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Sample records for aggregate distribution stability

  1. Stability and heavy metal distribution of soil aggregates affected by application of apatite, lime, and charcoal.

    PubMed

    Cui, Hongbiao; Ma, Kaiqiang; Fan, Yuchao; Peng, Xinhua; Mao, Jingdong; Zhou, Dongmei; Zhang, Zhongbin; Zhou, Jing

    2016-06-01

    Only a few studies have been reported on the stability and heavy metal distribution of soil aggregates after soil treatments to reduce the availability of heavy metals. In this study, apatite (22.3 t ha(-1)), lime (4.45 t ha(-1)), and charcoal (66.8 t ha(-1)) were applied to a heavy metal-contaminated soil for 4 years. The stability and heavy metal distribution of soil aggregates were investigated by dry and wet sieving. No significant change in the dry mean weight diameter was observed in any treatments. Compared with the control, three-amendment treatments significantly increased the wet mean weight diameter, but only charcoal treatment significantly increased the wet aggregate stability. The soil treatments increased the content of soil organic carbon, and the fraction 0.25-2 mm contained the highest content of soil organic carbon. Amendments' application slightly increased soil total Cu and Cd, but decreased the concentrations of CaCl2 -extractable Cu and Cd except for the fraction <0.053 mm. The fractions >2 and 0.25-2 mm contained the highest concentrations of CaCl2-extractable Cu and Cd, accounted for about 74.5-86.8 % of CaCl2-extractable Cu and Cd in soil. The results indicated that amendments' application increased the wet soil aggregate stability and decreased the available Cu and Cd. The distribution of available heavy metals in wet soil aggregates was not controlled by soil aggregate stability, but possibly by soil organic carbon.

  2. Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region

    NASA Astrophysics Data System (ADS)

    Tang, F. K.; Cui, M.; Lu, Q.; Liu, Y. G.; Guo, H. Y.; Zhou, J. X.

    2015-08-01

    Changes in soil utilization significantly affect aggregate stability and aggregate-associated soil organic carbon (SOC). A field investigation and indoor analysis were conducted in order to study the soil aggregate stability and organic carbon distribution in the water-stable aggregates (WSA) of the bare land (BL), grassland (GL), shrubland (SL), and woodland (WL) in a typical karst gorge region. The results indicated that the BL, GL, SL, and WL were dominated by particles with sizes > 5 mm under dry sieving treatment, and that the soil aggregate contents of various sizes decreased as the particle size decreased. In addition, the BL, GL, SL, and WL were predominantly comprised of WSA < 0.25 mm under wet sieving treatment, and that the WSA contents initially increased, then decreased, and then increased again as the particle size decreased. Furthermore, at a soil depth of 0-60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSA > 0.25 mm, MWD and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. The results of this study indicated that, as the SOC contents increased after vegetation restoration, the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. The total SOC and SOC associated in WSA of various sizes were the highest at a soil depth of 0-20 cm. In addition, the SOC contents of the WSA increased as the soil aggregate sizes decreased. The SOC contents of the WSA < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm, which ranged from 18.85 to 41.08 %, comprised the majority of the total aggregate SOC contents. The woodland and

  3. Dynamics of aggregate stability and soil organic C distribution as affected by climatic aggressiveness: a mesocosm approach

    NASA Astrophysics Data System (ADS)

    Pellegrini, Sergio; Elio Agnelli, Alessandro; Costanza Andrenelli, Maria; Barbetti, Roberto; Castelli, Fabio; Costantini, Edoardo A. C.; Lagomarsino, Alessandra; Pasqui, Massimiliano; Tomozeiu, Rodica; Razzaghi, Somayyeh; Vignozzi, Nadia

    2014-05-01

    In the framework of a research project aimed at evaluating the adaptation scenarios of the Italian agriculture to the current climate change, a mesocosm experiment under controlled conditions was set up for studying the dynamics of soil aggregate stability and organic C in different size fractions. Three alluvial loamy soils (BOV - Typic Haplustalfs coarse-loamy; CAS - Typic Haplustalfs fine-loamy; MED - Typic Hapludalfs fine-loamy) along a climatic gradient (from dryer to moister pedoclimatic conditions) in the river Po valley (northern Italy), under crop rotation for animal husbandry from more than 40 years, were selected. The Ap horizons (0-30cm) were taken and placed in 9 climatic chambers under controlled temperature and rainfall. Each soil was subjected to three different climate scenarios in terms of erosivity index obtained by combining Modified Fournier and Bagnouls-Gaussen indexes: i) typical (TYP), the median year of each site related to the 1961-1990 reference period; ii) maximum aggressive year (MAX) observed in the same period, and iii) the simulated climate (SIM), obtained by projections of climate change precipitation and temperature for the period 2021-2050 as provided by the IPCC-A1B emission scenario. In the climatic chambers the year climate was reduced to six months. The soils were analyzed for particle size distribution, aggregate stability by wet and dry sieving, and organic C content at the beginning and at the end of the trial. The soils showed different behaviour in terms of aggregate stability and dynamics of organic C in the diverse size fractions. The soils significantly differed in terms of initial mean weight diameter (MWD) (CAS>MED>BOV). A general reduction of MWD in all sites was observed at the end of the experiment, with the increase of the smallest aggregate fractions (0.250-0.05 mm). In particular, BOV showed the maximum decrease of the aggregate stability and MED the lowest. C distribution in aggregate fractions significantly

  4. Frozen-state storage stability of a monoclonal antibody: aggregation is impacted by freezing rate and solute distribution.

    PubMed

    Miller, Maria A; Rodrigues, Miguel A; Glass, Matthew A; Singh, Satish K; Johnston, Keith P; Maynard, Jennifer A

    2013-04-01

    Freezing of protein solutions perturbs protein conformation, potentially leading to aggregate formation during long-term storage in the frozen state. Macroscopic protein concentration profiles in small cylindrical vessels were determined for a monoclonal antibody frozen in a trehalose-based formulation for various freezing protocols. Slow cooling rates led to concentration differences between outer edges of the tank and the center, up to twice the initial concentration. Fast cooling rates resulted in much smaller differences in protein distribution, likely due to the formation of dendritic ice, which traps solutes in micropockets, limiting their transport by convection and diffusion. Analysis of protein stability after more than 6 months storage at either -10°C or -20°C [above glass transition temperature (T'g )] or -80°C (below T'g ) revealed that aggregation correlated with the cooling rate. Slow-cooled vessels stored above T'g exhibited increased aggregation with time. In contrast, fast-cooled vessels and those stored below T'g showed small to no increase in aggregation at any position. Rapid entrapment of protein in a solute matrix by fast freezing results in improved stability even when stored above T'g . © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1194-1208, 2013.

  5. Does thermophoresis reduce aggregate stability?

    NASA Astrophysics Data System (ADS)

    Sachs, Eyal; Sarah, Pariente

    2017-04-01

    Thermophoresis is mass flow driven by a thermal gradient. As a result of Seebeck effect and Soret effect, colloids can move from the hot to the cold region or vice versa, depending on the electrolyte composition and on the particle size. This migration of colloids can weaken aggregates. The effect of raindrop temperatures on runoff generation and erosion on clayey soil was investigated in sprinkling experiments with a laboratory rotating disk rain simulator. The experiments were applied to Rhodoxeralt (Terra Rossa) soil with two pre-prepared moisture contents: hygroscopic and field capacity. For each moisture content three rainfall temperatures were applied: 2, 20, and 35°C. Erosion was generally lower in the pre-wetted soil than in the dry soil (12.5 and 24.4 g m-2 per 40 mm of rain,respectively). Whereas there was no significant effect of raindrop temperature on the dry soil the soil that was pre-moistened to field capacity was affected by rainwater temperature: runoff and erosion were high when the temperature difference between rainfall and soil surface was high, sediment yields were 13.9, 5.2, and 18.3 g m-2 per 40 mm of rain, for rain temperature of 2, 20, and 35 °C, respectively. It is reasonable to conclude that thermophoresis caused by thermal gradients within the soil solution reduces the stability of aggregates and then increase the soil losses.

  6. Aggregate size distribution of the soil loss

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka; Józsa, Sándor; Szalai, Zoltán; Centeri, Csaba

    2016-04-01

    In agricultural areas the soil erosion and soil loss estimation is vital information in long-term planning. During the initial period of the erosion a part of the soil particles and aggregates get transportable and nutrients and organic matter could be transported due to the effect of water or wind. This preliminary phase was studied with laboratory-scale rainfall simulator. Developed surface crust and aggregate size composition of the runoff was examined in six different slope-roughness-moisture content combination of a Cambisol and a Regosol. The ratio of micro- and macro aggregates in the runoff indicate the stability of the aggregates and determine the transport capacity of the runoff. Both soil samples were taken from field where the water erosion is a potential hazard. During the experiment the whole amount of runoff and sediment was collected through sieve series to a bucket to separate the micro- and macro aggregates. In case of both samples the micro aggregates dominate in the runoff and the runoff rates are similar. Although the runoff of the Regosol - with dominant >1000μm macro aggregate content - contained almost nothing but <50μm sized micro aggregates. Meanwhile the runoff of the Cambisol - with more balanced micro and macro aggregate content - contained dominantly 50-250μm sized micro aggregates and in some case remarkable ratio 250-1000μm sized macro aggregates. This difference occurred because the samples are resistant against drop erosion differently. In case of both sample the selectivity of the erosion and substance matrix redistribution manifested in mineral crusts in the surface where the quartz deposited in place while the lighter organic matter transported with the sediment. The detachment of the aggregates and the redistribution of the particles highly effect on the aggregate composition of the runoff which is connected with the quality of the soil loss. So while the estimation of soil loss quantity is more or less is easy, measuring

  7. Seasonal variability of soil aggregate stability

    NASA Astrophysics Data System (ADS)

    Rohoskova, M.; Kodesova, R.; Jirku, V.; Zigova, A.; Kozak, J.

    2009-04-01

    Seasonal variability of soil properties measured in surface horizons of three soil types (Haplic Luvisol, Greyic Phaeozem, Haplic Cambisol) was studied in years 2007 and 2008. Undisturbed and disturbed soil samples were taken every month to evaluate field water content, bulk density, porosity, ration of gravitational and capillary pores, pHKCl and pHH2O, organic matter content and its quality, aggregate stability using WSA index. In addition, micromorphological features of soil aggregates were studied in thin soil sections that were made from undisturbed large soil aggregates. Results showed that soil aggregate stability depended on stage of the root zone development, soil management and climatic conditions. Larger aggregate stabilities and also larger ranges of measure values were obtained in the year 2007 then those measured in 2008. This was probably caused by lower precipitations and consequently lower soil water contents observed in 2007 than those measured in 2008. The highest aggregate stability was measured at the end of April in the years 2007 and 2008 in Haplic Luvisol and Greyic Phaeozem, and at the end of June in the year 2007 and at the beginning of June in 2008 in Haplic Cambisol. In all cases aggregate stability increased during the root growth and then gradually decreased due to summer rainfall events. Aggregate stability reflected aggregate structure and soil pore system development, which was documented on micromorphological images and evaluated using the ration of gravitational and capillary pores measured on the undisturbed sol samples. Acknowledgement: Authors acknowledge the financial support of the Grant Agency of the Czech Republic grant No. 526/08/0434, and the Ministry of Education, Youth and Sports grant No. MSM 6046070901.

  8. Quicklime application instantly increases soil aggregate stability

    NASA Astrophysics Data System (ADS)

    Keiblinger, Katharina M.; Bauer, Lisa M.; Deltedesco, Evi; Holawe, Franz; Unterfrauner, Hans; Zehetner, Franz; Peticzka, Robert

    2016-01-01

    Agricultural intensification, especially enhanced mechanisation of soil management, can lead to the deterioration of soil structure and to compaction. A possible amelioration strategy is the application of (structural) lime. In this study, we tested the effect of two different liming materials, ie limestone (CaCO3) and quicklime (CaO), on soil aggregate stability in a 3-month greenhouse pot experiment with three agricultural soils. The liming materials were applied in the form of pulverised additives at a rate of 2 000 kg ha-1. Our results show a significant and instantaneous increase of stable aggregates after quicklime application whereas no effects were observed for limestone. Quicklime application seems to improve aggregate stability more efficiently in soils with high clay content and cation exchange capacity. In conclusion, quicklime application may be a feasible strategy for rapid improvement of aggregate stability of fine textured agricultural soils.

  9. Organic carbon, water repellency and soil stability to slaking at aggregate and intra-aggregate scales

    NASA Astrophysics Data System (ADS)

    Jordán López, Antonio; García-Moreno, Jorge; Gordillo-Rivero, Ángel J.; Zavala, Lorena M.; Cerdà, Artemi; Alanís, Nancy; Jiménez-Compán, Elizabeth

    2015-04-01

    Water repellency (WR) is a property of some soils that inhibits or delays water infiltration between a few seconds and days or weeks. Inhibited or delayed infiltration contributes to ponding and increases runoff flow generation, often increasing soil erosion risk. In water-repellent soils, water infiltrates preferentially through cracks or macropores, causing irregular soil wetting patterns, the development of preferential flow paths and accelerated leaching of nutrients. Although low inputs of hydrophobic organic substances and high mineralization rates lead to low degrees of WR in cropped soils, it has been reported that conservative agricultural practices may induce soil WR. Although there are many studies at catchment, slope or plot scales very few studies have been carried out at particle or aggregate scale. Intra-aggregate heterogeneity of physical, biological and chemical properties conditions the transport of substances, microbial activity and biochemical processes, including changes in the amount, distribution and chemical properties of organic matter. Some authors have reported positive relationships between soil WR and aggregate stability, since it may delay the entry of water into aggregates, increase structural stability and contribute to reduce soil erosion risk. Organic C (OC) content, aggregate stability and WR are therefore strongly related parameters. In the case of agricultural soils, where both the type of management as crops can influence all these parameters, it is important to evaluate the interactions among them and their consequences. Studies focused on the intra-aggregate distribution of OC and WR are necessary to shed light on the soil processes at a detailed scale. It is extremely important to understand how the spatial distribution of OC in soil aggregates can protect against rapid water entry and help stabilize larger structural units or lead to preferential flow. The objectives of this research are to study [i] the OC content and the

  10. Stability of volcanic ash aggregates and break-up processes.

    PubMed

    Mueller, Sebastian B; Kueppers, Ulrich; Ametsbichler, Jonathan; Cimarelli, Corrado; Merrison, Jonathan P; Poret, Matthieu; Wadsworth, Fabian B; Dingwell, Donald B

    2017-08-07

    Numerical modeling of ash plume dispersal is an important tool for forecasting and mitigating potential hazards from volcanic ash erupted during explosive volcanism. Recent tephra dispersal models have been expanded to account for dynamic ash aggregation processes. However, there are very few studies on rates of disaggregation during transport. It follows that current models regard ash aggregation as irrevocable and may therefore overestimate aggregation-enhanced sedimentation. In this experimental study, we use industrial granulation techniques to artificially produce aggregates. We subject these to impact tests and evaluate their resistance to break-up processes. We find a dependence of aggregate stability on primary particle size distribution and solid particle binder concentration. We posit that our findings could be combined with eruption source parameters and implemented in future tephra dispersal models.

  11. Aggregate stability in soils cultivated with eucalyptus

    USDA-ARS?s Scientific Manuscript database

    Eucalyptus cultivation has increased in many Brazilian regions. In order to recommend good management practices, it is necessary to understand changes in soil properties where eucalyptus is planted. Aggregate stability analyses have proved to be a useful tool to measure soil effects caused by change...

  12. Impacts of Organic Farming on Soil Aggregate Stability

    NASA Astrophysics Data System (ADS)

    Petticrew, E. L.; Williams, N. D.

    2009-04-01

    Organic farming has expanded rapidly in the UK in recent years, amid increasing concerns for long term environmental and economic sustainability in agricultural systems. Much of the motivation for the shift away from conventional intensive agricultural practices has focused on soil nutrient management. Little attention has been directed toward the relative merits of organic farming for the physical structure of soils, despite aggregate structure and stability being of particular importance to soil erosion potential and sustainable soil quality. In this study, soil samples were collected from four arable sites within a small geographical area, in order to represent (1) an organic farm; (2) a conventional farm that only used artificial fertilizers; (3) a conventional farm that used artificial and cattle slurry fertilizers; and (4) a non-cultivated control site. Samples were analysed for living biomass and total organic content, bulk aggregate size and density distributions, bulk fragmentation fractal dimensions (which represent indices of soil erodibility), aggregate stability under simulated rainfall, and the stability of micro-aggregates that were mobilized in surface runoff generated by simulated rainfall. The relationships between the different soil properties were found to be complex. However, there were some significant differences between the samples, which were related to the different methods (or absence) of agriculture. The non-cultivated soil was determined to have the lowest erodibility and greatest aggregate stability. The conventional soil that was only fertilized by artificial means exhibited the lowest aggregate stability. There were few apparent differences between the organic soil and the conventional soil that received an input of organic fertilizer. The results of the physical analysis reflect the mining and replenishment of organic matter to each soil by the different management practices. This leads to the conclusion that the addition of organic

  13. A whole soil stability index (WSSI) for evaluating soil aggregation

    USDA-ARS?s Scientific Manuscript database

    Soil aggregate stability is an indicator of soil quality. However, there is no standard methodology for measuring soil aggregation or aggregate stability, particularly for determining a whole soil stability index. A whole soil stability index (WSSI) was developed here which combined data from dry ...

  14. Fire effects on soil aggregate stability: a review and synthesis

    NASA Astrophysics Data System (ADS)

    Mataix-Solera, J.; Cerdà, A.; Arcenegui, V.; Jordán, A.; Zavala, L. M.

    2012-04-01

    Fire can affect soil properties depending on a number of factors including fire severity and soil type. Aggregate stability (AS) refers to soil structure resilience in response to external mechanical forces. Many authors consider soil aggregation to be a parameter reflecting soil health, as it depends on chemical, physical and biological factors. The response of AS to forest fires is complex, since it depends on how fire has affected other related properties such as organic matter content, soil microbiology, water repellency and soil mineralogy. Opinions differ concerning the effect of fire on AS. Some authors have observed a decrease in AS in soils affected by intense wildfire or severe laboratory heating. However, others have reported increases. We provide an up to date review of the research on this topic and an analysis of the causes for the different effects observed. The implications for soil system functioning and for the hydrology of the affected areas are also discussed. Generally, low severity fires do not produce notable changes in AS, although in some cases an increase has been observed and attributed to increased water repellency. In contrast, high severity fires can induce important changes in this property, but with different effects depending on the type of soil affected. The patterns observed can vary from a disaggregation as a consequence of the organic matter destruction, to a strong aggregation if a recrystallization of some minerals such as Fe and Al oxyhydroxides occurs when they are present in sufficient quantities in the soil, after exposure to high temperatures. Because of the complexity of the different possible effects and reasons for the potential changes in the fire-affected soil aggregates, the inclusion of other parameters in the studies is necessary to understand the results. The suggested parameters to include in the examination of AS are: soil organic matter, microbial biomass, water repellency, texture, aggregate size distribution

  15. Effects of iron-aluminium oxides and organic carbon on aggregate stability of bauxite residues.

    PubMed

    Zhu, Feng; Li, Yubing; Xue, Shengguo; Hartley, William; Wu, Hao

    2016-05-01

    In order to successfully establish vegetation on bauxite residue, properties such as aggregate structure and stability require improvement. Spontaneous plant colonization on the deposits in Central China over the last 20 years has revealed that natural processes may improve the physical condition of bauxite residues. Samples from three different stacking ages were selected to determine aggregate formation and stability and its relationship with iron-aluminium oxides and organic carbon. The residue aggregate particles became coarser in both dry and wet sieving processes. The mean weight diameter (MWD) and geometry mean diameter (GMD) increased significantly, and the proportion of aggregate destruction (PAD) decreased. Natural stacking processes could increase aggregate stability and erosion resistant of bauxite residues. Free iron oxides and amorphous aluminium oxides were the major forms in bauxite residues, but there was no significant correlation between the iron-aluminium oxides and aggregate stability. Aromatic-C, alkanes-C, aliphatic-C and alkenes-C were the major functional groups present in the residues. With increasing stacking age, total organic carbon content and aggregate-associated organic carbon both increased. Alkanes-C, aliphatic-C and alkenes-C increased and were mainly distributed in macro-aggregates, whereas aromatic-C was mainly distributed in <0.05-mm aggregates. Organic carbon stability in micro-aggregates was higher than that in macro-aggregates and became more stable. Organic carbon contents in total residues, and within different aggregate sizes, were all negatively correlated with PAD. It indicated that organic materials had a more significant effect on macro-aggregate stability and the effects of iron-aluminium oxides maybe more important for stability of micro-aggregates.

  16. Soil aggregate stability within the morphologically diverse area

    NASA Astrophysics Data System (ADS)

    Jaksik, Ondrej; Kodesova, Radka; Kubis, Adam; Klement, Ales; Fer, Miroslav

    2013-04-01

    . The highest aggregate stability was measured on soils sampled at relatively flat upper parts, which were only slightly influenced by erosion processes. Higher stability was also obtained on base slope, where the sedimentation of previously eroded soil material occurred. Following correlations were obtained between different test results: R=0.911 for WSA and KV1, R=0.481 for WSA and KV2, R=0.700 for WSA and KV3. The statistical significant correlation was found between WSA index and SOM (R=0.403), WSA and pH_CaCl2 (R=-0.360), WSA and Mnd (R=0.408), WSA and Mno (R=0.355), KV1 and SOM (R=-0.377), KV1 and pH_CaCl2 (R=0.352), KV2 and CO3 (R=0.379), KV3 and pH_CaCl2 (R=0.376). We also found statistical significant correlation between WSA index and two terrain attributes (plan curvature R=-0.490, and total curvature R=-0.501). Acknowledgment: Authors acknowledge the financial support of the Ministry of Agriculture of the Czech Republic (QJ1230319). References Le Bissonnais Y. 1996. Aggregate stability and assessment of soil crustability and erodibility: Theory and methodology. Eur. J. Soil Sci. 47: 425-437. Nimmo J.R., Perkins K.S. 2002. Aggregate stability and size distribution, pp. 317-328. In: Dane J. H. & Topp G.C. (eds), Methods of Soil Analysis, Part 4 - Physical Methods. Soil Science Society of America, Inc. Madison, USA.

  17. Stability of zinc oxide nanofluids prepared with aggregated nanocrystalline powders.

    PubMed

    Leonard, J P; Chung, S J; Nettleship, I; Soong, Y; Martello, D V; Chyu, M K

    2008-12-01

    Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.

  18. Aggregation stability of titanium dioxide hydrosols

    SciTech Connect

    Grishchenko, L.I.; Medvedkova, N.G.; Nazarov, V.V.; Frolov, Yu.G.

    1994-03-01

    Titanium dioxide based ceramic membranes have recently attracted great interest because of their catalytic and photocatalytic abilities and other advantages typical of the ceramic membranes. For the preparation of the selective layer of the ultrafiltration ceramic TiO{sub 2}-based membranes, hydrosol, as a rule, is used as a starting material. The synthesis of a selective layer of the membrane with predetermined properties requires data on the colloid-chemical properties of these sols, which are rather scarce. The electrophoretic mobility and the size of the scattering centers of the TiO{sub 2} hydrosols obtained through titanium tetraethoxide hydrolysis were measured at 0.5-3.0 pH units. Coagulation thresholds were estimated in the presence of NaNO{sub 3} and Na{sub 2}SO{sub 4}. Under the conditions investigated, the aggregation stability was shown to be mainly dependent on the structural component of the disjoining pressure. The existence of a hydrated gel-layer on the surface of sol particles was proposed.

  19. A quantitative investigation of the effect of pore morphology on soil aggregate stability

    NASA Astrophysics Data System (ADS)

    Papadopoulos, A.

    2009-04-01

    Soil structure determines the operating environment for all physical, chemical and biological processes within the soil. Soil aggregate stability is an important measure for assessing soil structure quality. Non-destructive tomography techniques such as X-ray Computed Tomography (CT) offer great opportunities to quantitatively investigate the soil porous architecture which can provide important information for understanding soil processes and function in a multi-scale manner. For instance, the intra-aggregate pore space is of great importance for microbial activity, the sequestration of organic carbon and water flow. This paper investigates the effect of pore morphology on soil aggregate stability. Apparent porosity, pore size distribution, average pore size and fractal perimeter dimension (pore roughness) were measured from the images of the reconstructed 2-D image stacks. A new theoretical concept of soil aggregate stability is proposed. A strong relationship was observed between soil aggregate stability and pore morphological complexity.

  20. A Novel Method to Quantify Soil Aggregate Stability by Measuring Aggregate Bond Energies

    NASA Astrophysics Data System (ADS)

    Efrat, Rachel; Rawlins, Barry G.; Quinton, John N.; Watts, Chris W.; Whitmore, Andy P.

    2016-04-01

    Soil aggregate stability is a key indicator of soil quality because it controls physical, biological and chemical functions important in cultivated soils. Micro-aggregates are responsible for the long term sequestration of carbon in soil, therefore determine soils role in the carbon cycle. It is thus vital that techniques to measure aggregate stability are accurate, consistent and reliable, in order to appropriately manage and monitor soil quality, and to develop our understanding and estimates of soil as a carbon store to appropriately incorporate in carbon cycle models. Practices used to assess the stability of aggregates vary in sample preparation, operational technique and unit of results. They use proxies and lack quantification. Conflicting results are therefore drawn between projects that do not provide methodological or resultant comparability. Typical modern stability tests suspend aggregates in water and monitor fragmentation upon exposure to an un-quantified amount of ultrasonic energy, utilising a laser granulometer to measure the change in mean weight diameter. In this project a novel approach has been developed based on that of Zhu et al., (2009), to accurately quantify the stability of aggregates by specifically measuring their bond energies. The bond energies are measured operating a combination of calorimetry and a high powered ultrasonic probe, with computable output function. Temperature change during sonication is monitored by an array of probes which enables calculation of the energy spent heating the system (Ph). Our novel technique suspends aggregates in heavy liquid lithium heteropolytungstate, as opposed to water, to avoid exposing aggregates to an immeasurable disruptive energy source, due to cavitation, collisions and clay swelling. Mean weight diameter is measured by a laser granulometer to monitor aggregate breakdown after successive periods of calculated ultrasonic energy input (Pi), until complete dispersion is achieved and bond

  1. The effects of arbuscular mycorrhizal fungi on glomalin-related soil protein distribution, aggregate stability and their relationships with soil properties at different soil depths in lead-zinc contaminated area

    PubMed Central

    Huang, Li; Ban, Yihui; Tang, Ming

    2017-01-01

    Glomalin-related soil protein (GRSP), a widespread glycoprotein produced by arbuscular mycorrhizal fungi (AMF), is crucial for ecosystem functioning and ecological restoration. In the present study, an investigation was conducted to comprehensively analyze the effects of heavy metal (HM) contamination on AMF status, soil properties, aggregate distribution and stability, and their correlations at different soil depths (0–10, 10–20, 20–30, 30–40 cm). Our results showed that the mycorrhizal colonization (MC), hyphal length density (HLD), GRSP, soil organic matter (SOM) and soil organic carbon (SOC) were significantly inhibited by Pb compared to Zn at 0–20 cm soil depth, indicating that HM had significant inhibitory effects on AMF growth and soil properties, and that Pb exhibited greater toxicity than Zn at shallow layer of soil. Both the proportion of soil large macroaggregates (>2000 μm) and mean weight diameter (MWD) were positively correlated with GRSP, SOM and SOC at 0–20 cm soil depth (P < 0.05), proving the important contributions of GRSP, SOM and SOC for binding soil particles together into large macroaggregates and improving aggregate stability. Furthermore, MC and HLD had significantly positive correlation with GRSP, SOM and SOC, suggesting that AMF played an essential role in GRSP, SOM and SOC accumulation and subsequently influencing aggregate formation and particle-size distribution in HM polluted soils. Our study highlighted that the introduction of indigenous plant associated with AMF might be a successful biotechnological tool to assist the recovery of HM polluted soils, and that proper management practices should be developed to guarantee maximum benefits from plant-AMF symbiosis during ecological restoration. PMID:28771531

  2. Conformational stability as a design target to control protein aggregation.

    PubMed

    Costanzo, Joseph A; O'Brien, Christopher J; Tiller, Kathryn; Tamargo, Erin; Robinson, Anne Skaja; Roberts, Christopher J; Fernandez, Erik J

    2014-05-01

    Non-native protein aggregation is a prevalent problem occurring in many biotechnological manufacturing processes and can compromise the biological activity of the target molecule or induce an undesired immune response. Additionally, some non-native aggregation mechanisms lead to amyloid fibril formation, which can be associated with debilitating diseases. For natively folded proteins, partial or complete unfolding is often required to populate aggregation-prone conformational states, and therefore one proposed strategy to mitigate aggregation is to increase the free energy for unfolding (ΔGunf) prior to aggregation. A computational design approach was tested using human γD crystallin (γD-crys) as a model multi-domain protein. Two mutational strategies were tested for their ability to reduce/increase aggregation rates by increasing/decreasing ΔGunf: stabilizing the less stable domain and stabilizing the domain-domain interface. The computational protein design algorithm, RosettaDesign, was implemented to identify point variants. The results showed that although the predicted free energies were only weakly correlated with the experimental ΔGunf values, increased/decreased aggregation rates for γD-crys correlated reasonably well with decreases/increases in experimental ΔGunf, illustrating improved conformational stability as a possible design target to mitigate aggregation. However, the results also illustrate that conformational stability is not the sole design factor controlling aggregation rates of natively folded proteins.

  3. Aggregate stability of silicon dioxide hydrosols modified by molybdates

    SciTech Connect

    Valyukhov, A.A.; Frolov, Y.G.; Nazarov, V.V.

    1986-03-01

    Modification of the surface of silica hydrosol by molybdates changes the relationship between structural and electrostatic contributions to the disjoining pressure, which maintains the aggregate stability of the sol.

  4. Aggregation in ecosystem models and model stability

    NASA Astrophysics Data System (ADS)

    Giricheva, Evgeniya

    2015-05-01

    Using a multimodal approach to research ecosystems improves usage of available information on an object. This study presents several models of the Bering Sea ecosystem. The ecosystem is considered as a closed object, that is, the influence of the environment is not provided. We then add the links with the external medium in the models. The models differ in terms of the degree and method of grouping components. Our method is based on the differences in habitat and food source of groups, which allows us to determine the grouping of species with a greater effect on system dynamics. In particular, we determine whether benthic fish aggregation or pelagic fish aggregation can change the consumption structure of some groups of species, and consequently, the behavior of the entire model system.

  5. Aggregate stability in citrus plantations. The impact of drip irrigation

    NASA Astrophysics Data System (ADS)

    Cerdà, A.; Mataix-Solera, J.; Arcenegui, V.

    2012-04-01

    Soil aggregate stability is a key property for soil and water conservation, and a synthetic parameter to quantify the soil degradation. Aggregation is relevant in soils where vegetation cover is scarce (Cerdà, 1996). Most of the research carried out to determine the soil aggregate stability was done in forest soils (Mataix-Solera et al., 2011) and little is done on farms (Cerdà, 2000). The research have show the effect of vegetation cover on soil aggregate stability (Cerdà, 1998) but little is known when vegetation is scarce, rare or not found such it can be seeing in agriculture soils. Then, aggregation is the main factor to control the soil losses and to improve the water availability. Moreover, agriculture management can improve the soil aggregate characteristics and the first step in this direction should be to quantify the aggregate stability. There is no information about the aggregate stability of soils under citrus production, although the research did show that the soil losses in the farms with citrus plantations is very high (Cerdà et al., 2009), and that aggregation should play a key role as the soils are bare due to the widespread use of herbicides. From 2009 to 2011, samples were collected in summer and winter in a chemically managed farm in Montesa, Eastern Iberian Peninsula. Ten irrigated patches and ten non-irrigated patches were selected to compare the effect of the drip irrigation on the soil aggregate stability. The Ten Drop Impacts (TDI) and the Counting the number of drops (CND) tests were applied at 200 aggregates (10 samples x 10 aggregates x 2 sites) in winter and summer in 2009, 2010 and 2011. The results show that the irrigated patches had TDI values that ranged from 43 to 56 % and that the non-irrigated reached values of 41 to 54 %. The CND samples ranged from 29 to 38 drops in the non-irrigated patches to 32 to 42 drop-impacts in the irrigated soil patches. No trends were found from winter to summer during the three years time period

  6. Soil aggregation and slope stability related to soil density, root length, and mycorrhiza

    NASA Astrophysics Data System (ADS)

    Graf, Frank; Frei, Martin

    2013-04-01

    Eco-engineering measures combine the use of living plants and inert mechanical constructions to protect slopes against erosion and shallow mass movement. Whereas in geotechnical engineering several performance standards and guidelines for structural safety and serviceability of construction exist, there is a lack of comparable tools in the field of ecological restoration. Various indicators have been proposed, including the fractal dimension of soil particle size distribution, microbiological parameters, and soil aggregate stability. We present results of an soil aggregate stability investigation and compare them with literature data of the angle of internal friction ?' which is conventionally used in slope stability analysis and soil failure calculation. Aggregate stability tests were performed with samples of differently treated moraine, including soil at low (~15.5 kN/m³) and high (~19.0 kN/m³) dry unit weight, soil planted with Alnus incana (White Alder) as well as the combination of soil planted with alder and inoculated with the mycorrhizal fungus Melanogaster variegatus s.l. After a 20 weeks growth period in a greenhouse, a total of 100 samples was tested and evaluated. Positive correlations were found between the soil aggregate stability and the three variables dry unit weight, root length per soil volume, and degree of mycorrhization. Based on robust statistics it turned out that dry unit weight and mycorrhization degree were strongest correlated with soil aggregate stability. Compared to the non-inoculated control plants, mycorrhized White Alder produced significantly more roots and higher soil aggregate stability. Furthermore, the combined biological effect of plant roots and mycorrhizal mycelia on aggregate stability on soil with low density (~15.5 kN/m³) was comparable to the compaction effect of the pure soil from 15.5 to ~19.0 kN/m³. Literature data on the effect of vegetation on the angle of internal friction ?' of the same moraine showed

  7. Alteration of the aggregation stability of quantum dots by irradiation

    NASA Astrophysics Data System (ADS)

    Tsipotan, Aleksey; Aleksandrovsky, Aleksandr; Slabko, Vitaliy

    2017-09-01

    The influence of weak irradiation on the aggregation stability of quantum dots is considered. It was shown that under combined UV and visible light irradiation, a gradual increase in spontaneous aggregation takes place, testifying decrease in stabilizing potential barrier height. Thereby, the laser-induced controllable self-assembly of CdTe QDs is recommended to be performed over a time period between 80 and 100 min after the beginning of low intensity irradiation under conditions equivalent to those applied in this study.

  8. Improvements in Nanoparticle Tracking Analysis To Measure Particle Aggregation and Mass Distribution: A Case Study on Engineered Nanomaterial Stability in Incineration Landfill Leachates.

    PubMed

    Mehrabi, Kamyar; Nowack, Bernd; Arroyo Rojas Dasilva, Yadira; Mitrano, Denise M

    2017-05-16

    Numerous nanometrology techniques have been developed in recent years to determine the size, concentration, and a number of other characteristics of engineered nanomaterials (ENM) in environmental matrices. Among the many available techniques, nanoparticle tracking analysis (NTA) can measure individual particles to create a size distribution and measure the particle number. Therefore, we explore the possibility to use these data to calculate the particle mass distribution. Additionally, we further developed the NTA methodology to explore its suitability for analysis of ENM in complex matrices by measuring ENM agglomeration and sedimentation in municipal solid waste incineration landfill leachates over time. 100 nm Au ENM were spiked into DI H2O and synthetic and natural leachates. We present the possibility of measuring ENM in the presence of natural particles based on differences in particle refractivity indices, delineate the necessity of creating a calibration curve to adjust the given NTA particle number concentration, and determine the instruments linear range under different conditions. By measuring the particle size and the particle number distribution, we were able to calculate the ENM mass remaining in suspension. By combining these metrics together with transmission electron microscopy (TEM) analyses, we could assess the extent of both homo- and heteroagglomeration as well as particle sedimentation. Reporting both size and mass based metrics is common in atmospheric particle measurements, but now, the NTA can give us the possibility of applying the same approach also to aqueous samples.

  9. Decomposition-aggregation stability analysis of the spinning Skylab

    NASA Technical Reports Server (NTRS)

    Cuk, S. M.; Siljak, D. D.

    1974-01-01

    Stability of an 11-th order linear model of the spinning Skylab is determined by the decomposition-aggregation method based upon the comparison principle and vector Liapunov functions. To reduce the inherent conservativeness of the method an optimization problem is formulated and resolved producing the optimum comparison system. The system provides the best estimate of the stability region of the important structural parameter - asymmetry in the boom settings.

  10. Stability and structure of protein-polysaccharide coacervates in the presence of protein aggregates.

    PubMed

    Sanchez, Christian; Renard, Denis

    2002-08-21

    We have studied at pH 4.2 and three protein (Pr):polysaccharide (Pol) weight ratios (8:1, 2:1 and 1:1) the structure and stability of beta-lactoglobulin/acacia gum/water dispersions containing protein aggregates (BLG/AG/W) or free from aggregates (AF-BLG/AG/W). Phase diagrams were characteristic of complex coacervation. BLG/AG/W dispersions displayed a larger biphasic area than AF-BLG/AG/W dispersions, that moved towards the protein axis. It was concluded that protein aggregates affected complex coacervation both by entropic (size and molecular masses of aggregates) and enthalpic (surface properties of aggregates) effects. Laser light scattering measurements revealed that the particles diameter (d(43)) induced by demixing was controlled by protein aggregates in AF-BLG/AG/W dispersions. At 1 wt.% biopolymer concentration, particles were 15-20 times larger in AF-BLG/AG/W dispersions than in BLG/AG/W dispersions at (Pr:Pol) ratios of 2:1 or 1:1. Confocal scanning laser microscopy showed that AF-BLG/AG/W dispersions only contained spherical coacervates. BLG/AG/W dispersions contained both coacervates and aggregates coated with AG or/and BLG/AG coacervates. At a (Pr:Pol) ratio of 2:1 and 1:1, coacervates were vesicular or multivesicular. Coacervates were smaller in BLG/AG/W dispersions than in AF-BLG/AG/W dispersions. It was concluded that protein aggregates have the intrinsic ability to stabilize complex coacervates and could be used to design multifunctional delivery systems. This study showed that composite dispersions containing both protein aggregates embedded in protein-polysaccharide coacervates and free coacervates may be performed. In this respect, the design of protein aggregates with controlled size distribution and surface properties could open new possibilities both in the non-chemical control of coacervates stability and in the development of multifunctional delivery systems.

  11. Stability region maximization by decomposition-aggregation method. [Skylab stability

    NASA Technical Reports Server (NTRS)

    Siljak, D. D.; Cuk, S. M.

    1974-01-01

    This work is to improve the estimates of the stability regions by formulating and resolving a proper maximization problem. The solution of the problem provides the best estimate of the maximal value of the structural parameter and at the same time yields the optimum comparison system, which can be used to determine the degree of stability of the Skylab. The analysis procedure is completely computerized, resulting in a flexible and powerful tool for stability considerations of large-scale linear as well as nonlinear systems.

  12. Gravity as a factor of aggregative stability and coagulation.

    PubMed

    Dukhin, A S; Dukhin, S S; Goetz, P J

    2007-10-31

    Gravity is a potential factor of aggregative stability and/or coagulation for any heterogeneous system having a density contrast between the dispersed phase and its dispersion medium. However, gravity becomes comparable to other stability factors only when the particle size becomes large enough. Since the particle size may grow in time due to various other instabilities, even nano-systems may eventually become susceptible to gravity. There have been many attempts in the last century to incorporate gravity in the overall theory of aggregative stability, but the relevant papers are scattered over a wide variety of journals, some of which are very obscure. Reviews on this subject in modern handbooks are scarce and inadequate. No review describes the role of gravity at all three levels introduced by DLVO theory for characterizing aggregative stability, namely: particle pair interaction, collision frequency and population balance equation. Furthermore, the modern tendency towards numerical solutions overshadows existing analytical solutions. We present a consistent review at each DLVO level. First we describe the role of gravity in particle pair interactions, including both available analytical solutions as well as numerical stability diagrams. Next we discuss a number of works on collision frequency, including works for both charged and non-charged particles. Finally, we present analytical solutions of the population balance equation that takes gravity into account and then compare these analytical solutions with numerical solutions. In addition to the traditional aggregate model we also discuss work on a fractal model and its relevance to gravity controlled stability. Finally, we discuss many experimental works and their relationship to particular theoretical predictions.

  13. Organic carbon, water repellency and soil stability to slaking under different crops and managements: a case study at aggregate and intra-aggregate scales

    NASA Astrophysics Data System (ADS)

    Jordán, A.; García-Moreno, J.; Gordillo-Rivero, Á. J.; Zavala, L. M.; Cerdà, A.

    2014-08-01

    This research studies the distribution of organic C and intensity of water repellency in soil aggregates with different size and in the interior of aggregates from Mediterranean soils under different crops (apricot, citrus and wheat) and management (conventional tilling and no tilling/mulching). For this, undisturbed aggregates were sampled and carefully divided in size fractions (0.25-0.5, 0.5-1, 1-2, 2-5, 5-10 and 10-15 mm) or peeled to obtain separated aggregate layers (exterior, transitional and interior). Organic C content in the fine earth fraction of soils under different crops did not show important variations, although it increased significantly from conventionally tilled to mulched soils. The distribution of organic C content in aggregates with different size varied among soils under different crops, generally increasing with decreasing size. At the intra-aggregate level, organic C concentrated preferably in the exterior layer of aggregates from conventionally tilled soils, probably because of recent organic inputs or leachates. In the case of mulched soils, higher concentrations were observed, but no significant differences among aggregate regions were found. The intensity of water repellency, determined by the ethanol method, did not show great variations among crops, but increased significantly from conventionally tilled to mulched soils. Coarser aggregates were generally wettable, while finer aggregates showed slight water repellency. Regardless of variations in the distribution of organic C in aggregate layers from conventionally tilled soils, great or significant differences in the distribution of water repellency at the intra-aggregate level were not found in any case. Finally, the intensity of water repellency was much more important than the concentration of organic C in the stability to slaking of aggregates.

  14. Stabilized fiber-reinforced pavement base course with recycled aggregate

    NASA Astrophysics Data System (ADS)

    Sobhan, Khaled

    This study evaluates the benefits to be gained by using a composite highway base course material consisting of recycled crushed concrete aggregate, portland cement, fly ash, and a modest amount of reinforcing fibers. The primary objectives of this research were to (a) quantify the improvement that is obtained by adding fibers to a lean concrete composite (made from recycled aggregate and low quantities of Portland cement and/or fly ash), (b) evaluate the mechanical behavior of such a composite base course material under both static and repeated loads, and (c) utilize the laboratory-determined properties with a mechanistic design method to assess the potential advantages. The split tensile strength of a stabilized recycled aggregate base course material was found to be exponentially related to the compacted dry density of the mix. A lean mix containing 4% cement and 4% fly ash (by weight) develops sufficient unconfined compressive, split tensile, and flexural strengths to be used as a high quality stabilized base course. The addition of 4% (by weight) of hooked-end steel fibers significantly enhances the post-peak load-deformation response of the composite in both indirect tension and static flexure. The flexural fatigue behavior of the 4% cement-4% fly ash mix is comparable to all commonly used stabilized materials, including regular concrete; the inclusion of 4% hooked-end fibers to this mix significantly improves its resistance to fatigue failure. The resilient moduli of stabilized recycled aggregate in flexure are comparable to the values obtained for traditional soil-cement mixes. In general, the fibers are effective in retarding the rate of fatigue damage accumulation, which is quantified in terms of a damage index defined by an energy-based approach. The thickness design curves for a stabilized recycled aggregate base course, as developed by using an elastic layer approach, is shown to be in close agreement with a theoretical model (based on Westergaard

  15. Soil aggregate stability: comparison of field and laboratory data

    NASA Astrophysics Data System (ADS)

    Graf, Frank

    2014-05-01

    Eco-engineering first and foremost, aims at stabilising soil and slopes in order to protect humans and infrastructure from potential damages caused by soil failure, usually due to heavy rainstorms. Whereas the technical constructions are well-defined and their protective effects in general calculable, this is rarely the case for biological measures. Furthermore, unlike engineering structures which are immediately useable and operative after their completion, the effects of plants are developing as a function of time. Within this scope, soil aggregation processes play a decisive role in in the re-colonisation process and the re-establishing of a protective vegetation cover. The strength of soil aggregates is not only critical to the stability of slopes but plays a key role in ecosystem functioning in general as it affects water, gas and nutrient fluxes and storage influencing the activity and growth of living organisms. Not by chance, therefore, soil aggregate stability has been proposed as an indicator reflecting multiple aspects allowing extensive information on ecosystem status to be gathered in a relatively short time, in particular in respect of protecting slopes from erosion and shallow mass movements. Various methods and approaches have been used to quantify soil aggregate stability but the lack of standardisation complicates the comparison of different investigations. From this perspective we investigated soil samples from the field as well as samples artificially prepared in the laboratory using the same soil material and testing procedure. The field samples were collected at two sites in the landslide area of Dallenwil-Wirzweli in Central Switzerland, once in a gully recently affected by erosion and landslide processes bare of vegetation (control site) and once in a re-stabilised gully with 25 year old eco-engineering measures dominated by Alnus incana (re-vegetated site). The laboratory samples were prepared with the soil from the control site. Two

  16. Aggregation and colloidal stability of fine-particle coal suspensions

    SciTech Connect

    Schroeder, P.R.; Rubin, A.J.

    1984-01-01

    The aggregation and colloidal stability of colloidal coal suspensions in the presence of varying concentrations of hydrogen ions, neutral salts, and aluminum sulfate were investigated. Critical concentration and critical pH values for coagulation and stabilization were determined from turbidity changes during settling following aggregation. Two colloidal suspensions of a bituminous coal representing stability extremes due to oxidation were compared. In the absence of other coagulants, vigorous oxidation lowered the isoelectric point of the coal sol from pH 5.1 to pH 1.1 and the pH for stabilization from 7.5 to 2.6. The coagulation of the suspensions followed the Schulze-Hardy rule as hydrophobic sols although the oxidized coal sol was slightly less sensitive to neutral salts. The entire log aluminum sulfate concentration-pH stability limit diagram for the oxidized coal sol was established. The boundaries of settling of the coal in the presence of aluminum sulfate were similar to other hydrophobic sols except for small differences in alkaline solution. Regions of ionic coagulation, rapid coagulation due to enmeshment in aluminum hydroxide precipitate, and restabilization were also observed and delineated.

  17. Aggregate stability and water retention near saturation characteristics as affected by soil texture, aggregate size and polyacrylamide application

    USDA-ARS?s Scientific Manuscript database

    Understanding the effects of soil intrinsic properties and extrinsic conditions on aggregate stability is essential for the development of effective soil and water conservation practices. Our objective was to evaluate the combined role of soil texture, aggregate size and application of a stabilizing...

  18. A novel method for soil aggregate stability measurement by laser granulometry with sonication

    NASA Astrophysics Data System (ADS)

    Rawlins, B. G.; Lark, R. M.; Wragg, J.

    2012-04-01

    Regulatory authorities need to establish rapid, cost-effective methods to measure soil physical indicators - such as aggregate stability - which can be applied to large numbers of soil samples to detect changes of soil quality through monitoring. Limitations of sieve-based methods to measure the stability of soil macro-aggregates include: i) the mass of stable aggregates is measured, only for a few, discrete sieve/size fractions, ii) no account is taken of the fundamental particle size distribution of the sub-sampled material, and iii) they are labour intensive. These limitations could be overcome by measurements with a Laser Granulometer (LG) instrument, but this technology has not been widely applied to the quantification of aggregate stability of soils. We present a novel method to quantify macro-aggregate (1-2 mm) stability. We measure the difference between the mean weight diameter (MWD; μm) of aggregates that are stable in circulating water of low ionic strength, and the MWD of the fundamental particles of the soil to which these aggregates are reduced by sonication. The suspension is circulated rapidly through a LG analytical cell from a connected vessel for ten seconds; during this period hydrodynamic forces associated with the circulating water lead to the destruction of unstable aggregates. The MWD of stable aggregates is then measured by LG. In the next step, the aggregates - which are kept in the vessel at a minimal water circulation speed - are subject to sonication (18W for ten minutes) so the vast majority of the sample is broken down into its fundamental particles. The suspension is then recirculated rapidly through the LG and the MWD measured again. We refer to the difference between these two measurements as disaggregation reduction (DR) - the reduction in MWD on disaggregation by sonication. Soil types with more stable aggregates have larger values of DR. The stable aggregates - which are resistant to both slaking and mechanical breakdown by the

  19. Heparin binding confers prion stability and impairs its aggregation.

    PubMed

    Vieira, Tuane C R G; Cordeiro, Yraima; Caughey, Byron; Silva, Jerson L

    2014-06-01

    The conversion of the prion protein (PrP) into scrapie PrP (PrP(Sc)) is a central event in prion diseases. Several molecules work as cofactors in the conversion process, including glycosaminoglycans (GAGs). GAGs exhibit a paradoxical effect, as they convert PrP into protease-resistant PrP (PrP-res) but also exert protective activity. We compared the stability and aggregation propensity of PrP and the heparin-PrP complex through the application of different in vitro aggregation approaches, including real-time quaking-induced conversion (RT-QuIC). Transmissible spongiform encephalopathy-associated forms from mouse and hamster brain homogenates were used to seed RT-QuIC-induced fibrillization. In our study, interaction between heparin and cellular PrP (PrP(C)) increased thermal PrP stability, leading to an 8-fold decrease in temperature-induced aggregation. The interaction of low-molecular-weight heparin (LMWHep) with the PrP N- or C-terminal domain affected not only the extent of PrP fibrillization but also its kinetics, lowering the reaction rate constant from 1.04 to 0.29 s(-1) and increasing the lag phase from 12 to 19 h in RT-QuIC experiments. Our findings explain the protective effect of heparin in different models of prion and prion-like neurodegenerative diseases and establish the groundwork for the development of therapeutic strategies based on GAGs. © FASEB.

  20. Reduction in soil aggregate size distribution due to wind erosion

    NASA Astrophysics Data System (ADS)

    Swet, Nitzan; Katra, Itzhak

    2017-04-01

    Soil erosion process by wind causes emission of fine soil particles, and thus alters the topsoil's properties, fertility, and erodibility. Topsoil resistance to erosion depends on its physicochemical properties, especially on the soil aggregation. Although the key role of aggregates in soil erodibility, quantitative information on the relations between soil aggregate size distribution (ASD) and erosion is still lucking. This study focuses on ASD analyses before and after soil erosion by wind. Wind tunnel experiments and soil analyses were conducted on semiarid loess topsoils with different initial conditions of aggregation. The results show that in all initial soil conditions saltation of sand particles caused the breakdown of macro-aggregates > 500 µm, resulting in increase of micro-aggregates (63-250 µm). The micro-aggregate production increases with the wind shear velocity (up to 0.61 m s-1) for soils with available macro-aggregates. The findings highlight dynamics in soil aggregation in response to erosion process, and therefore the significance of ASD in quantifying soil degradation and soil loss potential.

  1. Microelectrode Measurements of the Activity Distribution in Nitrifying Bacterial Aggregates

    PubMed Central

    de Beer, D.; van den Heuvel, J. C.; Ottengraf, S. P. P.

    1993-01-01

    Microelectrodes for ammonium, oxygen, nitrate, and pH were used to study nitrifying aggregates grown in a fluidized-bed reactor. Local reactant fluxes and distribution of microbial activity could be determined from the microprofiles. The interfacial fluxes of the reactants closely reflected the stoichiometry of bacterial nitrification. Both ammonium consumption and nitrate production were localized in the outer shells, with a thickness of approximately 100 to 120 μm, of the aggregates. Under conditions in which ammonium and oxygen penetrated the whole aggregate, nitrification was restricted to this zone; oxygen was consumed in the central parts of the aggregates as well, probably because of oxidation of dead biomass. A sudden increase of the oxygen concentration to saturation (pure oxygen) was inhibitory to nitrification. The pH profiles showed acidification in the aggregates, but not to an inhibitory level. The distribution of activity was determined by the penetration depth of oxygen during aggregate development in the reactor. Mass transfer was significantly limited by the boundary layer surrounding the aggregates. Microelectrode measurements showed that the thickness of this layer was correlated with the diffusion coefficient of the species. Determination of the distribution of nitrifying activity required the use of ammonium or nitrate microelectrodes, whereas the use of oxygen microelectrodes alone would lead to erroneous results. Images PMID:16348875

  2. Aggregation behaviour and stability of maize germ oil body suspension.

    PubMed

    Sukhotu, Rujira; Shi, Xiaodi; Hu, Qi; Nishinari, Katsuyoshi; Fang, Yapeng; Guo, Shuntang

    2014-12-01

    To utilize maize germ oil bodies as ingredients in the food industry, zeta potential determination and particle diameter analysis were used in this study as indicators of the stability of maize germ oil body suspensions. The stability and aggregation properties of maize germ oil body suspensions were studied at different pH and ion strength conditions, and different thermal treatments. Zeta potential measurement, mean particle size determination, and confocal laser scanning microscopy were also performed. The zeta potential and mean particle diameter of the oil bodies were easily affected by salt (7.05 mV and d32=1.43 μm at 100mM NaCl) and pH (23.30, 15.00, -16.43 mV and d32=1.02, 2.55, and 0.95 μm at pH 3, pH 4, and pH 7, respectively). Results demonstrated that aggregation and instability of the oil bodies were promoted by high salt concentrations and acidic pH but not by heating. The association between oil bodies and surfactant properties resulted in the disruption of hydrophobic interactions among oil body surface proteins because of the smaller mean particle sizes and the reduced negative charges (-75.73 mV and d32=0.46 μm at pH 3). Thus, the oil body aggregation behavior and stability of proteins are based on hydrophobic interactions present on the surface of the oil bodies. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Stability of a Random Walk Model for Fruiting Body Aggregation in M. xanthus

    NASA Astrophysics Data System (ADS)

    McKenzie-Smith, G. C.; Schüttler, H. B.; Cotter, C.; Shimkets, L.

    2015-03-01

    Myxococcus xanthus exhibits the social starvation behavior of aggregation into a fruiting body containing myxospores able to survive harsh conditions. During fruiting body aggregation, individual bacteria follow random walk paths determined by randomly selected runtimes, turning angles, and speeds. We have simulated this behavior in terms of a continuous-time random walk (CTRW) model, re-formulated as a system of integral equations, describing the angle-resolved cell density, R(r, t, θ), at position r and cell orientation angle θ at time t, and angle-integrated ambient cell density ρ(r, t). By way of a linear stability analysis, we investigated whether a uniform cell density R0 will be unstable for a small non-uniform density perturbation δR(r, t, θ). Such instability indicates aggregate formation, whereas stability indicates absence of aggregation. We show that a broadening of CTRW distributions of the random speed and/or random runtimes strongly favors aggregation. We also show that, in the limit of slowly-varying (long-wavelength) density perturbations, the time-dependent linear density response can be approximated by a drift-diffusion model for which we calculate diffusion and drift coefficients as functions of the CTRW model parameters. Funded by the Fungal Genomics and Computational Biology REU at UGA.

  4. Soil aggregate stability as affected by clay mineralogy and polyacrylamide addition

    USDA-ARS?s Scientific Manuscript database

    The addition of polyacrylamide (PAM) to soil leads to stabilization of existing aggregates and improved bonding between, and aggregation of adjacent soil particles However, the dependence of PAM efficacy as an aggregate stabilizing agent on soil-clay mineralogy has not been studied. Sixteen soil sam...

  5. Settling Velocity, Aggregate Stability, and Interrill Erodibility of Soils Varying in Clay Mineralogy

    USDA-ARS?s Scientific Manuscript database

    The relation of soil structural stability with soil erodibility depends on the mechanisms of aggregate disruption of different aggregate sizes and the measurement technique. In this study, we evaluated the relationship between settling velocity and stability of aggregates of different sizes, and int...

  6. Polyacrylamide effects on aggregate and structure stability of soils with different clay mineralogy

    USDA-ARS?s Scientific Manuscript database

    Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples...

  7. Role of arginine in the stabilization of proteins against aggregation.

    PubMed

    Baynes, Brian M; Wang, Daniel I C; Trout, Bernhardt L

    2005-03-29

    The amino acid arginine is frequently used as a solution additive to stabilize proteins against aggregation, especially in the process of protein refolding. Despite arginine's prevalence, the mechanism by which it stabilizes proteins is not presently understood. We propose that arginine deters aggregation by slowing protein-protein association reactions, with only a small concomitant effect on protein folding. The associated rate effect was observed experimentally in association of globular proteins (insulin and a monoclonal anti-insulin) and in refolding of carbonic anhydrase. We suggest that this effect arises because arginine is preferentially excluded from protein-protein encounter complexes but not from dissociated protein molecules. Such an effect is predicted by our gap effect theory [Baynes and Trout (2004) Biophys. J. 87, 1631] for "neutral crowder" additives such as arginine which are significantly larger than water but have only a small effect on the free energies of isolated protein molecules. The effect of arginine on refolding of carbonic anhydrase was also shown to be consistent with this hypothesis.

  8. Fire induced changes in aggregate stability: the interacting effects of soil heating and ash leachate

    NASA Astrophysics Data System (ADS)

    Balfour, V.; Hatley, D.; Woods, S.

    2011-12-01

    Increases in runoff and erosion after wildfires are typically attributed to the combined effects of the loss of ground cover, water repellency and surface sealing. Surface sealing in burned areas is caused by raindrop compaction of mineral soils (structural seal formation), the clogging of soil pores by fine soil and ash, or the formation of low conductivity ash crusts (depositional seal formation). Structural sealing is more likely to occur if the fire reduces the aggregate stability of the mineral soil. Soil heating tends to reduce aggregate stability by combusting soil organic matter. Effects due to soil heating may be amplified or reduced by interactions between soil clays and ash leachate, but these effects are poorly understood. We are investigating the interacting effects of soil heating and exposure to ash leachate on the stability of soil aggregates in burned areas. During the 2011 fire season in the Rocky Mountains we collected soil samples (~1000g) from unburned areas adjacent to three recent wildfires. Soils were obtained from areas with sharply contrasting parent materials, leading to differences in the soil mineralogy. High severity ash was collected from within the burned areas. Each soil sample was divided into 6 subsamples with the first subsample acting as a control. The remaining five subsamples were heated to 100, 200, 300, 500, and 700C respectively. After heating, each subsample was split in two. Ash leachate was added to one half and DI water was added to the other half. The ash leachate was prepared by mixing 10 g of ash with 1000 mL of water in accordance with previous studies. All samples were then air dried and analyzed for porosity, bulk density, aggregate size distribution, aggregate stability and water repellency. Initial results suggest that there is an interacting effect of soil heating and exposure to ash leachate on the stability of soil aggregates, but the effect varies depending on the mineralogy of soil clays and the type of

  9. Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces

    PubMed Central

    Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

    2016-01-01

    The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate

  10. Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces.

    PubMed

    Wei, Yujie; Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

    2016-01-01

    The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate

  11. Aggregate distribution and associated organic carbon influenced by cover crops

    NASA Astrophysics Data System (ADS)

    Barquero, Irene; García-González, Irene; Benito, Marta; Gabriel, Jose Luis; Quemada, Miguel; Hontoria, Chiquinquirá

    2013-04-01

    Replacing fallow with cover crops during the non-cropping period seems to be a good alternative to diminish soil degradation by enhancing soil aggregation and increasing organic carbon. The aim of this study was to analyze the effect of replacing fallow by different winter cover crops (CC) on the aggregate distribution and C associated of an Haplic Calcisol. The study area was located in Central Spain, under semi-arid Mediterranean climate. A 4-year field trial was conducted using Barley (Hordeum vulgare L.) and Vetch (Vicia sativa L.) as CC during the intercropping period of maize (Zea mays L.) under irrigation. All treatments were equally irrigated and fertilized. Maize was directly sown over CC residues previously killed in early spring. Composite samples were collected at 0-5 and 5-20 cm depths in each treatment on autumn of 2010. Soil samples were separated by wet sieving into four aggregate-size classes: large macroaggregates ( >2000 µm); small macroaggregates (250-2000 µm); microaggregates (53-250 µm); and < 53 µm (silt + clay size). Organic carbon associated to each aggregate-size class was measured by Walkley-Black Method. Our preliminary results showed that the aggregate-size distribution was dominated by microaggregates (48-53%) and the <53 µm fraction (40-44%) resulting in a low mean weight diameter (MWD). Both cover crops increased aggregate size resulting in a higher MWD (0.28 mm) in comparison with fallow (0.20 mm) in the 0-5 cm layer. Barley showed a higher MWD than fallow also in 5-20 cm layer. Organic carbon concentrations in aggregate-size classes at top layer followed the order: large macroaggregates > small macroaggregates > microaggregates > silt + clay size. Treatments did not influence C concentration in aggregate-size classes. In conclusion, cover crops improved soil structure increasing the proportion of macroaggregates and MWD being Barley more effective than Vetch at subsurface layer.

  12. Visualizing Big Data Outliers through Distributed Aggregation.

    PubMed

    Wilkinson, Leland

    2017-08-29

    Visualizing outliers in massive datasets requires statistical pre-processing in order to reduce the scale of the problem to a size amenable to rendering systems like D3, Plotly or analytic systems like R or SAS. This paper presents a new algorithm, called hdoutliers, for detecting multidimensional outliers. It is unique for a) dealing with a mixture of categorical and continuous variables, b) dealing with big-p (many columns of data), c) dealing with big-n (many rows of data), d) dealing with outliers that mask other outliers, and e) dealing consistently with unidimensional and multidimensional datasets. Unlike ad hoc methods found in many machine learning papers, hdoutliers is based on a distributional model that allows outliers to be tagged with a probability. This critical feature reduces the likelihood of false discoveries.

  13. Soil aggregate stability as an indicator for eco-engineering effectiveness?

    NASA Astrophysics Data System (ADS)

    Graf, Frank

    2015-04-01

    Eco-engineering aims at stabilising soil and slopes by applying technical and biological measures. Engineering structures are commonly well defined, immediately usable and operative, and their stability effects quantifiable and verifiable. Differently, the use of plants requires more restrictive boundary conditions and the protection potential is rarely easily calculable and develop-ing as a function of growth rate. Although the use of vegetation is widely appreciated and their stabilising effect recognised, there is an increasing demand on sound facts on its efficiency, in particular, in relation to time. Conclusively, a certain necessity has been recognised to monitor, assess and quantify the effectiveness of ecological restora-tion measures in order to facilitate the transfer of technology and knowledge. Recent theoretical models emphasize the im-portance of taking an integrated monitoring approach that considers multiple variables. However, limited financial and time resources often prevent such comprehensive assessments. A solution to this problem may be to use integrated indicators that reflect multiple aspects and, therefore, allow extensive information on ecosystem status to be gathered in a relatively short time. Among various other indicators, such as fractal dimension of soil particle size distribution or microbiological parameters, soil aggregate stability seems the most appropriate indicator with regard to protecting slopes from superficial soil failure as it is critical to both plant growth and soil structure. Soil aggregation processes play a crucial role in re-establishing soil structure and function and, conclusively, for successful and sustainable re-colonisation. Whereas the key role of soil aggregate stability in ecosystem functioning is well known concerning water, gas, and nutrient fluxes, only limited information is available with regard to soil mechanical and geotechnical aspects. Correspondingly, in the last couple of years several studies

  14. Aggregate stability in mine residues after reclamation with biochar

    NASA Astrophysics Data System (ADS)

    Moreno-Barriga, Fabián; Díaz, Vicente; Acosta, José; Faz, Ángel; Zornoza, Raúl

    2016-04-01

    This study aims to assess how the addition of biochar and marble waste to acidic mine residues affected aggregate stability (AS) and contributed to the improvement of soil texture. For this purpose, a lab incubation was carried out for 90 days. Biochars derived from pig manure (PM), crop residues (CR) and municipal solid waste (MSW) were added to the soil at a rate of 20 g kg-1. The marble waste (MW) was added at a rate of 200 g kg-1, with the aim of increasing pH from 3 to 8 (pH of the native soils of the area). Biochars and MW were applied independently and combined. A control treatment was used without application of amendments. The evolution of AS was periodically monitored at 2, 4, 7, 15, 30 and 90 days by the method of artificial rainfall. Results showed, at the end of the incubation, that the addition of MW alone did not significantly increased AS with comparison to CT (30%). However, the biochar, alone or together with MW, significantly increased AS, the treatment receiving CR derived biochar being the one with the highest values (46%). Increments in AS were significant from the day 30 of incubation. AS showed a significant correlation with the total organic carbon content, but was not correlated with organic carbon fractions (soluble, labile, recalcitrant), inorganic carbon, microbial biomass carbon, enzyme activities, exchangeable fraction of heavy metals (As, Cd, Cu, Pb, Zn), pH, electrical conductivity nor greenhouse gas emissions (NO₂, CH₄). Thus, the application of biochar (alone or in combination with MW as a source of calcium carbonate) significantly increased the formation of stable aggregates in former acidic mine residues, favoring the development of soil structure, essential to create a soil from residues. It seems that the total content of organic carbon is directly controlling aggregation, rather than other labile organic sources. Moreover, pH, salinity or the presence of exchangeable metals did not seem to affect soil aggregation

  15. Effects of ionic strength and sugars on the aggregation propensity of monoclonal antibodies: influence of colloidal and conformational stabilities.

    PubMed

    Saito, Shuntaro; Hasegawa, Jun; Kobayashi, Naoki; Tomitsuka, Toshiaki; Uchiyama, Susumu; Fukui, Kiichi

    2013-05-01

    To develop a general strategy for optimizing monoclonal antibody (MAb) formulations. Colloidal stabilities of four representative MAbs solutions were assessed based on the second virial coefficient (B 2) at 20°C and 40°C, and net charges at different NaCl concentrations, and/or in the presence of sugars. Conformational stabilities were evaluated from the unfolding temperatures. The aggregation propensities were determined at 40°C and after freeze-thawing. The electrostatic potential of antibody surfaces was simulated for the development of rational formulations. Similar B 2 values were obtained at 20°C and 40°C, implying little dependence on temperature. B 2 correlated quantitatively with aggregation propensities at 40°C. The net charge partly correlated with colloidal stability. Salts stabilized or destabilized MAbs, depending on repulsive or attractive interactions. Sugars improved the aggregation propensity under freeze-thaw stress through improved conformational stability. Uneven and even distributions of potential surfaces were attributed to attractive and strong repulsive electrostatic interactions. Assessment of colloidal stability at the lowest ionic strength is particularly effective for the development of formulations. If necessary, salts are added to enhance the colloidal stability. Sugars further improved aggregation propensities by enhancing conformational stability. These behaviors are rationally predictable according to the surface potentials of MAbs.

  16. Stability of Soil Carbon Fractions - from molecules to aggregates

    NASA Astrophysics Data System (ADS)

    Mueller, C. W.; Mueller, K. E.; Freeman, K. H.; Eissenstat, D.; Kögel-Knabner, I.

