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) technique of heterostructures with single layer of arylene based polymer, poly[N-(2-ethylhexyl)2.7-carbazolyl vinylene]/AMC16 and poly[N-(2-ethylhexyl)2.7-carbazolyl 1.4-phenylene ethynylene]/AMC22, and with layers of these polymers mixed with Buckminsterfullerene/C60 in the weight ratio of 1:2 (AMC16:C60) and 1:3 (AMC22:C60). The deposited layers have been characterized by spectroscopic (UV-Vis-NIR, PL, FTIR) and microscopic (SEM, AFM) methods. The effect of the polymer particularities on the optical and electrical properties of the structures based on polymer and polymer:C60 mixed layer has been analyzed. The study of the electrical properties has revealed typical solar cell behavior for the heterostructure prepared by MAPLE on glass/ITO/PEDOT-PSS with AMC16, AMC22 and AMC22:C60 layer, confirming that this method is adequate for the preparation of polymeric and mixed active layers for solar cells applications. The highest photovoltaic effect was shown by the solar cell structure realized with single layer of AMC16 polymer: glass/ITO/PEDOT-PSS/AMC16/Al.

  18. Efficacy of different final irrigant activation protocols on smear layer removal by EDTA and citric acid.

    PubMed

    Herrera, Daniel R; Santos, Zarina T; Tay, Lidia Y; Silva, Emmanuel J; Loguercio, Alessandro D; Gomes, Brenda P F A

    2013-04-01

    The aim of this study was to evaluate the influence of different activation protocols for chelating agents used after chemo-mechanical preparation (CMP), for smear layer (SL) removal. Forty-five single-rooted human premolars with straight canals and fully formed apex were selected. The specimens were randomly divided into three groups depending on the chelating agent used for smear layer removal: distilled water (DW, control group); 17% ethylenediaminetetraacetic acid (EDTA); and 10% citric acid (CA). Each group was further divided into three subgroups according to the activation protocol used: no-activation (NA), manual dynamic activation (MDA), or sonic activation (SA). After CMP, all specimens were sectioned and processed for observation of the apical thirds by using scanning electron microscopy (SEM). Two calibrated evaluators attributed scores to each specimen. The differences between activation protocols were analyzed with Kruskal-Wallis and Mann-Whitney U tests. Friedman and Wilcoxon signed rank tests were used for comparison between each root canal third. When chelating agents were activated, either by MDA or SA, it was obtained the best cleaning results with no significant difference between EDTA and CA (P > 0.05). Sonic activation showed the best results when root canal thirds were analyzed, in comparison to MDA and NA groups (P < 0.05). The activation of chelating agents, independent of the protocol used, benefits smear layer removal from root canals.

  19. Antimicrobial Activity Evaluation on Silver Doped Hydroxyapatite/Polydimethylsiloxane Composite Layer

    PubMed Central

    Ciobanu, C. S.; Groza, A.; Iconaru, S. L.; Popa, C. L.; Chapon, P.; Chifiriuc, M. C.; Hristu, R.; Stanciu, G. A.; Negrila, C. C.; Ghita, R. V.; Ganciu, M.; Predoi, D.

    2015-01-01

    The goal of this study was the preparation, physicochemical characterization, and microbiological evaluation of novel hydroxyapatite doped with silver/polydimethylsiloxane (Ag:HAp-PDMS) composite layers. In the first stage, the deposition of polydimethylsiloxane (PDMS) polymer layer on commercially pure Si disks has been produced in atmospheric pressure corona discharges. Finally, the new silver doped hydroxyapatite/polydimethylsiloxane composite layer has been obtained by the thermal evaporation technique. The Ag:HAp-PDMS composite layers were characterized by various techniques, such as Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The antimicrobial activity of the Ag:HAp-PDMS composite layer was assessed against Candida albicans ATCC 10231 (ATCC—American Type Culture Collection) by culture based and confirmed by SEM and Confocal Laser Scanning Microscopy (CLSM) methods. This is the first study reporting the antimicrobial effect of the Ag:HAp-PDMS composite layer, which proved to be active against Candida albicans biofilm embedded cells. PMID:26504849

  20. Antimicrobial Activity Evaluation on Silver Doped Hydroxyapatite/Polydimethylsiloxane Composite Layer.

    PubMed

    Ciobanu, C S; Groza, A; Iconaru, S L; Popa, C L; Chapon, P; Chifiriuc, M C; Hristu, R; Stanciu, G A; Negrila, C C; Ghita, R V; Ganciu, M; Predoi, D

    2015-01-01

    The goal of this study was the preparation, physicochemical characterization, and microbiological evaluation of novel hydroxyapatite doped with silver/polydimethylsiloxane (Ag:HAp-PDMS) composite layers. In the first stage, the deposition of polydimethylsiloxane (PDMS) polymer layer on commercially pure Si disks has been produced in atmospheric pressure corona discharges. Finally, the new silver doped hydroxyapatite/polydimethylsiloxane composite layer has been obtained by the thermal evaporation technique. The Ag:HAp-PDMS composite layers were characterized by various techniques, such as Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The antimicrobial activity of the Ag:HAp-PDMS composite layer was assessed against Candida albicans ATCC 10231 (ATCC-American Type Culture Collection) by culture based and confirmed by SEM and Confocal Laser Scanning Microscopy (CLSM) methods. This is the first study reporting the antimicrobial effect of the Ag:HAp-PDMS composite layer, which proved to be active against Candida albicans biofilm embedded cells. PMID:26504849

  1. Modeling the gain and bandwidth of submicron active layer n+-i-p+ avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Majumder, Kanishka; Das, N. R.

    2012-10-01

    The electron initiated avalanche gain and bandwidth are calculated for thin submicron GaAs n+-i-p+ avalanche photodiode. A model is used to estimate the avalanche build-up of carriers in the active multiplication layer considering the dead-space effect. In the model, the carriers are identified both by their energy and position in the multiplication region. The excess energy of the carriers above threshold is assumed to be equally distributed among the carriers generated after impact ionization. The gain versus bias and bandwidth versus gain characteristics of the device are also demonstrated for different active layer thicknesses of the APD.

  2. Application of Spaceborne Scatterometer for Mapping Freeze-Thaw State in Northern Landscapes as a Measure of Ecological and Hydrological Processes

    NASA Technical Reports Server (NTRS)

    McDonald, Kyle; Kimball, John; Zimmermann, Reiner; Way, JoBea; Frolking, Steve; Running, Steve

    1999-01-01

    Landscape freeze/thaw transitions coincide with marked shifts in albedo, surface energy and mass exchange, and associated snow dynamics. Monitoring landscape freeze/thaw dynamics would improve our ability to quantify the interannual variability of boreal hydrology and river runoff/flood dynamics. The annual duration of frost-free period also bounds the period of photosynthetic activity in boreal and arctic regions thus affecting the annual carbon budget and the interannual variability of regional carbon fluxes. In this study, we use the NASA scatterometer (NSCAT) to monitor the temporal change in the radar backscatter signature across selected ecoregions of the boreal zone. We have measured vegetation tissue temperatures, soil temperature profiles, and micrometeorological parameters in situ at selected sites along a north-south transect extending across Alaska from Prudhoe Bay to the Kenai Peninsula and in Siberia near the Yenisey River. Data from these stations have been used to quantify the scatterometer's sensitivity to freeze/thaw state under a variety of terrain and landcover conditions. Analysis of the NSCAT temporal response over the 1997 spring thaw cycle shows a 3 to 5 dB change in measured backscatter that is well correlated with the landscape springtime thaw process. Having verified the instrument's capability to monitor freeze/thaw transitions, regional scale mosaicked data are applied to derive temporal series of freeze/thaw transition maps for selected circumpolar high latitude regions. These maps are applied to derive areal extent of frozen and thawed landscape and demonstrate the utility of spaceborne radar for operational monitoring of seasonal freeze-thaw dynamics and associated biophysical processes for the circumpolar high latitudes.

  3. Microbial diversity of active layer and permafrost in an acidic wetland from the Canadian High Arctic.

    PubMed

    Wilhelm, Roland C; Niederberger, Thomas D; Greer, Charles; Whyte, Lyle G

    2011-04-01

    The abundance and structure of archaeal and bacterial communities from the active layer and the associated permafrost of a moderately acidic (pH < 5.0) High Arctic wetland (Axel Heiberg Island, Nunavut, Canada) were investigated using culture- and molecular-based methods. Aerobic viable cell counts from the active layer were ∼100-fold greater than those from the permafrost (2.5 × 10(5) CFU·(g soil dry mass)(-1)); however, a greater diversity of isolates were cultured from permafrost, as determined by 16S rRNA gene sequencing. Isolates from both layers demonstrated growth characteristics of a psychrotolerant, halotolerant, and acidotolerant community. Archaea constituted 0.1% of the total 16S rRNA gene copy number and, in the 16S rRNA gene clone library, predominantly (71% and 95%) consisted of Crenarchaeota related to Group I. 1b. In contrast, bacterial communities were diverse (Shannon's diversity index, H = ∼4), with Acidobacteria constituting the largest division of active layer clones (30%) and Actinobacteria most abundant in permafrost (28%). Direct comparisons of 16S rRNA gene sequence data highlighted significant differences between the bacterial communities of each layer, with the greatest differences occurring within Actinobacteria. Comparisons of 16S rRNA gene sequences with those from other Arctic permafrost and cold-temperature wetlands revealed commonly occurring taxa within the phyla Chloroflexi, Acidobacteria, and Actinobacteria (families Intrasporangiaceae and Rubrobacteraceae). PMID:21491982

  4. Study of dopant activation in biaxially compressively strained SiGe layers using excimer laser annealing

    NASA Astrophysics Data System (ADS)

    Luong, G. V.; Wirths, S.; Stefanov, S.; Holländer, B.; Schubert, J.; Conde, J. C.; Stoica, T.; Breuer, U.; Chiussi, S.; Goryll, M.; Buca, D.; Mantl, S.

    2013-05-01

    Excimer Laser Annealing (ELA) with a wavelength of 248 nm is used to study doping of biaxialy compressively strained Si1-xGex/Si heterostructures. The challenge is to achieve a high activation of As in SiGe, while conserving the elastic strain and suppressing dopant diffusion. Doping of 20 nm Si0.64Ge0.36 layers by ion implantation of 1 × 1015 As+/cm2 and subsequent laser annealing using single 20 ns pulse with an energy density of 0.6 J/cm2 leads to an As activation of about 20% and a sheet resistance of 650 Ω/sq. At this laser energy density, the entire SiGe layer melts and the subsequent fast recrystallization on a nanosecond time scale allows high As incorporation into the lattice. Moreover, using these annealing parameters, the SiGe layer exhibits epitaxial regrowth with negligible strain relaxation. ELA at energy densities greater than 0.6 J/cm2 resembles Pulsed Lased Induced Epitaxy, leading to an intermixing of the SiGe layer with the Si substrate, thus to thicker single-crystalline strained SiGe layers with sheet resistance down to 62 Ω/sq. Effects of energy densities on composition, crystal quality, activation of As and co-doping with B are discussed and related to the spatial and temporal evolution of the temperature in the irradiated zone, as simulated by Finite Element Methods.

  5. Electrospun nanofiber layers with incorporated photoluminescence indicator for chromatography and detection of ultraviolet-active compounds.

    PubMed

    Kampalanonwat, Pimolpun; Supaphol, Pitt; Morlock, Gertrud E

    2013-07-19

    For the first time, electrospun nanofiber phases were fabricated with manganese-activated zinc silicate as photoluminescent indicator (UV254) to transfer and enlarge its application to the field of UV-active compounds. By integration of such an indicator, UV-active compounds got visible on the chromatogram. The separation of 7 preservatives and a beverage sample were studied on the novel luminescent polyacrylonitrile layers. The mat thickness and mean fiber diameters were calculated for additions of different UV254 indicator concentrations. The separation efficiency on the photoluminescent layers was characterized by comparison to HPTLC layers and calculation of the plate numbers and resolutions. Some benefits were the reduction in migration distance (3cm), migration time (12min), analyte (10-nL volumes) and mobile phase volumes (1mL). As ultrathin stationary phase, such layers are suited for their integration into the Office Chromatography concept. For the first time, electrospun nanofiber layers were hyphenated with mass spectrometry and the confirmation of compounds was successfully performed using the elution-head based TLC-MS Interface.

  6. Colloid centrifugation of fresh stallion semen before cryopreservation decreased microorganism load of frozen-thawed semen without affecting seminal kinetics.

    PubMed

    Guimarães, T; Lopes, G; Pinto, M; Silva, E; Miranda, C; Correia, M J; Damásio, L; Thompson, G; Rocha, A

    2015-01-15

    Freezability of equine semen may be influenced by microorganism population of semen. The objective of this study was to verify the effect of single-layer density gradient centrifugation (SLC) of fresh semen before cryopreservation on semen's microbial load (ML) and sperm cells kinetics after freezing-thawing. For that, one ejaculate was collected from 20 healthy stallions and split into control (C) samples (cryopreserved without previous SLC) and SLC samples (subjected to SLC). Semen cryopreservation was performed according to the same protocol in both groups. Microbial load of each microorganism species and total microbial load (TML) expressed in colony-forming units (CFU/mL) as well as frozen-thawed sperm kinetics were assessed in both groups. Additional analysis of the TML was performed, subdividing the frozen-thawed samples in "suitable" (total motility ≥ 30%) and "unsuitable" (total motility < 30%) semen for freezing programs, and comparing the C and SLC groups within these subpopulations. After thawing, SLC samples had less (P < 0.05) TML (88.65 × 10(2) ± 83.8 × 10(2) CFU/mL) than C samples (155.69 × 10(2) ± 48.85 × 10(2) CFU/mL), mainly due to a reduction of Enterococcus spp. and Bacillus spp. A relationship between post-thaw motility and SLC effect on ML was noted, as only in samples with more than 30% total motility was ML reduced (P < 0.05) by SLC (from 51.33 × 10(2) ± 33.26 × 10(2) CFU/mL to 26.68 × 10(2) ± 12.39 × 10(2) CFU/mL in "suitable" frozen-thawed semen vs. 240.90 × 10(2) ± 498.20 × 10(2) to 139.30 × 10(2) ± 290.30 × 10(2) CFU/mL in "unsuitable" frozen-thawed semen). The effect of SLC on kinetics of frozen-thawed sperm cells was negligible.

  7. Topographic control of the depth of ground thaw in a peat covered continuous permafrost site in the Canadian arctic tundra

    NASA Astrophysics Data System (ADS)

    Endrizzi, Stefano; Marsh, Philip; Quinton, William; Dall'Amico, Matteo

    2010-05-01

    Recent research has suggested an energy-based framework for delineating runoff contributing areas for permafrost dominated, tundra environments, where end of winter snow cover, and turbulent and radiant fluxes of energy and water are affected by topography, and control both snowmelt and the depth of ground thaw. The resulting spatially variable thaw depth, when combined with spatially variable water supply, spatially variable organic soil thickness, and depth variable hydraulic conductivity in organic soils, has a significant impact on the flow of water from uplands to the stream channel. In order to consider the effects of a spatially variable depth of thaw on runoff in a tundra basin, the hydrologic model GEOtop was applied to the Siksik Creek drainage basin located approximately 50 km north of Inuvik, NWT, Canada, characterized by a relatively gentle topography, with elevation ranging from 0 and 80 m a.s.l.. The small surface area of the basin (approximately 1 km2) allows the model to be run at a relatively high resolution. GEOtop is a grid based model with a complete surface energy balance scheme that accounts for variations in both the turbulent fluxes of sensible and latent heat, as well as for variations in radiant fluxes. The model also has a complete subsurface heat and water flux scheme that is able to route water and energy both vertically between a large number of soil layers, and horizontally between grids. Field data for model validation include meteorological data, depth of thaw, and runoff data for a 3 year period between 1992 and 1994, and high resolution DEM and vegetation height data obtained from airborne LiDAR in 2004. The purpose of this work is studying how topography controls the depth of thaw, and, therefore, the effects of a spatially variable snow cover are intentionally neglected. GEOtop was then run in a simple configuration, assuming an initial condition of uniform frost table at the ground surface at the end of snow melt, with snow

  8. Microbial Activity in Active and Upper Permafrost Layers in Axel Heiberg Island

    NASA Astrophysics Data System (ADS)

    Vishnivetskaya, T. A.; Allan, J.; Cheng, K.; Chourey, K.; Hettich, R. L.; Layton, A.; Liu, X.; Murphy, J.; Mykytczuk, N. C.; Phelps, T. J.; Pfiffner, S. M.; Saarunya, G.; Stackhouse, B. T.; Whyte, L.; Onstott, T. C.

    2011-12-01

    Data on microbial communities and their metabolic activity in Arctic wetlands and underlying permafrost sediments is lacking. Samples were collected from different depths of a cryosol (D1, D2) and upper permafrost (D3) at the Axel Heiberg Island in July 2009. Upper cryosol has lower H2O but higher C and N content when compared to deeper horizons including upper permafrost layer. Deep cryosol and upper permafrost contained SO42- (155 and 132 ppm) and NO3- (0.12 and 0.10 ppm), respectively. The phylogenetic analyses of the environmental 16S rRNA genes showed the putative SRB were more abundant in permafrost (8%) than in cryosols, D1 (0.2%) and D2 (1.1%). Putative denitrifying bacteria varied along depth with near 0.1% in D1 and a significant increase in D2 (2.7%) and D3 (2.2%). Methanogens were not detected; methanotrophs were present at low levels in D3 (1%). Two sets of microcosms were set up. Firstly, anaerobic microcosms, amended with 10 mM glucose, sulfate or nitrate, were cultivated at varying temperatures (15o, 6o, and 0o C) for 10 months. Metabolic activity was monitored by measuring CO2 and CH4 every 3 months. A total of 89.5% of the D3-originated microcosms showed higher activity in comparison to cryosols in first 3 months. CH4 was not detected in these microcosms, whereas CO2 production was higher at 15o C or with glucose. Metaproteomics analyses of microcosms with higher levels of CO2 production indicated the presence of stress responsive proteins (e.g. DnaK, GroEL) and proteins essential for energy production and survival under carbon starvation (e.g. F0F1 ATP synthase, acyl-CoA dehydrogenase). These proteins have been previously shown to be up-regulated at low temperatures by permafrost bacteria. Metaproteomics data based on the draft sequences indicated the presence of proteins from the genera Bradyrhizobium, Sphingomonas, Lysinibacillus and Methylophilaceae and these bacteria were also detected by pyrosequencing. Secondly, a duplicate set of anaerobic

  9. Application of Spaceborne Scatterometer for Mapping Freeze-Thaw State in Northern Landscapes as a Measure of Ecological and Hydrological Processes

    NASA Technical Reports Server (NTRS)

    McDonald, Kyle; Kimball, John; Zimmermann, Reiner; Way, JoBea; Frolking, Steve; Running, Steve

    1994-01-01

    Landscape freeze/thaw transitions coincide with marked shifts in albedo, surface energy and mass exchange, and associated snow dynamics. monitoring landscape freeze/thaw dynamics would improve our ability to quantify the interannual variability of boreal hydrology and river runoff/flood dynamics, The annual duration of frost-free period also bounds the period of photosynthetic activity in borel and arctic regions thus affecting the carbon budget and the interannual variability fo regional carbon fluxes.

  10. Soil nutrient processes during spring thaw along a thermokarst recovery chronosequence

    NASA Astrophysics Data System (ADS)

    Buckeridge, K. M.; Schaeffer, S. M.; Baron, A.; Mack, M. C.; Schuur, E. A.; Schimel, J.

    2012-12-01

    Arctic soils store large pools of carbon (C) that are sensitive to a warming climate. When upland permafrost thaws, soil organic matter, C and nutrients are mobilized by the resulting landscape erosion. The intermediate ecosystem recovery stage (~ 50 y) is characterized by strongly enhanced above-ground biomass (shrubbiness) relative to undisturbed, early or late successional stages. However, upland arctic terrestrial ecosystems are very strongly nutrient- limited to plant growth and microbial activity, so the source of nutrients for this intermediate recovery stage is unknown. We hypothesized that nutrient inputs from upslope during spring thaw, combined with differential retention between recovery stages could be a potential mechanism. Furthermore, we hypothesized that the leachate nutrients from upslope vegetation would be an important stimulant to soil microbial activity at thaw. In winter, we placed ion exchange resin bags at the base of the snowpack, along the top, middle and base of each recovery stage slope. These were collected in spring and analyzed to estimate relative C, N and P inputs and outputs for each recovery stage. Also in winter, we collected snow cores (n=5) from the surface horizon of each of the recovery stages of the thermokarst chronosequence, in addition to live (dormant) plants and surface litter from snow-covered, undisturbed tundra directly above the thermokarst, with which we made cold (0-2 oC) vegetation leachate. To test the response of soil microbes to thaw pulses of vegetation leachate, we added this leachate (or water) to the frozen soil cores, and stepped them up in temperature from -10 oC to +4 oC over the course of 6 days and measured changes in microbial biomass and extractable soil biogeochemistry at the end of the incubation. As an indicator of soil microbial activity, we measured soil respiration and gross N mineralization over the course of the incubation. Time since thermokarst disturbance was the most important predictor

  11. Reconstructing thawing quintessence with multiple datasets

    NASA Astrophysics Data System (ADS)

    Lima, Nelson A.; Liddle, Andrew R.; Sahlén, Martin; Parkinson, David

    2016-03-01

    In this work we model the quintessence potential in a Taylor series expansion, up to second order, around the present-day value of the scalar field. The field is evolved in a thawing regime assuming zero initial velocity. We use the latest data from the Planck satellite, baryonic acoustic oscillations observations from the Sloan Digital Sky Survey, and supernova luminosity distance information from Union2.1 to constrain our models parameters, and also include perturbation growth data from the WiggleZ, BOSS, and 6dF surveys. The supernova data provide the strongest individual constraint on the potential parameters. We show that the growth data performance is competitive with the other datasets in constraining the dark energy parameters we introduce. We also conclude that the combined constraints we obtain for our model parameters, when compared to previous works of nearly a decade ago, have shown only modest improvement, even with new growth of structure data added to previously existent types of data.

  12. Biofilm, ice recrystallization inhibition and freeze-thaw protection in an epiphyte community.

    PubMed

    Wu, Z; Kan, F W K; She, Y-M; Walker, V K

    2012-01-01

    Microbial communities found on the surface of overwintering plants may be exposed to low temperatures as well as multiple freeze-thaw events. To explore the adaptive mechanisms of these epiphytes, with the objective of identifying products for freeze-protection, enrichment libraries were made from frost-exposed leaves. Of 15 identified bacteria from 60 individual clones, approximately half had ice-association activities, with the great majority showing high freeze-thaw resistance. Isolates with ice nucleation activity and ice recrystallization inhibition activity were recovered. Of the latter, two (Erwinia billingiae J10, and Sphingobacterium kitahiroshimense Y2) showed culture and electron microscopic evidence of motility and/or biofilm production. Mass spectrometric characterization of the E. billingiae extracellular polymeric substance (EPS) identified the major proteins as 35 kDa outer membrane protein A and F, supporting its biofilm character. The addition of the EPS preparation increased the freeze-thaw survival of the more susceptible bacteria 1000-10000 times, and protection was at least partially dependent on the protein component.

  13. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen–Popper, Dion–Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  14. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen-Popper, Dion-Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  15. Management of severe ovarian hyperstimulation syndrome with thawed plasma

    PubMed Central

    Kamath, Mohan S; Joshi, Asmita; Kamath, Anne Marie; Aleyamma, TK

    2013-01-01

    Severe ovarian hyperstimulation syndrome remains one of the life threatening complication of assisted reproductive technology. In refractory cases of late ovarian hyperstimulation syndrome (OHSS), clinicians are left with limited therapeutic options. We report a case of refractory OHSS which was managed successfully using thawed plasma. Thawed plasma transfusion could be potential therapeutic option for managing patients with severe ovarian hyperstimulation not responding to conventional treatment. PMID:23869160

  16. A retrospective study of single frozen-thawed blastocyst transfer

    PubMed Central

    Ryu, Eun Kyung; Song, Seung Hyun; Yoon, San Hyun; Lim, Kyung Sil; Lee, Won Don; Lim, Jin Ho

    2016-01-01

    Objective To study the clinical outcomes of single frozen-thawed blastocyst transfer cycles according to the hatching status of frozen-thawed blastocysts. Methods Frozen-thawed blastocysts were divided into three groups according to their hatching status as follows: less-than-expanded blastocyst (≤EdB), hatching blastocyst (HgB), and hatched blastocyst (HdB). The female age and infertility factors of each group were evaluated. The quality of the single frozen-thawed blastocyst was also graded as grade A, tightly packed inner cell mass (ICM) and many cells organized in the trophectoderm epithelium (TE); grade B, several and loose ICM and TE; and grade C, very few ICM and a few cells in the TE. The clinical pregnancy and implantation rate were compared between each group. The data were analyzed by either t-test or chi-square analysis. Results There were no statistically significant differences in average female ages, infertility factors, or the distribution of blastocyst grades A, B, and C in each group. There was no significant difference in the clinical pregnancy and implantation rate of each group according to their blastocyst grade. However, there was a significant difference in the clinical pregnancy and implantation rate between each group. In the HdB group, the clinical pregnancy and implantation rate were similar regardless of the blastocyst quality. Conclusion There was an effect on the clinical outcomes depending on whether the blastocyst hatched during single frozen-thawed blastocyst transfer. When performing single frozen-thawed blastocyst transfer, the hatching status of the frozen-thawed blastocyst may be a more important parameter for clinical outcomes than the quality of the frozen-thawed blastocyst. PMID:27358829

  17. Activity induces traveling waves, vortices and spatiotemporal chaos in a model actomyosin layer

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Rajesh; Jülicher, Frank

    2016-02-01

    Inspired by the actomyosin cortex in biological cells, we investigate the spatiotemporal dynamics of a model describing a contractile active polar fluid sandwiched between two external media. The external media impose frictional forces at the interface with the active fluid. The fluid is driven by a spatially-homogeneous activity measuring the strength of the active stress that is generated by processes consuming a chemical fuel. We observe that as the activity is increased over two orders of magnitude the active polar fluid first shows spontaneous flow transition followed by transition to oscillatory dynamics with traveling waves and traveling vortices in the flow field. In the flow-tumbling regime, the active polar fluid also shows transition to spatiotemporal chaos at sufficiently large activities. These results demonstrate that level of activity alone can be used to tune the operating point of actomyosin layers with qualitatively different spatiotemporal dynamics.

