Science.gov

Sample records for aggregate size classes

  1. Distribution of a Population of Rhizobium leguminosarum bv. trifolii among Different Size Classes of Soil Aggregates.

    PubMed

    Mendes, I C; Bottomley, P J

    1998-03-01

    A combination of the plant infection-soil dilution technique (most-probable-number [MPN] technique) and immunofluorescence direct count (IFDC) microscopy was used to examine the effects of three winter cover crop treatments on the distribution of a soil population of Rhizobium leguminosarum bv. trifolii across different size classes of soil aggregates (<0.25, 0.25 to 0.5, 0.5 to 1.0, 1.0 to 2.0, and 2.0 to 5.0 mm). The aggregates were prepared from a Willamette silt loam soil immediately after harvest of broccoli (September 1995) and before planting and after harvest of sweet corn (June and September 1996, respectively). The summer crops were grown in soil that had been either fallowed or planted with a cover crop of red clover (legume) or triticale (cereal) from September to April. The Rhizobium soil population was heterogeneously distributed across the different size classes of soil aggregates, and the distribution was influenced by cover crop treatment and sampling time. On both September samplings, the smallest size class of aggregates (<0.25 mm) recovered from the red clover plots carried between 30 and 70% of the total nodulating R. leguminosarum population, as estimated by the MPN procedure, while the same aggregate size class from the June sampling carried only approximately 6% of the population. In June, IDFC microscopy revealed that the 1.0- to 2.0-mm size class of aggregates from the red clover treatment carried a significantly greater population density of the successful nodule-occupying serotype, AR18, than did the aggregate size classes of <0.5 mm, and 2 to 5 mm. In September, however, the population profile of AR18 had shifted such that the density was significantly greater in the 0.25- to 0.5-mm size class than in aggregates of <0.25 mm and >1.0 mm. The populations of two other Rhizobium serotypes (AR6 and AS36) followed the same trends of distribution in the June and September samplings. These data indicate the existence of structural microsites

  2. Differences in SOM decomposition and temperature sensitivity among soil aggregate size classes in a temperate grasslands.

    PubMed

    Wang, Qing; Wang, Dan; Wen, Xuefa; Yu, Guirui; He, Nianpeng; Wang, Rongfu

    2015-01-01

    The principle of enzyme kinetics suggests that the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is inversely related to organic carbon (C) quality, i.e., the C quality-temperature (CQT) hypothesis. We tested this hypothesis by performing laboratory incubation experiments with bulk soil, macroaggregates (MA, 250-2000 μm), microaggregates (MI, 53-250 μm), and mineral fractions (MF, <53 μm) collected from an Inner Mongolian temperate grassland. The results showed that temperature and aggregate size significantly affected on SOM decomposition, with notable interactive effects (P<0.0001). For 2 weeks, the decomposition rates of bulk soil and soil aggregates increased with increasing incubation temperature in the following order: MA>MF>bulk soil >MI(P <0.05). The Q10 values were highest for MA, followed (in decreasing order) by bulk soil, MF, and MI. Similarly, the activation energies (Ea) for MA, bulk soil, MF, and MI were 48.47, 33.26, 27.01, and 23.18 KJ mol-1, respectively. The observed significant negative correlations between Q10 and C quality index in bulk soil and soil aggregates (P<0.05) suggested that the CQT hypothesis is applicable to soil aggregates. Cumulative C emission differed significantly among aggregate size classes (P <0.0001), with the largest values occurring in MA (1101 μg g-1), followed by MF (976 μg g-1) and MI (879 μg g-1). These findings suggest that feedback from SOM decomposition in response to changing temperature is closely associated withsoil aggregation and highlights the complex responses of ecosystem C budgets to future warming scenarios.

  3. Class Size.

    ERIC Educational Resources Information Center

    Ellis, Thomas I.

    1985-01-01

    After a brief introduction identifying current issues and trends in research on class size, this brochure reviews five recent studies bearing on the relationship of class size to educational effectiveness. Part 1 is a review of two interrelated and highly controversial "meta-analyses" or statistical integrations of research findings on class size,…

  4. Does Class Size Matter?

    ERIC Educational Resources Information Center

    Ehrenberg, Ronald G.; Brewer, Dominic J.; Gamoran, Adam; Willms, J. Douglas

    2001-01-01

    Reports on the significance of class size to student learning. Includes an overview of class size in various countries, the importance of teacher adaptability, and the Asian paradox of large classes allied to high test scores. (MM)

  5. The Class Size Debate.

    ERIC Educational Resources Information Center

    Mishel, Lawrence, Ed.; Rothstein, Richard, Ed.

    This collection of papers debates the merits of smaller class sizes and research methods used to evaluate the efficacy of this education reform measure. Four chapters focus on (1) "Understanding the Magnitude and Effect of Class Size on Student Achievement" (Alan B. Krueger), which discusses expenditures per student and economic criterion; (2)…

  6. Financing Class Size Reduction

    ERIC Educational Resources Information Center

    Achilles, C. M.

    2005-01-01

    Class size reduction has been shown to, among other things, improve academic achievement for all students and particularly for low-income and minority students. With the No Child Left Behind Act's heavy emphasis on scientifically based research, adequate yearly progress, and disaggregated results, one wonders why all children aren't enrolled in…

  7. Class Size & School Size. Research Brief

    ERIC Educational Resources Information Center

    Hansen, Angela

    2005-01-01

    Class size is one of the most researched and heavily debated topics in American public education. Currently, at least 25 states have initiated class size reduction (CSR) programs. In the past twenty years, several major studies have been conducted which indicate that smaller class sizes produce an increase in student achievement as well as greater…

  8. 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

  9. Exact dynamics of a class of aggregation models

    NASA Astrophysics Data System (ADS)

    Majumdar, Satya N.; Sire, Clément

    1993-11-01

    The dynamics of a class of aggregation models proposed by Takayasu and co-workers are solved exactly in one dimension and in the mean field limit. These models describe the aggregation of positive and negative charges. In one dimension, we find the dynamical cluster-size exponents z=3/2 and zc=3/4 when the average flux of injected charges is nonzero and zero, respectively. We also find the crossover exponent near the transition to be φ=4/3. Within mean field theory, we find these exponents to be z=2, zc=1, and φ=1. Assuming dynamic scaling, we show that in any dimension, these exponents are related to one single static exponent.

  10. Class-Size Effects in Secondary School

    ERIC Educational Resources Information Center

    Krassel, Karl Fritjof; Heinesen, Eskil

    2014-01-01

    We analyze class-size effects on academic achievement in secondary school in Denmark exploiting an institutional setting where pupils cannot predict class size prior to enrollment, and where post-enrollment responses aimed at affecting realized class size are unlikely. We identify class-size effects combining a regression discontinuity design with…

  11. Effects of maximum aggregate size on UPV of brick aggregate concrete.

    PubMed

    Mohammed, Tarek Uddin; Mahmood, Aziz Hasan

    2016-07-01

    Investigation was carried out to study the effects of maximum aggregate size (MAS) (12.5mm, 19.0mm, 25.0mm, 37.5mm, and 50.0mm) on ultrasonic pulse velocity (UPV) of concrete. For investigation, first class bricks were collected and broken to make coarse aggregate. The aggregates were tested for specific gravity, absorption capacity, unit weight, and abrasion resistance. Cylindrical concrete specimens were made with different sand to aggregate volume ratio (s/a) (0.40 and 0.45), W/C ratio (0.45, 0.50, and 0.55), and cement content (375kg/m(3) and 400kg/m(3)). The specimens were tested for compressive strength and Young's modulus. UPV through wet specimen was measured using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). Results indicate that the pulse velocity through concrete increases with an increase in MAS. Relationships between UPV and compressive strength; and UPV and Young's modulus of concrete are proposed for different maximum sizes of brick aggregate. PMID:27085110

  12. Effects of maximum aggregate size on UPV of brick aggregate concrete.

    PubMed

    Mohammed, Tarek Uddin; Mahmood, Aziz Hasan

    2016-07-01

    Investigation was carried out to study the effects of maximum aggregate size (MAS) (12.5mm, 19.0mm, 25.0mm, 37.5mm, and 50.0mm) on ultrasonic pulse velocity (UPV) of concrete. For investigation, first class bricks were collected and broken to make coarse aggregate. The aggregates were tested for specific gravity, absorption capacity, unit weight, and abrasion resistance. Cylindrical concrete specimens were made with different sand to aggregate volume ratio (s/a) (0.40 and 0.45), W/C ratio (0.45, 0.50, and 0.55), and cement content (375kg/m(3) and 400kg/m(3)). The specimens were tested for compressive strength and Young's modulus. UPV through wet specimen was measured using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). Results indicate that the pulse velocity through concrete increases with an increase in MAS. Relationships between UPV and compressive strength; and UPV and Young's modulus of concrete are proposed for different maximum sizes of brick aggregate.