    2009-12-01

    The turnover of soil organic matter (SOM) is controlled both by its chemical composition, its spatial bioavailability and the association with the mineral phase. Separation by physical fractionation of bulk soils and subsequent chemical analysis of these fractions should give insights to how compositional differences in SOM drive turnover rates of different size-defined carbon pools. The main objective of the study was to elucidate the relative abundance and recalcitrance of lignin and plant lipids (e.g. cutin and suberin) in the course of SOM decomposition within aggregated bulk soils and SOM fractions. By the parallel incubation of physically-separated size fractions and bulk soils of the Ah horizon from a forested soil (Picea abies L.Karst) over a period of 400 days, a unique set of samples was created to study SOM dynamics. We used solid-state 13C-CPMAS NMR spectroscopy and GC-MS (after copper oxide oxidation and solvent extraction) to analyze the composition of the incubated samples. The abundance and isotopic composition (including 13C and 14C) of respired CO2 further enabled us to monitor the dynamics of SOM mineralization. This approach allowed for differentiating between C stabilization of soil fractions due to accessibility/aggregation and to recalcitrance at different scales of resolution (GC-MS, NMR). A relative enrichment of alkyl C and decreasing lignin contents in the order of sand < silt < clay were observed by 13C-NMR and GC-MS within soils and fractions before the incubation, resulting in increased lipid to lignin ratios with decreasing particle size. A relative enrichment of lignin in the incubated fractions compared to the incubated bulk soils clearly indicated the preferential mineralization of less recalcitrant C compounds that were spatially inaccessible in aggregates of the bulk soil. Differences in the abundance of various lignin, cutin, and suberin monomers measured by GC-MS before and after the incubation indicate selective degradation

  17. Multirobot autonomous landmine detection using distributed multisensor information aggregation

    NASA Astrophysics Data System (ADS)

    Jumadinova, Janyl; Dasgupta, Prithviraj

    2012-06-01

    We consider the problem of distributed sensor information fusion by multiple autonomous robots within the context of landmine detection. We assume that different landmines can be composed of different types of material and robots are equipped with different types of sensors, while each robot has only one type of landmine detection sensor on it. We introduce a novel technique that uses a market-based information aggregation mechanism called a prediction market. Each robot is provided with a software agent that uses sensory input of the robot and performs calculations of the prediction market technique. The result of the agent's calculations is a 'belief' representing the confidence of the agent in identifying the object as a landmine. The beliefs from different robots are aggregated by the market mechanism and passed on to a decision maker agent. The decision maker agent uses this aggregate belief information about a potential landmine and makes decisions about which other robots should be deployed to its location, so that the landmine can be confirmed rapidly and accurately. Our experimental results show that, for identical data distributions and settings, using our prediction market-based information aggregation technique increases the accuracy of object classification favorably as compared to two other commonly used techniques.

  18. Aggregate Stability of Tropical Soils Under Long-Term Eucalyptus Cultivation

    USDA-ARS?s Scientific Manuscript database

    Eucalyptus cultivation has increased in all Brazilian regions. Despite the large amount of cultivated area, little is known about how this kind of management system affects soil properties, mainly the aggregate stability. Aggregate stability analyses have proved to be a sensitive tool to measure soi...

  19. Highly magnetizable superparamagnetic colloidal aggregates with narrowed size distribution from ferrofluid emulsion.

    PubMed

    Lobaz, Volodymyr; Klupp Taylor, Robin N; Peukert, Wolfgang

    2012-05-15

    The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle-particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57 emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup-coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds.

  20. Strategies to stabilize compact folding and minimize aggregation of antibody-based fragments

    PubMed Central

    Schrum, Adam G.

    2015-01-01

    Monoclonal antibodies (mAbs) have proven to be useful for development of new therapeutic drugs and diagnostic techniques. To overcome the difficulties posed by their complex structure and folding, reduce undesired immunogenicity, and improve pharmacokinetic properties, a plethora of different Ab fragments have been developed. These include recombinant Fab and Fv segments that can display improved properties over those of the original mAbs upon which they are based. Antibody (Ab) fragments such as Fabs, scFvs, diabodies, and nanobodies, all contain the variable Ig domains responsible for binding to specific antigenic epitopes, allowing for specific targeting of pathological cells and/or molecules. These fragments can be easier to produce, purify and refold than a full Ab, and due to their smaller size they can be well absorbed and distributed into target tissues. However, the physicochemical and structural properties of the immunoglobulin (Ig) domain, upon which the folding and conformation of all these Ab fragments is based, can limit the stability of Ab-based drugs. The Ig domain is fairly sensitive to unfolding and aggregation when produced out of the structural context of an intact Ab molecule. When unfolded, Ab fragments may lose their specificity as well as establish non-native interactions leading to protein aggregation. Aggregated antibody fragments display altered pharmacokinetic and immunogenic properties that can augment their toxicity. Therefore, much effort has been placed in understanding the factors impacting the stability of Ig folding at two different levels: 1) intrinsically, by studying the effects of the amino acid sequence on Ig folding; 2) extrinsically, by determining the environmental conditions that may influence the stability of Ig folding. In this review we will describe the structure of the Ig domain, and the factors that impact its stability, to set the context for the different approaches currently used to achieve stable recombinant Ig

  1. Disorientation angle distribution of primary particles in potash alum aggregates

    NASA Astrophysics Data System (ADS)

    Kovačević, Tijana; Wiedmeyer, Viktoria; Schock, Jonathan; Voigt, Andreas; Pfeiffer, Franz; Sundmacher, Kai; Briesen, Heiko

    2017-06-01

    In order to fully characterize crystal aggregates, the orientation of primary particles has to be analyzed. A procedure for extracting this information from three-dimensional microcomputed tomography (μ CT) images was recently published by our group. We here extend this method for asymmetrical crystals and apply it for studying the disorientation angle distribution of four potash alum crystal samples that were obtained under various experimental conditions. The results show that for all considered supersaturation profiles, primary particle pairs tend to have the same orientation significantly more often than in theoretical considerations, in which the orientations of primary particles are assumed to be distributed randomly.

  2. Use of whey protein soluble aggregates for thermal stability-a hypothesis paper.

    PubMed

    Ryan, Kelsey N; Zhong, Qixin; Foegeding, Edward A

    2013-08-01

    Forming whey proteins into soluble aggregates is a modification shown to improve or expand the applications in foaming, emulsification, gelation, film-formation, and encapsulation. Whey protein soluble aggregates are defined as aggregates that are intermediates between monomer proteins and an insoluble gel network or precipitate. The conditions under which whey proteins denature and aggregate have been extensively studied and can be used as guiding principles of producing soluble aggregates. These conditions are reviewed for pH, ion type and concentration, cosolutes, and protein concentration, along with heating temperature and duration. Combinations of these conditions can be used to design soluble aggregates with desired physicochemical properties including surface charge, surface hydrophobicity, size, and shape. These properties in turn can be used to obtain target macroscopic properties, such as viscosity, clarity, and stability, of the final product. A proposed approach to designing soluble aggregates with improved thermal stability for beverage applications is presented.

  3. Soil Aggregate Stability and Grassland Productivity Associations in a Northern Mixed-Grass Prairie

    PubMed Central

    Reinhart, Kurt O.; Vermeire, Lance T.

    2016-01-01

    Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25–1 and 1–2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0–10 or 0–30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land’s capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations. PMID:27467598

  4. Assessment of the role of agricultural wastes in aggregate formation and their stability.

    PubMed

    Yilmaz, Erdem

    2014-11-01

    The purpose of this study was to evaluate the effects of three agricultural processing wastes (APWs) on aggregate formation and aggregate stability in a sandy loam textured soil (Typic Xerofluvent) in Antalya, Turkey. The effects of APW applications on aggregate formation and aggregate stability were observed for different aggregate size groups (>4; 4-2; 2-1; 1-0.5; 0.5-0.25; 0.25-0.050 and <0.050 mm). Sugar Beet Pulp (SBP), Apple Pomace (AP) and Cotton Gin Waste (CGW) were applied to soil as fresh material (dry weight basis 0, 10, 20 and 40 t ha(-1)), and a greenhouse pot experiment was conducted using a completely randomized design with five replicates of each treatment. The study consisted of two periods. The first period (P1) consisted of a six-month incubation period (1st sample period). The second period (P2) is a six-month period and includes an eight-week green bean (Phaseolus vulgaris L.) growing process (2nd sample period). At the end of the first six months and fourteen months in total, aggregate formation and aggregate stability were determined and their correlation to different C sources was explained. At the end of the experiment, formation of aggregates was increased with increase in the application level of organic wastes in particular intermediate aggregates. Increase in the incubation time significantly enhanced the formation of particular macroaggregates. Soil aggregate stability of all aggregate sizes generally increased with the increasing in the level of implementation. In addition, incubation time effects on aggregate stability for macroaggregates were not significant, but significant for macro and microaggregates. Copyright © 2014. Published by Elsevier Ltd.

  5. Denatured state aggregation parameters derived from concentration dependence of protein stability.

    PubMed

    Schön, Arne; Clarkson, Benjamin R; Siles, Rogelio; Ross, Patrick; Brown, Richard K; Freire, Ernesto

    2015-11-01

    Protein aggregation is a major issue affecting the long-term stability of protein preparations. Proteins exist in equilibrium between the native and denatured or partially denatured conformations. Often denatured or partially denatured conformations are prone to aggregate because they expose to solvent the hydrophobic core of the protein. The aggregation of denatured protein gradually shifts the protein equilibrium toward increasing amounts of denatured and ultimately aggregated protein. Recognizing and quantitating the presence of denatured protein and its aggregation at the earliest possible time will bring enormous benefits to the identification and selection of optimal solvent conditions or the engineering of proteins with the best stability/aggregation profile. In this article, a new approach that allows simultaneous determination of structural stability and the amount of denatured and aggregated protein is presented. This approach is based on the analysis of the concentration dependence of the Gibbs energy (ΔG) of protein stability. It is shown that three important quantities can be evaluated simultaneously: (i) the population of denatured protein, (ii) the population of aggregated protein, and (iii) the fraction of denatured protein that is aggregated.

  6. Effect of Organic Inputs on Strength and Stability of Soil Aggregates Under Rice-Wheat Rotation

    NASA Astrophysics Data System (ADS)

    Das, Bappa; Chakraborty, Debashis; Singh, Vinod K.; Aggarwal, Pramila; Singh, Ravender; Dwivedi, Brahm S.

    2014-04-01

    The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue- and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates <0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.

  7. Quasi-Equilibrium Density Distributions of Small Dust Aggregations in the Solar Nebula

    NASA Astrophysics Data System (ADS)

    Sekiya, Minoru

    1998-06-01

    The rotational velocity of a fluid element around the midplane of the solar nebula increased as dust settled toward the midplane. The Kelvin and Helmholtz instability due to velocity difference of a dust-rich region and a dust-poor region should have occurred and the dust layer became turbulent when the Richardson number decreased below the critical value. Then, dust aggregations stirred up due to turbulent diffusion and were prevented to settle further. In this paper, the sizes of dust aggregations are assumed to be equal to or smaller than the typical radius of chondrules (∼0.3 mm). In this case, even very weak turbulence stirs up dust aggregations. Therefore a dust density distribution is considered to be self regulated so that the Richardson number is nearly equal to the critical value. The quasi-equilibrium dust density distribution is derived analytically by assuming that the Richardson number is equal to the critical value. The derived dust density at the midplane is much smaller than the critical density of the gravitational stability, if the solar composition of dust to gas ratio is assumed. On the other hand, the dust aggregations concentrate around the midplane and the dust layer becomes gravitationally unstable, if more than 97% (at 1 AU from the Sun) of the gaseous components have been dissipated from the nebula, leaving dusty components. Two alternative scenarios of planetesimal formation are proposed: planetesimals were formed by (1) mutual sticking of dust aggregations by nongravitational forces or by (2) gravitational instabilities in the nebula where the dust to gas ratio is much larger than the ratio with solar elemental abundance. Case (2) might be realized due to dissipation of the nebular gas and/or addition of dust by the bipolar outflow. In case (1), chondrule sizes do not indicate the maximum size of dust aggregations in the solar nebula.

  8. Multiscale variability of soil aggregate stability: implications for rangeland hydrology and erosion

    USDA-ARS?s Scientific Manuscript database

    Conservation of soil and water resources in rangelands is a crucial step in stopping desertification processes. The formation of water-stable soil aggregates reduces soil erodibility and can increase infiltration capacity in many soils. Soil aggregate stability is highly variable at scales ranging f...

  9. Can distributed delays perfectly stabilize dynamical networks?

    NASA Astrophysics Data System (ADS)

    Omi, Takahiro; Shinomoto, Shigeru

    2008-04-01

    Signal transmission delays tend to destabilize dynamical networks leading to oscillation, but their dispersion contributes oppositely toward stabilization. We analyze an integrodifferential equation that describes the collective dynamics of a neural network with distributed signal delays. With the Γ distributed delays less dispersed than exponential distribution, the system exhibits reentrant phenomena, in which the stability is once lost but then recovered as the mean delay is increased. With delays dispersed more highly than exponential, the system never destabilizes.

  10. Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

    PubMed

    Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

    2015-01-01

    Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

  11. Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

    PubMed Central

    Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

    2015-01-01

    Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability. PMID:25874864

  12. Method of determination of stability of petroleum disperse systems against aggregation

    SciTech Connect

    Antoshkin, A.S.; Glagoleva, O.F.; Khaidura, K.M.; Syunyaev, R.Z.

    1984-03-01

    This article proposes that the stability of petroleum products against aggregation should be evaluated in a laboratory unit consisting of a thermostat holding the temperature to within + or - 0.02/sup 0/C, a thermostating compartment with 15 samples, and a laboratory stirrer (power 130 W). The problem of regulating the stability of petroleum products against aggregation (kinetic stability) is one of the most important problems in petroleum refining. The equilibrium temperature, the stability factor with respect to asphaltenes, and the distillation yield of the vacuum distillate as a function of the content of additive (lube oil solvent extract) are determined for an atmospheric resid from West Siberian crudes. It is concluded that the proposed method offers a means for a rapid and reliable evaluation of the stability of a petroleum stock against aggregation when exposed to the action of various factors, and a means for finding its active state.

  13. Physical and Biological Controls of Copepod Aggregation and Baleen Whale Distribution

    DTIC Science & Technology

    2010-09-30

    1 DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited. Physical and Biological Controls of Copepod Aggregation...distribution. OBJECTIVES The objectives of this study are to • Elucidate the mechanisms of copepod aggregation in the Great South Channel, a...Physical and Biological Controls of Copepod Aggregation and Baleen Whale Distribution 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT

  14. Friability and aggregate stability of loamy soil after 5 years of biochar application

    NASA Astrophysics Data System (ADS)

    Utomo, Wani; Ganika, Shaory; Wisnubroto, Erwin; Islami, Titiek

    2016-04-01

    The effect of biochar application on soil friability and aggregate stability of loamy soil was studied at Brawijaya University field experimental station, Jatikerto, Malang, Indonesia. The soil has been planted with cassava for 4 years continuously and 1 year planted with maiz. The biochar applied was made from cassava stem and farm yard manure. It was found that biochar application, either made from cassava stem or farm yard manure improved soil qualities. Soil applied with biochar was more friable compared to that of the no biochar soil, although biochar application did not influence Atterberg limits. It seems that the higher friability of biochar applied soil was associated with the higher soil organic matter. It was found that until 5 years application, the biochar treated soil had a higher soil organic matter content. Soil applied with biochar possessed a better soil aggregate stability, both dry and wet stability. This was shown by the higher aggregate mean weight diameter (MWD) of biochar applied soil. The cassava biochar applied soil had MWD of 2.22 mm (dry stability) and 1.56 mm (wet stability), whereas the control soil had MWD of 1.45 mm (dry stability) and 1.25 (wet stability). There was a significant positive correlation between soil friability and dry aggregate stability. The biochar applied soils also had higher soil permeability. Key words: soil qualities, soil physical properties, Atterberg limits, hydraulic conductivity

  15. Parasitoid aggregation and the stabilization of a salt marsh host-parasitoid system

    Treesearch

    John D. Reeve; James T. Cronin; Donald R. Strong

    1994-01-01

    We examine a salt marsh host-parasitoid system, consisting of the planthopper Prokelisia marginata and its egg parasitoid Anagrus delicatus, for evidence of stabilizing parasitoid behavior. We first determine if there is sufficient parasitoid aggregation to potentially stabilize the Prokelisia-Anagrus interactions, using methods that infer parasitoid behavior from the...

  16. Physical and Biological Controls of Copepod Aggregation and Baleen Whale Distribution

    DTIC Science & Technology

    2011-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Physical and Biological Controls of Copepod Aggregation and...DATES COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE Physical and Biological Controls of Copepod Aggregation and Baleen Whale Distribution...OBJECTIVES The objectives of this study are to: • Elucidate the mechanisms of copepod aggregation in the Great South Channel, a major

  17. Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

    NASA Astrophysics Data System (ADS)

    Hure, J.; El Shawish, S.; Cizelj, L.; Tanguy, B.

    2016-08-01

    In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of post-irradiated austenitic stainless steel in Light Water Reactor (LWR) environment, reliable predictions of intergranular stresses are required. Finite elements simulations have been performed on realistic polycrystalline aggregate with recently proposed physically-based crystal plasticity constitutive equations validated for neutron-irradiated austenitic stainless steel. Intergranular normal stress probability density functions are found with respect to plastic strain and irradiation level, for uniaxial loading conditions. In addition, plastic slip activity jumps at grain boundaries are also presented. Intergranular normal stress distributions describe, from a statistical point of view, the potential increase of intergranular stress with respect to the macroscopic stress due to grain-grain interactions. The distributions are shown to be well described by a master curve once rescaled by the macroscopic stress, in the range of irradiation level and strain considered in this study. The upper tail of this master curve is shown to be insensitive to free surface effect, which is relevant for IGSCC predictions, and also relatively insensitive to small perturbations in crystallographic texture, but sensitive to grain shapes.

  18. Role of organic matter on aggregate stability and related mechanisms through organic amendments

    NASA Astrophysics Data System (ADS)

    Zaher, Hafida

    2010-05-01

    To date, only a few studies have tried to simultaneously compare the role of neutral and uronic sugars and lipids on soil structural stability. Moreover, evidence for the mechanisms involved has often been established following wetting of moist aggregates after various pre-treatments thus altering aggregate structure and resulting in manipulations on altered aggregates on which the rapid wetting process may not be involved anymore. To the best of our knowledge, the objective of this work was to study the role of neutral and uronic sugars and lipids in affecting key mechanisms (swelling rate, pressure evolution) involved in the stabilization of soil structure. A long-term incubation study (48-wk) was performed on a clay loam and a silty-clay loam amended with de-inking-secondary sludge mix at three rates (8, 16 and 24 Mg dry matter ha-1), primary-secondary sludge mix at one rate (18 Mg oven-dry ha-1) and composted de-inking sludge at one rate (24 Mg ha-1). Different structural stability indices (stability of moist and dry aggregates, the amount of dispersible clay and loss of soil material following sudden wetting) were measured on a regular basis during the incubation, along with CO2 evolved, neutral and uronic sugar, and lipid contents. During the course of the incubations, significant increases in all stability indices were measured for both soil types. In general, the improvements in stability were proportional to the amount of C added as organic amendments. These improvements were linked to a very intense phase of C mineralization and associated with increases in neutral and uronic sugars as well as lipid contents. The statistical relationships found between the different carbonaceous fractions and stability indices were all highly significant and indicated no clear superiority of one fraction over another. Paper sludge amendments also resulted in significant decreases in maximum internal pressure of aggregate and aggregate swelling following immersion in water

  19. Modification of proteins with cyclodextrins prevents aggregation and surface adsorption and increases thermal stability.

    PubMed

    Prashar, Deepali; Cui, DaWei; Bandyopadhyay, Debjyoti; Luk, Yan-Yeung

    2011-11-01

    This work describes a general approach for preventing protein aggregation and surface adsorption by modifying proteins with β-cyclodextrins (βCD) via an efficient water-driven ligation. As compared to native unmodified proteins, the cyclodextrin-modified proteins (lysozyme and RNase A) exhibit significant reduction in aggregation, surface adsorption and increase in thermal stability. These results reveal a new chemistry for preventing protein aggregation and surface adsorption that is likely of different mechanisms than that by modifying proteins with poly(ethylene glycol).

  20. Medium-term evolution of water repellency and aggregate stability in Mediterranean calcareous soils after wildfire

    NASA Astrophysics Data System (ADS)

    Gordillo-Rivero, Ángel; García-Moreno, Jorge; Zavala, Lorena M.; Jordán, Antonio; Granged, Arturo JP; Gil, Juan

    2013-04-01

    Wildfires are a common feature of Mediterranean ecosystems due to environmental factors and anthropic influence, especially in those areas where land use change and the development of touristic infrastructures are more intense. Wildfires induce a series of soil changes affecting their physical and chemical properties and the hydrological and erosive response. Two of the properties that are commonly affected by burning are soil water repellency (WR) and aggregate stability (AS). Both properties play an important role in the hydrological response of soils and other processes, and may be used as indices for assessing burn severity (Gordillo-Rivero et al., 2013). OBJECTIVES The field study was carried out between August 2006 (date of burning) and August 2011 with the following objectives: [i] to study the changes in SWR and AS immediately after fire and in the medium-term (6 years after burning) and its distribution within aggregate size fractions (<2, 1-2, 0.5-1 and 0.25-0.5 mm), [ii] to assess the relationships between postfire AS and WR, and [iii] to investigate interactions between AS and WR and different factors (site, time since burning, lithology and vegetation type) in calcareous Mediterranean soils. METHODS Five areas affected by wildfires during summer 2006 were selected for this research. Vegetation was characterized by grassland and Mediterranean shrubland. Soils were calcareous, with loam to clayey texture. As shown from adjacent areas, soils were wettable or slightly water-repellent immediately before burning. Soil WR and AS were measured in soil samples (0-15 mm deep) in fine earth (<2 mm) and aggregate sieve fractions (1-2, 0.5-1 and 0.25-0.5 mm). WR was assessed using the WDPT test, and AS was determined as the percentage of stable aggregates after laboratory rainfall simulation. RESULTS Both properties showed different tendencies in different aggregate size fractions. Results showed that soil WR was induced in wettable soils or enhanced in slightly or

  1. Stabilizing Off-pathway Oligomers by Polyphenol Nanoassemblies for IAPP Aggregation Inhibition

    NASA Astrophysics Data System (ADS)

    Nedumpully-Govindan, Praveen; Kakinen, Aleksandr; Pilkington, Emily H.; Davis, Thomas P.; Chun Ke, Pu; Ding, Feng

    2016-01-01

    Experimental studies have shown that many naturally occurring polyphenols have inhibitory effect on the aggregation of several proteins. Here, we use discrete molecular dynamics (DMD) simulations and high-throughput dynamic light scattering (DLS) experiments to study the anti-aggregation effects of two polyphenols, curcumin and resveratrol, on the aggregation of islet amyloid polypeptide (IAPP or amylin). Our DMD simulations suggest that the aggregation inhibition is caused by stabilization of small molecular weight IAPP off-pathway oligomers by the polyphenols. Our analysis indicates that IAPP-polyphenol hydrogen bonds and π-π stacking combined with hydrophobic interactions are responsible for the stabilization of oligomers. The presence of small oligomers is confirmed with DLS measurements in which nanometer-sized oligomers are found to be stable for up to 7.5 hours, the time frame within which IAPP aggregates in the absence of polyphenols. Our study offers a general anti-aggregation mechanism for polyphenols, and further provides a computational framework for the future design of anti-amyloid aggregation therapeutics.

  2. Stabilizing Off-pathway Oligomers by Polyphenol Nanoassemblies for IAPP Aggregation Inhibition

    PubMed Central

    Nedumpully-Govindan, Praveen; Kakinen, Aleksandr; Pilkington, Emily H.; Davis, Thomas P.; Chun Ke, Pu; Ding, Feng

    2016-01-01

    Experimental studies have shown that many naturally occurring polyphenols have inhibitory effect on the aggregation of several proteins. Here, we use discrete molecular dynamics (DMD) simulations and high-throughput dynamic light scattering (DLS) experiments to study the anti-aggregation effects of two polyphenols, curcumin and resveratrol, on the aggregation of islet amyloid polypeptide (IAPP or amylin). Our DMD simulations suggest that the aggregation inhibition is caused by stabilization of small molecular weight IAPP off-pathway oligomers by the polyphenols. Our analysis indicates that IAPP-polyphenol hydrogen bonds and π-π stacking combined with hydrophobic interactions are responsible for the stabilization of oligomers. The presence of small oligomers is confirmed with DLS measurements in which nanometer-sized oligomers are found to be stable for up to 7.5 hours, the time frame within which IAPP aggregates in the absence of polyphenols. Our study offers a general anti-aggregation mechanism for polyphenols, and further provides a computational framework for the future design of anti-amyloid aggregation therapeutics. PMID:26763863

  3. The neuronal extracellular matrix restricts distribution and internalization of aggregated Tau-protein.

    PubMed

    Suttkus, A; Holzer, M; Morawski, M; Arendt, T

    2016-01-28

    Alzheimer's disease (AD) is a chronic degenerative disorder characterized by fibrillary aggregates of Aß and Tau-protein. Formation and progression of these pathological hallmarks throughout the brain follow a specific spatio-temporal pattern which provides the basis for neuropathological staging. Previously, we could demonstrate that cortical and subcortical neurons are less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called 'perineuronal net' (PN). PNs are composed of large aggregating chondroitin sulfate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R. Recently, PN-associated neurons were shown to be better protected against iron-induced neurodegeneration compared to neurons without PN, indicating a neuroprotective function. Here, we investigated the role of PNs in distribution and internalization of exogenous Tau-protein by using organotypic slice cultures of wildtype mice as well as mice lacking the ECM-components aggrecan, HAPLN1 or tenascin-R. We could demonstrate that PNs restrict both distribution and internalization of Tau. Accordingly, PN-ensheathed neurons were less frequently affected by Tau-internalization, than neurons without PN. Finally, the PNs as well as their three investigated components were shown to modulate the processes of distribution as well as internalization of Tau.

  4. Connecting high-temperature and low-temperature protein stability and aggregation.

    PubMed

    Rosa, Mónica; Roberts, Christopher J; Rodrigues, Miguel A

    2017-01-01

    Protein aggregation is a long-standing problem for preservation of proteins in both laboratory settings and for commercial biotechnology products. It is well established that heating (cooling) can accelerate (slow) aggregation by populating (depopulating) unfolded or partially unfolded monomer states that are key intermediates in aggregation processes. However, there is a long-standing question of whether the same mechanism(s) that lead to aggregation under high-temperature stress are relevant for low-temperature stress such as in refrigerated or supercooled liquids. This report shows the first direct comparison of "hot" and "cold" aggregation kinetics and folding/unfolding thermodynamics, using bovine hemoglobin as a model system. The results suggest that the same mechanism for non-native aggregation holds from "hot" to "cold" temperatures, with an aggregation temperature-of-maximum-stability slightly below 0°C. This highlights that sub-zero temperatures can induce cold-mediated aggregation, even in the absence of freezing stresses. From a practical perspective, the results suggests the possibility that cold-stress may be a useful alternative to heat-stress for extrapolating predictions of protein shelf life at refrigerated conditions, as well as providing a foundation for more mechanistic studies of cold-stress conditions in future work. A comparison between isochoric and isobaric methods is also briefly discussed.

  5. Connecting high-temperature and low-temperature protein stability and aggregation

    PubMed Central

    Rosa, Mónica; Roberts, Christopher J.

    2017-01-01

    Protein aggregation is a long-standing problem for preservation of proteins in both laboratory settings and for commercial biotechnology products. It is well established that heating (cooling) can accelerate (slow) aggregation by populating (depopulating) unfolded or partially unfolded monomer states that are key intermediates in aggregation processes. However, there is a long-standing question of whether the same mechanism(s) that lead to aggregation under high-temperature stress are relevant for low-temperature stress such as in refrigerated or supercooled liquids. This report shows the first direct comparison of “hot” and “cold” aggregation kinetics and folding/unfolding thermodynamics, using bovine hemoglobin as a model system. The results suggest that the same mechanism for non-native aggregation holds from “hot” to “cold” temperatures, with an aggregation temperature-of-maximum-stability slightly below 0°C. This highlights that sub-zero temperatures can induce cold-mediated aggregation, even in the absence of freezing stresses. From a practical perspective, the results suggests the possibility that cold-stress may be a useful alternative to heat-stress for extrapolating predictions of protein shelf life at refrigerated conditions, as well as providing a foundation for more mechanistic studies of cold-stress conditions in future work. A comparison between isochoric and isobaric methods is also briefly discussed. PMID:28472066

  6. Stability of system against aggregation in coking a compounded feedstock

    SciTech Connect

    Mimun, K.; Smidovich, E.V.; Zaitseva, N.P.

    1984-05-01

    This article examines a vacuum resid from West Siberian crude and a 250/sup 0/C+ fraction of pyrolysis tar. The pyrolysis tar consists of heavy aromatic hydrocarbons and asphaltenes in approximately equal amounts of 46-48%. The vacuum resid is a conventional straight-run feedstock with a predominance of light and medium aromatic hydrocarbons (37.6%) and a moderate content of asphaltenes (10.2%). The vacuum resid and the pyrolysis tar were subjected to coking in a laboratory still, being coked separately and also in blends with a paraffin wax having a density of 739 kg/m/sup 3/ at 68/sup 0/C, melting point of 54/sup 0/C, and molecular weight of 356. The stability factor was determined for each blend. It is concluded that paraffin wax, like highly aromatic additives, when it is blended with residual stocks with low contents of paraffinic/naphthenic hydrocarbons or none of these hydrocarbons at all (such stocks have a low stability factor), may increase the stability of these residual stocks against phase separation to a significant degree.

  7. Fatigue reduction during aggregated and distributed sequential stimulation.

    PubMed

    Bergquist, Austin J; Babbar, Vishvek; Ali, Saima; Popovic, Milos R; Masani, Kei

    2017-08-01

    Transcutaneous neuromuscular electrical stimulation (NMES) can generate muscle contractions for rehabilitation and exercise. However, NMES-evoked contractions are limited by fatigue when they are delivered "conventionally" (CONV) using a single active electrode. Researchers have developed "sequential" (SEQ) stimulation, involving rotation of pulses between multiple "aggregated" (AGGR-SEQ) or "distributed" (DISTR-SEQ) active electrodes, to reduce fatigue (torque-decline) by reducing motor unit discharge rates. The primary objective was to compare fatigue-related outcomes, "potentiation," "variability," and "efficiency" between CONV, AGGR-SEQ, and DISTR-SEQ stimulation of knee extensors in healthy participants. Torque and current were recorded during testing with fatiguing trains using each NMES type under isometric and isokinetic (180°/s) conditions. Compared with CONV stimulation, SEQ techniques reduced fatigue-related outcomes, increased potentiation, did not affect variability, and reduced efficiency. SEQ techniques hold promise for reducing fatigue during NMES-based rehabilitation and exercise; however, optimization is required to improve efficiency. Muscle Nerve 56: 271-281, 2017. © 2016 Wiley Periodicals, Inc.

  8. Distribution of chromium contamination and microbial activity in soil aggregates.

    PubMed

    Tokunaga, Tetsu K; Wan, Jiamin; Hazen, Terry C; Schwartz, Egbert; Firestone, Mary K; Sutton, Stephen R; Newville, Matthew; Olson, Keith R; Lanzirotti, Antonio; Rao, William

    2003-01-01

    Biogeochemical transformations of redox-sensitive chemicals in soils can be strongly transport-controlled and localized. This was tested through experiments on chromium diffusion and reduction in soil aggregates that were exposed to chromate solutions. Reduction of soluble Cr(VI) to insoluble Cr(II) occurred only within the surface layer of aggregates with higher available organic carbon and higher microbial respiration. Sharply terminated Cr diffusion fronts develop when the reduction rate increases rapidly with depth. The final state of such aggregates consists of a Cr-contaminated exterior, and an uncontaminated core, each having different microbial community compositions and activity. Microbial activity was significantly higher in the more reducing soils, while total microbial biomass was similar in all of the soils. The small fraction of Cr(VI) remaining unreduced resides along external surfaces of aggregates, leaving it potentially available to future transport down the soil profile. Using the Thiele modulus, Cr(VI) reduction in soil aggregates is shown to be diffusion rate- and reaction rate-limited in anaerobic and aerobic aggregates, respectively. Thus, spatially resolved chemical and microbiological measurements are necessary within anaerobic soil aggregates to characterize and predict the fate of Cr contamination. Typical methods of soil sampling and analyses that average over redox gradients within aggregates can erase important biogeochemical spatial relations necessary for understanding these environments.

  9. Server-side Filtering and Aggregation within a Distributed Environment

    NASA Astrophysics Data System (ADS)

    Currey, J. C.; Bartle, A.

    2015-12-01

    Intercalibration, validation, and data mining use cases require more efficient access to the massive volumes of observation data distributed across multiple agency data centers. The traditional paradigm of downloading large volumes of data to a centralized server or desktop computer for analysis is no longer viable. More analysis should be performed within the host data centers using server-side functions. Many comparative analysis tasks require far less than 1% of the available observation data. The Multi-Instrument Intercalibration (MIIC) Framework provides web services to find, match, filter, and aggregate multi-instrument observation data. Matching measurements from separate spacecraft in time, location, wavelength, and viewing geometry is a difficult task especially when data are distributed across multiple agency data centers. Event prediction services identify near coincident measurements with matched viewing geometries near orbit crossings using complex orbit propagation and spherical geometry calculations. The number and duration of event opportunities depend on orbit inclinations, altitude differences, and requested viewing conditions (e.g., day/night). Event observation information is passed to remote server-side functions to retrieve matched data. Data may be gridded, spatially convolved onto instantaneous field-of-views, or spectrally resampled or convolved. Narrowband instruments are routinely compared to hyperspectal instruments such as AIRS and CRIS using relative spectral response (RSR) functions. Spectral convolution within server-side functions significantly reduces the amount of hyperspectral data needed by the client. This combination of intelligent selection and server-side processing significantly reduces network traffic and data to process on local servers. OPeNDAP is a mature networking middleware already deployed at many of the Earth science data centers. Custom OPeNDAP server-side functions that provide filtering, histogram analysis (1D

  10. Aggregation of a Distributed Source in Morphogen Gradient Formation

    PubMed Central

    Lander, A. D.; Nie, Q.; Vargas, B.; Wan, F. Y. M.

    2007-01-01

    In the development of a biological entity, ligands (such as Decapentaplegic (Dpp) along the anterior–posterior axis of the Drosophila wing imaginal disc) are synthesized at a localized source and transported away from the source for binding with cell surface receptors to form concentration gradients of ligand–receptor complexes for cell signaling. Generally speaking, activities such as diffusion and reversible binding with degradable receptors also take place in the region of ligand production. The effects of such morphogen activities in the region of localized distributed ligand source on the ligand–receptor concentration gradient in the entire biological entity have been modeled and analyzed as System F in [1]. In this paper, we deduce from System F, a related end source model (System A) in which the effects of the distributed ligand source is replaced by an idealized point stimulus at the border between the (posterior) chamber and the ligand production region that simulates the average effects of the ligand activities in the production zone. This aggregated end source model is shown to adequately reproduce the significant implications of System F and to contain the corresponding ad hoc point source model, System R of [2], as a special case. Because of its simpler mathematical structure and the absence of any limitation on the ligand synthesis rate for the existence of steady-state gradients, System A type models are expected to be used widely. An example of such application is the recent study of the inhibiting effects of the formation of nonsignaling ligand–nonreceptor complexes [3]. PMID:17372620

  11. Optimum aggregation of geographically distributed flexible resources in strategic smart-grid/microgrid locations

    DOE PAGES

    Bhattarai, Bishnu P.; Myers, Kurt S.; Bak-Jensen, Brigitte; ...

    2017-05-17

    This paper determines optimum aggregation areas for a given distribution network considering spatial distribution of loads and costs of aggregation. An elitist genetic algorithm combined with a hierarchical clustering and a Thevenin network reduction is implemented to compute strategic locations and aggregate demand within each area. The aggregation reduces large distribution networks having thousands of nodes to an equivalent network with few aggregated loads, thereby significantly reducing the computational burden. Furthermore, it not only helps distribution system operators in making faster operational decisions by understanding during which time of the day will be in need of flexibility, from which specificmore » area, and in which amount, but also enables the flexibilities stemming from small distributed resources to be traded in various power/energy markets. A combination of central and local aggregation scheme where a central aggregator enables market participation, while local aggregators materialize the accepted bids, is implemented to realize this concept. The effectiveness of the proposed method is evaluated by comparing network performances with and without aggregation. Finally, for a given network configuration, steady-state performance of aggregated network is significantly accurate (≈ ±1.5% error) compared to very high errors associated with forecast of individual consumer demand.« less

  12. Biological and physical factors controlling aggregate stability under different climatic conditions in Southern Spain.

    NASA Astrophysics Data System (ADS)

    Ángel Gabarrón-Galeote, Miguel; Damián Ruiz-Sinoga, Jose; Francisco Martinez-Murillo, Juan; Lavee, Hanoch

    2013-04-01

    Soil aggregation is a key factor determining the soil structure. The presence of stable aggregates is essential to maintain a good soil structure, that in turn plays an important role in sustaining agricultural productivity and preserving environmental quality. A wide range of physical and biological soil components are involved in the aggregate formation and stabilization, namely clay mineral content; the quantity and quality of organic matter, that can be derived from plants, fungal hyphae, microorganism and soil animals; and the soil water content. Climatic conditions, through their effect on soil water content, vegetation cover and organic matter content, are supposed to affect soil aggregation. Thus the main objective of this research is to analyse the effect of organic matter, clay content and soil water content on aggregate stability along a climatic transect in Southern Spain. This study was conducted in four catchments along a pluviometric gradient in the South of Spain (rainfall depth decreases from west to east from more than 1000 mm year-1 to less than 300 mm year-1) and was based on a methodology approximating the climatic gradient in Mediterranean conditions. The selected sites shared similar conditions of geology, topography and soil use, which allowed making comparisons among them and relating the differences to the pluviometric conditions. In February 2007, 250 disturbed and undisturbed samples from the first 5cm of the soil were collected along the transect. We measured the aggregate stability, organic matter, clay content and bulk density of every sample. In the field we measured rainfall, air temperature, relative humidity, wind speed, wind direction, solar radiation, potential evapotranspiration, soil water content, vegetation cover and presence of litter. Our results suggest that aggregate stability is a property determined by a great number of highly variable factors, which can make extremely difficult to predict its behavior taking in

  13. Aggregation of stabilized TiO2 nanoparticle suspensions in the presence of inorganic ions.

    PubMed

    Shih, Yang-Hsin; Liu, Wei-Szu; Su, Yuh-Fan

    2012-08-01

    The present study aims to evaluate the effect of inorganic ions on the aggregation kinetics of stabilized titanium dioxide (TiO(2) ) nanoparticle (NP) suspension, an NP mode widely used in consumer goods and in aquatic environments. The point of zero charge of stabilized TiO(2) NPs was approximately pH 6.5. The particle size of the stabilized TiO(2) NP suspensions increased with the increase in salt concentrations. The additional salts caused the shift of zeta potentials of TiO(2) suspensions to a lower value. The TiO(2) NPs aggregated more obviously in the presence of anions than cations, and the effect of divalent anions was larger than that of monovalent anions. The critical coagulation concentration (CCC) values for commercial TiO(2) NP suspensions with positive surfaces were estimated as 290 and 2.3 meq/L for Cl(-) and SO 42-, respectively. These CCC values of stabilized TiO(2) NP suspensions are higher than those of TiO(2) NP powders, indicating greater stability of the commercial stabilized TiO(2) NP suspensions. The effects of commercial TiO(2) NP suspensions still need to be explored and defined. Derjaguin-Landau-Verwey-Overbeek (DLVO) analysis can explain the aggregation behaviors of stabilized TiO(2) NP suspensions. Such an understanding can facilitate the prediction of NP fate in the environment.

  14. How hydrophobically modified chitosans are stabilized by biocompatible lipid aggregates.

    PubMed

    Ruocco, Nino; Frielinghaus, Heide; Vitiello, Giuseppe; D'Errico, Gerardino; Leal, Leslie G; Richter, Dieter; Ortona, Ornella; Paduano, Luigi

    2015-08-15

    Nanostructured hydrogels composed by biocompatible molecules are formulated and characterized. They are based on a polymer network formed by hydrophobically modified chitosans (HMCHIT or CnCHIT) in which vesicles of monoolein (MO) and oleic acid or sodium oleate (NaO), depending on pH, are embedded. The best conditions for gel formation, in terms of pH, length of the hydrophobic moieties of chitosan, and weight proportion among the three components were estimated by visual inspection of a large number of samples. Among all possible combinations, the system C12CHIT-MO-NaO in the weight proportion (1:1:1) is optimal for the formation of a well-structured gel-like system, which is also confirmed by rheological experiments. Electron paramagnetic resonance (EPR) measurements unambiguously show the presence of lipid bilayers in this mixture, indicating that MO-NaO vesicles are stabilized by C12CHIT even at acid pH. A wide small angle neutron scattering investigation performed on several ternary systems of general formula CnCHIT-MO-NaO shows that the length of the hydrophobic tail Cn is a crucial parameter in stabilizing the polymer network in which lipid vesicles are embedded. Structural parameters for the vesicles are determined by using a multilamellar model that admits the possibility of displacement of the center of each shell. The number of shells tends to be reduced by increasing the polymer content. The thickness and the distance between consecutive lamellae are not influenced by either the polymer or MO-NaO concentration. The hydrogel presented in this work, being fully biocompatible and nanostructured, is well-suited for possible application in drug delivery.

  15. Effect of cover crops management in aggregate stability of a vineyard in Central Spain.

    NASA Astrophysics Data System (ADS)

    Ruiz-Colmenero, Marta; Bienes, Ramon; Marques, Maria-Jose

    2010-05-01

    Our research focuses in cover crop treatments used to avoid soil degradation in hillsides. The soil-plant interaction can influence the soil structure. In this study we pay special attention to the soil aggregates in a hillside vineyard (average slope of 14%), under Mediterranean semiarid climatic conditions (average annual temperature 14°C, annual rainfall around 400 mm), in the South East of Madrid located at an altitude of 800 masl. The soil classification according to USDA (2006) is Calcic Haploxeralf. Its particle size yields 58% sand, 18% silt and 24% clay, so that according to USDA classification it is a sandy clay loam soil. The bulk density of the first 10 cm of topsoil is 1.2 g cm-3 and its real density is 2.4 g cm-3. It has low organic matter content: 1.3 ± 0.1% (Walkley and Black, 1934). Three treatments were tested: i) traditional tillage ii) soil covered by Brachypodium distachyon allowing self-sowing, and iii) soil covered by Secale cereale, mown in early spring. In each treatment the aggregate stability was measured. These cover crops were established in a 2m wide strip at the center of the rows. We have collected samples of soil for each treatment along 2 years and we analyzed the aggregates, trying to find changes in their stability. Aggregates of 4 to 4.75 mm diameter were selected by dry sieving. The stability was measured with Drop-test: CND and TDI (Imeson and Vis, 1984). An improvement in the stability of aggregates was observed after two years of cover crop treatment. There are significant differences among the treatments analyzed with Kolmogorov-Smirnov test, being Brachypodium distachyon the treatment with more stable aggregates, it is necessary a mean higher than 8 drops to disintegrate every aggregate completely. Organic carbon was also measured by Loss on Ignition method (Schulte and Hopkins, 1996). This method can lead to an overestimation of the organic matter in soil samples but is considered suitable for aggregates. Again, those

  16. Stabilized fiber-optic frequency distribution system

    NASA Technical Reports Server (NTRS)

    Primas, L. E.; Lutes, G. F.; Sydnor, R. L.

    1989-01-01

    A technique for stabilizing reference frequencies transmitted over fiber-optic cable in a frequency distribution system is discussed. The distribution system utilizes fiber-optic cable as the transmission medium to distribute precise reference signals from a frequency standard to remote users. The stability goal of the distribution system is to transmit a 100-MHz signal over a 22-km fiber-optic cable and maintain a stability of 1 part in 10(17) for 1000-second averaging times. Active stabilization of the link is required to reduce phase variations produced by environmental effects, and is achieved by transmitting the reference signal from the frequency standard to the remote unit and then reflecting back to the reference unit over the same optical fiber. By comparing the phase of the transmitted and reflected signals at the reference unit, phase variations of the remote signal can be measured. An error voltage derived from the phase difference between the two signals is used to add correction phase.

  17. Protein engineering to stabilize soluble amyloid β-protein aggregates for structural and functional studies.

    PubMed

    Härd, Torleif

    2011-10-01

    The molecular biology underlying protein aggregation and neuronal death in Alzheimer's disease is not yet completely understood, but small soluble nonamyloid aggregates of the amyloid β-protein (Aβ) have been shown to play a fundamental neurotoxic role. The composition and biological action of such aggregates, known as oligomers and protofibrils, are therefore areas of intense study. However, research is complicated by the multitude of different interconverting aggregates that Aβ can form in vitro and in vivo, and by the inhomogeneity and instability of in vitro preparations. Here we review recent studies in which protein engineering, and in particular disulfide engineering, has been applied to stabilize different Aβ aggregates. For example, several techniques now exist to obtain stable and neurotoxic protofibrillar forms of Aβ, and engineered Aβ dimers, or larger aggregates formed by these, have been shown to specifically induce neuronal damage in a way that mimics Alzheimer's disease pathology. Disulfide engineering has also revealed structural properties of neurotoxic aggregates, for instance that Aβ in protofibrils and globular oligomers adopts a β-hairpin conformation that is similar to, but topologically distinct from, the conformation of Aβ in mature amyloid fibrils. Protein engineering is therefore a workable strategy to address many of the outstanding questions relating to the structure, interconversion and biological effects of oligomers and protofibrils of Aβ.

  18. Mechanisms of protein stabilization and prevention of protein aggregation by glycerol.

    PubMed

    Vagenende, Vincent; Yap, Miranda G S; Trout, Bernhardt L

    2009-11-24

    The stability of proteins in aqueous solution is routinely enhanced by cosolvents such as glycerol. Glycerol is known to shift the native protein ensemble to more compact states. Glycerol also inhibits protein aggregation during the refolding of many proteins. However, mechanistic insight into protein stabilization and prevention of protein aggregation by glycerol is still lacking. In this study, we derive mechanisms of glycerol-induced protein stabilization by combining the thermodynamic framework of preferential interactions with molecular-level insight into solvent-protein interactions gained from molecular simulations. Contrary to the common conception that preferential hydration of proteins in polyol/water mixtures is determined by the molecular size of the polyol and the surface area of the protein, we present evidence that preferential hydration of proteins in glycerol/water mixtures mainly originates from electrostatic interactions that induce orientations of glycerol molecules at the protein surface such that glycerol is further excluded. These interactions shift the native protein toward more compact conformations. Moreover, glycerol preferentially interacts with large patches of contiguous hydrophobicity where glycerol acts as an amphiphilic interface between the hydrophobic surface and the polar solvent. Accordingly, we propose that glycerol prevents protein aggregation by inhibiting protein unfolding and by stabilizing aggregation-prone intermediates through preferential interactions with hydrophobic surface regions that favor amphiphilic interface orientations of glycerol. These mechanisms agree well with experimental data available in the literature, and we discuss the extent to which these mechanisms apply to other cosolvents, including polyols, arginine, and urea.

  19. Whey utilization in furrow irrigation: effects on aggregate stability and erosion.

    PubMed

    Lehrsch, Gary A; Robbins, Charles W; Brown, Melvin J

    2008-11-01

    Improving soil structure often reduces furrow erosion and maintains adequate infiltration. Cottage cheese whey, the liquid byproduct from cottage cheese manufacture, was utilized to stabilize soil aggregates and reduce sediment losses from furrow irrigation. We applied either 2.4 or 1.9L of whey per meter of furrow (3.15 or 2.49Lm(-2), respectively) by gravity flow without incorporation to two fields of Portneuf silt loam (Durinodic Xeric Haplocalcid) near Kimberly, ID. Furrows were irrigated with water beginning four days later. We measured sediment losses with furrow flumes during each irrigation and measured aggregate stability by wet sieving about 10 days after the last irrigation. Overall, whey significantly increased aggregate stability 25% at the 0-15mm depth and 14% at 15-30mm, compared to controls. On average, whey reduced sediment losses by 75% from furrows sloped at 2.4%. Whey increased the aggregate stability of structurally degraded calcareous soil in irrigation furrows.

  20. Aggregate structure and stability linked to carbon dynamics in a south Chilean Andisol

    NASA Astrophysics Data System (ADS)

    Huygens, D.; Boeckx, P.; van Cleemput, O.; Godoy, R.; Oyarzún, C.

    2005-02-01

    The extreme vulnerability of soil organic carbon to climate and land use change emphasizes the need for further research in different terrestrial ecosystems. We have studied the aggregate stability and carbon dynamics in a chronosequence of three different land uses in a south Chilean Andisols: a second growth Nothofagus obliqua forest (SGFOR), a grassland (GRASS) and a Pinus radiata plantation (PINUS). The aim of this study was to investigate the role of Al as soil organic matter stabilizing agent in this Andisol. In a case study, we linked differences in carbon dynamics between the three land use treatments to physical protection and recalcitrance of the soil organic matter (SOM). In this study, C aggregate stability and dynamics were studied using size and density fractionation experiments of the SOM, δ13C and total carbon analysis of the different SOM fractions, and mineralization measurements. The results showed that electrostatic attractions between and among Al-oxides and clay minerals are mainly responsible for the stabilization of soil aggregates and the physical protection of the enclosed soil organic carbon. Whole soil C mineralization rate constants were highest for SGFOR and PINUS, followed by GRASS. In contrast, incubation experiments of isolated macro organic matter fractions showed that the recalcitrance of the SOM decreased in another order: PINUS > SGFOR > GRASS. We concluded that physical protection of soil aggregates was the main process determining whole soil C mineralization. Land use changes affected soil organic carbon dynamics in this south Chilean Andisol by altering soil pH and consequently available Al.

  1. Particle-bubble aggregate stability on static bubble generated by single nozzle on flotation process

    NASA Astrophysics Data System (ADS)

    Warjito, Harinaldi, Setyantono, Manus; Siregar, Sahala D.

    2016-06-01

    There are three sub-processes on flotation. These processes are intervening liquid film into critical thickness, rupture of liquid film forming three phase contact line, and expansion three phase contact line forming aggregate stability. Aggregate stability factor contribute to determine flotation efficiency. Aggregate stability has some important factors such as reagent and particle geometry. This research focussed on to understand effect of particle geometry to aggregate stability. Experimental setup consists of 9 x 9 x26 cm flotation column made of glass, bubble generator, particle feeding system, and high speed video camera. Bubble generator made from single nozzle with 0.3 mm diameter attached to programmable syringe pump. Particle feeding system made of pipette. Particle used in this research is taken from open pit Grasberg in Timika, Papua. Particle has sub-angular geometry and its size varies from 38 to 300 µm. Bubble-particle interaction are recorded using high speed video camera. Recordings from high speed video camera analyzed using image processing software. Experiment result shows that aggregate particle-bubble and induction time depends on particle size. Small particle (38-106 µm) has long induction time and able to rupture liquid film and also forming three phase contact line. Big particle (150-300 µm) has short induction time, so it unable to attach with bubble easily. This phenomenon is caused by apparent gravity work on particle-bubble interaction. Apparent gravity worked during particle sliding on bubble surface experience increase and reached its maximum magnitude at bubble equator. After particle passed bubble equator, apparent gravity force experience decrease. In conclusion particle size from 38-300 µm can form stable aggregate if particle attached with bubble in certain condition.

  2. Hierarchical distributed stabilization of power networks

    NASA Astrophysics Data System (ADS)

    Ishizaki, Takayuki; Sadamoto, Tomonori; Imura, Jun-ichi

    2014-10-01

    Large fluctuation of electric power due to high penetration of renewable energy sources such as photovoltaic and wind power generation increases the risk to make the whole power network system unstable. The conventional frequency control called load frequency control is based on PID (proportional-integral-derivative) control or more advanced centralized and decentralized/distributed control. If we could more effectively use information on the state of the other neighbor generators, we can expect to make the whole system more robust against the large frequency fluctuation. This paper proposes a fundamental framework towards the design of hierarchical distributed stabilizing controllers for a network of power generators and loads. This novel type of distributed controller, composed of a global controller and a set of local controllers, takes into account the effect of the interaction among the generators and loads to improve robustness for the variation of locally stabilizing controllers.

  3. Relationships between slope erosion processes and aggregate stability of Ultisols from subtropical China during rainstorms

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Xiao, Hai; Liu, Puling

    2017-04-01

    Soil aggregates, being a key soil structural unit, influence several soil physical properties such as water infiltration, runoff and erosion. The relationship between soil aggregate stability and interrill and rill erodibility is unclear but critical to process-based erosion prediction models. One obvious reason is that it is hard to distinguish between interrill and rill-eroded sediment during the erosion process. This study was designed to partition interrill and rill erosion rates and relates them to the aggregate stability of Ultisols in subtropical China. Six kinds of rare earth element (REE) were applied as tracers mixed with two cultivated soils derived from the Quaternary red clay soil and the shale soil at six slope positions. Soil aggregate stability was determined by the Le Bissonnais (LB)-method. Simulated rainfall with three intensities (60, 90 and 120 mm/h) were applied to a soil plot (2.25 m long, 0.5 m wide, 0.2 m deep) at three slope gradients (10°, 20° and 30°) with duration of 30 min after runoff initiation. The results indicated that interrill and rill erosion increased with increasing rainfall intensity and slope gradient for both types of soil. Rill and interrill erosion rates of the shale soil were much higher than those of the Quaternary red clay soil. Rill erosion contribution enhanced with increasing rainfall intensity and slope gradient for both soils. Percentage of the downslope area erosion to total erosion was the largest, followed by the mid-slope area and then upslope area. Equations using an aggregate stability index As to replace the erodibility factor of interrill and rill erosion in the Water Erosion Prediction Project (WEPP) model were constructed after analyzing the relationships between estimated and measured rill and interrill erosion data. It was shown that these equations based on the stability index, As, have the potential to improve methods for assessing interrill and rill erosion erodibility synchronously for the

  4. Stability and Aggregation Kinetics of Titania Nanomaterials under Environmentally Realistic Conditions.

    PubMed

    Raza, Ghulam; Amjad, Muhammad; Kaur, Inder; Wen, Dongsheng

    2016-08-16

    Nanoparticle morphology is expected to play a significant role in the stability, aggregation behavior, and ultimate fate of engineered nanomaterials in natural aquatic environments. The aggregation kinetics of ellipsoidal and spherical titanium dioxide (TiO2) nanoparticles (NPs) under different surfactant loadings, pH values, and ionic strengths were investigated in this study. The stability results revealed that alteration of surface charge was the stability determining factor. Among five different surfactants investigated, sodium citrate and Suwannee river fulvic acid (SRFA) were the most effective stabilizers. It was observed that both types of NPs were more stable in monovalent salts (NaCl and NaNO3) as compared with divalent salts (Ca(NO3)2 and CaCl2). The aggregation of spherical TiO2 NPs demonstrated a strong dependency on the ionic strength regardless of the presence of mono or divalent salts; while the ellipsoids exhibited a lower dependency on the ionic strength but was more stable. This work acts as a benchmark study toward understanding the ultimate fate of stabilized NPs in natural environments that are rich in Ca(CO3)2, NaNO3, NaCl, and CaCl2 along with natural organic matters.

  5. Stability of Iowa mutant and wild type Aβ-peptide aggregates

    SciTech Connect

    Alred, Erik J.; Scheele, Emily G.; Berhanu, Workalemahu M.; Hansmann, Ulrich H. E.

    2014-11-07

    Recent experiments indicate a connection between the structure of amyloid aggregates and their cytotoxicity as related to neurodegenerative diseases. Of particular interest is the Iowa Mutant, which causes early-onset of Alzheimer's disease. While wild-type Amyloid β-peptides form only parallel beta-sheet aggregates, the mutant also forms meta-stable antiparallel beta sheets. Since these structural variations may cause the difference in the pathological effects of the two Aβ-peptides, we have studied in silico the relative stability of the wild type and Iowa mutant in both parallel and antiparallel forms. We compare regular molecular dynamics simulations with such where the viscosity of the samples is reduced, which, we show, leads to higher sampling efficiency. By analyzing and comparing these four sets of all-atom molecular dynamics simulations, we probe the role of the various factors that could lead to the structural differences. Our analysis indicates that the parallel forms of both wild type and Iowa mutant aggregates are stable, while the antiparallel aggregates are meta-stable for the Iowa mutant and not stable for the wild type. The differences result from the direct alignment of hydrophobic interactions in the in-register parallel oligomers, making them more stable than the antiparallel aggregates. The slightly higher thermodynamic stability of the Iowa mutant fibril-like oligomers in its parallel organization over that in antiparallel form is supported by previous experimental measurements showing slow inter-conversion of antiparallel aggregates into parallel ones. Knowledge of the mechanism that selects between parallel and antiparallel conformations and determines their relative stability may open new avenues for the development of therapies targeting familial forms of early-onset Alzheimer's disease.

  6. Stability of Iowa mutant and wild type Aβ-peptide aggregates

    NASA Astrophysics Data System (ADS)

    Alred, Erik J.; Scheele, Emily G.; Berhanu, Workalemahu M.; Hansmann, Ulrich H. E.

    2014-11-01

    Recent experiments indicate a connection between the structure of amyloid aggregates and their cytotoxicity as related to neurodegenerative diseases. Of particular interest is the Iowa Mutant, which causes early-onset of Alzheimer's disease. While wild-type Amyloid β-peptides form only parallel beta-sheet aggregates, the mutant also forms meta-stable antiparallel beta sheets. Since these structural variations may cause the difference in the pathological effects of the two Aβ-peptides, we have studied in silico the relative stability of the wild type and Iowa mutant in both parallel and antiparallel forms. We compare regular molecular dynamics simulations with such where the viscosity of the samples is reduced, which, we show, leads to higher sampling efficiency. By analyzing and comparing these four sets of all-atom molecular dynamics simulations, we probe the role of the various factors that could lead to the structural differences. Our analysis indicates that the parallel forms of both wild type and Iowa mutant aggregates are stable, while the antiparallel aggregates are meta-stable for the Iowa mutant and not stable for the wild type. The differences result from the direct alignment of hydrophobic interactions in the in-register parallel oligomers, making them more stable than the antiparallel aggregates. The slightly higher thermodynamic stability of the Iowa mutant fibril-like oligomers in its parallel organization over that in antiparallel form is supported by previous experimental measurements showing slow inter-conversion of antiparallel aggregates into parallel ones. Knowledge of the mechanism that selects between parallel and antiparallel conformations and determines their relative stability may open new avenues for the development of therapies targeting familial forms of early-onset Alzheimer's disease.

  7. Soy protein nanoparticle aggregates as pickering stabilizers for oil-in-water emulsions.

    PubMed

    Liu, Fu; Tang, Chuan-He

    2013-09-18

    In recent years, there have been increasing interests in developing food-grade Pickering stabilizers, due to their potential applications in formulations of novel functional foods. The present work was to investigate the potential of soy proteins to be developed into a kind of Pickering-like stabilizer for oil-in-water emulsions. The nanoparticle aggregates of soy protein isolate (SPI) were formed by sequential treatments of heating at 95 °C for 15 min and then electrostatic screening with NaCl addition. The particle size and microstructure of these aggregates were characterized using dynamic light scattering and atomic force microscopy, indicating that the fabricated nanoparticle aggregates were ∼100 nm in size with more surface hydrophobic nature (relative to unheated SPI). The influence of particle concentration (c; 0.5-6.0%, w/w) and increasing oil fraction (ϕ; in the range 0.2-0.6) on the droplet size and coalescence and/or creaming stability of the emulsions stabilized by these nanoparticle aggregates was investigated. The results showed that, at ϕ = 0.2, increasing the c resulted in a progressive but slight decrease in droplet size, and improved the stability against coalescence and creaming; at a specific c, the creaming stability was progressively increased by increasing the ϕ, with better improvement observed at a higher c (e.g., 6.0% vs 2.0%). The improvement of creaming stability was largely associated with the formation of a gel-like network that could entrap the oil droplets within the network. The observations are generally consistent with those observed for the conventional Pickering emulsions, confirming that soy proteins could be applied as a kind of effective Pickering-like stabilizer. The finding may have important implications for the design and fabrication of protein-based emulsion formulations, and even for the development of soy protein products with some unique functions. To the authors' knowledge, this is the first work to report

  8. Impact of reduced tillage and organic inputs on aggregate stability and earthworm community in a Breton context in France

    NASA Astrophysics Data System (ADS)

    Paillat, Louise; Menasseri, Safya; Busnot, Sylvain; Roucaute, Marc; Benard, Yannick; Morvan, Thierry; Pérès, Guénola

    2017-04-01

    Soil aggregate stability, which refers to the ability of soil aggregates to resist breakdown when disruptive forces are applied (water, wind), is a good indicator of the sensitivity of soil to crusting and erosion and is a relevant indicator for soil stability. Within soil parameters which affect soil stability, organic matter is one of the main important by functioning as bonding agent between mineral soil particles, but soil organisms such as microorganisms and earthworms are also recognized as efficient agents. However the relationship between earthworms, fungal hyphae and aggregation is still unclear. In order to assess the influence of these biological agents on aggregate dynamics, we have combined a field study and a laboratory experiment. On a long term experiment trial in Brittany, SOERE PRO-EFELE, we have studied the effect of reduced tillage (vs. conventional tillage) combined to organic inputs (vs. mineral inputs) on earthworm community and soil stability. Aggregate stability was measured at different perturbations intensities: fast wetting (FW), slow wetting (SW) and mechanical breakdown (MB). This study showed that after 4 years of experiments, reduced tillage and organic inputs enhanced aggregate stability. Earthworms modulated aggregation process: endogeics reduced FW stability (mechanical binding by hyphae) and anecics increased SW stability (aggregate interparticular cohesion and hydrophobicity). Some precisions were provided by the laboratory experiment, using microcosms, which compared casts of the endogeic Aporectodea c. caliginosa (NCCT) and the anecic Lumbricus terrestris (LT). The presumed hyphae fragmentation by endogeics could not be highlight in NCCT casts. Nevertheless, hyphae were more abundant and C content and aggregate stability were higher in LT casts corroborating the positive contribution of anecics to aggregate stability.

  9. Scalable and fault tolerant orthogonalization based on randomized distributed data aggregation

    PubMed Central

    Gansterer, Wilfried N.; Niederbrucker, Gerhard; Straková, Hana; Schulze Grotthoff, Stefan

    2013-01-01

    The construction of distributed algorithms for matrix computations built on top of distributed data aggregation algorithms with randomized communication schedules is investigated. For this purpose, a new aggregation algorithm for summing or averaging distributed values, the push-flow algorithm, is developed, which achieves superior resilience properties with respect to failures compared to existing aggregation methods. It is illustrated that on a hypercube topology it asymptotically requires the same number of iterations as the optimal all-to-all reduction operation and that it scales well with the number of nodes. Orthogonalization is studied as a prototypical matrix computation task. A new fault tolerant distributed orthogonalization method rdmGS, which can produce accurate results even in the presence of node failures, is built on top of distributed data aggregation algorithms. PMID:24748902

  10. Effect of visible and UV irradiation on the aggregation stability of CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Tsipotan, Aleksei S.; Gerasimova, Marina A.; Aleksandrovsky, Aleksandr S.; Zharkov, Sergey M.; Slabko, Vitaliy V.

    2016-11-01

    The possibility of controlling the aggregation stability of CdTe quantum dots (QDs) stabilized by thioglycolic acid (TGA) is important for implementation of quasi-resonant laser-induced self-assembly. This study examines the influence of irradiation by the UV as well as by the visible light on the photostimulated aggregation of QDs. Different photochemical mechanisms are identified, depending on whether light wavelength falls into an interband transition or the first exciton transition. Irradiation by visible light does not lead to changes in the absorption spectra but decreases luminescence intensity through the detachment of TGA and the formation of dangling bonds, leading to the creation of radiativeless relaxation centers. UV irradiation (in the 300-370 nm range), at an intensity of 0.4 W/cm2, initially (during the first 75 min) leads to the degradation of the stabilizer and QDs' surface. After 75 min of combined UV and visible light irradiation, a gradual increase in spontaneous aggregation takes place, testifying excessive decrease in stabilizing potential barrier height. Hence, the laser-induced self-assembly of CdTe QDs is recommended to be performed over a time period of between 80 and 100 min after the beginning of low-intensity UV irradiation under conditions equivalent to those applied in this study.

  11. Anionic Polyacrylamide (PAM) and Extracellular Polysaccharides (EPS) effects on flocculation and aggregate stability of soil

    NASA Astrophysics Data System (ADS)

    Albalasmeh, A. A.; Gharaibeh, M. A.; Ghezzehei, T. A.

    2015-12-01

    Soil structure influences many soil properties including aeration, water retention, drainage, bulk density, and resistance to erosion and indirectly influences most biological and chemical processes that occur in and around soil. A significant amount of literature showed that PAM plays an important role to control erosion. However, researchers are looking for more natural alternative for PAM. This study evaluated two anionic polymers including low and high molecular weight (MW), root exudates and bacterial exudates. We evaluated their influence on the rate and efficacy of colloid flocculation and the percent of water stable aggregates. We found that PAM was more effective than EPS in flocculating the colloids and all polymers increased the percent of stable soil aggregates although the PAM was more effective. These data suggest that the EPS would be less effective than PAM for reducing water erosion owing to its lesser flocculation and aggregate stabilizing potential.

  12. Stability and aggregation of metal oxide nanoparticles in natural aqueous matrices.

    PubMed

    Keller, Arturo A; Wang, Hongtao; Zhou, Dongxu; Lenihan, Hunter S; Cherr, Gary; Cardinale, Bradley J; Miller, Robert; Ji, Zhaoxia

    2010-03-15

    There is a pressing need for information on the mobility of nanoparticles in the complex aqueous matrices found in realistic environmental conditions. We dispersed three different metal oxide nanoparticles (TiO(2), ZnO and CeO(2)) in samples taken from eight different aqueous media associated with seawater, lagoon, river, and groundwater, and measured their electrophoretic mobility, state of aggregation, and rate of sedimentation. The electrophoretic mobility of the particles in a given aqueous media was dominated by the presence of natural organic matter (NOM) and ionic strength, and independent of pH. NOM adsorbed onto these nanoparticles significantly reduces their aggregation, stabilizing them under many conditions. The transition from reaction to diffusion limited aggregation occurs at an electrophoretic mobility from around -2 to -0.8 microm s(-1) V(-1) cm. These results are key for designing and interpreting nanoparticle ecotoxicity studies in various environmental conditions.

  13. [Effect of Biochar Application on Soil Aggregates Distribution and Moisture Retention in Orchard Soil].

    PubMed

    An, Yan; Ji, Qiang; Zhao, Shi-xiang; Wang, Xu-dong

    2016-01-15

    Applying biochar to soil has been considered to be one of the important practices in improving soil properties and increasing carbon sequestration. In order to investigate the effects of biochar application on soil aggregates distribution and its organic matter content and soil moisture constant in different size aggregates, various particle-size fractions of soil aggregates were obtained with the dry-screening method. The results showed that, compared to the treatment without biochar (CK), the application of biochar reduced the mass content of 5-8 mm and < 0.25 mm soil aggregates at 0-10 cm soil horizon, while increased the content of 1-2 mm and 2-5 mm soil aggregates at this horizon, and the content of 1-2 mm aggregates significantly increased along with the rates of biochar application. The mean diameter of soil aggregates was reduced by biochar application at 0-10 cm soil horizon. However, the effect of biochar application on the mean diameter of soil aggregates at 10-20 cm soil horizon was not significant. Compared to CK, biochar application significantly increased soil organic carbon content in aggregates, especially in 1-2 mm aggregates which was increased by > 70% compared to CK. Both the water holding capacity and soil porosity were significantly increased by biochar application. Furthermore, the neutral biochar was more effective than alkaline biochar in increasing soil moisture.

  14. Glycosaminoglycan-mediated selective changes in the aggregation states, zeta potentials, and intrinsic stability of liposomes.