  18. Activity induces traveling waves, vortices and spatiotemporal chaos in a model actomyosin layer

    PubMed Central

    Ramaswamy, Rajesh; Jülicher, Frank

    2016-01-01

    Inspired by the actomyosin cortex in biological cells, we investigate the spatiotemporal dynamics of a model describing a contractile active polar fluid sandwiched between two external media. The external media impose frictional forces at the interface with the active fluid. The fluid is driven by a spatially-homogeneous activity measuring the strength of the active stress that is generated by processes consuming a chemical fuel. We observe that as the activity is increased over two orders of magnitude the active polar fluid first shows spontaneous flow transition followed by transition to oscillatory dynamics with traveling waves and traveling vortices in the flow field. In the flow-tumbling regime, the active polar fluid also shows transition to spatiotemporal chaos at sufficiently large activities. These results demonstrate that level of activity alone can be used to tune the operating point of actomyosin layers with qualitatively different spatiotemporal dynamics. PMID:26877263

  19. [Effects of human engineering activities on permafrost active layer and its environment in northern Qinghai-Tibetan plateau].

    PubMed

    Guo, Zhenggang; Wu, Qingbo; Niu, Fujun

    2006-11-01

    With disturbed and undisturbed belts during the construction of Qinghai-Tibet highway as test objectives, this paper studied the effects of human engineering activities on the permafrost ecosystem in northern Qinghai-Tibetan plateau. The results showed that the thickness of permafrost active layer was smaller in disturbed than in undisturbed belt, and decreased with increasing altitude in undisturbed belt while no definite pattern was observed in disturbed belt. Different vegetation types had different effects on the thickness of permafrost active layer, being decreased in the order of steppe > shrub > meadow. In the two belts, altitude was the main factor affecting the vertical distribution of soil moisture, but vegetation type was also an important affecting factor if the altitude was similar. Due to the human engineering activities, soil temperature in summer was lower in disturbed than in undisturbed belt.

  20. Toward Efficient Thick Active PTB7 Photovoltaic Layers Using Diphenyl Ether as a Solvent Additive.

    PubMed

    Zheng, Yifan; Goh, Tenghooi; Fan, Pu; Shi, Wei; Yu, Junsheng; Taylor, André D

    2016-06-22

    The development of thick organic photovoltaics (OPV) could increase absorption in the active layer and ease manufacturing constraints in large-scale solar panel production. However, the efficiencies of most low-bandgap OPVs decrease substantially when the active layers exceed ∼100 nm in thickness (because of low crystallinity and a short exciton diffusion length). Herein, we report the use of solvent additive diphenyl ether (DPE) that facilitates the fabrication of thick (180 nm) active layers and triples the power conversion efficiency (PCE) of conventional thienothiophene-co-benzodithiophene polymer (PTB7)-based OPVs from 1.75 to 6.19%. These results demonstrate a PCE 20% higher than those of conventional (PTB7)-based OPV devices using 1,8-diiodooctane. Morphology studies reveal that DPE promotes the formation of nanofibrillar networks and ordered packing of PTB7 in the active layer that facilitate charge transport over longer distances. We further demonstrate that DPE improves the fill factor and photocurrent collection by enhancing the overall optical absorption, reducing the series resistance, and suppressing bimolecular recombination.

  1. Diversity of aerobic methanotrophic bacteria in a permafrost active layer soil of the Lena Delta, Siberia.

    PubMed

    Liebner, Susanne; Rublack, Katja; Stuehrmann, Torben; Wagner, Dirk

    2009-01-01

    With this study, we present first data on the diversity of aerobic methanotrophic bacteria (MOB) in an Arctic permafrost active layer soil of the Lena Delta, Siberia. Applying denaturing gradient gel electrophoresis and cloning of 16S ribosomal ribonucleic acid (rRNA) and pmoA gene fragments of active layer samples, we found a general restriction of the methanotrophic diversity to sequences closely related to the genera Methylobacter and Methylosarcina, both type I MOB. In contrast, we revealed a distinct species-level diversity. Based on phylogenetic analysis of the 16S rRNA gene, two new clusters of MOB specific for the permafrost active layer soil of this study were found. In total, 8 out of 13 operational taxonomic units detected belong to these clusters. Members of these clusters were closely related to Methylobacter psychrophilus and Methylobacter tundripaludum, both isolated from Arctic environments. A dominance of MOB closely related to M. psychrophilus and M. tundripaludum was confirmed by an additional pmoA gene analysis. We used diversity indices such as the Shannon diversity index or the Chao1 richness estimator in order to compare the MOB community near the surface and near the permafrost table. We determined a similar diversity of the MOB community in both depths and suggest that it is not influenced by the extreme physical and geochemical gradients in the active layer. PMID:18592300

  2. Active Layer and Moisture Measurements for Intensive Site 0 and 1, Barrow, Alaska

    DOE Data Explorer

    John Peterson

    2015-04-17

    These are measurements of Active Layer Thickness collected along several lines beginning in September, 2011 to the present. The data were collected at several time periods along the Site0 L2 Line, the Site1 AB Line, and an ERT Monitoring Line near Area A in Site1.

  3. Extending the Diffuse Layer Model of Surface Acidity Behavior: III. Estimating Bound Site Activity Coefficients

    EPA Science Inventory

    Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...

  4. Toward Efficient Thick Active PTB7 Photovoltaic Layers Using Diphenyl Ether as a Solvent Additive.

    PubMed

    Zheng, Yifan; Goh, Tenghooi; Fan, Pu; Shi, Wei; Yu, Junsheng; Taylor, André D

    2016-06-22

    The development of thick organic photovoltaics (OPV) could increase absorption in the active layer and ease manufacturing constraints in large-scale solar panel production. However, the efficiencies of most low-bandgap OPVs decrease substantially when the active layers exceed ∼100 nm in thickness (because of low crystallinity and a short exciton diffusion length). Herein, we report the use of solvent additive diphenyl ether (DPE) that facilitates the fabrication of thick (180 nm) active layers and triples the power conversion efficiency (PCE) of conventional thienothiophene-co-benzodithiophene polymer (PTB7)-based OPVs from 1.75 to 6.19%. These results demonstrate a PCE 20% higher than those of conventional (PTB7)-based OPV devices using 1,8-diiodooctane. Morphology studies reveal that DPE promotes the formation of nanofibrillar networks and ordered packing of PTB7 in the active layer that facilitate charge transport over longer distances. We further demonstrate that DPE improves the fill factor and photocurrent collection by enhancing the overall optical absorption, reducing the series resistance, and suppressing bimolecular recombination. PMID:27253271

  5. Using Observational Data to Inform Physically Based Models of Subsurface Thermal Hydrology Properties and Active Layer Thickness at the Barrow Environmental Observatory, Alaska

    NASA Astrophysics Data System (ADS)

    Atchley, A. L.; Harp, D. R.; Painter, S. L.; Coon, E.; Wilson, C. J.; Romanovsky, V. E.; Liljedahl, A.

    2014-12-01

    Climate change is profoundly impacting permafrost regions and reshaping carbon rich tundra ecosystems from carbon sinks to potential carbon sources triggering a positive feedback to climate change. The annual maximum depth of ice-free soil with above 0°C temperatures, which is known as the active-layer thickness (ALT), determines the volume of carbon-rich stores available for decomposition and therefore potential greenhouse gas release into the atmosphere. Despite the increased vulnerability of permafrost regions to climate change, predictive tools and precise parameterization of physical characteristics to estimate projected ALT in tundra ecosystems have been developed slowly and often are not adequately representing natural systems due to the complex nature of corresponding atmospheric-surface-subsurface hydrological and energy interactions undergoing freeze-thaw dynamics. A model-observation-experiment process (ModEx) is employed to generate three 1D models representing characteristic micro-topographical land-formations, which are capable of simulating present ALT from current climate conditions. Observational soil temperature data from a tundra site located near Barrow, AK is used to calibrate thermal properties of moss, peat, and sandy loam soil to be used in the multiphysics Arctic Terrestrial Simulator (ATS) models. In the process of calibration and model formulation key physical processes and appropriate model parameters are identified, which showcases the importance of correctly representing physical processes and reformulating models based on observational data. Iterative execution of the ModEx concept identified key processes that control thermal propagation into the subsurface: 1) physical representation of thermal conduction, 2) liquid, ice, and gas partitioning in the subsurface, 3) snowpack distribution and dynamics, and 4) precipitation delivery of water to the surface/subsurface. This work was supported by LANL Laboratory Directed Research and

  6. Activation of ethylenediaminetetraacetic acid by a 940 nm diode laser for enhanced removal of smear layer.

    PubMed

    Lagemann, Manfred; George, Roy; Chai, Lei; Walsh, Laurence J

    2014-08-01

    Laser enhancement of ethylenediaminetetraacetic acid with cetrimide (EDTAC) has previously been shown to increase removal of smear layer, for middle-infrared erbium lasers. This study evaluated the efficiency of EDTAC activation using a near-infrared-pulsed 940 nm laser delivered by plain fibre tips into 15% EDTAC or 3% hydrogen peroxide. Root canals in 4 groups of 10 single roots were prepared using rotary files, with controls for the presence and absence of smear layer. After laser treatment (80 mJ pulse(-1) , 50 Hz, 6 cycles of 10 s), roots were split and the apical, middle and coronal thirds of the canal were examined using scanning electron microscopy, with the area of dentine tubules determined by a validated quantitative image analysis method. Lasing EDTAC considerably improved smear layer removal, while lasing into peroxide gave minimal smear layer removal. The laser protocol used was more effective for smear layer removal than the 'gold standard' protocol using EDTAC with sodium hypochlorite (NaOCl). In addition, lasers may also provide a benefit through photothermal disinfection. Further research is needed to optimise irrigant activation protocols using near-infrared diode lasers of other wavelengths.

  7. A Novel Surface Structure Consisting of Contact-active Antibacterial Upper-layer and Antifouling Sub-layer Derived from Gemini Quaternary Ammonium Salt Polyurethanes

    PubMed Central

    He, Wei; Zhang, Yi; Li, Jiehua; Gao, Yunlong; Luo, Feng; Tan, Hong; Wang, Kunjie; Fu, Qiang

    2016-01-01

    Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them. PMID:27561546

  8. A Novel Surface Structure Consisting of Contact-active Antibacterial Upper-layer and Antifouling Sub-layer Derived from Gemini Quaternary Ammonium Salt Polyurethanes

    NASA Astrophysics Data System (ADS)

    He, Wei; Zhang, Yi; Li, Jiehua; Gao, Yunlong; Luo, Feng; Tan, Hong; Wang, Kunjie; Fu, Qiang

    2016-08-01

    Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them.

  9. A Novel Surface Structure Consisting of Contact-active Antibacterial Upper-layer and Antifouling Sub-layer Derived from Gemini Quaternary Ammonium Salt Polyurethanes.

    PubMed

    He, Wei; Zhang, Yi; Li, Jiehua; Gao, Yunlong; Luo, Feng; Tan, Hong; Wang, Kunjie; Fu, Qiang

    2016-01-01

    Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them. PMID:27561546

  10. The development of the cell cryopreservation protocol with controlled rate thawing.

    PubMed

    Gurina, Tatyana M; Pakhomov, Alexandr V; Polyakova, Anna L; Legach, Evgeniy I; Bozhok, Galyna A

    2016-06-01

    Thawing in the water bath is often considered as a standard procedure. The thermal history of samples thawed in this way is poorly controlled, but cryopreservation and banking of cell-based products require standardization, automation and safety of all the technological stages including thawing. The programmable freezers allow implementation of the controlled cooling as well as the controlled thawing. As the cell damage occurs during the phase transformation that takes place in the cryoprotectant medium in the process of freezing-thawing, the choice of warming rates within the temperature intervals of transformations is very important. The goal of the study was to investigate the influence of warming rates within the intervals of the phase transformations in the DMSO-based cryoprotectant medium on the cell recovery and to develop a cryopreservation protocol with controlled cooling and warming rates. The temperature intervals of phase transformations such as melting of the eutectic mixture of the cryoprotectant solution (MEMCS), melting of the eutectic salt solution (MESS), melting of the main ice mass (MMIM), recrystallization before MEMCS, recrystallization before MESS and recrystallization before MMIM were determined by thermo-mechanical analysis. The biological experiments were performed on the rat testicular interstitial cells (TIC). The highest levels of the cell recovery and metabolic activity after cryopreservation were obtained using the protocol with the high (20 °C/min) warming rate in the temperature intervals of crystallization of the eutectics as well as recrystallizations and the low (1 °C/min) warming rate in the temperature intervals of melting of the eutectics as well as MMIM. The total cell recovery was 65.3 ± 2.1 %, the recovery of the 3-beta-HSD-positive (Leydig) cells was 82.9 ± 1.8 %, the MTT staining was 32.5 ± 0.9 % versus 42.1 ± 1.7 %; 57.4 ± 2.1 % and 24.0 ± 1.1 % respectively, when compared to the thawing in

  11. Nutrient Controls on Methane Emissions in a Permafrost Thaw Subarctic Peatland

    NASA Astrophysics Data System (ADS)

    Kashi, N. N.; Perryman, C. R.; Malhotra, A.; Marek, E. A.; Giesler, R.; Varner, R. K.

    2015-12-01

    Permafrost peatlands in northern latitudes are large reservoirs of sequestered carbon that are vulnerable to climate change. While peatlands account for a small fraction of total global land surfaces, their potential to release sequestered carbon in response to higher temperatures is of concern. Of particular relevance is the conversion of these carbon stores into methane (CH4), a strong greenhouse gas with a global warming potential 20 times greater than that of CO2 over a 100-year time frame. Here, we explore how key nutrients impact the consumption of CH4 at the Stordalen Mire in Abisko, Sweden, a discontinuous permafrost peatland with expanding thaw over the last century. Peatland CH4 emissions are highly spatially variable due to multiple emission pathways and strong dependence on several environmental factors. Among controls on CH4 emissions, such as temperature and water table depth, primary production of wetland vegetation is also a strong factor in the variability of CH4 emissions. Plant community shifts among permafrost thaw stages subsequently change nutrient cycling and availability, which in turn impacts primary production. Early stages of permafrost thaw are mosaicked with a variety of vascular plants and mosses. We analyzed potential enzymatic activities of chitinase, glucosidase, and phosphatase as proxies for organic nitrogen, carbon, and phosphorus cycling, respectively, in tandem with potential CH4 oxidation rates. In addition, stoichiometric ratios of carbon, nitrogen, and phosphorus concentrations are used to illustrate nutrient limitation controls on CH4 oxidation rates. While CH4 emissions are low throughout initial thaw stages, < 7 CH4 mg m-2 day-1, we found they had the highest rates of potential CH4 oxidation. These permafrost thaw-induced CH4 oxidation rates are 5 and 11 times higher, in the surface and depth of the peat profile respectively, than subsequent aerobic permafrost thaw stages. As CH4 emissions are low in intact permafrost

  12. Refreezing previously thawed fresh-frozen plasma. Stability of coagulation factors V and VIII:C.

    PubMed

    Dzik, W H; Riibner, M A; Linehan, S K

    1989-09-01

    With the growth in autologous blood programs and the increased scrutiny of the indications for transfusion of fresh-frozen plasma (FFP), an increase has been seen in the number of occasions on which FFP was requested and thawed but then not transfused. The coagulation properties of FFP units that were refrozen and then rethawed were therefore studied. Fifty-eight units of plasma were studied, with each experimental unit of FFP paired with an identical control unit. Experimental units were frozen, stored at -65 degrees C, thawed, stored at 1 to 6 degrees C for various periods of time up to 24 hours, and then refrozen, stored at -65 degrees C, rethawed, and stored again in the refrigerator for up to 24 hours. Control units were frozen once at the time the experimental units were first frozen and thawed once at the time of the second thaw of the experimental units. Aliquots of plasma were sampled periodically and were later batch-tested for prothrombin time (PT), activated partial thromboplastin time (aPTT), and factor V and VIII:C activity. The results of coagulation testing of the twice-frozen plasmas were always within the normal range. There was a slight but statistically valid prolongation of the PT and aPTT and a decrease in the factor V and VIII:C levels for twice-frozen plasma compared with control plasma. The greatest decline occurred in the level of factor VIII:C. The measured deterioration in coagulation of twice-frozen FFP is unlikely to be of clinical importance. Refreezing FFP may eventually prove useful for rare donor, autologous, and massive transfusion programs.

  13. Electrical and mechanical characterization of nanoscale-layered cellulose-based electro-active paper.

    PubMed

    Yun, Gyu-Young; Yun, Ki-Ju; Kim, Joo-Hyung; Kim, Jaehwan

    2011-01-01

    In order to understand the electro-mechanical behavior of piezoelectric electro active paper (EAPap), the converse and direct piezoelectric characterization of cellulose EAPap was studied and compared. A delay between the electrical field and the induced strain of EAPap was observed due to the inner nano-voids or the localized amorphous regions in layer-by-layered structure to capture or hold the electrical charges and remnant ions. The linear relation between electric field and induced strain is also observed. The electro-mechanical performance of EAPap is discussed in detail in this paper.

  14. Influences and interactions of inundation, peat, and snow on active layer thickness

    DOE PAGES

    Atchley, Adam L.; Coon, Ethan T.; Painter, Scott L.; Harp, Dylan R.; Wilson, Cathy J.

    2016-05-18

    The effect of three environmental conditions: 1) thickness of organic soil, 2) snow depth, and 3) soil moisture content or water table height above and below the soil surface, on active layer thickness (ALT) are investigated using an ensemble of 1D thermal hydrology models. Sensitivity analyses of the ensemble exposed the isolated influence of each environmental condition on ALT and their multivariate interactions. The primary and interactive influences are illustrated in the form of color maps of ALT change. Results show that organic layer acts as a strong insulator, and its thickness is the dominant control of ALT, but themore » strength of the effect of organic layer thickness is dependent on the saturation state. Snow depth, subsurface saturation, and ponded water depth are strongly codependent and positively correlated to ALT.« less

  15. Freeze-thaw cycles enhance decellularization of large tendons.

    PubMed

    Burk, Janina; Erbe, Ina; Berner, Dagmar; Kacza, Johannes; Kasper, Cornelia; Pfeiffer, Bastian; Winter, Karsten; Brehm, Walter

    2014-04-01

    The use of decellularized tendon tissue as a scaffold for tendon tissue engineering provides great opportunities for future clinical and current research applications. The aim of this study was to assess the effect of repetitive freeze-thaw cycles and two different detergents, t-octyl-phenoxypolyethoxyethanol (Triton X-100) and sodium dodecyl sulfate (SDS), on decellularization effectiveness and cytocompatibility in large tendons. Freshly collected equine superficial and deep digital flexor tendons were subjected to decellularization according to four different protocols (1 and 2: freeze-thaw cycles combined with either Triton X-100 or SDS; 3 and 4: Triton X-100 or SDS). Decellularization effectiveness was assessed based on the reduction of vital cell counts, histologically visible nuclei, and DNA content. Transmission electron microscopy was performed to evaluate cellular and extracellular matrix integrity. Further, cytocompatibility of scaffolds that had been decellularized according to the protocols including freeze-thaw cycles (protocols 1 and 2) was assessed by seeding the scaffolds with superparamagnetic iron oxide labeled mesenchymal stromal cells and monitoring the cells histologically and by magnetic resonance imaging for two weeks. Decellularization was significantly more effective when using the protocols including freeze-thaw cycles, leaving only roughly 1% residual nuclei and 20% residual DNA, whereas samples that had not undergone additional freeze-thaw cycles contained roughly 20% residual nuclei and 40% residual DNA. No morphological extracellular matrix alterations due to decellularization could be observed. Scaffolds prepared by both protocols including freeze-thaw cycles were cytocompatible, but the cell distribution into the scaffold tended to be better in scaffolds that had been decellularized using freeze-thaw cycles combined with Triton X-100 instead of SDS.

  16. BOREAS RSS-17 1994 ERS-1 Level-3 Freeze/Thaw Backscatter Change Images

    NASA Technical Reports Server (NTRS)

    Rignot, Eric; Nickeson, Jaime (Editor); Hall, Forrest G. (Editor); Way, JoBea; McDonald, Kyle C.; Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Remote Sensing Science (RSS)-17 team acquired and analyzed imaging radar data from the European Space Agency's (ESA's) European Remote Sensing Satellite (ERS)-1 over a complete annual cycle at the BOREAS sites in Canada in 1994 to detect shifts in radar backscatter related to varying environmental conditions. Two independent transitions corresponding to soil thaw and possible canopy thaw were revealed by the data. The results demonstrated that radar provides an ability to observe thaw transitions at the beginning of the growing season, which in turn helps constrain the length of the growing season. The data set presented here includes change maps derived from radar backscatter images that were mosaicked together to cover the southern BOREAS sites. The image values used for calculating the changes are given relative to the reference mosaic image. The data are stored in binary image format files. The imaging radar data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  17. Air-coupled piezoelectric transducers with active polypropylene foam matching layers.

    PubMed

    Gómez Alvarez-Arenas, Tomás E

    2013-05-10

    This work presents the design, construction and characterization of air-coupled piezoelectric transducers using 1-3 connectivity piezocomposite disks with a stack of matching layers being the outer one an active quarter wavelength layer made of polypropylene foam ferroelectret film. This kind of material has shown a stable piezoelectric response together with a very low acoustic impedance (<0.1 MRayl). These features make them a suitable candidate for the dual use or function proposed here: impedance matching layer and active material for air-coupled transduction. The transducer centre frequency is determined by the l/4 resonance of the polypropylene foam ferroelectret film (0.35 MHz), then, the rest of the transducer components (piezocomposite disk and passive intermediate matching layers) are all tuned to this frequency. The transducer has been tested in several working modes including pulse-echo and pitch-catch as well as wide and narrow band excitation. The performance of the proposed novel transducer is compared with that of a conventional air-coupled transducers operating in a similar frequency range.

  18. Activation of Extrasynaptic NMDARs at Individual Parallel Fiber–Molecular Layer Interneuron Synapses in Cerebellum

    PubMed Central

    Nahir, Ben

    2013-01-01

    NMDA receptors (NMDARs) expressed by cerebellar molecular layer interneurons (MLIs) are not activated by single exocytotic events but can respond to glutamate spillover following coactivation of adjacent parallel fibers (PFs), indicating that NMDARs are perisynaptic. Several types of synaptic plasticity rely on these receptors but whether they are activated at isolated synapses is not known. Using a combination of electrophysiological and optical recording techniques in acute slices of rat cerebellum, along with modeling, we find that repetitive activation of single PF–MLI synapses can activate NMDARs in MLIs. High-frequency stimulation, multivesicular release (MVR), or asynchronous release can each activate NMDARs. Frequency facilitation was found at all PF–MLI synapses but, while some showed robust MVR with increased release probability, most were limited to univesicular release. Together, these results reveal a functional diversity of PF synapses, which use different mechanisms to activate NMDARs. PMID:24107963

  19. Influence of the Halogen Activation on the Ozone Layer in XXIst Century

    NASA Astrophysics Data System (ADS)

    Larin, Igor; Aloyan, Artash; Yermakov, Alexandr

    2016-04-01

    The aim of the work is to evaluate a possible effect of heterophase chemical reactions (HCR) with participation of reservoir gases (ClONO2, HCl) and sulfate particles of the Junge layer on the ozone layer at mid-latitudes in the XXI century, which could be relevant for more accurate predicting a recovery of the ozone layer, taking into account that just these processes were the main cause of the ozone depletion at the end of XXth century. Required for calculating the dynamics of GHR data on the specific volume/surface of the sulfate aerosols in the lower stratosphere were taken from the data of field experiments. Their physico-chemical properties (chemical composition, density, water activity and free protons activity et al.) have been obtained with help of thermodynamic calculations (Atmospheric Inorganic Model, AIM). Altitude concentration profiles of individual gas components, as well as temperature and relative humidity (RH) at a given geographic location and season have been calculated using a two-dimensional model SOCRATES. The calculations have been made for the conditions of June 1995, 2040 and 2080 at 15 km altitude and 50° N latitude. It has been shown that the rate of ozone depletion as a result of processes involving halogen activation for the given conditions in 2040, 2080 is about 35% lower than a corresponding value in 1995 (a year of maximum effect of halogen activation). From this we can conclude that in the XXI century, despite the natural decline of ozone-depleting chlorofluorocarbons. processes of halogen activation of the ozone depletion with participation of sulfate aerosols should be taken into account in the calculations of the recovery of the ozone layer at mid-latitudes.

  20. Activity retention after nisin entrapment in a polyethylene oxide brush layer.

    PubMed

    Auxier, Julie A; Schilke, Karl F; McGuire, Joseph

    2014-09-01

    The cationic, amphiphilic peptide nisin is an effective inhibitor of gram-positive bacteria whose mode of action does not encourage pathogenic resistance, and its proper incorporation into food packaging could enhance food stability, safety, and quality in a number of circumstances. Sufficiently small peptides have been shown to integrate into otherwise nonfouling polyethylene oxide (PEO) brush layers in accordance with their amphiphilicity and ordered structure, including nisin, and we have recently shown that nisin entrapment within a PEO layer does not compromise the nonfouling character of that layer. In this work we test the hypothesis that surface-bound, pendant PEO chains will inhibit displacement of entrapped nisin by competing proteins and, in this way, prolong retention of nisin activity at the interface. For this purpose, the antimicrobial activity of nisinloaded, PEO-coated surfaces was evaluated against the gram-positive indicator strain, Pediococcus pentosaceous. The retained antimicrobial activity of nisin layers was evaluated on uncoated and PEO-coated surfaces after incubation in the presence of bovine serum albumin for contact periods up to 1 week. Nisin-loaded, uncoated and PEO-coated samples were withdrawn at selected times and were incubated on plates inoculated with P. pentosaceous to quantify nisin activity by determination of kill zone radii. Our results indicate that nisin activity is retained at a higher level for a longer period of time after entrapment within PEO than after direct adsorption in the absence of PEO, owing to inhibition of nisin exchange with dissolved protein afforded by the pendant PEO chains.