  13. Does Class Size Make a Difference?

    ERIC Educational Resources Information Center

    Glass, Gene V.; Down, A. Graham

    1979-01-01

    Argues that study findings indicate that lowered class size increases student achievement and improves school attitudes. Counter argument indicates there is little educational payoff and great monetary expense in small reductions in class size. (RH)

  14. Do Class Size Effects Differ across Grades?

    ERIC Educational Resources Information Center

    Nandrup, Anne Brink

    2016-01-01

    This paper contributes to the class size literature by analysing whether short-run class size effects are constant across grade levels in compulsory school. Results are based on administrative data on all pupils enrolled in Danish public schools. Identification is based on a government-imposed class size cap that creates exogenous variation in…

  15. School Class Size: Research and Policy

    ERIC Educational Resources Information Center

    Glass, Gene V.; And Others

    This book synthesizes research evidence to demonstrate that 1) class size is strongly related to pupil achievement; 2) smaller classes are more conducive to improved pupil performance than larger classes; 3) smaller classes provide more opportunities to adapt learning programs to individual needs; 4) pupils in smaller classes have more interest in…

  16. Reducing Class Size To Increase Student Involvement.

    ERIC Educational Resources Information Center

    Lottes, Christine R.

    Reducing class size was considered an important element in a revised health course at Gettysburg College (Pennsylvania). However, reducing class size to approximately 15 students per class would require 38 sections, more than the health faculty could handle. To recruit additional instructors, the course was marketed to faculty and administrators…

  17. Class Sizes and Dissadvantaged Schools.

    ERIC Educational Resources Information Center

    Warner, David

    1978-01-01

    Describes a program in which smaller class groups for socially and culturally deprived children resulted in enhanced social attitudes and more responsive, mature behavior in interaction with both adults and peers. (Author/IRT)

  18. Researcher Perspectives on Class Size Reduction

    ERIC Educational Resources Information Center

    Graue, Elizabeth; Rauscher, Erica

    2009-01-01

    This article applies to class size research Grant and Graue's (1999) position that reviews of research represent conversations in the academic community. By extending our understanding of the class size reduction conversation beyond published literature to the perspectives of researchers who have studied the topic, we create a review that includes…

  19. Reducing Class Size: Promises and Perils

    ERIC Educational Resources Information Center

    Bascia, Nina; Fredua-Kwarteng, Eric

    2008-01-01

    Reducing class size, especially in primary grades, can have tremendous academic and social benefits for children--benefits that endure well beyond those first years of school. But smaller class sizes are not a cure-all. Beyond the hoopla of enthusiasm for this seemingly simple change in educational practice lie serious consequences for students…

  20. Reducing Class Size Leads to Individualized Instruction.

    ERIC Educational Resources Information Center

    Zahorik, John A.

    1999-01-01

    SAGE is a five-year class-size-reduction program being implemented in 80 Wisconsin schools. A longitudinal, evaluative study is being conducted in 30 SAGE schools. Small classes have three effects leading to increased individualization: fewer discipline problems, greater knowledge of students, and more teacher enthusiasm (using directive methods).…

  1. So, Where Are We with Class Size?

    ERIC Educational Resources Information Center

    Johnson, Donald P.

    2001-01-01

    Although class-size reductions cannot guarantee better student performance, the Tennessee and Wisconsin experiences, along with other studies, suggest that successful programs share key characteristics: concentration in the primary schooling years, classes with not more than 20 students, greater benefits for urban minority students, and alignment…

  2. Microbial life in variably saturated soil aggregates - upscaling gaseous fluxes across distributed aggregate sizes in a soil profile

    NASA Astrophysics Data System (ADS)

    Or, D.; Ebrahimi, A.

    2015-12-01

    Recent studies revealed highly dynamic and rich behavior of microbial communities inhabiting soil aggregates. Modeling of these processes in three dimensional (unsaturated) pore networks provided insights into the unique conditions essential for coexistence of oxic and anoxic microsites that shape (and respond to) aerobic and anaerobic microbial communities. Soil hydration dynamics continuously alter the spatial extent of anoxic niches (hotspots) that flicker in time (hot moments) and support anaerobic microbial activity even in unsaturated and oxic soil profiles. We extend a model for individual-based microbial community growth in 3-D angular pore networks mimicking soil aggregates of different sizes placed in different ambient boundary conditions reflecting profiles of water, carbon, and oxygen in soil. An upscaling scheme was developed to account for aerobic and anaerobic activity within each aggregate class size and soil depth integrated over the aggregate size distribution in the soil for a range of hydration conditions. Results show that dynamic adjustments in microbial community composition affect CO2 and N2O production rates in good agreement with experimental data. The modeling approach addresses a long-standing challenge of linking hydration conditions to dynamic adjustments of microbial communities within "hotspots" with the emergence of "hot moments" reflecting high rates of denitrification and organic matter decomposition.

  3. Chiefs' Pocket Guide to Class Size: A Research Synthesis to Inform State Class Size Policies

    ERIC Educational Resources Information Center

    Council of Chief State School Officers, 2012

    2012-01-01

    Few questions in public education discourse benefit as much from research-based evidence as the question of class size--the pursuit of the ideal number of students that should be co-located for any particular period of instruction. But for policymakers, research on class size can be an embarrassment of riches, and much of the research appears to…

  4. Aggregate breakdown and surface seal development influenced by rain intensity, slope gradient and soil particle size

    NASA Astrophysics Data System (ADS)

    Arjmand Sajjadi, S.; Mahmoodabadi, M.

    2014-12-01

    Aggregate breakdown is an important process which controls infiltration rate (IR) and the availability of fine materials necessary for structural sealing under rainfall. The purpose of this study was to investigate the effects of different slope gradients, rain intensities and particle size distributions on aggregate breakdown and IR to describe the formation of surface sealing. To address this issue, 60 experiments were carried out in a 35 cm x 30 cm x 10 cm detachment tray using a rainfall simulator. By sieving a sandy loam soil, two sub-samples with different maximum aggregate sizes of 2 mm (Dmax 2 mm) and 4.75 mm (Dmax 4.75 mm) were prepared. The soils were exposed to two different rain intensities (57 and 80 mm h-1) on several slopes (0.5, 2.5, 5, 10, and 20%) each at three replications. The result showed that the most fraction percentages in soils Dmax 2 mm and Dmax 4.75 mm were in the finest size classes of 0.02 and 0.043 mm, respectively for all slope gradients and rain intensities. The soil containing finer aggregates exhibited higher transportability of pre-detached material than the soil containing larger aggregates. Also, IR increased with increasing slope gradient, rain intensity and aggregate size under unsteady state conditions because of less development of surface seal. But under steady state conditions, no significant relationship was found between slope and IR. The finding of this study revealed the importance of rain intensity, slope steepness and soil aggregate size on aggregate breakdown and seal formation, which can control infiltration rate and the consequent runoff and erosion rates.