    PubMed

    Nyren-Erickson, Erin K; Haldar, Manas K; Totzauer, Jessica R; Ceglowski, Riley; Patel, Dilipkumar S; Friesner, Daniel L; Srivastava, D K; Mallik, Sanku

    2012-11-20

    Though the aggregation of glycosaminoglycans (GAGs) in the presence of liposomes and divalent cations has been previously reported, the effects of different GAG species and minor changes in GAG composition on the aggregates that are formed are yet unknown. If minor changes in GAG composition produce observable changes in the liposome aggregate diameter or zeta potential, such a phenomenon may be used to detect potentially dangerous oversulfated contaminants in heparin. We studied the mechanism of the interactions between heparin and its oversulfated glycosaminoglycan contaminants with liposomes. Herein, we demonstrate that Mg(2+) acts to shield the incoming glycosaminoglycans from the negatively charged phosphate groups of the phospholipids and that changes in the aggregate diameter and zeta potential are a function of the glycosaminoglycan species and concentration as well as the liposome bilayer composition. These observations are supported by TEM studies. We have shown that the organizational states of the liposome bilayers are influenced by the presence of GAG and excess Mg(2+), resulting in a stabilizing effect that increases the T(m) value of DSPC liposomes; the magnitude of this effect is also dependent on the GAG species and concentration present. There is an inverse relationship between the percent change in aggregate diameter and the percent change in aggregate zeta potential as a function of GAG concentration in solution. Finally, we demonstrate that the diameter and zeta potential changes in POPC liposome aggregates in the presence of different oversulfated heparin contaminants at low concentrations allow for an accurate detection of oversulfated chondroitin sulfate at concentrations of as low as 1 mol %.

  15. [Effects of human disturbance on soil aggregates content and their organic C stability in Karst regions].

    PubMed

    Wei, Ya-wei; Su, Yi-rong; Chen, Xiang-bi; He, Xun-yang; Qin, Wen-geng; Wei, Guo-fu

    2011-04-01

    Taking the primary forest land (PF), natural restoration land (NR), grazing grassland burned annually in winter (GB), and maize-sweet potato cropland (MS) in Karst regions of Northwest Guangxi as test objects, this paper studied the soil aggregates content and their organic C stability in the four ecosystems under different human disturbance patterns. The soil water-stable aggregates (>0.25 mm) content in PF, NR, and GB accounted for more than 70%, while that in MS was only 37%. The destruction rate of soil aggregates structure in the four ecosystems decreased in the sequence of MS (54.9%) > GB (23.2%) > NR (9.8%) and PF (9.6%), with significant differences among them (P<0.05). With increasing incubation time, the mineralization rate of soil aggregate organic C decreased after an initial increase and kept stable after 20 days, and increased with decreasing aggregate size. In the same size aggregates, the mineralization rate of organic C in the four ecosystems increased in the sequence of MS < GB and NR < PF. In PF, the mineralization ratio of soil organic C was 1.7% - 3.8%, being significantly higher than that in NR, GB, and MS. The cumulative mineralization amount of soil organic C had the same change trend with the mineralization rate. The contents of soil organic C and aggregate organic C were significantly positively correlated with the mineralization rate and cumulative mineralization amount of organic C, respectively, and significantly negatively correlated with the mineralization ratio of organic C.

  16. Thermal aggregation of human immunoglobulin G in arginine solutions: Contrasting effects of stabilizers and destabilizers.

    PubMed

    Yoshizawa, Shunsuke; Arakawa, Tsutomu; Shiraki, Kentaro

    2017-11-01

    Arginine is widely used as aggregation suppressor of proteins in biotechnology and pharmaceutics. However, why the effect of arginine depends on the types of proteins and stresses, including monoclonal antibodies, is still unclear. Here we investigated the precise processes of the thermal aggregation of human immunoglobulin G (IgG) in the presence of additives. As expected, arginine was the best additive to suppress the formation of insoluble aggregates during heat treatment, though it was unable to preserve the monomer content. A systematic analysis of the additives showed that sugars and kosmotropic ion inhibit the formation of soluble oligomers. These behaviors indicate that the thermal aggregation of IgG occurs by (i) the formation of soluble oligomers, which is triggered by the unfolding process that can be stabilized by typical osmolytes, and (ii) the formation of insoluble aggregates through weak cluster-cluster interactions, which can be suppressed by arginine. Understanding the detailed mechanism of arginine will provide useful information for the rational formulation design of antibodies. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Applying a new procedure to assess the controls on aggregate stability - including soil parent material and soil organic carbon concentrations - at the landscape scale

    NASA Astrophysics Data System (ADS)

    Turner, Gren; Rawlins, Barry; Wragg, Joanna; Lark, Murray

    2014-05-01

    Aggregate stability is an important physical indicator of soil quality and influences the potential for erosive losses from the landscape, so methods are required to measure it rapidly and cost-effectively. Previously we demonstrated a novel method for quantifying the stability of soil aggregates using a laser granulometer (Rawlins et al., 2012). We have developed our method further to mimic field conditions more closely by incorporating a procedure for pre-wetting aggregates (for 30 minutes on a filter paper) prior to applying the test. The first measurement of particle-size distribution is made on the water stable aggregates after these have been added to circulating water (aggregate size range 1000 to 2000 µm). The second measurement is made on the disaggregated material after the circulating aggregates have been disrupted with ultrasound (sonication). We then compute the difference between the mean weight diameters (MWD) of these two size distributions; we refer to this value as the disaggregation reduction (DR; µm). Soils with more stable aggregates, which are resistant to both slaking and mechanical breakdown by the hydrodynamic forces during circulation, have larger values of DR. We made repeated analyses of DR using an aggregate reference material (RM; a paleosol with well-characterised disaggregation properties) and used this throughout our analyses to demonstrate our approach was reproducible. We applied our modified technique - and also the previous technique in which dry aggregates were used - to a set of 60 topsoil samples (depth 0-15 cm) from cultivated land across a large region (10 000 km2) of eastern England. We wished to investigate: (i) any differences in aggregate stability (DR measurements) using dry or pre-wet aggregates, and (ii) the dominant controls on the stability of aggregates in water using wet aggregates, including variations in mineralogy and soil organic carbon (SOC) content, and any interaction between them. The sixty soil

  18. Mucilaginous aggregates in the northern Adriatic in the period 1999-2002: typology and distribution.

    PubMed

    Precali, Robert; Giani, Michele; Marini, Mauro; Grilli, Federica; Ferrari, Carla R; Pecar, Osvin; Paschini, Elio

    2005-12-15

    The spatial and temporal distributions of different types of visible mucilaginous aggregates were investigated monthly by underwater video cameras in the northern Adriatic (NA) from June 1999 to July 2002. Small aggregates (flocs, macroflocs and stringers) were observed in all seasons with higher values in autumn and winter. Larger aggregates (ribbons, cobwebs, clouds, and false bottoms) formed only during late-spring and summer, particularly in 2000 and 2002, when the seasonal thermohaline stratification was marked. In fact, the process of mucilage formation took place mainly in the upper water column, above the main pycnocline. The spatial distribution shows that higher concentrations of small aggregates occur in the more productive coastal waters. The larger aggregates form or accumulate mainly in coastal waters in the southern part of the NA and in the central part of the Po River delta-Rovinj transect, where a gyre greatly influences the aggregates distribution. The fronts between low salinity coastal waters and high salinity waters of southern origin play an important role for accumulation and aggregation of the mucilage during spring and summer. Most of the aggregates accumulate in correspondence with strong pycnoclines with differences in density anomaly of 2 kg m(-3) or higher. False bottoms formed in correspondence with strong haloclines (DeltaS congruent with 2), while cobwebs and ribbons also occurred when the halocline was less marked (DeltaS<0.5). Meteorological conditions greatly influenced the aggregate formation. Calm weather and weak winds favour aggregation processes, while strong north-easterly winds, causing intense mixing, result in the dispersion of the mucilaginous aggregates, as occurred during the Bora event in July 2000.

  19. Field soil aggregate stability kit for soil quality and rangeland health evaluations

    USGS Publications Warehouse

    Herrick, J.E.; Whitford, W.G.; de Soyza, A. G.; Van Zee, J. W.; Havstad, K.M.; Seybold, C.A.; Walton, M.

    2001-01-01

    Soil aggregate stability is widely recognized as a key indicator of soil quality and rangeland health. However, few standard methods exist for quantifying soil stability in the field. A stability kit is described which can be inexpensively and easily assembled with minimal tools. It permits up to 18 samples to be evaluated in less than 10 min and eliminates the need for transportation, minimizing damage to soil structure. The kit consists of two 21??10.5??3.5 cm plastic boxes divided into eighteen 3.5??3.5 cm sections, eighteen 2.5-cm diameter sieves with 1.5-mm distance openings and a small spatula used for soil sampling. Soil samples are rated on a scale from one to six based on a combination of ocular observations of slaking during the first 5 min following immersion in distilled water, and the percent remaining on a 1.5-mm sieve after five dipping cycles at the end of the 5-min period. A laboratory comparison yielded a correlation between the stability class and percent aggregate stability based on oven dry weight remaining after treatment using a mechanical sieve. We have applied the method in a wide variety of agricultural and natural ecosystems throughout western North America, including northern Mexico, and have found that it is highly sensitive to differences in management and plant community composition. Although the field kit cannot replace the careful laboratory-based measurements of soil aggregate stability, it can clearly provide valuable information when these more intensive procedures are not possible.

  20. Effects of three different biochars on aggregate stability, organic carbon mobility and micronutrient bioavailability.

    PubMed

    Hartley, William; Riby, Philip; Waterson, James

    2016-10-01

    Previous studies have demonstrated both beneficial and detrimental effects on soil properties from biochar incorporation. Several biochars, with different feedstock origins, were evaluated for their effectiveness at improving soil quality of a sandy agricultural soil. A pot trial was used to investigate aggregate stability and microbial activity, pore water trace element mobility and micronutrient concentrations in grain of spring wheat after incorporation of three biochars. The feedstocks for biochar production were selected because they were established UK waste products, namely oversize woody material from green waste composting facilities, and rhododendron and soft wood material from forest clearance operations. Biochars were incorporated into the soil at a rate of 5% v/v. Aggregate stability was improved following addition of oversize biochar whilst microbial activity increased in all treatments. Dissolved organic carbon (DOC) concentrations in soil pore water from biochar-treated soils were raised, whilst micronutrient concentrations in wheat grain grown in the treated soils were significantly reduced. It was concluded that incorporation of biochar to temperate agricultural soils requires caution as it may result in reductions of essential grain micronutrients required for human health, whilst the effect on aggregate stability may be linked to organic carbon functional groups on biochar surfaces and labile carbon released from the char into the soil system. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Interfacial aggregation of a nonionic surfactant: Effect on the stability of silica suspensions

    SciTech Connect

    Giordano-Palmino, F.; Denoyel, R.; Rouquerol, J. . Centre de thermodynamique et Microcalorimetrie)

    1994-06-01

    Nonionic surfactants are in widespread use in technological applications such as flotation, detergency, suspension stabilization (paints, ceramic preparation, pharmaceuticals, cosmetics), and enhanced oil recovery. The adsorption of the nonionic surfactant TX 100 in two silica suspensions (Ludox HS40 and Syton W30) has been studied with the aim of relating the structure of the adsorbed layer to the stability of the suspension. First, a thermodynamic study based on the determination of adsorption isotherms and displacement enthalpies as a function of pH and solid/liquid ratio was carried out and lead to the conclusion that such a surfactant forms micelle-like aggregates on the silica surface. Then, a stability study based on visual observation, turbidimetry, and particle size determination (by photon correlation spectroscopy) was performed in order to determine the TX 100 concentration range in which flocculation occurs. Considering that the surface is covered with micelle-like aggregates in the flocculation range and that the [zeta]-potential (determined by microelectrophoresis) has varied only slightly at the onset of flocculation, it is concluded that the flocculation mechanism is a bridging of particles by surface micelles. This bridging of particles by aggregates similar in size and shape could be an explanation of the presence, in such systems, of optimum flocculation at half surface coverage.

  2. Stabilization of recombinant human growth hormone against emulsification-induced aggregation by Pluronic surfactants during microencapsulation.

    PubMed

    Wei, Gang; Lu, Li Fang; Lu, Wei Yue

    2007-06-29

    Protein aggregation upon exposing to the water/organic solvent interface is one of the most significant obstacles in developing poly(lactic-co-glycolic acid) (PLGA) microspheres with double emulsion process. The aim of present study is to devise a formulation strategy to prevent recombinant human growth hormone (rhGH) from aggregation during microencapsulation. The excipients used for stabilizing rhGH were selected from sugars, nonionic surfactants, polyol, and protein. Among the candidates, surfactants exhibited potentialities in protecting rhGH against emulsification-induced aggregation. It was also found that Pluronic F127 showed an outstanding as well as concentration-dependent stabilizing effect on rhGH, which was different to Pluronic F68 and Tween 20. After the rhGH solution comprising F127 and sucrose was emulsified with methylene chloride, the recovery of monomeric protein achieved 99.0%, principally attributed to the presence of F127. This solution was subsequently encapsulated as inner aqueous phase in the PLGA microspheres by a conventional double emulsion process, with the encapsulation efficiency higher than 98%. Improvement in the release of rhGH was observed for the microspheres co-encapsulating Pluronic F127 regardless in the presence or absence of sucrose, compared to the microspheres containing rhGH alone. The result further implied that co-encapsulation of Pluronic F127 in the microspheres played an important role in the stabilization of rhGH.

  3. Water stability of aggregates in subtropical and tropical soils (Georgia and China) and its relationships with the mineralogy and chemical properties

    NASA Astrophysics Data System (ADS)

    Alekseeva, T. V.; Sokolowska, Z.; Hajnos, M.; Alekseev, A. O.; Kalinin, P. I.

    2009-04-01

    Water-stable aggregates isolated from three subtropical and one tropical soil (Western Georgia and China) were studied for their organic carbon, cation exchange capacity (CEC), specific surface area, magnetic susceptibility, and total chemical elements. The soils were also studied for their particle-size distribution, mineralogy, and nonsilicate Fe and Al oxides. Describe the water stability, three indices have been used: the content of water-stable macroaggregates (>0.25 mm), the mean weighted diameter of the aggregates, and the numerical aggregation index. The yellow-cinnamonic soil (China) was neutral, and the three other soils were acid. The soils were degraded with a low content of organic matter. The yellow-cinnamonic soil was characterized by the lowest water stability due to the predominantly vermiculite composition of the clay. The high water stability of the Oxisol structure was determined by the kaolinites and high content of oxides. In three out of the four soils studied, the hierarchical levels of the soil structure organization were defined; they were identified by the content of organic matter and the Ca + Mg (in Oxisols). Iron oxides mainly participated in the formation of micro-aggregates; Al and Mn contributed to the formation of macroaggregates. The water-stable aggregates acted as sorption geochemical barriers and accumulated Pb, Zn, Cd, Cs, and other trace elements up to concentrations exceeding their levels in the soil by 5 times and more. The highest correlations were obtained with CEC, Mn, and P rather than with organic carbon and Fe.

  4. Optimum Aggregation and Control of Spatially Distributed Flexible Resources in Smart Grid

    SciTech Connect

    Bhattarai, Bishnu; Mendaza, Iker Diaz de Cerio; Myers, Kurt S.; Bak-Jensen, Brigitte; Paudyal, Sumit

    2017-01-01

    This study optimally aggregates spatially distributed flexible resources at strategic microgrid/smart-grid locations and reduces a distribution network having thousands of nodes to an equivalent network having few aggregated nodes. Such aggregation enables trading of aggregated flexible resources to different power/energy market on behalf of small distributed flexible resources. Moreover, a hierarchical control architecture comprising a combination of centralized and decentralized control approaches are proposed to deploy the aggregated flexibilities in fulfilling grid requirements and solving constraint violations. This serve as a great operational tool for distribution system operators (DSOs) to decide the exact amount of flexibilities from different network sections for solving particular grid constraints. The effectiveness of the proposed method is demonstrated through simulation of three operational scenarios performed in a real low voltage distribution system that is having high penetrations of electric vehicles and heat pumps. The simulation results demonstrated that the proposed method not only help DSOs in taking effective decision to utilize available flexibilities, but also in effective materialization of the demand flexibilities within a given aggregated area.

  5. Optimum Aggregation and Control of Spatially Distributed Flexible Resources in Smart Grid

    DOE PAGES

    Bhattarai, Bishnu; Mendaza, Iker Diaz de Cerio; Myers, Kurt S.; ...

    2017-03-24

    This paper presents an algorithm to optimally aggregate spatially distributed flexible resources at strategic microgrid/smart-grid locations. The aggregation reduces a distribution network having thousands of nodes to an equivalent network with a few aggregated nodes, thereby enabling distribution system operators (DSOs) to make faster operational decisions. Moreover, the aggregation enables flexibility from small distributed flexible resources to be traded to different power and energy markets. A hierarchical control architecture comprising a combination of centralized and decentralized control approaches is proposed to practically deploy the aggregated flexibility. The proposed method serves as a great operational tool for DSOs to decide themore » exact amount of required flexibilities from different network section(s) for solving grid constraint violations. The effectiveness of the proposed method is demonstrated through simulation of three operational scenarios in a real low voltage distribution system having high penetrations of electric vehicles and heat pumps. Finally, the simulation results demonstrated that the aggregation helps DSOs not only in taking faster operational decisions, but also in effectively utilizing the available flexibility.« less

  6. Formulation of artificial aggregates from dredged harbour sediments for coastline stabilization.

    PubMed

    Brakni, Samira; Abriak, Nor Edine; Hequette, Arnaud

    2009-07-01

    Coastal erosion is a common phenomenon along the shores of the member states of the European Union. In 2004, approximately 20,000 km of coastlines, accounting for 20% of the whole of the EU coastline, were considered particularly affected by this phenomenon. Coastal erosion and shoreline retreat already affect a significant proportion of the French coast, the beaches in the north of France being no exception, and will probably increase during the 21st Century because of climate change. Because erosion is often accentuated by sedimentary deficits, artificial beach replenishment often represents an appropriate engineering solution for coastline stabilization. Meanwhile, large quantities of sediments are dredged every year from ports, with approximately 25 to 45 million tons of sediments (dry matter) per year being dredged for the maintenance of harbours. The purpose of the study presented in this article is to report on the potential use of artificial aggregates formulated with harbour sediments in order to recharge beaches and/or nearshore environments. The manufacture of the aggregates consisted of several stages, beginning with the characterization and the preparation of the sediment before the fabrication of aggregates by extrusion, associating the sediments with a specific hydraulic binder. Various parameters, such as water content of the mixing sediment, the cement content and the shape of the aggregates, were taken into account, in order to ensure the criteria regarding the strength of these aggregates are entirely fulfilled. The first simulations in a wave flume are encouraging and reveal the possibilities for use of the aggregates in coastal engineering.

  7. Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China

    PubMed Central

    Fang, Xiang-Min; Chen, Fu-Sheng; Wan, Song-Ze; Yang, Qing-Pei; Shi, Jian-Min

    2015-01-01

    The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0–15 cm) and deep soil (30–45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years. PMID:26418563

  8. Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China.

    PubMed

    Fang, Xiang-Min; Chen, Fu-Sheng; Wan, Song-Ze; Yang, Qing-Pei; Shi, Jian-Min

    2015-01-01

    The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0-15 cm) and deep soil (30-45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years.

  9. Kinetic study of aggregation of milk protein and/or surfactant-stabilized oil-in-water emulsions by sedimentation field-flow fractionation.

    PubMed

    Kenta, Stella; Raikos, Vassilios; Vagena, Artemis; Sevastos, Dimitrios; Kapolos, John; Koliadima, Athanasia; Karaiskakis, George

    2013-08-30

    Milk proteins are able to facilitate the formation and stabilization of oil droplets in food emulsions. This study employed Sedimentation Field-Flow Fractionation (SdFFF) to monitor changes in particle size distribution of freshly prepared emulsions with varying weight contributions of sodium caseinate (SC) and whey protein concentrate (WPC). The effect of the addition of Tween 80 (T) on the initial droplet size was also investigated. The results indicated that emulsifying ability follows the order Tween 80>WPC>SC, with corresponding weight average droplet diameter of 0.319, 0.487 and 0.531μm respectively, when each of the above emulsifiers was used solely. The stability of sodium caseinate emulsions was studied at 30.5 and 80.0°C by measuring the particle size distribution for a period of 70h. Emulsions withstood the temperatures and exhibited an initial increase in particle size distribution caused by heat-induced droplet aggregation, followed by a decrease to approximately the initial droplet size. The rate of droplet aggregation depends on the severity of thermal processing, as revealed by the kinetics of particle aggregation during aging at different temperatures. Comparison of the experimental rate constants found from SdFFF, with those determined theoretically gives invaluable information about the oil droplet stability and the aggregation mechanism. Based on the proposed mechanistic scheme various physicochemical quantities, which are very important in explaining the stability of oil-in-water emulsions, were determined. Finally, the advantages of SdFFF in studying the aggregation of the oil-in-water droplets, in comparison with other methods used for the same purpose, are discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. Soil microbial parameters and stability of soil aggregate fractions under different grassland communities on the Loess Plateau, China

    USDA-ARS?s Scientific Manuscript database

    Over-grazing and large scale monocultures on the Loess plateau in China have caused serious soil erosion by water and wind. Grassland revegetation has been reported as one of the most effective counter measures. Therefore, we investigated soil aggregation, aggregate stability and soil microbial ac...

  11. Aggregates and their distributions determined from LOPC observations made using an autonomous profiling float

    NASA Astrophysics Data System (ADS)

    Petrik, Colleen M.; Jackson, George A.; Checkley, David M., Jr.

    2013-04-01

    The vertical flux of particles in the ocean drives the movement of organic carbon to the deep ocean. We have been studying the distribution and flux of these particles using the SOLOPC, a profiling Lagrangian (SOLO) float with a Laser Optical Particle Counter (LOPC). We have been able to distinguish between aggregate-like and zooplankton-like particles with diameters >2mm but needed a way to separate the smaller particles into aggregates and zooplankton. Observations included a lognormal-shaped fraction in the normalized volume distribution similar to that observed in results for simulations of particles in the euphotic zone. By fitting a lognormal distribution to the volume spectrum of particles with diameters ≤2mm, we have been successful at making a separation of marine snow material from other, presumably living, particles. The particle volumes derived using the separations are positively correlated with fluorescence, particulate organic carbon, and the volume of larger particles classified as aggregate-like, which supports the conclusion that these particles are truly aggregates, in some cases derived from phytoplankton. The residual volumes (total less the above fit) are highly correlated with the volumes of large, zooplankton-like particles. Downward velocities of the aggregate fraction calculated from time series of particle profiles are consistent with previous estimates of particle settling rates (20-70md-1). We now have a tool to estimate aggregate distributions, properties, and vertical fluxes in the euphotic zone, including when and where they change.

  12. Salt bridge stabilization of charged zwitterionic arginine aggregates in the gas phase.

    PubMed

    Julian, R R; Hodyss, R; Beauchamp, J L

    2001-04-18

    The discovery of several new unusually stable aggregates of arginine that are intermolecularly bound by salt bridges is reported. Quadrupole ion-trap mass spectrometry provides evidence for the stability of arginine in the zwitterionic state, where the protonated guanidinium group of one arginine interacts strongly with the carboxylate of another to form stable noncovalent complexes, coordinated to either a cation or anion. Clusters of arginine with itself, sodium, potassium, lithium, magnesium, chloride, fluoride, bromide, iodide, and nitrate are observed. DFT calculations at the B3LYP/6-31G level are used to assess the structures and energetics of particularly prominent clusters. An examination of mixtures of D-arginine with isotopically labeled L-arginine indicates that the stability of these clusters does not depend on arginine enantiomeric purity. The cyclic trimers of arginine, capped with either Cl(-) or NO(3)(-), possess exceptional stability.

  13. [Effects of Tillage on Distribution of Heavy Metals and Organic Matter Within Purple Paddy Soil Aggregates].

    PubMed

    Shi, Qiong-bin; Zhao, Xiu-lan; Chang, Tong-ju; Lu, Ji-wen

    2016-05-15

    A long-term experiment was utilized to study the effects of tillage methods on the contents and distribution characteristics of organic matter and heavy metals (Cu, Zn, Pb, Cd, Fe and Mn) in aggregates with different sizes (including 1-2, 0.25-1, 0.05-0.25 mm and < 0.05 mm) in a purple paddy soil under two tillage methods including flooded paddy field (FPF) and paddy-upland rotation (PR). The relationship between heavy metals and organic matter in soil aggregates was also analyzed. The results showed that the aggregates of two tillage methods were dominated by 0.05-0.25 mm and < 0.05 mm particle size, respectively. The contents of organic matter in each aggregate decreased with the decrease of aggregate sizes, however, compared to PR, FPF could significantly increase the contents of organic matter in soils and aggregates. The tillage methods did not significantly affect the contents of heavy metals in soils, but FPF could enhance the accumulation and distribution of aggregate, organic matter and heavy metals in aggregates with diameters of 1-2 mm and 0.25-1 mm. Correlation analysis found that there was a negative correlation between the contents of heavy metals and organic matter in soil aggregates, but a positive correlation between the amounts of heavy metal and organic matter accumulated in soil aggregates. From the slope of the correlation analysis equations, we could found that the sensitivities of heavy metals to the changes of soil organic matters followed the order of Mn > Zn > Pb > Cu > Fe > Cd under the same tillage. When it came to the same heavy metal, it was more sensitive in PR than in FPF.

  14. Physicochemical studies on the biopolymer inulin: a critical evaluation of its self-aggregation, aggregate-morphology, interaction with water, and thermal stability.

    PubMed

    Dan, Abhijit; Ghosh, Soumen; Moulik, Satya P

    2009-09-01

    Physicochemical properties viz., aggregation, molar mass, shape, and size of chicory inulin in solution were determined by fluorimetry, DLS, SLS, TEM, and viscometry methods. The thermal stability of the biopolymer was examined by TGA, DTA, and DSC measurements. The water vapor adsorption of desiccated inulin was also studied by the isopiestic method, and the data were analyzed in the light of the BET equation. On the basis of the obstruction to ion conductance by the inulin aggregates in solution and analysis of the data, the extent of hydration of inulin in solution was estimated. The result was coupled with the intrinsic viscosity, [eta], of inulin to ascertain the shape of the biopolymer aggregates in aqueous solution. The critical aggregation concentration (cac) of inulin in aqueous as well as in salt solution was assessed by fluorimetry. The weight average molar mass, Mw , of inulin monomer and its aggregate was found to be 4468 and 1.03 x 10(6) g/mol, respectively, in aqueous solution. This aggregated mass was 2.4 x 10(6) g/mol in 0.5M NH(4)SCN solution. The [eta] values of the soft supramolecular aggregates in solution (without and with salt) were small and comparable with globular proteins evidencing spherical geometry of the biopolymer aggregates as supported by the TEM results. In DMSO, rod-like aggregates of inulin was found by the TEM study. The [eta] of the biopolymer in the DMSO medium was therefore, higher than that in the aqueous medium. Unlike aqueous medium, the aggregation in DMSO was not associated with a cac.

  15. Linking soil permeability and soil aggregate stability with root development: a pots experiment (preliminary results)

    NASA Astrophysics Data System (ADS)

    Vergani, Chiara; Graf, Frank; Gerber, Werner

    2015-04-01

    Quantifying and monitoring the contribution of vegetation to the stability of the slopes is a key issue for implementing effective soil bioengineering measures. This topic is being widely investigated both from the hydrological and mechanical point of view. Nevertheless, due to the high variability of the biological components, we are still far from a comprehensive understanding of the role of plants in slope stabilization, especially if the different succession phases and the temporal development of vegetation is considered. Graf et al., 2014, found within the scope of aggregate stability investigations that the root length per soil volume of alder specimen grown for 20 weeks under laboratory conditions is comparable to the one of 20 years old vegetation in the field. This means that already relatively short time scales can provide meaningful information at least for the first stage of colonization of soil bioengineering measures, which is also the most critical. In the present study we analyzed the effect of root growth on two soil properties critical to evaluate the performance of vegetation in restoring and re-stabilizing slopes: permeability and soil aggregate stability. We set up a laboratory experiment in order to work under controlled conditions and limit as much as possible the natural variability. Alnus incana was selected as the study species as it is widely used in restoration projects in the Alps, also because of its capacity to fix nitrogen and its symbiosis with both ecto and arbuscular mycorrhizal fungi. After the first month of growth in germination pots, we planted one specimen each in big quasi cylindrical pots of 34 cm diameter and 35 cm height. The pots were filled with the soil fraction smaller than 10 mm coming from an oven dried moraine collected in a subalpine landslide area (Hexenrübi catchment, central Switzerland). The targeted dry unit weight was 16 kN/m3. The plants have been maintained at a daily temperature of 25°C and relative

  16. Kinetics and cluster morphology evolution of shear-driven aggregation of well-stabilized colloids.

    PubMed

    Meng, Xia; Wu, Hua; Morbidelli, Massimo

    2015-01-27

    We investigate the shear-driven aggregation of polystyrene colloids that are stabilized by both fixed and surfactant charges, using a microchannel device, in various particle volume fractions. The objective is to understand how the primary particles evolve to clusters with shearing time, how the cluster morphology develops along the aggregation with the effect of breakage and restructuring, and whether non-Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions are present, affecting the kinetics. The time evolution of the primary particle conversion to big clusters is characterized by an induction time, followed by an explosive increase when the cluster size reaches a certain critical value, which confirms the self-acceleration kinetics developed in the literature. The size of the critical clusters has been quantified for the first time, and its scaling with the shear rate follows the literature prediction well. Moreover, analysis of the shear-driven kinetics confirms the presence of substantial non-DLVO interactions in the given system.

  17. Fractal analysis of the effect of particle aggregation distribution on thermal conductivity of nanofluids

    NASA Astrophysics Data System (ADS)

    Wei, Wei; Cai, Jianchao; Hu, Xiangyun; Han, Qi; Liu, Shuang; Zhou, Yingfang

    2016-08-01

    A theoretical effective thermal conductivity model for nanofluids is derived based on fractal distribution characteristics of nanoparticle aggregation. Considering two different mechanisms of heat conduction including particle aggregation and convention, the model is expressed as a function of the fractal dimension and concentration. In the model, the change of fractal dimension is related to the variation of aggregation shape. The theoretical computations of the developed model provide a good agreement with the experimental results, which may serve as an effective approach for quantitatively estimating the effective thermal conductivity of nanofluids.

  18. Estimating equilibrium constants for aggregation from the product distribution of a dynamic combinatorial library.

    PubMed

    Hunt, Rosemary A R; Ludlow, R Frederick; Otto, Sijbren

    2009-11-19

    Multicomponent chemical systems that exhibit a network of covalent and intermolecular interactions may produce interesting and often unexpected chemical or physical behavior. The formation of aggregates is a well-recognized example and presents a particular analytical challenge. We now report the development of a numerical fitting method capable of estimating equilibrium constants for the formation of aggregates from the product distribution of a dynamic combinatorial library containing self-recognizing library members.

  19. Rational design of mutations that change the aggregation rate of a protein while maintaining its native structure and stability

    PubMed Central

    Camilloni, Carlo; Sala, Benedetta Maria; Sormanni, Pietro; Porcari, Riccardo; Corazza, Alessandra; De Rosa, Matteo; Zanini, Stefano; Barbiroli, Alberto; Esposito, Gennaro; Bolognesi, Martino; Bellotti, Vittorio; Vendruscolo, Michele; Ricagno, Stefano

    2016-01-01

    A wide range of human diseases is associated with mutations that, destabilizing proteins native state, promote their aggregation. However, the mechanisms leading from folded to aggregated states are still incompletely understood. To investigate these mechanisms, we used a combination of NMR spectroscopy and molecular dynamics simulations to compare the native state dynamics of Beta-2 microglobulin (β2m), whose aggregation is associated with dialysis-related amyloidosis, and its aggregation-resistant mutant W60G. Our results indicate that W60G low aggregation propensity can be explained, beyond its higher stability, by an increased average protection of the aggregation-prone residues at its surface. To validate these findings, we designed β2m variants that alter the aggregation-prone exposed surface of wild-type and W60G β2m modifying their aggregation propensity. These results allowed us to pinpoint the role of dynamics in β2m aggregation and to provide a new strategy to tune protein aggregation by modulating the exposure of aggregation-prone residues. PMID:27150430

  20. Rational design of mutations that change the aggregation rate of a protein while maintaining its native structure and stability

    NASA Astrophysics Data System (ADS)

    Camilloni, Carlo; Sala, Benedetta Maria; Sormanni, Pietro; Porcari, Riccardo; Corazza, Alessandra; De Rosa, Matteo; Zanini, Stefano; Barbiroli, Alberto; Esposito, Gennaro; Bolognesi, Martino; Bellotti, Vittorio; Vendruscolo, Michele; Ricagno, Stefano

    2016-05-01

    A wide range of human diseases is associated with mutations that, destabilizing proteins native state, promote their aggregation. However, the mechanisms leading from folded to aggregated states are still incompletely understood. To investigate these mechanisms, we used a combination of NMR spectroscopy and molecular dynamics simulations to compare the native state dynamics of Beta-2 microglobulin (β2m), whose aggregation is associated with dialysis-related amyloidosis, and its aggregation-resistant mutant W60G. Our results indicate that W60G low aggregation propensity can be explained, beyond its higher stability, by an increased average protection of the aggregation-prone residues at its surface. To validate these findings, we designed β2m variants that alter the aggregation-prone exposed surface of wild-type and W60G β2m modifying their aggregation propensity. These results allowed us to pinpoint the role of dynamics in β2m aggregation and to provide a new strategy to tune protein aggregation by modulating the exposure of aggregation-prone residues.

  1. Stabilization of bovine insulin against agitation-induced aggregation using RNA aptamers.

    PubMed

    Malik, Ravinder; Roy, Ipsita

    2013-08-16

    Stabilization of monomeric insulin is a primary requirement for preserving the efficacy of the final formulation. Degraded and/or aggregated protein as well as the presence of any of the conventional excipients can result in immunogenic or anaphylactic reactions, and reduced bioavailability of the protein drug. The aim of this work was to select novel RNA-based stabilizers of bovine insulin which would recognize and bind to the monomeric protein and help retain its bioactivity. RNA aptamers were selected by an in vitro selection method. They were screened for their ability to inhibit insulin fibrillation using agitation as a stress condition. The in vitro activity of insulin was determined by phosphorylation of downstream proteins in the cell. In vivo bioactivity was determined in a diabetic rat model. RNA aptamers, which bound to insulin with very low dissociation constants and high specificity, were selected. These sequences were aligned and consensus regions were found. The RNA sequences had no effect on the signalling cascade initiated by insulin. The bioactivity of insulin, as measured by its ability to lower plasma glucose level in a diabetic rat model, also remained unchanged. RNA aptamers are a novel class of protein stabilizers which have the ability to disrupt protein-protein interactions and hence inhibit protein aggregation. Their non-toxic and non-immunogenic nature makes such formulations safe for use.

  2. Stability and Vapor Pressure of Aqueous Aggregates and Aerosols Containing a Monovalent Ion.

    PubMed

    Perez Sirkin, Yamila A; Factorovich, Matías H; Molinero, Valeria; Scherlis, Damián A

    2017-04-06

    The incidence of charged particles on the nucleation and the stability of aqueous aggregates and aerosols was reported more than a century ago. Many studies have been conducted ever since to characterize the stability, structure, and nucleation barrier of ion-water droplets. Most of these studies have focused on the free-energy surface as a function of cluster size, with an emphasis on the role of ionic charge and radius. This knowledge is fundamental to go beyond the rudimentary ion-induced classical nucleation theory. In the present article, we address this problem from a different perspective, by computing the vapor pressures of (H2O)nLi(+) and (H2O)nCl(-) aggregates using molecular simulations. Our calculations shed light on the structure, the critical size, the range of stability, and the role of ion-water interactions in aqueous clusters. Moreover, they allow one to assess the accuracy of the classical thermodynamic model, highlighting its strengths and weaknesses.

  3. Seasonal distribution, aggregation, and habitat selection of common carp in Clear Lake, Iowa

    USGS Publications Warehouse

    Penne, C.R.; Pierce, C.L.

    2008-01-01

    The common carp Cyprinus carpio is widely distributed and frequently considered a nuisance species outside its native range. Common carp are abundant in Clear Lake, Iowa, where their presence is both a symptom of degradation and an impediment to improving water quality and the sport fishery. We used radiotelemetry to quantify seasonal distribution, aggregation, and habitat selection of adult and subadult common carp in Clear Lake during 2005-2006 in an effort to guide future control strategies. Over a 22-month period, we recorded 1,951 locations of 54 adults and 60 subadults implanted with radio transmitters. Adults demonstrated a clear tendency to aggregate in an offshore area during the late fall and winter and in shallow, vegetated areas before and during spring spawning. Late-fall and winter aggregations were estimated to include a larger percentage of the tracked adults than spring aggregations. Subadults aggregated in shallow, vegetated areas during the spring and early summer. Our study, when considered in combination with previous research, suggests repeatable patterns of distribution, aggregation, and habitat selection that should facilitate common carp reduction programs in Clear Lake and similar systems. ?? Copyright by the American Fisheries Society 2008.

  4. Influence of sustainable management on aggregate stability and soil organic matter on agricultural soil of southern Spain

    NASA Astrophysics Data System (ADS)

    Morugan-Coronado, Alicia; Arcenegui, Victoria; Mataix-Solera, Jorge; Gomez-Lucas, Ignacio; Garcia-Orenes, Fuensanta

    2016-04-01

    Intensive agriculture has increased crop yields but also posed severe environmental problems. Unsustainable land management such as excessive tillage can lead to a loss of soil fertility and a drastic reduction in the aggregate stability and soil organic matter content. However sustainable agriculture can keep good crop yields with minimal impact on ecological factors conserving the soil quality and its ecosystem services. Sustainable agriculture management promotes the maintenance of soil organic matter levels providing plant nutrients through the microbial decomposition of organic materials. Also this management has a positive effect on soil structure with the improvement of stability of aggregates. The resistance of soil aggregates to the slaking and dispersive effects of water (aggregate stability) is important for maintaining the structure in arable soils. Our purpose was to investigate and compare the effects of sustainable agricultural practices versus intensive agriculture on aggregate stability and soil organic matter. Three agricultural areas are being monitored in the southern of Spain, two of them with citrus orchards (AL) and (FE) and one with grapevine(PA). In all of them two agricultural treatments are being developed, organic with no-tillage management(O) and inorganic fertilization with herbicide application and intensive tillage (I). The sustainable agricultural management (manure, no tillage and vegetation cover) contributed to the improve of soil conditions, increasing organic matter and aggregate stability. Meanwhile, herbicide treatment and intensive tillage with inorganic fertilization managements resulted in the decreasing of aggregate stability and low levels of soil organic carbon. Soil organic matter content is generally low in all unsustainable treatments plots and tends to decline in aggregate stability and soil physical condition. In both treatments the crop yield are comparable.

  5. Aggregation and Colloidal Stability of Commercially Available Al2O3 Nanoparticles in Aqueous Environments

    PubMed Central

    Mui, Julie; Ngo, Jennifer; Kim, Bojeong

    2016-01-01

    The aggregation and colloidal stability of three, commercially-available, gamma-aluminum oxide nanoparticles (γ-Al2O3 NPs) (nominally 5, 10, and 20–30 nm) were systematically examined as a function of pH, ionic strength, humic acid (HA) or clay minerals (e.g., montmorillonite) concentration using dynamic light scattering and transmission electron microscopy techniques. NPs possess pH-dependent surface charges, with a point of zero charge (PZC) of pH 7.5 to 8. When pH < PZC, γ-Al2O3 NPs are colloidally stable up to 100 mM NaCl and 30 mM CaCl2. However, significant aggregation of NPs is pronounced in both electrolytes at high ionic strength. In mixed systems, both HA and montmorillonite enhance NP colloidal stability through electrostatic interactions and steric hindrance when pH ≤ PZC, whereas their surface interactions are quite limited when pH > PZC. Even when pH approximates PZC, NPs became stable at a HA concentration of 1 mg·L−1. The magnitude of interactions and dominant sites of interaction (basal planes versus edge sites) are significantly dependent on pH because both NPs and montmorillonite have pH-dependent (conditional) surface charges. Thus, solution pH, ionic strength, and the presence of natural colloids greatly modify the surface conditions of commercial γ-Al2O3 NPs, affecting aggregation and colloidal stability significantly in the aqueous environment. PMID:28335218

  6. Long-term manure amendments reduced soil aggregate stability via redistribution of the glomalin-related soil protein in macroaggregates

    PubMed Central

    Xie, Hongtu; Li, Jianwei; Zhang, Bin; Wang, Lianfeng; Wang, Jingkuan; He, Hongbo; Zhang, Xudong

    2015-01-01

    Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSPt and GRSPe) and their respective allocations in four soil aggregates (>2000 μm; 2000–250 μm; 250–53 μm; and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK), and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSPe and GRSPt in soil and SOC in each aggregate generally increased with increasing manure input, GRSPt and GRSPe in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000–250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture. PMID:26423355

  7. Long-term manure amendments reduced soil aggregate stability via redistribution of the glomalin-related soil protein in macroaggregates.

    PubMed

    Xie, Hongtu; Li, Jianwei; Zhang, Bin; Wang, Lianfeng; Wang, Jingkuan; He, Hongbo; Zhang, Xudong

    2015-10-01

    Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSPt and GRSPe) and their respective allocations in four soil aggregates (>2000 μm; 2000-250 μm; 250-53 μm; and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK), and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSPe and GRSPt in soil and SOC in each aggregate generally increased with increasing manure input, GRSPt and GRSPe in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000-250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture.

  8. Long-term manure amendments reduced soil aggregate stability via redistribution of the glomalin-related soil protein in macroaggregates

    NASA Astrophysics Data System (ADS)

    Xie, Hongtu; Li, Jianwei; Zhang, Bin; Wang, Lianfeng; Wang, Jingkuan; He, Hongbo; Zhang, Xudong

    2015-10-01

    Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSPt and GRSPe) and their respective allocations in four soil aggregates (>2000 μm 2000-250 μm 250-53 μm and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK), and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSPe and GRSPt in soil and SOC in each aggregate generally increased with increasing manure input, GRSPt and GRSPe in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000-250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture.

  9. Decomposition-aggregation stability analysis. [for large scale dynamic systems with application to spinning Skylab control system

    NASA Technical Reports Server (NTRS)

    Siljak, D. D.; Weissenberger, S.; Cuk, S. M.

    1973-01-01

    This report presents the development and description of the decomposition aggregation approach to stability investigations of high dimension mathematical models of dynamic systems. The high dimension vector differential equation describing a large dynamic system is decomposed into a number of lower dimension vector differential equations which represent interconnected subsystems. Then a method is described by which the stability properties of each subsystem are aggregated into a single vector Liapunov function, representing the aggregate system model, consisting of subsystem Liapunov functions as components. A linear vector differential inequality is then formed in terms of the vector Liapunov function. The matrix of the model, which reflects the stability properties of the subsystems and the nature of their interconnections, is analyzed to conclude over-all system stability characteristics. The technique is applied in detail to investigate the stability characteristics of a dynamic model of a hypothetical spinning Skylab.

  10. Stability Analysis of Distributed Order Fractional Chen System

    PubMed Central

    Aminikhah, H.; Refahi Sheikhani, A.; Rezazadeh, H.

    2013-01-01

    We first investigate sufficient and necessary conditions of stability of nonlinear distributed order fractional system and then we generalize the integer-order Chen system into the distributed order fractional domain. Based on the asymptotic stability theory of nonlinear distributed order fractional systems, the stability of distributed order fractional Chen system is discussed. In addition, we have found that chaos exists in the double fractional order Chen system. Numerical solutions are used to verify the analytical results. PMID:24489508

  11. The influence of organic amendments on soil aggregate stability from semiarid sites

    NASA Astrophysics Data System (ADS)

    Hueso Gonzalez, Paloma; Francisco Martinez Murillo, Juan; Damian Ruiz Sinoga, Jose

    2016-04-01

    Restoring the native vegetation is the most effective way to regenerate soil health. Under these conditions, vegetation cover in areas having degraded soils may be better sustained if the soil is amended with an external source of organic matter. The addition of organic materials to soils also increases infiltration rates and reduces erosion rates; these factors contribute to an available water increment and a successful and sustainable land management. The goal of this study was to analyze the effect of various organic amendments on the aggregate stability of soils in afforested plots. An experimental paired-plot layout was established in southern of Spain (homogeneous slope gradient: 7.5%; aspect: N170). Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. The vegetation was planted in a grid pattern with 0.5 m between plants in each plot. During the afforestation process the soil was tilled to 25 cm depth from the surface. Soil from the afforested plots was sampled in: i) 6 months post-afforestation; ii) 12 months post-afforestation; iii) 18 months post-afforestation; and iv) 24 months post-afforestation. The sampling strategy for each plot involved collection of 4 disturbed soil samples taken from the surface (0-10 cm depth). The stability of aggregates was measured by wet-sieving. Regarding to soil aggregate stability, the percentage of stable aggregates has increased slightly in all the treatments in relation to control. Specifically, the differences were recorded in the fraction of macroaggregates (≥ 0.250 mm). The largest increases have been associated with straw mulch, pinus mulch and sludge. Similar results have been registered for the soil organic carbon content

  12. Changes in soil aggregate stability under different irrigation doses of waste water

    NASA Astrophysics Data System (ADS)

    Morugán, Alicia; García-Orenes, Fuensanta; Mataix-Solera, Jorge; Arcenegui, Victoria; Bárcenas, Gema

    2010-05-01

    Freshwater availability and soil degradation are two of the most important environmental problems in the Mediterranean area acerbated by incorrect agricultural use of irrigation in which organic matter is not correctly managed, the use of low quality water for irrigation, and the inefficiency of dose irrigation. For these reasons strategies for saving water and for the restoration of the mean properties of soil are necessary. The use of treated waste water for the irrigation of agricultural land could be a good solution to these problems, as it reduces the utilization of fresh water and could potentially improve key soil properties. In this work we have been studying, for more than three years, the effects on soil properties of different doses of irrigation with waste water. Here we show the results on aggregate stability. The study is located in an agricultural area at Biar (Alicante, SE of Spain), with a crop of grape (Vitis labrusca). Three types of waters are being used in the irrigation of the soil: fresh water (control) (TC), and treated waste water from secondary (T2) and tertiary treatment (T3). Three different doses of irrigation have been applied to fit the efficiency of the irrigation to the crop and soil type: D10 (10 L m-2 every week during 17 months), D50 (50 L m-2 every fifteen days during 14 moths) and D30 (30 L m-2 every week during 6 months up to present day). The results showed a clear decrease of aggregate stability during the period we used the second dose (D50) independent of the type of water used. That dose of irrigation and frequency produced strong wetting and drying cycles (WD) in the soil, and this is suspected to be the main factor responsible for the results. When we changed the dose of irrigation to D30, reducing the quantity per event and increasing the frequency, the soil aggregate stability started to improve. This dose avoids strong drying periods between irrigation events and the aggregate stability is confirmed to be slowly

  13. Distribution of algal aggregates under summer sea ice in the Central Arctic.

    PubMed

    Katlein, Christian; Fernández-Méndez, Mar; Wenzhöfer, Frank; Nicolaus, Marcel

    The sea ice cover of the Arctic Ocean has changed dramatically in the last decades, and the resulting consequences for the sea-ice-associated ecosystem remain difficult to assess. Algal aggregates underneath sea ice are of great importance for the ice-associated ecosystem and the pelagic-benthic coupling. However, the frequency and distribution of their occurrence is not well quantified. During the IceArc expedition (ARK-27/3) of RV Polarstern in late summer 2012, we observed different types of algal aggregates floating underneath various ice types in the Central Arctic basins. We investigated the spatial distribution of ice algal aggregates and quantified their biomass, using under-ice image surveys obtained by an upward-looking camera on a remotely operated vehicle. On basin scale, filamentous aggregates of Melosira arctica are more frequently found in the inner part of the Central Arctic pack ice, while rounded aggregates mainly formed by pennate diatoms are found closer to the ice edge, under melting sea ice. On the scale of an ice floe, the distribution of algal aggregates in late summer is mainly regulated by the topography of the ice underside, with aggregates accumulating in dome-shaped structures and at the edges of pressure ridges. The average biomass of the aggregates from our sites and season was 0.1-6.0 mg C m(-2). However, depending on the approach used, differences in orders of magnitude for biomass estimates may occur. This highlights the difficulties of upscaling observations and comparing results from surveys conducted using different methods or on different spatial scales.

  14. Modulation of protein stability and aggregation properties by surface charge engineering.

    PubMed

    Raghunathan, Govindan; Sokalingam, Sriram; Soundrarajan, Nagasundarapandian; Madan, Bharat; Munussami, Ganapathiraman; Lee, Sun-Gu

    2013-09-01

    An attempt to alter protein surface charges through traditional protein engineering approaches often affects the native protein structure significantly and induces misfolding. This limitation is a major hindrance in modulating protein properties through surface charge variations. In this study, as a strategy to overcome such a limitation, we attempted to co-introduce stabilizing mutations that can neutralize the destabilizing effect of protein surface charge variation. Two sets of rational mutations were designed; one to increase the number of surface charged amino acids and the other to decrease the number of surface charged amino acids by mutating surface polar uncharged amino acids and charged amino acids, respectively. These two sets of mutations were introduced into Green Fluorescent Protein (GFP) together with or without stabilizing mutations. The co-introduction of stabilizing mutations along with mutations for surface charge modification allowed us to obtain functionally active protein variants (s-GFP(+15-17) and s-GFP(+5-6)). When the protein properties such as fluorescent activity, folding rate and kinetic stability were assessed, we found the possibility that the protein stability can be modulated independently of activity and folding by engineering protein surface charges. The aggregation properties of GFP could also be altered through the surface charge engineering.

  15. Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange.

    PubMed

    Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

    2014-07-25

    To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00-4.00, 0.50-1.00, and 0.25-0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere.

  16. Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands.

    PubMed

    Wen, Ding; He, Nianpeng; Zhang, Jinjing

    2016-01-01

    Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250-2000 μm], microaggregates [53-250 μm], and mineral fraction [< 53 μm]) at 0-20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China.

  17. The Relationship Between Carbon Input, Aggregation, and Soil Organic Carbon Stabilization in Sustainable Cropping Systems

    NASA Astrophysics Data System (ADS)

    Kong, A. Y.; Six, J.; Bryant, D. C.; Denison, R.; van Kessel, C.

    2003-12-01

    m and 250-2000μ m) in high C input systems. Our findings indicate that management practices directed towards improving annual production, thereby, increasing residue C input would result in greater aggregate stability and aggregate associated SOC levels and have the capability of long-term C stabilization.

  18. [Impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain].

    PubMed

    Li, Jian-Lin; Jiang, Chang-Sheng; Hao, Qing-Ju

    2014-12-01

    Soil aggregates have the important effect on soil fertility, soil quality and the sustainable utilization of soil, and they are the mass bases of water and fertilizer retention ability of soil and the supply or release of soil nutrients. In this paper, in order to study the impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain, we separated four land use types of soil, which are woodland, abandoned land, orchard and sloping farmland by wet sieving method, then we got the proportion of large macroaggregates (> 2 mm), small macroaggregates (0.25-2 mm), microaggregates (53 μm-0.25 mm) and silt + clay (< 53 μm) and measured the content of organic carbon in each aggregate fraction in soil depth of 0-60 cm and calculated the total content of organic carbon of all aggregates fraction in each soil. The results showed that reclamation of woodland will lead to fragmentation of macroaggregates and deterioration of soil structure, and the proportion of macroaggrgates (> 0.25 mm) were 44.62% and 32.28% respectively in the soils of orchard and sloping farmland, which reduced 38.58% (P < 0.05) and 91.52% (P < 0.05) compared with woodland. While after changing the sloping farmland to abandoned land, which lead to the conversion of soil fraction from silt + clay to large macroaggregates and small macroaggregates, so it will improve the soil structure. MWD (mean weight diameter) and GMD (geometric mean diameter) are important indicators of evaluating the stability of soil aggregates. We found the MWD and GWD in soil depth of 0-60 cm in orchards and sloping farmland were significantly lower than those in woodland (P < 0.05), while after changing the sloping farmland to abandoned land, the MWD and GWD increased significantly (P < 0.05), which indicated that reclamation of woodland will lead to the decrease of stability of soil aggregates, and they will be separated more easily by water. However, after changing the sloping farmland to abandoned

  19. Tsunami Size Distributions at Far-Field Locations from Aggregated Earthquake Sources

    NASA Astrophysics Data System (ADS)

    Geist, E. L.; Parsons, T.

    2015-12-01

    The distribution of tsunami amplitudes at far-field tide gauge stations is explained by aggregating the probability of tsunamis derived from individual subduction zones and scaled by their seismic moment. The observed tsunami amplitude distributions of both continental (e.g., San Francisco) and island (e.g., Hilo) stations distant from subduction zones are examined. Although the observed probability distributions nominally follow a Pareto (power-law) distribution, there are significant deviations. Some stations exhibit varying degrees of tapering of the distribution at high amplitudes and, in the case of the Hilo station, there is a prominent break in slope on log-log probability plots. There are also differences in the slopes of the observed distributions among stations that can be significant. To explain these differences we first estimate seismic moment distributions of observed earthquakes for major subduction zones. Second, regression models are developed that relate the tsunami amplitude at a station to seismic moment at a subduction zone, correcting for epicentral distance. The seismic moment distribution is then transformed to a site-specific tsunami amplitude distribution using the regression model. Finally, a mixture distribution is developed, aggregating the transformed tsunami distributions from all relevant subduction zones. This mixture distribution is compared to the observed distribution to assess the performance of the method described above. This method allows us to estimate the largest tsunami that can be expected in a given time period at a station.

  20. Rational approach for design and evaluation of anti-aggregation agents for protein stabilization: A case study of trehalose phenylalaninate.

    PubMed

    Kale, Smita S; Akamanchi, Krishnacharya G

    2017-03-30

    The present work introduces new anti-aggregation agent (AAA) derived through our new approach for design and evaluation of anti-aggregation agent as a multi-purpose excipient to combat protein aggregation. Therapeutic proteins undergo aggregation due to even minor changes in environmental conditions like temperature, pH, shear and stress. Excipients play a vital role in prevention of aggregation. To stabilize a protein formulation different classes of excipients are used in combination after carefully selecting through laborious and time consuming trial and error experiments. To resolve these concerns, we have developed a rational approach based on molecular docking analysis and have designed, synthesized AAAs, and validated the approach by experimental studies. Trehalose phenylalaninate (TPA) has been synthesized and evaluated for stabilization of Bovine serum albumin (BSA). TPA was found to be non-toxic with a LC50 of >80μg/ml. BSA solutions with and without TPA were subjected to thermal and agitation stress and aggregation was monitored using sophisticated analytical techniques. The helical structure of BSA was completely retained in stressed samples at 0.1% concentration of TPA. SEC-HPLC clearly demonstrated the absence of aggregates in presence of TPA. Although aggregation was not seen in fluorescence spectra but quenching due to TPA was evident. Moreover, molecular dynamics study on BSA-TPA complex showed lower RMSD.

  1. Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability.

    PubMed

    Zhang, Haoqiang; Liu, Zhenkun; Chen, Hui; Tang, Ming

    2016-01-01

    Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.

  2. Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability

    PubMed Central

    Zhang, Haoqiang; Liu, Zhenkun; Chen, Hui; Tang, Ming

    2016-01-01

    Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention. PMID:27064570

  3. Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development

    USDA-ARS?s Scientific Manuscript database

    Primary particle size distribution (PSD) of eroded sediments can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 x 40 x 4 cm), that had undergone either minimal aggregate...

  4. [Effects of gaps on distribution of soil aggregates and organic carbon in Pinus massoniana plantation].

    PubMed

    Song, Xiao-Yan; Zhang, Dan-Ju; Zhang, Jian; Li, Jian-Ping; Deng, Chang-Chun; Deng, Chao

    2014-11-01

    The effects of forest gap size on the distribution of soil aggregates, organic carbon and labile organic carbon were investigated in a 39-year-old Pinus massoniana plantation in Yibin, Sichuan Province. The results showed that the composition of soil aggregates was dominated by particles > 2 mm, which accounted for 51.7%-78.7% of the whole soil samples under different sized forest gaps and beneath P. massoniana plantation. Soil organic carbon content and labile organic carbon content in > 5 mm aggregates were significantly positively correlated with the soil organic carbon and labile organic carbon contents. Furthermore, the amounts of organic carbon and labile organic carbon storage > 5 mm particles were higher than those in other size particles. Therefore, particles > 5 mm of aggregates dominated the soil carbon pool. Compared with those P. massoniana plantations, the contents of organic carbon in aggregates and total topsoil decreased during the formation of forest gaps, whereas the soil organic carbon storage under 1225 m2 gap was higher. In addition, the soil labile organic carbon content under 225 and 400 m2 gaps and the labile organic carbon storage under 225, 400, 900 and 1225 m2 gaps were higher than those the plantations, but were lower than under the other gaps. It was suggested that an appropriate size of forest gap would increase the accumulation of soil organic carbon and labile organic carbon content. The size of forest gap had significant effects on the distribution of soil aggregates, organic carbon and labile organic carbon. The soil sample under 1225 m2 gap had the highest organic carbon content and storage and a better aggregate proportion, and the higher labile organic carbon storage. Therefore, it was suggested that 1225 m2 gap might be an optimal logging gap size.

  5. Shear-driven aggregation of binary colloids for randomly distributing nanoparticles in a matrix.

    PubMed

    Meng, Xia; Wu, Hua; Morbidelli, Massimo

    2016-04-20

    We propose a methodology for preparing composite materials where A nanoparticles (NPs) are uniformly and randomly distributed inside a matrix of B NPs. It is based on intense shear-driven aggregation of binary colloids composed of A and B NPs, without using any additives. Its feasibility has been demonstrated using stable binary colloids composed of poly-methyl methacrylate (PMMA) particles and polystyrene (PS) particles. The PS particles alone undergo shear-driven aggregation (shear-active), while the PMMA particles alone do not exhibit any aggregation under the same conditions (shear-inactive). It is found that the shear-driven aggregation of the binary colloids does occur, and the formed clusters are composed of both the "shear-active" PS and "shear-inactive" PMMA particles. The SEM pictures demonstrate that the PMMA particles are uniformly and randomly distributed among the PS particles in the clusters, thus confirming the feasibility of the proposed methodology. The mechanism leading to the aggregation of the binary colloids has been discussed based on the experimental observations.

  6. Primary and Aggregate Size Distributions of PM in Tail Pipe Emissions form Diesel Engines

    NASA Astrophysics Data System (ADS)

    Arai, Masataka; Amagai, Kenji; Nakaji, Takayuki; Hayashi, Shinji

    Particulate matter (PM) emission exhausted from diesel engine should be reduced to keep the clean air environment. PM emission was considered that it consisted of coarse and aggregate particles, and nuclei-mode particles of which diameter was less than 50nm. However the detail characteristics about these particles of the PM were still unknown and they were needed for more physically accurate measurement and more effective reduction of exhaust PM emission. In this study, the size distributions of solid particles in PM emission were reported. PMs in the tail-pipe emission were sampled from three type diesel engines. Sampled PM was chemically treated to separate the solid carbon fraction from other fractions such as soluble organic fraction (SOF). The electron microscopic and optical-manual size measurement procedures were used to determine the size distribution of primary particles those were formed through coagulation process from nuclei-mode particles and consisted in aggregate particles. The centrifugal sedimentation method was applied to measure the Stokes diameter of dry-soot. Aerodynamic diameters of nano and aggregate particles were measured with scanning mobility particle sizer (SMPS). The peak aggregate diameters detected by SMPS were fallen in the same size regime as the Stokes diameter of dry-soot. Both of primary and Stokes diameters of dry-soot decreased with increases of engine speed and excess air ratio. Also, the effects of fuel properties and engine types on primary and aggregate particle diameters were discussed.

  7. Cost-Efficient and Multi-Functional Secure Aggregation in Large Scale Distributed Application

    PubMed Central

    Zhang, Ping; Li, Wenjun; Sun, Hua

    2016-01-01

    Secure aggregation is an essential component of modern distributed applications and data mining platforms. Aggregated statistical results are typically adopted in constructing a data cube for data analysis at multiple abstraction levels in data warehouse platforms. Generating different types of statistical results efficiently at the same time (or referred to as enabling multi-functional support) is a fundamental requirement in practice. However, most of the existing schemes support a very limited number of statistics. Securely obtaining typical statistical results simultaneously in the distribution system, without recovering the original data, is still an open problem. In this paper, we present SEDAR, which is a SEcure Data Aggregation scheme under the Range segmentation model. Range segmentation model is proposed to reduce the communication cost by capturing the data characteristics, and different range uses different aggregation strategy. For raw data in the dominant range, SEDAR encodes them into well defined vectors to provide value-preservation and order-preservation, and thus provides the basis for multi-functional aggregation. A homomorphic encryption scheme is used to achieve data privacy. We also present two enhanced versions. The first one is a Random based SEDAR (REDAR), and the second is a Compression based SEDAR (CEDAR). Both of them can significantly reduce communication cost with the trade-off lower security and lower accuracy, respectively. Experimental evaluations, based on six different scenes of real data, show that all of them have an excellent performance on cost and accuracy. PMID:27551747

  8. Transformations in soil organic matter and aggregate stability after conversion of Mediterranean forest to agriculture

    NASA Astrophysics Data System (ADS)

    Recio Vázquez, Lorena; Almendros, Gonzalo; Carral, Pilar; Knicker, Heike; González Pérez, José Antonio; González Vila, Francisco Javier

    2013-04-01

    Conversion of forest ecosystems into croplands often leads to severe decrease of the soil organic matter (SOM) levels with the concomitant deterioration of soil structure. The present research focuses on the effects of cultivation on the stability of soil macroaggregates, as well as on the total quantity and quality of SOM. Three representative soils from central Spain (i.e., Petric Calcisol, Cutanic Luvisol and Calcic Vertisol) were sampled. Each site had natural vegetation (NV) dominated either by characteristic Mediterranean forest (dehesa) or cereal crops (CC) under conventional tillage. For each site, three spatial replicates of the NV and CC were sampled. Soil aggregate stability was measured by the wet sieving method. The structural stability index was then calculated as the mass of aggregated soil (>250 μm) remaining after wet sieving, as a percent of total aggregate weight. The analytical characterization of the SOM was carried out after chemical fractionation for quantifying the different organic pools: free organic matter (FOM), humic acids (HA), fulvic acids (FA) and humin (H). Furthermore, whole soil samples pretreated with 10 % HF solution were analyzed by CP-MAS 13C NMR and the purified HA fraction was characterized by elementary analysis, visible and infrared spectroscopies and Py-GC/MS. A marked reduction in the proportion of stable aggregates when the natural ecosystem was converted to agriculture was observed. Values of the structural stability index (%) changed over from 96.2 to 38.1, 95.1 to 83.7 and 98.5 to 60.6 for the Calcisol, Luvisol and Vertisol respectively. Comparatively higher contents of SOM were found in the soils under NV (11.69 to 0.93, 3.29 to 2.72 and 9.51 to 0.79 g C100 g-1soil) even though a quantitative rearrangement of the SOM pools was noticed. In all sites, the relative contribution of the labile C (FOM) to the total SOM content decreased when the forest soils were converted into croplands, whereas the proportion of both

  9. Distribution and Aggregate Thickness of Salt Deposits of the United States

    EPA Pesticide Factsheets

    The map shows the distribution and aggregate thickness of salt deposits of the United States. This information is from contour map sheets, scanned and processed for use in a global mineral resource assessment, produced by the U.S. Geological Survey. It is used here to provide a geospatial context to the distribution of rock-salt deposits in the US. It is useful in illustrating sources of chlorides.

  10. A microcomputer program for energy assessment and aggregation using the triangular probability distribution

    USGS Publications Warehouse

    Crovelli, R.A.; Balay, R.H.

    1991-01-01

    A general risk-analysis method was developed for petroleum-resource assessment and other applications. The triangular probability distribution is used as a model with an analytic aggregation methodology based on probability theory rather than Monte-Carlo simulation. Among the advantages of the analytic method are its computational speed and flexibility, and the saving of time and cost on a microcomputer. The input into the model consists of a set of components (e.g. geologic provinces) and, for each component, three potential resource estimates: minimum, most likely (mode), and maximum. Assuming a triangular probability distribution, the mean, standard deviation, and seven fractiles (F100, F95, F75, F50, F25, F5, and F0) are computed for each component, where for example, the probability of more than F95 is equal to 0.95. The components are aggregated by combining the means, standard deviations, and respective fractiles under three possible siutations (1) perfect positive correlation, (2) complete independence, and (3) any degree of dependence between these two polar situations. A package of computer programs named the TRIAGG system was written in the Turbo Pascal 4.0 language for performing the analytic probabilistic methodology. The system consists of a program for processing triangular probability distribution assessments and aggregations, and a separate aggregation routine for aggregating aggregations. The user's documentation and program diskette of the TRIAGG system are available from USGS Open File Services. TRIAGG requires an IBM-PC/XT/AT compatible microcomputer with 256kbyte of main memory, MS-DOS 3.1 or later, either two diskette drives or a fixed disk, and a 132 column printer. A graphics adapter and color display are optional. ?? 1991.

  11. A microcomputer program for energy assessment and aggregation using the triangular probability distribution

    NASA Astrophysics Data System (ADS)

    Crovelli, Robert A.; Balay, Richard H.

    A general risk-analysis method was developed for petroleum-resource assessment and other applications. The triangular probability distribution is used as a model with an analytic aggregation methodology based on probability theory rather than Monte-Carlo simulation. Among the advantages of the analytic method are its computational speed and flexibility, and the saving of time and cost on a microcomputer. The input into the model consists of a set of components (e.g. geologic provinces) and, for each component, three potential resource estimates: minimum, most likely (mode), and maximum. Assuming a triangular probability distribution, the mean, standard deviation, and seven fractiles ( F100, F95, F75, F50, F25, F5, and F0) are computed for each component, where for example, the probability of more than F95 is equal to 0.95. The components are aggregated by combining the means, standard deviations, and respective fractiles under three possible siutations (1) perfect positive correlation, (2) complete independence, and (3) any degree of dependence between these two polar situations. A package of computer programs named the TRIAGG system was written in the Turbo Pascal 4.0 language for performing the analytic probabilistic methodology. The system consists of a program for processing triangular probability distribution assessments and aggregations, and a separate aggregation routine for aggregating aggregations. The user's documentation and program diskette of the TRIAGG system are available from USGS Open File Services. TRIAGG requires an IBM-PC/XT/AT compatible microcomputer with 256kbyte of main memory, MS-DOS 3.1 or later, either two diskette drives or a fixed disk, and a 132 column printer. A graphics adapter and color display are optional.

  12. Photo-stability of peptide-bond aggregates: N-methylformamide dimers.

    PubMed

    Crespo-Otero, Rachel; Mardykov, Artur; Sanchez-Garcia, Elsa; Sander, Wolfram; Barbatti, Mario

    2014-09-21

    The formation of weakly-bound dimers of N-methylformamide (NMF) and the photochemistry of these dimers after irradiation at 248 nm were explored using matrix-isolation spectroscopy. Calculations were used to characterize the diverse isomers and assign their IR spectra; non-adiabatic dynamics was simulated to understand their photo-deactivation mechanism. The most stable dimers, and , were obtained by trans-trans aggregation (N-HO[double bond, length as m-dash]C interactions) and could be identified in the matrix. The main products formed after irradiation are the trans-cis dimers ( and ), also stabilized by N-HO[double bond, length as m-dash]C interactions. In contrast to the photochemistry of the monomers, no dissociative products were observed after 248 nm irradiation of the dimers. The absence of dissociative products can be explained by a proton-transfer mechanism in the excited state that is faster than the photo-dissociative mechanism. The fact that hydrogen bonding has such a significant effect on the photochemical stability of NMF has important implications to understand the stability of peptide-bonded systems to UV irradiation.