  1. Discovery of a novel methanogen prevalent in thawing permafrost

    NASA Astrophysics Data System (ADS)

    Mondav, Rhiannon; Woodcroft, Ben J.; Kim, Eun-Hae; McCalley, Carmody K.; Hodgkins, Suzanne B.; Crill, Patrick M.; Chanton, Jeffrey; Hurst, Gregory B.; Verberkmoes, Nathan C.; Saleska, Scott R.; Hugenholtz, Philip; Rich, Virginia I.; Tyson, Gene W.

    2014-02-01

    Thawing permafrost promotes microbial degradation of cryo-sequestered and new carbon leading to the biogenic production of methane, creating a positive feedback to climate change. Here we determine microbial community composition along a permafrost thaw gradient in northern Sweden. Partially thawed sites were frequently dominated by a single archaeal phylotype, Candidatus ‘Methanoflorens stordalenmirensis’ gen. nov. sp. nov., belonging to the uncultivated lineage ‘Rice Cluster II’ (Candidatus ‘Methanoflorentaceae’ fam. nov.). Metagenomic sequencing led to the recovery of its near-complete genome, revealing the genes necessary for hydrogenotrophic methanogenesis. These genes are highly expressed and methane carbon isotope data are consistent with hydrogenotrophic production of methane in the partially thawed site. In addition to permafrost wetlands, ‘Methanoflorentaceae’ are widespread in high methane-flux habitats suggesting that this lineage is both prevalent and a major contributor to global methane production. In thawing permafrost, Candidatus ‘M. stordalenmirensis’ appears to be a key mediator of methane-based positive feedback to climate warming.

  2. Metagenomic analysis of permafrost microbial community response to thaw

    SciTech Connect

    Mackelprang, R.; Waldrop, M.P.; DeAngelis, K.M.; David, M.M.; Chavarria, K.L.; Blazewicz, S.J.; Rubin, E.M.; Jansson, J.K.

    2011-07-01

    We employed deep metagenomic sequencing to determine the impact of thaw on microbial phylogenetic and functional genes and related this data to measurements of methane emissions. Metagenomics, the direct sequencing of DNA from the environment, allows for the examination of whole biochemical pathways and associated processes, as opposed to individual pieces of the metabolic puzzle. Our metagenome analyses revealed that during transition from a frozen to a thawed state there were rapid shifts in many microbial, phylogenetic and functional gene abundances and pathways. After one week of incubation at 5°C, permafrost metagenomes converged to be more similar to each other than while they were frozen. We found that multiple genes involved in cycling of C and nitrogen shifted rapidly during thaw. We also constructed the first draft genome from a complex soil metagenome, which corresponded to a novel methanogen. Methane previously accumulated in permafrost was released during thaw and subsequently consumed by methanotrophic bacteria. Together these data point towards the importance of rapid cycling of methane and nitrogen in thawing permafrost.

  3. Active layer hydrology for Imnavait Creek, Toolik, Alaska. Annual progress report, July 1984--January 1986

    SciTech Connect

    Kane, D.L.

    1986-12-31

    In the annual hydrologic cycle, snowmelt is the most significant event at Imnavait Creek located near Toolik Lake, Alaska. Precipitation that has accumulated for more than 6 months on the surface melts in a relatively short period of 7 to 10 days once sustained melting occurs. During the ablation period, runoff dominates the hydrologic cycle. Some meltwater goes to rewetting the organic soils in the active layer. The remainder is lost primarily because of evaporation, since transpiration is not a very active process at this time. Following the snowmelt period, evapotranspiration becomes the dominate process, with base flow contributing the other watershed losses. It is important to note that the water initally lost by evapotranspiration entered the organic layer during melt. This water from the snowpack ensures that each year the various plant communities will have sufficient water to start a new summer of growth.

  4. Dual Gate Thin Film Transistors Based on Indium Oxide Active Layers

    SciTech Connect

    Kekuda, Dhananjaya; Rao, K. Mohan; Tolpadi, Amita; Chu, C. W.

    2011-07-15

    Polycrystalline Indium Oxide (In{sub 2}O{sub 3}) thin films were employed as an active channel layer for the fabrication of bottom and top gate thin film transistors. While conventional SiO{sub 2} served as a bottom gate dielectric, cross-linked poly-4-vinylphenol (PVP) was used a top gate dielectric. These nano-crystalline TFTs exhibited n-channel behavior with their transport behavior highly dependent on the thickness of the channel. The correlation between the thickness of the active layer and TFT parameters such as on/off ratio, field-effect mobility, threshold voltage were carried out. The optical spectra revealed a high transmittance in the entire visible region, thus making them promising candidates for the display technology.

  5. Influence of active layer and support layer surface structures on organic fouling propensity of thin-film composite forward osmosis membranes.

    PubMed

    Lu, Xinglin; Arias Chavez, Laura H; Romero-Vargas Castrillón, Santiago; Ma, Jun; Elimelech, Menachem

    2015-02-01

    In this study, we investigate the influence of surface structure on the fouling propensity of thin-film composite (TFC) forward osmosis (FO) membranes. Specifically, we compare membranes fabricated through identical procedures except for the use of different solvents (dimethylformamide, DMF and N-methyl-2-pyrrolidinone, NMP) during phase separation. FO fouling experiments were carried out with a feed solution containing a model organic foulant. The TFC membranes fabricated using NMP (NMP-TFC) had significantly less flux decline (7.47 ± 0.15%) when compared to the membranes fabricated using DMF (DMF-TFC, 12.70 ± 2.62% flux decline). Water flux was also more easily recovered through physical cleaning for the NMP-TFC membrane. To determine the fundamental cause of these differences in fouling propensity, the active and support layers of the membranes were extensively characterized for physical and chemical characteristics relevant to fouling behavior. Polyamide surface roughness was found to dominate all other investigated factors in determining the fouling propensities of our membranes relative to each other. The high roughness polyamide surface of the DMF-TFC membrane was also rich in larger leaf-like structures, whereas the lower roughness NMP-TFC membrane polyamide layer contained more nodular and smaller features. The support layers of the two membrane types were also characterized for their morphological properties, and the relation between support layer surface structure and polyamide active layer formation was discussed. Taken together, our findings indicate that support layer structure has a significant impact on the fouling propensity of the active layer, and this impact should be considered in the design of support layer structures for TFC membranes.

  6. Influence of active layer and support layer surface structures on organic fouling propensity of thin-film composite forward osmosis membranes.

    PubMed

    Lu, Xinglin; Arias Chavez, Laura H; Romero-Vargas Castrillón, Santiago; Ma, Jun; Elimelech, Menachem

    2015-02-01

    In this study, we investigate the influence of surface structure on the fouling propensity of thin-film composite (TFC) forward osmosis (FO) membranes. Specifically, we compare membranes fabricated through identical procedures except for the use of different solvents (dimethylformamide, DMF and N-methyl-2-pyrrolidinone, NMP) during phase separation. FO fouling experiments were carried out with a feed solution containing a model organic foulant. The TFC membranes fabricated using NMP (NMP-TFC) had significantly less flux decline (7.47 ± 0.15%) when compared to the membranes fabricated using DMF (DMF-TFC, 12.70 ± 2.62% flux decline). Water flux was also more easily recovered through physical cleaning for the NMP-TFC membrane. To determine the fundamental cause of these differences in fouling propensity, the active and support layers of the membranes were extensively characterized for physical and chemical characteristics relevant to fouling behavior. Polyamide surface roughness was found to dominate all other investigated factors in determining the fouling propensities of our membranes relative to each other. The high roughness polyamide surface of the DMF-TFC membrane was also rich in larger leaf-like structures, whereas the lower roughness NMP-TFC membrane polyamide layer contained more nodular and smaller features. The support layers of the two membrane types were also characterized for their morphological properties, and the relation between support layer surface structure and polyamide active layer formation was discussed. Taken together, our findings indicate that support layer structure has a significant impact on the fouling propensity of the active layer, and this impact should be considered in the design of support layer structures for TFC membranes. PMID:25564877

  7. A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; Nowak, Robert J.

    2003-01-01

    Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

  8. Acoustic radiation from the submerged circular cylindrical shell treated with active constrained layer damping

    NASA Astrophysics Data System (ADS)

    Yuan, Li-Yun; Xiang, Yu; Lu, Jing; Jiang, Hong-Hua

    2015-12-01

    Based on the transfer matrix method of exploring the circular cylindrical shell treated with active constrained layer damping (i.e., ACLD), combined with the analytical solution of the Helmholtz equation for a point source, a multi-point multipole virtual source simulation method is for the first time proposed for solving the acoustic radiation problem of a submerged ACLD shell. This approach, wherein some virtual point sources are assumed to be evenly distributed on the axial line of the cylindrical shell, and the sound pressure could be written in the form of the sum of the wave functions series with the undetermined coefficients, is demonstrated to be accurate to achieve the radiation acoustic pressure of the pulsating and oscillating spheres respectively. Meanwhile, this approach is proved to be accurate to obtain the radiation acoustic pressure for a stiffened cylindrical shell. Then, the chosen number of the virtual distributed point sources and truncated number of the wave functions series are discussed to achieve the approximate radiation acoustic pressure of an ACLD cylindrical shell. Applying this method, different radiation acoustic pressures of a submerged ACLD cylindrical shell with different boundary conditions, different thickness values of viscoelastic and piezoelectric layer, different feedback gains for the piezoelectric layer and coverage of ACLD are discussed in detail. Results show that a thicker thickness and larger velocity gain for the piezoelectric layer and larger coverage of the ACLD layer can obtain a better damping effect for the whole structure in general. Whereas, laying a thicker viscoelastic layer is not always a better treatment to achieve a better acoustic characteristic. Project supported by the National Natural Science Foundation of China (Grant Nos. 11162001, 11502056, and 51105083), the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2012GXNSFAA053207), the Doctor Foundation of Guangxi

  9. Self-assembly Columnar Structure in Active Layer of Bulk Heterojunction Solar Cell

    NASA Astrophysics Data System (ADS)

    Pan, Cheng; Segui, Jennifer; Yu, Yingjie; Li, Hongfei; Akgun, Bulent; Satijia, Sushil. K.; Gersappe, Dilip; Nam, Chang-Yong; Rafailovich, Miriam

    2012-02-01

    Bulk Heterojunction (BHJ) polymer solar cells are an area of intense interest due to their flexibility and relatively low cost. However, due to the disordered inner structure in active layer, the power conversion efficiency of BHJ solar cell is relatively low. Our research provides the method to produce ordered self-assembly columnar structure within active layer of bulk heterojunction (BHJ) solar cell by introducing polystyrene (PS) into the active layer. The blend thin film of polystyrene, poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) at different ratio are spin coated on substrate and annealed in vacuum oven for certain time. Atomic force microscopy (AFM) images show uniform phase segregation on the surface of polymer blend thin film and highly ordered columnar structure is then proven by etching the film with ion sputtering. TEM cross-section technology is also used to investigate the column structure. Neutron reflectometry was taken to establish the confinement of PCBM at the interface of PS and P3HT. The different morphological structures formed via phase segregation will be correlated with the performance of the PEV cells to be fabricated at the BNL-CFN.

  10. Origin of photogenerated carrier recombination at the metal-active layer interface in polymer solar cells.

    PubMed

    Kumar, Mukesh; Dubey, Ashish; Reza, Khan Mamun; Adhikari, Nirmal; Qiao, Qiquan; Bommisetty, Venkat

    2015-11-01

    The role of the metal-active layer interface in photogenerated recombination has been investigated using nanoscale current sensing atomic force microscopy (CS-AFM) and intensity modulated photocurrent spectroscopy (IMPS) in as-deposited, pre-annealed and post-annealed bulk heterojunction (BHJ) solar cells. Aluminum (Al) confined post-annealed BHJ solar cells exhibited a significantly improved device efficiency compared to pre-annealed BHJ solar cells having similar photocarrier harvesting ability in the active layer. The nanoscale topography and CS-AFM results indicate a uniform PCBM rich phase at the metal-active layer interface in the post-annealed cells, but PCBM segregation in the pre-annealed cells. These two different annealing processes showed different carrier dynamics revealed using IMPS under various light intensities. The IMPS results suggest reduced photo generated carrier recombination in uniform PCBM rich post-annealed BHJ solar cells. This study reveals the importance of the metal-bend interface in BHJ solar cells in order to obtain efficient charge carrier extraction for high efficiency. PMID:26431263

  11. Architectural evolution of the Nojima fault and identification of the activated slip layer by Kobe earthquake

    NASA Astrophysics Data System (ADS)

    Tanaka, Hidemi; Omura, Kentaro; Matsuda, Tatsuo; Ikeda, Ryuji; Kobayashi, Kenta; Murakami, Masaki; Shimada, Koji

    2007-07-01

    Evolutionary history of Nojima Fault zone is clarified by comprehensive examinations of petrological, geophysical, and geochemical characterizations on a fault zone in deep-drilled core penetrating the Nojima Fault. On the basis of the results, we reconstruct a whole depth profile of the architecture of the Nojima Fault and identify the primal slip layer activated by 1995 Kobe earthquake. The deepest part (8- to 12-km depth) of the fault zone is composed of thin slip layers of pseudotachylite (5 to 10 mm thick each, 10 cm in total). Middle depth (4- to 8-km depth) of the fault zone is composed of fault core (6 to 10 m thick), surrounded by thick (100 m thick) damage zone, characterized by zeolite precipitation. The shallow part of the fault zone (1- to 4-km depth) is composed of distributed narrow shear zones, which are characterized by combination of thin (0.5 cm thick each, 10 cm in total) ultracataclasite layers at the core of shear zones, surrounded by thicker (1 to 3 m thick) damage zones associated with carbonate precipitation. An extremely thin ultracataclasite layer (7 mm thick), activated by the 1995 Kobe earthquake, is clearly identified from numerous past slip layers, overprinting one of the shear zones, as evidenced by conspicuous geological and geophysical anomalies. The Nojima Fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths. The thickening would be explained as a combination of physical and chemical effects as follows. (1) Thickening of "fault core" at middle depth would be attributed to normal stress dependence on thickness of the shear zone and (2) an extreme thickening of "damage zone" in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths. The high fluid pressure would result from faster sealing with low-temperature carbonate at the shallower fault zone.

  12. Effect of the addition of beta-mercaptoethanol to a thawing solution supplemented with caffeine on the function of frozen-thawed boar sperm and on the fertility of sows after artificial insemination.

    PubMed

    Yamaguchi, S; Funahashi, H

    2012-03-15

    We have reported that artificial insemination (AI) with frozen-thawed boar semen supplemented with caffeine increased the number of uterine sperm by inhibiting the migration of polymorphonuclear leukocytes (PMNs) into the uterine lumen, thereby improving the fertility of gilts and sows. The objective of the present study was to examine the effects of the addition of the antioxidant beta-mercaptoethanol (bME) and caffeine to the thawing solution on the function of frozen-thawed sperm, on the phagocytic activity of PMNs for sperm, and on the fertility of sows after AI. When frozen-thawed sperm were cultured in the presence of 25 or 50 μm bME, sperm capacitation and spontaneous acrosome reactions were inhibited (P < 0.01). There was no effect of bME on phagocytic activity of PMNs for sperm in vitro. When hormonally treated (400 IU of equine chorionic gonadotropin + 200 IU of human chorionic gonadotropin) weaned sows experienced a single intrauterine insemination with frozen-thawed sperm (25 × 10(8) sperm per 50 ml dose) 40 h after subsequent hCG administration, pregnancy and farrowing rates were unaffected by the addition of 50 μm bME (pregnancy rate, 20 vs 21% in controls; farrowing rate, 20 vs 21%; n = 15 and 14, respectively). However, litter size tended to be higher than in the presence of 50 μm bME compared to its absence (10.0 ± 1.0 vs 5.7 ± 1.5, respectively; P < 0.07). Thus, the addition of bME to the thawing solution containing caffeine could be of benefit for improving the function of frozen-thawed sperm without influencing the phagocytic activity of PMNs for sperm. Although there were no statistically significant effects of bME on pregnancy or farrowing rates, the litter size tended to be higher in the sows subjected to a fixed-time single AI treatment with synchronized ovulation.

  13. Consumer Attitudes Toward Storing and Thawing Chicken and Effects of the Common Thawing Practices on Some Quality Characteristics of Frozen Chicken

    PubMed Central

    Benli, Hakan

    2016-01-01

    In this study, a survey was conducted to both evaluate the consumers’ general attitudes for purchasing and storing the raw chicken and determine the thawing practices used for defrosting frozen chicken at home. About 75% of the consumers indicated purchasing chicken meat at least once a week or more. Furthermore, the majority (82.16%) of those who stored at least a portion of the raw chicken stated freezing the raw chicken meat at home. Freezing the chicken meat was considered to have no effect on the quality by 43.49% of the consumers while 56.51% thought that freezing had either negative or positive effects on the quality. The survey study indicated that top five most commonly used thawing practices included thawing on the kitchen counter, thawing in the refrigerator, thawing in the warm water, thawing in the microwave, and thawing under tap water. In addition, an experimental study was conducted to determine the effects of these most commonly used thawing practices on some quality characteristics of the chicken meat including pH, drip loss, cooking loss, color analysis and textural profile analysis. Although, L* value for thawing on the kitchen counter was the lowest, after cooking, none of the thawing treatments have a significant effect on the color values. Thawing in the microwave produced the highest drip loss of 3.47% while the lowest drip loss of 0.62% was observed with thawing in the refrigerator. On the other hand, thawing in the microwave and refrigerator caused the lowest cooking loss values of 18.29% and 18.53%, respectively. Nevertheless, there were no significant differences among textural parameter values of the defrosted and then cooked samples using the home based thawing practices, indicating similar quality characteristics among the samples. PMID:26732333

  14. Real-time monitoring of enzyme activity in a mesoporous silicon double layer

    NASA Astrophysics Data System (ADS)

    Orosco, Manuel M.; Pacholski, Claudia; Sailor, Michael J.

    2009-04-01

    The activity of certain proteolytic enzymes is often an indicator of disease states such as cancer, stroke and neurodegeneracy, so there is a need for rapid assays that can characterize the kinetics and substrate specificity of enzymatic reactions. Nanostructured membranes can efficiently separate biomolecules, but coupling a sensitive detection method to such a membrane remains difficult. Here, we demonstrate a single mesoporous nanoreactor that can isolate and quantify in real time the reaction products of proteases. The reactor consists of two layers of porous films electrochemically prepared from crystalline silicon. The upper layer, with large pore sizes (~100 nm in diameter), traps the protease and acts as the reactor. The lower layer, with smaller pore sizes (~6 nm), excludes the proteases and other large proteins and captures the reaction products. Infiltration of the digested fragments into the lower layer produces a measurable change in optical reflectivity, and this allows label-free quantification of enzyme kinetics in real time within a volume of ~5 nl.

  15. Microbial activities at the benthic boundary layer in the Aegean Sea

    NASA Astrophysics Data System (ADS)

    Bianchi, A.; Tholosan, O.; Garcin, J.; Polychronaki, T.; Tselepides, A.; Buscail, R.; Duineveld, G.

    2003-05-01

    During the Aegean Sea component of the EU MTP-MATER project, benthic samples were acquired along a depth gradient from two continental margins in the Aegean Sea. Sampling was undertaken during spring and summer 1997 and the microbial metabolic activities measured (Vmax for aminopeptidase activity, 14C-glutamate respiration and assimilation) displayed seasonal variability even in deep-sea conditions. The metabolic rates encountered in the North Aegean (average depth 566±234 m), were approximately five-fold higher than in the deeper (1336±140 m) Southern part of the Aegean. The aminopeptidase rates, however, were the exception with higher values recorded in the more oligotrophic sediments of the Southern stations (1383±152 vs. 766±297 nmol MCA cm -2 h -1). A discrepancy in bacterial metabolism also appeared in the near bottom waters. In the Southern stations, 80% of the glutamate uptake was used for energy yielding processes and only 20% devoted to biomass production, while in the North Aegean, most of the used glutamate was incorporated into bacterial cells. During the early burial stages, bacterial mineralization rates estimated from 14C-glutamate respiration decreased drastically compared to the rates of biopolymer hydrolysis estimated by aminopeptidase assays. Thus, at the 2-cm depth layer, these rates were only 32 and up to 77% of the corresponding average values, respectively, in the superficial layer. Such a discrepancy between the evolution of these two metabolic activities is possibly due to the rapid removal of readily utilizable monomers in the surface deposits. The correlation between bacterial respiration and total organic carbon, or total organic nitrogen, is higher in the surficial sediment (0-2 and 2-4 cm) than in the underlying layer. Conversely, it is only at 4-cm depth layer that the hydrolysis rates appear correlated with organic carbon and nitrogen concentrations. This pattern confirms the drastic degradation of organic matter during the

  16. Active layer thermal regime at different vegetation covers at Lions Rump, King George Island, Maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Almeida, Ivan C. C.; Schaefer, Carlos Ernesto G. R.; Fernandes, Raphael B. A.; Pereira, Thiago T. C.; Nieuwendam, Alexandre; Pereira, Antônio Batista

    2014-11-01

    Climate change impacts the biotic and abiotic components of polar ecosystems, affecting the stability of permafrost, active layer thickness, vegetation, and soil. This paper describes the active layer thermal regimes of two adjacent shallow boreholes, under the same soil but with two different vegetations. The study is location in Lions Rump, at King George Island, Maritime Antarctic, one of the most sensitive regions to climate change, located near the climatic limit of Antarctic permafrost. Both sites are a Turbic Cambic Cryosol formed on andesitic basalt, one under moss vegetation (Andreaea gainii, at 85 m a.s.l.) and another under lichen (Usnea sp., at 86 m a.s.l.), located 10 m apart. Ground temperature at same depths (10, 30 and 80 cm), water content at 80 cm depth and air temperature were recorded hourly between March 2009 and February 2011. The two sites showed significant differences in mean annual ground temperature for all depths. The lichen site showed a higher soil temperature amplitude compared to the moss site, with ground surface (10 cm) showing the highest daily temperature in January 2011 (7.3 °C) and the lowest daily temperature in August (- 16.5 °C). The soil temperature at the lichen site closely followed the air temperature trend. The moss site showed a higher water content at the bottommost layer, consistent with the water-saturated, low landscape position. The observed thermal buffering effect under mosses is primarily associated with higher moisture onsite, but a longer duration of the snowpack (not monitored) may also have influenced the results. Active layer thickness was approximately 150 cm at low-lying moss site, and 120 cm at well-drained lichen site. This allows to classify these soils as Cryosols (WRB) or Gelisols (Soil Taxonomy), with evident turbic features.

  17. Active but inoperable thrombin is accumulated in a plasma protein layer surrounding Streptococcus pyogenes.

    PubMed

    Naudin, Clément; Hurley, Sinead M; Malmström, Erik; Plug, Tom; Shannon, Oonagh; Meijers, Joost C M; Mörgelin, Matthias; Björck, Lars; Herwald, Heiko

    2015-10-01

    Activation of thrombin is a critical determinant in many physiological and pathological processes including haemostasis and inflammation. Under physiological conditions many of these functions are involved in wound healing or eradication of an invading pathogen. However, when activated systemically, thrombin can contribute to severe and life-threatening conditions by causing complications such as multiple multi-organ failure and disseminated intravascular coagulation. In the present study we investigated how the activity of thrombin is modulated when it is bound to the surface of Streptococcus pyogenes. Our data show that S. pyogenes bacteria become covered with a proteinaceous layer when incubated with human plasma, and that thrombin is a constituent of this layer. Though the coagulation factor is found attached to the bacteria with a functional active site, thrombin has lost its capacity to interact with its natural substrates and inhibitors. Thus, the interaction of bacteria with human plasma renders thrombin completely inoperable at the streptococcal surface. This could represent a host defense mechanism to avoid systemic activation of coagulation which could be otherwise induced when bacteria enter the circulation and cause systemic infection.

  18. Layer-by-layer assembly of TiO2 nanowire/carbon nanotube films and characterization of their photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Darányi, Mária; Csesznok, Tamás; Kukovecz, Ákos; Kónya, Zoltán; Kiricsi, Imre; Ajayan, Pulickel M.; Vajtai, Robert

    2011-05-01

    We report on the layer-by-layer (LbL) formation of TiO2-MWNT-TiO2 coatings on quartz with either trititanate derived TiO2 nanowires or Degussa P25 as the photocatalytically active material. The optimized deposition sequence is discussed in detail and the morphology of the prepared coatings is analyzed by SEM and XRD. The heterogeneous photocatalytic performance of the coatings was tested in the methyl orange oxidation reaction. The apparent first order rate constant fell in the 0.01-0.20 h - 1 range over a 2.5 × 2.5 cm2 film depending on the type and the thickness of the titanate coating. Building a multiwall carbon nanotube layer into the middle of the layer improved the photocatalytic activity for each material for all of the studied thicknesses. P25 based films performed 2-5 times better than TiO2 nanowire films; however, the pores in the P25 based films were largely blocked because the isotropic P25 nanoparticles form closely packed layers by themselves and even more so with the comparably sized multiwall carbon nanotubes. Therefore, films derived from titanate nanowires appear to be more suitable for use as multifunctional, photocatalytically active filtration media.

  19. Superior Photostability and Photocatalytic Activity of ZnO Nanoparticles Coated with Ultrathin TiO2 Layers through Atomic-Layer Deposition.