  5. Reactivity, swelling and aggregation of mixed-size silicate nanoplatelets.

    PubMed

    Segad, M; Cabane, B; Jönsson, Bo

    2015-10-21

    Montmorillonite is a key ingredient in a number of technical applications. However, little is known regarding the microstructure and the forces between silicate platelets. The size of montmorillonite platelets from different natural sources can vary significantly. This has an influence on their swelling behavior in water as well as in salt solutions, particularly when tactoid formation occurs, that is when divalent counterions are present in the system. A tactoid consists of a limited number of platelets aggregated in a parallel arrangement with a constant separation. The tactoid size increases with platelet size and with very small nanoplatelets, ∼30 nm, no tactoids are observed irrespectively of the platelet origin and concentration of divalent ions. The formation and dissociation of tactoids seem to be reversible processes. A large proportion of small nanoplatelets in a mixed-size system affects the tactoid formation, reduces the aggregation number and increases the extra-lamellar swelling in the system. PMID:26376952

  6. Reactivity, swelling and aggregation of mixed-size silicate nanoplatelets

    NASA Astrophysics Data System (ADS)

    Segad, M.; Cabane, B.; Jönsson, Bo

    2015-10-01

    Montmorillonite is a key ingredient in a number of technical applications. However, little is known regarding the microstructure and the forces between silicate platelets. The size of montmorillonite platelets from different natural sources can vary significantly. This has an influence on their swelling behavior in water as well as in salt solutions, particularly when tactoid formation occurs, that is when divalent counterions are present in the system. A tactoid consists of a limited number of platelets aggregated in a parallel arrangement with a constant separation. The tactoid size increases with platelet size and with very small nanoplatelets, ~30 nm, no tactoids are observed irrespectively of the platelet origin and concentration of divalent ions. The formation and dissociation of tactoids seem to be reversible processes. A large proportion of small nanoplatelets in a mixed-size system affects the tactoid formation, reduces the aggregation number and increases the extra-lamellar swelling in the system.

  7. Reducing Router Forwarding Table Size Using Aggregation and Caching

    ERIC Educational Resources Information Center

    Liu, Yaoqing

    2013-01-01

    The fast growth of global routing table size has been causing concerns that the Forwarding Information Base (FIB) will not be able to fit in existing routers' expensive line-card memory, and upgrades will lead to a higher cost for network operators and customers. FIB Aggregation, a technique that merges multiple FIB entries into one, is probably…

  8. Where Class Size Really Matters: Class Size and Student Ratings of Instructor Effectiveness

    ERIC Educational Resources Information Center

    Bedard, Kelly; Kuhn, Peter

    2008-01-01

    We examine the impact of class size on student evaluations of instructor performance using data on all economics classes offered at the University of California, Santa Barbara from Fall 1997 to Spring 2004. A particular strength of this data is the opportunity to control for both instructor and course fixed effects. In contrast to the literature…

  9. Exciton Theory for Supramolecular Chlorosomal Aggregates: 1. Aggregate Size Dependence of the Linear Spectra

    PubMed Central

    Prokhorenko, V. I.; Steensgaard, D. B.; Holzwarth, A. R.

    2003-01-01

    The interior of chlorosomes of green bacteria forms an unusual antenna system organized without proteins. The steady-spectra (absorption, circular dichroism, and linear dichroism) have been modeled using the Frenkel Hamiltonian for the large tubular aggregates of bacteriochlorophylls with geometries corresponding to those proposed for Chloroflexus aurantiacus and Chlorobium tepidum chlorosomes. For the Cf. aurantiacus aggregates we apply a structure used previously (V. I. Prokhorenko., D. B. Steensgaard, and A. R. Holzwarth, Biophys. J. 2000, 79:2105–2120), whereas for the Cb. tepidum aggregates a new extended model of double-tube aggregates, based on recently published solid-state nuclear magnetic resonance studies (B.-J. van Rossum, B. Y. van Duhl, D. B. Steensgaard, T. S. Balaban, A. R. Holzwarth, K. Schaffner, and H. J. M. de Groot, Biochemistry 2001, 40:1587–1595), is developed. We find that the circular dichroism spectra depend strongly on the aggregate length for both types of chlorosomes. Their shape changes from “type-II” (negative at short wavelengths to positive at long wavelengths) to the “mixed-type” (negative-positive-negative) in the nomenclature proposed in K. Griebenow, A. R. Holzwarth, F. van Mourik, and R. van Grondelle, Biochim. Biophys. Acta 1991, 1058:194–202, for an aggregate length of 30–40 bacteriochlorophyll molecules per stack. This “size effect” on the circular dichroism spectra is caused by appearance of macroscopic chirality due to circular distribution of the transition dipole moment of the monomers. We visualize these distributions, and also the corresponding Frenkel excitons, using a novel presentation technique. The observed size effects provide a key to explain many previously puzzling and seemingly contradictory experimental data in the literature on the circular and linear dichroism spectra of seemingly identical types of chlorosomes. PMID:14581217

  10. Effects of Soy Protein Nanoparticle Aggregate Size on the Viscoelastic Properties of Styrene-Butadiene Composites

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soy protein nanoparticle aggregates were prepared by alkaline hydrolysis of soy protein isolate (SPI). Light scattering measurements indicated a narrow size distribution of SPI aggregates. Nanocomposites were formed by mixing hydrolyzed SPI (HSPI) nanoparticle aggregates with styrene-butadiene (SB...

  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. A New Mass Mortality of Juvenile Protoceratops and Size-Segregated Aggregation Behaviour in Juvenile Non-Avian Dinosaurs

    PubMed Central

    Hone, David W. E.; Farke, Andrew A.; Watabe, Mahito; Shigeru, Suzuki; Tsogtbaatar, Khishigjav

    2014-01-01

    Background Monodominant bonebeds are a relatively common occurrence for non-avian dinosaurs, and have been used to infer associative, and potentially genuinely social, behavior. Previously known assemblages are characterized as either mixed size-classes (juvenile and adult-sized specimens together) or single size-classes of individuals (only juveniles or only adult-sized individuals within the assemblage). In the latter case, it is generally unknown if these kinds of size-segregated aggregations characterize only a particular size stage or represent aggregations that happened at all size stages. Ceratopsians (“horned dinosaurs”) are known from both types of assemblages. Methods/Principal Findings Here we describe a new specimen of the ceratopsian dinosaur Protoceratops andrewsi, Granger and Gregory 1923 from Mongolia representing an aggregation of four mid-sized juvenile animals. In conjunction with existing specimens of groups of P. andrewsi that includes size-clustered aggregations of young juveniles and adult-sized specimens, this new material provides evidence for some degree of size-clustered aggregation behaviour in Protoceratops throughout ontogeny. This continuity of size-segregated (and presumably age-clustered) aggregation is previously undocumented in non-avian dinosaurs. Conclusions The juvenile group fills a key gap in the available information on aggregations in younger ceratopsians. Although we support the general hypothesis that many non-avian dinosaurs were gregarious and even social animals, we caution that evidence for sociality has been overstated and advocate a more conservative interpretation of some data of ‘sociality’ in dinosaurs. PMID:25426957

  13. Spall Strength Measurements of Concrete for Varying Aggregate Sizes

    SciTech Connect

    Chhabildas, Lalit C.; Kipp, Marlin E.; Reinhart, William D.; Wilson, Leonard T.