  13. Solidification/stabilization of landfill leachate concentrate using different aggregate materials.

    PubMed

    Hunce, Selda Yigit; Akgul, Deniz; Demir, Goksel; Mertoglu, Bulent

    2012-07-01

    The application of reverse osmosis for the treatment of landfill leachate is becoming widespread in Turkey as well as in Europe. A major drawback of this process is the production of concentrate, which could be as much as 30% of the feed stream, and high concentrations of salts and contaminants. The reverse osmosis concentrate is disposed of by using several methods including re-infiltration, drying, incineration and solidification/stabilization. In this study, solidification/stabilization (S/S) technology was studied for the treatment of reverse osmosis concentrate produced from landfill leachate. In order to benefit from its capability to absorb heavy metals, ammonia and some other pollutants, zeolite and different aggregate materials were used in solidification experiments. Main pollutants in the leachate concentrate, TOC, DOC, TDS and ammonia were successfully solidified and approximately 1% of TOC, DOC, TDS and ammonia remained in the eluate water. The results indicated that the landfill disposal limits could be attained by solidification/stabilization process.

  14. Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands

    PubMed Central

    Wen, Ding; He, Nianpeng; Zhang, Jinjing

    2016-01-01

    Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250–2000 μm], microaggregates [53–250 μm], and mineral fraction [< 53 μm]) at 0–20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China. PMID:26751370

  15. Label free colorimetric sensing of thiocyanate based on inducing aggregation of Tween 20-stabilized gold nanoparticles.

    PubMed

    Zhang, Zhiyang; Zhang, Jun; Qu, Chengli; Pan, Dawei; Chen, Zhaopeng; Chen, Lingxin

    2012-06-07

    Based on inducing the aggregation of gold nanoparticles (AuNPs), a simple colorimetric method with high sensitivity and selectivity was developed for the sensing of thiocyanate (SCN(-)) in aqueous solutions. Citrate-capped AuNPs were prepared following a classic method and Tween 20 was subsequently added as a stabilizer. With the addition of SCN(-), citrate ions on AuNPs surfaces were replaced due to the high affinity between SCN(-) and Au. As a result, Tween 20 molecules adsorbed on the AuNPs surfaces were separated and the AuNPs aggregated. The process was accompanied by a visible color change from red to blue within 5 min. The sensing of SCN(-) can therefore be easily achieved by a UV-vis spectrophotometer or even by the naked eye. The potential effects of relevant experimental conditions, including concentration of Tween 20, pH, incubation temperature and time, were evaluated to optimize the method. Under optimized conditions, this method yields excellent sensitivity (LOD = 0.2 μM or 11.6 ppb) and selectivity toward SCN(-). Our attempt may provide a cost-effective, rapid and simple solution to the inspection of SCN(-) ions in saliva and environmental aqueous samples.

  16. Polythiophenes Inhibit Prion Propagation by Stabilizing Prion Protein (PrP) Aggregates*

    PubMed Central

    Margalith, Ilan; Suter, Carlo; Ballmer, Boris; Schwarz, Petra; Tiberi, Cinzia; Sonati, Tiziana; Falsig, Jeppe; Nyström, Sofie; Hammarström, Per; Åslund, Andreas; Nilsson, K. Peter R.; Yam, Alice; Whitters, Eric; Hornemann, Simone; Aguzzi, Adriano

    2012-01-01

    Luminescent conjugated polymers (LCPs) interact with ordered protein aggregates and sensitively detect amyloids of many different proteins, suggesting that they may possess antiprion properties. Here, we show that a variety of anionic, cationic, and zwitterionic LCPs reduced the infectivity of prion-containing brain homogenates and of prion-infected cerebellar organotypic cultured slices and decreased the amount of scrapie isoform of PrPC (PrPSc) oligomers that could be captured in an avidity assay. Paradoxically, treatment enhanced the resistance of PrPSc to proteolysis, triggered the compaction, and enhanced the resistance to proteolysis of recombinant mouse PrP(23–231) fibers. These results suggest that LCPs act as antiprion agents by transitioning PrP aggregates into structures with reduced frangibility. Moreover, ELISA on cerebellar organotypic cultured slices and in vitro conversion assays with mouse PrP(23–231) indicated that poly(thiophene-3-acetic acid) may additionally interfere with the generation of PrPSc by stabilizing the conformation of PrPC or of a transition intermediate. Therefore, LCPs represent a novel class of antiprion agents whose mode of action appears to rely on hyperstabilization, rather than destabilization, of PrPSc deposits. PMID:22493452

  17. Syntaxin 8 Regulates Platelet Dense Granule Secretion, Aggregation, and Thrombus Stability*

    PubMed Central

    Golebiewska, Ewelina M.; Harper, Matthew T.; Williams, Christopher M.; Savage, Joshua S.; Goggs, Robert; Fischer von Mollard, Gabriele; Poole, Alastair W.

    2015-01-01

    Platelet secretion not only drives thrombosis and hemostasis, but also mediates a variety of other physiological and pathological processes. The ubiquitous SNARE machinery and a number of accessory proteins have been implicated in regulating secretion in platelet. Although several platelet SNAREs have been identified, further members of the SNARE family may be needed to fine-tune platelet secretion. In this study we identified expression of the t-SNARE syntaxin 8 (STX8) (Qc SNARE) in mouse and human platelets. In mouse studies, whereas STX8 was not essential for α-granule or lysosome secretion, Stx8−/− platelets showed a significant defect in dense granule secretion in response to thrombin and CRP. This was most pronounced at intermediate concentrations of agonists. They also showed an aggregation defect that could be rescued with exogenous ADP and increased embolization in Stx8−/− mice in vivo consistent with an important autocrine and paracrine role for ADP in aggregation and thrombus stabilization. STX8 therefore specifically contributes to dense granule secretion and represents another member of a growing family of genes that play distinct roles in regulating granule release from platelets and thus platelet function in thrombosis and hemostasis. PMID:25404741

  18. Streptavidin-coated gold nanoparticles: critical role of oligonucleotides on stability and fractal aggregation

    PubMed Central

    D'Agata, Roberta; Palladino, Pasquale

    2017-01-01

    Gold nanoparticles (AuNPs) exhibit unique properties that can be modulated through a tailored surface functionalization, enabling their targeted use in biochemical sensing and medical diagnostics. In particular, streptavidin-modified AuNPs are increasingly used for biosensing purposes. We report here a study of AuNPs surface-functionalized with streptavidin-biotinylated oligonucleotide, focussing on the role played by the oligonucleotide probes in the stabilization/destabilization of the functionalized nanoparticle dispersion. The behaviour of the modified AuNP dispersion as a consequence of the competitive displacement of the biotinylated oligonucleotide has been investigated and the critical role of displaced oligonucletides in triggering the quasi one-dimensional aggregation of nanoparticles is demonstrated for the first time. The thorough understanding of the fundamental properties of bioconjugated AuNPs is of great importance for the design of highly sensitive and reliable functionalized AuNP-based assays. PMID:28144559

  19. Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields

    NASA Astrophysics Data System (ADS)

    Ershov, A. E.; Gavrilyuk, A. P.; Karpov, S. V.; Polyutov, S. P.

    2016-11-01

    We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles (resonant domains) in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions. These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates. To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action, we introduce the factor of spectral photomodification. Based on calculation of changes in thermodynamic, mechanical, and optical characteristics of the domains, the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps, an average particle size, and the degree of polydispersity. Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains. The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.

  20. Stabilization of aqueous nanoscale zerovalent iron dispersions by anionic polyelectrolytes: adsorbed anionic polyelectrolyte layer properties and their effect on aggregation and sedimentation

    NASA Astrophysics Data System (ADS)

    Phenrat, Tanapon; Saleh, Navid; Sirk, Kevin; Kim, Hye-Jin; Tilton, Robert D.; Lowry, Gregory V.

    2008-05-01

    Nanoscale zerovalent iron (NZVI) particles are 5-40 nm sized Fe0/Fe-oxide particles that rapidly transform many environmental contaminants to benign products and are a promising in situ remediation agent. Rapid aggregation and limited mobility in water-saturated porous media limits the ability to deliver NZVI dispersions in the subsurface. This study prepares stable NZVI dispersions through physisorption of commercially available anionic polyelectrolytes, characterizes the adsorbed polymer layer, and correlates the polymer coating properties with the ability to prevent rapid aggregation and sedimentation of NZVI dispersions. Poly(styrene sulfonate) with molecular weights of 70 k and 1,000 k g/mol (PSS70K and PSS1M), carboxymethyl cellulose with molecular weights of 90 k and 700 k g/mol (CMC90K and CMC700K), and polyaspartate with molecular weights of 2.5 k and 10 k g/mol (PAP2.5K and 10K) were compared. Particle size distributions were determined by dynamic light scattering during aggregation. The order of effectiveness to prevent rapid aggregation and stabilize the dispersions was PSS70K(83%) > ≈PAP10K(82%) > PAP2.5K(72%) > CMC700K(52%), where stability is defined operationally as the volume percent of particles that do not aggregate after 1 h. CMC90K and PSS1M could not stabilize RNIP relative to bare RNIP. A similar trend was observed for their ability to prevent sedimentation, with 40, 34, 32, 20, and 5 wt%, of the PSS70K, PAP10K, PAP2.5K, CMC700K, and CMC90K modified NZVI remaining suspended after 7 h of quiescent settling, respectively. The stable fractions with respect to both aggregation and sedimentation correlate well with the adsorbed polyelectrolyte mass and thickness of the adsorbed polyelectrolyte layers as determined by Oshima's soft particle theory. A fraction of the particles cannot be stabilized by any modifier and rapidly agglomerates to micron sized aggregates, as is also observed for unmodified NZVI. This non-dispersible fraction is

  1. DTE Energy Technologies With Detroit Edison Co. and Kinectrics Inc.: Distributed Resources Aggregation Modeling and Field Configuration Testing

    SciTech Connect

    Not Available

    2003-10-01

    Summarizes the work of DTE Energy Technologies, Detroit Edison, and Kinectrics, under contract to DOE's Distribution and Interconnection R&D, to develop distributed resources aggregation modeling and field configuration testing.

  2. Tryptophan-mPEGs: novel excipients that stabilize salmon calcitonin against aggregation by non-covalent PEGylation.

    PubMed

    Mueller, Claudia; Capelle, Martinus A H; Arvinte, Tudor; Seyrek, Emek; Borchard, Gerrit

    2011-11-01

    Protein aggregation, which is triggered by various factors, is still one of the most prevalent problems encountered during all stages of protein formulation development. In this publication, we present novel excipients, tryptophan-mPEGs (Trp-mPEGs) of 2 and 5 kDa molecular weight and suggest their use in protein formulation. The synthesis and physico-chemical characterization of the excipients are described. Possible cytotoxic and hemolytic activities of the Trp-mPEGs were examined. Turbidity, 90° static light scatter, intrinsic fluorescence, fluorescence after staining the samples with Nile Red and fluorescence microscopy were used to study the inhibitory effect of the Trp-mPEGs on the aggregation of salmon calcitonin (sCT) in different buffer systems and at various molar ratios. Aggregation of sCT was reduced significantly with increasing concentrations of Trp-mPEG 2 kDa. A 10-fold molar excess of Trp-mPEG 2 kDa suppressed almost completely the aggregation of sCT in 10mM sodium citrate buffer (pH 6) for up to 70 h. Trp-mPEG 5 kDa also reduced the aggregation of sCT, though less pronounced than Trp-mPEG 2 kDa. Low aggregation of sCT was measured after approximately 10 days in 10mM sodium citrate buffer, pH 5, with a 10-fold molar excess of Trp-mPEG 2 kDa. This paper shows that Trp-mPEGs are potent excipients in reducing the aggregation of sCT. Trp-mPEGs are superior to dansyl-PEGs concerning the stabilization of sCT in a harsh environment, wherein sCT is prone to aggregation. Trp-mPEGs might therefore also be used for stabilization of other biopharmaceuticals prone to aggregation.

  3. Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange

    PubMed Central

    Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

    2014-01-01

    To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00–4.00, 0.50–1.00, and 0.25–0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere. PMID:25059396

  4. Asymptotic stability of distributed order nonlinear dynamical systems

    NASA Astrophysics Data System (ADS)

    Fernández-Anaya, G.; Nava-Antonio, G.; Jamous-Galante, J.; Muñoz-Vega, R.; Hernández-Martínez, E. G.

    2017-07-01

    In this article we present a generalization of the Lyapunov direct method for distributed order nonlinear time-varying systems. By extending recently introduced properties of the Caputo fractional derivative to the distributed order case, we provide various ways to determine the stability or asymptotic stability of certain systems. The fractional results that inspired this work are recovered if an appropriate distribution function is chosen. Some examples are given to validate the obtained results.

  5. Depletion-Induced Encapsulation by Dumbbell-Shaped Patchy Colloids Stabilize Microspheres against Aggregation

    PubMed Central

    2017-01-01

    In this paper, we demonstrate the stabilization of polystyrene microspheres by encapsulating them with dumbbell-shaped colloids with a sticky and a nonsticky lobe. Upon adding a depletant, an effective short ranged attraction is induced between the microspheres and the smaller, smooth lobes of the dumbbells, making those specifically sticky, whereas the interaction with the larger lobes of the dumbbells is considerably less attractive due to their rough surface, which reduces the overlap volume and leaves them nonsticky. The encapsulation of the microspheres by these rough-smooth patchy dumbbells is investigated using a combination of experiments and computer simulations, both resulting in partial coverage of the template particles. For larger microspheres, the depletion attraction is stronger, resulting in a larger fraction of dumbbells that are attached with both lobes to the surface of microspheres. We thus find a template curvature dependent orientation of the dumbbells. In the Monte Carlo simulations, the introduction of such a small, curvature dependent attraction between the rough lobes of the dumbbells resulted in an increased coverage. However, kinetic constraints imposed by the dumbbell geometry seem to prevent optimal packing of the dumbbells on the template particles under all investigated conditions in experiments and simulations. Despite the incomplete coverage, the encapsulation by dumbbell particles does prevent aggregation of the microspheres, thus acting as a colloid-sized steric stabilizer. PMID:28272895

  6. Accelerated stability studies for moisture-induced aggregation of tetanus toxoid.

    PubMed

    Jain, Nishant Kumar; Roy, Ipsita

    2011-03-01

    The study was carried out to evaluate the effect of exposing solid tetanus toxoid to moisture in two different ways on the structure and function of the toxoid. Tetanus toxoid was exposed to moisture by (i) the addition of an optimized amount of buffer and (ii) incubation under an environment provided by a saturated solution of K(2)CrO(4.) The changes in the conformational, structural and antigenic properties of tetanus toxoid were measured and compared. Results show that even at a similar level of moisture-induced aggregation, the amounts of water absorbed by the two preparations of tetanus toxoid are different. Differences in antigenicity and changes in structure of the toxoid at primary, secondary and tertiary structure levels were seen. Although both conditions are used to mimic accelerated stability conditions in the laboratory, the final products are different in the two cases. Thus, conditions for 'accelerated stability studies' for therapeutic proteins need to be selected with care so that they resemble the fate of the actual product.

  7. Depletion-Induced Encapsulation by Dumbbell-Shaped Patchy Colloids Stabilize Microspheres against Aggregation.

    PubMed

    Wolters, Joost R; Verweij, Joanne E; Avvisati, Guido; Dijkstra, Marjolein; Kegel, Willem K

    2017-04-04

    In this paper, we demonstrate the stabilization of polystyrene microspheres by encapsulating them with dumbbell-shaped colloids with a sticky and a nonsticky lobe. Upon adding a depletant, an effective short ranged attraction is induced between the microspheres and the smaller, smooth lobes of the dumbbells, making those specifically sticky, whereas the interaction with the larger lobes of the dumbbells is considerably less attractive due to their rough surface, which reduces the overlap volume and leaves them nonsticky. The encapsulation of the microspheres by these rough-smooth patchy dumbbells is investigated using a combination of experiments and computer simulations, both resulting in partial coverage of the template particles. For larger microspheres, the depletion attraction is stronger, resulting in a larger fraction of dumbbells that are attached with both lobes to the surface of microspheres. We thus find a template curvature dependent orientation of the dumbbells. In the Monte Carlo simulations, the introduction of such a small, curvature dependent attraction between the rough lobes of the dumbbells resulted in an increased coverage. However, kinetic constraints imposed by the dumbbell geometry seem to prevent optimal packing of the dumbbells on the template particles under all investigated conditions in experiments and simulations. Despite the incomplete coverage, the encapsulation by dumbbell particles does prevent aggregation of the microspheres, thus acting as a colloid-sized steric stabilizer.

  8. Impact of Aggregation on the Photochemistry of Fullerene Films: Correlating Stability to Triplet Exciton Kinetics.

    PubMed

    Speller, Emily M; McGettrick, James D; Rice, Beth; Telford, Andrew M; Lee, Harrison K H; Tan, Ching-Hong; De Castro, Catherine S; Davies, Matthew L; Watson, Trystan M; Nelson, Jenny; Durrant, James R; Li, Zhe; Tsoi, Wing C

    2017-07-12

    The photochemistry and stability of fullerene films is found to be strongly dependent upon film nanomorphology. In particular, PC61BM blend films, dispersed with polystyrene, are found to be more susceptible to photobleaching in air than the more aggregated neat films. This enhanced photobleaching correlated with increased oxygen quenching of PC61BM triplet states and the appearance of a carbonyl FTIR absorption band indicative of fullerene oxidation, suggesting PC61BM photo-oxidation is primarily due to triplet-mediated singlet oxygen generation. PC61BM films were observed to undergo photo-oxidation in air for even modest (≤40 min) irradiation times, degrading electron mobility substantially, indicative of electron trap formation. This conclusion is supported by observation of red shifts in photo- and electro-luminescence with photo-oxidation, shown to be in agreement with time-dependent density functional theory calculations of defect generation. These results provide important implications on the environmental stability of PC61BM-based films and devices.

  9. Stabilization of heavy metals in lightweight aggregate made from sewage sludge and river sediment.

    PubMed

    Xu, Guoren; Liu, Mingwei; Li, Guibai

    2013-09-15

    The primary goal of this research is to investigate the stabilization of heavy metals in lightweight aggregate (LWA) made from sewage sludge and river sediment. The effects of the sintering temperature, the (Fe₂O₃+CaO+MgO)/(SiO₂+Al₂O₃) ratio (K ratio), SiO₂/Al₂O₃ and Fe₂O₃/CaO/MgO (at fixed K ratio), pH, and oxidative conditions on the stabilization of heavy metals were studied. Sintering at temperatures above 1100 °C effectively binds Cd, Cr, Cu and Pb in the LWA, because the stable forms of the heavy metals are strongly bound to the aluminosilicate or silicate frameworks. Minimum leachabilities of Cd, Cr, Cu and Pb were obtained at K ratios between 0.175 and 0.2. When the LWA was subjected to rigorous leaching conditions, the heavy metals remained in the solid even when the LWA bulk structure was broken. LWA made with sewage sludge and river sediment can therefore be used as an environmentally safe material for civil engineering and other construction applications.

  10. Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Bol, R.; Willbold, S.; Vereecken, H.; Klumpp, E.

    2015-07-01

    To maximize crop productivity fertilizer P is generally applied to arable soils, a significant proportion of which becomes stabilized by mineral components and in part subsequently becomes unavailable to plants. However, little is known about the relative contributions of the different organic and inorganic P bound to Fe/Al oxides in the smaller soil particles. The alkaline (NaOH-Na2EDTA) extraction with solution 31P-nuclear magnetic resonance (31P-NMR) spectroscopy is considered as a reliable method for extracting and quantifying organic P and (some) inorganic P. However, any so-called residual P after the alkaline extraction has remained unidentified. Therefore, in the present study, the amorphous (a) and crystalline (c) Fe/Al oxide minerals and related P in soil aggregate-sized fractions (> 20, 2-20, 0.45-2 and < 0.45 μm) were specifically extracted by oxalate (a-Fe/Al oxides) and dithionite (DCB, both a- and c-Fe/Al oxides). These soil aggregate-sized fractions with and without the oxalate and DCB pre-treatments were then sequentially extracted by alkaline extraction prior to solution 31P-NMR spectroscopy. This was done to quantify the various chemical P forms which were associated with a- and c-Fe/Al oxides both in alkaline extraction and in the residual P of different soil aggregate-sized fractions. The results showed that overall P contents increased with decreasing size of the soil aggregate-sized fractions. However, the relative distribution and speciation of varying P forms were found to be independent of soil aggregate-size. The majority of alkaline extractable P was in the a-Fe/Al oxide fraction (42-47 % of total P), most of which was orthophosphate (36-41 % of total P). Furthermore, still significant amounts of particularly monoester P were bound to the oxides. Intriguingly, however, Fe/Al oxides were not the main bonding sites for pyrophosphate. Residual P contained similar amounts of total P associated with both a- (10-13 % of total P) and c

  11. Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Bol, R.; Willbold, S.; Vereecken, H.; Klumpp, E.

    2015-11-01

    To maximize crop productivity fertilizer P is generally applied to arable soils, a significant proportion of which becomes stabilized by mineral components and in part subsequently becomes unavailable to plants. However, little is known about the relative contributions of the different organic and inorganic P bound to Fe/Al oxides in the smaller soil particles. Alkaline (NaOH-Na2EDTA) extraction with solution 31P-nuclear magnetic resonance (31P-NMR) spectroscopy is considered a reliable method for extracting and quantifying organic P and (some) inorganic P. However, any so-called residual P after the alkaline extraction has remained unidentified. Therefore, in the present study, the amorphous (a) and crystalline (c) Fe/Al oxide minerals and related P in soil aggregate-sized fractions (> 20, 2-20, 0.45-2 and < 0.45 μm) were specifically extracted by oxalate (a-Fe/Al oxides) and dithionite-citrate-bicarbonate (DCB, both a- and c-Fe/Al oxides). These soil aggregate-sized fractions with and without the oxalate and DCB pre-treatments were then sequentially extracted by alkaline extraction prior to solution 31P-NMR spectroscopy. This was done to quantify the P associated with a- and c-Fe/Al oxides in both alkaline extraction and the residual P of different soil aggregate-sized fractions. The results showed that overall P contents increased with decreasing size of the soil aggregate-sized fractions. However, the relative distribution and speciation of varying P forms were found to be independent of soil aggregate-size. The majority of alkaline-extractable P was in the a-Fe/Al oxide fraction (42-47 % of total P), most of which was ortho-phosphate (36-41 % of total P). Furthermore, still significant amounts of particularly monoester P were bound to these oxides. Intriguingly, however, Fe/Al oxides were not the main bonding sites for pyrophosphate. Residual P contained similar amounts of total P associated with both a- (11-15 % of total P) and c-Fe oxides (7-13 % of total P

  12. A theoretical formalism for aggregation of peroxidized lipids and plasma membrane stability during photolysis.

    PubMed Central

    Busch, N A; Yarmush, M L; Toner, M

    1998-01-01

    The objective of this investigation was to examine, from a theoretical perspective, the mechanism underlying the lysis of plasma membranes by photoinduced, chemically mediated damage such as is found in photolysis. Toward this end, a model is presented which relates the membrane lifetime to the thermodynamic parameters of the membrane components based upon the kinetic theory of aggregate formation. The formalism includes a standard birth/death process for the formation of damaged membrane components (i.e., peroxidized lipids) as well as a terminating condensation process for the formation of aggregates of peroxidized plasma membrane lipids. Our theory predicts that 1) the membrane lifetime is inversely correlated with predicted rate of membrane damage; 2) an upper limit on the duration of membrane damage exists, above which the mean and variance of the membrane lifetime is independent of further membrane damage; and 3) both the mean and variance of the time of membrane lifetime distribution are correlated with the number of sites that may be damaged to form a single membrane defect. The model provides a framework to optimize the lysis of cell membranes by photodynamic therapy. PMID:9826616

  13. Non-native plants and soil microbes: potential contributors to the consistent reduction in soil aggregate stability caused by the disturbance of North American grasslands.

    PubMed

    Duchicela, Jessica; Vogelsang, Keith M; Schultz, Peggy A; Kaonongbua, Wittaya; Middleton, Elizabeth L; Bever, James D

    2012-10-01

    • Soil aggregate stability is an important ecosystem property that is altered by anthropogenic disturbance. Yet, the generalization of these alterations and the identification of the main contributors are limited by the absence of cross-site comparisons and the application of inconsistent methodologies across regions. • We assessed aggregate stability in paired remnant and post-disturbance grasslands across California, shortgrass and tallgrass prairies, and in manipulative experiments of plant composition and soil microbial inoculation. • Grasslands recovering from anthropogenic disturbance consistently had lower aggregate stability than remnants. Across all grasslands, non-native plant diversity was significantly associated with reduced soil aggregate stability. A negative effect of non-native plants on aggregate stability was also observed in a mesocosm experiment comparing native and non-native plants from California grasslands. Moreover, an inoculation study demonstrated that the degradation of the microbial community also contributes to the decline in soil aggregate stability in disturbed grasslands. • Anthropogenic disturbance consistently reduced water-stable aggregates. The stability of aggregates was reduced by non-native plants and the degradation of the native soil microbial community. This latter effect might contribute to the sustained decline in aggregate stability following anthropogenic disturbance. Further exploration is advocated to understand the generality of these potential mechanisms.

  14. Relaxation times and modes of disturbed aggregate distribution in micellar solutions with fusion and fission of micelles

    SciTech Connect

    Zakharov, Anatoly I.; Adzhemyan, Loran Ts.; Shchekin, Alexander K.

    2015-09-28

    We have performed direct numerical calculations of the kinetics of relaxation in the system of surfactant spherical micelles under joint action of the molecular mechanism with capture and emission of individual surfactant molecules by molecular aggregates and the mechanism of fusion and fission of the aggregates. As a basis, we have taken the difference equations of aggregation and fragmentation in the form of the generalized kinetic Smoluchowski equations for aggregate concentrations. The calculations have been made with using the droplet model of molecular surfactant aggregates and two modified Smoluchowski models for the coefficients of aggregate-monomer and aggregate-aggregate fusions which take into account the effects of the aggregate size and presence of hydrophobic spots on the aggregate surface. A full set of relaxation times and corresponding relaxation modes for nonequilibrium aggregate distribution in the aggregation number has been found. The dependencies of these relaxation times and modes on the total concentration of surfactant in the solution and the special parameter controlling the probability of fusion in collisions of micelles with other micelles have been studied.

  15. Strength and Stability of Olivine Aggregates Under Wet and Dry Conditions

    NASA Astrophysics Data System (ADS)

    Boettcher, M. S.; Hirth, G.

    2005-12-01

    We investigate the micromechanical processes that control localization, strength, and sliding stability of olivine aggregates through laboratory experiments at temperatures and effective pressures similar to those at the base of the seismogenic zone on a typical transform fault. Triaxial compression tests were conducted under both wet and dry conditions on olivine powder (grain size ≤ 60 μ m) at effective pressures Peff between 50 and 300 MPa, temperatures T between 600°C and 1000°C, and displacement rates from 0.06 to 60 μ m/s. In all dry tests deformation localized onto a narrow shear plane oriented between 30-45 degrees to the shortening direction. Sample strength increased linearly with Peff}, nearly independent of both temperature and water content. A transition from velocity-weakening to velocity-strengthening behavior occurred at T= 1000°C in the dry experiments, while a transition from velocity-weakening frictional sliding to ductile deformation occurred at T=1000°C under wet conditions. The pressure-dependent strength and temperature-dependent stability can be explained with a Bowden/Tabor asperity hypothesis. At high temperatures and low strain rates, plastic yielding at the asperity stabilizes frictional sliding of the bulk sample. Rapid compaction occurred at the start of each experiment and was followed by deformation at approximately constant volume. Dilatant behavior was most pronounced at low pressure and high strain rates. Extrapolation of our experimental data is consistent with the observation that seismicity is restricted to T ≤ 600°C in the oceanic lithosphere.

  16. Do abundance distributions and species aggregation correctly predict macroecological biodiversity patterns in tropical forests?

    PubMed Central

    Wiegand, Thorsten; Lehmann, Sebastian; Huth, Andreas; Fortin, Marie‐Josée

    2016-01-01

    Abstract Aim It has been recently suggested that different ‘unified theories of biodiversity and biogeography’ can be characterized by three common ‘minimal sufficient rules’: (1) species abundance distributions follow a hollow curve, (2) species show intraspecific aggregation, and (3) species are independently placed with respect to other species. Here, we translate these qualitative rules into a quantitative framework and assess if these minimal rules are indeed sufficient to predict multiple macroecological biodiversity patterns simultaneously. Location Tropical forest plots in Barro Colorado Island (BCI), Panama, and in Sinharaja, Sri Lanka. Methods We assess the predictive power of the three rules using dynamic and spatial simulation models in combination with census data from the two forest plots. We use two different versions of the model: (1) a neutral model and (2) an extended model that allowed for species differences in dispersal distances. In a first step we derive model parameterizations that correctly represent the three minimal rules (i.e. the model quantitatively matches the observed species abundance distribution and the distribution of intraspecific aggregation). In a second step we applied the parameterized models to predict four additional spatial biodiversity patterns. Results Species‐specific dispersal was needed to quantitatively fulfil the three minimal rules. The model with species‐specific dispersal correctly predicted the species–area relationship, but failed to predict the distance decay, the relationship between species abundances and aggregations, and the distribution of a spatial co‐occurrence index of all abundant species pairs. These results were consistent over the two forest plots. Main conclusions The three ‘minimal sufficient’ rules only provide an incomplete approximation of the stochastic spatial geometry of biodiversity in tropical forests. The assumption of independent interspecific placements is most

  17. Do abundance distributions and species aggregation correctly predict macroecological biodiversity patterns in tropical forests?

    PubMed

    May, Felix; Wiegand, Thorsten; Lehmann, Sebastian; Huth, Andreas; Fortin, Marie-Josée

    2016-05-01

    It has been recently suggested that different 'unified theories of biodiversity and biogeography' can be characterized by three common 'minimal sufficient rules': (1) species abundance distributions follow a hollow curve, (2) species show intraspecific aggregation, and (3) species are independently placed with respect to other species. Here, we translate these qualitative rules into a quantitative framework and assess if these minimal rules are indeed sufficient to predict multiple macroecological biodiversity patterns simultaneously. Tropical forest plots in Barro Colorado Island (BCI), Panama, and in Sinharaja, Sri Lanka. We assess the predictive power of the three rules using dynamic and spatial simulation models in combination with census data from the two forest plots. We use two different versions of the model: (1) a neutral model and (2) an extended model that allowed for species differences in dispersal distances. In a first step we derive model parameterizations that correctly represent the three minimal rules (i.e. the model quantitatively matches the observed species abundance distribution and the distribution of intraspecific aggregation). In a second step we applied the parameterized models to predict four additional spatial biodiversity patterns. Species-specific dispersal was needed to quantitatively fulfil the three minimal rules. The model with species-specific dispersal correctly predicted the species-area relationship, but failed to predict the distance decay, the relationship between species abundances and aggregations, and the distribution of a spatial co-occurrence index of all abundant species pairs. These results were consistent over the two forest plots. The three 'minimal sufficient' rules only provide an incomplete approximation of the stochastic spatial geometry of biodiversity in tropical forests. The assumption of independent interspecific placements is most likely violated in many forests due to shared or distinct habitat preferences

  18. Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent Cations, pH, and Natural Organic Matter

    EPA Science Inventory

    The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, i...

  19. Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent Cations, pH, and Natural Organic Matter

    EPA Science Inventory

    The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, i...

  20. Stability of Child Behavioral Style in the First 30 Months of Life: Single Timepoint and Aggregated Measures

    ERIC Educational Resources Information Center

    Parade, Stephanie H.; Dickstein, Susan; Schiller, Masha; Hayden, Lisa; Seifer, Ronald

    2015-01-01

    The current study examined the stability of temperament over time. Observers and mothers rated child behavior at eight timepoints across three assessment waves (8, 15, and 30 months of age). Internal consistency reliability of aggregates of the eight observer reports and eight mother reports were high. When considering single timepoint…

  1. Stability of Child Behavioral Style in the First 30 Months of Life: Single Timepoint and Aggregated Measures

    ERIC Educational Resources Information Center

    Parade, Stephanie H.; Dickstein, Susan; Schiller, Masha; Hayden, Lisa; Seifer, Ronald

    2015-01-01

    The current study examined the stability of temperament over time. Observers and mothers rated child behavior at eight timepoints across three assessment waves (8, 15, and 30 months of age). Internal consistency reliability of aggregates of the eight observer reports and eight mother reports were high. When considering single timepoint…

  2. Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

    SciTech Connect

    Woehl, Taylor J.; Park, Chiwoo; Evans, James E.; Arslan, Ilke; Ristenpart, William D.; Browning, Nigel D.

    2014-01-08

    Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

  3. Clay minerals, metallic oxides and oxy-hydroxides and soil organic carbon distribution within soil aggregates in temperate forest soils

    NASA Astrophysics Data System (ADS)

    Gartzia-Bengoetxea, Nahia; Fernández-Ugalde, Oihane; Virto, Iñigo; Arias-González, Ander

    2017-04-01

    Soil mineralogy is of primary importance for key environmental services provided by soils like carbon sequestration. However, current knowledge on the effects of clay mineralogy on soil organic carbon (SOC) stabilization is based on limited and conflicting data. In this study, we investigated the relationship between clay minerals, metallic oxides and oxy-hydroxides and SOC distribution within soil aggregates in mature Pinus radiata D.Don forest plantations. Nine forest stands located in the same geographical area of the Basque Country (North of Spain) were selected. These stands were planted on different parent material (3 on each of the following: sandstone, basalt and trachyte). There were no significant differences in climate and forest management among them. Moreover, soils under these plantations presented similar content of clay particles. We determined bulk SOC storage, clay mineralogy, the content of Fe-Si-Al-oxides and oxyhydroxides and the distribution of organic C in different soil aggregate sizes at different soil depths (0-5 cm and 5-20 cm). The relationship between SOC and abiotic factors was investigated using a factor analysis (PCA) followed by stepwise regression analysis. Soils developed on sandstone showed significantly lower concentration of SOC (29 g C kg-1) than soils developed on basalts (97 g C kg-1) and trachytes (119 g C kg-1). The soils on sandstone presented a mixed clay mineralogy dominated by illite, with lesser amounts of hydroxivermiculite, hydrobiotite and kaolinite, and a total absence of interstratified chlorite/vermiculite. In contrast, the major crystalline clay mineral identified in the soils developed on volcanic rocks was interstratified chlorite/vermiculite. Nevertheless, no major differences were observed between basaltic and trachytic soils in the clay mineralogy. The selective extraction of Fe showed that the oxalate extractable iron was significantly lower in soils on sandstone (3.7%) than on basalts (11.2%) and

  4. Stabilizing two IgG1 monoclonal antibodies by surfactants: Balance between aggregation prevention and structure perturbation.

    PubMed

    Wang, Shujing; Wu, Guoliang; Zhang, Xinyi; Tian, Zhou; Zhang, Ning; Hu, Tao; Dai, Weiguo; Qian, Feng

    2017-05-01

    Surfactants are widely used as stabilizers in the biopharmaceutical formulations to minimize protein aggregation. Under a fixed stress condition, the protecting and destabilizing effects of surfactants are hypothesized to be highly dependent on the species and concentrations of surfactants and mAb. Therefore, we here studied the aggregation-prevention and structure-perturbation effects of eight commonly used surfactants (Tw20, Tw80, Brij35, Chaps, TrX-100, SDS, Pluronic F68 and F127) on two IgG1 solution formulations under agitation, using analytical methodologies including visual inspection, OD350 measurement, HPLC-SEC, circular dicroism, fluorescence spectroscopy and differential scanning calorimetry. We found that: (1) With concentrations range from 0.02 to 2mg/mL, nonionic surfactants were found to offer efficient aggregation-prevention effect, which is superior than the ionic surfactants; and higher surfactant concentration prevented mAb aggregation better especially under prolonged stability test under stress conditions. (2) The surfactant induced structure-perturbation emerged when even higher surfactant concentration (≥2mg/mL) was used, and such effect was surfactant-property dependent; and (3) the two IgG1 demonstrated different aggregation mechanisms and surfactant dependency, especially at high mAb concentrations. In conclusion, surfactants usage in mAb formulations, including the types and concentrations, should strike an optimal balance between the desirable aggregation-prevention and the detrimental structure-perturbation effects, while the consideration of mAb aggregation mechanism and concentration is also required for surfactant assessment. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Protein folding, misfolding and aggregation: The importance of two-electron stabilizing interactions

    PubMed Central

    2017-01-01

    Proteins associated with neurodegenerative diseases are highly pleiomorphic and may adopt an all-α-helical fold in one environment, assemble into all-β-sheet or collapse into a coil in another, and rapidly polymerize in yet another one via divergent aggregation pathways that yield broad diversity of aggregates’ morphology. A thorough understanding of this behaviour may be necessary to develop a treatment for Alzheimer’s and related disorders. Unfortunately, our present comprehension of folding and misfolding is limited for want of a physicochemical theory of protein secondary and tertiary structure. Here we demonstrate that electronic configuration and hyperconjugation of the peptide amide bonds ought to be taken into account to advance such a theory. To capture the effect of polarization of peptide linkages on conformational and H-bonding propensity of the polypeptide backbone, we introduce a function of shielding tensors of the Cα atoms. Carrying no information about side chain-side chain interactions, this function nonetheless identifies basic features of the secondary and tertiary structure, establishes sequence correlates of the metamorphic and pH-driven equilibria, relates binding affinities and folding rate constants to secondary structure preferences, and manifests common patterns of backbone density distribution in amyloidogenic regions of Alzheimer’s amyloid β and tau, Parkinson’s α-synuclein and prions. Based on those findings, a split-intein like mechanism of molecular recognition is proposed to underlie dimerization of Aβ, tau, αS and PrPC, and divergent pathways for subsequent association of dimers are outlined; a related mechanism is proposed to underlie formation of PrPSc fibrils. The model does account for: (i) structural features of paranuclei, off-pathway oligomers, non-fibrillar aggregates and fibrils; (ii) effects of incubation conditions, point mutations, isoform lengths, small-molecule assembly modulators and chirality of solid

  6. Sequentially modified, polymer-stabilized gold nanoparticle libraries: convergent synthesis and aggregation behavior.

    PubMed

    Gibson, Matthew I; Danial, Maarten; Klok, Harm-Anton

    2011-05-09

    This manuscript describes a versatile, yet experimentally facile, method for producing libraries of polymer-coated (core−shell type) gold nanoparticles. The synthetic principle relies on two, sequential postmodification reactions, which ensures homogeneity across each series. First, poly(pentafluorophenyl methacrylate) synthesized by RAFT polymerization is used here as a reactive precursor, which can be modified, postpolymerization, to create a library of functional polymers each bearing a ω-thiol end-group. In a second step, these well-defined polymers are then tethered by their ω-thiol group to the surface of prefabricated citrate-stabilized gold nanoparticles to give a library of 75 unique, yet sequentially modified organic−inorganic hybrid particles. The optical properties of the gold core were exploited to create a high-throughput assay for investigating the role of nanoparticle size and surface coating on aggregation in various biologically relevant media. These experiments demonstrated the importance of the type of dissolved salts present and also the strong influence of serum proteins in cell-culture media and their interactions with nanoparticles surfaces, which in turn might affect their biological profiles. Therefore, this method presents a powerful, yet accessible tool for creating model nanoparticle libraries with intrinsic sensing properties.

  7. Color stability of white mineral trioxide aggregate in contact with hypochlorite solution.

    PubMed

    Camilleri, Josette

    2014-03-01

    One of the uses of white mineral trioxide aggregate (MTA) is as an apical barrier in immature teeth. Although this treatment has been reported to have high success rates, a number of cases of discoloration have been noted. The aim of this research was to investigate the color stability of white MTA in contact with various solutions used in endodontics. The change in color of white MTA after immersion in water, sodium hypochlorite, or hydrogen peroxide was assessed by viewing the color change on digital photographs and also by using a spectrophotometer. White MTA, white Portland cement, and bismuth oxide were assessed. The changes in the material after immersion in the different solutions were assessed by x-ray diffraction analysis and Fourier transform infrared spectroscopy. Immersion of white MTA and bismuth oxide in sodium hypochlorite resulted in the formation of a dark brown discoloration. This change was not observed in Portland cement. X-ray diffraction analysis and Fourier transform infrared analysis displayed the reduction of sodium hypochlorite in contact with bismuth oxide and MTA to sodium chloride. Contact of white MTA and other bismuth-containing materials with sodium hypochlorite solution should be avoided. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  8. Effect of three cations on the stability and microstructure of protein aggregate from duck egg white under alkaline condition.

    PubMed

    Ganasen, P; Benjakul, S

    2011-08-01

    Pidan (alkaline egg) has been consumed widely in oriental countries and lead, a toxic element, has been used traditionally to yield the desirable characteristics. For safety concerns, alternative cations can be used for the production of pidan with comparable properties to traditionally prepared pidan. Turbidity measured as absorbance at 400 nm and microstructure of duck egg white proteins at pH 12 as influenced by three cations at various levels were investigated. Turbidity and particle size of egg white protein (20 g/kg) in 10 g/kg NaCl sample with CaCl2, PbO2 or ZnCl2 added at a level of 1 g/kg increased with time up to 1 h, followed by a decrease (p<0.05). Nevertheless, the turbidity was retained more in samples added with PbO2, suggesting high stability of the aggregate formed. Zeta potential showed that the aggregates treated with PbO2 had a comparatively lower negative charge. Light microscopic studies indicated that the aggregation of egg white proteins was induced by ions but varied with the types of ions and incubation time. Therefore, PbO2 exhibited the highest stabilizing effect on egg white protein under alkaline condition. However, ZnCl2 can be used as an alternative compound even if it had lower impact on stability of aggregate of duck egg white protein.

  9. In vivo distribution and therapeutic efficacy of a novel amphotericin B poly-aggregated formulation.

    PubMed

    Espada, R; Valdespina, S; Dea, M A; Molero, G; Ballesteros, M P; Bolás, F; Torrado, J J

    2008-05-01

    The purpose of this investigation is the study of toxicity, in vivo distribution and therapeutic activity against candidiasis of poly-aggregated amphotericin B, in two different formulations: not microencapsulated (P-AMB) or incorporated in albumin microspheres (MP-AMB). The therapeutic efficacy and toxicity of amphotericin B formulations was studied in an immunocompetent murine model of systemic candidiasis. A pharmacokinetic study was also performed to measure the plasma, kidney, liver and spleen amphotericin B concentrations after administration of the three formulations to mice. The acute toxicity of P-AMB in mice is lower than that of the conventional amphotericin B reference formulation (D-AMB). The 50% lethal doses were increased at least eight times. Intravenous bolus administration of doses up to 40 mg/kg of body weight of poly-aggregated amphotericin B, either P-AMB or MP-AMB, did not produce acute symptoms of toxicity. Interestingly, in the pharmacokinetic study, significant (P < 0.05) lower plasma and kidney amphotericin B concentrations and higher liver and spleen amphotericin B concentrations were achieved after poly-aggregated amphotericin B formulation (P-AMB and MP-AMB) administration in relation to the reference formulation (D-AMB). At high amphotericin B doses, no significant differences in efficacy (P > 0.05) were observed among the formulations (D-AMB, P-AMB and MP-AMB). Although the efficacy in the candidiasis treatment was decreased as a consequence of amphotericin B aggregation, it can be compensated by the possibility of increasing the doses with lower nephrotoxicity. Moreover, due to its lower toxicity while maintaining its effectiveness, the poly-aggregated formulations (P-AMB and MP-AMB) have a better therapeutic index than the conventional formulation (D-AMB).

  10. Thermal stability of human plasma electronegative low-density lipoprotein: A paradoxical behavior of low-density lipoprotein aggregation

    PubMed Central

    Rull, Anna; Jayaraman, Shobini; Gantz, Donald L.; Rivas-Urbina, Andrea; Pérez-Cuellar, Montserrat; Ordóñez-Llanos, Jordi; Sánchez-Quesada, Jose Luis; Gursky, Olga

    2017-01-01

    Low-density lipoprotein (LDL) aggregation is central in triggering atherogenesis. A minor fraction of electronegative plasma LDL, termed LDL(−), plays a special role in atherogenesis. To better understand this role, we analyzed the kinetics of aggregation, fusion and disintegration of human LDL and its fractions, LDL(+) and LDL(−). Thermal denaturation of LDL was monitored by spectroscopy and electron microscopy. Initially, LDL(−) aggregated and fused faster than LDL(+), but later the order reversed. Most LDL(+) disintegrated and precipitated upon prolonged heating. In contrast, LDL(−) partially retained lipoprotein morphology and formed soluble aggregates. Biochemical analysis of all fractions showed no significant degradation of major lipids, mild phospholipid oxidation, and anincrease in non-esterified fatty acid (NEFA) upon thermal denaturation. The main baseline difference between LDL subfractions was higher content of NEFA in LDL(−). Since NEFA promote lipoprotein fusion, increased NEFA content can explain rapid initial aggregation and fusion of LDL(−) but not its resistance to extensive disintegration. Partial hydrolysis of apoB upon heating was similar in LDL subfractions, suggesting that minor proteins importantly modulate LDL disintegration. Unlike LDL(+), LDL(−) contains small amounts of apoA-I and apoJ. Addition of exogenous apoA-I to LDL(+) hampered lipoprotein aggregation, fusion and precipitation, while depletion of endogenous apoJ had an opposite effect. Therefore, the initial rapid aggregation of LDL(−) is apparently counterbalanced by the stabilizing effects of minor proteins such as apoA-I and apoJ. These results help identify key determinants for LDL aggregation, fusion and coalescence into lipid droplets in vivo. PMID:27233433

  11. Self-consistent rate equation theory of cluster size distribution in aggregation phenomena

    NASA Astrophysics Data System (ADS)

    Family, Fereydoon; Popescu, Mihail N.; Amar, Jacques G.

    2002-04-01

    Cluster nucleation and growth by aggregation is the central feature of many physical processes, from polymerization and gelation in polymer science, flocculation and coagulation in aerosol and colloidal chemistry, percolation and coarsening in phase transitions and critical phenomena, agglutination and cell adhesion in biology, to island nucleation and thin-film growth in materials science. Detailed information about the kinetics of aggregation is provided by the time dependent cluster size-distribution, a quantity which can be measured experimentally. While the standard Smoluchowski rate-equation approach has been in general successful in predicting average quantities like the total cluster density, it fails to account for spatial fluctuations and correlations and thus predicts size distributions that are in significant disagreement with both experiments and kinetic Monte Carlo simulations. In this work we outline a new method which takes into account such correlations. We show that by coupling a set of evolution equations for the capture-zone distributions with a set of rate-equations for the island densities one may obtain accurate predictions for the time- and size-dependent rates of monomer capture. In particular, by using this method we obtain excellent results for the capture numbers and island-size distributions in irreversible growth on both one- and two-dimensional substrates.

  12. [Pollutant distribution in organo-mineral aggregates in topsoils from a site contaminated by organochlorine pesticides].

    PubMed

    Cong, Xin; Xue, Nan-dong; Liang, Gang; Wang, Shi-jie; Zhu, Shu-quan; Li, Fa-sheng

    2008-09-01

    Four different soil particle-size fractions that is clay, silt, fine sand and coarse sand ( <2 microm, 2-20 microm, 20-200 microm, > 200 microm) from the topsoils in an organochlorine pesticide (OCP) field were separated by physical method to characterize the OCPs distribution in soils and to study the effect of organic matter and mineral composition in different separates on pollutants distribution. The results show that the concentrations of HCHs and DDTs in silt with 463.1 mg x kg(-1) and 1225.6 mg x kg(-1) are higher than those in coarse sand, 157.8 mg x kg(-1) and 384.5 mg x kg(-1), respectively. There is a significant correlationship between IgKoc. and the contents of HCHs and DDTs in clay. The analysis on X-ray diffraction of organo-mineral aggregates demonstrates that clay and silt have a much higher content of the clay minerals than those in coarse sand within the contaminated soils. There are some differences with different particle-size fractions in the content and composition of the clay minerals in organo-mineral aggregates, which affect the OCP distribution in soils to some extents. The results also suggest that the distribution of HCHs and DDTs in the particle with more pollutants in the site is similar to that in airborne particles. So the environmental behavior of OCPs in topsoils from the contaminated site should be paid more attention especially in ambient air-soil interaction.

  13. Size distribution of particles in Saturn’s rings from aggregation and fragmentation

    PubMed Central

    Brilliantov, Nikolai; Krapivsky, P. L.; Bodrova, Anna; Spahn, Frank; Hayakawa, Hisao; Stadnichuk, Vladimir; Schmidt, Jürgen

    2015-01-01

    Saturn’s rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, ∼r−q with q≈3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75≤q≤3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn’s rings. PMID:26183228

  14. Evaluation of the physical properties, bulk density and aggregate stability of potential substrates in quarry restoration.

    NASA Astrophysics Data System (ADS)

    Jordan, M.; Garcia-Orenes, F.; Mataix-Solera, J.; Garcia-Sanchez, E.

    2012-04-01

    Quarrying activity entails significant environmental impact affecting the soil, water, plants, landscape, etc. One of the most important impacts is the loss of the productive layer of the soil and its vegetation cover. However, mining activities are absolutely necessary for human development; keeping them sustainable implicates looking for viable solutions for the restoration of these areas to prevent degradation during and after the exploitation period. The aim of this study was to evaluate different substrates obtained from different mixes of sewage sludge and different mine spoils, to check how they are effective in quarry restoration, and to establish good practises in mining restoration. Also, the study tried to approach two refuses, one deriving from mining activity, as are the mine spoils that need to be reused for their valorisation, and the other, sewage sludge, obtained in the water depuration process to acquire a cheap substrate for soil rehabilitation. This preliminary work, which is included in a larger study, shows the results obtained from two physical properties studied, bulk density and aggregate stability, as key properties in the substrate structure for use in mining area restoration. Two doses of composted sewage sludge (30 and 90 Tm/Ha), both very rich in calcium carbonate, were applied to two different mine spoils under lab conditions. The first material, of poor quality, originated from the acquisition of arid particles in crushed limestone (Z). It is characterized by stable ''coarse elements'' predominance (up to 75% of its weight), and by the presence of elevated percentages of sand. The other waste material tested comes from limestone extraction (basically formed by the levels of interspersed non-limestone materials and the remains of stripped soils (D)). The results show that the high dose of sewage sludge applied to a mix of the two mine spoils significantly increased the percentage of stable aggregates by more than 50% than the control

  15. Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China.

    PubMed

    Zhang, Man; Cheng, Gong; Feng, Hao; Sun, Benhua; Zhao, Ying; Chen, Haixin; Chen, Jing; Dyck, Miles; Wang, Xudong; Zhang, Jianguo; Zhang, Afeng

    2017-04-01

    Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550 °C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8 t ha(-1) with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8 t ha(-1) (B8) and 16 t ha(-1) (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8 t ha(-1) straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2 mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2 mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16

  16. Stabilization of insulin against agitation-induced aggregation by the GMO cubic phase gel.

    PubMed

    Sadhale, Y; Shah, J C

    1999-11-25

    The main objective of the study was to evaluate if the liquid crystalline cubic phase gel of glyceryl monooleate (GMO) protects insulin from agitation induced aggregation. The aggregation of Humulin(R), Regular Iletin I(R) and Regular Iletin II(R), in cubic phase GMO gels at 30 U/g of gel was compared with that in PBS at 100 oscillations/min at 37 degrees C using optical density at 600 nm. The effect of agitation on the secondary structure of insulin in solution and in the gels was determined with circular dichroism (CD) spectroscopy, and the time course of aggregation was also followed by HPLC. A sigmoidal increase in optical density of solution with time indicated formation of increasing amounts of insoluble insulin aggregates. However, in the gels, optical density values stayed at, or around, the initial optical density value, comparable with that of a blank gel suggesting that insulin had not aggregated in the gel. CD spectroscopy of the soluble insulin showed a total loss of native conformation upon aggregation of insulin in solution. In contrast, CD spectra of insulin in the gel were unaltered suggesting protection from aggregation during agitation. Furthermore, agitation of insulin in gels for a duration as long as 2 months at 37 degrees C, had very little adverse effect on the native conformation of insulin, as indicated by the lack of a significant change in its CD spectrum. Therefore, the cubic phase gel was indeed able to protect insulin from agitation-induced aggregation and subsequent precipitation. Although the majority of insulin in solution appeared to have aggregated and precipitated after 8 days by UV and CD spectroscopy, RP-HPLC results indicated the presence of some soluble aggregates of insulin. In summary, the liquid crystalline cubic phase gel of GMO protects peptides, like insulin, from agitation-induced aggregation.

  17. Secure and Cost-Effective Distributed Aggregation for Mobile Sensor Networks

    PubMed Central

    Guo, Kehua; Zhang, Ping; Ma, Jianhua

    2016-01-01

    Secure data aggregation (SDA) schemes are widely used in distributed applications, such as mobile sensor networks, to reduce communication cost, prolong the network life cycle and provide security. However, most SDA are only suited for a single type of statistics (i.e., summation-based or comparison-based statistics) and are not applicable to obtaining multiple statistic results. Most SDA are also inefficient for dynamic networks. This paper presents multi-functional secure data aggregation (MFSDA), in which the mapping step and coding step are introduced to provide value-preserving and order-preserving and, later, to enable arbitrary statistics support in the same query. MFSDA is suited for dynamic networks because these active nodes can be counted directly from aggregation data. The proposed scheme is tolerant to many types of attacks. The network load of the proposed scheme is balanced, and no significant bottleneck exists. The MFSDA includes two versions: MFSDA-I and MFSDA-II. The first one can obtain accurate results, while the second one is a more generalized version that can significantly reduce network traffic at the expense of less accuracy loss. PMID:27120599

  18. Secure and Cost-Effective Distributed Aggregation for Mobile Sensor Networks.

    PubMed

    Guo, Kehua; Zhang, Ping; Ma, Jianhua

    2016-04-23

    Secure data aggregation (SDA) schemes are widely used in distributed applications, such as mobile sensor networks, to reduce communication cost, prolong the network life cycle and provide security. However, most SDA are only suited for a single type of statistics (i.e., summation-based or comparison-based statistics) and are not applicable to obtaining multiple statistic results. Most SDA are also inefficient for dynamic networks. This paper presents multi-functional secure data aggregation (MFSDA), in which the mapping step and coding step are introduced to provide value-preserving and order-preserving and, later, to enable arbitrary statistics support in the same query. MFSDA is suited for dynamic networks because these active nodes can be counted directly from aggregation data. The proposed scheme is tolerant to many types of attacks. The network load of the proposed scheme is balanced, and no significant bottleneck exists. The MFSDA includes two versions: MFSDA-I and MFSDA-II. The first one can obtain accurate results, while the second one is a more generalized version that can significantly reduce network traffic at the expense of less accuracy loss.

  19. Aluminum induces neurofilament aggregation by stabilizing cross-bridging of phosphorylated c-terminal sidearms.

    PubMed

    Kushkuley, Jacob; Metkar, Shailesh; Chan, Walter K-H; Lee, Sangmook; Shea, Thomas B

    2010-03-31

    Exposure to neurotoxin aluminum neurotoxicity is accompanied by the perikaryal accumulation of tangles of phosphorylated neurofilaments (NFs). We examined their formation and reversibility under cell-free conditions. AlCl3 induced dose-dependent formation of NF aggregates, ultimately incorporating 100% of detectable NFs. The same concentration of CaCl2 induced approximately 25% of NFs to form longitudinal dimers and did not induce aggregation. AlCl3 induced similar percentages of aggregates in the presence or absence of CaCl2, and CaCl2 could not reduce pre-formed aggregates. CaCl(2)-induced dimers and AlCl(3)-induced aggregates were prevented by prior NF dephosphorylation. While CaCl(2)-induced dimers were dissociated by phosphatase treatment, AlCl(3)-induced aggregates were only reduced by approximately 50%, suggesting that aggregates may sequester phosphorylation sites. Since phosphatases regulate NF phosphorylation within perikarya, inhibition of NF dephosphorylation by aluminum would promote perikaryal NF phosphorylation and foster precocious phospho-dependent NF-NF associations. These findings are consistent with the notion that prolonged interactions induced among phospho-NFs by the trivalent aluminum impairs axonal transport and promotes perikaryal aggregation. Copyright 2010. Published by Elsevier B.V.

  20. Some Cautionary Notes regarding the Use of Aggregated Scores as a Measure of Behavioral Stability.

    ERIC Educational Resources Information Center

    Day, H.D.; And Others

    1983-01-01

    Examined the utility of the aggregation method as a measure of behavioral consistency in 26 studies involving computer-generated, repeated-measurement data. Concluded that aggregation produces spuriously high estimates of behavioral consistency. The Spearman-Brown prophecy formula and coefficient alpha accurately predict the results of the…

  1. Effects of fire on organic matter content and aggregate stability of soils in South of Spain.

    NASA Astrophysics Data System (ADS)

    Martínez-Murillo, Juan F.; Ruiz-Sinoga, José D.; Jiménez-Donaire, Virginia; Hueso-González, Paloma; Gabarrón-Galeote, Miguel A.

    2014-05-01

    Wildfires affect dramatically to soil physical, chemical and biological properties, which changes the hydrological and erosive soil response. The objectives of this study are to compare some soil properties affected by fire in field conditions. The experimental area is located in the South of Spain, 32 km western of the city of Málaga. In general, the area is characterized by a sub-humid Mediterranean climate (mean annual precipitation: 699 mm year-1; mean annual temperature: 17°C), with a substratum of alkaline metamorphic rocks. Vegetation cover consists on a mixed open wood of Quercus spp. and Pinus spp. with typical degraded Mediterranean scrub, where the dominant genus are Ulex spp. and Cistus spp. This area was partially affected by a wildfire on September 11th 2011. Soil samples were taken in burned and unburned areas: soil covered by shrubs, trees and bare soils. Unburned area was adjacent to the burned one and both of them had the same general conditions. On each microenvironment samples of the first 5 cm of soil were collected on September 19th 2011. The analyzed properties in the laboratory were organic matter (OM) and aggregate stability (AS). In general, fire affected mainly to OM (p<0.01). When we performed the analyses dividing the samples according to vegetal cover, the ANOVA showed that the wildfire only affected the OM content in soil covered by shrubs. In soil covered by trees and bare soil OM decreased, but it was insignificant. AS were not affected in any sampled environment.

  2. Distribution of Sulfate-Reducing and Methanogenic Bacteria in Anaerobic Aggregates Determined by Microsensor and Molecular Analyses

    PubMed Central

    Santegoeds, Cecilia M.; Damgaard, Lars Riis; Hesselink, Gijs; Zopfi, Jakob; Lens, Piet; Muyzer, Gerard; de Beer, Dirk

    1999-01-01

    Using molecular techniques and microsensors for H2S and CH4, we studied the population structure of and the activity distribution in anaerobic aggregates. The aggregates originated from three different types of reactors: a methanogenic reactor, a methanogenic-sulfidogenic reactor, and a sulfidogenic reactor. Microsensor measurements in methanogenic-sulfidogenic aggregates revealed that the activity of sulfate-reducing bacteria (2 to 3 mmol of S2− m−3 s−1 or 2 × 10−9 mmol s−1 per aggregate) was located in a surface layer of 50 to 100 μm thick. The sulfidogenic aggregates contained a wider sulfate-reducing zone (the first 200 to 300 μm from the aggregate surface) with a higher activity (1 to 6 mmol of S2− m−3 s−1 or 7 × 10−9 mol s−1 per aggregate). The methanogenic aggregates did not show significant sulfate-reducing activity. Methanogenic activity in the methanogenic-sulfidogenic aggregates (1 to 2 mmol of CH4 m−3 s−1 or 10−9 mmol s−1 per aggregate) and the methanogenic aggregates (2 to 4 mmol of CH4 m−3 s−1 or 5 × 10−9 mmol s−1 per aggregate) was located more inward, starting at ca. 100 μm from the aggregate surface. The methanogenic activity was not affected by 10 mM sulfate during a 1-day incubation. The sulfidogenic and methanogenic activities were independent of the type of electron donor (acetate, propionate, ethanol, or H2), but the substrates were metabolized in different zones. The localization of the populations corresponded to the microsensor data. A distinct layered structure was found in the methanogenic-sulfidogenic aggregates, with sulfate-reducing bacteria in the outer 50 to 100 μm, methanogens in the inner part, and Eubacteria spp. (partly syntrophic bacteria) filling the gap between sulfate-reducing and methanogenic bacteria. In methanogenic aggregates, few sulfate-reducing bacteria were detected, while methanogens were found in the core. In the sulfidogenic aggregates, sulfate-reducing bacteria were

  3. Soil aggregate stability and wind erodible fraction in a semi-arid environment of White Nile State, Sudan

    NASA Astrophysics Data System (ADS)

    Elhaja, Mohamed Eltom; Ibrahim, Ibrahim Saeed; Adam, Hassan Elnour; Csaplovics, Elmar

    2014-11-01

    One of the most important recent issues facing White Nile State, Sudan, as well as Sub Saharan Africa, is the threat of continued land degradation and desertification as a result of climatic factors and human activities. Remote sensing and satellites imageries with multi-temporal and spectral and GIS capability, plays a major role in developing a global and local operational capability for monitoring land degradation and desertification in dry lands, as well as in White Nile State. The process of desertification in form of sand encroachment in White Nile State has increased rapidly, and much effort has been devoted to define and study its causes and impacts. This study depicts the capability afforded by remote sensing and GIS to analyze and map the aggregate stability as indicator for the ability of soil to wind erosion process in White Nile State by using Geo-statistical techniques. Cloud-free subset Landsat; Enhance Thematic Mapper plus (ETM +) scenes covering the study area dated 2008 was selected in order to identify the different features covering the study area as well as to make the soil sampling map. Wet-sieving method was applied to determine the aggregate stability. The geo-statistical methods in EARDAS 9.1 software was used for mapping the aggregate stability. The results showed that the percentage of aggregate stability ranged from (0 to 61%) in the study area, which emphasized the phenomena of sand encroachment from the western part (North Kordofan) to the eastern part (White Nile State), following the wind direction. The study comes out with some valuable recommendations and comments, which could contribute positively in reducing sand encroachments

  4. Particle Restabilization in Silica/PEG/Ethanol Suspensions: How Strongly do Polymers Need To Adsorb To Stabilize Against Aggregation?

    SciTech Connect

    Kim, So Youn; Zukoski, Charles F.

    2014-09-24

    We study the effects of increasing the concentration of a low molecular weight polyethylene glycol on the stability of 44 nm diameter silica nanoparticles suspended in ethanol. Polymer concentration, c{sub p}, is increased from zero to that characterizing the polymer melt. Particle stability is accessed through measurement of the particle second-virial coefficient, B{sub -2}, performed by light scattering and ultrasmall angle X-ray scattering (USAXS). The results show that at low polymer concentration, c{sub p} < 3 wt %, B{sub -2} values are positive, indicating repulsive interactions between particles. B{sub -2} decreases at intermediate concentrations (3 wt % < c{sub p} < 50 wt %), and particles aggregates are formed. At high concentrations (50 wt % < c{sub p}) B{sub -2} increases and stabilizes at a value expected for hard spheres with a diameter near 44 nm, indicating the particles are thermodynamically stable. At intermediate polymer concentrations, rates of aggregation are determined by measuring time-dependent changes in the suspension turbidity, revealing that aggregation is slowed by the necessity of the particles diffusing over a repulsive barrier in the pair potential. The magnitude of the barrier passes through a minimum at c{sub p} {approx} 12 wt % where it has a value of {approx}12kT. These results are understood in terms of a reduction of electrostatic repulsion and van der Waals attractions with increasing c{sub p}. Depletion attractions are found to play a minor role in particle stability. A model is presented suggesting displacement of weakly adsorbed polymer leads to slow aggregation at intermediate concentration, and we conclude that a general model of depletion restabilization may involve increased strength of polymer adsorption with increasing polymer concentration.

  5. [Profile distribution of soil aggregates organic carbon in primary forests in Karst cluster-peak depression region].

    PubMed

    Lu, Ling-Xiao; Song, Tong-Qing; Peng, Wan-Xia; Zeng, Fu-Ping; Wang, Ke-Lin; Xu, Yun-Lei; Yu, Zi; Liu, Yan

    2012-05-01

    Soil profiles were collected from three primary forests (Itoa orientalis, Platycladus orientalis, and Radermachera sinica) in Karst cluster-peak depression region to study the composition of soil aggregates, their organic carbon contents, and the profile distribution of the organic carbon. In the three forests, >2 mm soil aggregates were dominant, occupying about 76% of the total. The content of soil total organic carbon ranged from 12.73 to 68.66 g x kg(-1), with a significant difference among the forests. The organic carbon content in <1 mm soil aggregates was slightly higher than that in >2 mm soil aggregates, but most of soil organic carbon was stored in the soil aggregates with greater particle sizes. About 70% of soil organic carbon came from >2 mm soil aggregates. There was a significant positive relationship between the contents of 2-5 and 5-8 mm soil aggregates and the content of soil organic carbon. To increase the contents of 2-8 mm soil aggregates could effectively improve the soil carbon sequestration in Karst region. In Itoa orientalis forest, 2-8 mm soil aggregates accounted for 46% of the total, and the content of soil total organic carbon reached to 37.62 g x kg(-1), which implied that Itoa orientalis could be the suitable tree species for the ecological restoration in Karst region.

  6. Effects of black carbon on aggregate stability, runoff generation, splash erosion and slopewash of a clay loam under simulated rainfall

    NASA Astrophysics Data System (ADS)

    Aston, Steve; Doerr, Stefan; Street-Perrott, Alayne

    2013-04-01

    Black (pyrogenic) carbon (BC) was produced from native hardwoods pyrolysed in a ring kiln at ~400° C and ground and sieved to < 2 mm. The BC was then added to a clay loam (sieved to 3.35 mm remaining. After 200 days of incubation, the remainder of each sample was air-dried and sieved to < 5 mm. Each sample was then placed in a square plot and subjected to 40 minutes of simulated rainfall. Runoff and subsurface drainage were measured at 2 minute intervals and runoff was collected at 5 minute intervals to enable subsequent determination of sediment concentrations, sediment yields and erosion rates of soil and BC. Splash cups were placed on each side of the plot to allow measurement of overall splash detachment for each simulation. A BC content of 5g kg-1 did not affect the mean aggregate stability of the clay loam, but a content of 25 g kg-1 led to a decrease in mean aggregate stability of >40%, with a further significant reduction observed when the BC content was 50 g kg-1. There were no statistically significant changes in aggregate stability between 50, 100 and 150 days of incubation for any of the application rates. Results showing the effects of BC on runoff generation, splash erosion and slopewash will also be presented.

  7. Stabilization of linear distributed control systems with unbounded delay

    NASA Astrophysics Data System (ADS)

    Henríquez, Hernán R.; Hernández M., Eduardo

    2005-07-01

    In this paper we study the asymptotic stabilization of linear distributed parameter control systems with unbounded delay. Assuming that the semigroup of operators associated with the uncontrolled and nondelayed equation is compact and that the phase space is a uniform fading memory space, we characterize those systems that can be stabilized using a feedback control. As consequence we conclude that every system of this type is stabilizable with an appropriated finite dimensional control.

  8. Indexes of Land Use Change to Predict Aggregate Stability in a Mollisol and a Vertisol of Argentina

    NASA Astrophysics Data System (ADS)

    Novelli, L. E.; Caviglia, O. P.; Wilson, M. G.; Sasal, M. C.