    PubMed

    Sridharan, Kishore; Jang, Eunyong; Park, Young Min; Park, Tae Joo

    2015-12-21

    Atomic-layer deposition (ALD) is a thin-film growth technology that allows for conformal growth of thin films with atomic-level control over their thickness. Although ALD is successful in the semiconductor manufacturing industry, its feasibility for nanoparticle coating has been less explored. Herein, the ALD coating of TiO2 layers on ZnO nanoparticles by employing a specialized rotary reactor is demonstrated. The photocatalytic activity and photostability of ZnO nanoparticles coated with TiO2 layers by ALD and chemical methods were examined by the photodegradation of Rhodamine B dye under UV irradiation. Even though the photocatalytic activity of the presynthesized ZnO nanoparticles is higher than that of commercial P25 TiO2 nanoparticles, their activity tends to decline due to severe photocorrosion. The chemically synthesized TiO2 coating layer on ZnO resulted in severely declined photoactivity despite the improved photostability. However, ultrathin and conformal ALD TiO2 coatings (≈ 0.75-1.5 nm) on ZnO improved its photostability without degradation of photocatalytic activity. Surprisingly, the photostability is comparable to that of pure TiO2, and the photocatalytic activity to that of pure ZnO.

  20. Study on Na layer response to geomagnetic activities based on Odin/OSIRIS Na density data

    NASA Astrophysics Data System (ADS)

    Tsuda, Takuo; Nakamura, Takuji; Hedin, Jonas; Gumbel, Jorg; Hosokawa, Keisuke; Ejiri, Mitsumu K.; Nishiyama, Takanori; Takahashi, Toru

    2016-07-01

    The Na layer is normally distributed from 80 to 110 km, and the height range is corresponding to the ionospheric D and E region. In the polar region, the energetic particles precipitating from the magnetosphere can often penetrate into the E region and even into the D region. Thus, the influence of the energetic particles to the Na layer is one of interests in the aspect of the atmospheric composition change accompanied with the auroral activity. There are several previous studies in this issue. For example, recently, we have reported an initial result on a clear relationship between the electron density increase (due to the energetic particles) and the Na density decrease from observational data sets obtained by Na lidar, EISCAT VHF radar, and optical instruments at Tromsoe, Norway on 24-25 January 2012. However, all of the previous studies had been carried out based on case studies by ground-based lidar observations. In this study, we have performed, for the first time, statistical analysis using Na density data from 2004 to 2009 obtained with the Optical Spectrograph and InfraRed Imager System (OSIRIS) onboard Odin satellite. In the presentation, we will show relationship between the Na density and geomagnetic activities, and its latitudinal variation. Based on these results, the Na layer response to the energetic particles will be discussed.

  1. Enhancing the performance of nanofiltration membranes by modifying the active layer with aramide dendrimers.

    PubMed

    de Jubera, Ana M Saenz; Gao, Yuan; Moore, Jeffrey S; Cahill, David G; Mariñas, Benito J

    2012-09-01

    The fully aromatic polyamide active layer of a commercial nanofiltration membrane was modified with three generations (G1, G2, and G3) of aramide dendrimers, all with oligoethylene glycol chains on their peripheries. Permeation experiments revealed that the rejection of Rhodamine WT, used as a surrogate for organic contaminants, improved 1-2 orders of magnitude for membranes modified with G2 and G3 dendrimers at loadings of 0.7-3.5 μg/cm(2) (dendrimer layer thicknesses of ~1-6 nm) compared to the performance of unmodified membranes. In contrast, the corresponding water permeability of dendrimer-modified membranes decreased by only ~30%. Although an enhancement in the rejection of H(3)AsO(3), NaCl, and BaCl(2) was also observed for dendritic membranes, the effect was less pronounced than that for rhodamine WT. Characterization of membranes modified with 3.5 μg/cm(2) dendrimers G2 and G3 by Rutherford backscattering spectrometry with the aid of heavy ion probes (Ag(+) and Ba(2+)) revealed that accessibility of the larger Ba(2+) probe to carboxylate groups on the active layer decreased for the membranes modified with dendrimers.

  2. Statistical analysis on Na layer response to geomagnetic activities using Odin/OSIRIS data

    NASA Astrophysics Data System (ADS)

    Tsuda, Takuo T.; Nakamura, Takuji; Ejiri, Mitsumu K.; Nishiyama, Takanori; Hosokawa, Keisuke; Takahashi, Toru; Gumbel, Jörg; Hedin, Jonas

    2016-04-01

    The Na layer is normally distributed from 80 to 110 km, and the height range is corresponding to the ionospheric D and E region. In the polar region, the energetic particles precipitating from the magnetosphere can often penetrate into the E region and even into the D region. Thus, the influence of the energetic particles to the Na layer is one of interests in the aspect of the atmospheric composition change accompanied with the auroral activity. There are several previous studies in this issue. For example, recently, we have reported an initial result on a clear relationship between the electron density increase (due to the energetic particles) and the Na density decrease from observational dataset obtained by Na lidar, EISCAT VHF radar, and optical instruments at Tromsoe, Norway on 24-25 January 2012. However, all of the previous studies had been carried out based on case studies by ground-based lidar observations. In this study, we have performed, for the first time, statistical analysis using Na density data from 2004 to 2009 obtained with the Optical Spectrograph and InfraRed Imager System (OSIRIS) onboard Odin satellite. In the presentation, we will show relationship between the Na density and geomagnetic activities, and its latitudinal variation. Based on these results, the Na layer response to the energetic particles will be discussed.

  3. Design method of the layered active magnetic regenerator (AMR) for hydrogen liquefaction by numerical simulation

    NASA Astrophysics Data System (ADS)

    Park, Inmyong; Kim, Youngkwon; Park, Jiho; Jeong, Sangkwon

    2015-09-01

    The design procedure of an active magnetic regenerator (AMR) operating between liquid nitrogen temperature and liquid hydrogen temperature is discussed with the selected magnetic refrigerants. Selected magnetic refrigerants (GdNi2, Dy0.85Er0.15Al2, Dy0.5Er0.5Al2, and Gd0.1Dy0.9Ni2) that have different transition temperatures are layered in an AMR to widen the temperature span. The optimum volume fraction of the layered refrigerants for the maximum COP with minimum volume is designed in a two-stage active magnetic regenerative refrigerator (AMRR) using one dimensional numerical simulation. The entropy generation in each stage of the AMR is calculated by the numerical simulation to optimize the proposed design. The main sources of the entropy generation in the AMR are pressure drop, convection and conduction heat transfers in the AMR. However, the entropy generation by the convective heat transfer is mostly dominant in the optimized cases. In this paper, the design parameters and the operating conditions such as the distribution of the selected refrigerants in the layered AMR, the intermediate temperature between two stages and the mass flow rate of heat transfer fluid are specifically determined to maximize the performance of the AMR. The proposed design method will facilitate the construction of AMR systems with various magnetic refrigerants and conditions such as AMR size, operating temperature range, and magnetic field variation.

  4. Layer V Perirhinal Cortical Ensemble Activity during Object Exploration: A Comparison between Young and Aged Rats

    PubMed Central

    Burke, S.N.; Hartzell, A.L.; Lister, J.P.; Hoang, L.T.; Barnes, C.A.

    2012-01-01

    Object recognition memory requires the perirhinal cortex (PRC) and this cognitive function declines during normal aging. Recent electrophysiological recordings from young rats have shown that neurons in layer V of the PRC are activated by 3-dimensional objects. Thus, it is possible that age-related object recognition deficits result from alterations in PRC neuron activity in older animals. To examine this, the present study used cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) with confocal microscopy to monitor cellular distributions of activity-induced Arc RNA in layer V of the PRC. Activity was monitored during two distinct epochs of object exploration. In one group of rats (6 young/6 aged) animals were placed in a familiar testing arena and allowed to explore five different 3-dimensional objects for two 5-min sessions separated by a 20-min rest (AA). The second group of animals (6 young/6 aged) also explored the same objects for two 5-min sessions, but the environment was changed between the first and the second epoch (AB). Behavioral data showed that both age groups spent less time exploring objects during the second epoch, even when the environment changed, indicating successful recognition. Although the proportion of active neurons between epochs did not change in the AA group, in the AB group more neurons were active during epoch 2 of object exploration. This recruitment of neurons into the active neural ensemble could serve to signal that familiar stimuli are being encountered in a new context. When numbers of Arc positive neurons were compared between age groups, the old rats had significantly lower proportions of Arc-positive PRC neurons in both the AA and AB behavioral conditions. These data support the hypothesis that age-associated functional alterations in the PRC contribute to declines in stimulus recognition over the lifespan. PMID:22987683

  5. Layer V perirhinal cortical ensemble activity during object exploration: a comparison between young and aged rats.

    PubMed

    Burke, S N; Hartzell, A L; Lister, J P; Hoang, L T; Barnes, C A

    2012-10-01

    Object recognition memory requires the perirhinal cortex (PRC) and this cognitive function declines during normal aging. Recent electrophysiological recordings from young rats have shown that neurons in Layer V of the PRC are activated by three-dimensional objects. Thus, it is possible that age-related object recognition deficits result from alterations in PRC neuron activity in older animals. To examine this, the present study used cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) with confocal microscopy to monitor cellular distributions of activity-induced Arc RNA in layer V of the PRC. Activity was monitored during two distinct epochs of object exploration. In one group of rats (6 young/6 aged) animals were placed in a familiar testing arena and allowed to explore five different three-dimensional objects for two 5-min sessions separated by a 20-min rest (AA). The second group of animals (6 young/6 aged) also explored the same objects for two 5-min sessions, but the environment was changed between the first and the second epoch (AB). Behavioral data showed that both age groups spent less time exploring objects during the second epoch, even when the environment changed, indicating successful recognition. Although the proportion of active neurons between epochs did not change in the AA group, in the AB group more neurons were active during epoch 2 of object exploration. This recruitment of neurons into the active neural ensemble could serve to signal that familiar stimuli are being encountered in a new context. When numbers of Arc positive neurons were compared between age groups, the old rats had significantly lower proportions of Arc-positive PRC neurons in both the AA and AB behavioral conditions. These data support the hypothesis that age-associated functional alterations in the PRC contribute to declines in stimulus recognition over the lifespan.

  6. Supplementation freeze-thawed media with selenium protect adipose-derived mesenchymal stem cells from freeze-thawed induced injury.

    PubMed

    Valadbeygi, Arash; Naji, Tahere; Pirnia, Afshin; Gholami, Mohammadreza

    2016-10-01

    Successful freezed-thaw of adipose-derived mesenchymal stem cells (ADMSCs) could be a major step in regenerative medicine as well as in the cloning of animal breeds. The aim of this study was to evaluate the efficacy of selenium on the optimizing of freezed-thaw media in the ADMSCs. ADMSCs were extracted from NMRI mice and purified with positive selection Monoclonal CD105 Antibody (PE) and negative selection Monoclonal CD31 and CD45 Antibody using MACS method as well as differentiation to adipose and bone tissue. ADMSCs were divided into four groups. ADMSCs were freezed-thaw under standard condition with or without the addition of 5 ng/ml selenium to both the cryopreservation and thawing solutions. Frozen cells were thawed after four months and viability and cytotoxicity of the cells were analyzed by the Trypan blue test and MTT assay respectively. RNA was extracted and cDNA was synthesized and the expression of apoptotic genes (P53, Fas, Bax, Caspase3, and Bcl2) was examined using Real time-PCR Rotor gene 2009. This study compares slow and rapid methods of cryopreservation. After thawing, viability of the cells treated with selenium was higher than the control group in rapid and slow cryopreserved ADMSCs. Also, the percentage of living cells in the slow cooling method was considerably more than with the rapid cooling method. After analysis of the results using Real time-PCR, the Bcl2 gene was shown to be expressed in both the rapid and slow cooling methods. In the rapid cooling group in addition to the BCL-2 gene, p53 was also expressed. It appears that selenium prevented the apoptotic genes from expression due to its anti-apoptotic effects. The slow cooling method is better and more optimized for ADMSCs protecting them from oxidative damage to a greater extent compared to the rapid cooling method. PMID:27546222

  7. Low-noise encoding of active touch by layer 4 in the somatosensory cortex.

    PubMed

    Hires, Samuel Andrew; Gutnisky, Diego A; Yu, Jianing; O'Connor, Daniel H; Svoboda, Karel

    2015-08-06

    Cortical spike trains often appear noisy, with the timing and number of spikes varying across repetitions of stimuli. Spiking variability can arise from internal (behavioral state, unreliable neurons, or chaotic dynamics in neural circuits) and external (uncontrolled behavior or sensory stimuli) sources. The amount of irreducible internal noise in spike trains, an important constraint on models of cortical networks, has been difficult to estimate, since behavior and brain state must be precisely controlled or tracked. We recorded from excitatory barrel cortex neurons in layer 4 during active behavior, where mice control tactile input through learned whisker movements. Touch was the dominant sensorimotor feature, with >70% spikes occurring in millisecond timescale epochs after touch onset. The variance of touch responses was smaller than expected from Poisson processes, often reaching the theoretical minimum. Layer 4 spike trains thus reflect the millisecond-timescale structure of tactile input with little noise.

  8. Atomic layer deposition encapsulated activated carbon electrodes for high voltage stable supercapacitors.

    PubMed

    Hong, Kijoo; Cho, Moonkyu; Kim, Sang Ouk

    2015-01-28

    Operating voltage enhancement is an effective route for high energy density supercapacitors. Unfortunately, widely used activated carbon electrode generally suffers from poor electrochemical stability over 2.5 V. Here we present atomic layer deposition (ALD) encapsulation of activated carbons for high voltage stable supercapacitors. Two-nanometer-thick Al2O3 dielectric layers are conformally coated at activated carbon surface by ALD, well-maintaining microporous morphology. Resultant electrodes exhibit excellent stability at 3 V operation with 39% energy density enhancement from 2.5 V operation. Because of the protection of surface functional groups and reduction of electrolyte degradation, 74% of initial voltage was maintained 50 h after full charge, and 88% of capacitance was retained after 5000 cycles at 70 °C accelerated test, which correspond to 31 and 17% improvements from bare activated carbon, respectively. This ALD-based surface modification offers a general method to enhance electrochemical stability of carbon materials for diverse energy and environmental applications.

  9. On Active Layer Environments and Processes in Western Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Hansen, C. D.; Meiklejohn, I.; Nel, W.

    2012-12-01

    The current understanding of Antarctic permafrost is poor, particularly regarding its evolution, the current thermal characteristics, and relationships with pedogenesis, hydrology, geomorphic, dynamics, biotic activity and response to global changes. Results from borehole temperature measurements over a four-year period in Western Dronning Maud Land suggest that the active layer depth is dependent on the substrate, latitude, altitude and the volume of ground exposed; the latter alludes to the potential impact of surrounding ice on the ground thermal regime. The active layer depths at the monitoring sites, varied between 16 cm at Vesleskarvet, a small nunatak at 850 masl to 28 cm in granitic till at Jutulsessen (1 270 masl). The mean near surface (1.5 cm depth) ground temperatures from 2009 to 2012 in the region have a narrow range from -16.4°C at 850m to -17.5°C at 1270 masl. Permafrost temperatures for the same locations vary between -16.3°C and -18.3°C. While little variability exists between the mean temperatures at the study locations, each site is distinct and seasonal and shorter-term frost cycles have produced landforms that are characteristic of both permafrost and diurnal frost environments. One of the key aspects of investigation is the control that the active layer has on autochthonous blockfield development in the region. The, thus far, exploratory research is being used to understand controls on the landscape and the relationship between distribution and abundance of biota. Given the rapidly changing climates in the region, improving knowledge of what drives patterns of biodiversity at a local and regional scale is vital to assess consequences of environmental change.

  10. Physical degradation of membrane electrode assemblies undergoing freeze/thaw cycling: Diffusion media effects

    NASA Astrophysics Data System (ADS)

    Kim, Soowhan; Ahn, Byung Ki; Mench, M. M.

    In this work, the effects of properties of diffusion media (DM) (stiffness, thickness and micro-porous layer (MPL)) on the physical damage of membrane electrode assembly (MEA) subjected to freeze/thaw cycling were studied. Pressure uniformity of the diffusion media onto the catalyst layer (CL) was determined to be a key parameter to mitigate freeze-induced physical damage. Stiffer diffusion media, enabling more uniform compression under the channels and lands, can mitigate surface cracks, but flexible cloth diffusion media experienced severe catalyst layer surface damage. The thickness of the diffusion media and existence of a micro-porous layer were not observed to be major factors to mitigate freeze-damage when the catalyst layer is in contact with liquid. Interfacial delamination between diffusion media and catalyst layers, but not between the catalyst layer and membrane, was observed. This permanent deformation of the stiff diffusion media in the channel locations as well as fractures of carbon fibers increased electrical resistance, and may increase water flooding, resulting in reduced longevity and operational losses. Although use of a freeze-tolerable MEA design (negligible virgin cracked catalyst layers with thinner reinforced membrane) [S. Kim, M.M. Mench, J. Power Sources, in press] with stiff diffusion media can reduce the freeze-damage in the worst case scenario test condition of direct liquid contact, extensive irreversible damage (diffusion media/catalyst layer interfacial delamination) was not completely prevented. In addition to proper material selection, liquid water contact with the catalyst layer should be removed prior to shutdown to a frozen state to permit long-term cycling damage and facilitate frozen start.

  11. Supplementation of soybean lecithin-based semen extender by antioxidants: complementary flowcytometric study on post-thawed ram spermatozoa.

    PubMed

    Sharafi, Mohsen; Zhandi, Mahdi; Akbari Sharif, Abbas

    2015-06-01

    The purpose of the current study was to evaluate the effects of cysteine (C) and glutathione (G) on the post-thawed ram sperm quality. Collected semen samples from four mature rams were diluted with five soybean lecithin (SL)-based extenders containing: no antioxidant (SL-0), 5 mM cysteine (SL-C5), 10 mM cysteine (SL-C10), 5 mM glutathione (SL-G5) and 10 mM glutathione (SL-G10). After freeze-thawing process, motion and velocity parameters, plasma membrane integrity and functionality, morphological abnormality, lipid peroxidation, acrosomal status, mitochondria activity, and apoptosis status of post-thawed ram spermatozoa were assessed. The results showed that SL-C10 increased the total motility and plasma membrane integrity (p < 0.05) of post-thawed ram spermatozoa (55.86 ± 1.37 and 60.57 ± 1.34 %) compared to other extenders. Progressive motility was significantly higher in SL-C10 (24.71 ± 1.13 %) compared to SL-0 (20 ± 1.13 %) and SL-G10 (15 ± 1.13 %). Mitochondrial activity was significantly higher in SL-C10 (56.83 ± 2.29 %) compared to SL-G10 (38.75 ± 2.29 %). Capacitation and acrosomal status, lipid peroxidation, and the percentage of dead spermatozoa were not affected by different extenders. The percentage of live spermatozoa was higher in SL-C10 (56.33 ± 1.35 %) compared to other extenders. Also, SL-C10 resulted in a lower percentage of apoptotic spermatozoa (14.17 ± 0.53 %) compared to other extenders. The results of this study showed that supplementation of SL-based ram semen extender with 10 mM cysteine resulted in an improved quality of post-thawed ram spermatozoa.

  12. Variety, State and Origin of Drained Thaw Lake Basins in West-Siberian North

    NASA Astrophysics Data System (ADS)

    Kirpotin, S.; Polishchuk, Y.; Bryksina, N.; Sugaipova, A.; Pokrovsky, O.; Shirokova, L.; Kouraev, A.; Zakharova, E.; Kolmakova, M.; Dupre, B.

    2009-04-01

    Drained thaw lake basins in Western Siberia have a local name "khasyreis" [1]. Khasyreis as well as lakes, ponds and frozen mounds are invariable element of sub-arctic frozen peat bogs - palsas and tundra landscapes. In some areas of West-Siberian sub-arctic khasyreis occupy up to 40-50% of total lake area. Sometimes their concentration is so high that we call such places ‘khasyrei's fields". Khasyreis are part of the natural cycle of palsa complex development [1], but their origin is not continuous and uniform in time and, according to our opinion, there were periods of more intensive lake drainage and khasyrei development accordingly. These times were corresponding with epochs of climatic warming and today we have faced with one of them. So, last years this process was sufficiently activated in the south part of West-Siberian sub-arctic [2]. It was discovered that in the zone of continuous permafrost thermokarst lakes have expanded their areas by about 10-12%, but in the zone of discontinuous permafrost the process of their drainage prevails. These features are connected with the thickness of peat layers which gradually decreases to the North, and thus have reduced the opportunity for lake drainage in northern areas. The most typical way of khasyrei origin is their drainage to the bigger lakes which are always situated on the lower levels and works as a collecting funnels providing drainage of smaller lakes. The lower level of the big lake appeared when the lake takes a critical mass of water enough for subsidence of the lake bottom due to the melting of underlaying rocks [2]. Another one way of lake drainage is the lake intercept by any river. Lake drainage to the subsurface (underlaying rocks) as some authors think [3, 4] is not possible in Western Siberia, because the thickness of permafrost is at list 500 m here being safe confining bed. We mark out few stages of khasyrei development: freshly drained, young, mature and old. This row reflects stages of

  13. Understanding the cellular mechanism of recovery from freeze-thaw injury in spinach: possible role of aquaporins, heat shock proteins, dehydrin and antioxidant system.

    PubMed

    Chen, Keting; Arora, Rajeev

    2014-03-01

    Recovery from reversible freeze-thaw injury in plants is a critical component of ultimate frost survival. However, little is known about this aspect at the cellular level. To explore possible cellular mechanism(s) for post-thaw recovery (REC), we used Spinacia oleracea L. cv. Bloomsdale leaves to first determine the reversible freeze-thaw injury point. Freeze (-4.5°C)-thaw-injured tissues (32% injury vs <3% in unfrozen control) fully recovered during post-thaw, as assessed by an ion leakage-based method. Our data indicate that photosystem II efficiency (Fv/Fm) was compromised in injured tissues but recovered during post-thaw. Similarly, the reactive oxygen species (O2 (•-) and H2 O2 ) accumulated in injured tissues but dissipated during recovery, paralleled by the repression and restoration, respectively, of activities of antioxidant enzymes, superoxide dismutase (SOD) (EC. 1.14.1.1), and catalase (CAT) (EC.1.11.1.6) and ascorbate peroxidase (APX) (EC.1.11.1.11). Restoration of CAT and APX activities during recovery was slower than SOD, concomitant with a slower depletion of H2 O2 compared to O2 (•-) . A hypothesis was also tested that the REC is accompanied by changes in the expression of water channels [aquaporines (AQPs)] likely needed for re-absorption of thawed extracellular water. Indeed, the expression of two spinach AQPs, SoPIP2;1 and SoδTIP, was downregulated in injured tissues and restored during recovery. Additionally, a notion that molecular chaperones [heat shock protein of 70 kDa (HSP70s)] and putative membrane stabilizers [dehydrins (DHNs)] are recruited during recovery to restore cellular homeostasis was also tested. We noted that, after an initial repression in injured tissues, the expression of three HSP70s (cytosolic, endoplasmic reticulum and mitochondrial) and a spinach DHN (CAP85) was significantly restored during the REC. PMID:23981077

  14. Understanding the cellular mechanism of recovery from freeze-thaw injury in spinach: possible role of aquaporins, heat shock proteins, dehydrin and antioxidant system.

    PubMed

    Chen, Keting; Arora, Rajeev

    2014-03-01

    Recovery from reversible freeze-thaw injury in plants is a critical component of ultimate frost survival. However, little is known about this aspect at the cellular level. To explore possible cellular mechanism(s) for post-thaw recovery (REC), we used Spinacia oleracea L. cv. Bloomsdale leaves to first determine the reversible freeze-thaw injury point. Freeze (-4.5°C)-thaw-injured tissues (32% injury vs <3% in unfrozen control) fully recovered during post-thaw, as assessed by an ion leakage-based method. Our data indicate that photosystem II efficiency (Fv/Fm) was compromised in injured tissues but recovered during post-thaw. Similarly, the reactive oxygen species (O2 (•-) and H2 O2 ) accumulated in injured tissues but dissipated during recovery, paralleled by the repression and restoration, respectively, of activities of antioxidant enzymes, superoxide dismutase (SOD) (EC. 1.14.1.1), and catalase (CAT) (EC.1.11.1.6) and ascorbate peroxidase (APX) (EC.1.11.1.11). Restoration of CAT and APX activities during recovery was slower than SOD, concomitant with a slower depletion of H2 O2 compared to O2 (•-) . A hypothesis was also tested that the REC is accompanied by changes in the expression of water channels [aquaporines (AQPs)] likely needed for re-absorption of thawed extracellular water. Indeed, the expression of two spinach AQPs, SoPIP2;1 and SoδTIP, was downregulated in injured tissues and restored during recovery. Additionally, a notion that molecular chaperones [heat shock protein of 70 kDa (HSP70s)] and putative membrane stabilizers [dehydrins (DHNs)] are recruited during recovery to restore cellular homeostasis was also tested. We noted that, after an initial repression in injured tissues, the expression of three HSP70s (cytosolic, endoplasmic reticulum and mitochondrial) and a spinach DHN (CAP85) was significantly restored during the REC.

  15. Role of interfacial friction for flow instabilities in a thin polar-ordered active fluid layer

    NASA Astrophysics Data System (ADS)

    Sarkar, Niladri; Basu, Abhik

    2015-11-01

    We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient Γ . Being controlled by Γ , our model provides a unified framework to describe the long-wavelength behavior of a variety of thin polar-ordered systems, ranging from wet to dry active matter and free-standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system that can depend sensitively on Γ . Based on our results, we discuss estimation of bounds on Γ in experimentally accessible systems.

  16. Delicious ice cream, why does salt thaw ice?

    NASA Astrophysics Data System (ADS)

    Bagnoli, Franco

    2016-04-01

    During winter, we use to spread salt to thaw ice on the streets. In a physics show, one can be almost sure that after showing this effect, the answer to what happens to temperature will be "it increases". But no! It goes down, in such amount that one can complement the show by producing hand-made ice creams [1].

  17. Effects of permafrost thaw on northern wetland methane emissions

    NASA Astrophysics Data System (ADS)

    Turetsky, M. R.; Olefeldt, D.; Waddington, J. M.