    1999-05-05

    Controlled impact experiments have been performed to determine the spall strength of four different concrete compositions. The four concrete compositions are identified as, `SAC-5, CSPC', ("3/4") large, and ("3/8") small, Aggregate. They differ primarily in aggregate size but with average densities varying by less than five percent. Wave profiles from sixteen experiments, with shock amplitudes of 0.07 to 0.55 GPa, concentrate primarily within the elastic regime. Free-surface particle velocity measurements indicate consistent pullback signals in the release profiles, denoting average span strength of approximately 40 MPa. It is the purpose of this paper to present spall measurements under uniaxial strain loading. Notwithstanding considerable wave structure that is a unique characteristic to the heterogeneous nature of the scaled concrete, the spall amplitudes appear reproducible and consistent over the pressure range reported in this study.

  14. Are Small Classes Better? Understanding Relationships between Class Size, Classroom Processes and Pupils' Learning

    ERIC Educational Resources Information Center

    Pedder, David

    2006-01-01

    Twelve years ago Blatchford and Mortimore's authoritative review of class size research appeared in this journal. They concluded that a major problem with class size research was the lack of detailed studies of complex classroom processes that might mediate class size effects on pupils' learning. This article reviews two UK class size reviews and…

  15. Influence of particle size on diffusion-limited aggregation.

    PubMed

    Tan, Z J; Zou, X W; Zhang, W B; Jin, Z Z

    1999-11-01

    The influence of particle size on diffusion-limited aggregation (DLA) has been investigated by computer simulations. For DLA clusters consisting of two kinds of particles with different sizes, when large particles are in the minority, the patterns of clusters appear asymmetrical and nonuniform, and their fractal dimensions D(f) increase compared with one-component DLA. With increasing size of large particles, D(f) increases. This increase can be attributed to two reasons: one is that large particles become new growth centers; the other is the big masses of large particles. As the concentration ratio x(n) of large particles increases, D(f) will reach a maximum value D(f(m)) and then decrease. When x(n) exceeds a certain value, the morphology and D(f) of the two-component DLA clusters are similar to those of one-component DLA clusters. PMID:11970534

  16. Aggregation dynamics explain vegetation patch-size distributions.

    PubMed

    Irvine, M A; Bull, J C; Keeling, M J

    2016-04-01

    Vegetation patch-size distributions have been an intense area of study for theoreticians and applied ecologists alike in recent years. Of particular interest is the seemingly ubiquitous nature of power-law patch-size distributions emerging in a number of diverse ecosystems. The leading explanation of the emergence of these power-laws is due to local facilitative mechanisms. There is also a common transition from power law to exponential distribution when a system is under global pressure, such as grazing or lack of rainfall. These phenomena require a simple mechanistic explanation. Here, we study vegetation patches from a spatially implicit, patch dynamic viewpoint. We show that under minimal assumptions a power-law patch-size distribution appears as a natural consequence of aggregation. A linear death term also leads to an exponential term in the distribution for any non-zero death rate. This work shows the origin of the breakdown of the power-law under increasing pressure and shows that in general, we expect to observe a power law with an exponential cutoff (rather than pure power laws). The estimated parameters of this distribution also provide insight into the underlying ecological mechanisms of aggregation and death.

  17. Policy from the Hip: Class-Size Reduction in California

    ERIC Educational Resources Information Center

    Schrag, Peter

    2007-01-01

    California was, and remains, the largest "experiment" in class-size reduction (CSR) in the country's history. Its sweeping program to reduce the state's classes in kindergarten through the third grade covered nearly 2 million students and dropped the average class size from almost twenty-nine students per class, and often a great many more, to…

  18. Multi-Positioning Mathematics Class Size: Teachers' Views

    ERIC Educational Resources Information Center

    Handal, Boris; Watson, Kevin; Maher, Marguerite

    2015-01-01

    This paper explores mathematics teachers' perceptions about class size and the impact class size has on teaching and learning in secondary mathematics classrooms. It seeks to understand teachers' views about optimal class sizes and their thoughts about the education variables that influence these views. The paper draws on questionnaire responses…

  19. Online Class Size, Note Reading, Note Writing and Collaborative Discourse

    ERIC Educational Resources Information Center

    Qiu, Mingzhu; Hewitt, Jim; Brett, Clare

    2012-01-01

    Researchers have long recognized class size as affecting students' performance in face-to-face contexts. However, few studies have examined the effects of class size on exact reading and writing loads in online graduate-level courses. This mixed-methods study examined relationships among class size, note reading, note writing, and collaborative…

  20. Class Size and Student Science Achievement: Not as Easy as It Sounds.

    ERIC Educational Resources Information Center

    Miller-Whitehead, Marie

    The effects of class size on student achievement in science were studied using grade 8 science achievement mean scale scores for 138 Tennessee public school districts, focusing on the total population of districts and on districts in the upper and lower quartile of science performance (n=52). The dependent variable was district aggregate science…

  1. How Consistent Are Class Size Effects?

    ERIC Educational Resources Information Center

    Konstantopoulos, Spyros

    2011-01-01

    Thus far researchers have focused on computing average differences in student achievement between smaller and larger classes. In this study, the author focus on the distribution of the small class effects at the school level and compute the inconsistency of the small class effects across schools. The author use data from Project STAR to estimate…

  2. Transitional grain-size-sensitive flow of milky quartz aggregates

    NASA Astrophysics Data System (ADS)

    Fukuda, J. I.; Holyoke, C. W., III; Kronenberg, A. K.

    2014-12-01

    Fine-grained (~15 μm) milky quartz aggregates exhibit reversible flow strengths in triaxial compression experiments conducted at T = 800-900oC, Pc = 1.5 GPa when strain rates are sequentially decreased (typically from 10-3.5 to 10-4.5 and 10-5.5 s-1), and then returned to the original rate (10-3.5 s-1), while samples that experience grain growth at 1000oC (to 35 μm) over the same sequence of strain rates exhibit an irreversible increase in strength. Polycrystalline quartz aggregates have been synthesized from natural milky quartz powders (ground to 5 μm) by HIP methods at T = 1000oC, Pc = 1.5 GPa and t = 24 hours, resulting in dense, fine-grained aggregates of uniform water content of ~4000 ppm (H/106Si), as indicated by a broad OH absorption band at 3400 cm-1. In experiments performed at 800o and 900oC, grain sizes of the samples are essentially constant over the duration of each experiment, though grain shapes change significantly, and undulatory extinction and deformation lamellae indicate that much of the sample shortening (to 50%) is accomplished, over the four strain-rate steps, by dislocation creep. Differential stresses measured at T = 800oC decrease from 160 to 30 MPa as strain rate is reduced from 10-4.6 to 10-5.5 s-1, and a stress of 140 MPa is measured when strain rate is returned to 10-4.5 s-1. Samples deformed at 1000o and 1100oC experience normal grain growth, with grain boundary energy-driven grain-coarsening textures superposed by undulatory extinction and deformation lamellae. Differential stresses measured at 1000oC and strain rates of 10-3.6, 10-4.6, and 10-5.5 s-1 are 185, 80, and 80 MPa, respectively, while an increased flow stress of 260 MPa is measured (following ~28 hours of prior high temperature deformation and grain growth) when strain rate is returned to 10-3.6 s-1. While all samples exhibit lattice preferred orientations, the stress exponent n inferred for the fine-grained 800oC sample is 1.5 and the stress exponent of the coarse

  3. LOW-VELOCITY COLLISIONS OF CENTIMETER-SIZED DUST AGGREGATES

    SciTech Connect

    Beitz, E.; Guettler, C.; Blum, J.; Meisner, T.; Teiser, J.; Wurm, G.