    2012-04-01

    In several areas of South America, the extensive cropping systems in traditional agricultural lands have increase the area cropped with soybean, mainly as a single annual crop. Also nowadays agriculture has a progressive expansion toward more environmentally fragile areas that were traditionally occupied by livestock or native forests. This change of land use may be characterized through different indexes as the length of the growth period or the frequency of a particular crop in the cropping sequence. On the other hand the consequences of land-use changes on soil physical condition may be monitored through the aggregate stability, which is directly related to soil functionality. However, there are different methods for aggregate stability analysis, which may vary in their potential for prediction. The aim of our work was to assess different quantitative indexes of change in the land use on aggregate stability through two methods in two soils differing in the main agents of aggregation. The study was conducted in a Mollisol and a Vertisol from Argentina. Eleven fields (agricultural and crop-pasture rotation) under no-tillage and one natural grassland were selected in each soil type. The fraction of annual time with vegetal cover (as a measure of the intensification in the land use - ISI) and the frequency of a given crop (soybean - SCF; wheat - WCF; and wheat plus maize - CCF) in the cropping sequence over a 6-year period were calculated. Samples were collected at 0-5 and 5-15 cm depths from each soil. The mean weight diameter (MWD) of the soil aggregates where determined by two methods: Le Bissonnais with three pretreatment (fast wetting, slow wetting and stirring after prewetting) and by wet sieving using an instrument similar to the Yoder apparatus. The MWD by wet-sieving was affected by ISI and SCF, but the impact only was recorded in 0-5cm depth of the Mollisol. The MWD by fast and slow wetting and the means of three pretreatments (MWDm) were directly related

  9. Aggregation for Computing Multi-Modal Stationary Distributions in 1-D Gene Regulatory Networks.

    PubMed

    Avcu, Neslihan; Pekergin, Nihal; Pekergin, Ferhan; Guzelis, Cuneyt

    2017-04-27

    This paper proposes aggregation-based, three-stage algorithms to overcome the numerical problems encountered in computing stationary distributions and mean first passage times for multi-modal birth-death processes of large state space sizes. The considered birth-death processes which are defined by Chemical Master Equations are used in modeling stochastic behavior of gene regulatory networks. Computing stationary probabilities for a multi-modal distribution from Chemical Master Equations is subject to have numerical problems due to the probability values running out of the representation range of the standard programming languages with the increasing size of the state space. The aggregation is shown to provide a solution to this problem by analyzing first reduced size subsystems in isolation and then considering the transitions between these subsystems. The proposed algorithms are applied to study the bimodal behavior of the lac operon of E. coli described with a one-dimensional birth-death model. Thus the determination of the entire parameter range of bimodality for the stochastic model of lac operon is achieved.

  10. EPPRD: An Efficient Privacy-Preserving Power Requirement and Distribution Aggregation Scheme for a Smart Grid

    PubMed Central

    Zhang, Lei; Zhang, Jing

    2017-01-01

    A Smart Grid (SG) facilitates bidirectional demand-response communication between individual users and power providers with high computation and communication performance but also brings about the risk of leaking users’ private information. Therefore, improving the individual power requirement and distribution efficiency to ensure communication reliability while preserving user privacy is a new challenge for SG. Based on this issue, we propose an efficient and privacy-preserving power requirement and distribution aggregation scheme (EPPRD) based on a hierarchical communication architecture. In the proposed scheme, an efficient encryption and authentication mechanism is proposed for better fit to each individual demand-response situation. Through extensive analysis and experiment, we demonstrate how the EPPRD resists various security threats and preserves user privacy while satisfying the individual requirement in a semi-honest model; it involves less communication overhead and computation time than the existing competing schemes. PMID:28783122

  11. EPPRD: An Efficient Privacy-Preserving Power Requirement and Distribution Aggregation Scheme for a Smart Grid.

    PubMed

    Zhang, Lei; Zhang, Jing

    2017-08-07

    A Smart Grid (SG) facilitates bidirectional demand-response communication between individual users and power providers with high computation and communication performance but also brings about the risk of leaking users' private information. Therefore, improving the individual power requirement and distribution efficiency to ensure communication reliability while preserving user privacy is a new challenge for SG. Based on this issue, we propose an efficient and privacy-preserving power requirement and distribution aggregation scheme (EPPRD) based on a hierarchical communication architecture. In the proposed scheme, an efficient encryption and authentication mechanism is proposed for better fit to each individual demand-response situation. Through extensive analysis and experiment, we demonstrate how the EPPRD resists various security threats and preserves user privacy while satisfying the individual requirement in a semi-honest model; it involves less communication overhead and computation time than the existing competing schemes.

  12. Thermal stabilization of low level RF distribution systems at SLAC

    SciTech Connect

    McCormick, D.; Ross, M.; Himel, T.; Spencer, N.

    1993-07-01

    Analysis of SLC accelerator operator activity, in particular control system knob turns, indicated poor thermal stability performance of the low level RF distribution system in the SLC injector and positron production complex. Daily drifts of up to 15 S-band delay, about 30 times the tolerance, were observed. In this paper we describe the tool used to track down and quantify operator knob turn activity, the low level RF distribution stabilization systems, and some fixes used to correct the problem. In order to identify poorly performing components, a beam timing or phase monitor diagonstic has been developed. Initial results from it will be presented.

  13. Positive evolution features in soil restoration assessed by means of glomalin and its relationship to aggregate stability

    NASA Astrophysics Data System (ADS)

    Luna Ramos, Lourdes; Miralles Mellado, Isabel; Gispert Negrell, María; Pardini, Giovanni; Solé Benet, Albert

    2014-05-01

    Restoration of limestone quarries in arid environments mainly consists of regenerating a highly degraded soil and/or creating a soil-like substrate with minimal physico-chemical and biological properties. In an experimental soil restoration in limestone quarries from Sierra de Gádor (Almería), SE Spain, with the aim to improve soil/substrate properties and to reduce evaporation and erosion, 18 plots 15 x 5 m were prepared to test organic amendments (sludge, compost, control) and different mulches (gravel, chopped forest residue, control). In order to evaluate the soil quality of the different treatments, their chemical, physical and biological properties were analyzed. Among the most efficient biological indicators are arbuscular mycorrhizal fungi (AMF). AMF play an important role in aggregate stability due to the production of a glycoprotein called glomalin. Therefore, the aim of this study was to quantify, 5 years after the start the experiment, the content of total glomalin (TG) and to analyze its relationship with other soil parameters such as organic matter (OM) and aggregate stability soil (AE). Results indicated a remarkable effect of organic amendments on glomalin content, which was higher in the treatments with compost (6.96 mg g -1) than in sludge and control (0.54 and 0.40 mg g-1, respectively). Amendments also significantly influenced aggregate stability: the highest values were recorded in treatments with sludge and compost (23.14 and 25.09%, respectively) compared to control (13.37%). The gravel mulch had a negative influenced on AE: an average of 16% compared to 23.4% for chopped forest residues and 23.1% of control. Data showed a positive and significant correlation between values of TG and OM content (r = 0.95). We also found a positive and significant correlation between abundance of TG and AE when OM contents were lower than 4% (r = 0.93), however, there was no significant correlation to higher OM when it was higher than 4% (r = 0.34). This

  14. Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: influence of aggregate formation on process stability.

    PubMed

    Kleyböcker, A; Liebrich, M; Kasina, M; Kraume, M; Wittmaier, M; Würdemann, H

    2012-06-01

    Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH>7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4) the degradation of volatile fatty acids in the aggregates. Furthermore, this mechanism enabled a stable process performance after re-activation of biogas production. In contrast, during the counter measure with NaOH aggregate formation was only minor resulting in a rapid process failure subsequent the increase of the organic loading rate.

  15. Stability analysis of 4-species Aβ aggregation model: A novel approach to obtaining physically meaningful rate constants.

    PubMed

    Ghag, G; Ghosh, P; Mauro, A; Rangachari, V; Vaidya, A

    2013-11-01

    Protein misfolding and concomitant aggregation towards amyloid formation is the underlying biochemical commonality among a wide range of human pathologies. Amyloid formation involves the conversion of proteins from their native monomeric states (intrinsically disordered or globular) to well-organized, fibrillar aggregates in a nucleation-dependent manner. Understanding the mechanism of aggregation is important not only to gain better insight into amyloid pathology but also to simulate and predict molecular pathways. One of the main impediments in doing so is the stochastic nature of interactions that impedes thorough experimental characterization and the development of meaningful insights. In this study, we have utilized a well-known intermediate state along the amyloid-β peptide aggregation pathway called protofibrils as a model system to investigate the molecular mechanisms by which they form fibrils using stability and perturbation analysis. Investigation of protofibril aggregation mechanism limits both the number of species to be modeled (monomers, and protofibrils), as well as the reactions to two (elongation by monomer addition, and protofibril-protofibril lateral association). Our new model is a reduced order four species model grounded in mass action kinetics. Our prior study required 3200 reactions, which makes determining the reaction parameters prohibitively difficult. Using this model, along with a linear perturbation argument, we rigorously determine stable ranges of rate constants for the reactions and ensure they are physically meaningful. This was accomplished by finding the ranges in which the perturbations dieout in a five-parameter sweep, which includes the monomer and protofibril equilibrium concentrations and three of the rate constants. The results presented are a proof-of-concept method in determining meaningful rate constants that can be used as a bonafide way for determining accurate rate constants for other models involving complex

  16. Effect of Surface Curvature and Chemistry on Protein Stability, Adsorption and Aggregation

    NASA Astrophysics Data System (ADS)

    Radhakrishna, Mithun

    Enzyme immobilization has been of great industrial importance because of its use in various applications like bio-fuel cells, bio-sensors, drug delivery and bio-catalytic films. Although research on enzyme immobilization dates back to the 1970's, it has been only in the past decade that scientists have started to address the problems involved systematically. Most of the previous works on enzyme immobilization have been retrospective in nature i.e enzymes were immobilized on widely used substrates without a compatibility study between the enzyme and the substrate. Consequently, most of the enzymes lost their activity upon immobilization onto these substrates due to many governing factors like protein-surface and inter-protein interactions. These interactions also play a major role biologically in cell signaling, cell adhesion and inter-protein interactions specifically is believed to be the major cause for neurodegenerative diseases like Alzheimer's and Parkinson's disease. Therefore understanding the role of these forces on proteins is the need of the hour. In my current research, I have mainly focused on two factors a) Surface Curvature b) Surface Chemistry as both of these play a pivotal role in influencing the activity of the enzymes upon immobilization. I study the effect of these factors computationally using a stochastic method known as Monte Carlo simulations. My research work carried out in the frame work of a Hydrophobic-Polar (HP) lattice model for the protein shows that immobilizing enzymes inside moderately hydrophilic or hydrophobic pores results in an enhancement of the enzymatic activity compared to that in the bulk. Our results also indicate that there is an optimal value of surface curvature and hydrophobicity/hydrophilicity where this enhancement of enzymatic activity is highest. Further, our results also show that immobilization of enzymes inside hydrophobic pores of optimal sizes are most effective in mitigating protein-aggregation. These

  17. Aggregate size distribution in a biochar-amended tropical Ultisol under conventional hand-hoe tillage.

    PubMed

    Fungo, Bernard; Lehmann, Johannes; Kalbitz, Karsten; Thionģo, Margaret; Okeyo, Irene; Tenywa, Moses; Neufeldt, Henry

    2017-01-01

    Biochar (or pyrogenic organic matter) is increasingly proposed as a soil amendment for improving fertility, carbon sequestration and reduction of greenhouse gas emissions. However, little is known about its effects on aggregation, an important indicator of soil quality and functioning. The aim of this study was to assess the effect of Eucalyptus wood biochar (B, pyrolyzed at 550 °C, at 0 or 2.5 t ha(-1)), green manure (T, from Tithonia diversifolia at 0, 2.5 or 5.0 t ha(-1)) and mineral nitrogen (U, urea, at 0, or 120 kg N ha(-1)) on soil respiration, aggregate size distribution and SOC in these aggregate size fractions in a 2-year field experiment on a low-fertility Ultisol in western Kenya under conventional hand-hoe tillage. Air-dry 2-mm sieved soils were divided into four fractions by wet sieving: Large Macro-aggregates (LM; >1000 μm); Small Macro-aggregates (SM, 250-1000 μm); Micro-aggregates (M, 250-53 μm) and Silt + Clay (S + C, < 53 μm). We found that biochar alone did not affect a mean weight diameter (MWD) but combined application with either T. diversifolia (BT) or urea (BU) increased MWD by 34 ± 5.2 μm (8%) and 55 ± 5.4 μm (13%), respectively, compared to the control (P = 0.023; n = 36). The B + T + U combination increased the proportion of the LM and SM by 7.0 ± 0.8%, but reduced the S + C fraction by 5.2 ± 0.23%. SOC was 30%, 25% and 23% in S + C, M and LM/SM fractions, and increased by 9.6 ± 1.0, 5.7 ± 0.8, 6.3 ± 1.1 and 4.2 ± 0.9 g kg(-1) for LM, SM, M and S + C, respectively. MWD was not related to either soil respiration or soil moisture but decreased with higher SOC (R(2)  = 0.37, P = 0.014, n = 26) and increased with greater biomass production (R(2)  = 0.11, P = 0.045, n = 33). Our data suggest that within the timeframe of the study, biochar is stored predominantly as free particulate OC in the silt and clay fraction and promoted a movement of native SOC from larger

  18. Suspension stability and aggregation of multi-walled carbon nanotubes as affected by dissolved organic matters extracted from agricultural wastes.

    PubMed

    Li, Helian; Qiu, Yanhua; Wang, Xiaonuan; Liu, Wenhao; Chen, Guangcai; Ma, Yibing; Xing, Baoshan

    2016-03-01

    Dissolved organic matters (DOMs) extracted from wheat straw (SDOM) and cow manure (MDOM) were used to investigate their effects on the suspension stability and aggregation of multi-walled carbon nanotubes (MWCNTs). Two types of DOM can effectively disperse and stabilize the MWCNTs. At initial MWCNT concentration of 500 mg/L, suspended MWCNT concentration ranged from 8.0 to 17.9 mg/L as DOM were varied from 50 to 200 mg/L dissolved organic carbon (DOC). The critical coagulation concentration (CCC) values were estimated to be 41.4 mM NaCl and 5.3 mM CaCl2 in the absence of DOM. The presence of SDOM and MDOM significantly retarded the aggregation rate of MWCNTs. The CCC values increased to 120 mM NaCl and 14.8 mM CaCl2 at SDOM concentration of 20 mg/L DOC. Due to its higher aromaticity and molecular weight, MDOM showed higher ability to stabilize MWCNTs, with CCC values of 201 mM and 15.8 mM at 20 mg/L DOC. These findings revealed that DOMs originated from agricultural wastes will have great impact on the dispersion and stabilization of MWCNTs, thus their fate in the aquatic environment.

  19. Adjusting particle-size distributions to account for aggregation in tephra-deposit model forecasts

    NASA Astrophysics Data System (ADS)

    Mastin, Larry G.; Van Eaton, Alexa R.; Durant, Adam J.

    2016-07-01

    Volcanic ash transport and dispersion (VATD) models are used to forecast tephra deposition during volcanic eruptions. Model accuracy is limited by the fact that fine-ash aggregates (clumps into clusters), thus altering patterns of deposition. In most models this is accounted for by ad hoc changes to model input, representing fine ash as aggregates with density ρagg, and a log-normal size distribution with median μagg and standard deviation σagg. Optimal values may vary between eruptions. To test the variance, we used the Ash3d tephra model to simulate four deposits: 18 May 1980 Mount St. Helens; 16-17 September 1992 Crater Peak (Mount Spurr); 17 June 1996 Ruapehu; and 23 March 2009 Mount Redoubt. In 192 simulations, we systematically varied μagg and σagg, holding ρagg constant at 600 kg m-3. We evaluated the fit using three indices that compare modeled versus measured (1) mass load at sample locations; (2) mass load versus distance along the dispersal axis; and (3) isomass area. For all deposits, under these inputs, the best-fit value of μagg ranged narrowly between ˜ 2.3 and 2.7φ (0.20-0.15 mm), despite large variations in erupted mass (0.25-50 Tg), plume height (8.5-25 km), mass fraction of fine ( < 0.063 mm) ash (3-59 %), atmospheric temperature, and water content between these eruptions. This close agreement suggests that aggregation may be treated as a discrete process that is insensitive to eruptive style or magnitude. This result offers the potential for a simple, computationally efficient parameterization scheme for use in operational model forecasts. Further research may indicate whether this narrow range also reflects physical constraints on processes in the evolving cloud.

  20. Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: Influence of aggregate formation on process stability

    SciTech Connect

    Kleyboecker, A.; Liebrich, M.; Kasina, M.; Kraume, M.; Wittmaier, M.; Wuerdemann, H.

    2012-06-15

    Highlights: Black-Right-Pointing-Pointer Mechanism of process recovery with calcium oxide. Black-Right-Pointing-Pointer Formation of insoluble calcium salts with long chain fatty acids and phosphate. Black-Right-Pointing-Pointer Adsorption of VFAs by the precipitates resulting in the formation of aggregates. Black-Right-Pointing-Pointer Acid uptake and phosphate release by the phosphate-accumulating organisms. Black-Right-Pointing-Pointer Microbial degradation of volatile fatty acids in the aggregates. - Abstract: Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH > 7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4

  1. Stability and gelation behavior of bovine serum albumin pre-aggregates in the presence of calcium chloride.

    PubMed

    Wu, Hua; Arosio, Paolo; Podolskaya, Olga Gennadievna; Wei, Dan; Morbidelli, Massimo

    2012-04-14

    We study, using wide-angle and small-angle light scattering techniques, the stability and aggregation/gelation behaviors of denatured filamentous bovine serum albumin pre-aggregates (BSA-PAs), induced by CaCl(2). It is observed that transparent filamentous gels can be formed not only at low CaCl(2) concentrations but also at high CaCl(2) concentrations, while turbid gels are obtained at intermediate CaCl(2) concentrations. Although the filamentous gels at low CaCl(2) concentrations and the turbid gels at intermediate CaCl(2) concentrations are consistent with the literature observations, the filamentous gels at high CaCl(2) concentrations have to be explained by different mechanisms. The latter is attributed to the repulsive hydration interactions originating from increased surface dipoles generated by counterion binding. Since such surface dipole-induced hydration is very short-range and occurs mainly on charged or polar patches of proteins (thus protected from aggregation), the aggregation of the filamentous BSA-PAs at hydrophobic patches at the two ends is still possible, leading to formation of the filamentous gels.

  2. Effects of biodegradable plastics on the predominant culturable bacteria associated with soil aggregate formation and stability after 9 months of incubation in natural soil

    USDA-ARS?s Scientific Manuscript database

    An in vitro study of the effects of biodegradable plastics on the predominant soil aggregating bacteria associated to soil aggregate formation and stability after 9 months of incubation in soil. Caesar-TonThat TC, Fukui R*, Caesar AJ., Lartey, RT, and Gaskin, JF. USDA-Agricultural Research Service, ...

  3. Biochar Improves Soil Aggregate Stability and Water Availability in a Mollisol after Three Years of Field Application

    PubMed Central

    Zhang, Yulan; Yang, Lijie; Yu, Chunxiao; Yin, Guanghua; Doane, Timothy A.; Wu, Zhijie; Zhu, Ping; Ma, Xingzhu

    2016-01-01

    A field experiment was carried out to evaluate the effect of organic amendments on soil organic carbon, total nitrogen, bulk density, aggregate stability, field capacity and plant available water in a representative Chinese Mollisol. Four treatments were as follows: no fertilization (CK), application of inorganic fertilizer (NPK), combined application of inorganic fertilizer with maize straw (NPK+S) and addition of biochar with inorganic fertilizer (NPK+B). Our results showed that after three consecutive years of application, the values of soil bulk density were significantly lower in both organic amendment-treated plots than in unamended (CK and NPK) plots. Compared with NPK, NPK+B more effectively increased the contents of soil organic carbon, improved the relative proportion of soil macro-aggregates and mean weight diameter, and enhanced field capacity as well as plant available water. Organic amendments had no obvious effect on soil C/N ratio or wilting coefficient. The results of linear regression indicated that the improvement in soil water retention could be attributed to the increases in soil organic carbon and aggregate stability. PMID:27191160

  4. Assessment of optimum threshold and particle shape parameter for the image analysis of aggregate size distribution of concrete sections

    NASA Astrophysics Data System (ADS)

    Ozen, Murat; Guler, Murat

    2014-02-01

    Aggregate gradation is one of the key design parameters affecting the workability and strength properties of concrete mixtures. Estimating aggregate gradation from hardened concrete samples can offer valuable insights into the quality of mixtures in terms of the degree of segregation and the amount of deviation from the specified gradation limits. In this study, a methodology is introduced to determine the particle size distribution of aggregates from 2D cross sectional images of concrete samples. The samples used in the study were fabricated from six mix designs by varying the aggregate gradation, aggregate source and maximum aggregate size with five replicates of each design combination. Each sample was cut into three pieces using a diamond saw and then scanned to obtain the cross sectional images using a desktop flatbed scanner. An algorithm is proposed to determine the optimum threshold for the image analysis of the cross sections. A procedure was also suggested to determine a suitable particle shape parameter to be used in the analysis of aggregate size distribution within each cross section. Results of analyses indicated that the optimum threshold hence the pixel distribution functions may be different even for the cross sections of an identical concrete sample. Besides, the maximum ferret diameter is the most suitable shape parameter to estimate the size distribution of aggregates when computed based on the diagonal sieve opening. The outcome of this study can be of practical value for the practitioners to evaluate concrete in terms of the degree of segregation and the bounds of mixture's gradation achieved during manufacturing.

  5. Interaction between soil mineralogy and the application of crop residues on aggregate stability and hydraulic conductivity of the soil

    NASA Astrophysics Data System (ADS)

    Lado, M.; Kiptoon, R.; Bar-Tal, A.; Wakindiki, I. I. C.; Ben-Hur, M.

    2012-04-01

    One of the main goals of modern agriculture is to achieve sustainability by maintaining crop productivity while avoiding soil degradation. Intensive cultivation could lead to a reduction in soil organic matter that could affect the structure stability and hydraulic conductivity of the soil. Moreover, crops extract nutrients from the soil that are taken away from the field when harvested, and as a consequence, the addition of fertilizers to the soil is necessary to maintain crop productivity. One way to deal with these problems is to incorporate crop residues into the soil after harvest. Crop residues are a source of organic matter that could improve soil physical properties, such as aggregate stability and soil hydraulic conductivity. However, this effect could vary according to other soil properties, such as clay content, clay mineralogy, and the presence of other cementing materials in the soil (mainly carbonates and aluminum and iron oxides). In the present work, the interaction between the addition of chickpea crop residues to the soil and clay mineralogy on aggregate stability and saturated hydraulic conductivity were studied. Chickpea plant residues were added at a rate of 0.5% (w/w) to smectitic, kaolinitic, illitic and non-phyllosilicate soils from different regions. The soils without (control) and with chickpea residues were incubated for 0, 3, 7 and 30 days, and the saturated hydraulic conductivity of the soils was measured in columns after each incubation time. The response of hydraulic conductivity to the addition of residues and incubation time was different in the soils with various mineralogies, although in general, the addition of chickpea residues increased the saturated hydraulic conductivity as compared with the control soils. This positive effect of crop residues on hydraulic conductivity was mainly a result of improved aggregate stability and resistance to slaking during wetting.

  6. Do aggregate stability and soil organic matter content increase following organic inputs?

    NASA Astrophysics Data System (ADS)

    Lehtinen, Taru; Gísladóttir, Guðrún; van Leeuwen, Jeroen P.; Bloem, Jaap; Steffens, Markus; Vala Ragnarsdóttir, Kristin

    2014-05-01

    Agriculture is facing several challenges such as loss of soil organic matter (SOM); thus, sustainable farming management practices are needed. Organic farming is growing as an alternative to conventional farming; in Iceland approximately 1% and in Austria 16% of utilized agricultural area is under organic farming practice. We analyzed the effect of different farming practices (organic, and conventional) on soil physicochemical and microbiological properties in grassland soils in Iceland and cropland soils in Austria. Organic farms differed from conventional farms by absence of chemical fertilizers and pesticide use. At these farms, we investigated soil physicochemical (e.g. soil texture, pH, CAL-extractable P and K) and microbiological properties (fungal and bacterial biomass and activity). The effects of farming practices on soil macroaggregate stability and SOM quantity, quality and distribution between different fractions were studied following a density fractionation. In Iceland, we sampled six grassland sites on Brown (BA) and Histic (HA) Andosols; two sites on extensively managed grasslands, two sites under organic and two sites under conventional farming practice. In Austria, we sampled four cropland sites on Haplic Chernozems; two sites under organic and two sites under conventional farming practice. We found significantly higher macroaggregate stability in the organic compared to the conventional grasslands in Iceland. In contrast, slightly higher macroaggregation in conventional compared to the organic farming practice was found in croplands in Austria, although the difference was not significant. Macroaggregates were positively correlated with fungal biomass in Iceland, and with Feo and fungal activity in Austria. In Austria, SOM content and nutrient status (except for lower CAL-extractable P at one site) were similar between organic and conventional farms. Our results show that the organic inputs may have enhanced macroaggregation in organic farming

  7. Effects of core muscle stability training on the weight distribution and stability of the elderly.

    PubMed

    Kang, Kwon-Young

    2015-10-01

    [Purpose] This study investigated the effects of core muscle stability training on the weight distribution and stability of the elderly. [Subjects and Methods] Thirty elderly persons were randomly divided into an experimental group which performed core strengthening exercises, and a control group which performed standard strengthening exercises for 8 weeks. A Tetrax Interactive Balance System was used to evaluate the weight distribution index (WDI) and the stability index (SI). [Results] The experimental group showed a significant improvement in terms of WDI and the SI. However, the control group showed no significant improvement in either. [Conclusion] Core muscle stability training should be considered as a therapeutic method for the elderly to improve their WDI, and SI, and as a fall prevention measure.

  8. Local-aggregate modeling for big data via distributed optimization: Applications to neuroimaging.

    PubMed

    Hu, Yue; Allen, Genevera I

    2015-12-01

    Technological advances have led to a proliferation of structured big data that have matrix-valued covariates. We are specifically motivated to build predictive models for multi-subject neuroimaging data based on each subject's brain imaging scans. This is an ultra-high-dimensional problem that consists of a matrix of covariates (brain locations by time points) for each subject; few methods currently exist to fit supervised models directly to this tensor data. We propose a novel modeling and algorithmic strategy to apply generalized linear models (GLMs) to this massive tensor data in which one set of variables is associated with locations. Our method begins by fitting GLMs to each location separately, and then builds an ensemble by blending information across locations through regularization with what we term an aggregating penalty. Our so called, Local-Aggregate Model, can be fit in a completely distributed manner over the locations using an Alternating Direction Method of Multipliers (ADMM) strategy, and thus greatly reduces the computational burden. Furthermore, we propose to select the appropriate model through a novel sequence of faster algorithmic solutions that is similar to regularization paths. We will demonstrate both the computational and predictive modeling advantages of our methods via simulations and an EEG classification problem.

  9. The distribution of deep-sea sponge aggregations in the North Atlantic and implications for their effective spatial management

    NASA Astrophysics Data System (ADS)

    Howell, Kerry-Louise; Piechaud, Nils; Downie, Anna-Leena; Kenny, Andrew

    2016-09-01

    Sponge aggregations have been recognised as key component of shallow benthic ecosystems providing several important functional roles including habitat building and nutrient recycling. Within the deep-sea ecosystem, sponge aggregations may be extensive and available evidence suggests they may also play important functional roles, however data on their ecology, extent and distribution in the North Atlantic is lacking, hampering conservation efforts. In this study, we used Maximum Entropy Modelling and presence data for two deep-sea sponge aggregation types, Pheronema carpenteri aggregations and ostur aggregations dominated by geodid sponges, to address the following questions: 1) What environmental factors drive the broad-scale distribution of these selected sponge grounds? 2) What is the predicted distribution of these grounds in the northern North Atlantic, Norwegian and Barents Sea? 3) How are these sponge grounds distributed between Exclusive Economic Zones (EEZs) and High Seas areas? 4) What percentage of these grounds in High Seas areas are protected by the current High Seas MPA network? Our results suggest that silicate concentration, temperature, depth and amount of particulate organic carbon are the most important drivers of sponge distribution. Most of the sponge grounds are located within national EEZs rather than in the High Seas. Coordinated conservation planning between nations with significant areas of sponge grounds such as Iceland, Greenland and Faroes (Denmark), Norway (coastal Norway and Svalbard), Portugal and the UK, should be implemented in order to effectively manage these communities in view of the increasing level of human activity within the deep-sea environment.

  10. Simultaneous Monitoring of Peptide Aggregate Distributions, Structure, and Kinetics Using Amide Hydrogen Exchange: Application to Aβ(1–40) Fibrillogenesis

    PubMed Central

    Qi, Wei; Zhang, Aming; Patel, Dhara; Lee, Sungmun; Harrington, Jamie L.; Zhao, Liming; Schaefer, David; Good, Theresa A.; Fernandez, Erik J.

    2009-01-01

    Increasing evidence indicates that soluble aggregates of amyloid beta protein (Aβ) are neurotoxic. However, difficulty in isolating these unstable, dynamic species impedes studies of Aβ and other aggregating peptides and proteins. In this study, hydrogen–deuterium exchange (HX) detected by mass spectrometry (MS) was used to measure Aβ(1–40) aggregate distributions without purification or modification that might alter the aggregate structure or distribution. Different peaks in the mass spectra were assigned to monomer, low molecular weight oligomer, intermediate, and fibril based on HX labeling behavior and complementary assays. After 1 h labeling, the intermediates incorporated approximately ten more deuterons relative to fibrils, indicating a more solvent exposed structure of such intermediates. HX-MS also showed that the intermediate species dissociated much more slowly to monomer than did the very low molecular weight oligomers that were formed at very early times in Aβ aggregation. Atomic force microscopy (AFM) measurements revealed the intermediates were roughly spherical with relatively homogenous diameters of 30–50 nm. Quantitative analysis of the HX mass spectra showed that the amount of intermediate species was correlated with Aβ toxicity patterns reported in a previous study under the same conditions. This study also demonstrates the potential of the HX-MS approach to characterizing complex, multi-component oligomer distributions of aggregating peptides and proteins. PMID:18351682

  11. Stabilization of copper nanoparticles with volume- and surface-distribution inside ion-exchange matrices

    NASA Astrophysics Data System (ADS)

    Kravchenko, T. A.; Sakardina, E. A.; Kalinichev, A. I.; Zolotukhina, E. V.

    2015-09-01

    Nanocomposites characterized by the surface and volume distributions of deposited copper nanoparticles are obtained via the chemical deposition of copper onto sulfonic acid and carboxylic cation exchanger and strongly basic anion exchanger matrices. The electrode behavior of the synthesized composites in CuSO4 solution is studied by open-circuit chronopotentiometry. The effect the nature of the fixed centers of the ion-exchange matrix has on the initial state of metallic particles and the processes that occur in solutions of their metal ions is established from the deviation of the nanocomposites' electrode potential from the potential of a compact electrode and the nature of its change over time. It is shown that the mechanism behind the interaction of the matrix and metal ions (ion exchange, non-exchange absorption, complexation) determines not only the initial size and distribution of metal particles, but also the rate at which they achieve aggregative stability.

  12. Colorimetric detection of biothiols based on aggregation of chitosan-stabilized silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Mohammadi, Somayeh; Khayatian, Gholamreza

    2017-10-01

    We have described a simple and reliable colorimetric method for the sensing of biothiols such as cysteine, homocysteine, and glutathione in biological samples. The selective binding of chitosan capped silver nanoparticles to biothiols induced aggregation of the chitosan-Ag NPs. But the other amino acids that do not have thiol group cannot aggregate the chitosan-Ag NPs. Aggregation of chitosan-Ag NPs has been confirmed with UV-vis absorption spectra, zeta potential and transmission electron microscopy images. Under optimum conditions, good linear relationships existed between the absorption ratios (at A500/A415) and the concentrations of cysteine, homocysteine, and glutathione in the range of 0.1-10.0 μM with detection limits of 15.0, 84.6 and 40.0 nM, respectively. This probe was successfully applied to detect these biothiols in biological samples (urine and plasma).

  13. On the Role of Aggregation Prone Regions in Protein Evolution, Stability, and Enzymatic Catalysis: Insights from Diverse Analyses

    PubMed Central

    Buck, Patrick M.; Kumar, Sandeep; Singh, Satish K.

    2013-01-01

    The various roles that aggregation prone regions (APRs) are capable of playing in proteins are investigated here via comprehensive analyses of multiple non-redundant datasets containing randomly generated amino acid sequences, monomeric proteins, intrinsically disordered proteins (IDPs) and catalytic residues. Results from this study indicate that the aggregation propensities of monomeric protein sequences have been minimized compared to random sequences with uniform and natural amino acid compositions, as observed by a lower average aggregation propensity and fewer APRs that are shorter in length and more often punctuated by gate-keeper residues. However, evidence for evolutionary selective pressure to disrupt these sequence regions among homologous proteins is inconsistent. APRs are less conserved than average sequence identity among closely related homologues (≥80% sequence identity with a parent) but APRs are more conserved than average sequence identity among homologues that have at least 50% sequence identity with a parent. Structural analyses of APRs indicate that APRs are three times more likely to contain ordered versus disordered residues and that APRs frequently contribute more towards stabilizing proteins than equal length segments from the same protein. Catalytic residues and APRs were also found to be in structural contact significantly more often than expected by random chance. Our findings suggest that proteins have evolved by optimizing their risk of aggregation for cellular environments by both minimizing aggregation prone regions and by conserving those that are important for folding and function. In many cases, these sequence optimizations are insufficient to develop recombinant proteins into commercial products. Rational design strategies aimed at improving protein solubility for biotechnological purposes should carefully evaluate the contributions made by candidate APRs, targeted for disruption, towards protein structure and activity. PMID

  14. Allometric degree distributions facilitate food-web stability.

    PubMed

    Otto, Sonja B; Rall, Björn C; Brose, Ulrich

    2007-12-20

    In natural ecosystems, species are linked by feeding interactions that determine energy fluxes and create complex food webs. The stability of these food webs enables many species to coexist and to form diverse ecosystems. Recent theory finds predator-prey body-mass ratios to be critically important for food-web stability. However, the mechanisms responsible for this stability are unclear. Here we use a bioenergetic consumer-resource model to explore how and why only particular predator-prey body-mass ratios promote stability in tri-trophic (three-species) food chains. We find that this 'persistence domain' of ratios is constrained by bottom-up energy availability when predators are much smaller than their prey and by enrichment-driven dynamics when predators are much larger. We also find that 97% of the tri-trophic food chains across five natural food webs exhibit body-mass ratios within the predicted persistence domain. Further analyses of randomly rewired food webs show that body mass and allometric degree distributions in natural food webs mediate this consistency. The allometric degree distributions hold that the diversity of species' predators and prey decreases and increases, respectively, with increasing species' body masses. Our results demonstrate how simple relationships between species' body masses and feeding interactions may promote the stability of complex food webs.

  15. A zwitterion-DNA coating stabilizes nanoparticles against Mg2+ driven aggregation enabling attachment to DNA nanoassemblies

    NASA Astrophysics Data System (ADS)

    Mudalige, Thilak Kumara; Gang, Oleg; Sherman, William B.

    2012-04-01

    Plasmonics and photonics demand new methods for the controlled construction of nanoparticle (NP) arrays. Complex, low-symmetry configurations of DNA-functionalized NPs are obtained by connection to scaffolds of branched and folded DNA nanostructures. However, the stabilization of these branched structures by Mg2+ counterions also drives the uncontrolled aggregation of NPs. We demonstrate, using a two-dimensional DNA scaffold, that derivatizing gold nanoparticles (AuNPs) with zwitterionic ligands overcomes this problem.Plasmonics and photonics demand new methods for the controlled construction of nanoparticle (NP) arrays. Complex, low-symmetry configurations of DNA-functionalized NPs are obtained by connection to scaffolds of branched and folded DNA nanostructures. However, the stabilization of these branched structures by Mg2+ counterions also drives the uncontrolled aggregation of NPs. We demonstrate, using a two-dimensional DNA scaffold, that derivatizing gold nanoparticles (AuNPs) with zwitterionic ligands overcomes this problem. Electronic supplementary information (ESI) available: Visual survey of ligand stabilization of AuNPs, experimental methods, and DNA details. See DOI: 10.1039/c2nr30479a

  16. Stabilized Fiber-Optic Distribution of Reference Frequency

    NASA Technical Reports Server (NTRS)

    Calhoun, Malcolm; Tjoelker, Robert; Diener, William; Dick, G. John; Wang, Rabi; Kirk, Albert

    2003-01-01

    An optoelectronic system distributes a reference signal of low noise and highly stabilized phase and frequency (100 MHz) from an atomic frequency standard to a remote facility at a distance up to tens of kilometers. The reference signal is transmitted to the remote station as amplitude modulation of an optical carrier signal propagating in an optical fiber. The stabilization scheme implemented in this system is intended particularly to suppress phase and frequency fluctuations caused by vibrations and by expansion and contraction of the optical fiber and other components in diurnal and seasonal heating and cooling cycles. The system (see figure) comprises several subsystems, the main one being (1) a hydrogen-maser or linear-ion-trap frequency standard in an environmentally controlled room in a signal-processing center (SPC), (2) a stabilized fiber-optic distribution assembly (SFODA), (3) a compensated sapphire oscillator (CSO) in an environmentally controlled room in the remote facility, (4) thermally stabilized distribution amplifiers and cabling from the environmentally controlled room to end users, and (5) performance- measuring equipment.

  17. Effects of heterogeneous competitor distribution and ramet aggregation on the growth and size structure of a clonal plant.

    PubMed

    Dong, Bi-Cheng; Wang, Jiu-Zhong; Liu, Rui-Hua; Zhang, Ming-Xiang; Yu, Fei-Hai

    2013-01-01

    Spatially heterogeneous distribution of interspecific competitors and intraspecific aggregation of offspring ramets may affect the growth and size structure of clonal plant populations, but these have been rarely studied. We conducted a greenhouse experiment in which we grew a population of eight offspring ramets (plants) of the stoloniferous clonal plant Hydrocotyle vulgaris aggregately or segregately in two homogeneous treatments with or without a competing grass Festuca elata and a heterogeneous treatment with a patchy distribution of the grass. In patchy grass treatments, H. vulgaris produced markedly more biomass, ramets and stolons in open patches (without grasses) than in grass patches, but displayed lower size variations as measured by coefficient of variation of biomass, ramets and stolons among the eight plants. In open areas, H. vulgaris produced statistically the same amounts of biomass and even more stolons and showed higher size variations in patchy grass treatments than in open (no grass) treatments. In grass areas, H. vulgaris grew much worse and displayed higher size variations in patchy grass treatments than in full grass treatments. Ramet aggregation decreased the growth of H. vulgaris in open treatments and in both open and grass patches in patchy grass treatments, but had little effect in full grass treatments. Ramet aggregation had little effect on size variations. Therefore, heterogeneous distribution of competitors can affect the growth and size structure of clonal plant populations, and ramet aggregation may decrease population growth when they grow in open environments or heterogeneous environments with a patchy distribution of interspecific competitors.

  18. The predictive performance and stability of six species distribution models.

    PubMed

    Duan, Ren-Yan; Kong, Xiao-Quan; Huang, Min-Yi; Fan, Wei-Yi; Wang, Zhi-Gao

    2014-01-01

    Predicting species' potential geographical range by species distribution models (SDMs) is central to understand their ecological requirements. However, the effects of using different modeling techniques need further investigation. In order to improve the prediction effect, we need to assess the predictive performance and stability of different SDMs. We collected the distribution data of five common tree species (Pinus massoniana, Betula platyphylla, Quercus wutaishanica, Quercus mongolica and Quercus variabilis) and simulated their potential distribution area using 13 environmental variables and six widely used SDMs: BIOCLIM, DOMAIN, MAHAL, RF, MAXENT, and SVM. Each model run was repeated 100 times (trials). We compared the predictive performance by testing the consistency between observations and simulated distributions and assessed the stability by the standard deviation, coefficient of variation, and the 99% confidence interval of Kappa and AUC values. The mean values of AUC and Kappa from MAHAL, RF, MAXENT, and SVM trials were similar and significantly higher than those from BIOCLIM and DOMAIN trials (p<0.05), while the associated standard deviations and coefficients of variation were larger for BIOCLIM and DOMAIN trials (p<0.05), and the 99% confidence intervals for AUC and Kappa values were narrower for MAHAL, RF, MAXENT, and SVM. Compared to BIOCLIM and DOMAIN, other SDMs (MAHAL, RF, MAXENT, and SVM) had higher prediction accuracy, smaller confidence intervals, and were more stable and less affected by the random variable (randomly selected pseudo-absence points). According to the prediction performance and stability of SDMs, we can divide these six SDMs into two categories: a high performance and stability group including MAHAL, RF, MAXENT, and SVM, and a low performance and stability group consisting of BIOCLIM, and DOMAIN. We highlight that choosing appropriate SDMs to address a specific problem is an important part of the modeling process.

  19. VARIATIONS IN SOIL AGGREGATE STABILITY AND ENZYME ACTIVITIES IN A TEMPERATE AGROFORESTRY PRACTICE

    USDA-ARS?s Scientific Manuscript database

    Agroforestry and grass buffers have been shown to improve soil properties and overall environmental quality. The objective of this study was to examine management and landscape effects on water stable soil aggregates (WSA), soil carbon, soil nitrogen, enzyme activity, and microbial community DNA co...

  20. Soil Aggregates and Organic Carbon Distribution in Red Soils after Long-term Fertilization with Different Fertilizer Treatments

    NASA Astrophysics Data System (ADS)

    Tang, J.; Wang, Y.

    2013-12-01

    Red soils, a typical Udic Ferrosols, widespread throughout the subtropical and tropical region in southern China, support the majority of grain production in this region. The red soil is naturally low in pH values, cation exchange capacity, fertility, and compaction, resulting in low organic matter contents and soil aggregation. Application of chemical fertilizers and a combination of organic-chemical fertilizers are two basic approaches to improve soil structure and organic matter contents. We studied the soil aggregation and the distribution of aggregate-associated organic carbon in red soils with a long-term fertilization experiment during 1988-2009. We established treatments including 1) NPK and NK in the chemical fertilizer plots, 2) CK (Control), and 3) CK+ Peanut Straw (PS), CK+ Rice Straw (RS), CK+ Fresh Radish (FR), and CK + Pig Manure (PM) in the organic-chemical fertilizer plots. Soil samples were fractionated into 6 different sized aggregate particles through the dry-wet sieving method according to the hierarchical model of aggregation. Organic carbon in the aggregate/size classes was analyzed. The results showed that the distribution of mechanically stable aggregates in red soils after long-term fertilization decreased with the size, from > 5mm, 5 ~ 2 mm, 2 ~ 1 mm, 1~ 0.25 mm, to < 0.25 mm, but the distribution of water-stable aggregates did not follow this pattern. Compared with the chemical fertilizer application alone, the addition of pig manure and green manure can significantly improve the distribution of aggregates in the 5-2 mm, 2-1 mm and 1-0.25 mm classes. The organic carbon (OC) contents in red soils were all increased after the long-term fertilization. Compared with Treatment NK, soil OC in Treatment NPK was increased by 45.4%. Compared with Treatment CK (low chemical fertilizer), organic fertilizer addition increased soil OC. The OC in the different particle of water-stable aggregates were all significantly increased after long

  1. Conformational and Colloidal Stabilities of Human Immunoglobulin G Fc and Its Cyclized Variant: Independent and Compensatory Participation of Domains in Aggregation of Multidomain Proteins.

    PubMed

    Yageta, Seiki; Shibuya, Risa; Imamura, Hiroshi; Honda, Shinya

    2017-03-06

    Monoclonal immunoglobulin G (IgG) is a multidomain protein. It has been reported that the conformational and colloidal stabilities of each domain are different, and it is predicted that limited domains participate in IgG aggregation. In contrast, the influence of interdomain interactions on IgG aggregation remains unclear. The fragment crystallizable (Fc) region is also a multidomain protein consisting of two sets of CH2 and CH3 domains. Here, we have analyzed the conformational change and aggregate size of an aglycosylated Fc region induced by both acid and salt stresses and have elucidated the influence of interdomain interactions between CH2 and CH3 domains on the conformational and colloidal stabilities of the aglycosylated Fc region. Singular value decomposition analyses demonstrated that the CH2 and CH3 domains unfolded almost independently from each other in the aglycosylated Fc region. Meanwhile, the colloidal stabilities of the CH2 and CH3 domains affect the aggregation process of the unfolded aglycosylated Fc region in a compensatory way. Moreover, the influence of an additional interdomain disulfide bond, introduced at the C-terminal end of the CH3 domains to produce the Fc variant, cyclized Fc, was evaluated. This interdomain disulfide bond increased the conformational stability of the CH3 domain. The stabilization of the CH3 domain in the cyclized Fc successfully improved aggregation tolerance following acid stress, although the sizes of aggregates produced were comparable to those of the aglycosylated Fc region.

  2. L2-stability of distributed feedback systems: Singular perturbation

    NASA Technical Reports Server (NTRS)

    Barman, J. F.; Callier, F. M.; Desoer, C. A.

    1972-01-01

    A continuous time, single input-single output, linear, time-invariant, distributed feedback system F sup epsilon, containing a small delay of length epsilon in the loop, is considered. Conditions are given under which L2-stability and L2-instability of this feedback system can be deduced from those of the reduced model obtained by neglecting the delay. The two system models associated with F sup epsilon are the low-frequency model F and the high frequency model F. The condition for neglecting the small delay is the L2-stability of the family of high-frequency models, where epsilon or = 0 is sufficiently small. A lemma and a theorem are given. The lemma gives sharp Nyquist-type conditions for the L2-stability and L2-instability of the family of high frequency models for sufficiently small epsilon or = 0, while the Theorem gives explicit conditions under which the small delay may or may not be neglected.

  3. Adjusting particle-size distributions to account for aggregation in tephra-deposit model forecasts

    USGS Publications Warehouse

    Mastin, Larry G.; Van Eaton, Alexa; Durant, A.J.

    2016-01-01

    Volcanic ash transport and dispersion (VATD) models are used to forecast tephra deposition during volcanic eruptions. Model accuracy is limited by the fact that fine-ash aggregates (clumps into clusters), thus altering patterns of deposition. In most models this is accounted for by ad hoc changes to model input, representing fine ash as aggregates with density ρagg, and a log-normal size distribution with median μagg and standard deviation σagg. Optimal values may vary between eruptions. To test the variance, we used the Ash3d tephra model to simulate four deposits: 18 May 1980 Mount St. Helens; 16–17 September 1992 Crater Peak (Mount Spurr); 17 June 1996 Ruapehu; and 23 March 2009 Mount Redoubt. In 192 simulations, we systematically varied μagg and σagg, holding ρagg constant at 600 kg m−3. We evaluated the fit using three indices that compare modeled versus measured (1) mass load at sample locations; (2) mass load versus distance along the dispersal axis; and (3) isomass area. For all deposits, under these inputs, the best-fit value of μagg ranged narrowly between  ∼  2.3 and 2.7φ (0.20–0.15 mm), despite large variations in erupted mass (0.25–50 Tg), plume height (8.5–25 km), mass fraction of fine ( <  0.063 mm) ash (3–59 %), atmospheric temperature, and water content between these eruptions. This close agreement suggests that aggregation may be treated as a discrete process that is insensitive to eruptive style or magnitude. This result offers the potential for a simple, computationally efficient parameterization scheme for use in operational model forecasts. Further research may indicate whether this narrow range also reflects physical constraints on processes in the evolving cloud.

  4. Cavity filling mutations at the thyroxine-binding site dramatically increase transthyretin stability and prevent its aggregation.

    PubMed

    Sant'Anna, Ricardo; Almeida, Maria Rosário; Varejāo, Nathalia; Gallego, Pablo; Esperante, Sebastian; Ferreira, Priscila; Pereira-Henriques, Alda; Palhano, Fernando L; de Carvalho, Mamede; Foguel, Debora; Reverter, David; Saraiva, Maria João; Ventura, Salvador

    2017-03-24

    More than a hundred different Transthyretin (TTR) mutations are associated with fatal systemic amyloidoses. They destabilize the protein tetrameric structure and promote the extracellular deposition of TTR as pathological amyloid fibrils. So far, only mutations R104H and T119M have been shown to stabilize significantly TTR, acting as disease suppressors. We describe a novel A108V non-pathogenic mutation found in a Portuguese subject. This variant is more stable than wild type TTR both in vitro and in human plasma, a feature that prevents its aggregation. The crystal structure of A108V reveals that this stabilization comes from novel intra and inter subunit contacts involving the thyroxine (T4) binding site. Exploiting this observation, we engineered a A108I mutation that fills the T4 binding cavity, as evidenced in the crystal structure. This synthetic protein becomes one of the most stable TTR variants described so far, with potential application in gene and protein replacement therapies.

  5. Differential anion effects on thermal stability of collagen in the dispersed and aggregated states.

    PubMed

    Russell, A E

    1974-03-01

    The effects of KCNS and KI on thermal transition temperatures of calf skin collagen molecules in dilute acid solution and precipitated collagen fibrils from the same source were compared as a function of salt concentration and pH. The two salts produced qualitatively similar effects on each collagen form, but the response shown by single collagen molecules in dilute solution differed from that observed for molecular aggregates present in native-type fibrils.

  6. The capture and stabilization of curcumin using hydrophobically modified polyacrylate aggregates and hydrogels.

    PubMed

    Harada, Takaaki; Pham, Duc-Truc; Lincoln, Stephen F; Kee, Tak W

    2014-08-07

    Hydrophobically modified polyacrylates are shown to suppress the degradation of the medicinal pigment curcumin under physiological conditions. In aqueous solution, the 3% octadecyl randomly substituted polyacrylate, PAAC18, forms micelle-like aggregates at a concentration of <1 wt % and a hydrogel at >1 wt %. Under both conditions, PAAC18 shows a remarkable ability to suppress the degradation of curcumin at pH 7.4 and 37 °C such that its degradation half-life is increased by 1600-2000-fold. The suppression of degradation is attributed to hydrophobic interactions between curcumin and the octadecyl substituents of PAAC18 within the micelle-like aggregates and the hydrogel, as indicated by 2D NOESY (1)H NMR spectroscopy. UV-visible absorption titration results are consistent with the interaction of curcumin with five octadecyl substituents on average, which appears to substantially exclude water and greatly decrease the curcumin degradation rate. Dynamic light scattering and zeta potential measurements show the average hydrodynamic diameters of the PAAC18 aggregates to be 0.86-1.15 μm with a negative surface charge. In contrast to the octadecyl substitution, the 3% dodecyl randomly substituted polyacrylate, PAAC12, shows a negligible effect on slowing the degradation of curcumin, consistent with the dodecyl substituents being insufficiently long to capture curcumin in a adequately hydrophobic environment. These observations indicate the potential for PAAC18 to act as a model drug delivery system.

  7. Comparison of the aerodynamic size distribution of chain-like aggregates measured with a cascade impactor and a spiral centrifuge.

    PubMed

    Allen, M D; Briant, J K; Moss, O R

    1979-06-01

    Several authors have suggested that chain-like aggregates fragment in the jets of cascade impactors and that the impactor consequently underestimates the median aerodynamic diameter and overestimates the geometric standard deviation (GSD). The aerodynamic size distribution of (Pu0.14U0.86)02.2 aggregates were measured simultaneously with two Mercer cascade impactors and a LAPS spiral centrifuge to investigate this problem. Although the median aerodynamic diameters were generally in good agreement, the impactor consistently measured higher values for the GSD than did the spiral centrifuge. Based on experiments in which losses in the centrifuge inlet were measured, it was concluded that the centrifuge had measured the aerodynamic size distribution more accurately than the impactor. Interception of chain-like aggregates on the first few impactor stages may have been the primary reason for the disparity between the impactor and centrifuge measurements.

  8. Investigating Mutations to Reduce Huntingtin Aggregation by Increasing Htt-N-Terminal Stability and Weakening Interactions with PolyQ Domain

    PubMed Central

    Mazza-Anthony, Cody; Waldispühl, Jérôme

    2016-01-01

    Huntington's disease is a fatal autosomal genetic disorder characterized by an expanded glutamine-coding CAG repeat sequence in the huntingtin (Htt) exon 1 gene. The Htt protein associated with the disease misfolds into toxic oligomers and aggregate fibril structures. Competing models for the misfolding and aggregation phenomena have suggested the role of the Htt-N-terminal region and the CAG trinucleotide repeats (polyQ domain) in affecting aggregation propensities and misfolding. In particular, one model suggests a correlation between structural stability and the emergence of toxic oligomers, whereas a second model proposes that molecular interactions with the extended polyQ domain increase aggregation propensity. In this paper, we computationally explore the potential to reduce Htt aggregation by addressing the aggregation causes outlined in both models. We investigate the mutation landscape of the Htt-N-terminal region and explore amino acid residue mutations that affect its structural stability and hydrophobic interactions with the polyQ domain. Out of the millions of 3-point mutation combinations that we explored, the (L4K E12K K15E) was the most promising mutation combination that addressed aggregation causes in both models. The mutant structure exhibited extreme alpha-helical stability, low amyloidogenicity potential, a hydrophobic residue replacement, and removal of a solvent-inaccessible intermolecular side chain that assists oligomerization. PMID:28096892

  9. Aggregation and stability of Fe2O3:Influence of humic acid concentration, Fe2O3 concentration and pH

    NASA Astrophysics Data System (ADS)

    Ahmad, Nur Suraya; Radiman, Shahidan; Yaacob, Wan Zuhairi Wan

    2016-11-01

    The scenario of released nanoparticles from consumer product into the environment especially natural waters are increased concern nowadays. Assessing their aggregation and stability under environmental conditions are important to determining their fate and behavior in natural waters. The aggregation behavior of Fe2O3 nanoparticles (NPs) was investigated at variable concentration of humic acid, Fe2O3 NPs concentration and pH variation in solution using dynamic light scattering to measure their z-average hydrodynamic diameter and zeta potential value. The stability are then evaluated by assessing their aggregation and disaggregation. Increasing humic acid concentration induced the disaggregation of Fe2O3 NPs. At a lower concentrations of Fe2O3 (< 30 mg/L), aggregate formed and disaggregation take place with increasing Fe2O3 concentration (50, 100, 150, 200 mg/L). The maximum aggregation was found in pH 4 at a constant concentration of humic acid of 100 mg/L and concentration of Fe2O3 (100 mg/L). High pH (>5) of solution induced disaggregation of suspensions and make it stable in the solution. TEM imaging have confirmed that Fe2O3 NPs aggregate and disaggregate in the presence of humic acid. Our study result shows that aggregation and stability of Fe2O3 NPs were depends on concentration of humic acid, concentration of NPs itself and the pH of the solutions.

  10. Fracture resistance and stress distribution of simulated immature teeth after apexification with mineral trioxide aggregate.

    PubMed

    Brito-Júnior, M; Pereira, R D; Veríssimo, C; Soares, C J; Faria-e-Silva, A L; Camilo, C C; Sousa-Neto, M D

    2014-10-01

    To evaluate the effect of adhesive restorations on fracture resistance and stress distribution in teeth with simulated immature apices and apical plugs of mineral trioxide aggregate (MTA). Sixty bovine incisors were sectioned 8 mm above and 12 mm below the cemento-enamel junction (CEJ). The root canal was enlarged using a diamond bur, resulting in remaining root canal walls with 0.1-0.2 mm of thickness. A 5-mm apical plug of MTA was placed and the teeth were restored according to the following groups: GP--the root canal was filled with gutta-percha and endodontic sealer; CR--the root canal was filled with light-cured composite resin inserted incrementally; FP--a fibre post was cemented into the root canal; and RFP--the fibre post was relined with composite resin prior to the cementation into the root canal. A load was applied on the crown of all teeth at 135° to their long axis until fracture. Data was analysed by one-way anova and SNK tests (α = 0.05), whilst the fracture pattern was evaluated according to the position of the fracture. Stress distributions in the restored teeth were verified by finite element analysis. Teeth restored with fibre posts and relined fibre posts were associated with the highest fracture resistance, whilst the GP group had the lowest values. GP and RC groups had similar fracture resistance values (P = 0.109). All fractures types involved the cervical and middle thirds of roots. The GP model had high levels of stress concentration in the cervical and middle thirds of roots. No difference was found amongst the stress concentration in the RC, FP and RFP models. Restorative protocols alter the fracture resistance and stress distribution of immature teeth after placement of MTA apical plugs. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  11. AGGREGATION PATHWAYS OF THE AMYLOID β(1–42) PEPTIDE DEPEND ON ITS COLLOIDAL STABILITY AND ORDERED β-SHEET STACKING

    PubMed Central

    Jiang, Dianlu; Rauda, Iris; Han, Shubo; Chen, Shu; Zhou, Feimeng

    2012-01-01

    Amyloid β (Aβ) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer’s disease (AD). Diffuse plaques (non-fibrous, loosely packed Aβ aggregates) containing amorphous Aβ aggregates are also formed in brain. This work examines the influence of Cu2+ complexation by Aβ on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aβ molecules due to Cu2+ binding, measured with a zeta potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the “colloid-like” stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently Cu2+ enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the β-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aβ aggregation pathway in the absence of Cu2+ and taking other factors affecting Aβ aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same β-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aβ also plays a role in the Aβ aggregation process. A kinetic model was proposed to account for the effects of the Cu2+ binding on these two aggregation pathways in terms of charge and structural variations. PMID:22870885

  12. Crosslinked Enzyme Aggregates in Hierarchically-Ordered Mesoporous Silica: A Simple and Effective Method for Enzyme Stabilization

    SciTech Connect

    Kim, Moon Il; Kim, Jungbae; Lee, Jinwoo; Jia, Hongfei; Na, Hyon Bin; Youn, Jongkyu; Kwak, Ja Hun; Dohnalkova, Alice; Grate, Jay W.; Wang, Ping; Hyeon, Taeghwan; Park, Hyun-Gyu; Chang, Ho Nam

    2007-02-01

    alpha-chymotrypsin (CT) and lipase (LP) were immobilized in hierarchically-ordered mesocellular mesoporous silica (HMMS) in a simple but effective way for the enzyme stabilization, which was achieved by the enzyme adsorption followed by glutaraldehyde (GA) crosslinking. This resulted in the formation of nanometer scale crosslinked enzyme aggregates (CLEAs) entrapped in the mesocellular pores of HMMS (37 nm), which did not leach out of HMMS through narrow mesoporous channels (13 nm). CLEA of alpha-chymotrypsin (CLEA-CT) in HMMS showed a high enzyme loading capacity and significantly increased enzyme stability. No activity decrease of CLEA-CT was observed for two weeks under even rigorously shaking condition, while adsorbed CT in HMMS and free CT showed a rapid inactivation due to the enzyme leaching and presumably autolysis, respectively. With the CLEA-CT in HMMS, however, there was no tryptic digestion observed suggesting that the CLEA-CT is not susceptible to autolysis. Moreover, CLEA of lipase (CLEA-LP) in HMMS retained 30% specific activity of free lipase with greatly enhanced stability. This work demonstrates that HMMS can be efficiently employed as host materials for enzyme immobilization leading to highly enhanced stability of the immobilized enzymes with high enzyme loading and activity.

  13. Beneath aggregate stability - quantifying thermodynamic properties that drive soil structure dynamics

    NASA Astrophysics Data System (ADS)

    Hallett, Paul; Ogden, Mike; Karim, Kamal; Schmidt, Sonja; Yoshida, Shuichiro

    2014-05-01

    Soil aggregates are a figment of your energy input and initial boundary conditions, so the basic thermodynamics that drive soil structure formation are needed to understand soil structure dynamics. Using approaches from engineering and materials science, it is possible quantify basic thermodynamic properties, but at present tests are generally limited to highly simplified, often remoulded, soil structures. Although this presents limitations, the understanding of underlying processes driving soil structure dynamics is poor, which could be argued is due to the enormity of the challenge of such an incredibly complex system. Other areas of soil science, particularly soil water physics, relied on simplified structures to develop theories that can now be applied to more complex pore structures. We argue that a similar approach needs to gain prominence in the study of soil aggregates. An overview will be provided of approaches adapted from other disciplines to quantify particle bonding, fracture resistance, rheology and capillary cohesion of soil that drive its aggregation and structure dynamics. All of the tests are limited as they require simplified soil structures, ranging from repacked soils to flat surfaces coated with mineral particles. A brief summary of the different approaches will demonstrate the benefits of collecting basic physical data relevant to soil structure dynamics, including examples where they are vital components of models. The soil treatments we have tested with these engineering and materials science approaches include field soils from a range of management practices with differing clay and organic matters contents, amendment and incubation of soils with a range of microorganisms and substrates in the laboratory, model clay-sand mixes and planar mineral surfaces with different topologies. In addition to advocating the wider adoption of these approaches, we will discuss limitations and hope to stimulate discussion on how approaches could be improved

  14. Storage and stability of organic carbon in soils as related to depth, occlusion within aggregates, and attachment to minerals

    NASA Astrophysics Data System (ADS)

    Schrumpf, M.; Kaiser, K.; Guggenberger, G.; Persson, T.; Kögel-Knabner, I.; Schulze, E.-D.

    2012-09-01

    Conceptual models suggest that stability and age of organic carbon (OC) in soil depends on the source of plant litter, occlusion within aggregates, incorporation in organo-mineral complexes, and location within the soil profile. Various tools like density fractionation, mineralization experiments, and radiocarbon analyses have been used to study the importance of these mechanisms. We systematically apply them to a range of European soils to test whether general controls emerge even for soils that vary in vegetation, soil types, parent material, and land use. At each of the 12 study sites, 10 soil cores were sampled in 10 cm depth intervals to 60 cm depth and subjected to density separation. Bulk soil samples and density fractions (free light fractions - fLF, occluded light fractions - oLF, heavy fractions - HF) were analysed for OC, total nitrogen (TN), δ13C, and Δ14C. Bulk samples were also incubated to determine mineralizable OC. Declining OC-normalized CO2 release and increasing age with soil depth confirm greater stability of OC in subsoils across sites. Depth profiles of LF-OC matched those of roots, which in turn reflect plant functional types in soil profiles not subject to ploughing. Modern Δ14C signatures and positive correlation between mineralizable C and fLF-OC indicate the fLF is an easily available energy and nutrient source for subsurface microbes. Fossil C derived from the geogenic parent material affected the age of OC especially in the LF at three study sites. The overall importance of OC stabilization by binding to minerals was demonstrated by declining OC-normalized CO2 release rates with increasing contributions of HF-OC to bulk soil OC and the low Δ14C values of HF-OC. The stability of HF-OC was greater in subsoils than in topsoils; nevertheless, a portion of HF-OC was active throughout the profile. The decrease in Δ14C (increase in age) of HF-OC with soil depth was related to soil pH as well as to dissolved OC fluxes. This indicates that

  15. The Effects of Aggregation and Disaggregation on Particle Size Distributions and Water Clarity in the Coastal Ocean

    DTIC Science & Technology

    2016-06-07

    The effects of aggregation and disaggregation on particle size distributions and water clarity in the coastal ocean Paul S. Hill Department of...of fine siliciclastics on water clarity in the coastal ocean. Scattering of light by suspended particles depends on sediment concentration...composition, and size distribution. Particle size distribu- tions in coastal waters are dynamic because high concentrations of suspended sediment in coastal

  16. Kinetics of aggregation and crystallization of polyaspartic Acid stabilized calcium phosphate particles at high concentrations.

    PubMed

    Krogstad, Daniel V; Wang, Dongbo; Lin-Gibson, Sheng

    2015-05-11

    Bone is an important material to study due to its exceptional mechanical properties and relevance with respect to hard tissue regeneration and repair. A significant effort has been directed toward understanding the bone formation process and the production of synthetic bone mimicking materials. Here, the formation and structural evolution of calcium phosphate (CaP) was investigated in the presence of relatively high concentrations of calcium, phosphate, and polyaspartic acid (pAsp) using dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM). The incipient CaP aggregates were comprised of spherical nanoparticles (diameter ≈ 3-4 nm); they became preferentially aligned over time and eventually transformed into nanorods. The nanorods remained stable in suspension with no signs of further aggregation for at least four months. Detailed cryo-TEM suggested that the CaP nanorods formed through an oriented attachment mechanism. These results show that the reaction concentration greatly influences the mechanism and final properties of CaP. Mechanistic insights gained from this study will facilitate better design and fabrication of bioinspired materials.

  17. Enhancing stabilities of lipase by enzyme aggregate coating immobilized onto ionic liquid modified mesoporous materials

    NASA Astrophysics Data System (ADS)

    Zou, Bin; Song, Chunyan; Xu, Xiaping; Xia, Jiaojiao; Huo, Shuhao; Cui, Fengjie

    2014-08-01

    Mesoporous material SBA-15 as the matrix and hydrophilic methyl imidazolium ionic liquids [MSiIM]+BF4- as modifier were involved in preparing ionic liquid modified materials as enzyme carriers through after-grafting silane coupling reaction. The method of enzyme aggregates coating was firstly used to immobilize porcine pancreatic lipase (PPL) onto ionic liquid modified SBA-15. Characterization before and after modification and immobilization were conducted using infrared spectroscopy (FT-IR), differential thermal-thermal analysis (DTA-TG) and N2 adsorption-desorption method (BET). The results indicated that the ordering degree of SBA-15 declined after ionic liquid modification, but mesoporous structure remained. After enzyme immobilization, pore size and specific surface area of carrier became smaller. The cross-linking agent amount, reaction temperature and pH were optimized in this paper. The result demonstrated that the initial activity of enzyme was raised from 35% to 53% after five times recycle by enzyme aggregate coating. 74% of the original activity remained after 25 days storage.

  18. Changes in speed distribution: Applying aggregated safety effect models to individual vehicle speeds.

    PubMed

    Vadeby, Anna; Forsman, Åsa

    2017-03-31

    This study investigated the effect of applying two aggregated models (the Power model and the Exponential model) to individual vehicle speeds instead of mean speeds. This is of particular interest when the measure introduced affects different parts of the speed distribution differently. The aim was to examine how the estimated overall risk was affected when assuming the models are valid on an individual vehicle level. Speed data from two applications of speed measurements were used in the study: an evaluation of movable speed cameras and a national evaluation of new speed limits in Sweden. The results showed that when applied on individual vehicle speed level compared with aggregated level, there was essentially no difference between these for the Power model in the case of injury accidents. However, for fatalities the difference was greater, especially for roads with new cameras where those driving fastest reduced their speed the most. For the case with new speed limits, the individual approach estimated a somewhat smaller effect, reflecting that changes in the 15th percentile (P15) were somewhat larger than changes in P85 in this case. For the Exponential model there was also a clear, although small, difference between applying the model to mean speed changes and individual vehicle speed changes when speed cameras were used. This applied both for injury accidents and fatalities. There were also larger effects for the Exponential model than for the Power model, especially for injury accidents. In conclusion, applying the Power or Exponential model to individual vehicle speeds is an alternative that provides reasonable results in relation to the original Power and Exponential models, but more research is needed to clarify the shape of the individual risk curve. It is not surprising that the impact on severe traffic crashes was larger in situations where those driving fastest reduced their speed the most. Further investigations on use of the Power and/or the

  19. Erythrocyte aggregation may promote uneven spatial distribution of NO/O2 in the downstream vessel of arteriolar bifurcations.