    2012-12-01

    There has been a renewed interest in northern, high latitude methane emissions because of 1) the recent unexpected increase in atmospheric methane concentrations after a period of stability, 2) large releases of methane in bubbles from arctic thermokarst lakes, and 3) the recent discovery that high latitude soil carbon stocks are much larger than previously recognized. Global inverse modeling shows that Arctic methane emissions increased by 30% from 2003-2007, and that high latitude emissions were more sensitive to warming than water table fluctuations. Arctic wetlands and lakes likely have contributed at least partly to recent increases in atmospheric methane concentrations. Across the circumpolar region, thermokarst associated with permafrost thaw is creating lakes and wetlands that tend to have elevated methane emissions. Thaw wetlands in interior Alaska release methane primarily through plants, especially Carex species, as well as ebullition (bubbles). Ebullition was sensitive to soil temperature both in the field and in a laboratory experiment, indicating that continued warming may contribute to increases in northern wetland methane emissions by increasing the area of thaw wetlands on the landscape as well as by stimulating bubble formation and release. A meta-analysis of data from more than 300 sites suggests that increased methane emissions following permafrost thaw are more likely related to altered water table position, soil temperature and vegetation composition, rather than increases in unfrozen soil carbon stocks.

  18. Hydrologic impacts of thawing permafrost—A review

    USGS Publications Warehouse

    Walvoord, Michelle Ann; Kurylyk, Barret L.

    2016-01-01

    Where present, permafrost exerts a primary control on water fluxes, flowpaths, and distribution. Climate warming and related drivers of soil thermal change are expected to modify the distribution of permafrost, leading to changing hydrologic conditions, including alterations in soil moisture, connectivity of inland waters, streamflow seasonality, and the partitioning of water stored above and below ground. The field of permafrost hydrology is undergoing rapid advancement with respect to multiscale observations, subsurface characterization, modeling, and integration with other disciplines. However, gaining predictive capability of the many interrelated consequences of climate change is a persistent challenge due to several factors. Observations of hydrologic change have been causally linked to permafrost thaw, but applications of process-based models needed to support and enhance the transferability of empirical linkages have often been restricted to generalized representations. Limitations stem from inadequate baseline permafrost and unfrozen hydrogeologic characterization, lack of historical data, and simplifications in structure and process representation needed to counter the high computational demands of cryohydrogeologic simulations. Further, due in part to the large degree of subsurface heterogeneity of permafrost landscapes and the nonuniformity in thaw patterns and rates, associations between various modes of permafrost thaw and hydrologic change are not readily scalable; even trajectories of change can differ. This review highlights promising advances in characterization and modeling of permafrost regions and presents ongoing research challenges toward projecting hydrologic and ecologic consequences of permafrost thaw at time and spatial scales that are useful to managers and researchers.

  19. Sperm vacuoles are not modified by freezing--thawing procedures.

    PubMed

    Gatimel, Nicolas; Leandri, Roger; Parinaud, Jean

    2013-03-01

    Since the development of the motile sperm organellar morphology examination (MSOME) in 2001 for observing the cephalic vacuoles at high magnification, no study as yet assessed the effect of cryopreservation on these vacuoles, although sperm freezing-thawing procedures are known to affect sperm quality. Examination of the vacuoles before and after freezing-thawing would indicate whether the same normality criteria can be applied for frozen as for fresh spermatozoa when performing intracytoplasmic morphologically selected sperm injection. In 27 sperm samples from fertile men, analysis of conventional sperm parameters (motility, vitality, percentage of normal forms) and a morphological analysis at high magnification (×6000) using image analysis software was performed before freezing and after thawing. Whereas there were expected decreases in motility (P<0.0001), vitality (P<0.001) and percentage of normal forms (P<0.05) after cryopreservation, there was no evidence for any difference in any vacuolar criteria (relative vacuole area, total vacuole area, vacuole area in the anterior, median and basal parts of the head, percentage of spermatozoa with a vacuole area ≤6.5% and percentage of spermatozoa with a vacuole area >13%). Freezing-thawing procedures have no effect on human sperm vacuoles.

  20. Field observations, experiments, and modeling of sediment production from freeze and thaw action on a bare, weathered granite slope in a temperate region of Japan

    NASA Astrophysics Data System (ADS)

    Tsutsumi, Daizo; Fujita, Masaharu

    2016-08-01

    In the present study, field observations and model simulations were conducted to examine the process of sediment production due to freeze and thaw action in a temperate climate region. Two small areas were designated and observations were conducted to determine the mechanisms of sediment production due to freeze and thaw action on a bare, weathered granite slope in the Tanakami Mountains in the southern part of Shiga Prefecture, Japan. During the cold season from 2004 to 2005, air, surface, and subsurface temperatures were measured at 10-min intervals. The sediment produced on plot 1 was collected and weighed once per week, whereas the sediment produced on plot 2 was left untouched until the end of the cold season. The freeze and thaw cycle occurred repeatedly, with the frozen zone (i.e., temperature < 0 °C) extending to a depth of 10 cm. Sediment was produced as a result of active freeze and thaw processes and, accordingly, there was no longer sediment production at the end of the cold season. Plots 1 and 2 produced 108 and 44 kg m- 2 year- 1 of sediment, respectively. This difference indicates that sediment cover of the saprolite surface mitigated the destructive effects of freezing. During the cold season from 2005 to 2006, a half of plot 1 was covered by broadleaves (Quercus serrata) and the other half was covered by coniferous leaves (Pinus densiflora); plot 2 was covered by no leaves to understand the effects of surface cover on the reduction in sediment production. The results showed that surface leaf cover dramatically decreased sediment production due to freeze and thaw action versus the no-surface cover. A simulation model combining a thermal conductivity analysis and a simple and empirical sediment production model was developed to estimate the amount of sediment produced by the freeze and thaw action. The observation results of temperature change and amount of sediment during the first season, from 2004 to 2005, were simulated with the model. The model

  1. Aminosilane layers on the plasma activated thermoplastics: influence of solvent on its structure and morphology.

    PubMed

    Sunkara, Vijaya; Cho, Yoon-Kyoung

    2013-12-01

    The chemistry and the structure of aminosilane layer on the plasma activated thermoplastic substrates, e.g., polycarbonate (PC), polystyrene (PS), poly(methyl methacrylate) (PMMA), and cyclic olefin co-polymer (COC) were investigated at the molecular level. The nature of the surface functional groups of the silane layers prepared by solution phase deposition in aqueous and anhydrous solvents were studied using various techniques including ellipsometry, goniometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance infrared spectroscopy (ATR-IR). The XPS analyses revealed the presence of various oxygen functionalities on the plasma activated thermoplastics. Considerable differences were observed for the structure of aminosilane depending on the solvent used for the reaction. Deposition from aqueous solution resulted in relatively flat and smooth surfaces with consistent thickness compared to the anhydrous solution deposition. In the former case, 33% of the total nitrogen accounted for protonated amine and 16% for the free amino groups. In the latter, only 6% accounted for the protonated amine. The point of zero charge (pzc), on the aminosilane modified PC was found to be around 7, indicated that the surface is positively charged below pH 7 and negatively charged above pH 7. The surface analysis data suggested that various interactions are possible between the plasma activated thermoplastic surface and the aminosilane. In general, they are bound to the surface through covalent bond formation between the oxygen functionalities on the thermoplastic surface and the amino or the silanol groups of the aminosilane.

  2. Optimal freezing and thawing for the survival of peripheral nerves in severed rabbit limbs.

    PubMed

    Zhu, Zexing; Qiao, Lin; Zhao, Yandong; Zhang, Shuming

    2014-01-01

    This study aimed to investigate the optimal freezing and thawing procedures for the survival of peripheral nerves in severed rabbit limbs. Twenty New Zealand White rabbits were randomized into four groups: normal control, slow-freezing fast-thawing, slow-freezing slow-thawing, fast-freezing fast-thawing, with five animals in each group. The hind limbs of the rabbits were severed at 1 cm above the knee joint. The severed limbs were cryopreserved with various freezing and thawing procedures. The sciatic nerves were harvested and trypsinized into single nerve fibers for morphological evaluation. The cell viability of the nerve fibers was examined by staining with Calcein-AM and propidium iodide. The fluorescent intensity of the nerve fibers was measured with a laser scanning confocal microscope. The morphology of the nerve fibers in the slow-freezing fast-thawing group was very similar with that of the normal control group, with only mild demyelination. The slow-freezing fast-thawing group and slow-freezing slow-thawing group showed severely damaged nerve fibers. The fluorescent intensities of the nerve fibers was significantly different among the four groups, with a decreasing order of normal control, slow-freezing fast-thawing, slow-freezing slow-thawing, and fast-freezing fast-thawing (P < 0.05). Of the various cryopreservative procedures, slow-freezing fast thawing has the minimal effects on the survival of nerve fibers in severed rabbit limbs.

  3. Calculated and Measured Air and Soil Freeze-Thaw Frequencies.

    NASA Astrophysics Data System (ADS)

    Baker, Donald G.; Ruschy, David L.

    1995-10-01

    Freeze-thaw frequencies calculated by eight different counting methods were compared using daily maximum and minimum temperatures from eight north-central United States National Weather Service (NWS) stations. These frequencies were also compared to those obtained using hourly air temperature data from six of the same NWS stations. In addition, the calculated frequencies were compared to measured freeze-thaw frequencies at several depths in a bare soil and a sod-covered soil at the University of Minnesota St. Paul campus climatological observatory.The necessary acceptance of the idealized daily heating cycle when using daily maximum and minimum air temperature data resulted in a higher occurrence of calculated freeze-thaw events than those obtained with hourly data; one method gave 23% more freeze-thaw events with the daily maximum and minimum temperatures.With the freeze-thaw phenomenon centered upon those months in which the mean temperature hovers near O°C, a bimodal frequency occurs at the northern stations (October and April, as at International Falls, Minnesota, and November and March at Fargo, North Dakota), while in warmer climates the bimodal characteristic is replaced by a single-peak frequency in January as at Sedalia and West Plains, Missouri.In the comparison between the calculated freeze-thaw frequencies based on daily maximum and minimum values and the hourly temperature measurements at several heights between the surface and the temperature shelter at the climatological observatory, it was found that the annual total frequencies increased as the height above the surface decreased. For the shallowest height above the surface there was an approximate 13% increase over those measured in the shelter with hourly temperature data.The annual total frequencies of the calculated freeze-thaw events obtained with the daily maximum and minimum temperature measurements in the shelter approximated those actually occurring at the 1-cm depth in a bare soil at the

  4. Hot-Film and Hot-Wire Anemometry for a Boundary Layer Active Flow Control Test

    NASA Technical Reports Server (NTRS)

    Lenahan, Keven C.; Schatzman, David M.; Wilson, Jacob Samuel

    2013-01-01

    Unsteady active flow control (AFC) has been used experimentally for many years to minimize bluff-body drag. This technology could significantly improve performance of rotorcraft by cleaning up flow separation. It is important, then, that new actuator technologies be studied for application to future vehicles. A boundary layer wind tunnel was constructed with a 1ft-x-3ft test section and unsteady measurement instrumentation to study how AFC manipulates the boundary layer to overcome adverse pressure gradients and flow separation. This unsteady flow control research requires unsteady measurement methods. In order to measure the boundary layer characteristics, both hot-wire and hot-film Constant Temperature Anemometry is used. A hot-wire probe is mounted in the flow to measure velocity while a hot-film array lays on the test surface to measure skin friction. Hot-film sensors are connected to an anemometer, a Wheatstone bridge circuit with an output that corresponds to the dynamic flow response. From this output, the time varying flow field, turbulence, and flow reversal can be characterized. Tuning the anemometers requires a fan test on the hot-film sensors to adjust each output. This is a delicate process as several variables drastically affect the data, including control resistance, signal input, trim, and gain settings.

  5. Evidence for reduced charge recombination in carbon nanotube/perovskite-based active layers

    NASA Astrophysics Data System (ADS)

    Bag, Monojit; Renna, Lawrence A.; Jeong, Seung Pyo; Han, Xu; Cutting, Christie L.; Maroudas, Dimitrios; Venkataraman, D.

    2016-10-01

    Using impedance spectroscopy and computation, we show that incorporation of multi-walled carbon nanotubes (MWCNTs) in the bulk of the active layer of perovskite-based solar cells reduces charge recombination and increases the open circuit voltage. An ∼87% reduction in recombination was achieved when MWCNTs were introduced in the planar-heterostructure perovskite solar cell containing mixed counterions. The open circuit voltage (Voc) of perovskite/MWCNTs devices was increased by 70 mV, while the short circuit current density (Jsc) and fill factor (FF) remained unchanged.

  6. Improved Power Conversion Efficiency of Inverted Organic Solar Cells by Incorporating Au Nanorods into Active Layer.

    PubMed

    He, Yeyuan; Liu, Chunyu; Li, Jinfeng; Zhang, Xinyuan; Li, Zhiqi; Shen, Liang; Guo, Wenbin; Ruan, Shengping

    2015-07-29

    This Research Article describes a cooperative plasmonic effect on improving the performance of organic solar cells. When Au nanorods(NRs) are incorporated into the active layers, the designed project shows superior enhanced light absorption behavior comparing with control devices, which leads to the realization of organic solar cell with power conversion efficiency of 6.83%, accounting for 18.9% improvement. Further investigations unravel the influence of plasmonic nanostructures on light trapping, exciton generation, dissociation, and charge recombination and transport inside the thin films devices. Moreover, the introduction of high-conductivity Au NRs improves electrical conductivity of the whole device, which contributes to the enhanced fill factor.

  7. Methane dynamics regulated by microbial community response to permafrost thaw.

    PubMed

    McCalley, Carmody K; Woodcroft, Ben J; Hodgkins, Suzanne B; Wehr, Richard A; Kim, Eun-Hae; Mondav, Rhiannon; Crill, Patrick M; Chanton, Jeffrey P; Rich, Virginia I; Tyson, Gene W; Saleska, Scott R

    2014-10-23

    Permafrost contains about 50% of the global soil carbon. It is thought that the thawing of permafrost can lead to a loss of soil carbon in the form of methane and carbon dioxide emissions. The magnitude of the resulting positive climate feedback of such greenhouse gas emissions is still unknown and may to a large extent depend on the poorly understood role of microbial community composition in regulating the metabolic processes that drive such ecosystem-scale greenhouse gas fluxes. Here we show that changes in vegetation and increasing methane emissions with permafrost thaw are associated with a switch from hydrogenotrophic to partly acetoclastic methanogenesis, resulting in a large shift in the δ(13)C signature (10-15‰) of emitted methane. We used a natural landscape gradient of permafrost thaw in northern Sweden as a model to investigate the role of microbial communities in regulating methane cycling, and to test whether a knowledge of community dynamics could improve predictions of carbon emissions under loss of permafrost. Abundance of the methanogen Candidatus 'Methanoflorens stordalenmirensis' is a key predictor of the shifts in methane isotopes, which in turn predicts the proportions of carbon emitted as methane and as carbon dioxide, an important factor for simulating the climate feedback associated with permafrost thaw in global models. By showing that the abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw, we establish a basis for scaling changing microbial communities to ecosystem isotope dynamics. Our findings indicate that microbial ecology may be important in ecosystem-scale responses to global change. PMID:25341787

  8. Freeze/thaw stress in Ceanothus of southern California chaparral.

    PubMed

    Ewers, Frank W; Lawson, Michael C; Bowen, Timothy J; Davis, Stephen D

    2003-07-01

    Freeze/thaw stress was examined in chaparral shrubs of the genus Ceanothus to determine the interactive effects of freezing and drought and to consider which is the more vulnerable component, the living leaves (symplast) or the non-living water transport system (apoplast). We hypothesized that where Ceanothus species co-occurred, the more inland species C. crassifolius would be more tolerant of low temperatures than the coastal species C. spinosus, both in terms of leaf survival (LT(50), or the temperature at which there is 50% loss of function or viability) and in terms of resistance to freezing-induced embolism (measurements of percent loss hydraulic conductivity due to embolism following freeze/thaw). Cooling experiments on 2 m long winter-acclimated shoots resulted in LT(50) values of about -10 degrees C for C. spinosus versus -18 degrees C for C. crassifolius. Freeze-thaw cycles resulted in no change in embolism when the plants were well hydrated (-0.7 to -2.0 MPa). However, when plants were dehydrated to -5.0 MPa, C. spinosus became 96% embolized with freeze/thaw, versus only 61% embolism for C. crassifolius. Stems of C. crassifolius became 90% and 97% embolized at -6.6 and -8.0 MPa, respectively, meaning that even in this species, stems could be more vulnerable than leaves under conditions of extreme water stress combined with freeze/thaw events. The dominance of C. crassifolius at colder sites and the restriction of C. spinosus to warmer sites are consistent with both the relative tolerance of their symplasts to low temperatures and the relative tolerance of their apoplasts to freeze events in combination with drought stress.

  9. Simulating the thermal regime and thaw processes of ice-rich permafrost ground with the land-surface model CryoGrid 3

    NASA Astrophysics Data System (ADS)

    Westermann, S.; Langer, M.; Boike, J.; Heikenfeld, M.; Peter, M.; Etzelmüller, B.; Krinner, G.

    2016-02-01

    Thawing of permafrost in a warming climate is governed by a complex interplay of different processes of which only conductive heat transfer is taken into account in most model studies. However, observations in many permafrost landscapes demonstrate that lateral and vertical movement of water can have a pronounced influence on the thaw trajectories, creating distinct landforms, such as thermokarst ponds and lakes, even in areas where permafrost is otherwise thermally stable. Novel process parameterizations are required to include such phenomena in future projections of permafrost thaw and subsequent climatic-triggered feedbacks. In this study, we present a new land-surface scheme designed for permafrost applications, CryoGrid 3, which constitutes a flexible platform to explore new parameterizations for a range of permafrost processes. We document the model physics and employed parameterizations for the basis module CryoGrid 3, and compare model results with in situ observations of surface energy balance, surface temperatures, and ground thermal regime from the Samoylov permafrost observatory in NE Siberia. The comparison suggests that CryoGrid 3 can not only model the evolution of the ground thermal regime in the last decade, but also consistently reproduce the chain of energy transfer processes from the atmosphere to the ground. In addition, we demonstrate a simple 1-D parameterization for thaw processes in permafrost areas rich in ground ice, which can phenomenologically reproduce both formation of thermokarst ponds and subsidence of the ground following thawing of ice-rich subsurface layers. Long-term simulation from 1901 to 2100 driven by reanalysis data and climate model output demonstrate that the hydrological regime can both accelerate and delay permafrost thawing. If meltwater from thawed ice-rich layers can drain, the ground subsides, as well as the formation of a talik, are delayed. If the meltwater pools at the surface, a pond is formed that enhances heat

  10. Effect of addition of coconut water (Cocos nucifera) to the freezing media on post-thaw viability of boar sperm.

    PubMed

    Bottini-Luzardo, María; Centurión-Castro, Fernando; Alfaro-Gamboa, Militza; Aké-López, Ricardo; Herrera-Camacho, José

    2013-01-01

    The aims of this experiment were to evaluate the addition of coconut water in natura to the freezing media, compare the effect of deionized water vs filtered water of coconut over the post-thaw seminal characteristics, and evaluate the effect of the deionized water and in natura coconut water on the seminal characteristics of boar sperm at different post-thaw times. Thirty-four ejaculates were used divided in three aliquots which received one of the following treatments (T): T1, LEY (bidistilled water, lactose, and egg yolk) and LEYGO (LEY + glycerol and Orvus ET paste); T2, LEY(A) (coconut deionized water, lactose, and egg yolk)-LEYGO(A); and T3, LEY(B) (in natura coconut water, lactose, and egg yolk)-LEYGO(B). Samples of boar semen were frozen according to the Westendorf method, thawed at 38°C, and evaluated at three incubation times (0, 30, and 60 min). Seminal characteristics assessed were motility (Mot), acrosomal integrity (AInt), membrane integrity (MInt), and mitochondrial activity (MAct). T1 showed a higher percentage of viable sperm than T3 (Mot 36.5 vs 5.4 %, AInt 61.8 vs 41.2 %, MInt 50.4 vs 41.3 %, and MAct 56.9 vs 50.5 %). T2 kept a higher percentage of viable sperm at all incubation times. In natura coconut water showed a detrimental effect over the viability of the frozen-thawed boar semen. Deionized coconut water improved the boar semen viability post-thaw, outperforming results of in natura coconut water.

  11. Layer-by-layer grown scalable redox-active ruthenium-based molecular multilayer thin films for electrochemical applications and beyond.

    PubMed

    Kaliginedi, Veerabhadrarao; Ozawa, Hiroaki; Kuzume, Akiyoshi; Maharajan, Sivarajakumar; Pobelov, Ilya V; Kwon, Nam Hee; Mohos, Miklos; Broekmann, Peter; Fromm, Katharina M; Haga, Masa-aki; Wandlowski, Thomas

    2015-11-14

    Here we report the first study on the electrochemical energy storage application of a surface-immobilized ruthenium complex multilayer thin film with anion storage capability. We employed a novel dinuclear ruthenium complex with tetrapodal anchoring groups to build well-ordered redox-active multilayer coatings on an indium tin oxide (ITO) surface using a layer-by-layer self-assembly process. Cyclic voltammetry (CV), UV-Visible (UV-Vis) and Raman spectroscopy showed a linear increase of peak current, absorbance and Raman intensities, respectively with the number of layers. These results indicate the formation of well-ordered multilayers of the ruthenium complex on ITO, which is further supported by the X-ray photoelectron spectroscopy analysis. The thickness of the layers can be controlled with nanometer precision. In particular, the thickest layer studied (65 molecular layers and approx. 120 nm thick) demonstrated fast electrochemical oxidation/reduction, indicating a very low attenuation of the charge transfer within the multilayer. In situ-UV-Vis and resonance Raman spectroscopy results demonstrated the reversible electrochromic/redox behavior of the ruthenium complex multilayered films on ITO with respect to the electrode potential, which is an ideal prerequisite for e.g. smart electrochemical energy storage applications. Galvanostatic charge-discharge experiments demonstrated a pseudocapacitor behavior of the multilayer film with a good specific capacitance of 92.2 F g(-1) at a current density of 10 μA cm(-2) and an excellent cycling stability. As demonstrated in our prototypical experiments, the fine control of physicochemical properties at nanometer scale, relatively good stability of layers under ambient conditions makes the multilayer coatings of this type an excellent material for e.g. electrochemical energy storage, as interlayers in inverted bulk heterojunction solar cell applications and as functional components in molecular electronics applications

  12. Methane transport from the active layer to lakes in the Arctic using Toolik Lake, Alaska, as a case study.

    PubMed

    Paytan, Adina; Lecher, Alanna L; Dimova, Natasha; Sparrow, Katy J; Kodovska, Fenix Garcia-Tigreros; Murray, Joseph; Tulaczyk, Slawomir; Kessler, John D

    2015-03-24

    Methane emissions in the Arctic are important, and may be contributing to global warming. While methane emission rates from Arctic lakes are well documented, methods are needed to quantify the relative contribution of active layer groundwater to the overall lake methane budget. Here we report measurements of natural tracers of soil/groundwater, radon, and radium, along with methane concentration in Toolik Lake, Alaska, to evaluate the role active layer water plays as an exogenous source for lake methane. Average concentrations of methane, radium, and radon were all elevated in the active layer compared with lake water (1.6 × 10(4) nM, 61.6 dpm⋅m(-3), and 4.5 × 10(5) dpm⋅m(-3) compared with 1.3 × 10(2) nM, 5.7 dpm⋅m(-3), and 4.4 × 10(3) dpm⋅m(-3), respectively). Methane transport from the active layer to Toolik Lake based on the geochemical tracer radon (up to 2.9 g⋅m(-2)⋅y(-1)) can account for a large fraction of methane emissions from this lake. Strong but spatially and temporally variable correlations between radon activity and methane concentrations (r(2) > 0.69) in lake water suggest that the parameters that control methane discharge from the active layer also vary. Warming in the Arctic may expand the active layer and increase the discharge, thereby increasing the methane flux to lakes and from lakes to the atmosphere, exacerbating global warming. More work is needed to quantify and elucidate the processes that control methane fluxes from the active layer to predict how this flux might change in the future and to evaluate the regional and global contribution of active layer water associated methane inputs.

  13. Methane transport from the active layer to lakes in the Arctic using Toolik Lake, Alaska, as a case study

    PubMed Central

    Paytan, Adina; Lecher, Alanna L.; Dimova, Natasha; Sparrow, Katy J.; Kodovska, Fenix Garcia-Tigreros; Murray, Joseph; Tulaczyk, Slawomir; Kessler, John D.