    2011-07-20

    Collisions between centimeter- and decimeter-sized dusty bodies are important in understanding the mechanisms leading to the formation of planetesimals. We performed laboratory experiments to study the collisional behavior of dust aggregates in this size range at velocities below and around the fragmentation threshold. We developed two independent experimental setups with the same goal: to study the effects of bouncing, fragmentation, and mass transfer in free particle-particle collisions. The first setup is an evacuated drop tower with a free-fall height of 1.5 m, providing us with 0.56 s of microgravity time, so that we observed collisions with velocities between 8 mm s{sup -1} and 2 m s{sup -1}. The second setup is designed to study the effect of partial fragmentation (when only one of the two aggregates is destroyed) and mass transfer in more detail. It allows for the measurement of the accretion efficiency because the samples are safely recovered after the encounter. At very low velocities, we found that bouncing was as expected, while the fragmentation velocity of 20 cm s{sup -1} was significantly lower than expected. We present the critical energy for disruptive collisions Q*, which were at least two orders of magnitude lower than previous experiments in the literature. In the wide range between bouncing and disruptive collisions, only one of the samples fragmented in the encounter, while the other gained mass. The accretion efficiency on the order of a few percentage points of the particle's mass depends on the impact velocity and the sample porosity. Our results will have consequences for dust evolution models in protoplanetary disks as well as for the strength of large, porous planetesimal bodies.

  4. Effective-medium theory for finite-size aggregates.

    PubMed

    Guérin, Charles-Antoine; Mallet, Pierre; Sentenac, Anne

    2006-02-01

    We propose an effective-medium theory for random aggregates of small spherical particles that accounts for the finite size of the embedding volume. The technique is based on the identification of the first two orders of the Born series within a finite volume for the coherent field and the effective field. Although the convergence of the Born series requires a finite volume, the effective constants that are derived through this identification are shown to admit of a large-scale limit. With this approach we recover successively, and in a simple manner, some classical homogenization formulas: the Maxwell Garnett mixing rule, the effective-field approximation, and a finite-size correction to the quasi-crystalline approximation (QCA). The last formula is shown to coincide with the usual low-frequency QCA in the limit of large volumes, while bringing substantial improvements when the dimension of the embedding medium is of the order of the probing wavelength. An application to composite spheres is discussed.

  5. Class Size and Cost in ADN Programs

    ERIC Educational Resources Information Center

    Boehret, Alice C.; Larowe, Ann

    1978-01-01

    The article discusses the cost-effective use of faculty and facilities in associate degree nursing programs, as a large number of programs with small classes is uneconomical. Appraisal of admissions to reach an enrollment level sufficient to justify program cost is suggested. (MF)

  6. The False Promise of Class-Size Reduction

    ERIC Educational Resources Information Center

    Chingos, Matthew M.

    2011-01-01

    Class-size reduction, or CSR, is enormously popular with parents, teachers, and the public in general. Many parents believe that their children will benefit from more individualized attention in a smaller class and many teachers find smaller classes easier to manage. The pupil-teacher ratio is an easy statistic for the public to monitor as a…

  7. New class of aggregates in aqueous solution: an NMR, thermodynamic, and dynamic light scattering study.

    PubMed

    Sanna, Cecilia; La Mesa, Camillo; Mannina, Luisa; Stano, Pasquale; Viel, Stéphane; Segre, Annalaura

    2006-07-01

    We investigated the aggregation properties of two classes of aromatic and hydrophobic compounds, namely chloroacetamides and ethyl 3-phenyl-2-nitropropionates, in moderately concentrated aqueous solution (millimolar range). The identification of all species present in solution under specific experimental conditions was performed by 1D and 2D NMR, pulsed gradient spin-echo NMR, and dynamic light scattering techniques. Some physical-chemical properties (viscosity, surface tension, and colligative properties) of the aqueous solutions were also determined. Both classes of compounds behave quite similarly: in solution, three distinct species, namely a monomeric species, small and mobile aggregates, and large and stiff aggregates, are observed. The results give insight into a new class of aggregates, held together by pi-pi interactions, which show an unusual associative behavior in water.

  8. How Class Size Makes a Difference. Research & Development.

    ERIC Educational Resources Information Center

    Egelson, Paula; Harman, Patrick; Hood, Art; Achilles, C. M.

    Landmark studies in the late 1970s and 1980s, including Tennessee's Project STAR (Student Teacher Achievement Ratio), raised the nation's awareness that reduced class size does have a positive impact on students' academic achievement. This report provides a sketch of class-size reduction's history in a prefatory overview. Chapter 1 describes…

  9. Class Size: A Battle between Accountability and Quality Instruction

    ERIC Educational Resources Information Center

    Januszka, Cynthia; Dixon-Krauss, Lisbeth

    2008-01-01

    A substantial amount of controversy surrounds the issue of class size in public schools. Parents and teachers are on one side, touting the benefits of smaller class sizes (e.g., increased academic achievement, greater student-teacher interaction, utilization of more innovative teaching strategies, and a decrease in discipline problems). On the…

  10. Serendipitous Policy Implications from Class-Size-Initiated Inquiry: IAQ?

    ERIC Educational Resources Information Center

    Achilles, C. M.; Prout, Jean; Finn, J. D.; Bobbett, Gordon C.

    The level of carbon dioxide in a classroom can have a significant negative effect on teaching and learning. Carbon dioxide (CO2) level is affected by class size and time of day. Six urban schools were studied to characterize the effects of these three factors on different class sizes. Carbon monoxide, CO2, temperature, and relative humidity…

  11. Fluorescence spectroscopy in probing spontaneous and induced aggregation amongst size-selective gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Rahman, Dewan S.; Ghosh, Sujit Kumar

    2014-06-01

    Gold nanoparticles have been synthesized by borohydride reduction using poly(N-vinyl 2-pyrrolidone) as the stabilizing agent in aqueous medium in the size regime of 1-5 nm. Aggregation amongst these polymer-stabilized gold nanoparticles has been accomplished by the controlled addition of hydrazine or aggregation may occur spontaneously (devoid of any chemicals) that is ubiquitous to nanoparticulate systems. Now, fluorescencein isothiocyanate (FITC), a prototype molecular probe has been employed in understanding the physical principles of aggregation phenomenon of the size-selective gold nanoparticles undergoing spontaneous and induced-aggregation under stipulated conditions. It is seen that there is enhancement of fluorescence intensity of FITC in the presence of both spontaneously and induced-aggregated gold nanoclusters as compared to free FITC. Interestingly, it is observed that the fluorescence sensitivity is able to distinguish seven different sizes of the gold nanoparticles in the aggregates and maximum enhancement of intensity arises at higher concentration with increase in size of gold particles within the aggregates. With increase in concentration of gold nanoparticle aggregates, the intensity increases, initially, reaches a maximum at a threshold concentration and then, gradually decreases in the presence of both spontaneously and induced-aggregated gold particles. However, the salient feature of physical significance is that the maximum enhancement of intensity with time has remained almost same for induced-aggregated gold while decreases exponentially with spontaneously aggregated gold particles.

  12. How Class Size Makes a Difference: What the Research Says. The Impact of Class-Size Reduction (CSR).

    ERIC Educational Resources Information Center

    Achilles, C. M.

    Class size in elementary grades has taken on added importance recently. Research on the topic is finally getting some attention. Legislative and administrative actions to reduce deficits are pushing for larger class sizes, in addition to eliminating nonessential curricular activities, such as music, drama, and art. In Florida, various institutions…

  13. Class-Size Policy: The STAR Experiment and Related Class-Size Studies. NCPEA Policy Brief. Volume 1, Number 2

    ERIC Educational Resources Information Center

    Achilles, Charles M.