    PubMed

    Ng, Yan Cheng; Namgung, Bumseok; Leo, Hwa Liang; Kim, Sangho

    2016-07-26

    This study examined the effect of red blood cell (RBC) aggregation on nitric oxide (NO) and oxygen (O2) distributions in the downstream vessels of arteriolar bifurcations. Particular attention was paid to the inherent formation of asymmetric cell-free layer (CFL) widths in the downstream vessels and its consequential impact on the NO/O2 bioavailability after the bifurcations. A microscopic image-based two-dimensional transient model was used to predict the NO/O2 distribution by utilizing the in vivo CFL width data obtained under non-, normal- and hyper-aggregating conditions at the pseudoshear rate of 15.6±2.0s(-1). In vivo experimental result showed that the asymmetry of CFL widths was enhanced by the elevation in RBC aggregation level. The model demonstrated that NO bioavailability was regulated by the dynamic fluctuation of the local CFL widths, which is corollary to its modulation of wall shear stress. Accordingly, the uneven distribution of NO/O2 was prominent at opposite sides of the arterioles up to six vessel-diameter (6D) away from the bifurcating point, and this was further enhanced by increasing the levels of RBC aggregation. Our findings suggested that RBC aggregation potentially augments both the formation of asymmetric CFL widths and its influence on the uneven distribution of NO/O2 in the downstream flow of an arteriolar bifurcation. The extended heterogeneity of NO/O2 downstream (2D-6D) also implied its potential propagation throughout the entire arteriolar microvasculature.

  20. Stability of distributed MPC in an intersection scenario

    NASA Astrophysics Data System (ADS)

    Sprodowski, T.; Pannek, J.

    2015-11-01

    The research topic of autonomous cars and the communication among them has attained much attention in the last years and is developing quickly. Among others, this research area spans fields such as image recognition, mathematical control theory, communication networks, and sensor fusion. We consider an intersection scenario where we divide the shared road space in different cells. These cells form a grid. The cars are modelled as an autonomous multi-agent system based on the Distributed Model Predictive Control algorithm (DMPC). We prove that the overall system reaches stability using Optimal Control for each multi-agent and demonstrate that by numerical results.

  1. Free-surface stability criterion as affected by velocity distribution

    USGS Publications Warehouse

    Cheng-Lung, Chen

    1995-01-01

    This paper examines how the velocity distribution of flow in open channels affects the kinematic and dynamic wave velocities, from which the various forms of the Vedernikov number V can be formulated. When V >1, disturbances created in open-channel flow will amplify in the form of roll waves; when V <1, some (though not all) disturbances will attenuate. A study of the Vedernikov stability criterion reveals that it can be readily deduced within the framework of the kinematic and dynamic wave theories by comparing the kinematic wave velocity to the corresponding dynamic wave velocity. -from Author

  2. Simulation of infrared scattering from ice aggregates by use of a size-shape distribution of circular ice cylinders.

    PubMed

    Baran, Anthony J

    2003-05-20

    The scalar optical properties (extinction coefficient, mass extinction coefficient, single-scattering albedo, and asymmetry parameter) of a distribution of randomly oriented ice aggregates are simulated generally to well within 4% accuracy by use of a size-shape distribution of randomly oriented circular ice cylinders at wavelengths in the terrestrial window region. The single-scattering properties of the ice aggregates are calculated over the whole size distribution function by the finite-difference time-domain and improved geometric optics methods. The single-scattering properties of the size-shape distribution of circular ice cylinders are calculated by the T-matrix method supplemented by scattering solutions obtained from complex-angular-momentum theory. Moreover, radiative-transfer studies demonstrate that the maximum error in brightness temperature space when the size-shape distribution of circular ice cylinders is used to represent scattering from ice aggregates is only approximately 0.4 K The methodology presented should find wide applicability in remote sensing of ice cloud and parameterization of cirrus cloud scalar optical properties in climate models.

  3. Kinetics of Formation and Asymmetrical Distribution of Hsp104-Bound Protein Aggregates in Yeast.

    PubMed

    Paoletti, Camille; Quintin, Sophie; Matifas, Audrey; Charvin, Gilles

    2016-04-12

    Budding yeast cells have a finite replicative life span; that is, a mother cell produces only a limited number of daughter cells before it slows division and dies. Despite the gradual aging of the mother cell, all daughters are born rejuvenated and enjoy a full replicative lifespan. It has been proposed that entry of mother cells into senescence is driven by the progressive accumulation and retention of damaged material, including protein aggregates. This additionally allows the daughter cells to be born damage free. However, the mechanism underlying such asymmetrical segregation of protein aggregates by mother and daughter cells remains controversial, in part because of the difficulties inherent in tracking the dynamics and fate of protein aggregates in vivo. To overcome such limitations, we have developed single-cell real-time imaging methodology to track the formation of heat-induced protein aggregates in otherwise unperturbed dividing cells. By combining the imaging data with a simple computational model of protein aggregation, we show that the establishment of asymmetrical partitioning of protein aggregates upon division is driven by the large bud-specific dilution rate associated with polarized growth and the absence of significant mother/bud exchange of protein aggregates during the budded phase of the cell cycle. To our knowledge, this study sheds new light on the mechanism of establishment of a segregation bias, which can be accounted for by simple physical arguments.

  4. Global asymptotic stability of Hopfield neural network involving distributed delays.

    PubMed

    Zhao, Hongyong

    2004-01-01

    In the paper, we study dynamical behaviors of Hopfield neural networks system with distributed delays. Some new criteria ensuring the existence and uniqueness, and the global asymptotic stability (GAS) of equilibrium point are derived. In the results, we do not assume that the signal propagation functions satisfy the Lipschitz condition and do not require them to be bounded, differentiable or strictly increasing. Moreover, the symmetry of the connection matrix is not also necessary. Thus, we improve some previous works of other researchers. These conditions are presented in terms of system parameters and have importance leading significance in designs and applications of the GAS for Hopfield neural networks system with distributed delays. Two examples are also worked out to demonstrate the advantages of our results.

  5. Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse-grained soil in an alpine eco-engineering field experiment?

    NASA Astrophysics Data System (ADS)

    Bast, A.; Wilcke, W.; Graf, F.; Lüscher, P.; Gärtner, H.

    2016-08-01

    Steep vegetation-free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco-engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small-scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotal = 1248) and soil core (ntotal = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long-term field experimental monitoring before transferring laboratory results to the field.

  6. Influence of Scots pine encroachment into alpine grassland in the quality and stability of soil organic matter aggregation

    NASA Astrophysics Data System (ADS)

    Ortiz, Carlos; Díaz-Pinés, Eugenio; Benito, Marta; José Fernández, María; Rubio, Agustín

    2013-04-01

    Ecotone areas are dynamic zones potentially suitable for detecting ecosystem sensitivity to climate change effects. Climate change scenarios proposed by IPCC predict a temperature increase in Mediterranean areas with the consequent altitudinal advance of Scots pine treeline (Pinus sylvestris L.) at the extent of grassland-shrubland areas. Therefore, variations in physical, chemical and biological properties of soils due to plant dynamics are expected. We present a study located in the grassland-forest ecotone of Scots pine on a Mediterranean mountain in Central Spain, considering three different vegetation types: high mountain grassland-shrubland, shrubland-Scots pine high mountain forest and Scots pine mountain forest. We worked on the hypothesis that different plant species compositions influence both the size distribution and aggregate protection of the organic carbon (C), as a result of the different quality of C inputs to the soil from different vegetation types. To test this assumption, topsoil samples were firstly separated into four aggregate fractions (6-2 mm, 2-0.250 mm, 0.250-0.053 mm and < 0.053 mm) by dry sieving; secondly, free light fraction was isolated from intra-aggregate particulate organic matter (iPOM) in a soil/water suspension by centrifuging and decanting the supernatants; and thirdly, different iPOM (coarse iPOM and fine iPOM) and mineral associated soil organic C were released from each remaining aggregate fraction by sonication at 300 J ml-1 and further quantified by wet sieving. We expect differences between light fraction, different iPOM and mineral associated soil organic C from the different aggregates fractions obtained among vegetation types as a result of different quality and quantity organic matter inputs to the soil. Thus, we will be able to predict (i) the evolution of protected soil organic matter with the encroachment of Scots pine on Mediterranean mountains due to climate change effects, (ii) the rate of macroaggregate

  7. Semigroup approximation and robust stabilization of distributed parameter systems

    NASA Technical Reports Server (NTRS)

    Kurdila, A. J.; Fabiano, R.; Strganac, T.; Hsu, S.

    1994-01-01

    Theoretical results that enable rigorous statements of convergence and exponential stability of Galerkin approximations of LQR controls for infinite dimensional, or distributed parameter, systems have proliferated over the past ten years. In addition, extensive progress has been made over the same time period in the derivation of robust control design strategies for finite dimensional systems. However, the study of the convergence of robust finite dimensional controllers to robust controllers for infinite dimensional systems remains an active area of research. We consider a class of soft-constrained differential games evolving in a Hilbert space. Under certain conditions, a saddle point control can be given in feedback form in terms of a solution to a Riccati equation. By considering a related LQR problem, we can show a convergence result for finite dimensional approximations of this differential game. This yields a computational algorithm for the feedback gain that can be derived from similar strategies employed in infinite dimensional LQR control design problems. The approach described in this paper also inherits the additional properties of stability robustness common to game theoretic methods in finite dimensional analysis. These theoretical convergence and stability results are verified in several numerical experiments.

  8. Improved activity and stability of lysozyme at the water/CH2Cl2 interface: enzyme unfolding and aggregation and its prevention by polyols.

    PubMed

    Pérez, C; Griebenow, K

    2001-09-01

    Protein inactivation and aggregation at the water/CH2Cl2 interface is one of the most detrimental events hindering the encapsulation of structurally unperturbed proteins into poly(lactide-co-glycolide) (PLG) microspheres for their clinical application as sustained release dosage forms. We have investigated the inactivation and aggregation of the model protein hen egg-white lysozyme at this interface and devised methods to prevent both events. When lysozyme was exposed to a large water/CH2Cl2 interface achieved by homogenization, lysozyme aggregation occurred. Fourier-transform infrared (FTIR) spectroscopic data demonstrated that the aggregates formed contained intermolecular beta-sheets. The aggregates were of a noncovalent nature because they slowly dissolved in D2O and the IR spectral bands typical for the intermolecular beta-sheets disappeared at approximately 1617 and 1690 cm(-1). The observed loss in specific enzyme activity of soluble lysozyme was caused by the irreversible formation of an unfolded lysozyme species, which was found to be monomeric, and was able to leave the water/CH2Cl2 interface and accumulate in the aqueous phase. Polyols were, in a concentration dependent fashion, efficient in ameliorating lysozyme unfolding and aggregation. However, prevention of lysozyme aggregation and activity loss in the various samples were unrelated. Thus, polyols must work by more than one mechanism preventing the two events. For the first time, an excipient effect on the conformational stability of lysozyme has been excluded from contributing to the prevention of lysozyme unfolding and aggregation.

  9. Stabilizing effects of caprylate and acetyltryptophanate on heat-induced aggregation of bovine serum albumin.

    PubMed

    Arakawa, T; Kita, Y

    2000-06-15

    Acetyltryptophanate (AT) and caprylate (Cap) have been used to stabilize serum albumin against heat treatment. However, the mechanism of stabilization by these additives has never been fully elucidated. Here we used thermal melting to determine the effects of these additives on the melting temperature of bovine serum albumin (BSA) and heat stress at 60 degrees C to follow degradation of the protein in the presence of varying concentrations of AT or Cap. Native polyacrylamide gel electrophoresis was used to examine degradation products generated by heat treatment. Both additives increased the melting temperature of BSA, resulting in an increase by 12 degrees C at 5 mM AT and 3 degrees C at 1 mM Cap. They also conferred stability to BSA against heat stress at 60 degrees C. Complete protection was observed at 5 mM AT and 1 mM Cap. Comparison of AT and Cap in their effects on melting temperature and heat stress-induced degradation showed that a greater protection occurs with Cap which has a weaker effect on melting temperature. Based on this observation it was concluded that the observed protection by AT may be explained by its effects on melting temperature while that of Cap should be ascribed to other mechanisms.

  10. Physical and Biological Controls of Copepod Aggregation and Baleen Whale Distribution

    DTIC Science & Technology

    2009-09-30

    behavior of top predators, including those that feed directly on zooplankton (e.g., basking sharks , manta rays, right whales). While all marine mammals...predators, including those that feed directly on zooplankton (e.g., basking sharks , manta rays, right whales). While all marine mammals rely on prey...aggregation processes in the Great South Channel. IMPACT/APPLICATIONS By understanding aggregation mechanisms, critical marine mammal habitats can be

  11. Structure and Thermodynamic Stability of Islet Amyloid Polypeptide Monomers and Small Aggregates

    NASA Astrophysics Data System (ADS)

    Chiu, Chi-Cheng; Singh, Sadanand; de Pablo, Juan

    2013-03-01

    Human islet amyloid polypeptide (hIAPP, also known as human amylin) is associated with the development of type II diabetes. It is known to form amyloid fibrils that are found in pancreatic islets. Pramlintide, a synthetic analog of hIAPP with three proline substitutions, is not amyloidogenic and has been applied in amylin replacement treatments. In this work, we use molecular simulations with advanced sampling techniques to examine the effect of these proline substitutions on hIAPP monomer conformations. We find that all three proline substitutions are required to attenuate the formation of β-sheets encountered in amylin. Furthermore, we investigate the formation of hIAPP dimers and trimers, and investigate how that process is affected by the presence of various additives. Our simulations show that hIAPP can form a β-sheet at the N-terminus and the C-terminus independently, in agreement with experimental observations. Our results provide valuable insights into the mechanism of hIAPP early aggregation and the design of fibril formation inhibitors.

  12. Proteoglycans from bovine fetal epiphyseal cartilage. Sedimentation velocity and light scattering studies of the effect of link protein on proteoglycan aggregate size and stability.

    PubMed

    Tang, L H; Rosenberg, L C; Reihanian, H; Jamieson, A M; Blackwell, J

    1989-01-01

    Proteoglycan monomer and link proteins were isolated from bovine fetal epiphyseal cartilage and characterized. The physical characteristics of proteoglycan monomer were: s0(20) = 21.3 S, D0t,z = 4.25 x 10(-8)cm2/sec, Mw = 3 x 10(6) and Rg,z = 980A. Link protein preparations contained link proteins 1 and 2, but little or none of the fragment, link protein 3. Link protein-stabilized and link protein-free proteoglycan aggregates were reassembled from proteoglycan monomer, link protein and hyaluronate. The effect of epiphyseal cartilage link protein on aggregate size and stability was examined in sedimentation velocity studies. Compared with link protein from mature bovine nasal and articular cartilages, which contain appreciable amounts of link protein 3, epiphyseal cartilage link protein dramatically stabilized aggregates at pH 5. In the presence of link protein, 92% of the proteoglycan monomers were bound as aggregate at pH 7, and 81% were bound at pH 5. In the absence of link protein, 51% of monomers were bound at pH 7, and only 32% were bound at pH 5. The progressive dissociation of link protein-free aggregates as a function of decreasing pH, and of increasing temperature, was also examined in dynamic light scattering studies. The results of the light scattering studies were in perfect accord with the results of the sedimentation velocity studies. However, compared with the sedimentation velocity studies, the dynamic light scattering studies provided a more detailed and informative description of the dissociation of the link-free aggregate as a function of pH, as a function of temperature, and of the capacity of link protein to stabilize aggregate against dissociation at decreased pH or elevated temperature.

  13. Aggregation and stability of anisotropic charged clay colloids in aqueous medium in the presence of salt.

    PubMed

    Ali, Samim; Bandyopadhyay, Ranjini

    2016-01-01

    Na-montmorillonite nanoclay is a colloid of layered mineral silicate. When dispersed in water, this mineral swells on absorption of water and exfoliates into platelets with electric double layers on their surfaces. Even at low particle concentration, the aqueous dispersion can exhibit a spontaneous ergodicity breaking phase transition from a free flowing liquid to nonequilibrium, kinetically arrested and disordered states such as gels and glasses. In an earlier publication [Applied Clay Science, 2015, 114, 8592], we showed that the stability of clay gels can be enhanced by adding a salt later to the clay dispersion prepared in deionized water, rather than by adding the clay mineral to a previously mixed salt solution. Here, we directly track the collapsing interface of sedimenting clay gels using an optical method and show that adding salt after dispersing the clay mineral does indeed result in more stable gels even in very dilute dispersions. These weak gels are seen to exhibit a transient collapse after a finite delay time, a phenomenon observed previously in depletion gels. The velocity of the collapse oscillates with the age of the sample. However, the average velocity of collapse increases with sample age up to a peak value before decreasing at higher ages. With increasing salt concentration, the delay time for transient collapse decreases, while the peak value of the collapsing velocity increases. Using ultrasound attenuation spectroscopy, rheometry and cryogenic scanning electron microscopy, we confirm that morphological changes of the gel network assembly, facilitated by thermal fluctuations, lead to the observed collapse phenomenon. Since clay minerals are used extensively in polymer nanocomposites, as rheological modifiers, stabilizers and gas absorbents, we believe that the results reported in this work are extremely useful for several practical applications and also for understanding geophysical phenomena such as the formation and stability of quicksand

  14. Deposition-rate dependence of granular size distribution in Cu aggregate on liquid substrate studied by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Chen, Miao-Gen; Yu, Sen-Jiang; Jiao, Zhi-Wei; Yu, Ming-Zhou; Bao, Fu-Bing

    2012-03-01

    In this article, we report an atomic force microscopy study on the microstructure and the deposition-rate dependence of granular size distribution in copper (Cu) ramified aggregates on a liquid substrate. This study shows that the ramified Cu aggregates are composed of Gaussian size distribution granules, which form immediately after the Cu atoms are deposited. The interesting phenomenon is that the mean diameter Φm of the granules exponentially decays and approaches a stable value Φc with an increase in the deposition rate f. The granular mean diameter Φm slightly changes with the time interval Δt during which the film is kept in the vacuum chamber, owing to the large diffusion coefficient of the Cu granules on the liquid substrates. The experimental behavior strongly depends on the properties of the liquid substrate.

  15. Controlled Aggregation and Increased Stability of β-Glucuronidase by Cellulose Binding Domain Fusion.

    PubMed

    Yeom, Soo-Jin; Han, Gui Hwan; Kim, Moonjung; Kwon, Kil Koang; Fu, Yaoyao; Kim, Haseong; Lee, Hyewon; Lee, Dae-Hee; Jung, Heungchae; Lee, Seung-Goo

    2017-01-01

    Cellulose-binding domains (CBDs) are protein domains with cellulose-binding activity, and some act as leaders in the localization of cellulosomal scaffoldin proteins to the hydrophobic surface of crystalline cellulose. In this study, we found that a CBD fusion enhanced and improved soluble β-glucuronidase (GusA) enzyme properties through the formation of an artificially oligomeric state. First, a soluble CBD fused to the C-terminus of GusA (GusA-CBD) was obtained and characterized. Interestingly, the soluble GusA-CBD showed maximum activity at higher temperatures (65°C) and more acidic pH values (pH 6.0) than free GusA did (60°C and pH 7.5). Moreover, the GusA-CBD enzyme showed higher thermal and pH stabilities than the free GusA enzyme did. Additionally, GusA-CBD showed higher enzymatic activity in the presence of methanol than free GusA did. Evaluation of the protease accessibility of both enzymes revealed that GusA-CBD retained 100% of its activity after 1 h incubation in 0.5 mg/ml protease K, while free GusA completely lost its activity. Simple fusion of CBD as a single domain may be useful for tunable enzyme states to improve enzyme stability in industrial applications.

  16. Controlled Aggregation and Increased Stability of β-Glucuronidase by Cellulose Binding Domain Fusion

    PubMed Central

    Kim, Moonjung; Kwon, Kil Koang; Fu, Yaoyao; Kim, Haseong; Lee, Hyewon; Lee, Dae-Hee; Jung, Heungchae; Lee, Seung-Goo

    2017-01-01

    Cellulose-binding domains (CBDs) are protein domains with cellulose-binding activity, and some act as leaders in the localization of cellulosomal scaffoldin proteins to the hydrophobic surface of crystalline cellulose. In this study, we found that a CBD fusion enhanced and improved soluble β-glucuronidase (GusA) enzyme properties through the formation of an artificially oligomeric state. First, a soluble CBD fused to the C-terminus of GusA (GusA-CBD) was obtained and characterized. Interestingly, the soluble GusA-CBD showed maximum activity at higher temperatures (65°C) and more acidic pH values (pH 6.0) than free GusA did (60°C and pH 7.5). Moreover, the GusA-CBD enzyme showed higher thermal and pH stabilities than the free GusA enzyme did. Additionally, GusA-CBD showed higher enzymatic activity in the presence of methanol than free GusA did. Evaluation of the protease accessibility of both enzymes revealed that GusA-CBD retained 100% of its activity after 1 h incubation in 0.5 mg/ml protease K, while free GusA completely lost its activity. Simple fusion of CBD as a single domain may be useful for tunable enzyme states to improve enzyme stability in industrial applications. PMID:28099480

  17. An alternative method for determining particle-size distribution of forest road aggregate and soil with large-sized particles

    Treesearch

    Hakjun Rhee; Randy B. Foltz; James L. Fridley; Finn Krogstad; Deborah S. Page-Dumroese

    2014-01-01

    Measurement of particle-size distribution (PSD) of soil with large-sized particles (e.g., 25.4 mm diameter) requires a large sample and numerous particle-size analyses (PSAs). A new method is needed that would reduce time, effort, and cost for PSAs of the soil and aggregate material with large-sized particles. We evaluated a nested method for sampling and PSA by...

  18. Cavity filling mutations at the thyroxine-binding site dramatically increase transthyretin stability and prevent its aggregation

    PubMed Central

    Sant’Anna, Ricardo; Almeida, Maria Rosário; Varejāo, Nathalia; Gallego, Pablo; Esperante, Sebastian; Ferreira, Priscila; Pereira-Henriques, Alda; Palhano, Fernando L.; de Carvalho, Mamede; Foguel, Debora; Reverter, David; Saraiva, Maria João; Ventura, Salvador

    2017-01-01

    More than a hundred different Transthyretin (TTR) mutations are associated with fatal systemic amyloidoses. They destabilize the protein tetrameric structure and promote the extracellular deposition of TTR as pathological amyloid fibrils. So far, only mutations R104H and T119M have been shown to stabilize significantly TTR, acting as disease suppressors. We describe a novel A108V non-pathogenic mutation found in a Portuguese subject. This variant is more stable than wild type TTR both in vitro and in human plasma, a feature that prevents its aggregation. The crystal structure of A108V reveals that this stabilization comes from novel intra and inter subunit contacts involving the thyroxine (T4) binding site. Exploiting this observation, we engineered a A108I mutation that fills the T4 binding cavity, as evidenced in the crystal structure. This synthetic protein becomes one of the most stable TTR variants described so far, with potential application in gene and protein replacement therapies. PMID:28338000

  19. Adsorption and chemical stability of a cationic aggregating ester - propantheline bromide - on silica surfaces in aqueous dispersions.

    PubMed

    Daniels, R; Rupprecht, H

    1985-07-01

    The adsorption behavior of cationic aggregating substances such as antimicrobial quats or phenothiazine derivatives on silica surfaces in aqueous media has been extensively investigated. However, the chemical stability of adsorbates in such systems was unknown. Propantheline bromide (PPBr) was selected as a model to investigate the stability of hydrolyzable substances in silica-containing aqueous dispersions or in adsorbates on silica carriers used for solid drugs. The quaternary ester PPBr showed an appreciable adsorption on the silica surface, the extent of which was increased by raising the pH of the aqueous phase or by the addition of neutral salts such as NaNO3. In parallel to the adsorption process, hydrolysis of PPBr occurs in these aqueous silica dispersions to yield xanthene carbonic acid and a quaternary alcohol component. Adsorption and hydrolysis were found to be mutually influencing reactions. Because of the adsorption of PPBr, the rate of ester decomposition was enhanced in these silica dispersions when compared to aqueous solutions of PPBr at the same pH. Simultaneously, an increase in PPBr adsorption is observed, as well as adsorption of the decomposition product xanthene carbonic acid. This result can be attributed to ion-pair adsorption of the latter with PPBr. The rate constants of PPBr decomposition were found to depend directly on the silica content of the dispersion, although at higher concentrations a decreased catalytic effect was observed. These phenomena are discussed on the basis of the adsorbate structure and exchange processes.

  20. Stability and effectiveness of chlorine disinfectants in water distribution systems.

    PubMed

    Olivieri, V P; Snead, M C; Krusé, C W; Kawata, K

    1986-11-01

    A test system for water distribution was used to evaluate the stability and effectiveness of three residual disinfectants--free chlorine, combined chlorine, and chlorine dioxide--when challenged with a sewage contaminant. The test distribution system consisted of the street main and internal plumbing for two barracks at Fort George G. Meade, MD. To the existing pipe network, 152 m (500 ft) of 13-mm (0.5 in.) copper pipe were added for sampling, and 60 m (200 ft) of 2.54-cm (1.0 in.) plastic pipe were added for circulation. The levels of residual disinfectants tested were 0.2 mg/L and 1.0 mg/L as available chlorine. In the absence of a disinfectant residual, microorganisms in the sewage contaminant were consistently recovered at high levels. The presence of any disinfectant residual reduced the microorganism level and frequency of occurrence at the consumer's tap. Free chlorine was the most effective residual disinfectant and may serve as a marker or flag in the distribution network. Free chlorine and chlorine dioxide were the least stable in the pipe network. The loss of disinfectant in the pipe network followed first-order kinetics. The half-life determined in static tests for free chlorine, chlorine dioxide, and combined chlorine was 140, 93, and 1680 min.

  1. Stability and effectiveness of chlorine disinfectants in water distribution systems

    SciTech Connect

    Olivieri, V.P.; Snead, M.C.; Kruse, C.W.; Kawata, K.

    1986-11-01

    A test system for water distribution was used to evaluate the stability and effectiveness of three residual disinfectants - free chlorine, combined chlorine, and chlorine dioxide - when challenged with a sewage contaminant. The test distribution system consisted of the street main and internal plumbing for two barracks at Fort George G. Meade, MD. To the existing pipe network, 152 m (500 ft) of 13-mm (0.5 in.) copper pipe were added for sampling, and 60 m (200 ft) of 2.54-cm (1.0 in.) plastic pipe were added for circulation. The levels of residual disinfectants tested were 0.2 mg/L and 1.0 mg/L as available chlorine. In the absence of a disinfectant residual, microorganisms in the sewage contaminant were consistently recovered at high levels. The presence of any disinfectant residual reduced the microorganism level and frequency of occurrence at the consumer's tap. Free chlorine was the most effective residual disinfectant and may serve as a marker or flag in the distribution network. Free chlorine and chlorine dioxide were the least stable in the pipe network. The loss of disinfectant in the pipe network followed first-order kinetics. The half-life determined in static tests for free chlorine, chlorine dioxide, and combined chlorine was 140, 93, and 1680 min.

  2. PEG-stabilized core-shell nanoparticles: impact of linear versus dendritic polymer shell architecture on colloidal properties and the reversibility of temperature-induced aggregation.

    PubMed

    Gillich, Torben; Acikgöz, Canet; Isa, Lucio; Schlüter, A Dieter; Spencer, Nicholas D; Textor, Marcus

    2013-01-22

    Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used experimentally and also clinically tested in diverse areas of biology and medicine. Applications include magnetic resonance imaging, cell sorting, drug delivery, and hyperthermia. Physicochemical surface properties are particularly relevant in the context of achieving high colloidal nanoparticle (NP) stability and preventing agglomeration (particularly challenging in biological fluids), increasing blood circulation time, and possibly targeting specific cells or tissues through the presentation of bioligands. Traditionally, NP surfaces are sterically stabilized with hydrophilic polymeric matrices, such as dextran or linear poly(ethylene glycol) brushes. While dendrimers have found applications as drug carriers, dispersants with dendritic ("dendrons") or hyperbranched structures have been comparatively neglected despite their unique properties, such as a precisely defined molecular structure and the ability to present biofunctionalities at high density at the NP periphery. This work covers the synthesis of SPIONs and their stabilization based on poly(ethylene glycol) (PEG) and oligo(ethylene glycol) (OEG) chemistry and compares the physicochemical properties of NPs stabilized with linear and dendritic macromolecules of comparable molecular weight. The results highlight the impact of the polymeric interface architecture on solubility, colloidal stability, hydrodynamic radius, and thermoresponsive behavior. Dendron-stabilized NPs were found to provide excellent colloidal stability, despite a smaller hydrodynamic radius and lower degree of soft shell hydration compared to linear PEG analogues. Moreover, for the same grafting density and molecular weight of the stabilizers, OEG dendron-stabilized NPs show a reversible temperature-induced aggregation behavior, in contrast to the essentially irreversible aggregation and sedimentation observed for the linear PEG analogues. This new class of

  3. Drying-induced decomposition and associated changes in aggregation and carbon distribution in subalpine meadow soils: implication of drought

    NASA Astrophysics Data System (ADS)

    Berhe, A. A.; Arnold, C. L.; Ghezzehei, T. A.

    2016-12-01

    While peatlands are garnering much attention for their greenhouse gas feedback potential in a warming climate, the coupled biogeochemical and hydrological impact of structural and physical changes in these types of systems as a result of drought-induced drying and desiccation has not been studied in detail. The cyclic drawdown/recharge of the water table that exists in most peatland systems impose important controls on organic matter storage and decomposition as well as soil physical properties. In order to better understand how high elevation peatlands will respond to increasingly dry years, we incubated meadow soils collected along a hydrologic gradient at 5 different water potentials and measured the CO2 flux at intervals for over one year to determine how desiccation of meadow soils (from the Harvey Monroe Hall Research Natural Area at the crest of the Sierra Nevada) influences gaseous fluxes of C, as well as aggregation of the organic-rich soils and distribution of the soil C in different physical pools (macro- vs. micro-aggregate, and silt+ clay fractions). We found that the cumulative carbon mineralization was greatest at the highest (0.1 bar) and lowest (4 bar) water potential, across all regions of the meadow, indicating the presence of two separate pools of labile carbon that can be accessed only after a threshold of drying is reached in the soil. We also observe important changes associated with aggregate size distributions and fraction of total carbon distributed in three distinct pools.

  4. Scheduling and routing algorithm for aggregating large data files from distributed databases to super-computers on lambda grid

    NASA Astrophysics Data System (ADS)

    Sun, Shen; Guo, Wei; Sun, Weiqiang; Jin, Yaohui; Hu, Weisheng

    2008-11-01

    These days while the traditional Internet cannot meet the requirement of data-intensive communications in large scale escience grid applications, Optical network which is also referred to as Lambda Grid provide a simple means of achieving guaranteed high bandwidth, guaranteed latency and deterministic connection. Lots of e-science applications like e-VLBI and GTL require aggregating several hundred GB data files from distributed databases to super-computers frequently at real time. Thus minimizing the aggregation time can improve the overall system performance. We consider the problem of aggregating large data files from distributed databases to distributed computational resources on lambda grid. We modify the model of Time-Path Scheduling Problem (TPSP) which has been proposed and propose a new N-destination TPSP (NDTPSP) model. We present the proof of NDTPSP's NP-completeness. We also propose a list scheduling algorithm and a modified list scheduling algorithm for our problem. The performance of different algorithms will be compared and analyzed by simulations.

  5. Change in Chirality of Semiconducting Single-Walled Carbon Nanotubes Can Overcome Anionic Surfactant Stabilization: A Systematic Study of Aggregation Kinetics.

    PubMed

    Khan, Iftheker A; Flora, Joseph R V; Nabiul Afrooz, A R M; Aich, Nirupam; Schierz, P Ariette; Ferguson, P Lee; Sabo-Attwood, Tara; Saleh, Navid B

    2015-05-20

    Single-walled carbon nanotubes' (SWNT) effectiveness in applications is enhanced by debundling or stabilization. Anionic surfactants are known to effectively stabilize SWNTs. However, the role of specific chirality on surfactant-stabilized SWNT aggregation has not been studied to date. The aggregation behavior of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalized with three anionic surfactants-sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium deoxycholate (SDOCO)-was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and di-valent (CaCl2) electrolytes as well as a 2.5 mg TOC/L Suwannee River humic acid (SRHA) were used as background chemistry. Overall, SDBS showed the most effectiveness in SWNT stability, followed by SDOCO and SDS. However, the relatively larger diameter (7,6) chiral tubes compromised the surfactant stability, compared to (6,5) chiral enrichment, due to enhanced van der Waals interaction. The presence of di-valent electrolytes overshadowed the chirality effects and resulted in similar aggregation behavior for both the SWNT samples. Molecular modeling results enumerated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of SRHA under 10 mM monovalent and mixed electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilization of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure.

  6. Change in Chirality of Semiconducting Single-Walled Carbon Nanotubes Can Overcome Anionic Surfactant Stabilization: A Systematic Study of Aggregation Kinetics

    PubMed Central

    Khan, Iftheker A.; Flora, Joseph R. V.; Nabiul Afrooz, A. R. M.; Aich, Nirupam; Schierz, P. Ariette; Ferguson, P. Lee; Sabo-Attwood, Tara; Saleh, Navid B.

    2015-01-01

    Single-walled carbon nanotubes’ (SWNT) effectiveness in applications is enhanced by debundling or stabilization. Anionic surfactants are known to effectively stabilize SWNTs. However, the role of specific chirality on surfactant-stabilized SWNT aggregation has not been studied to date. The aggregation behavior of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalized with three anionic surfactants—sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium deoxycholate (SDOCO)—was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and di-valent (CaCl2) electrolytes as well as a 2.5 mg TOC/L Suwannee River humic acid (SRHA) were used as background chemistry. Overall, SDBS showed the most effectiveness in SWNT stability, followed by SDOCO and SDS. However, the relatively larger diameter (7,6) chiral tubes compromised the surfactant stability, compared to (6,5) chiral enrichment, due to enhanced van der Waals interaction. The presence of di-valent electrolytes overshadowed the chirality effects and resulted in similar aggregation behavior for both the SWNT samples. Molecular modeling results enumerated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of SRHA under 10 mM monovalent and mixed electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilization of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure. PMID:26855611

  7. Investigating the Impact of Wind Turbines on Distribution System Stability

    SciTech Connect

    Jain, Rishabh; Zhang, Yingchen; Hodge, Bri-Mathias

    2016-12-12

    Modern wind turbines utilize power electronic converters to regulate their output and optimize their performance. Their impact on the distribution system is not as well understood as for transmission system. The novelty of this work is in studying the impact of wind turbines given its proximity to faults or severe voltage events, and the influence on system stability given its location relative to the substation (representing the conventional grid). This paper presents the frequency and voltage swing plots for various study scenarios. The responses are analyzed two fold - Steady state operation, and performance given a fault or voltage events occurs in the system. The findings are presented, with crucial differences from transmission systems highlighted.

  8. Cellular Proteomes Have Broad Distributions of Protein Stability

    PubMed Central

    Ghosh, Kingshuk; Dill, Ken

    2010-01-01

    Biological cells are extremely sensitive to temperature. What is the mechanism? We compute the thermal stabilities of the whole proteomes of Escherichia coli, yeast, and Caenorhabditis elegans using an analytical model and an extensive database of stabilities of individual proteins. Our results support the hypothesis that a cell's thermal sensitivities arise from the collective instability of its proteins. This model shows a denaturation catastrophe at temperatures of 49–55°C, roughly the thermal death point of mesophiles. Cells live on the edge of a proteostasis catastrophe. According to the model, it is not that the average protein is problematic; it is the tail of the distribution. About 650 of E. coli's 4300 proteins are less than 4 kcal mol−1 stable to denaturation. And upshifting by only 4° from 37° to 41°C is estimated to destabilize an average protein by nearly 20%. This model also treats effects of denaturants, osmolytes, and other physical stressors. In addition, it predicts the dependence of cellular growth rates on temperature. This approach may be useful for studying physical forces in biological evolution and the role of climate change on biology. PMID:21156142

  9. Modeling capsid kinetics assembly from the steady state distribution of multi-sizes aggregates

    NASA Astrophysics Data System (ADS)

    Hozé, Nathanaël; Holcman, David

    2014-01-01

    The kinetics of aggregation for particles of various sizes depends on their diffusive arrival and fusion at a specific nucleation site. We present here a mean-field approximation and a stochastic jump model for aggregates at equilibrium. This approach is an alternative to the classical Smoluchowski equations that do not have a close form and are not solvable in general. We analyze these mean-field equations and obtain the kinetics of a cluster formation. Our approach provides a simplified theoretical framework to study the kinetics of viral capsid formation, such as HIV from the self-assembly of the structural proteins Gag.

  10. TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability.

    PubMed

    Loosli, Frédéric; Le Coustumer, Philippe; Stoll, Serge

    2013-10-15

    The behavior of manufactured TiO2 nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO2 nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO2 nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO2 nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO2 nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO2 nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO2 nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO2 nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO2 nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO2 nanoparticles. Copyright © 2013 Elsevier Ltd. All rights reserved.

  11. Effect of sustainable land management practices on soil aggregation and stabilization of organic carbon in semiarid mediterranean ecosystems

    NASA Astrophysics Data System (ADS)

    Garcia-Franco, Noelia; Albaladejo, Juan; Almagro, María; Wiesmeier, Martin; Martínez-Mena, María

    2016-04-01

    Arid and semiarid regions represent about 47% of the total land area of the world (UNEP, 1992). At present, there is a priority interest for carbon (C) sequestration in drylands. These areas are considered as very fragile ecosystems with low organic carbon (OC) saturation, and potentially, high capacity for soil OC sequestration. In addition, the restoration of these areas is one of the major challenges for scientists, who will be able to identify and recommended the best land uses and sustainable land management (SLM) practices for soil conservation and mitigation of climate change in these environments. In this regard, in semiarid Mediterranean ecosystems there is an urgent need for the implementation of SLM practices regardless of land-use type (forest, agricultural and shrubland) to maintain acceptable levels of soil organic matter (SOM) and the physico-chemical protection of the OC. Long- and short-term effects of SLM practices on soil aggregation and SOC stabilization were studied in two land uses. The long-term experiment was conducted in a reforestation area with Pinus halepensis Mill., where two afforestation techniques were implemented 20 years ago: a) mechanical terracing with a single application of organic waste of urban soil refuse, and b) mechanical terracing without organic amendment. An adjacent shrubland was considered as the reference plot. The short-term experiment was conducted in a rain-fed almond (Prunus dulcis Mill., var. Ferragnes) orchard where two SLM practices were introduced 4 years ago: a) reduced tillage plus green manure, and b) no tillage. Reduced tillage was considered as the reference plot given that it is the habitual management practice. Four aggregate size classes were differentiated by sieving (large and small macroaggregates, microaggregates, and the silt plus clay fraction), and the microaggregates occluded within small macroaggregates (SMm) were isolated. In addition, different organic C fractions corresponding with active

  12. Aggregated Particle-size distributions for tephra-deposit model forecasts

    NASA Astrophysics Data System (ADS)

    Mastin, L. G.; Durant, A. J.; Van Eaton, A. R.

    2015-12-01

    The accuracy of models that forecast atmospheric transport and deposition of tephra to anticipate hazards during volcanic eruptions is limited by the fact that fine ash tends to aggregate and fall out more rapidly than the individual constituent particles. Aggregation is generally accounted for by representing fine ash as aggregates with density ρagg and a log-normal size range with median μagg and standard deviation σagg. Values of these parameters likely vary with eruption type, grain size, and atmospheric conditions. To date, no studies have examined how the values vary from one eruption or deposit to another. In this study, we used the Ash3d tephra model to simulate four deposits: 18 May 1980 Mount St. Helens, 16-17 September 1992 Crater Peak (Mount Spurr), Alaska, 17 June 1996 Ruapehu, and 23 March 2009 Mount Redoubt volcano. In 158 simulations, we systematically varied μagg (1-2.3Φ) and σagg (0.1-0.3Φ), using ellipsoidal aggregates with =600 kg m-3 and a shape factor F≡((b+c)/2a)=0.44 . We evaluated the goodness of fit using three statistical comparisons: modeled versus measured (1) mass load at individual sample locations; (2) mass load versus distance along the dispersal axis; and (3) isomass area. For all deposits, the best-fit μagg ranged narrowly between ~1.6-2.0Φ (0.33-0.25mm), despite large variations in erupted mass (0.25-50 Tg), plume height (8.5-25 km), mass fraction of fine (<0.063mm) ash (3-59%), atmospheric temperature, aggregation mechanism, and water content between these eruptions. This close agreement suggests that the aggregation process may be modeled as a discrete process that is agnostic to the eruptive style or magnitude of eruption. This result paves the way to a simple, computationally-efficient parameterization of aggregation that is suitable for use in operational deposit forecasts. Further research may indicate whether this narrow range also reflects physical constraints on processes in the evolving cloud.

  13. Uniform distribution of graphene oxide sheets into a poly-vinylidene fluoride nanoparticle matrix through shear-driven aggregation.

    PubMed

    Sheng, Xinxin; Xie, Delong; Zhang, Xinya; Zhong, Li; Wu, Hua; Morbidelli, Massimo

    2016-07-06

    A general methodology has been developed for preparing nanocomposites with uniform, random distribution of fillers in polymer matrices, purely based on intense shear-driven aggregation, while avoiding filler aggregation. This procedure is demonstrated for a binary colloid composed of graphene oxide (GO) sheets and poly-vinylidene fluoride (PVDF) nanoparticles (NPs), both negatively charged and stable at rest. On the other hand, the PVDF NPs are shear-active (i.e. aggregation occurs under intensive shear), while the GO sheets are shear-inactive. It is found that when the two suspensions are mixed and the resulting binary colloid is forced to pass through a microchannel (MC) device (at a very high shear rate, G = 1.2 × 10(6) s(-1)), the shear-inactive GO sheets are captured and well distributed inside the PVDF NP clusters or gels. In addition, it is shown that in order to have 100% capture efficiency for the GO sheets, a minimum solid content of the binary colloid is required, which can be identified experimentally as the minimum leading to gelation after passing through the MC only one time.

  14. Distributed microbially- and chemically-mediated redox processes controlling arsenic dynamics within Mn-/Fe-oxide constructed aggregates

    NASA Astrophysics Data System (ADS)

    Ying, Samantha C.; Masue-Slowey, Yoko; Kocar, Benjamin D.; Griffis, Sarah D.; Webb, Samuel; Marcus, Matthew A.; Francis, Christopher A.; Fendorf, Scott

    2013-03-01

    The aggregate-based structure of soils imparts physical heterogeneity that gives rise to variation in microbial and chemical processes which influence the speciation and retention of trace elements such as As. To examine the impact of distributed redox conditions on the fate of As in soils, we imposed various redox treatments upon constructed soil aggregates composed of ferrihydrite- and birnessite-coated sands presorbed with As(V) and inoculation with the dissimilatory metal reducing bacterium Shewanella sp. ANA-3. Aeration of the advecting solution surrounding the aggregates was varied to simulate environmental conditions. We find that diffusion-limited transport within high dissolved organic carbon environments allows reducing conditions to persist in the interior of aggregates despite aerated advecting external solutes, causing As, Mn, and Fe to migrate from the reduced aggregate interiors to the aerated exterior region. Upon transitioning to anoxic conditions in the external solutes, pulses of As, Mn and Fe are released into the advecting solution, while, conversely, a transition to aerated conditions in the exterior resulted in a cessation of As, Mn, and Fe release. Importantly, we find that As(III) oxidation by birnessite is appreciable only in the presence of O2; oxidation of As(III) to As(V) by Mn-oxides ceases under anaerobic conditions apparently as a result of microbially mediated Mn(IV/III) reduction. Our results demonstrate the importance of considering redox conditions and the physical complexity of soils in determining As dynamics, where redox transitions can either enhance or inhibit As release due to speciation shifts in both sorbents (solubilization versus precipitation of Fe and Mn oxides) and sorbates (As).

  15. Effects of water on aggregation and stability of monoglycerides in hydrophobic solutions.

    PubMed

    Chen, C H; Terentjev, E M

    2010-03-02

    We apply a set of different techniques to analyze the physical properties and phase transitions of monoglyceride (MG)-oil-water ternary systems. The effect of MGs on water absorption in food-grade hazelnut oil and in pure hydrocarbon oil (decane) is reported. Comparison between decane and hazelnut oil backgrounds indicates that the effect of water absorption is significant and universal in different MG ternary systems. Adding small amounts of cosurfactant (stearic acid) is necessary to stabilize the MGs in oil-water combinations by enhancing the swelling capacity of lamellar layers; as a result, the structures become sensitive to the pH of the aqueous phase used. The dramatic changes on increasing the aqueous content are recorded by the calorimetry. In samples with small quantities of water, the phase behavior is almost independent of the pH. Once the proportion of water increases, the effect of pH is prominent. At low pH, the solubility of MG in water is limited, and the ternary system retains key features of the oil-dominated environment, such as the sequence of two transitions on cooling, with the low-temperature sub-alpha crystalline phase. At high pH and a sufficient amount of water, the MG layers remain properly swollen, and the crystalline phase disappears from the phase diagram. We spend considerable effort identifying the inverse lamellar phase of MGs in an oil-dominated environment with the so-called alpha-gel phase that is well-established in water-dominated systems, and distinguishing "demixing" from water and from oil. The rheology is examined in different fluid and gel phases; the storage modulus generally decreased on increasing the water proportion, but a gel-like response is found in the high-temperature lamellar phase over a wide range of water dilution. We then focus on aging phenomena in the inverse lamellar (or alpha-gel) phase and show that the rearranging of hydrogen bonds is slowed down and disrupted by the presence of water, giving the

  16. Burst analysis spectroscopy: a versatile single-particle approach for studying distributions of protein aggregates and fluorescent assemblies.

    PubMed

    Puchalla, Jason; Krantz, Kelly; Austin, Robert; Rye, Hays

    2008-09-23

    Many essential cellular functions depend on the assembly and disassembly of macromolecular complexes. The size, form, and distribution of these assemblies can be heterogeneous and complex, rendering their detailed characterization difficult. Here we describe a simple non-correlation-based method capable of directly measuring population distributions at very low sample concentrations. Specifically, we exploit the highest signal-to-noise light bursts from single fluorescent particles transiting a confocal excitation spot to recursively determine the brightness and size distribution of complex mixtures of fluorescent objects. We refer to this method as burst analysis spectroscopy (BAS) and demonstrate the sensitivity of this technique by examining the free-solution, time-resolved distribution of assembled protein aggregates by using two fluorescently labeled proteins: the aggregation-prone, chaperonin-dependent, folding model protein ribulose-bisphosphate carboxylase/oxygenase (RuBisCO), and an amyloidogenic fragment of the yeast prion protein Sup35. We find that the assembly kinetics of both proteins display complex multimodal behavior not readily quantifiable with other methods.

  17. Burst analysis spectroscopy: A versatile single-particle approach for studying distributions of protein aggregates and fluorescent assemblies

    PubMed Central

    Puchalla, Jason; Krantz, Kelly; Austin, Robert; Rye, Hays

    2008-01-01

    Many essential cellular functions depend on the assembly and disassembly of macromolecular complexes. The size, form, and distribution of these assemblies can be heterogeneous and complex, rendering their detailed characterization difficult. Here we describe a simple non-correlation-based method capable of directly measuring population distributions at very low sample concentrations. Specifically, we exploit the highest signal-to-noise light bursts from single fluorescent particles transiting a confocal excitation spot to recursively determine the brightness and size distribution of complex mixtures of fluorescent objects. We refer to this method as burst analysis spectroscopy (BAS) and demonstrate the sensitivity of this technique by examining the free-solution, time-resolved distribution of assembled protein aggregates by using two fluorescently labeled proteins: the aggregation-prone, chaperonin-dependent, folding model protein ribulose-bisphosphate carboxylase/oxygenase (RuBisCO), and an amyloidogenic fragment of the yeast prion protein Sup35. We find that the assembly kinetics of both proteins display complex multimodal behavior not readily quantifiable with other methods. PMID:18780782

  18. Principles of moment distribution applied to stability of structures composed of bars or plates

    NASA Technical Reports Server (NTRS)

    Lundquist, Eugene E; Stowell, Elbridge Z; Schuette, Evan H

    1943-01-01

    Principles of the cross method of moment distribution, which have previously been applied to the stability of structures composed of bars under axial load, are applied to the stability of structures composed of long plates under longitudinal load.

  19. Static and dynamic microscopy of the chemical stability and aggregation state of silver nanowires in components of murine pulmonary surfactant

    PubMed Central

    Theodorou, Ioannis G.; Botelho, Danielle; Schwander, Stephan; Zhang, Junfeng (Jim); Chung, Kian Fan; Tetley, Teresa D.; Shaffer, Milo S. P.; Gow, Andrew; Ryan, Mary P.; Porter, Alexandra E.

    2016-01-01

    The increase of production volumes of silver nanowires (AgNWs) and of consumer products incorporating them, may lead to increased health risks from occupational and public exposures. There is currently limited information about the putative toxicity of AgNWs upon inhalation, and incomplete understanding of the properties that control their bioreactivity. The lung lining fluid (LLF), which contains phospholipids and surfactant proteins, represents a first contact site with the respiratory system. In this work, the impact of Dipalmitoylphosphatidylcholine (DPPC), Curosurf® and murine LLF on the stability of AgNWs was examined. Both the phospholipid and protein components of the LLF modified the dissolution kinetics of AgNWs, due to the formation of a lipid corona or aggregation of the AgNWs. Moreover, the hydrophilic, but neither the hydrophobic surfactant proteins nor the phospholipids, induced agglomeration of the AgNWs. Finally, the generation of a secondary population of nano-silver was observed and attributed to the reduction of Ag+ ions by the surface capping of the AgNWs. Our findings highlight that combinations of spatially resolved dynamic and static techniques are required to develop a holistic understanding of which parameters govern AgNW behavior at the point of exposure and to accurately predict their risks on human health and the environment. PMID:26061974

  20. Static and Dynamic Microscopy of the Chemical Stability and Aggregation State of Silver Nanowires in Components of Murine Pulmonary Surfactant.

    PubMed

    Theodorou, Ioannis G; Botelho, Danielle; Schwander, Stephan; Zhang, Junfeng; Chung, Kian Fan; Tetley, Teresa D; Shaffer, Milo S P; Gow, Andrew; Ryan, Mary P; Porter, Alexandra E

    2015-07-07

    The increase of production volumes of silver nanowires (AgNWs) and of consumer products incorporating them may lead to increased health risks from occupational and public exposures. There is currently limited information about the putative toxicity of AgNWs upon inhalation and incomplete understanding of the properties that control their bioreactivity. The lung lining fluid (LLF), which contains phospholipids and surfactant proteins, represents a first contact site with the respiratory system. In this work, the impact of dipalmitoylphosphatidylcholine (DPPC), Curosurf, and murine LLF on the stability of AgNWs was examined. Both the phospholipid and protein components of the LLF modified the dissolution kinetics of AgNWs, due to the formation of a lipid corona or aggregation of the AgNWs. Moreover, the hydrophilic proteins, but neither the hydrophobic surfactant proteins nor the phospholipids, induced agglomeration of the AgNWs. Finally, the generation of a secondary population of nanosilver was observed and attributed to the reduction of Ag(+) ions by the surface capping of the AgNWs. Our findings highlight that combinations of spatially resolved dynamic and static techniques are required to develop a holistic understanding of which parameters govern AgNW behavior at the point of exposure and to accurately predict their risks on human health and the environment.

  1. Monte Carlo simulation for morphology of nanoparticles and particle size distributions: comparison of the cluster-cluster aggregation model with the sectional method

    NASA Astrophysics Data System (ADS)

    Ono, Kiminori; Matsukawa, Yoshiya; Saito, Yasuhiro; Matsushita, Yohsuke; Aoki, Hideyuki; Era, Koki; Aoki, Takayuki; Yamaguchi, Togo

    2015-06-01

    This study presents the validity and ability of an aggregate mean free path cluster-cluster aggregation (AMP-CCA) model, which is a direct Monte Carlo simulation, to predict the aggregate morphology with diameters form about 15-200 nm by comparing the particle size distributions (PSDs) with the results of the previous stochastic approach. The PSDs calculated by the AMP-CCA model with the calculated aggregate as a coalesced spherical particle are in reasonable agreement with the results of the previous stochastic model regardless of the initial number concentration of particles. The shape analysis using two methods, perimeter fractal dimension and the shape categories, has demonstrated that the aggregate structures become complex with increasing the initial number concentration of particles. The AMP-CCA model provides a useful tool to calculate the aggregate morphology and PSD with reasonable accuracy.

  2. Distribution of Amyloid-Like and Oligomeric Species from Protein Aggregation Kinetics.

    PubMed

    Silva, Alexandra; Almeida, Bruno; Fraga, Joana S; Taboada, Pablo; Martins, Pedro M; Macedo-Ribeiro, Sandra

    2017-09-14

    Amyloid fibrils and soluble oligomers are two types of protein aggregates associated with neurodegeneration. Classic therapeutic strategies try to prevent the nucleation and spread of amyloid fibrils, whilst diffusible oligomers have emerged as promising drug targets affecting downstream pathogenic processes. We developed a generic protein aggregation model and validate it against measured compositions of fibrillar and non-fibrillar assemblies of ataxin-3, a protein implicated in Machado-Joseph disease. The derived analytic rate-law equations can be used to 1) identify the presence of parallel aggregation pathways and 2) estimate the critical sizes of amyloid fibrils. The discretized population balance supporting our model is the first to quantitatively fit time-resolved measurements of size and composition of both amyloid-like and oligomeric species. The new theoretical framework can be used to screen a new class of drugs specifically targeting toxic oligomers. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. A competitive aggregation model for flash nanoprecipitation.

    PubMed

    Cheng, Janine Chungyin; Vigil, R D; Fox, R O

    2010-11-15

    Flash NanoPrecipitation (FNP) is a novel approach for producing functional nanoparticles stabilized by amphiphilic block copolymers. FNP involves the rapid mixing of a hydrophobic active (organic) and an amphiphilic di-block copolymer with a non-solvent (water) and subsequent co-precipitation of nanoparticles composed of both the organic and copolymer. During this process, the particle size distribution (PSD) is frozen and stabilized by the hydrophilic portion of the amphiphilic di-block copolymer residing on the particle surface. That is, the particle growth is kinetically arrested and thus a narrow PSD can be attained. To model the co-precipitation process, a bivariate population balance equation (PBE) has been formulated to account for the competitive aggregation of the organic and copolymer versus pure organic-organic or copolymer-copolymer aggregation. Aggregation rate kernels have been derived to account for the major aggregation events: free coupling, unimer insertion, and aggregate fusion. The resulting PBE is solved both by direct integration and by using the conditional quadrature method of moments (CQMOM). By solving the competitive aggregation model under well-mixed conditions, it is demonstrated that the PSD is controlled primarily by the copolymer-copolymer aggregation process and that the energy barrier to aggregate fusion plays a key role in determining the PSD. It is also shown that the characteristic aggregation times are smaller than the turbulent mixing time so that the FNP process is always mixing limited.

  4. Complex aggregation patterns in drying nanocolloidal suspensions: size matters when it comes to the thermomechanical stability of nanoparticle-based structures.

    PubMed

    Darwich, Samer; Mougin, Karine; Haidara, Hamidou

    2010-11-16

    We report the results of a model study on the interrelation among the occurrence of complex aggregation patterns in drying nanofluids, the size of the constitutive nanoparticles (NPs), and the drying temperature, which is a critical issue in the genesis of complex drying patterns that was never systematically reported before. We show that one can achieve fine control over the occurrence and topological features of these drying-mediated complex structures through the combination of the particle size, the drying temperature, and the substrate surface energy. Most importantly, we show that a transition in the occurrence of the patterns appears with the temperature and the particle size, which accounts for the size dependence of the thermomechanical stability of the aggregates in the nanoscale range. Using simple phenomenological and scaling considerations, we showed that the thermomechanical stability of the aggregates was underpinned by physical quantities that scale with the size of the NPs (R) either as R(-2) or R(-3). These insights into the size-dependent dissipation mechanisms in nanoclusters should help in designing NPs-based structures with tailored thermomechanical and environmental stability and hence with an optimized morphological stability that guarantees their long-term functional properties.

  5. Grazing cessation changes quantity, quality and distribution of soil organic matter and (micro-)aggregates in a semiarid steppe ecosystem in Inner Mongolia

    NASA Astrophysics Data System (ADS)

    Steffens, M.; Wiesmeier, M.; Koelbl, A.; Kogel-Knabner, I.

    2012-12-01

    Grazing is one of the most important factors that may reduce soil organic carbon (SOC) stocks and subsequently deteriorate aggregate stability in grassland soils. Improvements to land use management, e.g. grazing reduction, are assumed to increase the carbon sequestration of steppe ecosystems which may act as one of the big global carbon sinks. The central aims of this study were to investigate the effects of grazing on semiarid steppe ecosystems and to evaluate the benefits and potentials of grazing management to mitigate the detrimental effects of grazing. Special emphasize was placed on changes in the amount, composition and turnover of soil organic matter (SOM) and its effects on soil structure and aggregation. We sampled 5 differently grazed plots (ungrazed since 1979 = Ug79, ungrazed since 1999 = Ug99, winter grazing = Wg, continuously grazed = Cg, heavily grazed = Hg) and a 7-year grazing experiment with regular orthogonal grids and representative soil pits in a semiarid steppe ecosystem in Inner Mongolia, China. Topsoil and vegetation samples from grids were analysed statistically and geostatistically. Differently sized grids allowed the exploration of scale effects. Pit samples were taken from three horizons and were analysed for aggregate stability and physically fractionated according to aggregate size, density and particle size. Statistical analyses showed that physical and chemical parameters of bulked steppe topsoils deteriorated significantly following heavy grazing, remained stable if grazing was reduced or excluded for five years and recovered significantly after 25 years of grazing exclusion. Spatial heterogeneity of topsoil properties increased with decreasing grazing intensity from a homogeneous to a patchy distribution. This is attributed to vegetation recovery/succession and deposition of windblown material in ungrazed areas. On the large scale (>50 m) spatial variability of topsoil and vegetation was controlled by topography or soil erosion

  6. Characterizing Single-Scattering Properties of Snow Aggregate Particles Integrated over Size Distributions in the Microwave Spectrum

    NASA Astrophysics Data System (ADS)

    Kuo, K.; Van Aartsen, B.; Haddad, Z. S.; Tanelli, S.; Skofronick Jackson, G.; Olson, W. S.

    2012-12-01

    Approximately 7000 snow aggregate particles have been synthesized, using a heuristic aggregation algorithm, from 9 realistic snowflake habits simulated using the now famous Snowfake ice crystal growth model. These particles exhibit mass-dimension relations consistent with those derived from observations. In addition, ranging from 0.1 to 3.5 mm in liquid-equivalent diameter, the sizes of these particle cover ranges wide enough for assemblies of realistic particle size distributions. The single-scattering properties, such as scattering/absorption/extinction/backscatter cross sections, single-scattering albedo, asymmetry factor, as well as the scattering matrix, are obtained for each aggregate particle using the discrete-dipole approximation (DDA) code DDSCAT at 13 microwave frequencies, ranging from 10 to 190 GHz. Preliminary radiative transfer calculations show that the single-scattering properties so obtained yield much more reasonable brightness temperatures than those derived from "fluffy sphere" Mie approximations. However, in order to achieve better retrievals involving these complex particles, we need to be able to characterize their single-scattering with only a few parameters. In this study, we present such an attempt using a pair of generalized effective radii, expressed as ratios of particle volume to particle surface area and to orientation-averaged particle cross section, in addition to mass content. It is shown that these effective radii are indeed effective in characterizing the PSD-integrated single-scattering properties of these complex particles. Pristine ice crystals simulated using the "Snowfake" ice crystal growth mode (3rd row from top) and example aggregates generated using the corresponding pristine particles (bottom 3 rows, i.e. 4th to 6th rows from top).

  7. Dynamics of soil GHG emissions shaped by hydration state, aggregate size distribution and carbon placement: Column experiments using artificial soil aggregates

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Ali; Or, Dani

    2017-04-01

    Dynamics of soil hydration affect microbial community dynamics and various biogeochemical processes (soil respiration, denitrification, methane production). Evidence suggests that anoxic conditions may persist in soil aggregates (long after bulk soil is aerated) thereby providing niches for anaerobic microbial communities (hot spots). Despite their recognized role in mediating soil biogeochemical fluxes, systematic studies of the impact of different environmental conditions on CO2, N2O and CH4 emissions from soil aggregates remain rare. We constructed artificial aggregates using a silt loam soil of different sizes and different carbon configurations (mixed, core, no addition) to study effects of hydration, aggregate size and carbon source configuration on GHG emissions. An assembly of aggregates of three sizes (18, 12, and 6 mm aggregates) was embedded in sand columns at four distinct layers (3 replicates for each aggregate-carbon source, 9 columns) and the water level was varied periodically to quantify effects of wetting/drying and submersion on GHG fluxes. Several gas samples were taken from the headspaces of each column (after closure) and analyzed using GC with the proper detectors to resolve fluxes. Results illustrate the critical role of hydration states on GHG emission, for example, lowering the water table (unsaturated conditions) decreases CH4 emissions while increasing N2O flux. We observe links between aerobic processes (e.g., nitrification) and anaerobic denitrification presumably by promoting alternative pathways (e.g., ammonia and nitrite oxidation). Methane production was activated under highly anoxic conditions (prolonged inundation). N2O production was highest form aggregates with carbon placed in the (anoxic) core whereas CO2 production rates were comparable from mixed and centered carbon sources (at rates that fluctuated with hydration conditions). Experimental results of artificial soil aggregates are of interest for improvement of physically

  8. The SAWO (Small And Well Organized) avatar teaches the importance of the aggregates on the soil system and how to determine their stability

    NASA Astrophysics Data System (ADS)

    Mataix-Solera, Jorge; Cerdà, Artemi; Jordán, Antonio; Úbeda, Xavier; Pereira, Paulo

    2015-04-01

    Soil structure is the key factor that determine the soil quality as control the organic matter turnnover, soil biology and soil erodibility (Cerdà, 1996; 1998; Wick et al., 2014; Gelaw, 2015). There is a need to understand better the factors and the processes that act on the soil aggregation and the dynamics of the soil aggregation, which will make easier to understand the soil system functioning (Jordán et al., 2011; Jordán et al., 2012; Pulido Moncada et al., 2013). Fire, mines, grazing and agricultura (Cerdà, 2000; Mataix Solera et al., 2011; Cerdà et al., 2012; Hallett et al., 2014; Lozano et al., 2013) determines how the soil structure is highly affected by the humankind. And this determines the sustainability of the land managements (García Orenes et al., 2012; K¨ropfl et al., 2013; Mekuria and Aynekulu, 2013; Taguas et al., 2013; Zhao et al., 2013). Aggregates are Small And Well Organized (SAWO) structures that allow the water to flow, the air fill the porous and the life to be diverse and abundant in the soil. The SAWO avatar will teach the importance of the functions and the services of the aggregates to students and other scientists, but also to any audience. This means that the experiments and the vocabulary to be used by SAWO will be very wide and rich. The Avatar SAWO will use different strategies and skills to teach the soil aggregation properties and characteristics. And also, how to measure. Easy to carry out experiments will be shown by SAWO to measure the aggregate stability in the field and in the laboratory, and the soil sampling in the field. The SAWO avatar will play a special attention to the impact of forest fires on aggregate stability changes and how to measure. The SAWO avatar will teach how to take samples in the field, how to transport and manage in the laboratory, and finally which measurements and test can be done to determine the aggregate stability. Acknowledgements To the "Ministerio de Economía and Competitividad" of

  9. N-Terminal Truncation of an Isolated Human IgG1 CH2 Domain Significantly Increases its Stability and Aggregation Resistance

    PubMed Central

    Gong, Rui; Wang, Yanping; Ying, Tianlei; Feng, Yang; Streaker, Emily; Prabakaran, Ponraj; Dimitrov, Dimiter S.

    2013-01-01

    Isolated human immunoglobulin G (IgG) CH2 domains are promising scaffolds for novel candidate therapeutics. Unlike other human IgG domains, CH2 is not involved in strong interchain interactions and isolated CH2 is relatively stable. However, isolated single CH2 is prone to aggregation. In native IgG and Fc molecules, the N-terminal residues of CH2 from the two heavy chains interact with each other and form hinge regions. By contrast, the N-terminal residues are highly disordered in isolated CH2. We have hypothesized that removal of the CH2 N-terminal residues may not only increase its stability but also its aggregation resistance. To test this hypothesis we constructed a shortened variant of IgG1 CH2 (CH2s) where the first seven residues of the N-terminus were deleted. We found that the thermal stability of CH2s was increased by 5°C compared to CH2. Importantly, we demonstrated that CH2s is significantly less prone to aggregation than CH2 as measured by Thioflavin T (ThT) fluorescence, turbidity and light scattering. We also found that the CH2s exhibited pH-dependent binding to a soluble single-chain human neonatal Fc receptor (shFcRn) which was significantly stronger than the very weak shFcRn binding to CH2 as measured by flow cytometry. Computer modeling suggested a possible mode of CH2 aggregation involving its N-terminal residues. Therefore, deletion of the N-terminal residues could increase drugability of CH2-based therapeutic candidates. This strategy to increase stability and aggregation resistance could also be applicable to other Ig-related proteins. PMID:23641816

  10. Distribution of Two C Cycle Enzymes in Soil Aggregates of a Prairie Chronosequence

    SciTech Connect

    Fansler, Sarah J.; Smith, Jeffery L.; Bolton, Harvey; Bailey, Vanessa L.

    2005-11-01

    Recently attention has focused on the potential of using soil as a sink for atmospheric CO2. The objective of this study was to use soil enzymes and classical methods of soil aggregate fractionation to explore the relationship between microbial community function and soil structure of a tallgrass prairie chronosequence. The soils within the chronosequence were: (1) remnant native prairie, (2) agricultural soil, and (3, 4) tallgrass prairies restored from agriculture in 1979 and 1993. β-glucosidase (E.C. 3.2.1.21) and N-acetyl-β-glucosaminidase (NAGase, EC 3.2.1.30) assays were conducted on four different aggregate size fractions (>2 mm, 1 -2 mm, 250µm-1 mm, and 2 - 250 µm) from each soil. Specific activities for both enzymes (µg PNP g-1 soil h-1) were greatest in the microaggregate (2 µm -250 µm) fractions across the chronosequence; however, this size fraction makes up only a small proportion of the whole soil. Therefore, it is the larger macroaggregate-derived enzyme activities that have the greatest impact on the activity of the whole soil. Analyzing both enzymes and the physical structure, a reversion from an agricultural soil through the restored to more like the prairie soil, was not detected. It appears that the function of these microbial community systems in the native tallgrass prairie and agricultural soils of the chronosequence are in equilibria while the lands restored to tallgrass prairie are in an ongoing state of recovery.

  11. Measurement of particle size distribution of soil and selected aggregate sizes using the hydrometer method and laser diffractometry

    NASA Astrophysics Data System (ADS)

    Guzmán, G.; Gómez, J. A.; Giráldez, J. V.