    2015-01-01

    Methane emissions in the Arctic are important, and may be contributing to global warming. While methane emission rates from Arctic lakes are well documented, methods are needed to quantify the relative contribution of active layer groundwater to the overall lake methane budget. Here we report measurements of natural tracers of soil/groundwater, radon, and radium, along with methane concentration in Toolik Lake, Alaska, to evaluate the role active layer water plays as an exogenous source for lake methane. Average concentrations of methane, radium, and radon were all elevated in the active layer compared with lake water (1.6 × 104 nM, 61.6 dpm⋅m−3, and 4.5 × 105 dpm⋅m−3 compared with 1.3 × 102 nM, 5.7 dpm⋅m−3, and 4.4 × 103 dpm⋅m−3, respectively). Methane transport from the active layer to Toolik Lake based on the geochemical tracer radon (up to 2.9 g⋅m−2⋅y−1) can account for a large fraction of methane emissions from this lake. Strong but spatially and temporally variable correlations between radon activity and methane concentrations (r2 > 0.69) in lake water suggest that the parameters that control methane discharge from the active layer also vary. Warming in the Arctic may expand the active layer and increase the discharge, thereby increasing the methane flux to lakes and from lakes to the atmosphere, exacerbating global warming. More work is needed to quantify and elucidate the processes that control methane fluxes from the active layer to predict how this flux might change in the future and to evaluate the regional and global contribution of active layer water associated methane inputs. PMID:25775530

  14. Methane transport from the active layer to lakes in the Arctic using Toolik Lake, Alaska, as a case study.

    PubMed

    Paytan, Adina; Lecher, Alanna L; Dimova, Natasha; Sparrow, Katy J; Kodovska, Fenix Garcia-Tigreros; Murray, Joseph; Tulaczyk, Slawomir; Kessler, John D

    2015-03-24

    Methane emissions in the Arctic are important, and may be contributing to global warming. While methane emission rates from Arctic lakes are well documented, methods are needed to quantify the relative contribution of active layer groundwater to the overall lake methane budget. Here we report measurements of natural tracers of soil/groundwater, radon, and radium, along with methane concentration in Toolik Lake, Alaska, to evaluate the role active layer water plays as an exogenous source for lake methane. Average concentrations of methane, radium, and radon were all elevated in the active layer compared with lake water (1.6 × 10(4) nM, 61.6 dpm⋅m(-3), and 4.5 × 10(5) dpm⋅m(-3) compared with 1.3 × 10(2) nM, 5.7 dpm⋅m(-3), and 4.4 × 10(3) dpm⋅m(-3), respectively). Methane transport from the active layer to Toolik Lake based on the geochemical tracer radon (up to 2.9 g⋅m(-2)⋅y(-1)) can account for a large fraction of methane emissions from this lake. Strong but spatially and temporally variable correlations between radon activity and methane concentrations (r(2) > 0.69) in lake water suggest that the parameters that control methane discharge from the active layer also vary. Warming in the Arctic may expand the active layer and increase the discharge, thereby increasing the methane flux to lakes and from lakes to the atmosphere, exacerbating global warming. More work is needed to quantify and elucidate the processes that control methane fluxes from the active layer to predict how this flux might change in the future and to evaluate the regional and global contribution of active layer water associated methane inputs. PMID:25775530

  15. Ultrahigh Enzyme Activity Assembled in Layered Double Hydroxides via Mg(2+)-Allosteric Effector.

    PubMed

    Wang, Min; Huang, Shu-Wan; Xu, Dan; Bao, Wen-Jing; Xia, Xing-Hua

    2015-06-01

    It is well-known that some metal ions could be allosteric effectors of allosteric enzymes to activate/inhibit the catalytic activities of enzymes. In nanobiocatalytic systems constructed based on the positive metal ion-induced allosteric effect, the incorporated enzymes will be activated and thus exhibit excellent catalytic performance. Herein, we present an environmentally friendly strategy to construct a novel allosteric effect-based β-galactosidase/Mg-Al layered double hydroxide (β-gal/Mg-Al-LDH) nanobiocatalytic system via the delamination-reconstruction method. The intercalated β-gal in the LDH galleries changes its conformation significantly due to the Mg(2+)-induced allosteric interactions and other weak interactions, which causes the activation of enzymatic activity. The β-gal/Mg-Al-LDH nanobiocatalytic system shows much higher catalytic activity and affinity toward its substrate and about 30 times higher catalytic reaction velocity than the free β-gal, which suggests that Mg(2+)-induced allosteric effect plays a vital role in the improvement of enzymatic performance.

  16. Permafrost and active layer monitoring in the maritime Antarctic: Preliminary results from CALM sites on Livingston and Deception Islands

    USGS Publications Warehouse

    Ramos, M.; Vieira, G.; Blanco, J.J.; Hauck, C.; Hidalgo, M.A.; Tome, D.; Nevers, M.; Trindade, A.

    2007-01-01

    This paper describes results obtained from scientific work and experiments performed on Livingston and Deception Islands. Located in the South Shetland Archipelago, these islands have been some of the most sensitive regions over the last 50 years with respect to climate change with a Mean Annual Air Temperature (MAAT) close to -2 ºC. Three Circumpolar Active Layer Monitoring (CALM) sites were installed to record the thermal regime and the behaviour of the active layer in different places with similar climate, but with different soil composition, porosity, and water content. The study’s ultimate aim is to document the influence of climate change on permafrost degradation. Preliminary results, obtained in 2006, on maximum active-layer thickness (around 40 cm in the CALM of Deception Island), active layer temperature evolution, snow thickness, and air temperatures permit early characterization of energy exchange mechanisms between the ground and the atmosphere in the CALM-S sites.

  17. Design of Bicontinuous Donor/Acceptor Morphologies for Use as Organic Solar Cell Active Layers

    NASA Astrophysics Data System (ADS)

    Kipp, Dylan; Mok, Jorge; Verduzco, Rafael; Ganesan, Venkat

    Two of the primary challenges limiting the marketability of organic solar cells are i) the smaller device efficiency of the organic solar cell relative to the conventional silicon-based solar cell and ii) the long term thermal instability of the device active layer. The achievement of equilibrium donor/acceptor morphologies with the characteristics believed to yield high device performance characteristics could address each of these two challenges. In this work, we present the results of a combined simulations and experiments-based approach to investigate if a conjugated BCP additive can be used to control the self-assembled morphologies taken on by conjugated polymer/PCBM mixtures. First, we use single chain in mean field Monte Carlo simulations to identify regions within the conjugated polymer/PCBM composition space in which addition of copolymers can lead to bicontinuous equilibrium morphologies with high interfacial areas and nanoscale dimensions. Second, we conduct experiments as directed by the simulations to achieve such morphologies in the PTB7 + PTB7- b-PNDI + PCBM model blend. We characterize the results of our experiments via a combination of transmission electron microscopy and X-ray scattering techniques and demonstrate that the morphologies from experiments agree with those predicted in simulations. Accordingly, these results indicate that the approach utilized represents a promising approach to intelligently design the morphologies taken on by organic solar cell active layers.

  18. Hydrogenated Amorphous Silicon Germanium Active Layer for Top Cell of a Multi Junction Cell Structure.

    PubMed

    Cho, Jaehyun; Iftiquar, S M; Kim, Minbum; Park, Jinjoo; Jung, Junhee; Kim, Jiwoong; Yi, Junsin

    2016-05-01

    Intrinsic hydrogenated amorphous silicon-germanium (a-SiGe:H) alloy is generally used in the bottom cell because of its low band gap. The a-SiGe:H has a higher photo conductivity in comparison to the a-Si:H; thus, it is expected that the a-SiGe:H can show better short circuit current density than that of the a-Si:H based solar cell. Therefore, we optimized a-SiGe:H active layer that can be a suitable choice for the front cell of a multi junction.solar cell. Furthermore, we carried out a comparative study of the solar cells that have a-SiGe:H and a-Si:H as respective active layers. The a-SiGe:H based solar cells show higher short circuit current density, while the a-Si:H based cells show higheropen circuit voltage. The current-voltage characteristics of these cells are as follows: (a) V(oc) = 770 mV, J(sc) = 15.0 mA/cm2, FF = 64.5%, and η = 7.47% for a-SiGe:H based cell; and (b) V(oc) = 826 mV, J(sc) = 13.63 mA/cm2, FF = 72.0%, and η = 8.1% for a-Si:H based cell.

  19. Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions.

    PubMed

    Shirazi, Mahdi; Elliott, Simon D

    2015-04-14

    Atomic layer deposition (ALD) is a technique for producing conformal layers of nanometre-scale thickness, used commercially in non-planar electronics and increasingly in other high-tech industries. ALD depends on self-limiting surface chemistry but the mechanistic reasons for this are not understood in detail. Here we demonstrate, by first-principle calculations of growth of HfO2 from Hf(N(CH3)2)4-H2O and HfCl4-H2O and growth of Al2O3 from Al(CH3)3-H2O, that, for all these precursors, co-adsorption plays an important role in ALD. By this we mean that previously-inert adsorbed fragments can become reactive once sufficient numbers of molecules adsorb in their neighbourhood during either precursor pulse. Through the calculated activation energies, this 'cooperative' mechanism is shown to have a profound influence on proton transfer and ligand desorption, which are crucial steps in the ALD cycle. Depletion of reactive species and increasing coordination cause these reactions to self-limit during one precursor pulse, but to be re-activated via the cooperative effect in the next pulse. This explains the self-limiting nature of ALD.

  20. Topology optimization of magnetorheological fluid layers in sandwich plates for semi-active vibration control

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaopeng; Kang, Zhan

    2015-08-01

    This paper investigates topology optimization of the magnetorheological (MR) fluid layer in a sandwich plate for improving the semi-active vibration control performance. Therein, a uniform magnetic field is applied across the MR fluid layer to provide a semi-active damping control effect. In the optimization model, the pseudo-densities describing the MR fluid material distribution are taken as design variables, and an artificial magneto-rheological fluid model (AMRF) with penalization is proposed to suppress intermediate density values. For reducing the vibration level under harmonic excitations, the dynamic compliance under a specific excitation frequency, or the frequency-aggregated dynamic compliance in a given frequency band, is taken as the objective function to be minimized. In this context, the adjoint-variable sensitivity analysis scheme is derived. The effectiveness and efficiency of the proposed method are demonstrated by numerical examples, in which the structural dynamic performance can be remarkably improved through optimization. The influences of several key factors on the optimal designs are also explored. It is shown that the AMRF model is effective in yielding clear boundaries in the final optimal solutions without use of additional regularization techniques.

  1. Blended Wing Body Systems Studies: Boundary Layer Ingestion Inlets With Active Flow Control

    NASA Technical Reports Server (NTRS)

    Geiselhart, Karl A. (Technical Monitor); Daggett, David L.; Kawai, Ron; Friedman, Doug

    2003-01-01

    A CFD analysis was performed on a Blended Wing Body (BWB) aircraft with advanced, turbofan engines analyzing various inlet configurations atop the aft end of the aircraft. The results are presented showing that the optimal design for best aircraft fuel efficiency would be a configuration with a partially buried engine, short offset diffuser using active flow control, and a D-shaped inlet duct that partially ingests the boundary layer air in flight. The CFD models showed that if active flow control technology can be satisfactorily developed, it might be able to control the inlet flow distortion to the engine fan face and reduce the powerplant performance losses to an acceptable level. The weight and surface area drag benefits of a partially submerged engine shows that it might offset the penalties of ingesting the low energy boundary layer air. The combined airplane performance of such a design might deliver approximately 5.5% better aircraft fuel efficiency over a conventionally designed, pod-mounted engine.

  2. Interplay of solvent additive concentration and active layer thickness on the performance of small molecule solar cells.

    PubMed

    Love, John A; Collins, Samuel D; Nagao, Ikuhiro; Mukherjee, Subhrangsu; Ade, Harald; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    A relationship between solvent additive concentration and active layer thickness in small-molecule solar cells is investigated. Specifically, the additive concentration must scale with the amount of semiconductor material and not as absolute concentration in solution. Devices with a wide range of active layers with thickness up to 200 nm can readily achieve efficiencies close to 6% when the right concentration of additive is used.

  3. Threshold improvement in uniformly lying helix cholesteric liquid crystal laser using auxiliary π-conjugated polymer active layer

    NASA Astrophysics Data System (ADS)

    Yoshida, Hiroyuki; Shiozaki, Yusuke; Inoue, Yo; Takahashi, Masaya; Ogawa, Yasuhiro; Fujii, Akihiko; Ozaki, Masanori

    2013-05-01

    We propose a device structure to lower the lasing threshold of a uniformly lying helix cholesteric liquid crystal (ChLC) laser. We place a π-conjugated polymer active layer beneath the ChLC layer to provide auxiliary gain, and demonstrate an improvement in the lasing threshold by a factor of 2.3. We also perform finite difference time domain calculations coupled with rate equations for a four-level system, and clarify the effect of the additional active layer on both the photonic density of states and the inversion population density. Although the addition of an extra layer lowers the photonic density of states, the gain provided by the auxiliary layer is sufficient to overcome the losses and decrease the lasing threshold. Our concept is useful for obtaining high-performance ChLC lasers.

  4. Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

    PubMed

    Abdelhafiz, Ali; Vitale, Adam; Joiner, Corey; Vogel, Eric; Alamgir, Faisal M

    2015-03-25

    In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

  5. Hypoxia Activates Calpains in the Nerve Fiber Layer of Monkey Retinal Explants

    PubMed Central

    Hirata, Masayuki; Shearer, Thomas R.; Azuma, Mitsuyoshi

    2015-01-01

    Purpose The vascular ischemic hypothesis attributes nerve damage in the retina to decreased blood flow in the ophthalmic artery, reduced oxygenation, and impaired axonal transport. Activation of calpain enzymes contributes to retinal cell death during hypoxia. However, we still do not know in which specific retinal layers calpains are activated. Thus, the purpose of the present study was to investigate where and when calpains are activated in an improved culture model of hypoxic monkey retina. Methods Monkey retinal explants were cultured on microporous membranes with the retinal ganglion cell (RGC) side facing up. Explants were incubated under hypoxic conditions, with or without additional reoxygenation. When it was used, the calpain inhibitor SNJ-1945 was maintained throughout the culture period. Immunohistochemistry and immunoblotting assays for α-spectrin, calpains 1 and 2, calpastatin, β-III tubulin, and γ-synuclein were performed with specific antibodies. Cell death was assessed by TUNEL staining. Results Under normoxic conditions, TUNEL-positive cells were minimal in our improved culture conditions. As early as 8 hours after hypoxia, the 150-kDa calpain-specific α-spectrin breakdown product appeared in the nerve fiber layer (NFL), where calpains 1 and 2 were localized. TUNEL-positive RGCs then increased at later time periods. The calpain inhibitor SNJ-1945 ameliorated changes induced by hypoxia or hypoxia/reoxygenation. Conclusions During hypoxia/reoxygenation in an improved, relevant monkey model, calpains were first activated in the NFL, followed by death of the parent RGCs. This observation suggest that calpain-induced degeneration of retinal nerve fibers may be an underlying mechanism for RGC death in hypoxic retinal neuropathies. PMID:26393472

  6. Availability of Fe(III) for Anaerobic Respiration across an Age Gradient of Drained Thaw Lake Basins in the Arctic Coastal Plain

    NASA Astrophysics Data System (ADS)

    Lipson, D.; Raab, T. K.; Bozzolo, F.; Emerson, C.; Hale, I.; Mauritz, M.; Miller, K.

    2010-12-01

    Our previous work demonstrated that Fe(III) reduction is an important respiratory pathway in a drained thaw lake basin (DTLB) of the Arctic coastal plain in northern Alaska (Lipson et al. 2010). When Fe(III) is available in anoxic environments that otherwise lack electron acceptors, it can act as a terminal electron acceptor, allowing anaerobic respiration to occur in favor of methanogenesis. Therefore, Fe(III) availability could be a key control over CO2 and CH4 emission from such ecosystems. Our previous work focused on a DTLB of medium age (50-300 years old). As DTLB’s age, the organic layer thickens, eventually to the point where the underlying mineral layers are buried completely in permafrost. The mineral layers are likely to be the source for the majority of Fe available for redox transformations by soil microbes. We therefore hypothesized that older basins with permanently frozen mineral layers would have lower Fe(III) availability than younger basins with active layers that include mineral material. To test this hypothesis we studied a gradient that comprised four DTLB, including young (<50 y), medium (50-300 y), old (300-2000 y) and ancient (2000-5500 y). We compared extractable Fe minerals in depth profiles from each DTLB, soluble Fe species in soil pore water, and other properties of soils and soil water. As expected, the youngest DTLB had the thinnest organic layer, a shallow mineral layer, and hence the largest total amount of HCl-extractable Fe(III) in the upper 25 cm. The medium DTLB had the lowest amounts of extractable Fe(III), while the old and ancient basins had intermediate amounts of extractable Fe(III). The amount of total Fe(III) present was related to the amount of mineral material found in the profile; the larger amounts in the old and ancient site relative to the medium site could be explained by cryoturbation, a process which mixes organic and mineral layers in older gelisols. S and Mn followed the same trends, but were orders of

  7. Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

    PubMed Central

    Husain, Kabir; Iljazi, Elda; Bhat, Abrar; Bieling, Peter; Mullins, R. Dyche; Rao, Madan; Mayor, Satyajit

    2016-01-01

    The surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. Previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. We reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors. Upon complete consumption of ATP, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. These depend on actin concentration, filament length, and actin/myosin ratio. During formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. Regeneration of ATP supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. In a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phase-segregating domains. These results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization. PMID:26929326

  8. Identifying active functionalities on few-layered graphene catalysts for oxidative dehydrogenation of isobutane.

    PubMed

    Dathar, Gopi Krishna Phani; Tsai, Yu-Tung; Gierszal, Kamil; Xu, Ye; Liang, Chengdu; Rondinone, Adam J; Overbury, Steven H; Schwartz, Viviane

    2014-02-01

    The general consensus in the studies of nanostructured carbon catalysts for oxidative dehydrogenation (ODH) of alkanes to olefins is that the oxygen functionalities generated during synthesis and reaction are responsible for the catalytic activity of these nanostructured carbons. Identification of the highly active oxygen functionalities would enable engineering of nanocarbons for ODH of alkanes. Few-layered graphenes were used as model catalysts in experiments to synthesize reduced graphene oxide samples with varying oxygen concentrations, to characterize oxygen functionalities, and to measure the activation energies for ODH of isobutane. Periodic density functional theory calculations were performed on graphene nanoribbon models with a variety of oxygen functionalities at the edges to calculate their thermal stability and to model reaction mechanisms for ODH of isobutane. Comparing measured and calculated thermal stability and activation energies leads to the conclusion that dicarbonyls at the zigzag edges and quinones at armchair edges are appropriately balanced for high activity, relative to other model functionalities considered herein. In the ODH of isobutane, both dehydrogenation and regeneration of catalytic sites are relevant at the dicarbonyls, whereas regeneration is facile compared with dehydrogenation at quinones. The catalytic mechanism involves weakly adsorbed isobutane reducing functional oxygen and leaving as isobutene, and O2 in the feed, weakly adsorbed on the hydrogenated functionality, reacting with that hydrogen and regenerating the catalytic sites.

  9. Polyethylene/organically-modified layered-silicate nanocomposites with antimicrobial activity

    NASA Astrophysics Data System (ADS)

    Songtipya, P.; Jimenez-Gasco, M. M.; Manias, E.

    2009-03-01

    Despite the very intensive research on polymer nanocomposites, the opportunities for new functionalities possible by nanofillers still remain largely untapped. Here, we present polyethylene/inorganic nanocomposites that exhibit strongly enhanced mechanical performance and, at the same time, also an antimicrobial activity originating from the organo-filler nature. Specifically, PE/organically-modified layered-silicate nanocomposites were prepared via melt-processing, and antimicrobial activity was designed by proper choice of their organic modification. Their antimicrobial activity was measured against three micotoxinogen fungal strains (Penicillium roqueforti and claviforme, and Fusarium graminearum) as model soil-borne plant and food contaminants. Montmorillonite-based organofillers, which only differ in their organic modification, were used to exemplify how these surfactants can be designed to render antifungal activity to the nanocomposites. The comparative discussion of the growth of fungi on unfilled PE and nanocomposite PE films is used to demonstrate how the antimicrobial efficacy is dictated by the surfactant chemistry and, further, how the nanocomposites' inhibitory activity compares to that of the organo-fillers and the surfactants.

  10. Ionization behavior, stoichiometry of association, and accessibility of functional groups in the active layers of reverse osmosis and nanofiltration membranes.

    PubMed

    Coronell, Orlando; González, Mari I; Mariñas, Benito J; Cahill, David G

    2010-09-01

    We characterized the fully aromatic polyamide (PA) active layers of six commercial reverse osmosis (RO) and nanofiltration (NF) membranes and found that in contrast to their similar elemental composition, total concentration of functional groups, and degree of polymerization, the ionization behavior and spatial distribution of carboxylic (R-COOH) groups within the active layers can be significantly different. We also studied the steric effects experienced by barium ion (Ba2+) in the active layers by determining the fraction of carboxylate (R-COO-) groups accessible to Ba2+; such fraction, referred to as the accessibility ratio (AR), was found to vary within the range AR=0.40-0.81, and to be generally independent of external solution pH. Additionally, we studied an NF membrane with a sulfonated polyethersulfone (SPES) active layer, and found that the concentration of sulfonate (R-SO3-) groups in the active layer was 1.67 M, independent of external solution pH and approximately three times higher than the maximum concentration (approximately 0.45+/-0.25 M) of R-COO- groups in PA active layers. The R-SO3- groups were found to be highly accessible to Ba2+ (AR=0.95+/-0.01).

  11. Contribution of Sp1 to Telomerase Expression and Activity in Skin Keratinocytes Cultured With a Feeder Layer.

    PubMed

    Bisson, Francis; Paquet, Claudie; Bourget, Jean-Michel; Zaniolo, Karine; Rochette, Patrick J; Landreville, Solange; Damour, Odile; Boudreau, François; Auger, François A; Guérin, Sylvain L; Germain, Lucie

    2015-02-01

    The growth of primary keratinocytes is improved by culturing them with a feeder layer. The aim of this study was to assess whether the feeder layer increases the lifespan of cultured epithelial cells by maintaining or improving telomerase activity and expression. The addition of an irradiated fibroblast feeder layer of either human or mouse origin (i3T3) helped maintain telomerase activity as well as expression of the transcription factor Sp1 in cultured keratinocytes. In contrast, senescence occurred earlier, together with a reduction of Sp1 expression and telomerase activity, in keratinocytes cultured without a feeder layer. Telomerase activity was consistently higher in keratinocytes grown on the three different feeder layers tested relative to cells grown without them. Suppression of Sp1 expression by RNA inhibition (RNAi) reduced both telomerase expression and activity in keratinocytes and also abolished their long-term growth capacity suggesting that Sp1 is a key regulator of both telomerase gene expression and cell cycle progression of primary cultured human skin keratinocytes. The results of the present study therefore suggest that the beneficial influence of the feeder layer relies on its ability to preserve telomerase activity in cultured human keratinocytes through the maintenance of stable levels of Sp1 expression.

  12. Contribution of Sp1 to Telomerase Expression and Activity in Skin Keratinocytes Cultured With a Feeder Layer.

    PubMed

    Bisson, Francis; Paquet, Claudie; Bourget, Jean-Michel; Zaniolo, Karine; Rochette, Patrick J; Landreville, Solange; Damour, Odile; Boudreau, François; Auger, François A; Guérin, Sylvain L; Germain, Lucie

    2015-02-01

    The growth of primary keratinocytes is improved by culturing them with a feeder layer. The aim of this study was to assess whether the feeder layer increases the lifespan of cultured epithelial cells by maintaining or improving telomerase activity and expression. The addition of an irradiated fibroblast feeder layer of either human or mouse origin (i3T3) helped maintain telomerase activity as well as expression of the transcription factor Sp1 in cultured keratinocytes. In contrast, senescence occurred earlier, together with a reduction of Sp1 expression and telomerase activity, in keratinocytes cultured without a feeder layer. Telomerase activity was consistently higher in keratinocytes grown on the three different feeder layers tested relative to cells grown without them. Suppression of Sp1 expression by RNA inhibition (RNAi) reduced both telomerase expression and activity in keratinocytes and also abolished their long-term growth capacity suggesting that Sp1 is a key regulator of both telomerase gene expression and cell cycle progression of primary cultured human skin keratinocytes. The results of the present study therefore suggest that the beneficial influence of the feeder layer relies on its ability to preserve telomerase activity in cultured human keratinocytes through the maintenance of stable levels of Sp1 expression. PMID:24962522

  13. Layer-specific entrainment of gamma-band neural activity by the alpha rhythm in monkey visual cortex

    PubMed Central

    Spaak, Eelke; Bonnefond, Mathilde; Maier, Alexander; Leopold, David A.; Jensen, Ole

    2012-01-01

    Summary While the mammalian neocortex has a clear laminar organization, layer-specific neuronal computations remain to be uncovered. Several studies suggest that gamma band activity in primary visual cortex (V1) is produced in granular and superficial layers and is associated with the processing of visual input [1–3]. Oscillatory alpha band activity in deeper layers has been proposed to modulate neuronal excitability associated with changes in arousal and cognitive factors [4–7]. To investigate the layer-specific interplay between these two phenomena, we characterized the coupling between alpha and gamma band activity of the local field potential (LFP) in V1 of the awake macaque. Using multicontact laminar electrodes to measure spontaneous signals simultaneously from all layers of V1, we found a robust coupling between alpha phase in the deeper layers and gamma amplitude in granular and superficial layers. Moreover, the power in the two frequency bands was anticorrelated. Taken together, these findings demonstrate robust inter-laminar cross-frequency coupling in the visual cortex, supporting the view that neuronal activity in the alpha frequency range phasically modulates processing in the cortical microcircuit in a top-down manner [7]. PMID:23159599

  14. Induction and modulation of persistent activity in a layer V PFC microcircuit model

    PubMed Central

    Papoutsi, Athanasia; Sidiropoulou, Kyriaki; Cutsuridis, Vassilis; Poirazi, Panayiota

    2013-01-01

    Working memory refers to the temporary storage of information and is strongly associated with the prefrontal cortex (PFC). Persistent activity of cortical neurons, namely the activity that persists beyond the stimulus presentation, is considered the cellular correlate of working memory. Although past studies suggested that this type of activity is characteristic of large scale networks, recent experimental evidence imply that small, tightly interconnected clusters of neurons in the cortex may support similar functionalities. However, very little is known about the biophysical mechanisms giving rise to persistent activity in small-sized microcircuits in the PFC. Here, we present a detailed biophysically—yet morphologically simplified—microcircuit model of layer V PFC neurons that incorporates connectivity constraints and is validated against a multitude of experimental data. We show that (a) a small-sized network can exhibit persistent activity under realistic stimulus conditions. (b) Its emergence depends strongly on the interplay of dADP, NMDA, and GABAB currents. (c) Although increases in stimulus duration increase the probability of persistent activity induction, variability in the stimulus firing frequency does not consistently influence it. (d) Modulation of ionic conductances (Ih, ID, IsAHP, IcaL, IcaN, IcaR) differentially controls persistent activity properties in a location dependent manner. These findings suggest that modulation of the microcircuit's firing characteristics is achieved primarily through changes in its intrinsic mechanism makeup, supporting the hypothesis of multiple bi-stable units in the PFC. Overall, the model generates a number of experimentally testable predictions that may lead to a better understanding of the biophysical mechanisms of persistent activity induction and modulation in the PFC. PMID:24130519

  15. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

    SciTech Connect

    Xie, Shuifen; Choi, Sang; Lu, Ning; Roling, Luke T.; Herron, Jeffrey A.; Zhang, Lei; Park, Jinho; Wang, Jinguo; Kim, Moon J.; Xie, Zhaoxiong; Mavrikakis, Manos; Xia, Younan

    2014-06-11

    An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

  16. Transformation of organic-inorganic hybrid films obtained by molecular layer deposition to photocatalytic layers with enhanced activity.