    2012-01-01

    This brief summarizes findings on class size from over 25 years of work on the Tennessee Student Teacher Achievement Ratio (STAR) randomized, longitudinal experiment, and other Class-Size Reduction (CSR) studies throughout the United States, Australia, Hong Kong, Sweden, Great Britain, and elsewhere. The brief concludes with recommendations. The…

  14. An online detection system for aggregate sizes and shapes based on digital image processing

    NASA Astrophysics Data System (ADS)

    Yang, Jianhong; Chen, Sijia

    2016-07-01

    Traditional aggregate size measuring methods are time-consuming, taxing, and do not deliver online measurements. A new online detection system for determining aggregate size and shape based on a digital camera with a charge-coupled device, and subsequent digital image processing, have been developed to overcome these problems. The system captures images of aggregates while falling and flat lying. Using these data, the particle size and shape distribution can be obtained in real time. Here, we calibrate this method using standard globules. Our experiments show that the maximum particle size distribution error was only 3 wt%, while the maximum particle shape distribution error was only 2 wt% for data derived from falling aggregates, having good dispersion. In contrast, the data for flat-lying aggregates had a maximum particle size distribution error of 12 wt%, and a maximum particle shape distribution error of 10 wt%; their accuracy was clearly lower than for falling aggregates. However, they performed well for single-graded aggregates, and did not require a dispersion device. Our system is low-cost and easy to install. It can successfully achieve online detection of aggregate size and shape with good reliability, and it has great potential for aggregate quality assurance.

  15. Rates of microbial sulfate reduction control the sizes of biogenic iron sulfide aggregates

    NASA Astrophysics Data System (ADS)

    Jin, Q.

    2005-12-01

    Sulfide minerals occur widely in freshwater and marine sediments as byproducts of microbial sulfate reduction and as end products of heavy metal bioremediation. They form when metals in the environments combine with sulfide produced from the metabolism of sulfate reducing bacteria. We used chemostat bioreactors to study sizes and crystal structures of iron sulfide (FeS) minerals produced by Desulfovibrio vulgaris, D. desulfuricans strain G20, and subspecies desulfuricans. FeS nanoparticles and their aggregates are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scattering (DLS). FeS nanoparticles produced by sulfate reducing bacteria are extremely small, usually less than around 10 nm in diameter. Nanoparticles do not occur as individual nanoparticles, but as aggregates. The sizes of FeS aggregates are affected by sulfate reduction rates, Fe(II) concentration, pH, ionic strength, organic matter concentration, bacterial species, etc. Aggregate size ranges from about 500 nm at very large sulfate reduction rates to about 1,500 nm at very small rates. Variations in Fe(II) concentration also lead to a difference up to 500 nm in FeS aggregate size. Different bacterial species produce nanoparticle aggregates of different sizes under similar growth conditions. For example, D. vulgaris produces FeS aggregates with sizes 500 nm smaller than those by strain G20. The inverse relationship between FeS aggregate sizes and sulfate reduction rates is important in evaluating metal bioremediation strategies. Previous approaches have focused on stimulating microbial activities in natural environments. However, our experimental results suggest that increasing metabolic rates may decrease the aggregate size, increasing the mobility of colloidal aggregates. Therefore, the balance between microbial activities and sizes of biogenic aggregates may be an important consideration in the design and

  16. Focus on California's Class-Size Reduction: Smaller Classes Aim To Launch Early Literacy.

    ERIC Educational Resources Information Center

    McRobbie, Joan

    Smaller class sizes in California were viewed as a way to improve K-3 education, especially in the area of literacy. The urgency to act prompted state leaders to adopt class-size reduction (CSR) without knowing for sure that it would work and without establishing a formal procedure for evaluating the program. This report looks at past research on…

  17. Class Size and Student Performance: A Framework for Policy Analysis.

    ERIC Educational Resources Information Center

    Addonizio, Michael F.; Phelps, James L.

    2000-01-01

    A survey of one national and three statewide studies (in Tennessee, Texas, and Alabama) of class-size achievement effects revealed no consistent pattern across various subjects and grade levels. However, smaller classes can improve student achievement, particularly in early grades and when teacher quality remains constant. (Contains 36 footnotes.)…

  18. Class Size Reduction and Urban Students. ERIC Digest.

    ERIC Educational Resources Information Center

    Schwartz, Wendy

    Researchers have long investigated whether smaller classes improve student achievement. Their conclusions suggest that class size reduction (CSR) can result in greater in-depth coverage of subject matter by teachers, enhanced learning and stronger engagement by students, more personalized teacher-student relationships, and safer schools with fewer…

  19. Making Class Size Work in the Middle Grades

    ERIC Educational Resources Information Center

    Tienken, C. H.; Achilles, C. M.

    2006-01-01

    Most research on the positive effects of class-size reduction (CSR) has occurred in the elementary level (Word, Johnston, Bain, Fulton, Zaharias, Lintz, Achilles, Folger, & Breda, 1990; Molnar, Smith, Zahorik, Palmer, Halbach, & Ehrle, 1999). Is CSR an important variable in improving education in the middle grades? Can small classes be achieved in…

  20. The Relationship of Class Size Effects and Teacher Salary

    ERIC Educational Resources Information Center

    Peevely, Gary; Hedges, Larry; Nye, Barbara A.

    2005-01-01

    The effects of class size on academic achievement have been studied for decades. Although the results of small-scale, randomized experiments and large-scale, econometric studies point to positive effects of small classes, some scholars see the evidence as ambiguous. Recent analyses from a 4-year, large-scale, randomized experiment on the effects…

  1. Introductory Class Size and Student Performance in Intermediate Theory Courses.

    ERIC Educational Resources Information Center

    Raimondo, Henry J.; And Others

    1990-01-01

    Examines whether class size in the introductory-level economics course affects subsequent performance in intermediate-level economics courses. Studies University of Massachusetts (Boston) students who are allowed to choose large or small lecture classes. Finds that students enrolled in large sections received lower grades in subsequent…

  2. Aggregate size distribution evolution for Brownian coagulation-sensitivity to an improved rate constant.

    PubMed

    Zurita-Gotor, M; Rosner, D E

    2004-06-15

    Brownian motion causes small aggregates to encounter one another and grow in gaseous environments, often under conditions in which the coalescence rate (say, spheroidization by "sintering") cannot compete. The polydisperse nature of the aerosol population formed by this mechanism is typically accounted for by formulating an evolution equation for the joint PDF of the state variables needed for describing individual particles. In the simple case of fractal-like aggregates (prescribed morphology and state, characterized just by the number of aggregated spherules, or total aggregate volume), we use the quadrature method of moments and Monte Carlo simulations to show that recent improvements in the laws governing free molecule regime coagulation frequency (rate "constant") of these aggregates cause systematic changes in the shape of the asymptotic aggregate size distribution, with significant implications for the light-scattering power and inertial impaction behavior of such aggregate populations.

  3. Sizing up Class Size: A Deeper Classroom Investigation of Central Tendency

    ERIC Educational Resources Information Center

    Lesser, Lawrence M.

    2009-01-01

    Being able to select, use, and interpret measures of center is expected of all secondary students. Discussing average class size can be a motivational vehicle for exploring this topic because students (and teachers) at all grade levels notice when they have significantly bigger classes and high school juniors and seniors see average class size…

  4. Leaner Class Sizes Add Fiscal Stress to Florida Districts

    ERIC Educational Resources Information Center

    McNeil, Michele

    2008-01-01

    With a total price tag pushing $10 billion, Florida's "class-size-reduction mandate"--the nation's toughest--is under fire, as school districts call on lawmakers to weaken the 2002 constitutional requirement before it is fully phased in later this year. Starting with the 2008-09 school year, individual districts must meet new size caps in each…

  5. SIZE AND SURFACE AREA OF ICY DUST AGGREGATES AFTER A HEATING EVENT AT A PROTOPLANETARY NEBULA

    SciTech Connect

    Sirono, Sin-iti

    2013-03-01

    The activity of a young star rises abruptly during an FU Orionis outburst. This event causes a temporary temperature increase in the protoplanetary nebula. H{sub 2}O icy grains are sublimated by this event, and silicate cores embedded inside the ice are ejected. During the high-temperature phase, the silicate grains coagulate to form silicate core aggregates. After the heating event, the temperature drops, and the ice recondenses onto the aggregates. I determined numerically the size distribution of the ice-covered aggregates. The size of the aggregates exceeds 10 {mu}m around the snow line. Because of the migration of the ice to large aggregates, only a small fraction of the silicate core aggregate is covered with H{sub 2}O ice. After the heating event, the surface of an ice-covered aggregate is totally covered by silicate core aggregates. This might reduce the fragmentation velocity of aggregates when they collide. It is possible that the covering silicate cores shield the UV radiation field which induces photodissociation of H{sub 2}O ice. This effect may cause the shortage of cold H{sub 2}O vapor observed by Herschel.