    2010-05-01

    Soil particle size distribution has been traditionally determined by the hydrometer or the sieve-pipette methods, both of them time consuming and requiring a relatively large soil sample. This might be a limitation in situations, such as for instance analysis of suspended sediment, when the sample is small. A possible alternative to these methods are the optical techniques such as laser diffractometry. However the literature indicates that the use of this technique as an alternative to traditional methods is still limited, because the difficulty in replicating the results obtained with the standard methods. In this study we present the percentages of soil grain size determined using laser diffractometry within ranges set between 0.04 - 2000 μm. A Beckman-Coulter ® LS-230 with a 750 nm laser beam and software version 3.2 in five soils, representative of southern Spain: Alameda, Benacazón, Conchuela, Lanjarón and Pedrera. In three of the studied soils (Alameda, Benacazón and Conchuela) the particle size distribution of each aggregate size class was also determined. Aggregate size classes were obtained by dry sieve analysis using a Retsch AS 200 basic ®. Two hundred grams of air dried soil were sieved during 150 s, at amplitude 2 mm, getting nine different sizes between 2000 μm and 10 μm. Analyses were performed by triplicate. The soil sample preparation was also adapted to our conditions. A small amount each soil sample (less than 1 g) was transferred to the fluid module full of running water and disaggregated by ultrasonication at energy level 4 and 80 ml of sodium hexametaphosphate solution during 580 seconds. Two replicates of each sample were performed. Each measurement was made for a 90 second reading at a pump speed of 62. After the laser diffractometry analysis, each soil and its aggregate classes were processed calibrating its own optical model fitting the optical parameters that mainly depends on the color and the shape of the analyzed particle. As a

  12. Projecting the Effects of 21st Century Climate Change on the Distribution and Phenology of Reef Fish Spawning Aggregations

    NASA Astrophysics Data System (ADS)

    Asch, R. G.; Erisman, B.

    2016-02-01

    Spawning fishes often have a narrower window of thermal tolerance than other life history stages. As a result, spawning has been hypothesized to constrain how species will respond to climate change. We assess this hypothesis by combining a global database of fish spawning aggregations with earth system and ecological niche models to project shifts in the spawning distribution and phenology of reef fishes under the RCP 8.5 climate change scenario. Nassau grouper (Epinephelus striatus) was selected as the species for a proof-of-concept analysis since it is a top predator on Caribbean coral reefs and is listed by IUCN as endangered due to overfishing at its spawning grounds. The highest probability of encountering E. striatus aggregations occurred at sea surface temperatures (SSTs) of 24.5-26.5° C and seasonal SST gradients of 0 to -1° C. Based on a 1981-2000 climatology, our model projected that the highest probability of spawning would occur around Cuba, the Mesoamerican barrier reef, the Bahamas, and other areas of the Caribbean. This coincides with the observed distribution of E. striatus aggregations. By 2081-2100, a 50% decline is projected in the number of months and locations with adequate conditions for E. striatus spawning. Potential spawning habitat for E. striatus shifts northward and eastward, with slight increases in the probability of spawning around Aruba, Curacao, and Bonaire. At spawning sites, primary production is projected to increase by a mean of 14%. Higher planktonic production could benefit larval fish growth and survival by providing a greater availability of prey. The E. striatus spawning season is projected to contract and occur later in the year. Two-month delays in phenology are projected at 78% of the sites where E. striatus populations are managed through spawning season sales bans and time/area fishing closures. This implies that adaptive management in response to climate change will be needed for these measures to remain effective.

  13. Statistical distributions for monthly aggregations of precipitation and streamflow in drought indicator applications

    NASA Astrophysics Data System (ADS)

    Svensson, Cecilia; Hannaford, Jamie; Prosdocimi, Ilaria

    2017-02-01

    Drought indicators are used as triggers for action and so are the foundation of drought monitoring and early warning. The computation of drought indicators like the standardized precipitation index (SPI) and standardized streamflow index (SSI) require a statistical probability distribution to be fitted to the observed data. Both precipitation and streamflow have a lower bound at zero, and their empirical distributions tend to have positive skewness. For deriving the SPI, the Gamma distribution has therefore often been a natural choice. The concept of the SSI is newer and there is no consensus regarding distribution. In the present study, twelve different probability distributions are fitted to streamflow and catchment average precipitation for four durations (1, 3, 6, and 12 months), for 121 catchments throughout the UK. The more flexible three- and four-parameter distributions generally do not have a lower bound at zero, and hence may attach some probability to values below zero. As a result, there is a censoring of the possible values of the calculated SPIs and SSIs. This can be avoided by using one of the bounded distributions, such as the reasonably flexible three-parameter Tweedie distribution, which has a lower bound (and potentially mass) at zero. The Tweedie distribution has only recently been applied to precipitation data, and only for a few sites. We find it fits both precipitation and streamflow data nearly as well as the best of the traditionally used three-parameter distributions, and should improve the accuracy of drought indices used for monitoring and early warning.

  14. An aggregate analysis of personal care products in the environment: Identifying the distribution of environmentally-relevant concentrations.

    PubMed

    Hopkins, Zachary R; Blaney, Lee

    2016-01-01

    Over the past 3-4 decades, per capita consumption of personal care products (PCPs) has steadily risen, resulting in increased discharge of the active and inactive ingredients present in these products into wastewater collection systems. PCPs comprise a long list of compounds employed in toothpaste, sunscreen, lotions, soaps, body washes, and insect repellants, among others. While comprehensive toxicological studies are not yet available, an increasing body of literature has shown that PCPs of all classes can impact aquatic wildlife, bacteria, and/or mammalian cells at low concentrations. Ongoing research efforts have identified PCPs in a variety of environmental compartments, including raw wastewater, wastewater effluent, surface water, wastewater solids, sediment, groundwater, and drinking water. Here, an aggregate analysis of over 5000 reported detections was conducted to better understand the distribution of environmentally-relevant PCP concentrations in, and between, these compartments. The distributions were used to identify whether aggregated environmentally-relevant concentration ranges intersected with available toxicity data. For raw wastewater, wastewater effluent, and surface water, a clear overlap was present between the 25th-75th percentiles and identified toxicity levels. This analysis suggests that improved wastewater treatment of antimicrobials, UV filters, and polycyclic musks is required to prevent negative impacts on aquatic species. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Detangling the Effects of Environmental Filtering and Dispersal Limitation on Aggregated Distributions of Tree and Shrub Species: Life Stage Matters

    PubMed Central

    Liu, He-Ming; Wang, Zhang-Hua; Ma, Zun-Ping; Fang, Xiao-Feng; Zhang, Jian; Wang, Xi-Hua

    2016-01-01

    The pervasive pattern of aggregated tree distributions in natural communities is commonly explained by the joint effect of two clustering processes: environmental filtering and dispersal limitation, yet little consensus remains on the relative importance of the two clustering processes on tree aggregations. Different life stages of examined species were thought to be one possible explanation of this disagreement, because the effect of environmental filtering and dispersal limitation are expected to increase and decrease with tree life stages, respectively. However, few studies have explicitly tested these expectations. In this study, we evaluated these expectations by three different methods (species-habitat association test based on Poisson Clustering model and spatial point pattern analyses based on Heterogeneous Poisson model and the jointly modeling approach) using 36 species in a 20-ha subtropical forest plot. Our results showed that the percentage of species with significant habitat association increased with life stages, and there were fewer species affected by dispersal limitation in later life stages compared with those in earlier stages. Percentage of variance explained by the environmental filtering and dispersal limitation also increases and decreases with life stages. These results provided a promising alternative explanation on the existing mixed results about the relative importance of the two clustering processes. These findings also highlighted the importance of plant life stages for fully understanding species distributions and species coexistence. PMID:27227538

  16. Tillage and liming effects on aggregate distribution and associated carbon and nitrogen in acid soils of SW Spain

    NASA Astrophysics Data System (ADS)

    Gómez-Paccard, Clara; Zabaleta, Javier; Benito, Marta; León, Paloma; Mariscal-Sancho, Ignacio; Espejo, Rafael; Hontoria, Chiquinquirá

    2013-04-01

    Beneficial effects of conservation tillage are well known on a wide variety of environmental aspects. The lack of ploughing in no till systems conserves soil structure, enhances the accumulation of organic carbon in the surface layer and promotes the development of soil microorganisms. On the other hand, liming is a common practice in acid soils. Lime raises the pH, reduces Al toxicity enhancing root development, but controversial results have been found about the effects of liming on soil structure. Ultisols from SW of Spain present severe chemical constraints as poor nutrient availability and high Al contents in the exchange complex. On the other hand, traditional practices as conventional tillage led to a dramatic decrease on soil organic carbon and a degraded soil structure. No till plus liming might be recommendable to achieve a sustainable and productive agriculture in these particular soils, but little is known about the effect of these practices on soil structure when applied together. The aim of this study was to evaluate the effect of traditional tillage (TT) versus no tillage (NT), and liming versus no liming on aggregate size distribution and associated carbon and nitrogen. The study was conducted on a Plinthic Palexerult (Soil Survey Staff, 1999) in the Cañamero's Raña (SW Spain) under Mediterranean climate (mean annual temperature: 15.0° C; mean annual precipitation: 869 mm). The experimental design was a split-plot with four replications. The main factor was tillage (no till versus traditional till) while the second was the inclusion or not of Ca-amendment (sugar foam plus red gypsum). Samples were collected in 2011 after six years of treatment at a 0-5, 5-10 and 10-25 cm depths. The aggregate distribution was determined by wet sieving method to separate four aggregate size classes: (i) >2000 µm (large macroaggregates), (ii) 250-2000 µm (small macroaggregates), (iii) 53-250 µm (microaggregates), (iv) <53 µm (silt and clay fraction). Soil

  17. Nonspecific shielding of unfavorable electrostatic intramolecular interactions in the erythropoietin native-state increase conformational stability and limit non-native aggregation

    PubMed Central

    Banks, Douglas D

    2015-01-01

    Previous equilibrium and kinetic folding studies of the glycoprotein erythropoietin indicate that sodium chloride increases the conformational stability of this therapeutically important cytokine, ostensibly by stabilizing the native-state [Banks DD, (2011) The Effect of Glycosylation on the Folding Kinetics of Erythropoietin. J Mol Biol 412:536–550]. The focus of the current report is to determine the underlying cause of the salt dependent increase in erythropoietin conformational stability and to understand if it has any impact on aggregation, an instability that remains a challenge to the biotech industry in maintaining the efficacy and shelf-life of protein therapeutics. Isothermal urea denaturation experiments conducted at numerous temperatures in the absence and presence of sodium chloride indicated that salt stabilizes erythropoietin primarily by increasing the difference in enthalpy between the native and unfolded sates. This result, and the finding that the salt induced increases in erythropoietin melting temperatures were independent of the identity of the salt cation and anion, indicates that salt likely increases the conformational stability of erythropoietin at neutral pH by nonspecific shielding of unfavorable electrostatic interaction(s) in the native-state. The addition of salt (even low concentrations of the strong chaotrope salt guanidinium hydrochloride) also exponentially decreased the initial rate of soluble erythropoietin non-native aggregation at 37 °C storage. PMID:25628168

  18. Geotechnical Characteristics and Stability Analysis of Rock-Soil Aggregate Slope at the Gushui Hydropower Station, Southwest China

    PubMed Central

    Shi, Chong; Xu, Fu-gang

    2013-01-01

    Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope. PMID:24082854

  19. Geotechnical characteristics and stability analysis of rock-soil aggregate slope at the Gushui Hydropower Station, southwest China.

    PubMed

    Zhou, Jia-wen; Shi, Chong; Xu, Fu-gang

    2013-01-01

    Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope.

  20. Changes in carbon stability and microbial activity in size fractions of micro-aggregates in a rice soil chronosequence under long term rice cultivation

    NASA Astrophysics Data System (ADS)

    Pan, Genxing; Liu, Yalong; Wang, Ping; Li, Lianqinfg; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Bian, Rongjun; Ding, Yuanjun; Ma, Chong

    2016-04-01

    Recent studies have shown soil carbon sequestration through physical protection of relative labile carbon intra micro-aggregates with formation of large sized macro-aggregates under good management of soil and agricultural systems. While carbon stabilization had been increasingly concerned as ecosystem properties, the mechanisms underspin bioactivity of soil carbon with increased carbon stability has been still poorly understood. In this study, topsoil samples were collected from rice soils derived from salt marsh under different length of rice cultivation up to 700 years from eastern China. Particle size fractions (PSF) of soil aggregates were separated using a low energy dispersion protocol. Carbon fractions in the PSFs were analyzed either with FTIR spectroscopy. Soil microbial community of bacterial, fungal and archaeal were analyzed with molecular fingerprinting using specific gene primers. Soil respiration and carbon gain from amended maize as well as enzyme activities were measured using lab incubation protocols. While the PSFs were dominated by the fine sand (200-20μm) and silt fraction (20-2μm), the mass proportion both of sand (2000-200μm) and clay (<2μm) fraction increased with prolonged rice cultivation, giving rise to an increasing trend of mean weight diameter of soil aggregates (also referred to aggregate stability). Soil organic carbon was found most enriched in coarse sand fraction (40-60g/kg), followed by the clay fraction (20-24.5g/kg), but depleted in the silt fraction (~10g/kg). Phenolic and aromatic carbon as recalcitrant pool were high (33-40% of total SOC) in both coarse sand and clay fractions than in both fine sand and silt fractions (20-29% of total SOC). However, the ratio of LOC/total SOC showed a weak decreasing trend with decreasing size of the aggregate fractions. Total gene content in the size fractions followed a similar trend to that of SOC. Bacterial and archaeal gene abundance was concentrated in both sand and clay fractions

  1. Aggregation and Push-Based Distribution of THREDDS Catalogs in Operational Information Systems

    NASA Astrophysics Data System (ADS)

    Manzella, G. M.; Mazzetti, P.; Nativi, S.; Bigagli, L.; Pecci, L.

    2006-12-01

    We present a solution for the implementation of a catalog service in the context of an European infrastructure; this has the strategic objective of providing an integrated service for global and regional ocean resources to intermediate users and policy makers. The current European information systems (e.g. MERSEA Marine Environment and Security for the European Area, MOON Mediterranean Operational Oceanography Network and SeaDataNet PanEuropean infrastructure for Ocean and marine data management) are characterized by a three-level hierarchy. At the bottom level we find the regional and local data sources, providing observation data and model outputs. At the intermediate level, the operational projects have Thematic Portals (TEP's) aggregating the information on logical basis, e.g. Observation data portals (In situ and Satellite), Forcing (meteorological portal), Modelling/forecasting portals. At the top level, the Information Management Portal provides query services and links to TEP's. Currently, several architectural and technological general solutions are available for implementing catalog services, for typical use-cases in the context of geospatial information systems. However, if we consider Operational Oceanography a particular case, characterised by tighter non-functional characteristics -such as seamless integration with other services, responsiveness, etc.- we must conceive a tailored architectural solution. In the particular cases of operational projects, the hierarchical structure of the information system can be considered near-static and the needed scalability in terms of data sources is small; thus, a simpler solution based on datasets aggregation can be suitable and profitable. In such a schema, upper level catalogs are built merging lower-level catalogs. On the other hand, to adopt this approach, it is necessary that any update is notified to the upper-level catalogs, whenever a lower level catalog is modified. Hence, our solution implemented a push

  2. Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol.

    PubMed

    Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

    2017-01-01

    Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate-associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical-stable aggregates (MSAs) formation and stability as well as MSAs-associated C/N concentration and storage were observed in different aggregate sizes (>5, 5-2, 2-1, 1.0-0.5, 0.50-0.25 and <0.25 mm). The proportion of MSAs >5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0-0.5 mm, MSAs 0.50-0.25 mm and MSAs <0.25 mm significantly decreased. Both mean weight diameter and geometric mean diameter were highest in T5, which improved soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72-82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs <0.25 mm and TN in MSAs 2-1 mm were independent variables affecting SOC and TN concentrations in bulk soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco-friendly way to improve soil quality in an Ultisol.

  3. Molecular chaperones and stress-inducible protein-sorting factors coordinate the spatiotemporal distribution of protein aggregates

    PubMed Central

    Malinovska, Liliana; Kroschwald, Sonja; Munder, Matthias C.; Richter, Doris; Alberti, Simon

    2012-01-01

    Acute stress causes a rapid redistribution of protein quality control components and aggregation-prone proteins to diverse subcellular compartments. How these remarkable changes come about is not well understood. Using a phenotypic reporter for a synthetic yeast prion, we identified two protein-sorting factors of the Hook family, termed Btn2 and Cur1, as key regulators of spatial protein quality control in Saccharomyces cerevisiae. Btn2 and Cur1 are undetectable under normal growth conditions but accumulate in stressed cells due to increased gene expression and reduced proteasomal turnover. Newly synthesized Btn2 can associate with the small heat shock protein Hsp42 to promote the sorting of misfolded proteins to a peripheral protein deposition site. Alternatively, Btn2 can bind to the chaperone Sis1 to facilitate the targeting of misfolded proteins to a juxtanuclear compartment. Protein redistribution by Btn2 is accompanied by a gradual depletion of Sis1 from the cytosol, which is mediated by the sorting factor Cur1. On the basis of these findings, we propose a dynamic model that explains the subcellular distribution of misfolded proteins as a function of the cytosolic concentrations of molecular chaperones and protein-sorting factors. Our model suggests that protein aggregation is not a haphazard process but rather an orchestrated cellular response that adjusts the flux of misfolded proteins to the capacities of the protein quality control system. PMID:22718905

  4. Molecular chaperones and stress-inducible protein-sorting factors coordinate the spatiotemporal distribution of protein aggregates.

    PubMed

    Malinovska, Liliana; Kroschwald, Sonja; Munder, Matthias C; Richter, Doris; Alberti, Simon

    2012-08-01

    Acute stress causes a rapid redistribution of protein quality control components and aggregation-prone proteins to diverse subcellular compartments. How these remarkable changes come about is not well understood. Using a phenotypic reporter for a synthetic yeast prion, we identified two protein-sorting factors of the Hook family, termed Btn2 and Cur1, as key regulators of spatial protein quality control in Saccharomyces cerevisiae. Btn2 and Cur1 are undetectable under normal growth conditions but accumulate in stressed cells due to increased gene expression and reduced proteasomal turnover. Newly synthesized Btn2 can associate with the small heat shock protein Hsp42 to promote the sorting of misfolded proteins to a peripheral protein deposition site. Alternatively, Btn2 can bind to the chaperone Sis1 to facilitate the targeting of misfolded proteins to a juxtanuclear compartment. Protein redistribution by Btn2 is accompanied by a gradual depletion of Sis1 from the cytosol, which is mediated by the sorting factor Cur1. On the basis of these findings, we propose a dynamic model that explains the subcellular distribution of misfolded proteins as a function of the cytosolic concentrations of molecular chaperones and protein-sorting factors. Our model suggests that protein aggregation is not a haphazard process but rather an orchestrated cellular response that adjusts the flux of misfolded proteins to the capacities of the protein quality control system.

  5. Optimal exploitation of spatially distributed trophic resources and population stability

    USGS Publications Warehouse

    Basset, A.; Fedele, M.; DeAngelis, D.L.

    2002-01-01

    The relationships between optimal foraging of individuals and population stability are addressed by testing, with a spatially explicit model, the effect of patch departure behaviour on individual energetics and population stability. A factorial experimental design was used to analyse the relevance of the behavioural factor in relation to three factors that are known to affect individual energetics; i.e. resource growth rate (RGR), assimilation efficiency (AE), and body size of individuals. The factorial combination of these factors produced 432 cases, and 1000 replicate simulations were run for each case. Net energy intake rates of the modelled consumers increased with increasing RGR, consumer AE, and consumer body size, as expected. Moreover, through their patch departure behaviour, by selecting the resource level at which they departed from the patch, individuals managed to substantially increase their net energy intake rates. Population stability was also affected by the behavioural factors and by the other factors, but with highly non-linear responses. Whenever resources were limiting for the consumers because of low RGR, large individual body size or low AE, population density at the equilibrium was directly related to the patch departure behaviour; on the other hand, optimal patch departure behaviour, which maximised the net energy intake at the individual level, had a negative influence on population stability whenever resource availability was high for the consumers. The consumer growth rate (r) and numerical dynamics, as well as the spatial and temporal fluctuations of resource density, which were the proximate causes of population stability or instability, were affected by the behavioural factor as strongly or even more strongly than by the others factors considered here. Therefore, patch departure behaviour can act as a feedback control of individual energetics, allowing consumers to optimise a potential trade-off between short-term individual fitness

  6. Estimation of air void and aggregate spatial distributions in concrete under uniaxial compression using computer tomography scanning

    SciTech Connect

    Wong, R.C.K. . E-mail: rckwong@ucalgary.ca; Chau, K.T.

    2005-08-01

    Normal- and high-strength concrete cylinders (designed compressive strengths of 30 and 90 MPa at 28 days) were loaded uniaxially. Computer tomography (CT) scanning technique was used to examine the evolution of air voids inside the specimens at various loading states up to 85% of the ultimate compressive strength. The normal-strength concrete yielded a very different behaviour in changes of internal microstructure as compared to the high-strength concrete. There were significant instances of nucleation and growth in air voids in the normal-strength concrete specimen, while the increase in air voids in the high-strength concrete specimen was insignificant. In addition, CT images were used for mapping the aggregate spatial distributions within the specimens. No intrinsic anisotropy was detected from the fabric analysis.

  7. Influence of the Guest on Aggregation of the Host by Exciton-Polaron Interactions and Its Effects on the Stability of Phosphorescent Organic Light-Emitting Devices.

    PubMed

    Zhang, Yingjie; Aziz, Hany

    2016-06-08

    The root causes of the differences in electroluminescence stability among phosphorescent organic light-emitting devices (PHOLEDs) utilizing different emitter guests are studied. The results show that the host material plays a more influential role in limiting device stability in comparison to the guest. During the operation of a PHOLED, the host undergoes aggregation as a result of interactions between the excitons and positive polarons. The rate of this aggregation is found to be the limiting factor for device lifetime and is influenced by the choice of the guest material and its concentration. Finally, it is shown that phase segregation between the host and the guest is an important aspect of the aggregation process. As a result of this segregation, energy transfer from the host to the guest becomes increasingly less efficient, resulting in the observed gradual loss in electroluminescence efficiency in the devices over time. The findings explain why PHOLEDs utilizing different guest materials but otherwise identical material systems can have significantly different lifetimes and provide an answer to a long-lasting question in the field.

  8. Supramolecular Low-Molecular-Weight Hydrogelator Stabilization of SERS-Active Aggregated Nanoparticles for Solution and Gas Sensing.

    PubMed

    Canrinus, Tjalling R; Lee, Wendy W Y; Feringa, Ben L; Bell, Steven E J; Browne, Wesley R

    2017-09-05

    The potential of surface-enhanced Raman scattering (SERS) spectroscopy in both laboratory and field analyses depends on the reliable formation of so-called SERS hot spots, such as those formed during gold or silver nanoparticle aggregation. Unfortunately such aggregates are not stable in solution because they typically grow until they precipitate. Here we describe the use of low-molecular-weight hydrogels formed through pH-triggered self-assembly that occurs at a rate that well matches the rates of aggregation of Au or Ag colloids, allowing them to be trapped at the SERS-active point in the aggregation process. We show that the colloid-containing gels give SERS signals similar to the parent colloid but are stable over several months. Moreover, lyophilized gels can be stored as dry powders for subsequent use in the analyses of gases and dissolved analytes by contact with either solutions or vapors. The present system shows how the combination of pH-switchable low-molecular-weight gelators and pH-induced colloid aggregation can be combined to make a highly stable, low-cost SERS platform for the detection of volatile organic compounds and the microvolume analysis of solutions.

  9. Distributive Effects of Forest Service Attempts to Maintain Community Stability

    Treesearch

    Steven E. Daniels; William F. Hyde; David N. Wear

    1991-01-01

    Community stability is an objective of USDA Forest Service timber sales. This paper examines that objective, and the success the Forest Service can have in attaining it, through its intended maintenance of a constant volume timber harvest schedule. We apply a three-factor, two-sector modified general equilibrium model with empirical evidence from the timber-based...

  10. Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol

    PubMed Central

    Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

    2017-01-01

    Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate—associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical—stable aggregates (MSAs) formation and stability as well as MSAs—associated C/N concentration and storage were observed in different aggregate sizes (>5, 5–2, 2–1, 1.0–0.5, 0.50–0.25 and <0.25 mm). The proportion of MSAs >5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0–0.5 mm, MSAs 0.50–0.25 mm and MSAs <0.25 mm significantly decreased. Both mean weight diameter and geometric mean diameter were highest in T5, which improved soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72–82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs <0.25 mm and TN in MSAs 2–1 mm were independent variables affecting SOC and TN concentrations in bulk soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco—friendly way to improve soil quality in an Ultisol. PMID:28125647

  11. Cross-linked enzyme aggregates (CLEAs) of Pencilluim notatum lipase enzyme with improved activity, stability and reusability characteristics.

    PubMed

    Rehman, Saima; Bhatti, Haq Nawaz; Bilal, Muhammad; Asgher, Muhammad

    2016-10-01

    Cross-linked enzyme aggregates (CLEAs) are considered as an effective tool for the immobilization of enzyme. In this study, Pencillium notatum lipase (PNL) was immobilized as carrier free cross-linked enzyme aggregates using glutaraldehyde (GLA) and Ethylene glycol-bis [succinic acid N-hydroxysuccinimide] (EG-NHS) as cross-linking agents. The optimal conditions for the synthesis of an efficient lipase CLEAs such as precipitant type, the nature and amount of cross-linking reagent, and cross-linking time were optimized. The recovered activities of CLEAs were considerably dependent on the concentration of GLA; however, the activity recovery was not severely affected by EG-NHS as a mild cross-linker. The EG-NHS aggregates displayed superior hydrolytic (52.08±2.52%) and esterification (64.42%) activities as compared to GLA aggregates which showed 23.8±1.86 and 34.54% of hydrolytic and esterification activity, respectively. Morphological analysis by fluorescence and scanning electron microscope revealed that EG-NHS aggregates were smaller in size with larger surface area compared to GLA aggregates. The pH optima of both types of CLEAs were displaced to slightly alkaline region and higher temperature as compared to native enzyme. Highest enzyme activity of CLEAs was achieved at the pH of 9.0 and 42°C temperature. Moreover, a significant improvement in the thermal resistance was also recorded after immobilization. After ten reusability cycles in aqueous medium, GLA and EG-NHS cross-linked lipase CLEAs preserved 63.62% and 70.9% of their original activities, respectively. The results suggest that this novel CLEA-lipase is potentially usable in many industrial applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. Understanding the stabilization of liquid-phase-exfoliated graphene in polar solvents: molecular dynamics simulations and kinetic theory of colloid aggregation.

    PubMed

    Shih, Chih-Jen; Lin, Shangchao; Strano, Michael S; Blankschtein, Daniel

    2010-10-20

    Understanding the solution-phase dispersion of pristine, unfunctionalized graphene is important for the production of conducting inks and top-down approaches to electronics. This process can also be used as a higher-quality alternative to chemical vapor deposition. We have developed a theoretical framework that utilizes molecular dynamics simulations and the kinetic theory of colloid aggregation to elucidate the mechanism of stabilization of liquid-phase-exfoliated graphene sheets in N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), and water. By calculating the potential of mean force between two solvated graphene sheets using molecular dynamics (MD) simulations, we have found that the dominant barrier hindering the aggregation of graphene is the last layer of confined solvent molecules between the graphene sheets, which results from the strong affinity of the solvent molecules for graphene. The origin of the energy barrier responsible for repelling the sheets is the steric repulsions between solvent molecules and graphene before the desorption of the confined single layer of solvent. We have formulated a kinetic theory of colloid aggregation to model the aggregation of graphene sheets in the liquid phase in order to predict the stability using the potential of mean force. With only one adjustable parameter, the average collision area, which can be estimated from experimental data, our theory can describe the experimentally observed degradation of the single-layer graphene fraction in NMP. We have used these results to rank the potential solvents according to their ability to disperse pristine, unfunctionalized graphene as follows: NMP ≈ DMSO > DMF > GBL > H(2)O. This is consistent with the widespread use of the first three solvents for this purpose.

  13. Distribution and Ecology of Cytotypes of the Aster amellus Aggregates in the Czech Republic

    PubMed Central

    MANDÁKOVÁ, TEREZIE; MÜNZBERGOVÁ, ZUZANA

    2006-01-01

    • Background and Aims Polyploidy is viewed as an important mechanism of sympatric speciation, but only a few studies have documented patterns of distribution and ecology of different cytotypes in their contact zone. Aster amellus agg. (Asteraceae) is one of the species with documented multiple ploidy levels. The aim of this study was to determine spatial distribution and ecology of two cytotypes, diploid (2n = 18) and hexaploid (2n = 54), of Aster amellus agg. at their contact zone in the Czech Republic. • Methods Root-tip squashes and flow cytometry were used to determine the ploidy of 2175 individuals from 87 populations. To test whether some differences in ecology between the two ploidy levels exist, in each locality relevés were recorded and abiotic conditions of the sites were studied by estimating potential direct solar radiation, Ellenberg indicator values and above-ground biomass. • Key Results Together with diploid and hexaploids, minorite cytotypes (triploid, pentaploid and nonaploid) were found. No significant ecological differences between diploid and hexaploid cytotypes were found. In spite of this, no population consisting of both of the two basic cytotypes was found. • Conclusions The results of this study show that the contact zone of diploid and hexaploid cytotypes in the Czech Republic is much more diffuse than indicated in previous records. Although populations of both cytotypes occur in close proximity (the closest populations of different cytotypes were 500 m apart), each individual population consists of only one basic ploidy level. This was unexpected since there are no clear differences in abiotic conditions between populations. Taken together with the absence of an intermediate tetraploid cytotype and with reference to published world distributional patterns of different ploidy levels, this suggests a secondary contact zone. Detailed genetic study is, however, necessary to confirm this. PMID:16870643

  14. Distribution and ecology of cytotypes of the Aster amellus aggregates in the Czech Republic.

    PubMed

    Mandáková, Terezie; Münzbergová, Zuzana

    2006-10-01

    Polyploidy is viewed as an important mechanism of sympatric speciation, but only a few studies have documented patterns of distribution and ecology of different cytotypes in their contact zone. Aster amellus agg. (Asteraceae) is one of the species with documented multiple ploidy levels. The aim of this study was to determine spatial distribution and ecology of two cytotypes, diploid (2n = 18) and hexaploid (2n = 54), of Aster amellus agg. at their contact zone in the Czech Republic. Root-tip squashes and flow cytometry were used to determine the ploidy of 2175 individuals from 87 populations. To test whether some differences in ecology between the two ploidy levels exist, in each locality relevés were recorded and abiotic conditions of the sites were studied by estimating potential direct solar radiation, Ellenberg indicator values and above-ground biomass. Together with diploid and hexaploids, minorite cytotypes (triploid, pentaploid and nonaploid) were found. No significant ecological differences between diploid and hexaploid cytotypes were found. In spite of this, no population consisting of both of the two basic cytotypes was found. The results of this study show that the contact zone of diploid and hexaploid cytotypes in the Czech Republic is much more diffuse than indicated in previous records. Although populations of both cytotypes occur in close proximity (the closest populations of different cytotypes were 500 m apart), each individual population consists of only one basic ploidy level. This was unexpected since there are no clear differences in abiotic conditions between populations. Taken together with the absence of an intermediate tetraploid cytotype and with reference to published world distributional patterns of different ploidy levels, this suggests a secondary contact zone. Detailed genetic study is, however, necessary to confirm this.

  15. Stability analysis of linear fractional differential system with distributed delays

    NASA Astrophysics Data System (ADS)

    Veselinova, Magdalena; Kiskinov, Hristo; Zahariev, Andrey

    2015-11-01

    In the present work we study the Cauchy problem for linear incommensurate fractional differential system with distributed delays. For the autonomous case with distributed delays with derivatives in Riemann-Liouville or Caputo sense, we establish sufficient conditions under which the zero solution is globally asymptotic stable. The established conditions coincide with the conditions which guaranty the same result in the particular case of system with constant delays and for the case of system without delays in the commensurate case too.

  16. Biophysical Characterization of Met-G-CSF: Effects of Different Site-Specific Mono-Pegylations on Protein Stability and Aggregation

    PubMed Central

    Natalello, Antonino; Ami, Diletta; Collini, Maddalena; D’Alfonso, Laura; Chirico, Giuseppe; Tonon, Giancarlo; Scaramuzza, Silvia; Schrepfer, Rodolfo; Doglia, Silvia Maria

    2012-01-01

    The limited stability of proteins in vitro and in vivo reduces their conversion into effective biopharmaceuticals. To overcome this problem several strategies can be exploited, as the conjugation of the protein of interest with polyethylene glycol, in most cases, improves its stability and pharmacokinetics. In this work, we report a biophysical characterization of the non-pegylated and of two different site-specific mono-pegylated forms of recombinant human methionyl-granulocyte colony stimulating factor (Met-G-CSF), a protein used in chemotherapy and bone marrow transplantation. In particular, we found that the two mono-pegylations of Met-G-CSF at the N-terminal methionine and at glutamine 135 increase the protein thermal stability, reduce the aggregation propensity, preventing also protein precipitation, as revealed by circular dichroism (CD), Fourier transform infrared (FTIR), intrinsic fluorescence spectroscopies and dynamic light scattering (DLS). Interestingly, the two pegylation strategies were found to drastically reduce the polydispersity of Met-G-CSF, when incubated under conditions favouring protein aggregation, as indicated by DLS measurements. Our in vitro results are in agreement with preclinical studies, underlining that preliminary biophysical analyses, performed in the early stages of the development of new biopharmaceutical variants, might offer a useful tool for the identification of protein variants with improved therapeutic values. PMID:22905140

  17. Rhamnolipid biosurfactant and soy protein act as effective stabilizers in the aggregation and transport of palladium-doped zerovalent iron nanoparticles in saturated porous media.

    PubMed

    Basnet, Mohan; Ghoshal, Subhasis; Tufenkji, Nathalie

    2013-01-01

    Palladium-doped nanosized zerovalent iron (Pd-NZVI) particles can contribute to the transformation of chlorinated solvents and various other contaminants into innocuous products. To make Pd-NZVI an effective in situ subsurface remediation agent, these particles need to migrate through a targeted contaminated area. However, previous studies have reported very limited mobility of these particles in the groundwater environment and attributed it to rapid aggregation and subsequent pore plugging. In this study, we systematically investigated the influence of selected natural and nontoxic organic macromolecules (carboxymethyl cellulose, rhamnolipid biosurfactants, and soy protein) on the aggregation and transport behavior of bare and coated Pd-NZVI. Aggregation behavior was investigated using dynamic light scattering by monitoring the evolution of hydrodynamic diameter as a function of time, whereas transport behavior was investigated by conducting water-saturated sand-packed column experiments. While bare Pd-NZVI is prone to rapid aggregation, we observed good colloidal stability and concurrent enhanced transport of Pd-NZVI coated with carboxymethyl cellulose, rhamnolipid biosurfactants, and soy protein. Each surface modifier performed well at lower ionic strength (IS) (10 mM NaHCO3), and one of the rhamnolipid surface modifiers (JBR215) significantly enhanced transport of 150 mg/L Pd-NZVI at concentrations as low as 10 mg/L total organic carbon. However, an increase in the solution IS induced significant Pd-NZVI aggregation with a simultaneous decrease in the transport potential in accordance with the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory of colloidal stability. Nonetheless, at the highest IS (300 mM NaHCO3) investigated, the mobility of rhamnolipid-coated Pd-NZVI is significantly higher than that of Pd-NZVI coated with the other surface modifiers, suggesting that biosurfactants may be the most suitable surface modifiers in field application. Overall

  18. Distribution of molecular weight in glyceride polymerizates or aggregates of them after contact with lunar grains

    NASA Technical Reports Server (NTRS)

    Asunmaa, S. K.; Haack, R.

    1977-01-01

    An attempt is made to report on experiments in which a molecular-weight increase was determined in thin layers of triglyceride-containing glycerides after thin-layer contact for two years with lunar topsoil grains at 25 C without any thermal activation. It is noted that solidification was observed on both dielectric grains and metal-rich areas and that changes in viscosity and molecular weights were first detected by solidification of surface layers. Gel permeation chromatography is described which detected a general shift of the Gaussian distribution of the molecular-weight data toward generally higher molecular weights as well as an increase in mean molecular weight. Reaction mechanisms are considered, and results of spectrographic analysis are cited which support the interpretations of the molecular-weight data.

  19. Distribution of molecular weight in glyceride polymerizates or aggregates of them after contact with lunar grains

    NASA Technical Reports Server (NTRS)

    Asunmaa, S. K.; Haack, R.

    1977-01-01

    An attempt is made to report on experiments in which a molecular-weight increase was determined in thin layers of triglyceride-containing glycerides after thin-layer contact for two years with lunar topsoil grains at 25 C without any thermal activation. It is noted that solidification was observed on both dielectric grains and metal-rich areas and that changes in viscosity and molecular weights were first detected by solidification of surface layers. Gel permeation chromatography is described which detected a general shift of the Gaussian distribution of the molecular-weight data toward generally higher molecular weights as well as an increase in mean molecular weight. Reaction mechanisms are considered, and results of spectrographic analysis are cited which support the interpretations of the molecular-weight data.

  20. Stability and Aggregation of Silver and Titanium Dioxide Nanoparticles in Seawater: Role of Salinity and Dissolved Organic Matter

    EPA Science Inventory

    The behavior and fate of nanoparticles (NPs) in the marine environment is largely unknown and has the potential to have important environmental and human health implications. The aggregation state and fate of NPs in the marine environment is greatly influenced by their interactio...

  1. Stability and Aggregation of Silver and Titanium Dioxide Nanoparticles in Seawater: Role of Salinity and Dissolved Organic Matter

    EPA Science Inventory

    The behavior and fate of nanoparticles (NPs) in the marine environment is largely unknown and has the potential to have important environmental and human health implications. The aggregation state and fate of NPs in the marine environment is greatly influenced by their interactio...

  2. Aggregate stability and magnetic characteristics of colloidal Fe m O n -SiO2 particles obtained by sol-gel method

    NASA Astrophysics Data System (ADS)

    Vezo, O. S.; Gareev, K. G.; Korolev, D. V.; Kuryshev, I. A.; Lebedev, S. V.; Moshnikov, V. A.; Sergienko, E. S.; Kharitonskii, P. V.

    2017-05-01

    Composite Fe m O n -SiO2 particles have been obtained by precipitation of iron oxide from aqueous solution with the addition of tetraethoxysilane. The shapes and sizes of separate single particles and their aggregates have been determined by scanning electron microscopy. Changes in the stability of the colloidal suspension due to external magnetic field and the addition of NaCl have been evaluated. Based on magnetization curves obtained on a vibrating-sample magnetometer and characteristics calculated within the theoretical model of magnetostatically interacting particles, it is shown that the composite particles are superparamagnetic.

  3. Coherent modelling switch between pointwise and distributed representations of cell aggregates.

    PubMed

    Colombi, A; Scianna, M; Preziosi, L

    2017-03-01

    Biological systems are typically formed by different cell phenotypes, characterized by specific biophysical properties and behaviors. Moreover, cells are able to undergo differentiation or phenotypic transitions upon internal or external stimuli. In order to take these phenomena into account, we here propose a modelling framework in which cells can be described either as pointwise/concentrated particles or as distributed masses, according to their biological determinants. A set of suitable rules then defines a coherent procedure to switch between the two mathematical representations. The theoretical environment describing cell transition is then enriched by including cell migratory dynamics and duplication/apoptotic processes, as well as the kinetics of selected diffusing chemicals influencing the system evolution. Finally, biologically relevant numerical realizations are presented: in particular, they deal with the growth of a tumor spheroid and with the initial differentiation stages of the formation of the zebrafish posterior lateral line. Both phenomena mainly rely on cell phenotypic transition and differentiated behaviour, thereby constituting biological systems particularly suitable to assess the advantages of the proposed model.

  4. A simple and sensitive fluorimetric aptasensor for the ultrasensitive detection of arsenic(III) based on cysteamine stabilized CdTe/ZnS quantum dots aggregation.

    PubMed

    Ensafi, Ali A; Kazemifard, N; Rezaei, B

    2016-03-15

    A new approach for developing a fluorimetric aptasensor has been described and applied for determination of a highly toxic cation, As(III). In this method an aptamer was used to aggregate cationic cysteamine-stabilized CdTe/ZnS core/shell quantum dots, as a result fluorescence quenching was accrued. In the presence of As(III), the aptamer and As(III) make a complex, which prevents aggregation of the quantum dots. Thus, the fluorescence intensity of the quantum dots was enhanced upon the de-aggregation, which depends on the concentration of As(III). The fluorimetric assay has a very low detection limit of 1.3 pmolL(-1) As(III) with a dynamic range of 1.0 × 10(-11) to 1.0 × 10(-6) molL(-1). The interference effect of a wide variety of cations and anions was investigated, and the obtained results confirm high selectivity of the aptasensor for As(III) detection. The present assay was successfully applied for the determination of As(III) in several water samples.

  5. Final technical report for project titled Quantitative Characterization of Cell Aggregation/Adhesion as Predictor for Distribution and Transport of Microorganisms in Subsurface Environment

    SciTech Connect

    Gu, April Z.; Wan, Kai-tak

    2014-09-02

    This project aims to explore and develop enabling methodology and techniques for nano-scale characterization of microbe cell surface contact mechanics, interactions and adhesion quantities that allow for identification and quantification of indicative properties related to microorganism migration and transport behavior in porous media and in subsurface environments. Microbe transport has wide impact and therefore is of great interest in various environmental applications such as in situ or enhanced subsurface bioremediation,filtration processes for water and wastewater treatments and protection of drinking water supplies. Although great progress has been made towards understanding the identities and activities of these microorganisms in the subsurface, to date, little is known of the mechanisms that govern the mobility and transport of microorganisms in DOE’s contaminated sites, making the outcomes of in situ natural attenuation or contaminant stability enhancement unpredictable. Conventionally, movement of microorganisms was believed to follows the rules governing solute (particle) transport. However, recent studies revealed that cell surface properties, especially those pertaining to cell attachment/adhesion and aggregation behavior, can cause the microbe behavior to deviate from non-viable particles and hence greatly influence the mobility and distribution of microorganisms in porous media.This complexity highlights the need to obtain detailed information of cell-cell and cell-surface interactions in order to improve and refine the conceptual and quantitative model development for fate and transport of microorganisms and contaminant in subsurface. Traditional cell surface characterization methods are not sufficient to fully predict the deposition rates and transport behaviors of microorganism observed. A breakthrough of methodology that would allow for quantitative and molecular-level description of intrinsic cell surface properties indicative for cell

  6. On the observation of the need for an unusually high concentration of cysteine and homocysteine to induce aggregation of polymer-stabilized gold nano particles

    NASA Astrophysics Data System (ADS)

    Radhakumary, C.; Sreenivasan, K.

    2013-02-01

    This study reports the interaction of chitosan-stabilized gold nanoparticles (CH-AuNPs) with cysteine (Cys) and homocysteine (Hcys) in aqueous media at pH 1.4. Since the polymer precipitates at higher pH, and the amino acids Cys and HCys are soluble at acidic pH, we kept the pH around 1.4 for stabilizing the particles. Zeta potential of CH-AuNPs was found to be positive and it is reasonable to assume that +ve Cys or Hcys at pH 1.4 will experience repulsive force. However, TEM images and absorption spectra indicated formation of aggregates including rod-like assembly. An interesting observation was the need for unusually high concentration of analytes (Cys and Hcys) to induce the assembly of CH-AuNPs. We also found time bound variation of the optical properties probably indicating the interaction is kinetically controlled and only a fraction of the analyte molecules having sufficient energy can bind onto the particles. We observed that at elevated temperature, the reaction was faster with a lower concentration of Cys or Hcys. These observations were supported by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory which describes the interparticle interaction and the colloidal stability in solution. Only molecules possessing enough energy to cross this force barrier can cause the aggregation. We also noted a time lag between Cys and Hcys to influence optical properties reflecting the possibility of using this simple approach to discriminate these two clinically relevant molecules. Our observation shows that simple sensing as well as generation of novel nanostructures could be manipulated by a judicious choice of conditions such as stabilizing agents, pH, etc.

  7. Stability Analysis of Distributed Delay Neural Networks Based on Relaxed Lyapunov-Krasovskii Functionals.

    PubMed

    Zhang, Baoyong; Lam, James; Xu, Shengyuan

    2015-07-01

    This paper revisits the problem of asymptotic stability analysis for neural networks with distributed delays. The distributed delays are assumed to be constant and prescribed. Since a positive-definite quadratic functional does not necessarily require all the involved symmetric matrices to be positive definite, it is important for constructing relaxed Lyapunov-Krasovskii functionals, which generally lead to less conservative stability criteria. Based on this fact and using two kinds of integral inequalities, a new delay-dependent condition is obtained, which ensures that the distributed delay neural network under consideration is globally asymptotically stable. This stability criterion is then improved by applying the delay partitioning technique. Two numerical examples are provided to demonstrate the advantage of the presented stability criteria.

  8. Structure, Stability, and Aggregation of β-2 Microglobulin Mutants: Insights from a Fourier Transform Infrared Study in Solution and in the Crystalline State

    PubMed Central

    Ami, Diletta; Ricagno, Stefano; Bolognesi, Martino; Bellotti, Vittorio; Doglia, Silvia Maria; Natalello, Antonino

    2012-01-01

    β-2 microglobulin (β2m) is an amyloidogenic protein involved in dialysis-related amyloidosis. We report here the study of the structural properties of the protein in solution and in the form of single crystals by Fourier transform infrared (FTIR) spectroscopy and microspectroscopy. The investigation has been extended to four β2m mutants previously characterized by x-ray crystallography: Asp53Pro, Asp59Pro, Trp60Gly, and Trp60Val. These variants displayed very similar three-dimensional structures but different thermal stability and aggregation propensity, investigated here by FTIR spectroscopy. For each variant, appreciable spectral differences were found between the protein in solution and in single crystals, consisting in a downshift of the main β-sheet band and in better resolved turn and loop bands, indicative of reduced protein secondary structure dynamics in the crystalline state. Notably, the well-resolved spectra of the β2m crystalline variants enabled us to identify structural differences induced by the single amino acid mutations. Such differences encompass turn and loop structures that might affect the stability and aggregation propensity of the investigated β2m variants. This study highlights the potential of FTIR microspectroscopy to acquire useful structural information on protein crystals, complementary to the crystallographic analyses. PMID:22500768

  9. On the Stability of Distributions of the Type Described by Trueswell.

    ERIC Educational Resources Information Center

    Kantor, Paul B.

    1980-01-01

    Library collection weeding criteria based upon unequal distribution of demand require that distribution remain stable over time. A mathematical expression is derived that tests that stability. Verification is not inordinately time consuming and is facilitated by the use of automated circulation systems. (Author/RAA)

  10. Unfolding and aggregation of monoclonal antibodies on cation exchange columns: effects of resin type, load buffer, and protein stability.

    PubMed

    Guo, Jing; Carta, Giorgio

    2015-04-03

    The chromatographic behavior of a monoclonal antibody (mAb) that exhibits a pronounced two-peak elution behavior is studied for a range of strong cation exchange resins and with varying load buffer pH and composition. Six stationary phases are considered, including two tentacle-type resins (Fractogel EMD SO3-(M) and Eshmuno S), a resin with grafted polymeric surface extenders (Nuvia S), a resin with a bimodal pore size distribution (POROS HS 50), and two macroporous resins without polymer grafts (Source 30S and UNOsphere Rapid S). The two-peak elution behavior is very pronounced for the tentacle and polymer-grafted resins and for POROS HS 50, but is essentially absent for the two macroporous resins. The extent of this behavior decreases as the buffer pH and concentration increase and, consequently, mAb binding becomes weaker. Replacing sodium with arginine as the buffer counterion, which is expected to decrease the mAb binding strength, nearly completely eliminates the two-peak behavior, while replacing sodium with tetra-n-butylammonium hydroxide, which is expected to increase the mAb binding strength, dramatically exacerbate the effect. As shown by hydrogen-deuterium exchange mass spectrometry (HX-MS), the two-peak elution behavior is related to conformational changes that occur when the mAb binds. These changes result in increased solvent exposure of specific peptides in the Fc-region for either the Fractogel or the Nuvia resin. No significant conformational changes were seen by HX-MS when the mAb was bound to the UNOsphere resin or on the Fractogel resin when arginine was used in lieu of sodium as the load buffer counterion. Experiments with two additional mAbs on the Fractogel resin show that the two-peak elution behavior is dependent on the particular antibody. Circular dichroism suggests that the propensity of different mAbs to either precipitate directly or to form stabilizing intermolecular structures upon exposure to thermal stress can be related to their

  11. Volcanic hotspots on Io - Stability and longitudinal distribution

    NASA Technical Reports Server (NTRS)

    Johnson, T. V.; Matson, D. L.; Veeder, G. J.; Nelson, R. M.; Morrison, D.; Brown, R. H.

    1984-01-01

    The first results of a program to determine the longitudinal distribution of volcanic activity on Jupiter's satellite Io are presented. Infrared measurements at 8.7, 10, and 20 micrometers have been taken at a variety of orbital longitudes: strong variation in the 8.7- and 10-micrometer flux with longitude demonstrates that infrared emission arising from volcanic hotspots on Io is strongly concentrated in a few locations. Analysis of these data suggests that the active volcanic regions observed by the Voyager experimenters are still active, particularly the region around the feature known as Loki. Another source of flux, although of somewhat smaller magnitude, is indicated on the opposite hemisphere. If these sources are the only major volcanic centers on Io, then current global heat flow estimates must be revised downward. However, heat flow from as yet unobserved longitudes, hotspots at high latitudes, and conducted heat flow must still be measured.

  12. Volcanic hotspots on io: stability and longitudinal distribution.

    PubMed

    Johnson, T V; Morrison, D; Matson, D L; Veeder, G J; Brown, R H; Nelson, R M

    1984-10-12

    We report the first results of a program to determine the longitudinal distribution of volcanic activity on Jupiter's satellite Io. Infrared measurements at 8.7, 10, and 20 micrometers have been taken at a variety of orbital longitudes: strong variation in the 8.7- and 10-micrometer flux with longitude demonstrates that infrared emission arising from volcanic hotspots on Io is strongly concentrated in a few locations. Analysis of these data suggests that the active volcanic regions observed by the Voyager experimenters are still active, particularly the region around the feature known as Loki. Another source of flux, although of somewhat smaller magnitude, is indicated on the opposite hemisphere. If these sources are the only major volcanic centers on Io, then current global heat flow estimates must be revised downward. However, heat flow from as yet unobserved longitudes, hotspots at high latitudes, and conducted heat flow must still be measured.

  13. The long-term effects on aggregate stability (AS) from a forest fire of varying intensity in a Mediterranean environment (1994-2012).

    NASA Astrophysics Data System (ADS)

    Velasco, Antonio; Alcañiz, Meritxell; Úbeda, Xavier; Pereira, Paulo; Mataix-Solera, Jorge

    2013-04-01

    Forest fires can affect many soil properties and this fact is deeply connected with fire severity, intensity, soil type and many others factors. Aggregate stability (AS) indicates the soil structure resilience in response to external mechanical forces. AS is one of the factors that strongly affect on soil erodibility and infiltration. This property can be used as an indicator of the state of the soil structure and physical stability. The aim of this study is to analyze the soil AS of a determined area that suffered a wildfire in 1994 and compare them with a control area with the same characteristics. The study area is located in the Cadiretes Massif, in the northernmost zone of the Catalan Coastal Ranges, northeast Spain, at an altitude of around 190 - 250 m.a.m.s.l. The Cadiretes Massif is predominantly granite, although soils developed over Paleozoic metamorphic rocks such as schist and slates can also be found. In some areas metamorphic features underlie this relief. The massif is covered by dense Mediterranean vegetation, e.g. Quercus suber, Arbutus unedo, Erica arborea, and in some places Pinus pinaster plantations are found. This area receives about 700 - 800 mm of annual rainfall, with a fairly marked seasonal variability. The maximum is registered in autumn. Summer temperatures often surpass 25°C, while in winter temperatures are generally mild. The predominant soil type in Cadiretes is classified as a Lithic Xerept, with a 15 cm deep sandy-loam A horizon. In the control forest area, this horizon is protected by a 3 cm deep O horizon of moder humus. Three areas with different burnt intensity were identified in 1994 and they are the same plots that were chosen to sample in 2012. The 4 plots (Low intensity, Medium Intensity, High Intensity and Control) had the same orientation (S) and slope (5%). The TDI (Ten Drop Impact) test, that simulates rainfall impact on aggregates, was used to measure AS in the laboratory. Twenty samples were collected per plot. Ten

  14. Distribution and stability of eelgrass beds at Izembek Lagoon, Alaska

    USGS Publications Warehouse

    Ward, David H.; Markon, Carl J.; Douglas, David C.

    1997-01-01

    Spatial change in eelgrass meadows, Zostera marina L., was assessed between 1978 and 1987 and between 1987 and 1995 at Izembek Lagoon, Alaska. Change in total extent was evaluated through a map to map comparison of data interpreted from a 1978 Landsat multi-spectral scanner image and 1987 black and white aerial photographs. A ground survey in 1995 was used to assess spatial change from 1987. Eelgrass beds were the predominant vegetation type in the lagoon, comprising 44-47% (15000-16000 ha) of the total area in 1978 and 1987. Izembek Lagoon contains the largest bed of seagrass along the Pacific Coast of North America and largest known single stand of eelgrass in the world. There was a high degree of overlap in the spatial distribution of eelgrass among years of change detection. The overall net change was a 6% gain between, 1978 and 1987 and a <1% gain between 1987 and 1995. The lack of significant change in eelgrass cover suggests that eelgrass meadows in Izembek Lagoon have been stable during the 17-year period of our study.

  15. Stability of Spatial Distributions of Stink Bugs, Boll Injury, and NDVI in Cotton.

    PubMed

    Reay-Jones, Francis P F; Greene, Jeremy K; Bauer, Philip J

    2016-10-01

    A 3-yr study was conducted to determine the degree of aggregation of stink bugs and boll injury in cotton, Gossypium hirsutum L., and their spatial association with a multispectral vegetation index (normalized difference vegetation index [NDVI]). Using the spatial analysis by distance indices analyses, stink bugs were less frequently aggregated (17% for adults and 4% for nymphs) than boll injury (36%). NDVI values were also significantly aggregated within fields in 19 of 48 analyses (40%), with the majority of significant indices occurring in July and August. Paired NDVI datasets from different sampling dates were frequently associated (86.5% for weekly intervals among datasets). Spatial distributions of both stink bugs and boll injury were less stable than for NDVI, with positive associations varying from 12.5 to 25% for adult stink bugs for weekly intervals, depending on species. Spatial distributions of boll injury from stink bug feeding were more stable than stink bugs, with 46% positive associations among paired datasets with weekly intervals. NDVI values were positively associated with boll injury from stink bug feeding in 11 out of 22 analyses, with no significant negative associations. This indicates that NDVI has potential as a component of site-specific management. Future work should continue to examine the value of remote sensing for insect management in cotton, with an aim to develop tools such as risk assessment maps that will help growers to reduce insecticide inputs.

  16. Stabilization and improvement of catalytic activity of a low molar mass cellobiase by cellobiase-sucrase aggregation in the culture filtrate of Termitomyces clypeatus.

    PubMed

    Saha, Rina; Roy, Sujata Burman; Sengupta, S

    2002-01-01

    The extracellular cellobiase (EC 3.2.1.21) of Termitomyces clypeatus separated in two protein fractions when culture filtrate or ammonium sulfate precipitated proteins were chromatographed on BioGel P-200 column. During purification of cellobiase (CBS) from the lower molar mass (LMM) protein fraction, the enzyme behaved like a low molecular weight multimeric protein. The purified enzyme gave a single 56 kDa band in SDS-PAGE but ladderlike bands (14, 28, 42, and 56 kDa) on denaturation by reducing-SDS and urea. The protein, however, dissociated on dilution and protomeric (14 kDa) and multimeric forms (28 and 60 kDa) were eluted separately during HPGPLC. Specific activity of CBS gradually decreased as the molar mass of the enzyme was lowered in different eluted peaks. Protein present in all CBS pool fractions had the same amino acid composition and all displayed the same, single protein peak in reverse-phase HPLC and 56 kDa band in SDS-PAGE. Thus, T. clypeatus CBS was a multimeric 14 kDa protein that was optimally active as a tetramer. CBS purified from the higher molar mass fraction (HMM) as a SDS-PAGE homogeneous 110-kDa protein did not dissociate on dilution or by SDS-urea. The purified protein was a protein aggregate as CBS consistently contained 20 +/- 5% sucrase (SUC) Units in the preparation. The aggregate resolved during reverse-phase chromatography on a C(4) column, and an additional protein peak other than CBS was detected. The aggregated CBS had a higher temperature optimum and was more stable toward thermal and chemical denaturations than SUC-free CBS. Increase of stability and catalytic activity of CBS by aggregation with SUC was much higher than those by the multimerization of CBS itself. All of these observations for the first time suggested that the heterologous protein-protein aggregation, observed for a long time for fungal enzymes, might have a significant role in modulating physicochemical properties of the extracellular enzyme.

  17. Effects of Asphaltene Aggregation in Model Heptane-Toluene Mixtures on Stability of Water-in-Oil Emulsions

    PubMed

    McLean; Kilpatrick

    1997-12-01

    As part of an ongoing investigation into the stability of water-in-crude oil emulsions, model oils have been utilized to further probe the effects of crude solvency as well as specific resin-asphaltene interactions on emulsion stability. These model oils were constructed by dissolving varying amounts of resins and/or asphaltenes in a mixture of heptane and toluene. The resins and asphaltenes used in this study were isolated from four different crude types-Arab Berri (AB), Arab Heavy (AH), Alaska North Slope (ANS), and San Joaquin Valley (SJV)-and characterized in a previous study using heptane precipitation of the asphaltenes followed by an extrographic separation of the resins from silica gel. Asphaltenes dissolved in heptol at concentrations of just 0.5% were shown to generate emulsions which were even more stable than those generated from their respective whole crude oils. Some types of resins (e.g., from AH and SJV) also demonstrated an ability to stabilize emulsions although these resin-stabilized emulsions were considerably less stable than those prepared with asphaltenes. The primary factors governing the stability of these model emulsions were the aromaticity of the crude medium (as controlled by the heptane:toluene ratio), the concentration of asphaltenes, and the availability of solvating resins in the oil (i.e., the resin/asphaltene or R/A ratio). The model emulsions were the most stable when the crude medium was 30-40% toluene and in many cases at small R/A ratios (i.e., R/A stabilizing emulsions when they are near the point of incipient precipitation. The types of resins and asphaltenes used to construct these model oils also played a role in determining the resultant emulsion stability which indicates the importance of specific resin-asphaltene interactions. The interfacially active components that stabilized these model systems were the most polar and/or condensed

  18. Formation of Rod Shape Secondary Aggregation of Copper Nanoparticles in Aqueous Solution of Sodium Borohydride with Stabilizing Polymer

    NASA Astrophysics Data System (ADS)

    Harada, Takuya; Fujiwara, Hidemichi

    2007-03-01

    Morphological variations of copper nanoparticles synthesized by the reduction of copper acetate with sodium borohydride in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) have been investigated. The results indicate that the specific rod shape secondary aggregation of copper nanoparticles are formed in the case that the oxygen is dissolved in the reacting solutions. Furthermore, it is also demonstrated that the copper nanorods with the aspect ratio of 2 - 20 and the average short axis length of 5 nm are synthesized in the weak oxidizing ambiance with a medium amount of PVP. The anomalous variations of copper nanoparticles are explained by the alignments of precursor copper ions and their reducing rates, which are modified by the density of resolved oxygen and the amount of PVP.

  19. Stabilizing operation point technique based on the tunable distributed feedback laser for interferometric sensors

    NASA Astrophysics Data System (ADS)

    Mao, Xuefeng; Zhou, Xinlei; Yu, Qingxu

    2016-02-01

    We describe a stabilizing operation point technique based on the tunable Distributed Feedback (DFB) laser for quadrature demodulation of interferometric sensors. By introducing automatic lock quadrature point and wavelength periodically tuning compensation into an interferometric system, the operation point of interferometric system is stabilized when the system suffers various environmental perturbations. To demonstrate the feasibility of this stabilizing operation point technique, experiments have been performed using a tunable-DFB-laser as light source to interrogate an extrinsic Fabry-Perot interferometric vibration sensor and a diaphragm-based acoustic sensor. Experimental results show that good tracing of Q-point was effectively realized.

  20. On the distribution of intranuclear and cytoplasmic aggregates in the brainstem of patients with spinocerebellar ataxia type 2 and 3.

    PubMed

    Seidel, Kay; Siswanto, Sonny; Fredrich, Michaela; Bouzrou, Mohamed; den Dunnen, Wilfred F A; Özerden, Inci; Korf, Horst-Werner; Melegh, Bela; de Vries, Jeroen J; Brunt, Ewout R; Auburger, Georg; Rüb, Udo

    2017-05-01

    The polyglutamine (polyQ) diseases are a group of genetically and clinically heterogeneous neurodegenerative diseases, characterized by the expansion of polyQ sequences in unrelated disease proteins, which form different types of neuronal aggregates. The aim of this study was to characterize the aggregation pathology in the brainstem of spinocerebellar ataxia type 2 (SCA2) and 3 (SCA3) patients. For good recognition of neurodegeneration and rare aggregates, we employed 100 µm PEG embedded brainstem sections, which were immunostained with the 1C2 antibody, targeted at polyQ expansions, or with an antibody against p62, a reliable marker of protein aggregates. Brainstem areas were scored semiquantitatively for neurodegeneration, severity of granular cytoplasmic staining (GCS) and frequency of neuronal nuclear inclusions (NNI). SCA2 and SCA3 tissue exhibited the same aggregate types and similar staining patterns. Several brainstem areas showed statistically significant differences between disease groups, whereby SCA2 showed more severe GCS and SCA3 showed more numerous NNI. We observed a positive correlation between GCS severity and neurodegeneration in SCA2 and SCA3 and an inverse correlation between the frequency of NNI and neurodegeneration in SCA3. Although their respective disease proteins are unrelated, SCA2 and SCA3 showed the same aggregate types. Apparently, the polyQ sequence alone is sufficient as a driver of protein aggregation. This is then modified by protein context and intrinsic properties of neuronal populations. The severity of GCS was the best predictor of neurodegeneration in both disorders, while the inverse correlation of neurodegeneration and NNI in SCA3 tissue implies a protective role of these aggregates. © 2016 International Society of Neuropathology.

  1. Stabilization and control of distributed systems with time-dependent spatial domains

    NASA Technical Reports Server (NTRS)

    Wang, P. K. C.

    1990-01-01

    This paper considers the problem of the stabilization and control of distributed systems with time-dependent spatial domains. The evolution of the spatial domains with time is described by a finite-dimensional system of ordinary differential equations, while the distributed systems are described by first-order or second-order linear evolution equations defined on appropriate Hilbert spaces. First, results pertaining to the existence and uniqueness of solutions of the system equations are presented. Then, various optimal control and stabilization problems are considered. The paper concludes with some examples which illustrate the application of the main results.

  2. Effects of Changing Body Weight Distribution on Mediolateral Stability Control during Gait Initiation

    PubMed Central

    Caderby, Teddy; Yiou, Eric; Peyrot, Nicolas; de Viviés, Xavier; Bonazzi, Bruno; Dalleau, Georges

    2017-01-01

    During gait initiation, anticipatory postural adjustments (APA) precede the execution of the first step. It is generally acknowledged that these APA contribute to forward progression but also serve to stabilize the whole body in the mediolateral direction during step execution. Although previous studies have shown that changes in the distribution of body weight between both legs influence motor performance during gait initiation, it is not known whether and how such changes affect a person’s postural stability during this task. The aim of this study was to investigate the effects of changing initial body weight distribution between legs on mediolateral postural stability during gait initiation. Changes in body weight distribution were induced under experimental conditions by modifying the frontal plane distribution of an external load located at the participants’ waists. Fifteen healthy adults performed a gait initiation series at a similar speed under three conditions: with the overload evenly distributed over both legs; with the overload strictly distributed over the swing-limb side; and with the overload strictly distributed over the stance-leg side. Our results showed that the mediolateral location of center-of-mass (CoM) during the initial upright posture differed between the experimental conditions, indicating modifications in the initial distribution of body weight between the legs according to the load distribution. While the parameters related to the forward progression remained unchanged, the alterations in body weight distribution elicited adaptive changes in the amplitude of APA in the mediolateral direction (i.e., maximal mediolateral shift of the center of pressure (CoP)), without variation in their duration. Specifically, it was observed that the amplitude of APA was modulated in such a way that mediolateral dynamic stability at swing foot-contact, quantified by the margin of stability (i.e., the distance between the base of support boundary and

  3. Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China

    PubMed Central

    Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S.

    2016-01-01

    Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250–2000 μm), rather than within the microaggregates (53–250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions. PMID:26964101

  4. Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China.

    PubMed

    Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S

    2016-01-01

    Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250-2000 μm), rather than within the microaggregates (53-250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions.

  5. Chemical stability and phase distribution of all-trans-retinol in nanoparticle-coated emulsions.

    PubMed

    Eskandar, Nasrin Ghouchi; Simovic, Spomenka; Prestidge, Clive A

    2009-07-06

    The influence of silica nanoparticle coating on the chemical stability and phase distribution of all-trans-retinol in submicron oil-in-water emulsions is reported. The chemical stability was studied as a function of UVA+UVB irradiation, and storage temperature (4 degrees C, ambient temperature, and 40 degrees C) for emulsions stabilised with lecithin and oleylamine as the initial emulsifier with and without silica nanoparticle layers. The chemical stability of all-trans-retinol was highly dependent on the emulsifier type and charge, with negligible influence of the initial loading phase of silica nanoparticles. A significant stability improvement (approximately 2-fold increase in the half-life of the drug) was observed by nanoparticle incorporation into oleylamine-stabilised droplets (i.e. electrostatically coated), with no considerable effect for partially coated lecithin-stabilised droplets. The chemical stability of all-trans-retinol incorporated into nanoparticle-coated emulsions was well-correlated to the phase distribution of the active agent, and the interfacial structure of emulsions as determined by freeze fracture-SEM. Specifically engineered nanoparticle layers can be used to enhance the chemical stability of active ingredients in emulsion carriers.

  6. Equilibrium and stability in a heliotron with anisotropic hot particle slowing-down distribution

    SciTech Connect

    Cooper, W. A.; Asahi, Y.; Narushima, Y.; Suzuki, Y.; Watanabe, K. Y.; Graves, J. P.; Isaev, M. Yu.

    2012-10-15

    The equilibrium and linear fluid Magnetohydrodynamic (MHD) stability in an inward-shifted large helical device heliotron configuration are investigated with the 3D ANIMEC and TERPSICHORE codes, respectively. A modified slowing-down distribution function is invoked to study anisotropic pressure conditions. An appropriate choice of coefficients and exponents allows the simulation of neutral beam injection in which the angle of injection is varied from parallel to perpendicular. The fluid stability analysis concentrates on the application of the Johnson-Kulsrud-Weimer energy principle. The growth rates are maximum at <{beta}>{approx}2%, decrease significantly at <{beta}>{approx}4.5%, do not vary significantly with variations of the injection angle and are similar to those predicted with a bi-Maxwellian hot particle distribution function model. Stability is predicted at <{beta}>{approx}2.5% with a sufficiently peaked energetic particle pressure profile. Electrostatic potential forms from the MHD instability necessary for guiding centre orbit following are calculated.

  7. Sufficient condition for velocity-space stability of the alpha particle distribution in a tokamak reactor

    SciTech Connect

    Cordey, J.G.; Goldston, R.J.; Mikkelsen, D.R.

    1980-08-01

    A condition is derived for the velocity-space distribution of suprathermal alpha particles to be monotonically decreasing with energy - and hence stable to homogeneous plasma instabilities - during the heating phase of a tokamak reactor. This stability condition is easily satisfied for presently envisaged neutral injection heating of reactors, but may be violated in strong heating of smaller plasmas or during fast compressional heating.

  8. Stability of diameter distributions in a managed uneven-aged oak forest in the Ozark Highlands

    Treesearch

    Zhiming Wang; Paul S. Johnson; H. E. Garrett; Stephen R. Shifley

    1997-01-01

    We studied a privately owned 156,000-acre oak-dominated forest in the Ozark Highlands of southern Missouri. The forest has been managed by the single-tree selection method since 1952. Using 40 years of continuous forest inventory records, we analyzed the stability of the shape of tree diameter distributions at the forest-wide scale. Results show that for trees ...