    PubMed

    Ishchuk, Sergey; Taffa, Dereje Hailu; Hazut, Ori; Kaynan, Niv; Yerushalmi, Roie

    2012-08-28

    We present the transformation of organic-inorganic hybrid titanicone films formed by TiCl(4) as metal precursor and ethylene glycol (EG) using solvent-free MLD to highly active photocatalytic films. The photocatalytic activities of the films were investigated using hydroxyl-functionalized porphyrin as a spectroscopic marker. TEM imaging and electron diffraction, XPS, UV-vis spectroscopy, and spectroscsopic ellipsometry were employed for structural and composition analyses of the films. The photocatalytic activity of Ti-EG films was investigated for different anneal temperatures and compared to TiO(2) films prepared by ALD using TiCl(4) as metal precursor and H(2)O (TiO(2) films). Overall, our results indicate that the photocatalytic activity of the thermally annealed Ti-EG film is about 5-fold increased compared to that of the TiO(2) film prepared by ALD for optimal process conditions. The combined results indicate that the structural and photocatalytic properties can be assigned to three states: (I) amorphous state, intermediate dye loading, low photocatalytic activity, (II) intermediate film state with both crystalline and amorphous regions, high dye loading, high catalytic activity, and (III) highly crystalline film with low dye loading and low photocatalytic activity. The formation of photocatalytic nanotubes (NTs) is demonstrated using sacrificial Ge nanowires (NWs) scaffolds to yield Ti-EG NT structures with controllable wall thickness structures and enhanced dye loading capacity. Our results demonstrate the feasibility and high potential of MLD to form metal oxides with high photocatalytic activity. PMID:22768917

  17. Absorption of the selenite anion from aqueous solutions by thermally activated layered double hydroxide.

    PubMed

    Liu, Rui; Frost, Ray L; Martens, Wayde N

    2009-03-01

    The presence of selenite or selenate in potable water is a health hazard especially when consumed over a long period of time. Its removal from potable water is of importance. This paper reports technology for the removal of selenite from water through the use of thermally activated layered double hydroxides. Mg/Al hydrotalcites with selenite in the interlayer were prepared at different times from 0.5 to 20 h through ion exchange. X-ray diffraction of the MgAlSeO3 hydrotalcites indicates that the selenite anion entered the interlayer spacing of Mg/Al hydrotalcite and MgAlSeO3 hydrotalcite was formed. Raman spectra proved the presence of selenite anion in the hydrotalcite interlayer as the counter anion. The band intensity and width of MgAlSeO3 hydrotalcite in the region of 3800-3000 cm(-1) increase with the adsorption of selenite by the Mg/Al hydrotalcite. The characteristic bands of free selenite anions in the MgAlSeO3 hydrotalcites are located between the region between 850 and 800 cm(-1). The Raman spectra of the lower wave number region of 550-500 cm(-1) show a shift toward higher wave numbers with adsorption of the selenite. An estimation of the amount of selenite anion removed by the thermally activated layered double hydroxide was obtained through the measurement of the intensity of the selenite Raman bands at 814 and 835 cm(-1) resulting from the amount of selenite anion remaining in solution. Thermally activated LDHs provide a mechanism for removing selenite anions from aqueous solutions.

  18. Effect of Salvia miltiorrhiza polysaccharides on boar spermatozoa during freezing-thawing.

    PubMed

    Shen, Tao; Jiang, Zhong-Liang; Liu, Hong; Li, Qing-Wang

    2015-08-01

    Salvia miltiorrhiza polysaccharides (SMPs) were extracted from S. miltiorrhiza in this study. The aim of the present study was to evaluate the effect of SMP on the motility of boar sperm, including the antioxidant effect of SMP on boar sperm and the effect of SMP on the in vivo fertilizing ability of frozen-thawed boar sperm. Fifty ejaculates from 5 Swagger boars were collected and diluted with an extender, which contained 3% glycerol (v/v) with five concentrations of SMP (0.2, 0.4, 0.6, 0.8, and 1.0mg/mL). The semen was frozen in 0.25mL straws at 1.0×10(9) cells/mL. Sixty gilts were inseminated using fresh semen, frozen semen with 0.4mg/mL of SMP and frozen semen without SMP. The results indicate that the addition of SMP to the extender results in a higher percentage of motile sperm post-thaw (P<0.05). The activities of superoxide dismutase, lactate dehydrogenase, glutamic-oxalacetic transaminease and catalase were all determined to be significantly higher than the control group after adding SMP to the extender (P<0.05). The artificial insemination (AI) results demonstrated that the litter size was significantly higher in the 0.4mg/mL of SMP group than in the control group (P<0.05). In conclusion, during the process of freezing, SMP can protect boar sperm from peroxidative damage and increase sperm motility and litter size during the process of freezing-thawing. The optimal concentration of SMP for the frozen extenders in this study was determined to be 0.4mg/mL. PMID:26077771

  19. PEMFC catalyst layers: the role of micropores and mesopores on water sorption and fuel cell activity.

    PubMed

    Soboleva, Tatyana; Malek, Kourosh; Xie, Zhong; Navessin, Titichai; Holdcroft, Steven

    2011-06-01

    The effects of carbon microstructure and ionomer loading on water vapor sorption and retention in catalyst layers (CLs) of PEM fuel cells are investigated using dynamic vapor sorption. Catalyst layers based on Ketjen Black and Vulcan XC-72 carbon blacks, which possess distinctly different surface areas, pore volumes, and microporosities, are studied. It is found that pores <20 nm diameter facilitate water uptake by capillary condensation in the intermediate range of relative humidities. A broad pore size distribution (PSD) is found to enhance water retention in Ketjen Black-based CLs whereas the narrower mesoporous PSD of Vulcan CLs is shown to have an enhanced water repelling action. Water vapor sorption and retention properties of CLs are correlated to electrochemical properties and fuel cell performance. Water sorption enhances electrochemical properties such as the electrochemically active surface area (ESA), double layer capacitance and proton conductivity, particularly when the ionomer content is very low. The hydrophilic properties of a CL on the anode and the cathode are adjusted by choosing the PSD of carbon and the ionomer content. It is shown that a reduction of ionomer content on either cathode or anode of an MEA does not necessarily have a significant detrimental effect on the MEA performance compared to the standard 30 wt % ionomer MEA. Under operation in air and high relative humidity, a cathode with a narrow pore size distribution and low ionomer content is shown to be beneficial due to its low water retention properties. In dry operating conditions, adequate ionomer content on the cathode is crucial, whereas it can be reduced on the anode without a significant impact on fuel cell performance.

  20. Novel biohybrids of layered double hydroxide and lactate dehydrogenase enzyme: Synthesis, characterization and catalytic activity studies

    NASA Astrophysics Data System (ADS)

    Djebbi, Mohamed Amine; Braiek, Mohamed; Hidouri, Slah; Namour, Philippe; Jaffrezic-Renault, Nicole; Ben Haj Amara, Abdesslem

    2016-02-01

    The present work introduces new biohybrid materials involving layered double hydroxides (LDH) and biomolecule such as enzyme to produce bioinorganic system. Lactate dehydrogenase (Lac Deh) has been chosen as a model enzyme, being immobilized onto MgAl and ZnAl LDH materials via direct ion-exchange (adsorption) and co-precipitation methods. The immobilization efficiency was largely dependent upon the immobilization methods. A comparative study shows that the co-precipitation method favors the immobilization of great and tunable amount of enzyme. The structural behavior, chemical bonding composition and morphology of the resulting biohybrids were determined by X-ray diffraction (XRD) study, Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM), respectively. The free and immobilized enzyme activity and kinetic parameters were also reported using UV-Visible spectroscopy. However, the modified LDH materials showed a decrease in crystallinity as compared to the unmodified LDH. The change in activity of the immobilized lactate dehydrogenase was considered to be due, to the reduced accessibility of substrate molecules to the active sites of the enzyme and the partial conformational change of the Lac Deh molecules as a result of the immobilization way. Finally, it was proven that there is a correlation between structure/microstructure and enzyme activity dependent on the immobilization process.

  1. Spaceborne Microwave Remote Sensing of Seasonal Freeze-Thaw Processes in the Terrestrial High Latitudes: Relationships with Land-Atmosphere CO2 exchange

    NASA Technical Reports Server (NTRS)

    McDonald, Kyle C.; Kimball, John S.; Zhao, Maosheng; Njoku, Eni; Zimmermann, Reiner; Running, Steven W.

    2004-01-01

    Landscape transitions between seasonally frozen and thawed conditions occur each year over roughly 50 million square kilometers of Earth's Northern Hemisphere. These relatively abrupt transitions represent the closest analog to a biospheric and hydrologic on/off switch existing in nature, affecting surface meteorological conditions, ecological trace gas dynamics, energy exchange and hydrologic activity profoundly. We utilize time series satellite-borne microwave remote sensing measurements from the Special Sensor Microwave Imager (SSM/I) to examine spatial and temporal variability in seasonal freeze/thaw cycles for the pan-Arctic basin and Alaska. Regional measurements of spring thaw timing are derived using daily brightness temperature measurements from the 19 GHz, horizontally polarized channel, separately for overpasses with 6 AM and 6 PM equatorial crossing times. Spatial and temporal patterns in regional freeze/thaw dynamics show distinct differences between North America and Eurasia, and boreal forest and Arctic tundra biomes. Annual anomalies in the timing of thawing in spring also correspond closely to seasonal atmospheric CO2 concentration anomalies derived from NOAA CMDL arctic and subarctic monitoring stations. Classification differences between AM and PM overpass data average approximately 5 days for the region, though both appear to be effective surrogates for monitoring annual growing seasons at high latitudes.

  2. Spaceborne microwave remote sensing of seasonal freeze-thaw processes in theterrestrial high l atitudes : relationships with land-atmosphere CO2 exchange

    NASA Technical Reports Server (NTRS)

    McDonald, Kyle C.; Kimball, John S.; Zhao, Maosheng; Njoku, Eni; Zimmermann, Reiner; Running, Steven W.

    2004-01-01

    Landscape transitions between seasonally frozen and thawed conditions occur each year over roughly 50 million square kilometers of Earth's Northern Hemisphere. These relatively abrupt transitions represent the closest analog to a biospheric and hydrologic on/off switch existing in nature, affecting surface meteorological conditions, ecological trace gas dynamics, energy exchange and hydrologic activity profoundly. We utilize time series satellite-borne microwave remote sensing measurements from the Special Sensor Microwave Imager (SSM/I) to examine spatial and temporal variability in seasonal freeze/thaw cycles for the pan-Arctic basin and Alaska. Regional measurements of spring thaw timing are derived using daily brightness temperature measurements from the 19 GHz, horizontally polarized channel, separately for overpasses with 6 AM and 6 PM equatorial crossing times. Spatial and temporal patterns in regional freeze/thaw dynamics show distinct differences between North America and Eurasia, and boreal forest and Arctic tundra biomes. Annual anomalies in the timing of thawing in spring also correspond closely to seasonal atmospheric CO2 concentration anomalies derived from NOAA CMDL arctic and subarctic monitoring stations. Classification differences between AM and PM overpass data average approximately 5 days for the region, though both appear to be effective surrogates for monitoring annual growing seasons at high latitudes.

  3. Low-noise encoding of active touch by layer 4 in the somatosensory cortex

    PubMed Central

    Andrew Hires, Samuel; Gutnisky, Diego A; Yu, Jianing; O'Connor, Daniel H; Svoboda, Karel

    2015-01-01

    Cortical spike trains often appear noisy, with the timing and number of spikes varying across repetitions of stimuli. Spiking variability can arise from internal (behavioral state, unreliable neurons, or chaotic dynamics in neural circuits) and external (uncontrolled behavior or sensory stimuli) sources. The amount of irreducible internal noise in spike trains, an important constraint on models of cortical networks, has been difficult to estimate, since behavior and brain state must be precisely controlled or tracked. We recorded from excitatory barrel cortex neurons in layer 4 during active behavior, where mice control tactile input through learned whisker movements. Touch was the dominant sensorimotor feature, with >70% spikes occurring in millisecond timescale epochs after touch onset. The variance of touch responses was smaller than expected from Poisson processes, often reaching the theoretical minimum. Layer 4 spike trains thus reflect the millisecond-timescale structure of tactile input with little noise. DOI: http://dx.doi.org/10.7554/eLife.06619.001 PMID:26245232

  4. Vibration and damping characteristics of cylindrical shells with active constrained layer damping treatments

    NASA Astrophysics Data System (ADS)

    Zheng, Ling; Zhang, Dongdong; Wang, Yi

    2011-02-01

    In this paper, the application of active constrained layer damping (ACLD) treatments is extended to the vibration control of cylindrical shells. The governing equation of motion of cylindrical shells partially treated with ACLD treatments is derived on the basis of the constitutive equations of elastic, piezoelectric and visco-elastic materials and an energy approach. The damping of a visco-elastic layer is modeled by the complex modulus formula. A finite element model is developed to describe and predict the vibration characteristics of cylindrical shells partially treated with ACLD treatments. A closed-loop control system based on proportional and derivative feedback of the sensor voltage generated by the piezo-sensor of the ACLD patches is established. The dynamic behaviors of cylindrical shells with ACLD treatments such as natural frequencies, loss factors and responses in the frequency domain are further investigated. The effects of several key parameters such as control gains, location and coverage of ACLD treatments on vibration suppression of cylindrical shells are also discussed. The numerical results indicate the validity of the finite element model and the control strategy approach. The potential of ACLD treatments in controlling vibration and sound radiation of cylindrical shells used as major critical structures such as cabins of aircraft, hulls of submarines and bodies of rockets and missiles is thus demonstrated.

  5. Influence of quaternization of ammonium on antibacterial activity and cytocompatibility of thin copolymer layers on titanium.

    PubMed

    Waßmann, Marco; Winkel, Andreas; Haak, Katharina; Dempwolf, Wibke; Stiesch, Meike; Menzel, Henning

    2016-10-01

    Antimicrobial coatings are able to improve the osseointegration of dental implants. Copolymers are promising materials for such applications due to their combined properties of two different monomers. To investigate the influence of different monomer mixtures, we have been synthesized copolymers of dimethyl (methacryloxyethyl) phosphonate (DMMEP) and dipicolyl aminoethyl methacrylate in different compositions and have them characterized to obtain the r-parameters. Some of the copolymers with different compositions have also been alkylated with 1-bromohexane, resulting in quaternized ammonium groups. The copolymers have been deposited onto titanium surfaces resulting in ultrathin, covalently bound layers. These layers have been characterized by water contact angle measurements and ellipsometry. The influence of quaternary ammonium groups on antibacterial properties and cytocompatibility was studied: Activity against bacteria was tested with a gram positive Staphylococcus aureus strain. Cytocompatibility was tested with a modified LDH assay after 24 and 72 h to investigate adhesion and proliferation of human fibroblast cells on modified surfaces. The copolymer with the highest content of DMMEP showed a good reduction of S. aureus and in the alkylated version a very good reduction of about 95%. On the other hand, poor cytocompatibility is observed. However, our results show that this trend cannot be generalized for this copolymer system.

  6. Effect of permafrost thawing on the organic carbon and metal speciation

    NASA Astrophysics Data System (ADS)

    Pokrovsky, Oleg; Shirokova, Liudmila; Kirpotin, Sergey; Dupre, Bernard

    2010-05-01

    Ongoing processes of the permafrost thawing in Western Siberia are likely to increase the surface of water reservoirs via forming so-called thermokarst (thaw) lakes, mobilizing the organic carbon from the soil pool to the rivers and, finally, to the ocean, and also modifying the fluxes of methane and CO2 to the atmosphere. In order to better understand the mechanisms of carbon mobilization and organic matter biodegradation during permafrost thawing and to establish the link between the organic carbon, microbial activity and geochemistry of major and trace elements in forming thermokarstic lakes, we performed a comparative multidisciplinary study on the biogeochemistry of organic carbon and bacterioplankton in lakes located in the northern part of Western Siberia. Towards this goal, fifteen lakes and three surface streams draining neogenic deposits on continuous permafrost ground of the Urengoy region. There is a sequence of ecosystem stages during evolution from peat thawing in depressions and palsa degradation due to permafrost subsidence in small ponds to large, km - size lakes subject to drainage and, finally, the khasyrei formation (remaining central parts of drained lakes). In the chronosequence of lake formation, there is a clear decrease of the relative proportion of < 1 kDa (1 kDa is close to 1 nm) organic carbon concentration along with concentration of total dissolved (< 0.45 µm) organic carbon. Other dissolved components such as major cations and Fe also decrease their concentration in the chronosequence of ecosystem evolution. Independent on the state of ecosystem development and organic carbon concentration, there is significant proportion of insoluble metals (Fe, Al, Ti, Ga, Y, REEs, Th, Zr, Hf), from 80 to 99%, in the colloidal form (1 kDa - 0.45 µm) present as organic (humic and fulvic) complexes. There is a systematic decrease of these element concentrations concomitant with OC concentration decrease in consecutive filtrates (5 micron - 0

  7. Cryoprotection mechanisms of polyethylene glycols on lactate dehydrogenase during freeze-thawing.

    PubMed

    Mi, Yanli; Wood, George; Thoma, Laura

    2004-01-01

    The purpose of this study was to explore the cryoprotection mechanisms of high molecular weight polyethylene glycols (PEGs) (eg, PEG 4000 and PEG 8000) on lactate dehydrogenase (LDH). Ultraviolet activity assays, circular dichroism (CD) spectroscopy, gel filtration, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), (14)C-PEG 4000 labeling and binding, and cryostage microscopic study were conducted. Different molecular weights and concentrations of PEGs in LDH formulations were treated by freeze-thawing. Higher molecular weights and concentrations of PEGs in LDH-PEG formulations obtained better activity and secondary structure recoveries of LDH after freeze-thawing. Insoluble aggregation of LDH was not observed in gel filtration studies. SDS-PAGE results suggested surface characteristic modifications of LDH by the larger molecular weight PEGs. The 14C-PEG 4000 labeling and binding study showed extensive nonspecific interactions between the PEG 4000 and LDH molecules in a concentration-dependent manner. The bound LDH-PEG 4000/free PEG 4000 ratio increased when LDH or PEG 4000 concentrations increased. Cryostage microscopic study showed that PEG 8000 delayed the ice crystallization and eutectic transition of LDH formulation. It appeared that multiple mechanisms were at work during PEGs' cryoprotection of LDH. It was unclear whether the delayed eutectic characteristics of PEGs contributed to LDH cryoprotection. The favorable interaction, rather than preferential exclusion, between LDH and PEGs (eg, 4000) cryoprotected LDH. PMID:15760107

  8. Elemental composition and optical properties reveal changes in dissolved organic matter along a permafrost thaw chronosequence in a subarctic peatland

    NASA Astrophysics Data System (ADS)

    Hodgkins, Suzanne B.; Tfaily, Malak M.; Podgorski, David C.; McCalley, Carmody K.; Saleska, Scott R.; Crill, Patrick M.; Rich, Virginia I.; Chanton, Jeffrey P.; Cooper, William T.

    2016-08-01

    The fate of carbon stored in permafrost-zone peatlands represents a significant uncertainty in global climate modeling. Given that the breakdown of dissolved organic matter (DOM) is often a major pathway for decomposition in peatlands, knowledge of DOM reactivity under different permafrost regimes is critical for determining future climate feedbacks. To explore the effects of permafrost thaw and resultant plant succession on DOM reactivity, we used a combination of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), UV/Vis absorbance, and excitation-emission matrix spectroscopy (EEMS) to examine the DOM elemental composition and optical properties of 27 pore water samples gathered from various sites along a permafrost thaw sequence in Stordalen Mire, a thawing subarctic peatland in northern Sweden. The presence of dense Sphagnum moss, a feature that is dominant in the intermediate thaw stages, appeared to be the main driver of variation in DOM elemental composition and optical properties at Stordalen. Specifically, DOM from sites with Sphagnum had greater aromaticity, higher average molecular weights, and greater O/C, consistent with a higher abundance of phenolic compounds that likely inhibit decomposition. These compounds are released by Sphagnum and may accumulate due to inhibition of phenol oxidase activity by the acidic pH at these sites. In contrast, sites without Sphagnum, specifically fully-thawed rich fens, had more saturated, more reduced compounds, which were high in N and S. Optical properties at rich fens indicated the presence of microbially-derived DOM, consistent with the higher decomposition rates previously measured at these sites. These results indicate that Sphagnum acts as an inhibitor of rapid decomposition and CH4 release in thawing subarctic peatlands, consistent with lower rates of CO2 and CH4 production previously observed at these sites. However, this inhibitory effect may disappear if Sphagnum-dominated bogs

  9. Carbon dynamics in highly heterotrophic subarctic thaw ponds

    NASA Astrophysics Data System (ADS)

    Roiha, T.; Laurion, I.; Rautio, M.

    2015-12-01

    Global warming has accelerated the formation of permafrost thaw ponds in several subarctic and arctic regions. These ponds are net heterotrophic as evidenced by their greenhouse gas (GHG) supersaturation levels (CO2 and CH4), and generally receive large terrestrial carbon inputs from the thawing and eroding permafrost. We measured seasonal and vertical variations in the concentration and type of dissolved organic matter (DOM) in five subarctic thaw (thermokarst) ponds in northern Quebec, and explored how environmental gradients influenced heterotrophic and phototrophic biomass and productivity. Late winter DOM had low aromaticity indicating reduced inputs of terrestrial carbon, while the high concentration of dissolved organic carbon (DOC) suggests that some production of non-chromophoric dissolved compounds by the microbial food web took place under the ice cover. Summer DOM had a strong terrestrial signature, but was also characterized with significant inputs of algal-derived carbon, especially at the pond surface. During late winter, bacterial production was low (maximum of 0.8 mg C m-3 d-1) and was largely based on free-living bacterioplankton (58 %). Bacterial production in summer was high (up to 58 mg C m-3 d-1), dominated by particle-attached bacteria (67 %), and strongly correlated with the amount of terrestrial carbon. Primary production was restricted to summer surface waters due to strong light limitation deeper in the water column or in winter. The phototrophic biomass was equal to the heterotrophic biomass, but as the algae were mostly composed of mixotrophic species, most probably they used bacteria rather than solar energy in such shaded ponds. Our results point to a strong heterotrophic energy pathway in these thaw pond ecosystems, where bacterioplankton dominates the production of new carbon biomass in both summer and winter.

  10. Dissolved organic matter photolysis in Canadian arctic thaw ponds

    NASA Astrophysics Data System (ADS)

    Laurion, Isabelle; Mladenov, Natalie

    2013-09-01

    The abundant thaw lakes and ponds in the circumarctic receive a new pool of organic carbon as permafrost peat soils degrade, which can be exposed to significant irradiance that potentially increases as climate warms and ice cover shortens. Exposure to sunlight is known to accelerate the transformation of dissolved organic matter (DOM) into molecules that can be more readily used by microbes. We sampled the water from two common classes of ponds found in the ice-wedge system of continuous permafrost regions of Canada, polygonal and runnel ponds, and followed the transformation of DOM over 12 days by looking at dissolved organic carbon (DOC) concentration and DOM absorption and fluorescence properties. The results indicate a relatively fast decay of color (3.4 and 1.6% loss d-1 of absorption at 320 nm for the polygonal and runnel pond, respectively) and fluorescence (6.1 and 8.3% loss d-1 of total fluorescent components, respectively) at the pond surface, faster in the case of humic-like components, but insignificant losses of DOC over the observed period. This result indicates that direct DOM mineralization (photochemical production of CO2) is apparently minor in thaw ponds compared to the photochemical transformation of DOM into less chromophoric and likely more labile molecules with a greater potential for microbial mineralization. Therefore, DOM photolysis in arctic thaw ponds can be considered as a catalytic mechanism, accelerating the microbial turnover of mobilized organic matter from thawing permafrost and the production of greenhouse gases, especially in the most shallow ponds. Under a warming climate, this mechanism will intensify as summers lengthen.

  11. Carbon dynamics in highly heterotrophic subarctic thaw ponds

    NASA Astrophysics Data System (ADS)

    Roiha, T.; Laurion, I.; Rautio, M.