  6. Bacterial density and community structure associated with aggregate size fractions of soil-feeding termite mounds.

    PubMed

    Fall, S; Nazaret, S; Chotte, J L; Brauman, A

    2004-08-01

    The building and foraging activities of termites are known to modify soil characteristics such as the heterogeneity. In tropical savannas the impact of the activity of soil-feeding termites ( Cubitermes niokoloensis) has been shown to affect the properties of the soil at the aggregate level by creating new soil microenvironments (aggregate size fractions) [13]. These changes were investigated in greater depth by looking at the microbial density (AODC) and the genetic structure (automated rRNA intergenic spacer analysis: ARISA) of the communities in the different aggregate size fractions (i.e., coarse sand, fine sand, coarse silt, fine silt, and dispersible clays) separated from compartments (internal and external wall) of three Cubitermes niokoloensis mounds. The bacterial density of the mounds was significantly higher (1.5 to 3 times) than that of the surrounding soil. Within the aggregate size fractions, the termite building activity resulted in a significant increase in bacterial density within the coarser fractions (>20 mum). Multivariate analysis of the ARISA profiles revealed that the bacterial genetic structures of unfractionated soil and soil aggregate size fractions of the three mounds was noticeably different from the savanna soil used as a reference. Moreover, the microbial community associated with the different microenvironments in the three termite mounds revealed three distinct clusters formed by the aggregate size fractions of each mound. Except for the 2-20 mum fraction, these results suggest that the mound microbial genetic structure is more dependent upon microbial pool affiliation (the termite mound) than on the soil location (aggregate size fraction). The causes of the specificity of the microbial community structure of termite mound aggregate size fractions are discussed.

  7. Sizing aerosolized fractal nanoparticle aggregates through Bayesian analysis of wide-angle light scattering (WALS) data

    NASA Astrophysics Data System (ADS)

    Huber, Franz J. T.; Will, Stefan; Daun, Kyle J.

    2016-11-01

    Inferring the size distribution of aerosolized fractal aggregates from the angular distribution of elastically scattered light is a mathematically ill-posed problem. This paper presents a procedure for analyzing Wide-Angle Light Scattering (WALS) data using Bayesian inference. The outcome is probability densities for the recovered size distribution and aggregate morphology parameters. This technique is applied to both synthetic data and experimental data collected on soot-laden aerosols, using a measurement equation derived from Rayleigh-Debye-Gans fractal aggregate (RDG-FA) theory. In the case of experimental data, the recovered aggregate size distribution parameters are generally consistent with TEM-derived values, but the accuracy is impaired by the well-known limited accuracy of RDG-FA theory. Finally, we show how this bias could potentially be avoided using the approximation error technique.

  8. Size Matters. The Relevance and Hicksian Surplus of Preferred College Class Size

    ERIC Educational Resources Information Center

    Mandel, Philipp; Susmuth, Bernd

    2011-01-01

    The contribution of this paper is twofold. First, we examine the impact of class size on student evaluations of instructor performance using a sample of approximately 1400 economics classes held at the University of Munich from Fall 1998 to Summer 2007. We offer confirmatory evidence for the recent finding of a large, highly significant, and…

  9. Class Size and Student Outcomes: Research and Policy Implications

    ERIC Educational Resources Information Center

    Chingos, Matthew M.

    2013-01-01

    Schools across the United States are facing budgetary pressures on a scale not seen in generations. Times of fiscal exigency force policymakers and education practitioners to pay more attention to the return on various categories of public investment in education. The sizes of the classes in which students are educated are often a focus of these…

  10. International Evidence on Expenditures and Class Size: A Review

    ERIC Educational Resources Information Center

    Woessmann, Ludger

    2007-01-01

    In the United States, evidence abounds on the effects of expenditures and class size on student achievement, but often it is controversial. In other parts of the world, hard evidence is not as easy to come by, mostly because of data limitations. But over the years, testing agencies have started to collect data on student performance and family…

  11. Making Class Size Reduction Work: Stories from California's Public Schools.

    ERIC Educational Resources Information Center

    Lewis, Anne C.

    This report details the impact of Class Size Reduction (CSR) on six school districts in California. The schools were chosen because they were typical of the changing demographics that affect almost all the state's districts. Data were gathered from interviews with administrators and teachers in the Spring of 1997. Results show that some of the…

  12. The Influence of Class Size upon Numeracy and Literacy Performance

    ERIC Educational Resources Information Center

    Watson, Kevin; Handal, Boris; Maher, Marguerite

    2016-01-01

    Purpose: The purpose of this paper was to investigate the influences of calendar year, year level, gender and language background other than English (LBOTE) on student achievement in literacy and numeracy relative to class size. Design/methodology/approach: Data for this study were collected over five years (2008-2012) as test results from the…

  13. Effects of Class Size on Alternative Educational Outcomes across Disciplines

    ERIC Educational Resources Information Center

    Cheng, Dorothy A.

    2011-01-01

    This is the first study to use self-reported ratings of student learning, instructor recommendations, and course recommendations as the outcome measure to estimate class size effects, doing so across 24 disciplines. Fixed-effects models controlling for heterogeneous courses and instructors reveal that increasing enrollment has negative and…

  14. The Impact of Class Size Reduction on Student Achievement.

    ERIC Educational Resources Information Center

    Fidler, Penny

    This study examined the impact of class size reduction (CSR) on achievement among 3rd, 4th, and 5th grade students with different numbers of years of participation in CSR. Single-year matched gains were calculated for the 1997-1998 and 1999-2000 school years. Student progress was assessed using scores from the SAT/9 reading, mathematics, and…

  15. Biomimetic control over size, shape and aggregation in magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Sommerdijk, Nico

    2013-03-01

    Magnetite (Fe3O4) is a widespread magnetic iron oxide encountered in both geological and biomineralizing systems, which also has many technological applications, e.g. in ferrofluids, inks, magnetic data storage materials and as contrast agents in magnetic resonance imaging. As its magnetic properties depend largely on the size and shape of the crystals, control over crystal morphology is an important aspect in the application of magnetite nanoparticles, both in biology and synthetic systems. Indeed, in nature organisms such as magnetotactic bacteria demonstrate a precise control over the magnetite crystal morphology, resulting in uniform and monodisperse nanoparticles. The magnetite formation in these bacteria is believed to occur through the co-precipitation of Fe(II) and Fe(III) ions, which is also the most widely applied synthetic route in industry. Synthetic strategies to magnetite with controlled size and shape exist, but involve high temperatures and rather harsh chemical conditions. However, synthesis via co-precipitation generally yields poor control over the morphology and therefore over the magnetic properties of the obtained crystals. Here we demonstrate that by tuning the reaction kinetics we can achieve biomimetic control over the size and shape of magnetite crystals but also over their organization in solution as well as their magnetic properties. We employ amino acids-based polymers to direct the formation of magnetite in aqueous media at room temperature via both the co-precipitation and the partial oxidation method. By using 2D and 3D (cryo)TEM it is shown that acidic amino acid monomers are most effective in affecting the magnetite particle morphology. By changing the composition of the polymers we can tune the morphology, the dispersibility as well as the magnetic properties of these nanoparticles.