  9. Effects of temperature distribution on boundary layer stability for a circular cone at Mach 10

    NASA Astrophysics Data System (ADS)

    Rigney, Jeffrey M.

    A CFD analysis was conducted on a circular cone at 3 degrees angle of attack at Mach 10 using US3D and STABL 3D to determine the effect of wall temperature on the stability characteristics that lead to laminar-to-turbulent transition. Wall temperature distributions were manipulated while all other flow inputs and geometric qualities were held constant. Laminar-to-turbulent transition was analyzed for isothermal and adiabatic wall conditions, a simulated short-duration wind tunnel case, and several hot-nose temperature distributions. For this study, stability characteristics include maximum N-factor growth and the corresponding frequency range, disturbance spatial amplification rate and the corresponding modal frequency, and stability neutral point location. STABL 3D analysis indicates that temperature distributions typical of those in short-duration hypersonic wind tunnels do not result in any significant difference on the stability characteristics, as compared to an isothermal wall boundary condition. Hypothetical distributions of much greater temperatures at and past the nose tip do show a trend of dampening of second-mode disturbances, most notably on the leeward ray. The most pronounced differences existed between the isothermal and adiabatic cases.

  10. Spawning aggregation of white-streaked grouper Epinephelus ongus: spatial distribution and annual variation in the fish density within a spawning ground.

    PubMed

    Nanami, Atsushi; Sato, Taku; Kawabata, Yuuki; Okuyama, Junichi

    2017-01-01

    White-streaked grouper (Epinephelus ongus) is an important fisheries target and forms spawning aggregations at particular spawning grounds. The aims of the present study were to investigate the ecological characteristics of annual spawning aggregations such as (1) spatial variations in the density of E. ongus at the spawning ground, (2) the relationship between fish density and environmental variables, (3) inter-annual variations in the spawning aggregation, (4) the proportion of males to females at the spawning ground for several days pre-and post-spawning and (5) the relationship between male density and female density at the protected spawning ground, based on observations over five years at an Okinawan coral reef. Although the protected spawning ground area was large (ca. 2,500 m × 700 m), high density of E. ongus (over 25 individuals per 100 m(2)) was found in a limited area (within c.a. 750 m × 50 m). Current velocity and coverage of rocks had significant positive effects on the spatial distribution of E. ongus at the spawning ground. Inter-annual variation in the degree of aggregation was found and this variation was explained by the annual variation of mean seawater temperature during 40 days before the spawning day. The male-female ratio (male:female) at the spawning ground was ca. 3:1 for three years (May 2012, May 2014 and May 2015) whereas >13:1 for one year (May 2013). Significant positive relationships between male density and female density were found at the aggregation sites. It is suggested that E. ongus use aggregation sites with greater current velocity to reduce the risk of egg predation and seawater temperature is one of the main factors that is responsible for determining the degree of aggregation. It is also suggested that females possibly select sites with a greater density of males and this selection behavior might be the reason why females arrived at the spawning ground after the arrival of the males. For effective management of

  11. Spawning aggregation of white-streaked grouper Epinephelus ongus: spatial distribution and annual variation in the fish density within a spawning ground

    PubMed Central

    Sato, Taku; Kawabata, Yuuki; Okuyama, Junichi

    2017-01-01

    White-streaked grouper (Epinephelus ongus) is an important fisheries target and forms spawning aggregations at particular spawning grounds. The aims of the present study were to investigate the ecological characteristics of annual spawning aggregations such as (1) spatial variations in the density of E. ongus at the spawning ground, (2) the relationship between fish density and environmental variables, (3) inter-annual variations in the spawning aggregation, (4) the proportion of males to females at the spawning ground for several days pre—and post-spawning and (5) the relationship between male density and female density at the protected spawning ground, based on observations over five years at an Okinawan coral reef. Although the protected spawning ground area was large (ca. 2,500 m × 700 m), high density of E. ongus (over 25 individuals per 100 m2) was found in a limited area (within c.a. 750 m × 50 m). Current velocity and coverage of rocks had significant positive effects on the spatial distribution of E. ongus at the spawning ground. Inter-annual variation in the degree of aggregation was found and this variation was explained by the annual variation of mean seawater temperature during 40 days before the spawning day. The male–female ratio (male:female) at the spawning ground was ca. 3:1 for three years (May 2012, May 2014 and May 2015) whereas >13:1 for one year (May 2013). Significant positive relationships between male density and female density were found at the aggregation sites. It is suggested that E. ongus use aggregation sites with greater current velocity to reduce the risk of egg predation and seawater temperature is one of the main factors that is responsible for determining the degree of aggregation. It is also suggested that females possibly select sites with a greater density of males and this selection behavior might be the reason why females arrived at the spawning ground after the arrival of the males. For effective management of

  12. On the effect of spatial aggregation of source regions on the stability of greenhouse gas emission estimates calculated by an inverse Lagrangian box model

    NASA Astrophysics Data System (ADS)

    Pieterse, G.; Vermeulen, A.

    2005-12-01

    Estimation of emission rates from atmospheric concentration observations has proven to remain a big challenge. In this paper, a new approach is chosen for the source strength estimation algorithm based on Source Receptor Matrices (SRM's) as derived for the COMET trajectory model for methane (Vermeulen et al., 2001). In the new approach, source regions are identified automatically by calculation of the Potential Source Region Contribution (PSRC) to measurements performed at multiple sites and spatial aggregation of these regions to achieve uniform PSRC in the aggregated Source-Receptor Matrix (aSRM). The emission strengths are then estimated using Singular Value Decomposition (SVD) of the aSRM. The SVD procedure also yields a Covariance Matrix (CM), which describes the statistical accuracies and mutual dependencies of the solutions. A recursive algorithm is implemented to further accumulate source regions in order to improve covariance and accuracy for the source strength estimates. The aSRM of Europe was constructed using the influence functions for the year 2002 for the locations of the CHIOTTO Tall Tower sites. Measurement data was not available for all sites. The results indicate that the new approach will enable accurate and stable methane budget calculations for the monitored region. As expected, the spatial distribution of the aggregated source regions will not be uniform, because the individual sources are not represented uniformly in the measured signals. Currently, the method is also evaluated for estimation of other greenhouse gas budgets of Europe, like CO2, SF6 and N2O. In principle, the aSRM method can be applied to SRM's of any transport model and component, provided that the forward performance of the model is adequate and that matching observations exist.

  13. Relationships between aggregates size classes and SOC content using aggregate settling velocity measurements in interrill areas

    NASA Astrophysics Data System (ADS)

    Quijano, Laura; Kuhn, Nikolaus J.; Navas, Ana

    2017-04-01

    Soil aggregate stability is one of the main factors of soil physics and structure. Formation and stabilization of soil aggregates facilitates soil carbon sequestration and reduces the susceptibility of soil to erosion. The gain or loss of C in agricultural systems is largely influenced by aggregate-associated soil organic carbon that affects the settling velocity and C content of soils. Settling velocity measurements are useful to provide direct information on soil aggregate size distribution that can be used as indicators of the potential soil erodibility. This study aims to analyze the effect of settling velocity on soil aggregate dynamics and the relationships between the particle size distributions and the associated carbon in a cultivated field of typical Mediterranean agroecosystems in mountain landscapes. Calcisol topsoil samples (n=10) were collected in an interrill area within the field at two contrasting slope positions (i.e. upslope and downslope). Furthermore, a total of ten Calcisol soil samples were collected in an adjacent area under forest vegetation cover and stable conditions. According to Stokes's Law, the fine soil fraction <2 mm was fractionated into five velocity settling classes: > 0.045, 0.045-0.015, 0.015-0.003, 0.003-0.001 and < 0.001 m s-1 using a settling tube procedure followed by the analysis of the SOC content of each settling size classes. The results evidenced the inverse correlation between grain size and SOC content, smaller and lighter settling size classes were enriched in SOC and the effect of cultivation on soil aggregation by the lower proportion of macroaggregates compared to forest soils. Moreover, it was found a preferential transport of fine particles from upslope to downslope during interrill erosion processes. In this study, settling velocity measurements provide a useful tool for assessing changes in soil aggregation under different land uses and for identifying the relationship between aggregates size classes and SOC

  14. A strategic approach for direct recovery and stabilization of Fusarium sp. ICT SAC1 cutinase from solid state fermented broth by carrier free cross-linked enzyme aggregates.

    PubMed

    Chaudhari, Sandeep A; Singhal, Rekha S

    2017-05-01

    The major hurdles in commercial exploitation of cutinase (having both esterolytic and lipolytic activities) with potent industrial applications are its high production cost, operational instability and reusability. Although commercially available in immobilized form, its immobilization process (synthesis of support/carrier) makes it expensive. Herein we tried to address multiple issues of production cost, stability, and reusability, associated with cutinase. Waste watermelon rinds, an agroindustrial waste was considered as a cheap support for solid state fermentation (SSF) for cutinase production by newly isolated Fusarium sp. ICT SAC1. Subsequently, carrier free cross-linked enzyme aggregates of cutinase (cut-CLEA) directly from the SSF crude broth were developed. All the process variables affecting CLEA formation along with the different additives were evaluated. It was found that 50% (w/v) of ammonium sulphate, 125μmol of glutaraldehyde, cross-linking for 1h at 30°C and broth pH of 7.0, yielded 58.12% activity recovery. All other additives (hexane, butyric acid, sodium dodecyl sulphate, Trition-X 100, Tween-20, BSA) evaluated presented negative results to our hypothesis. Kinetics and morphology studies confirmed the diffusive nature of cut-CLEA and BSA cut-CLEA. Developed CLEA showed better thermal, solvent, detergent and storage stability, making it more elegant and efficient for industrial biocatalytic process.

  15. Molecular-scale investigations of structures and surface charge distribution of surfactant aggregates by three-dimensional force mapping

    SciTech Connect

    Suzuki, Kazuhiro; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi; Kobayashi, Kei

    2014-02-07

    Surface charges on nanoscale structures in liquids, such as biomolecules and nano-micelles, play an essentially important role in their structural stability as well as their chemical activities. These structures interact with each other through electric double layers (EDLs) formed by the counter ions in electrolyte solution. Although static-mode atomic force microscopy (AFM) including colloidal-probe AFM is a powerful technique for surface charge density measurements and EDL analysis on a submicron scale in liquids, precise surface charge density analysis with single-nanometer resolution has not been made because of its limitation of the resolution and the detection sensitivity. Here we demonstrate molecular-scale surface charge measurements of self-assembled micellar structures, molecular hemicylinders of sodium dodecyl sulfate (SDS), by three-dimensional (3D) force mapping based on frequency modulation AFM. The SDS hemicylindrical structures with a diameter of 4.8 nm on a graphite surface were clearly imaged. We have succeeded in visualizing 3D EDL forces on the SDS hemicylinder surfaces and obtaining the molecular-scale charge density for the first time. The results showed that the surface charge on the trench regions between the hemicylinders was much smaller than that on the hemicylinder tops. The method can be applied to a wide variety of local charge distribution studies, such as spatial charge variation on a single protein molecule.

  16. Effect of Au nanoparticle spatial distribution on the stability of thin polymer films.

    PubMed

    Amarandei, George; O'Dwyer, Colm; Arshak, Arousian; Thiele, Uwe; Steiner, Ullrich; Corcoran, David

    2013-06-04

    The stability of thin poly(methyl-methacrylate) (PMMA) films of low molecular weight on a solid substrate is controlled by the areal coverage of gold nanoparticles (NPs) present at the air-polymer interface. As the polymer becomes liquid the Au NPs are free to diffuse, coalesce, and aggregate while the polymer film can change its morphology through viscous flow. These processes lead at the same time to the formation of a fractal network of Au NPs and to the development of spinodal instabilities of the free surface of the polymer films. For thinner films a single wavelength is observed, while for thicker films two wavelengths compete. With continued heating the aggregation process results in a decrease in coverage, the networks evolve into disordered particle assemblies, while the polymer films flatten again. The disordering occurs first on the smallest scales and coincides (in thicker films) with the disappearance of the smaller wavelength. The subsequent disordering on larger scales causes the films to flatten.

  17. Runaway electron distributions and their stability with respect to the anomalous Doppler resonance

    SciTech Connect

    Fuchs, V.; Shoucri, M.; Teichmann, J.; Bers, A.

    1986-06-01

    The stability of non-relativistic runaway electron distributions with respect to the anomalous Doppler resonance is examined in a range of parameters of interest to tokamaks, i.e., for Y identical to ..omega../sub pe//..cap omega../sub ce/ less than or equal to 2 and for ohmic electric fields epsilon identical to E/E/sub c/ less than or equal to 0.1. Distribution functions are calculated numerically within a region up to 35 v/sub e/ (thermal velocities) using a finite-element 2-D Fokker-Planck code. Alternatively, an analytic approximation for the runaway distribution function is used, valid beyond the critical velocity v/sub c/ approx. = v/sub e/ (E/sub c//E)/sup 1/2/. Stability thresholds in (..omega.., k/sub parallel/) - space are then determined.

  18. Elongation of the C-terminal domain of an anti-amyloid β single-chain variable fragment increases its thermodynamic stability and decreases its aggregation tendency

    PubMed Central

    Rivera-Hernández, Geovanny; Marín-Argany, Marta; Blasco-Moreno, Bernat; Bonet, Jaume; Oliva, Baldomero; Villegas, Sandra

    2013-01-01

    Amyloid β (Aβ) immunotherapy is considered a promising approach to Alzheimer disease treatment. In contrast to the use of complete antibodies, administration of single-chain variable fragments (scFv) has not been associated with either meningoencephalitis or cerebral hemorrhage. ScFv-h3D6 is known to preclude cytotoxicity of the Aβ1–42 peptide by removing its oligomers from the amyloid pathway. As is the case for other scFv molecules, the recombinant production of scFv-h3D6 is limited by its folding and stability properties. Here, we show that its urea-induced unfolding pathway is characterized by the presence of an intermediate state composed of the unfolded VL domain and the folded VH domain, which suggests the VL domain as a target for thermodynamic stability redesign. The modeling of the 3D structure revealed that the VL domain, located at the C-terminal of the molecule, was ending before its latest β-strand was completed. Three elongation mutants, beyond VL-K107, showed increased thermodynamic stability and lower aggregation tendency, as determined from urea denaturation experiments and Fourier-transform infrared spectroscopy, respectively. Because the mutants maintained the capability of removing Aβ-oligomers from the amyloid pathway, we expect these traits to increase the half-life of scFv-h3D6 in vivo and, consequently, to decrease the effective doses. Our results led to the improvement of a potential Alzheimer disease treatment and may be extrapolated to other class-I scFv molecules of therapeutic interest. PMID:23924802

  19. Elongation of the C-terminal domain of an anti-amyloid β single-chain variable fragment increases its thermodynamic stability and decreases its aggregation tendency.

    PubMed

    Rivera-Hernández, Geovanny; Marin-Argany, Marta; Blasco-Moreno, Bernat; Bonet, Jaume; Oliva, Baldo; Villegas, Sandra

    2013-01-01

    Amyloid β (Aβ) immunotherapy is considered a promising approach to Alzheimer disease treatment. In contrast to the use of complete antibodies, administration of single-chain variable fragments (scFv) has not been associated with either meningoencephalitis or cerebral hemorrhage. ScFv-h3D6 is known to preclude cytotoxicity of the Aβ 1-42 peptide by removing its oligomers from the amyloid pathway. As is the case for other scFv molecules, the recombinant production of scFv-h3D6 is limited by its folding and stability properties. Here, we show that its urea-induced unfolding pathway is characterized by the presence of an intermediate state composed of the unfolded VL domain and the folded VH domain, which suggests the VL domain as a target for thermodynamic stability redesign. The modeling of the 3D structure revealed that the VL domain, located at the C-terminal of the molecule, was ending before its latest β-strand was completed. Three elongation mutants, beyond VL-K107, showed increased thermodynamic stability and lower aggregation tendency, as determined from urea denaturation experiments and Fourier-transform infrared spectroscopy, respectively. Because the mutants maintained the capability of removing Aβ-oligomers from the amyloid pathway, we expect these traits to increase the half-life of scFv-h3D6 in vivo and, consequently, to decrease the effective doses. Our results led to the improvement of a potential Alzheimer disease treatment and may be extrapolated to other class-I scFv molecules of therapeutic interest.

  20. Non-Arrhenius protein aggregation.

    PubMed

    Wang, Wei; Roberts, Christopher J

    2013-07-01

    Protein aggregation presents one of the key challenges in the development of protein biotherapeutics. It affects not only product quality but also potentially impacts safety, as protein aggregates have been shown to be linked with cytotoxicity and patient immunogenicity. Therefore, investigations of protein aggregation remain a major focus in pharmaceutical companies and academic institutions. Due to the complexity of the aggregation process and temperature-dependent conformational stability, temperature-induced protein aggregation is often non-Arrhenius over even relatively small temperature windows relevant for product development, and this makes low-temperature extrapolation difficult based simply on accelerated stability studies at high temperatures. This review discusses the non-Arrhenius nature of the temperature dependence of protein aggregation, explores possible causes, and considers inherent hurdles for accurately extrapolating aggregation rates from conventional industrial approaches for selecting accelerated conditions and from conventional or more advanced methods of analyzing the resulting rate data.

  1. Exponential Stability of Almost Periodic Solutions for Memristor-Based Neural Networks with Distributed Leakage Delays.

    PubMed

    Xu, Changjin; Li, Peiluan; Pang, Yicheng

    2016-12-01

    In this letter, we deal with a class of memristor-based neural networks with distributed leakage delays. By applying a new Lyapunov function method, we obtain some sufficient conditions that ensure the existence, uniqueness, and global exponential stability of almost periodic solutions of neural networks. We apply the results of this solution to prove the existence and stability of periodic solutions for this delayed neural network with periodic coefficients. We then provide an example to illustrate the effectiveness of the theoretical results. Our results are completely new and complement the previous studies Chen, Zeng, and Jiang ( 2014 ) and Jiang, Zeng, and Chen ( 2015 ).

  2. Stability and Hopf bifurcation for a regulated logistic growth model with discrete and distributed delays

    NASA Astrophysics Data System (ADS)

    Fang, Shengle; Jiang, Minghui

    2009-12-01

    In this paper, we investigate the stability and Hopf bifurcation of a new regulated logistic growth with discrete and distributed delays. By choosing the discrete delay τ as a bifurcation parameter, we prove that the system is locally asymptotically stable in a range of the delay and Hopf bifurcation occurs as τ crosses a critical value. Furthermore, explicit algorithm for determining the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions is derived by normal form theorem and center manifold argument. Finally, an illustrative example is also given to support the theoretical results.

  3. Analysis of topsoil aggregation with linkage to dust emission potential

    NASA Astrophysics Data System (ADS)

    Swet, Nitzan; Katra, Itzhak

    2015-04-01

    Dust emission by soil erosion has environmental and socioeconomic significances due to loss of a natural resource and air pollution. Topsoil resistance to erosion depends on its physicochemical properties, especially on the soil aggregation. Aggregate size distribution of soil samples is commonly used for the assessment of soil stability and fertility. It is suggested that aggregates larger than 840 µm in their effective diameter are stable to aeolian (wind) soil erosion. However the physicochemical properties of aggregates should be considered in determining the dust emission potential from soils. This study focuses on quantitative analyses of physical and chemical properties of aggregates in order to develop a soil stability index for dust emission. The study integrates laboratory analyses of soil samples and aeolian experiments of dust emission. Soil samples were taken from different land uses in a semi-arid loess soil that is subjected to aeolian erosion and dust emission. Laboratory tests include particle size distribution (PSD), soil organic carbon (SOC), inorganic carbon (CaCO3), water content (WC), and elemental composition by XRF technique. The size analysis shows significant differences in aggregation between natural-soil plots (N) and grazing-soil plots (G). The MWD index was higher in N (1204 µm) than that of G (400 µm). Basic aeolain experiments with a boundary layer wind tunnel showed dust emission of particulate matter (PM10) from both soils, although the concentrations were significantly lower in N plots. Aggregates at specific size fractions are characterized by different content of cementing agents. The content of fine particles (< 20 µm) and SOM were higher in macro-aggregates (500-2000 µm), while the CaCO3 content was higher in aggregate fraction of 63-250 µm. WC values were highest in micro-aggregates (< 63 µm). However the lowest content of these cementing agents were mostly found in the aggregate size fraction of 1000 µm. Differences

  4. Control over Particle Size Distribution by Autoclaving Poloxamer-Stabilized Trimyristin Nanodispersions.

    PubMed

    Göke, Katrin; Roese, Elin; Arnold, Andreas; Kuntsche, Judith; Bunjes, Heike

    2016-09-06

    Lipid nanoparticles are under investigation as delivery systems for poorly water-soluble drugs. The particle size in these dispersions strongly influences important pharmaceutical properties like biodistribution and drug loading capacity; it should be below 500 nm for direct injection into the bloodstream. Consequently, small particles with a narrow particle size distribution are desired. Hitherto, there are, however, only limited possibilities for the preparation of monodisperse, pharmaceutically relevant dispersions. In this work, the effect of autoclaving at 121 °C on the particle size distribution of lipid nanoemulsions and -suspensions consisting of the pharmaceutically relevant components trimyristin and poloxamer 188 was studied. Additionally, the amount of emulsifier needed to stabilize both untreated and autoclaved particles was assessed. In our study, four dispersions of mean particle sizes from 45 to 150 nm were prepared by high-pressure melt homogenization. The particle size distribution before and after autoclaving was characterized using static and dynamic light scattering, differential scanning calorimetry, and transmission electron microscopy. Asymmetrical flow field-flow fractionation was used for particle size distribution analyses and for the determination of free poloxamer 188. Upon autoclaving, the mean particle size increased to up to 200 nm, but not proportionally to the initial size. At the same time, the particle size distribution width decreased remarkably. Heat treatment thus seems to be a promising approach to achieve the desired narrow particle size distribution of such dispersions. Related to the lipid content, suspension particles needed more emulsifier for stabilization than emulsion droplets, and smaller particles more than larger ones.

  5. A unified kinetic model for particle aggregation

    SciTech Connect

    Gardner, K.H.; Theis, T.L.

    1996-06-01

    Aggregation of submicrometer particles is a process with significant implications for the fate and transport of contaminants and major nutrients in many coastal, estuarine, and freshwater bodies as well as groundwater systems. A unified model has been developed that describes the kinetics of particle aggregation. The model is unique in the incorporation of surface chemical phenomena along with solution chemistry in the determination of the stability of a colloidal dispersion. The aggregation process is treated in a truly kinetic fashion, the main output from the model being the evolution of complete particle size distributions over time. The model was developed to interpret laboratory data and, as such, has the capacity to estimate a (variable) set of system parameters by fitting the size distribution over time data to that measured. It was found that the attachment distance, a parameter frequently approximated in practice, has a profound influence on the predicted aggregation kinetics as does the choice of a solid/solution interfacial model. Furthermore, simulation of relatively long-term aggregation, which was the principal focus of this work, indicates that values of the collision efficiency factor should be much smaller than those reported elsewhere in the literature.

  6. Aggregation patterns in alpha,alpha'-stabilized carbanions: assembly of a sodium cage polymer by slip-stacking of dimers.

    PubMed

    Henderson, Kenneth W; Kennedy, Alan R; MacDougall, Dugald J

    2003-04-21

    The alpha,alpha'-stabilized carbanion complexes [PhSO(2)CHCNNa.THF], 3, [t-BuSO(2)CHCNNa], 4, [PhSO(2)CHCNK], 5, [t-BuSO(2)CHCNK], 6, and [MeSO(2)CHCNLi.TMEDA], 7, have been synthesized via the metalation of the parent (organo)sulfonylacetonitriles by BuLi, BuNa, or BnK in THF solution (or THF/TMEDA in the case of 7). In addition, complexes 3 and 7 have been characterized by single-crystal X-ray analyses and have been found to adopt related structures in the solid state. Complex 7 is a molecular dimer containing a central 12-membered (OSCCNLi)(2) ring core, with each metal rendered tetracoordinate by binding to a chelating TMEDA molecule. As found in related complexes, no direct carbanion to lithium contacts are present in the structure of 7. Complex 3 forms a polymeric cage structure composed of associated "dimeric" (OSCCNNa)(2) rings, similar to those found in 7. The larger sodium cations, and the presence of only one THF molecule/metal, allow additional contacts with the anions, leading to hexacoordination at the metal centers. These contacts include long-range transannular Na-N interactions (2.8042(14) A) across the central dimeric ring and "interdimer" Na-C connections (2.8718(15) A). Dissolution of complexes 3-6 and their lithiated derivatives [PhSO(2)CHCNLi.TMEDA], 1, and [t-BuSO(2)CHCNLi.THF], 2, in DMSO-d(6) results in almost identical chemical shifts for each type of ligand. This suggests that charge-separated complexes of the form [RSO(2)CHCN](-)[M(DMSO-d(6))(n)()](+) are formed in highly polar solution.

  7. Stimulus-responsive Au@(MeO2MAx-co-OEGMAy) nanoparticles stabilized by non-DLVO interactions: implications of ionic strength and copolymer (x:y) fraction on aggregation kinetics.

    PubMed

    Gambinossi, Filippo; Chanana, Munish; Mylon, Steven E; Ferri, James K

    2014-02-25

    Functionalized nanoparticles can assist in stabilizing fluid-fluid interfaces; however, developing and applying the appropriate surface modification presents a challenge because successful application of these nanomaterials for biotechnological, food processing, and environmental applications requires their long-term stability in elevated ionic strength media. This work studies stimulus responsive polymeric materials based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x = MeO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y= OEGMA) which, when grafted to gold nanoparticles, show significant, tunable, colloidal stability. The nanoparticles Au@(MeO2MAx-co-OEGMAy) display tunable, reversible aggregation that is highly dependent on the (x:y) ratio and ionic strength. Effects of these parameters on the initial rate constant of aggregation (k11) are studied by time-resolved dynamic light scattering (TR-DLS) experiments. At the same nanoparticle concentration, a strong sensitivity to salt concentration is observed. Over less than 300 mM increase in NaCl concentration, we observed a two-order of magnitude increase in aggregation rate constants, 4.2 × 10(-20) < k11 < 1.8 × 10(-18) m(3)s(-1). Additionally, for the same gold nanoparticles, a higher fraction of OEGMA requires a higher salt concentration to induce aggregation. A linear relationship between the critical NaCl coagulation concentration (CCC) and the copolymer composition is observed. Analysis of the experimental data with an extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory that includes hydration and osmotic forces is used to explain the stability of these systems. We find the hydration pressure, 2.4 < P(h,0) < 7.2 MPa, scales linearly both with the osmotic pressure and the OEGMA monomer concentration (5 < y < 20%). Specific knowledge of P(h,0)(y, C(NaCl)) enables design of both aggregation kinetics and stability as a function of the copolymer ratio and external

  8. Impact of Distribution-Connected Large-Scale Wind Turbines on Transmission System Stability during Large Disturbances: Preprint

    SciTech Connect

    Zhang, Y.; Allen, A.; Hodge, B. M.

    2014-02-01

    This work examines the dynamic impacts of distributed utility-scale wind power during contingency events on both the distribution system and the transmission system. It is the first step toward investigating high penetrations of distribution-connected wind power's impact on both distribution and transmission stability.

  9. Thermal stability and long-chain fatty acid positional distribution on glycerol of argan oil.

    PubMed

    Khallouki, Farid; Mannina, Luisa; Viel, Stéphane; Owen, Robert W

    2008-09-01

    The primary aim of this study was to determine the oxidative stability of argan oils by using peroxides and conjugated diene hydroperoxides measurements as analytical indicators. Both food and cosmetic argan oils were investigated. Their oxidative stability was also determined by monitoring the relative changes of their fatty acid profiles by (1)H NMR. In addition, valuable information regarding minor components as well as the acyl positional distribution, were obtained for both grades by high field (1)H and (13)C NMR, respectively. Given that the cosmetic and food grades have a similar profile and content of phenolic antioxidants, vitamers, and squalene, it appears that the ratio of fatty acid aliphatic to bisallylic CH2 groups, much higher in argan oils than in other vegetable oils, is responsible for their higher thermal stability. Copyright © 2008 Elsevier Ltd. All rights reserved.

  10. Linear Stability Analysis of a Collisionless Distribution Function for the Force-Free Harris Sheet

    NASA Astrophysics Data System (ADS)

    Wilson, Fiona; Neukirch, Thomas

    2013-04-01

    A discussion is presented of the first linear stability analysis of the collisionless distribution function recently found by Harrison and Neukirch for the force-free Harris sheet (Physical Review Letters 102, 135003, 2009). Macroscopic instabilities are considered, and the perturbations are assumed to be two-dimensional only. The stability analysis is based on the technique of integration over unperturbed orbits. Similarly to the Harris sheet case (Nuovo Cimento, 23:115, 1962), this is only possible by using approximations to the exact orbits, which are unknown. Furthermore, the approximations for the Harris sheet case cannot be used for the force-free Harris sheet, and so new techniques have to be developed in order to make analytical progress. In addition to the full problem, the long wavelength limit is considered, and the results of the two cases are compared. The dependence of the stability on various equilibrium parameters is investigated.

  11. A Study of Strong Stability of Distributed Systems. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Cataltepe, Tayfun

    1989-01-01

    The strong stability of distributed systems is studied and the problem of characterizing strongly stable semigroups of operators associated with distributed systems is addressed. Main emphasis is on contractive systems. Three different approaches to characterization of strongly stable contractive semigroups are developed. The first one is an operator theoretical approach. Using the theory of dilations, it is shown that every strongly stable contractive semigroup is related to the left shift semigroup on an L(exp 2) space. Then, a decomposition for the state space which identifies strongly stable and unstable states is introduced. Based on this decomposition, conditions for a contractive semigroup to be strongly stable are obtained. Finally, extensions of Lyapunov's equation for distributed parameter systems are investigated. Sufficient conditions for weak and strong stabilities of uniformly bounded semigroups are obtained by relaxing the equivalent norm condition on the right hand side of the Lyanupov equation. These characterizations are then applied to the problem of feedback stabilization. First, it is shown via the state space decomposition that under certain conditions a contractive system (A,B) can be strongly stabilized by the feedback -B(*). Then, application of the extensions of the Lyapunov equation results in sufficient conditions for weak, strong, and exponential stabilizations of contractive systems by the feedback -B(*). Finally, it is shown that for a contractive system, the first derivative of x with respect to time = Ax + Bu (where B is any linear bounded operator), there is a related linear quadratic regulator problem and a corresponding steady state Riccati equation which always has a bounded nonnegative solution.

  12. Free gas in the regional hydrate stability zone: Implications for hydrate distribution and fracturing behavior

    NASA Astrophysics Data System (ADS)

    Daigle, H.; Dugan, B.

    2010-12-01

    We show that hydrate distribution and fracture genesis in the hydrate stability zone are largely governed by the phase of methane supply. In systems where methane is supplied primarily as free gas, hydrate saturation increases upwards in the hydrate stability zone, and fractures nucleate in the middle of the stability zone where hydrate saturation is highest. In systems where methane is supplied primarily as a dissolved phase in the pore water, hydrate saturation decreases upwards in the stability zone, and fractures nucleate at the base of the stability zone. These interpretations are based on our one-dimensional model that incorporates multiphase flow and free gas within the regional hydrate stability zone (RHSZ). The RHSZ is defined as the interval in which methane hydrate may occur at seawater salinity (3.35% by mass). As hydrate forms and excludes salt from the crystal structure, the porewater salinity increases. Free gas enters the RHSZ when the porewater salinity increases to the value required for three-phase (dissolved methane + gas hydrate + free gas) equilibrium. Our model also incorporates changes to capillary pressure as hydrate forms and occludes the pore system. We model the system until the excess pore pressure exceeds the vertical effective stress in the domain due to capillary effects and pore occlusion, at which point we assume fractures nucleate. We test our model at Hydrate Ridge, where methane supply is dominantly in the gas phase, and show that hydrate saturation increases upwards and fractures nucleate high within the stability zone, eventually allowing gas to vent to the seafloor. We also model Blake Ridge, where methane supply is dominantly in the dissolved phase, and show that hydrate saturation is greatest at the base of the stability zone; fractures nucleate here and in some cases could propagate through the regional hydrate stability zone, allowing methane-charged water to vent to the seafloor. These two systems represent endmembers of

  13. Characterizing short-term stability for Boolean networks over any distribution of transfer functions

    SciTech Connect

    Seshadhri, C.; Smith, Andrew M.; Vorobeychik, Yevgeniy; Mayo, Jackson R.; Armstrong, Robert C.

    2016-07-05

    Here we present a characterization of short-term stability of random Boolean networks under arbitrary distributions of transfer functions. Given any distribution of transfer functions for a random Boolean network, we present a formula that decides whether short-term chaos (damage spreading) will happen. We provide a formal proof for this formula, and empirically show that its predictions are accurate. Previous work only works for special cases of balanced families. Finally, it has been observed that these characterizations fail for unbalanced families, yet such families are widespread in real biological networks.

  14. Characterizing short-term stability for Boolean networks over any distribution of transfer functions

    SciTech Connect

    Seshadhri, C.; Smith, Andrew M.; Vorobeychik, Yevgeniy; Mayo, Jackson R.; Armstrong, Robert C.

    2016-07-05

    Here we present a characterization of short-term stability of random Boolean networks under arbitrary distributions of transfer functions. Given any distribution of transfer functions for a random Boolean network, we present a formula that decides whether short-term chaos (damage spreading) will happen. We provide a formal proof for this formula, and empirically show that its predictions are accurate. Previous work only works for special cases of balanced families. Finally, it has been observed that these characterizations fail for unbalanced families, yet such families are widespread in real biological networks.

  15. Characterizing short-term stability for Boolean networks over any distribution of transfer functions

    NASA Astrophysics Data System (ADS)

    Seshadhri, C.; Smith, Andrew M.; Vorobeychik, Yevgeniy; Mayo, Jackson R.; Armstrong, Robert C.

    2016-07-01

    We present a characterization of short-term stability of Kauffman's N K (random) Boolean networks under arbitrary distributions of transfer functions. Given such a Boolean network where each transfer function is drawn from the same distribution, we present a formula that determines whether short-term chaos (damage spreading) will happen. Our main technical tool which enables the formal proof of this formula is the Fourier analysis of Boolean functions, which describes such functions as multilinear polynomials over the inputs. Numerical simulations on mixtures of threshold functions and nested canalyzing functions demonstrate the formula's correctness.

  16. Characterizing short-term stability for Boolean networks over any distribution of transfer functions.

    PubMed

    Seshadhri, C; Smith, Andrew M; Vorobeychik, Yevgeniy; Mayo, Jackson R; Armstrong, Robert C

    2016-07-01

    We present a characterization of short-term stability of Kauffman's NK (random) Boolean networks under arbitrary distributions of transfer functions. Given such a Boolean network where each transfer function is drawn from the same distribution, we present a formula that determines whether short-term chaos (damage spreading) will happen. Our main technical tool which enables the formal proof of this formula is the Fourier analysis of Boolean functions, which describes such functions as multilinear polynomials over the inputs. Numerical simulations on mixtures of threshold functions and nested canalyzing functions demonstrate the formula's correctness.

  17. Stability analysis of a discrete Hutchinson equation with discrete and distributed delay

    NASA Astrophysics Data System (ADS)

    Suryanto, A.; Yanti, I.; Kusumawinahyu, W. M.

    2014-02-01

    In this paper a Hutchinson equation with discrete and distributed delay is discretized by the Euler method. The dynamics of the obtained discrete system is then investigated. Specifically the stability of the positive fixed point is analyzed. It is found that for sufficiently small time-step of integration, the positive equilibrium undergoes a Neimark-Sacker bifurcation which is controlled by the discrete time delay. The results of analysis are then confirmed by some numerical simulations.

  18. Control of IgG LC:HC ratio in stably transfected CHO cells and study of the impact on expression, aggregation, glycosylation and conformational stability.

    PubMed

    Ho, Steven C L; Koh, Esther Y C; van Beers, Miranda; Mueller, Monika; Wan, Corrine; Teo, Gavin; Song, Zhiwei; Tong, Yen Wah; Bardor, Muriel; Yang, Yuansheng

    2013-06-10

    Immunoglobulin G (IgG), the most common class of commercial monoclonal antibodies (mAbs), exists as multimers of two identical light chains (LC) and two identical heavy chains (HC) assembled together by disulfide bridges. Due to the kinetics of mAb assembly, it is suggested that expression of LC and HC in equal amounts is not optimal for IgG production. We designed a set of vectors using internal ribosome entry site (IRES) elements to control LC and HC expression. The intracellular LC:HC ratio of stable IgG expressing Chinese hamster ovary (CHO) cell pools can be controlled effectively at four different ratios of 3.43, 1.24, 1.12, and 0.32. The stable pools were used to study the impact of LC:HC ratio on mAb expression and quality. Gene amplification was most effective for pools with excess LC and generated the highest mAb titers among the transfected pools. When LC:HC ratio was greater than one, more than 97% of the secreted products were IgG monomers. The products also have similar N-glycosylation profiles and conformational stabilities at those ratios. For pools presented a lower LC:HC ratio of 0.32, monomers only constituted half of the product with the other half being aggregates and mAb fragments. High mannose-type N-glycans increased while fucosylated and galactosylated glycans decreased significantly at the lowest LC:HC ratio. Product stability was also adversely affected. The results obtained provide insights to the impact of different LC:HC ratios on stable mAb production and useful information for vector design during generation of mAb producing cell lines. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. Distributed Multi-Agent-Based Protection Scheme for Transient Stability Enhancement in Power Systems

    NASA Astrophysics Data System (ADS)

    Rahman, M. S.; Mahmud, M. A.; Pota, H. R.; Hossain, M. J.; Orchi, T. F.

    2015-04-01

    This paper presents a new distributed agent-based scheme to enhance the transient stability of power systems by maintaining phase angle cohesiveness of interconnected generators through proper relay coordination with critical clearing time (CCT) information. In this distributed multi-agent infrastructure, intelligent agents represent various physical device models to provide dynamic information and energy flow among different physical processes of power systems. The agents can communicate with each other in a distributed manner with a final aim to control circuit breakers (CBs) with CCT information as this is the key issue for maintaining and enhancing the transient stability of power systems. The performance of the proposed scheme is evaluated on a standard IEEE 39-bus New England benchmark system under different large disturbances such as three-phase short-circuit faults and changes in loads within the systems. From the simulation results, it is found that the proposed scheme significantly enhances the transient stability of power systems as compared to a conventional scheme of static CB operation.

  20. A Byzantine-Fault Tolerant Self-Stabilizing Protocol for Distributed Clock Synchronization Systems

    NASA Technical Reports Server (NTRS)

    Malekpour, Mahyar R.

    2006-01-01

    Embedded distributed systems have become an integral part of safety-critical computing applications, necessitating system designs that incorporate fault tolerant clock synchronization in order to achieve ultra-reliable assurance levels. Many efficient clock synchronization protocols do not, however, address Byzantine failures, and most protocols that do tolerate Byzantine failures do not self-stabilize. Of the Byzantine self-stabilizing clock synchronization algorithms that exist in the literature, they are based on either unjustifiably strong assumptions about initial synchrony of the nodes or on the existence of a common pulse at the nodes. The Byzantine self-stabilizing clock synchronization protocol presented here does not rely on any assumptions about the initial state of the clocks. Furthermore, there is neither a central clock nor an externally generated pulse system. The proposed protocol converges deterministically, is scalable, and self-stabilizes in a short amount of time. The convergence time is linear with respect to the self-stabilization period. Proofs of the correctness of the protocol as well as the results of formal verification efforts are reported.

  1. A Byzantine-Fault Tolerant Self-Stabilizing Protocol for Distributed Clock Synchronization Systems

    NASA Technical Reports Server (NTRS)

    Malekpour, Mahyar R.

    2006-01-01

    Embedded distributed systems have become an integral part of safety-critical computing applications, necessitating system designs that incorporate fault tolerant clock synchronization in order to achieve ultra-reliable assurance levels. Many efficient clock synchronization protocols do not, however, address Byzantine failures, and most protocols that do tolerate Byzantine failures do not self-stabilize. Of the Byzantine self-stabilizing clock synchronization algorithms that exist in the literature, they are based on either unjustifiably strong assumptions about initial synchrony of the nodes or on the existence of a common pulse at the nodes. The Byzantine self-stabilizing clock synchronization protocol presented here does not rely on any assumptions about the initial state of the clocks. Furthermore, there is neither a central clock nor an externally generated pulse system. The proposed protocol converges deterministically, is scalable, and self-stabilizes in a short amount of time. The convergence time is linear with respect to the self-stabilization period. Proofs of the correctness of the protocol as well as the results of formal verification efforts are reported.

  2. Influence of humic acid applications on modulus of rupture, aggregate stability, electrical conductivity, carbon and nitrogen content of a crusting problem soil

    NASA Astrophysics Data System (ADS)

    Gümüş, İ.; Şeker, C.

    2015-11-01

    Soil structure is often said to be the key to soil productivity since a fertile soil, with desirable soil structure and adequate moisture supply, constitutes a productive soil. Soil structure influences soil water movement and retention, erosion, crusting, nutrient recycling, root penetration and crop yield. The objective of this work is to study humic acid (HA) application on some physical and chemical properties in weakly structured soils. The approach involved establishing a plot experiment in laboratory conditions. Different rates of HA (control, 0.5, 1, 2 and 4 %) were applied to soil during three incubation periods (21, 42 and 62 days). At the end of the each incubation period, the changes in physicochemical properties were measured. Generally, HA addition increased electrical conductivity values during all incubation periods. HA applications decreased soil modulus of rupture. Application of HA at the rate of 4 % significantly increased soil organic carbon contents. HA applications at the rate of 4 % significantly increased both mean soil total nitrogen content and aggregate stability after three incubation periods (p < 0.05). Therefore, HA has the potential to improve the structure of soil in the short term.

  3. Does the Spatial Distribution of the Parasitic Mite Varroa jacobsoni Oud. (Mesostigmata: Varroidae) in Worker Brood of Honey Bee Apis Mellifera L. (Hymenoptera: Apidae) Rely on an Aggregative Process?

    NASA Astrophysics Data System (ADS)

    Salvy, M.; Capowiez, Y.; Le Conte, Y.; Salvy, M.; Clément, J.-L.

    Varroa jacobsoni is an ectoparasite of honey bees which reproduces in capped brood cells. Multi-infestation is frequently observed in worker brood and can be interpreted as an aggregative phenomenon. The aim of this study was to determine whether the distribution of V. jacobsoni in worker brood cells relies on a random or an aggregative process. We studied the distribution of Varroa females in capped worker brood at similar age by comparing, by a Monte Carlo test, the observed frequency distribution of mites per cell to simulated distributions based on a random process. A complementary approach, using the "nearest neighbor distances" (NND) with Monte Carlo tests, was investigated to study the spatial distribution (a) between mites in different cells and (b) between infested cells in brood. The observed distributions did not differ significantly from that expected by a random process, and we conclude that there is no aggregation during invasion of V. jacobsoni in worker brood.

  4. Does the spatial distribution of the parasitic mite varroa jacobsoni oud. (Mesostigmata: varroidae) in worker brood of honey bee apis mellifera L. (Hymenoptera: apidae) rely on an aggregative process?

    PubMed

    Salvy; Capowiez; Le Conte Y; Clement

    1999-11-01

    Varroa jacobsoni is an ectoparasite of honey bees which reproduces in capped brood cells. Multi-infestation is frequently observed in worker brood and can be interpreted as an aggregative phenomenon. The aim of this study was to determine whether the distribution of V. jacobsoni in worker brood cells relies on a random or an aggregative process. We studied the distribution of Varroa females in capped worker brood at similar age by comparing, by a Monte Carlo test, the observed frequency distribution of mites per cell to simulated distributions based on a random process. A complementary approach, using the "nearest neighbor distances" (NND) with Monte Carlo tests, was investigated to study the spatial distribution (a) between mites in different cells and (b) between infested cells in brood. The observed distributions did not differ significantly from that expected by a random process, and we conclude that there is no aggregation during invasion of V. jacobsoni in worker brood.

  5. Stable Colloidal Drug Aggregates Catch and Release Active Enzymes

    PubMed Central

    McLaughlin, Christopher K.; Duan, Da; Ganesh, Ahil N.; Torosyan, Hayarpi

    2016-01-01

    Small molecule aggregates are considered nuisance compounds in drug discovery, but their unusual properties as colloids could be exploited to form stable vehicles to preserve protein activity. We investigated the co-aggregation of seven molecules chosen because they had been previously intensely studied as colloidal aggregators, co-formulating them with bis-azo dyes. The co-formulation reduced colloid sizes to <100 nm, and improved uniformity of the particle size distribution. The new colloid formulations are more stable than previous aggregator particles. Specifically, co-aggregation of Congo Red with sorafenib, tetraiodophenolphthalein (TIPT) or vemurafenib produced particles that are stable in solutions of high ionic strength and high protein concentrations. Like traditional, single compound colloidal aggregates, the stabilized colloids adsorbed and inhibited enzymes like β-lactamase, malate dehydrogenase and trypsin. Unlike traditional aggregates, the co-formulated colloid-protein particles could be centrifuged and re-suspended multiple times, and from re-suspended particles, active trypsin could be released up to 72 hours after adsorption. Unexpectedly, the stable colloidal formulations can sequester, stabilize, and isolate enzymes by spin-down, resuspension and release. PMID:26741163

  6. Characterization and modeling of thermal diffusion and aggregation in nanofluids.

    SciTech Connect

    Gharagozloo, Patricia E.; Goodson, Kenneth E.

    2010-05-01

    Fluids with higher thermal conductivities are sought for fluidic cooling systems in applications including microprocessors and high-power lasers. By adding high thermal conductivity nanoscale metal and metal oxide particles to a fluid the thermal conductivity of the fluid is enhanced. While particle aggregates play a central role in recent models for the thermal conductivity of nanofluids, the effect of particle diffusion in a temperature field on the aggregation and transport has yet to be studied in depth. The present work separates the effects of particle aggregation and diffusion using parallel plate experiments, infrared microscopy, light scattering, Monte Carlo simulations, and rate equations for particle and heat transport in a well dispersed nanofluid. Experimental data show non-uniform temporal increases in thermal conductivity above effective medium theory and can be well described through simulation of the combination of particle aggregation and diffusion. The simulation shows large concentration distributions due to thermal diffusion causing variations in aggregation, thermal conductivity and viscosity. Static light scattering shows aggregates form more quickly at higher concentrations and temperatures, which explains the increased enhancement with temperature reported by other research groups. The permanent aggregates in the nanofluid are found to have a fractal dimension of 2.4 and the aggregate formations that grow over time are found to have a fractal dimension of 1.8, which is consistent with diffusion limited aggregation. Calculations show as aggregates grow the viscosity increases at a faster rate than thermal conductivity making the highly aggregated nanofluids unfavorable, especially at the low fractal dimension of 1.8. An optimum nanoparticle diameter for these particular fluid properties is calculated to be 130 nm to optimize the fluid stability by reducing settling, thermal diffusion and aggregation.

  7. Stability Analysis of SIR Model with Distributed Delay on Complex Networks

    PubMed Central

    Huang, Chuangxia; Cao, Jie; Wen, Fenghua; Yang, Xiaoguang

    2016-01-01

    In this paper, by taking full consideration of distributed delay, demographics and contact heterogeneity of the individuals, we present a detailed analytical study of the Susceptible-Infected-Removed (SIR) epidemic model on complex population networks. The basic reproduction number R0 of the model is dominated by the topology of the underlying network, the properties of individuals which include birth rate, death rate, removed rate and infected rate, and continuously distributed time delay. By constructing suitable Lyapunov functional and employing Kirchhoff’s matrix tree theorem, we investigate the globally asymptotical stability of the disease-free and endemic equilibrium points. Specifically, the system shows threshold behaviors: if R0≤1, then the disease-free equilibrium is globally asymptotically stable, otherwise the endemic equilibrium is globally asymptotically stable. Furthermore, the obtained results show that SIR models with different types of delays have different converge time in the process of contagion: if R0>1, then the system with distributed time delay stabilizes fastest; while R0≤1, the system with distributed time delay converges most slowly. The validness and effectiveness of these results are demonstrated through numerical simulations. PMID:27490363

  8. Stability Analysis of SIR Model with Distributed Delay on Complex Networks.

    PubMed

    Huang, Chuangxia; Cao, Jie; Wen, Fenghua; Yang, Xiaoguang

    2016-01-01

    In this paper, by taking full consideration of distributed delay, demographics and contact heterogeneity of the individuals, we present a detailed analytical study of the Susceptible-Infected-Removed (SIR) epidemic model on complex population networks. The basic reproduction number [Formula: see text] of the model is dominated by the topology of the underlying network, the properties of individuals which include birth rate, death rate, removed rate and infected rate, and continuously distributed time delay. By constructing suitable Lyapunov functional and employing Kirchhoff's matrix tree theorem, we investigate the globally asymptotical stability of the disease-free and endemic equilibrium points. Specifically, the system shows threshold behaviors: if [Formula: see text], then the disease-free equilibrium is globally asymptotically stable, otherwise the endemic equilibrium is globally asymptotically stable. Furthermore, the obtained results show that SIR models with different types of delays have different converge time in the process of contagion: if [Formula: see text], then the system with distributed time delay stabilizes fastest; while [Formula: see text], the system with distributed time delay converges most slowly. The validness and effectiveness of these results are demonstrated through numerical simulations.

  9. Large grains matter: bed stability and morphodynamics for two experiments with nearly identical bed material distributions

    NASA Astrophysics Data System (ADS)

    Eaton, B. C.; MacKenzie, L.

    2016-12-01

    While the role of large grains has long been recognized for steep streams with step-pool morphology, the role they play in controlling the morphology and dynamics of streams with gravel-beds and riffle-pool morphologies is less clear. Traditionally, the stability of gravel beds has been assessed using a critical dimensionless shear stress approach applied to the median bed surface grain size. The result is that channel stability and bed material transport have been more-or-less equated with each other, at least in gravel-bed streams. Two mobile bed and bank experiments were conducted which demonstrate the effect that a slight change to the coarse tail of the bed material distribution can have on channel morphodynamics. The two distributions had the same range of particle sizes, and had nearly identical bulk d50 values (1.6 mm); the d90 of GSD 1 was slightly finer (3.7 mm) than that for GSD 2 (3.9 mm). Despite the small differences between the distributions, the experiment with GSD 1 had transport rates nearly 4 times greater than GSD 2, and developed a meandering channel pattern with well developed riffles, pools and bars. In contrast, the GSD 2 experiments were unable to alter the initial rectangular channel alignment, and developed a series of poorly defined, low amplitude alternate bars (see Fig. 1). While there were small differences in the bed surface texture for the two experiments, the estimated dimensionless shear stress for the unstable GSD 1 experiment was significantly lower than that for the GSD 2 experiment, which is contrary to expectations based on existing theories about channel stability. The failure of our existing models to explain the observed differences in the channel morphodynamics implies that we need to refine our ideas about what controls channel stability.

  10. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1995-01-01

    Part of the 1994 Industrial Minerals Review. The production, consumption, and applications of construction aggregates are reviewed. In 1994, the production of construction aggregates, which includes crushed stone and construction sand and gravel combined, increased 7.7 percent to 2.14 Gt compared with the previous year. These record production levels are mostly a result of funding for highway construction work provided by the Intermodal Surface Transportation Efficiency Act of 1991. Demand is expected to increase for construction aggregates in 1995.

  11. [Impact of Land Utilization Pattern on Distributing Characters of Labile Organic Carbon in Soil Aggregates in Jinyun Mountain].

    PubMed

    Li, Rui; Jiang, Chang-sheng; Hao, Qing-ju

    2015-09-01

    Four land utilization patterns were selected for this study in Jinyun mountain, including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land. Soil samples were taken every 10 cm in the depth of 60 cm soil and proportions of large macroaggregates (> 2 mm), small macroaggregates (0. 25-2 mm), microaggregates (0. 053 - 0. 25 mm) and silt + clay (<0. 053 mm) were obtained by wet sieving method to measure the content of organic carbon and labile organic carbon in each aggregate fraction and analyze impacts of land uses on organic carbon and labile organic carbon of soil aggregates. LOC content of four soil aggregates were significantly reduced with the increase of soil depth; in layers of 0-60 cm soil depth, our results showed that LOC contents of forest and abandoned land were higher than orchard and sloping farmland. Reserves of labile organic carbon were estimated by the same soil quality, it revealed that forest (3. 68 Mg.hm-2) > abandoned land (1. 73 Mg.hm-2) > orchard (1. 43 Mg.hm-2) >sloping farmland (0.54 Mg.hm-2) in large macroaggregates, abandoned land (7.77, 5. 01 Mg.hm-2) > forest (4. 96, 2.71 Mg.hm-2) > orchard (3. 33, 21. 10 Mg.hm-2) > sloping farmland (1. 68, 1. 35 Mg.hm-2) in small macroaggregates and microaggregates, and abandoned land(4. 32 Mg.hm-2) > orchard(4. 00 Mg.hm-2) > forest(3. 22 Mg.hm-2) > sloping farmland (2.37 Mg.hm-2) in silt + clay, forest and abandoned land were higher than orchard and sloping farmland in other three soil aggregates except silt + clay. It was observed that the level of organic carbon and labile organic carbon were decreased when bringing forest under cultivation to orchard or farmland, and augments on organic carbon and labile organic carbon were found after exchanging farmland to abandoned land. The most reverses of forest and abandoned land emerged in small macroaggregates, orchard and sloping farmland were in microaggregates. That was, during the

  12. Cell death response of U87 glioma cells on hypericin photoactivation is mediated by dynamics of hypericin subcellular distribution and its aggregation in cellular organelles.

    PubMed

    Huntosova, Veronika; Nadova, Zuzana; Dzurova, Lenka; Jakusova, Viera; Sureau, Franck; Miskovsky, Pavol

    2012-09-01

    Hypericin (Hyp) is a hydrophobic natural photosensitizer that is considered to be a promising molecule for photodynamic treatment of tumor cells and photo-diagnosis of early epithelial cancers. Its hydrophobicity is the main driving force that governs its redistribution process. Low-density lipoproteins (LDL), a natural in vivo carrier of cholesterol present in the vascular system, have been used for targeted transport of Hyp to U87 glioma cells. For low Hyp-LDL ratios (≤10 : 1), the cellular uptake of Hyp is characterized by endocytosis of the [Hyp-LDL] complex, while Hyp alone can enter cells by passive diffusion. Photo-induced cell death and the mitochondrial membrane potential, observed for glioma cells after various times of incubation with the [Hyp-LDL] complex or Hyp alone, were monitored by flow-cytometry analysis using Annexin-V-FITC propidium iodide and DiOC(6)(3) staining. Differences of the results are discussed in view of the respective dynamic subcellular distributions of the drugs that were obtained by co-localization experiments using confocal fluorescence microscopy. In order to give clear evidence of specific intracellular localization and to identify possible Hyp aggregation in cellular organelles, fluorescence resonance energy transfer (FRET) between selected fluorescent organelle probes and Hyp was also assessed. It is shown, that the observed photo-induced cell deaths can be correlated with the sub-cellular distribution of the active fluorescent monomer form of Hyp in lysosomes (as determined from steady-state fluorescence experiments), but that possible aggregation of Hyp in some organelles, as determined from FRET experiments, should be taken into account for interpretation of the real dynamics of the subcellular redistribution. Results of the present study underline the fact that photo-induced cell death processes are strongly influences by dynamics of Hyp subcellular redistribution processes involving monomer-aggregate equilibrium

  13. Stability characterization and modeling of robust distributed benthic microbial fuel cell (DBMFC) system.

    PubMed

    Karra, Udayarka; Huang, Guoxian; Umaz, Ridvan; Tenaglier, Christopher; Wang, Lei; Li, Baikun

    2013-09-01

    A novel and robust distributed benthic microbial fuel cell (DBMFC) was developed to address the energy supply issues for oceanographic sensor network applications, especially under scouring and bioturbation by aquatic life. Multi-anode/cathode configuration was employed in the DBMFC system for enhanced robustness and stability in the harsh ocean environment. The results showed that the DBMFC system achieved peak power and current densities of 190mW/m(2) and 125mA/m(2) respectively. Stability characterization tests indicated the DBMFC with multiple anodes achieved higher power generation over the systems with single anode. A computational model that integrated physical, electrochemical and biological factors of MFCs was developed to validate the overall performance of the DBMFC system. The model simulation well corresponded with the experimental results, and confirmed the hypothesis that using a multi anode/cathode MFC configuration results in reliable and robust power generation.

  14. Model Checking a Self-Stabilizing Distributed Clock Synchronization Protocol for Arbitrary Digraphs

    NASA Technical Reports Server (NTRS)

    Malekpour, Mahyar R.

    2011-01-01

    This report presents the mechanical verification of a self-stabilizing distributed clock synchronization protocol for arbitrary digraphs in the absence of faults. This protocol does not rely on assumptions about the initial state of the system, other than the presence of at least one node, and no central clock or a centrally generated signal, pulse, or message is used. The system under study is an arbitrary, non-partitioned digraph ranging from fully connected to 1-connected networks of nodes while allowing for differences in the network elements. Nodes are anonymous, i.e., they do not have unique identities. There is no theoretical limit on the maximum number of participating nodes. The only constraint on the behavior of the node is that the interactions with other nodes are restricted to defined links and interfaces. This protocol deterministically converges within a time bound that is a linear function of the self-stabilization period.

  15. Pressure Distribution Tests on a Series of Clark Y Biplane Cellules with Special Reference to Stability

    NASA Technical Reports Server (NTRS)

    Noyes, Richard W

    1933-01-01

    The pressure distribution data discussed in this report represents the results of part of an investigation conducted on the factors affecting the aerodynamic safety of airplanes. The present tests were made on semispan, circular-tipped Clark Y airfoil models mounted in the conventional manner on a separation plane. Pressure readings were made simultaneously at all test orifices at each of 20 angles of attack between -8 degrees and +90 degrees. The results of the tests on each wing arrangement are compared on the bases of maximum normal force coefficient, lateral stability at a low rate of roll, and relative longitudinal stability. Tabular data are also presented giving the center of pressure location of each wing.

  16. The effect of pulsewidth of pumping pulse on the stability of distributed feedback dye laser

    NASA Astrophysics Data System (ADS)

    Pasandideh, K.; Rahbari, M.; Sadighi Bonabi, R.

    2017-04-01

    The generation of a single and stable picosecond pulse by distributed feedback dye laser is investigated in this work. The numerical result for the rate equation system that includes the thermal effects in the lasing medium is provided. By applying this model to Rhodamine 6G, it is found that considerable improvement in the stability of the laser can be achieved by pumping the system with narrower laser pulses. The simulation shows that if the dye solution is pumped by sub-200 ps pulse, the laser can be operated in single-pulse output mode with acceptable stability in pulsewidth over a long range of pumping intensity. This result is confirmed by a more complicated model composed of non-averaged Maxwell and rate equations. Even though the thermal effects do not play a significant role in equivalent cavity lifetime, they result in considerable wavelength shift toward the shorter wavelengths.

  17. Discrete- and finite-bandwidth-frequency distributions in nonlinear stability applications

    NASA Astrophysics Data System (ADS)

    Kuehl, Joseph J.

    2017-02-01

    A new "wave packet" formulation of the parabolized stability equations method is presented. This method accounts for the influence of finite-bandwidth-frequency distributions on nonlinear stability calculations. The methodology is motivated by convolution integrals and is found to appropriately represent nonlinear energy transfer between primary modes and harmonics, in particular nonlinear feedback, via a "nonlinear coupling coefficient." It is found that traditional discrete mode formulations overestimate nonlinear feedback by approximately 70%. This results in smaller maximum disturbance amplitudes than those observed experimentally. The new formulation corrects this overestimation, accounts for the generation of side lobes responsible for spectral broadening, and results in disturbance representation more consistent with the experiment than traditional formulations. A Mach 6 flared-cone example is presented.

  18. Runaway electron distributions and their stability with respect to the anomalous Doppler resonance

    SciTech Connect

    Fuchs, V.; Shoucri, M.; Teichmann, J.; Bers, A.

    1988-08-01

    The stability of nonrelativistic runaway electron distributions with respect to the anomalous Doppler resonance is examined in a range of parameters of interest to tokamaks, i.e., for Yequivalent..omega../sub p//sub e//..cap omega../sub c//sub e/less than or equal to2 and for Ohmic electric fields epsilonequivalentE/E/sub c/less than or equal to0.1. Distribution functions are calculated numerically within a region up to 35v/sub e/ (thermal velocities) using a finite-element 2-D Fokker--Planck code. Alternatively, an analytic approximation for the runaway distribution function is used, valid beyond the critical velocity v/sub c/approx. =v/sub e/(E/sub c//E)/sup 1//sup ///sup 2/. Stability thresholds in (..omega..,k/sub parallel/) space are then determined. For example, for Y = 1 and epsilon = 0.1, and providing that the runaway tail extends at least to 30v/sub e/, unstable waves exist having ..omega..less than or equal to0.6..cap omega../sub c//sub e/ and k/sub parallel/less than or equal to0.03..cap omega../sub c//sub e//v/sub e/.

  19. Modeling sediment mobilization using a distributed hydrological model coupled with a bank stability model

    NASA Astrophysics Data System (ADS)

    Stryker, J.; Wemple, B.; Bomblies, A.

    2017-03-01

    In addition to surface erosion, stream bank erosion and failure contributes significant sediment and sediment-bound nutrients to receiving waters during high flow events. However, distributed and mechanistic simulation of stream bank sediment contribution to sediment loads in a watershed has not been achieved. Here we present a full coupling of existing distributed watershed and bank stability models and apply the resulting model to the Mad River in central Vermont. We fully coupled the Bank Stability and Toe Erosion Model (BSTEM) with the Distributed Hydrology Soil Vegetation Model (DHSVM) to allow the simulation of stream bank erosion and potential failure in a spatially explicit environment. We demonstrate the model's ability to simulate the impacts of unstable streams on sediment mobilization and transport within a watershed and discuss the model's capability to simulate watershed sediment loading under climate change. The calibrated model simulates total suspended sediment loads and reproduces variability in suspended sediment concentrations at watershed and subbasin outlets. In addition, characteristics such as land use and road-to-stream ratio of subbasins are shown to impact the relative proportions of sediment mobilized by overland erosion, erosion of roads, and stream bank erosion and failure in the subbasins and watershed. This coupled model will advance mechanistic simulation of suspended sediment mobilization and transport from watersheds, which will be particularly valuable for investigating the potential impacts of climate and land use changes, as well as extreme events.

  20. Stability, intermittency and universal Thorpe length distribution in a laboratory turbulent stratified shear flow

    DOE PAGES

    Odier, Philippe; Ecke, Robert E.

    2017-02-21

    Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbersmore » $$0.05\\lesssim Ri\\lesssim 1$$. In order to find a stability parameter that allows close comparison with linear theory and with idealized experiments and numerics, we investigate different definitions of$Ri$$. We find that a gradient Richardson number defined on fluid interface sections where there is no overturning at or adjacent to the maximum density gradient position provides an excellent stability parameter, which captures the Miles–Howard linear stability criterion. For small $$Ri$$ the flow exhibits robust Kelvin–Helmholtz instability, whereas for larger $$Ri$$ interfacial overturning is more intermittent with less frequent Kelvin–Helmholtz events and emerging Holmboe wave instability consistent with a thicker velocity layer compared with the density layer. We compute the perturbed fraction of interface as a quantitative measure of the flow intermittency, which is approximately 1 for the smallest $$Ri$$ but decreases rapidly as $$Ri$ increases, consistent with linear theory. For the perturbed regions, we use the Thorpe scale to characterize the overturning properties of these flows. The probability distribution of the non-zero Thorpe length yields a universal exponential form, suggesting that much of the overturning results from increasingly intermittent Kelvin–Helmholtz instability events. Finally, the distribution of turbulent kinetic energy, conditioned on the intermittency fraction, has a similar form, suggesting an explanation for the universal scaling collapse of the Thorpe length distribution.« less

  1. Measuring and Modeling Root Distribution and Root Reinforcement in Forested Slopes for Slope Stability Calculations

    NASA Astrophysics Data System (ADS)

    Cohen, D.; Giadrossich, F.; Schwarz, M.; Vergani, C.

    2016-12-01

    Roots provide mechanical anchorage and reinforcement of soils on slopes. Roots also modify soil hydrological properties (soil moisture content, pore-water pressure, preferential flow paths) via subsurface flow path associated with root architecture, root density, and root-size distribution. Interactions of root-soil mechanical and hydrological processes are an important control of shallow landslide initiation during rainfall events and slope stability. Knowledge of root-distribution and root strength are key components to estimate slope stability in vegetated slopes and for the management of protection forest in steep mountainous area. We present data that show the importance of measuring root strength directly in the field and present methods for these measurements. These data indicate that the tensile force mobilized in roots depends on root elongation (a function of soil displacement), root size, and on whether roots break in tension of slip out of the soil. Measurements indicate that large lateral roots that cross tension cracks at the scarp are important for slope stability calculations owing to their large tensional resistance. These roots are often overlooked and when included, their strength is overestimated because extrapolated from measurements on small roots. We present planned field experiments that will measure directly the force held by roots of different sizes during the triggering of a shallow landslide by rainfall. These field data are then used in a model of root reinforcement based on fiber-bundle concepts that span different spacial scales, from a single root to the stand scale, and different time scales, from timber harvest to root decay. This model computes the strength of root bundles in tension and in compression and their effect on soil strength. Up-scaled to the stand the model yields the distribution of root reinforcement as a function of tree density, distance from tree, tree species and age with the objective of providing quantitative

  2. Evidences of Changes in Surface Electrostatic Charge Distribution during Stabilization of HPV16 Virus-Like Particles

    PubMed Central

    Vega, Juan F.; Vicente-Alique, Ernesto; Núñez-Ramírez, Rafael; Wang, Yang; Martínez-Salazar, Javier

    2016-01-01

    The stabilization of human papillomavirus type 16 virus-like particles has been examined by means of different techniques including dynamic and static light scattering, transmission electron microscopy and electrophoretic mobility. All these techniques provide different and often complementary perspectives about the aggregation process and generation of stabilized virus-like particles after a period of time of 48 hours at a temperature of 298 K. Interestingly, static light scattering results point towards a clear colloidal instability in the initial systems, as suggested by a negative value of the second virial coefficient. This is likely related to small repulsive electrostatic interactions among the particles, and in agreement with relatively small absolute values of the electrophoretic mobility and, hence, of the net surface charges. At this initial stage the small repulsive interactions are not able to compensate binding interactions, which tend to aggregate the particles. As time proceeds, an increase of the size of the particles is accompanied by strong increases, in absolute values, of the electrophoretic mobility and net surface charge, suggesting enhanced repulsive electrostatic interactions and, consequently, a stabilized colloidal system. These results show that electrophoretic mobility is a useful methodology that can be applied to screen the stabilization factors for virus-like particles during vaccine development. PMID:26885635

  3. Global stability of a multi-group model with vaccination age, distributed delay and random perturbation.

    PubMed

    Xu, Jinhu; Zhou, Yicang

    2015-10-01

    A multi-group epidemic model with distributed delay and vaccination age has been formulated and studied. Mathematical analysis shows that the global dynamics of the model is determined by the basic reproduction number R0: the disease-free equilibrium is globally asymptotically stable if R0 ≤ 1, and the endemic equilibrium is globally asymptotically stable if R0 > 1. Lyapunov functionals are constructed by the non-negative matrix theory and a novel grouping technique to establish the global stability. The stochastic perturbation of the model is studied and it is proved that the endemic equilibrium of the