    2015-07-01

    Global warming has accelerated the formation of permafrost thaw ponds in several subarctic and arctic regions. These ponds are net heterotrophic as evidenced by their greenhouse gas (GHG) supersaturation levels (CO2 and CH4), and generally receive large terrestrial carbon inputs from the thawing and eroding permafrost. We measured seasonal and vertical variations in the concentration and type of dissolved organic matter (DOM) in five subarctic thaw (thermokarst) ponds in northern Quebec, and explored how environmental gradients influenced heterotrophic and phototrophic biomass and productivity. Late winter DOM had low aromaticity indicating reduced inputs of terrestrial carbon, while the high concentration of dissolved organic carbon (DOC) suggests that some production of non-chromophoric dissolved compounds by the microbial food web took place under the ice cover. Summer DOM had a strong terrestrial signature, but was also characterized with significant inputs of algal-derived carbon, especially at the pond surface. During late winter, bacterial production was low (maximum of 0.8 mg C m-3 d-1) and was largely based on free-living bacterioplankton (58 %). Bacterial production in summer was high (up to 58 mg C m-3 d-1), dominated by particle-attached bacteria (67 %), and strongly correlated to the amount of terrestrial carbon. Primary production was restricted to summer surface waters due to strong light limitation deeper in the water column or in winter. The phototrophic biomass was equal to the heterotrophic biomass, but as the algae were mostly composed of mixotrophic species, most probably they used bacteria rather than solar energy in such shaded ponds. According to the δ13C analyses, non-algal carbon supported 51 % of winter and 37 % of summer biomass of the phantom midge larvae, Chaoborus sp., that are at the top of the trophic chain. Our results point to a strong heterotrophic energy pathway in these thaw pond ecosystems, where bacterioplankton dominates

  12. Nanocomposites of polymers with layered inorganic nanofillers: Antimicrobial activity, thermo-mechanical properties, morphology, and dispersion

    NASA Astrophysics Data System (ADS)

    Songtipya, Ponusa

    In the first part of the thesis, polyethylene/layered silicate nanocomposites that exhibit an antimicrobial activity were synthesized and studied. Their antimicrobial activity was designed to originate from non-leaching, novel cationic modifiers---amine-based surfactants---used as the organic-modification of the fillers. Specifically, PE/organically-modified montmorillonite ( mmt) nanocomposites were prepared via melt-processing, and simultaneous dispersion and antimicrobial activity was designed by proper choice of the fillers' organic modification. The antimicrobial activity was measured against three micotoxinogen fungal strains (Penicillium roqueforti and claviforme, and Fusarium graminearum ). Various mmt-based organofillers, which only differ in the type or amount of their organic modification, were used to exemplify how these surfactants can be designed to render antifungal activity to the fillers themselves and the respective nanocomposites. A comparative discussion of the growth of fungi on unfilled PE and nanocomposite PE films is used to demonstrate how the antimicrobial efficacy is dictated by the surfactant chemistry and, further, how the nanocomposites' inhibitory activity compares to that of the organo-fillers and the surfactants. An attempt to improve the thermomechanical reinforcement of PE/mmt nanocomposites while maintaining their antimicrobial activity, was also carried out by combining two different organically modified montmorillonites. However, a uniform microscopic dispersion could not be achieved through this approach. In the second part of this thesis, a number of fundamental studies relating to structure-property relations in nanocomposites were carried out, towards unveiling strategies that can concurrently optimize selected properties of polymers by the addition of nanofillers. Specifically, the dispersion-crystallinity-reinforcement relations in HDPE/mmt nanocomposites was investigated. The influence of a functional HDPE compatibilizer

  13. Assessment of freshness and freeze-thawing of sea bream fillets (Sparus aurata) by a cytosolic enzyme: Lactate dehydrogenase.

    PubMed

    Diop, Mamadou; Watier, Denis; Masson, Pierre-Yves; Diouf, Amadou; Amara, Rachid; Grard, Thierry; Lencel, Philippe

    2016-11-01

    The evaluation of freshness and freeze-thawing of fish fillets was carried out by assessment of autolysis of cells using a cytosolic enzyme lactate dehydrogenase. Autolysis plays an important role in spoilage of fish and postmortem changes in fish tissue are due to the breakdown of the cellular structures and release of cytoplasmic contents. The outflow of a cytosolic enzyme, lactate dehydrogenase, was studied in sea bream fillets and the Sparus aurata fibroblasts (SAF-1) cell-line during an 8day storage period at +4°C. A significant increase of lactate dehydrogenase release was observed, especially after 5days of storage. The ratio between the free and the total lactate dehydrogenase activity is a promising predictive marker to measure the quality of fresh fish fillets. The effect of freeze-thawing on cytosolic lactate dehydrogenase and lysosomal α-d-glucosidase activities was also tested. Despite the protecting effect of the tissue compared to the cell-line, a loss of lactate dehydrogenase activity, but not of α-d-glucosidase, was observed. In conclusion, lactate dehydrogenase may be used as a marker to both assess freshness of fish and distinguish between fresh and frozen-thawed fish fillets.

  14. Assessment of freshness and freeze-thawing of sea bream fillets (Sparus aurata) by a cytosolic enzyme: Lactate dehydrogenase.

    PubMed

    Diop, Mamadou; Watier, Denis; Masson, Pierre-Yves; Diouf, Amadou; Amara, Rachid; Grard, Thierry; Lencel, Philippe

    2016-11-01

    The evaluation of freshness and freeze-thawing of fish fillets was carried out by assessment of autolysis of cells using a cytosolic enzyme lactate dehydrogenase. Autolysis plays an important role in spoilage of fish and postmortem changes in fish tissue are due to the breakdown of the cellular structures and release of cytoplasmic contents. The outflow of a cytosolic enzyme, lactate dehydrogenase, was studied in sea bream fillets and the Sparus aurata fibroblasts (SAF-1) cell-line during an 8day storage period at +4°C. A significant increase of lactate dehydrogenase release was observed, especially after 5days of storage. The ratio between the free and the total lactate dehydrogenase activity is a promising predictive marker to measure the quality of fresh fish fillets. The effect of freeze-thawing on cytosolic lactate dehydrogenase and lysosomal α-d-glucosidase activities was also tested. Despite the protecting effect of the tissue compared to the cell-line, a loss of lactate dehydrogenase activity, but not of α-d-glucosidase, was observed. In conclusion, lactate dehydrogenase may be used as a marker to both assess freshness of fish and distinguish between fresh and frozen-thawed fish fillets. PMID:27211667

  15. Comparison of Plasma Activation of Thin Water Layers by Direct and Remote Plasma Sources

    NASA Astrophysics Data System (ADS)

    Kushner, Mark

    2014-10-01

    Plasma activation of liquids is now being investigated for a variety of biomedical applications. The plasma sources used for this activation can be generally classified as direct (the plasma is in contact with the surface of the liquid) or remote (the plasma does not directly touch the liquid). The direct plasma source may be a dielectric barrier discharge (DBD) where the surface of the liquid is a floating electrode or a plasma jet in which the ionization wave forming the plasma plume reaches the liquid. The remote plasma source may be a DBD with electrodes electrically isolated from the liquid or a plasma jet in which the ionization wave in the plume does not reach the liquid. In this paper, a comparison of activation of thin water layers on top of tissue, as might be encountered in wound healing, will be discussed using results from numerical investigations. We used the modeling platform nonPDPSIM to simulate direct plasma activation of thin water layers using DBDs and remote activation using plasma jets using up to hundreds of pulses. The DBDs are sustained in humid air while the plasma jets consist of He/O2 mixtures flowed into humid air. For similar number of pulses and energy deposition, the direct DBD plasma sources produce more acidification and higher production of nitrates/nitrites in the liquid. This is due to the accumulation of NxOy plasma jets, the convective flow removes many of these species prior to their diffusing into the water or reacting to form higher nitrogen oxides. This latter effect is sensitive to the repetition rate which determines whether reactive species formed during prior pulses overlap with newly produced reactive species. in the gas phase. In the plasma jets, the convective flow removes many of these species prior to their diffusing into the water or reacting to form higher nitrogen oxides. This latter effect is sensitive to the repetition rate which determines whether reactive species formed during prior pulses overlap with

  16. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems. PMID:27124717

  17. Some enzyme activities associated with the chlorophyll containing layers of the immature barley pericarp.

    PubMed

    Duffus, C M; Rosie, R

    1973-09-01

    Some photosynthetic and biochemical properties of the chlorophyl containing layers of the pericarp of developing barley have been investigated. The tissue changes from pale green to bright green early in development, chlorophyll disappearing only at the later stages of maturity. It contains chloroplasts and probably amyloplasts and starch bearing chloroplasts. It is capable of high rates of light dependent oxygen evolution. It has been shown that the enzyme phosphoenol pyruvate carboxylase (EC 4.1.1.31) is present in the pericarp and is 100 times as active in carbon dioxide fixation as ribulose diphosphate carboxylase (EC 4.1.1.39). Other enzymes present in the pericarp are phosphoenol pyruvate synthetase, pyrophosphatase (EC 3.6.1.1), malate NAD and NADP dehydrogenases (EC 1.1.1.37), malic enzyme (EC 1.1.1.40), and fructose 1,6 diphosphatase (EC 3.1.3.11). PMID:24458756

  18. Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation.

    PubMed

    Birkner, Nancy; Nayeri, Sara; Pashaei, Babak; Najafpour, Mohammad Mahdi; Casey, William H; Navrotsky, Alexandra

    2013-05-28

    Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn(3+)/Mn(4+) ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states.

  19. Modeling of the polymer solar cell with a P3HT:PCBM active layer

    NASA Astrophysics Data System (ADS)

    Jelić, Ž.; Petrović, J.; Matavulj, P.; Melancon, J.; Sharma, A.; Zellhofer, C.; Živanović, S.

    2014-09-01

    In this paper we present a theoretical model for simulating the behavior of a polymer solar cell with a poly(3-hexylthiophene):1-(3-methoxycarbonyl) propyl-1-phenyl-[6, 6]-methanofullerene (P3HT:PCBM) active layer. Two different types of boundary conditions were considered, Dirichlet’s and mixed. For Dirichlet’s boundary conditions we have achieved an excellent agreement with the experiment. The influence of boundary conditions on the appearance of the s-shaped current-voltage characteristic (sometimes observed in experiments) has been investigated. When mixed boundary conditions are applied, calculated current-voltage characteristics are inevitably s-shaped. By altering the boundary carrier concentration, an s-shaped deformation in current-voltage characteristics is numerically simulated by using Dirichlet’s boundary conditions.

  20. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

  1. Materials for the active layer of organic photovoltaics: ternary solar cell approach.

    PubMed

    Chen, Yung-Chung; Hsu, Chih-Yu; Lin, Ryan Yeh-Yung; Ho, Kuo-Chuan; Lin, Jiann T

    2013-01-01

    Power conversion efficiencies in excess of 7% have been achieved with bulk heterojunction (BHJ)-type organic solar cells using two components: p- and n-doped materials. The energy level and absorption profile of the active layer can be tuned by introduction of an additional component. Careful design of the additional component is required to achieve optimal panchromatic absorption, suitable energy-level offset, balanced electron and hole mobility, and good light-harvesting efficiency. This article reviews the recent progress on ternary organic photovoltaic systems, including polymer/small molecule/functional fullerene, polymer/polymer/functional fullerene, small molecule/small molecule/functional fullerene, polymer/functional fullerene I/functional fullerene II, and polymer/quantum dot or metal/functional fullerene systems.

  2. Reduction of Free Edge Peeling Stress of Laminated Composites Using Active Piezoelectric Layers

    PubMed Central

    Huang, Bin; Kim, Heung Soo

    2014-01-01

    An analytical approach is proposed in the reduction of free edge peeling stresses of laminated composites using active piezoelectric layers. The approach is the extended Kantorovich method which is an iterative method. Multiterms of trial function are employed and governing equations are derived by taking the principle of complementary virtual work. The solutions are obtained by solving a generalized eigenvalue problem. By this approach, the stresses automatically satisfy not only the traction-free boundary conditions, but also the free edge boundary conditions. Through the iteration processes, the free edge stresses converge very quickly. It is found that the peeling stresses generated by mechanical loadings are significantly reduced by applying a proper electric field to the piezoelectric actuators. PMID:25025088

  3. Sensitivity of boreal forest carbon balance to soil thaw

    USGS Publications Warehouse

    Goulden, M.L.; Wofsy, S.C.; Harden, J.W.; Trumbore, S.E.; Crill, P.M.; Gower, S.T.; Fries, T.; Daube, B.C.; Fan, S.-M.; Sutton, D.J.; Bazzaz, A.; Munger, J.W.

    1998-01-01

    We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 ?? 0.5 metric ton of carbon per hectare per year (ton C ha-1 year-1) from 1994 to 1997, with a gain of 0.6 ?? 0.2 ton C ha-1 year-1 in moss and wood offset by a loss of 0.8 ?? 0.5 ton C ha-1 year-1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool (~150 tons C ha-1) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.

  4. Effects of storage in different semen extenders on the pre-freezing and post-thawing quality of boar spermatozoa.

    PubMed

    Dziekońska, A; Zasiadczyk, Ł; Lecewicz, M; Strzeżek, R; Koziorowska-Gilun, M; Fraser, L; Mogielnicka-Brzozowska, M; Kordan, W

    2015-01-01

    The aim of this study was to investigate the effects of storage of semen in different commercial extenders on the pre-freezing and post-thawing quality of boar spermatozoa. Semen was diluted in BTS, Androhep (AH) and Gedil (GD), stored for 24 h at 17°C, and then frozen in accordance with the cryopreservation protocol. Analyses of the quality of spermatozoa included: motility, normal apical ridge (NAR) acrosome, plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), measurements of ATP content and activity of superoxidase dismutase (SOD) and glutathione peroxidase (GPx). Prior to the freezing process, no significant effect of the extender on the sperm quality parameters was noted. After thawing the spermatozoa it was demonstrated that the type of extender used influenced PMI, MMP, ATP content and activity of GPx. In the AH extender the percentage of spermatozoa with PMI and ATP content in spermatozoa was significantly higher (P<0.05) as compared to the BTS or GD extenders. In addition, semen stored in the AH was characterised by a statistically higher (P<0.05) percentage of spermatozoa with MMP and increased activity of GPx as compared with the BTS. The results obtained indicate that for the cryopreservation process, boar spermatozoa stored for 24 hours in liquid state can be used. However, the type of extender used prior to freezing may have a significant effect on the post-thawing quality of the spermatozoa. The AH extender better secured the quality of thawed boar spermatozoa as compared with the BTS or GD. PMID:26812814

  5. Behaviour of polycyclic aromatic hydrocarbons (PAH) in soils under freeze-thaw cycles

    NASA Astrophysics Data System (ADS)

    Zschocke, Anne; Schönborn, Maike; Eschenbach, Annette

    2010-05-01

    The arctic region will be one of the most affected regions by climate change due to the predicted temperature rise. As a result of anthropogenic actions as mining, exploration and refining as well as atmospheric transport pollutions can be found in arctic soils. Therefore questions on the behaviour of organic contaminants in permafrost influenced soils are of high relevance. First investigations showed that permafrost can act as a semi-permeable layer for PAH (Curtosi et al., 2007). Therefore it can be assumed that global warming could result in a mobilization of PAH in these permafrost influenced soils. On the other hand a low but detectable mineralization of organic hydrocarbons by microorganisms under repeated freeze-thaw cycles was analysed (Börresen et al. 2007, Eschenbach et al. 2000). In this study the behaviour and distribution of PAH under freezing and periodically freezing and thawing were investigated in laboratory column experiments with spiked soil materials. Two soil materials which are typical for artic regions, a organic matter containing melt water sand and a well decomposed peat, were homogeneously spiked with a composite of a crude oil and the PAH anthracene and benzo(a)pyrene. After 14days preincubation time the soil material was filled in the laboratory columns (40cm high and 10 cm in diameter). Based on studies by Chuvilin et al. (2001) the impact of freezing of the upper third of the column from the surface downwards was examined. The impact of freezing was tested in two different approaches the first one with a single freezing step and the second one with a fourfold repeated cycle of freezing and thawing which takes about 6 or 7 days each. The experimental design and very first results will be shown and discussed. In some experiments with the peat a higher concentration of anthracene and benzo(a)pyrene could be detected below the freezing front in the unfrozen part of the column. Whereas the concentration of PAH had slightly decreased in

  6. Post-Thaw Non-Cultured and Post-Thaw Cultured Equine Cord Blood Mesenchymal Stromal Cells Equally Suppress Lymphocyte Proliferation In Vitro

    PubMed Central

    Williams, Lynn B.; Tessier, Laurence; Koenig, Judith B.; Koch, Thomas G.

    2014-01-01

    Multipotent mesenchymal stromal cells (MSC) are receiving increased attention for their non-progenitor immunomodulatory potential. Cryopreservation is commonly used for long-term storage of MSC. Post-thaw MSC proliferation is associated with a lag-phase in vitro. How this lag-phase affect MSC immunomodulatory properties is unknown. We hypothesized that in vitro there is no difference in lymphocyte suppression potential between quick-thawed cryopreserved equine cord blood (CB) MSC immediately included in mixed lymphocyte reaction (MLR) and same MSC allowed post-thaw culture time prior to inclusion in MLR. Cryopreserved CB-MSC from five unrelated foals were compared using two-way MLR. For each of the five unrelated MSC cultures, paired MLR assays of MSC allowed five days of post-thaw culture and MSC included in MLR assay immediately post-thawing were evaluated. We report no difference in the suppression of lymphocyte proliferation by CB-MSC that had undergone post-thaw culture and MSC not cultured post-thaw (p<0.0001). Also, there was no inter-donor variability between the lymphocyte suppressive properties of MSC harvested from the five different donors (p = 0.13). These findings suggest that cryopreserved CB-MSC may have clinical utility immediately upon thawing. One implication hereof is the possibility of using cryopreserved CB-MSC at third party locations without the need for cell culture equipment or competencies. PMID:25438145

  7. Many-body microhydrodynamics of colloidal particles with active boundary layers

    NASA Astrophysics Data System (ADS)

    Singh, Rajesh; Ghose, Somdeb; Adhikari, R.

    2015-06-01

    Colloidal particles with active boundary layers—regions surrounding the particles where non-equilibrium processes produce large velocity gradients—are common in many physical, chemical and biological contexts. The velocity or stress at the edge of the boundary layer determines the exterior fluid flow and, hence, the many-body interparticle hydrodynamic interaction. Here, we present a method to compute the many-body hydrodynamic interaction between N spherical active particles induced by their exterior microhydrodynamic flow. First, we use a boundary integral representation of the Stokes equation to eliminate bulk fluid degrees of freedom. Then, we expand the boundary velocities and tractions of the integral representation in an infinite-dimensional basis of tensorial spherical harmonics and, on enforcing boundary conditions in a weak sense on the surface of each particle, obtain a system of linear algebraic equations for the unknown expansion coefficients. The truncation of the infinite series, fixed by the degree of accuracy required, yields a finite linear system that can be solved accurately and efficiently by iterative methods. The solution linearly relates the unknown rigid body motion to the known values of the expansion coefficients, motivating the introduction of propulsion matrices. These matrices completely characterize hydrodynamic interactions in active suspensions just as mobility matrices completely characterize hydrodynamic interactions in passive suspensions. The reduction in the dimensionality of the problem, from a three-dimensional partial differential equation to a two-dimensional integral equation, allows for dynamic simulations of hundreds of thousands of active particles on multi-core computational architectures. In our simulation of 104 active colloidal particle in a harmonic trap, we find that the necessary and sufficient ingredients to obtain steady-state convective currents, the so-called ‘self-assembled pump’, are (a) one

  8. Kinetic Monte Carlo simulations of thermally activated magnetization reversal in dual-layer Exchange Coupled Composite recording media

    NASA Astrophysics Data System (ADS)

    Plumer, M. L.; Almudallal, A. M.; Mercer, J. I.; Whitehead, J. P.; Fal, T. J.

    The kinetic Monte Carlo (KMC) method developed for thermally activated magnetic reversal processes in single-layer recording media has been extended to study dual-layer Exchange Coupled Composition (ECC) media used in current and next generations of disc drives. The attempt frequency is derived from the Langer formalism with the saddle point determined using a variant of Bellman Ford algorithm. Complication (such as stagnation) arising from coupled grains having metastable states are addressed. MH-hysteresis loops are calculated over a wide range of anisotropy ratios, sweep rates and inter-layer coupling parameter. Results are compared with standard micromagnetics at fast sweep rates and experimental results at slow sweep rates.

  9. Freshly frozen E18 rat cortical cells can generate functional neural networks after standard cryopreservation and thawing procedures.

    PubMed

    Quasthoff, Kim; Ferrea, Stefano; Fleischer, Wiebke; Theiss, Stephan; Schnitzler, Alfons; Dihné, Marcel; Walter, Janine

    2015-05-01

    Primary dissociated brain tissue from rodents is widely used in a variety of different scientific methods to investigate cellular processes in vitro. Often, for this purpose cell cultures need to be generated just on time, requiring extensive animal lab infrastructure. We show here that cryopreservation and thawing of dissociated tissue from rat cerebral cortex at embryonic day 18 is feasible without affecting its ability to form functional neuronal networks in vitro. Vitality of fresh and re-thawed cortical cells was comparable, assessed by CellTiter-Blue-assay, CytoTox-ONE assay, immunocytochemical characterization and in vitro neuronal network activity recordings on microelectrode arrays. These findings suggest that planning and execution of experiments might be considerably facilitated by using cryo-preserved neurons instead of acutely dissociated neural cultures due to fewer logistical issues with regard to animal breeding and pregnancy timed preparations.

  10. Surface modification of polypropylene non-woven fibers with TiO2 nanoparticles via layer-by-layer self assembly method: Preparation and photocatalytic activity.

    PubMed

    Pavasupree, Suttipan; Dubas, Stephan T; Rangkupan, Ratthapol

    2015-11-01

    Polypropylene (PP) meltblown fibers were coated with titanium dioxide (TiO2) nanoparticles using layer-by-layer (LbL) deposition technique. The fibers were first modified with 3 layers of poly(4-styrenesulfonic acid) (PSS) and poly(diallyl-dimethylammonium chloride) (PDADMAC) to improve the anchoring of the TiO2 nanoparticle clusters. PDADMAC, which is positively charged, was then used as counter polyelectrolyte in tandem with anionic TiO2 nanoparticles to construct TiO2/PDADMAC bilayer in the LbL fashion. The number of deposited TiO2/PDADMAC layers was varied from 1 to 7 bilayer, and could be used to adjust TiO2 loading. The LbL technique showed higher TiO2 loading efficiency than the impregnation approach. The modified fibers were tested for their photocatalytic activity against a model dye, Methylene Blue (MB). Results showed that the TiO2 modified fibers exhibited excellent photocatalytic activity efficiency similar to that of TiO2 powder dispersed in solution. The deposition of TiO2 3 bilayer on the PP substrate was sufficient to produce nanocomposite fibers that could bleach the MB solution in less than 4hr. TiO2-LbL constructions also preserved TiO2 adhesion on substrate surface after 1cycle of photocatalytic test. Successive photocatalytic test showed decline in MB reduction rate with loss of TiO2 particles from the substrate outer surface. However, even in the third cycle, the TiO2 modified fibers are still moderately effective as it could remove more than 95% of MB after 8hr of treatment. PMID:26574088

  11. Cryopreservation of Iberian pig spermatozoa. Comparison of different freezing extenders based on post-thaw sperm quality.

    PubMed

    De Mercado, Eduardo; Rodríguez, Ana; Gómez, Emilio; Sanz, Elena

    2010-03-01

    The aim of this study was to evaluate the cryoprotective effect of different freezing extenders against cryopreservation injuries on Iberian boar sperm. The sperm-rich fraction was collected and pooled from six sexually mature Iberian boars, and was frozen in different extenders containing glucose, lactose or fructose as sugar source and including Orvus ES Paste only in the freezing extender-2 (Glucose; Lactose and Fructose) or in both freezing extenders (Glucose2; Lactose2 and Fructose2). During the cryopreservation process, the supernatant was removed after the centrifugation step, then was extended with freezing extender-1 for the equilibration period and with freezing extender-2 immediately before freezing. Post-thaw sperm characteristics, such as plasma membrane integrity (SYBR-14/PI), mitochondrial function (Rhodamine 123) and acrosome integrity (NAR), were monitored. Overall sperm motility and the individual kinematic parameters of motile spermatozoa (assessed by the computer-aided sperm analysis system Sperm Class Analyzer [SCA]) were recorded in the different experimental treatments. Measurements were taken at 30 and 150 min post-thaw. The state of the acrosome after thawing did not show significant differences between the freezing extenders studied. Freezing-thawing caused a significant decrease (P<0.001) in plasma membrane integrity and in mitochondrial activity in the spermatozoa frozen with Orvus ES Paste in both freezing extenders. Furthermore, spermatozoa frozen with Orvus ES Paste in both freezing extenders exhibited lower (P<0.05) motility and kinematic parameters than those frozen in the absence of Orvus ES Paste in the first freezing extender. The spermatozoa frozen with the Lactose extender and with Orvus ES Paste only in the second freezing extender showed a better evolution of the motility and kinematic characteristics (P<0.05) over time. The deterioration in post-thaw sperm motility and kinematic parameters were concurrent with reduced sperm

  12. Unpinning the Open-Circuit Voltage in Organic Solar Cells through Tuning Ternary Blend Active Layer Morphology

    NASA Astrophysics Data System (ADS)

    Khlyabich, Petr; Thompson, Barry; Loo, Yueh-Lin

    2015-03-01

    The use of ternary, as opposed to binary, blends having complementary absorption in active layers of organic bulk heterojunction solar cells is a simple approach to increase overall light absorption. While the open-circuit voltage (Voc) of such solar cells have generally been shown to be pinned by the smallest energy level difference between the donor and acceptor constituents, there have been materials systems, that when incorporated into active layers of solar cells, exhibit composition dependent and tunable Voc. Herein, we demonstrate that this Voc tunability in ternary blend solar cells is correlated with the morphology of the active layer. Chemical compatibility between the constituents in the blend, as probed by grazing-incidence X-ray diffraction (GIXD) measurements, affords Voc tuning. The constituents need not ``co-crystallize'' limited miscibility between the constituents in the active layers of solar cells affords Voc tunability. Poor physical interactions between the constituent domains within the active layers, on the other hand, result in devices that exhibit an invariant Voc that is pinned by the smallest energy level difference between the donor(s) and the acceptor(s). Our morphological studies thus support the proposed alloying model that was put forth originally.

  13. Efficient solar photocatalytic activity of TiO2 coated nano-porous silicon by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Sampath, Sridhar; Maydannik, Philipp; Ivanova, Tatiana; Shestakova, Marina; Homola, Tomáš; Bryukvin, Anton; Sillanpää, Mika; Nagumothu, Rameshbabu; Alagan, Viswanathan

    2016-09-01

    In the present study, TiO2 coated nano-porous silicon (TiO2/PS) was prepared by atomic layer deposition (ALD) whereas porous silicon was prepared by stain etching method for efficient solar photocatalytic