  16. Size dependent fractal aggregation mediated through surfactant in silica nanoparticle solution

    NASA Astrophysics Data System (ADS)

    Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

    2012-06-01

    Small-angle neutron scattering (SANS) has been used to study aggregation of anionic silica nanoparticles in presence of cationic surfactant (DTAB) in aqueous solution. The measurements were carried out for different sizes of nanoparticles (8.2, 16.4 and 26.4 nm) at fixed (1 wt%) nanoparticles and surfactant concentration. It is found that the adsorption of surfactant micelles on the silica nanoparticles leads to the aggregation of nanoparticles, which is characterized by a fractal structure. The number of adsorbed micelles on nanoparticle increases from 7 to 152 with the increase in the size of the nanoparticle from 8.2 to 26.4 nm, whereas interestingly the fractal dimension remains same. The aggregate morphology in these systems is expected to be governed by the diffusion limited aggregation.

  17. Hydrodynamic size-based separation and characterization of protein aggregates from total cell lysates

    PubMed Central

    Tanase, Maya; Zolla, Valerio; Clement, Cristina C; Borghi, Francesco; Urbanska, Aleksandra M; Rodriguez-Navarro, Jose Antonio; Roda, Barbara; Zattoni, Andrea; Reschiglian, Pierluigi; Cuervo, Ana Maria; Santambrogio, Laura

    2016-01-01

    Herein we describe a protocol that uses hollow-fiber flow field-flow fractionation (FFF) coupled with multiangle light scattering (MALS) for hydrodynamic size-based separation and characterization of complex protein aggregates. The fractionation method, which requires 1.5 h to run, was successfully modified from the analysis of protein aggregates, as found in simple protein mixtures, to complex aggregates, as found in total cell lysates. In contrast to other related methods (filter assay, analytical ultracentrifugation, gel electrophoresis and size-exclusion chromatography), hollow-fiber flow FFF coupled with MALS allows a flow-based fractionation of highly purified protein aggregates and simultaneous measurement of their molecular weight, r.m.s. radius and molecular conformation (e.g., round, rod-shaped, compact or relaxed). The polyethersulfone hollow fibers used, which have a 0.8-mm inner diameter, allow separation of as little as 20 μg of total cell lysates. In addition, the ability to run the samples in different denaturing and nondenaturing buffer allows defining true aggregates from artifacts, which can form during sample preparation. The protocol was set up using Paraquat-induced carbonylation, a model that induces protein aggregation in cultured cells. This technique will advance the biochemical, proteomic and biophysical characterization of molecular-weight aggregates associated with protein mutations, as found in many CNS degenerative diseases, or chronic oxidative stress, as found in aging, and chronic metabolic and inflammatory conditions. PMID:25521790

  18. Effect of the slope and initial moisture content on soil loss, aggregate and particle size distribution

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka

    2015-04-01

    Soil structure degradation has effect through the soil water balance and nutrient supply on the agricultural potential of an area. The soil erosion process comprises two phases: detachment and transport by water. To study the transport phase nozzle type laboratory-scale rainfall simulator was used with constant 80 mmhr-1 intensity on an arable haplic Cambisol. Measuring the aggregate and particle size distribution of the soil loss gives a good approach the erosion process. The primary objective of this study was to examine the sediment concentration, and detect the quality and quantity change of the soil loss during a single precipitation under six treatment combinations (recently tilled and crusty soil surface on two different slope steepness, inland inundation and drought soil conditions). Soil loss were collected continually, and separated per aggregate size fractions with sieves in three rounds during a rain to measure the weights. The particle size distribution was measured with Horiba LA-950 particle size analyzer. In general the ratio of the macro aggregates decreases and the ratio of the micro aggregates and clay fraction increases in the sediment with time during the precipitation due to the raindrop impact. Sediment concentration depends on the slope steepness, as from steeper slopes the runoff can transport bigger amount of sediment, but from the tilled surface bigger aggregates were washing down. Micro aggregate fraction is one of the indicators of good soil structure. The degradation of micro aggregates occurs in steeper slopes and the most erosive time period depends on the micromorphology of the surface. And while the aggregate size distribution of the soil loss of the treatments shows high variety of distribution and differs from the original soil, the particle size distribution of each aggregate size fraction shows similar trends except the 50-250 µm fraction where the fine sand fraction is dominating instead of the loam. This anomaly may be

  19. Sizing highly-ordered buckyball-shaped aggregates of colloidal nanoparticles by light extinction spectroscopy

    NASA Astrophysics Data System (ADS)

    Onofri, F. R. A.; Barbosa, S.; Touré, O.; Woźniak, M.; Grisolia, C.

    2013-09-01

    We produced self-assembled, densely-packed and highly-ordered aggregates of silica nanoparticles arranged in a rather regular hexagonal-pentagonal surface lattice. To investigate the formation of these aggregates, produced by means of a spray drying method, we developed a light extinction setup and all related models. It is shown that with a geodesic dome model, to describe their morphology, and a T-matrix method to calculate their extinction cross sections, the size distribution and concentration of these flowing aggregates may be recovered from the inversion of transmission spectra.

  20. Messenger RNA in early sea-urchin embryos: size classes.

    PubMed

    Nemer, M; Infante, A A

    1965-10-01

    Rapidly labeled RNA from four-cell embryos and blastulae of sea urchins was analyzed by sedimentation and for ability to form DNA-RNA hybrids. The RNA was derived from polyribosomes and from the "gel interphase," an extraction compartment resulting from treatment of whole embryos with phenol and known to be enriched with nuclei. The RNA from both sources displayed a high degree of structural complementarity to DNA. This DNA-like RNA of the polyribosomes sedimented in discrete classes, rather than in the sedimentation continuum demonstrable for the labeled RNA of the gel interphase. Thus messenger RNA appears to emerge in the cytoplasm in discrete size classes. PMID:5837338

  1. Unimodal tree size distributions possibly result from relatively strong conservatism in intermediate size classes.

    PubMed

    Bin, Yue; Ye, Wanhui; Muller-Landau, Helene C; Wu, Linfang; Lian, Juyu; Cao, Honglin

    2012-01-01

    Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes. PMID:23300714

  2. Collision of oil droplets with marine aggregates: Effect of droplet size

    NASA Astrophysics Data System (ADS)

    Lambert, Ruth A.; Variano, Evan A.

    2016-05-01

    Interactions between oil droplets and marine particle aggregates, such as marine snow, may affect the behavior of oil spills. Marine snow is known to scavenge fine particles from the water column, and has the potential to scavenge oil droplets in the same manner. To determine the degree to which such a process is important in the evolution of oil spills, we quantify the collision of oil droplets and marine aggregates using existing collision rate equations. Results show that interaction of drops and aggregates can substantially influence the drop size distribution, but like all such processes this result is sensitive to the local concentration of oil and aggregates. The analysis also shows that as the size distribution of oil droplets shifts toward larger droplets, a greater fraction of the total oil volume collides with marine aggregates. This result is robust to a variety of different assumptions in the collision model. Results also show that there is not always a dominant collision mechanism. For example, when droplets and aggregates are both close to 10 μm in radius, shear and differential settling contribute nearly equally to the collision rate. This overlap suggests that further research on the interaction of shear and differential settling could be useful.

  3. Accretion of Fine Particles: Sticking Probability Estimated by Optical Sizing of Fractal Aggregates

    NASA Astrophysics Data System (ADS)

    Sugiura, N.; Higuchi, Y.

    1993-07-01

    Sticking probability of fine particles is an important parameter that determines (1) the settling of fine particles to the equatorial plane of the solar nebula and hence the formation of planetesimals, and (2) the thermal structure of the nebula, which is dependent on the particle size through opacity. It is generally agreed that the sticking probability is 1 for submicrometer particles, but at sizes larger than 1 micrometer, there exist almost no data on the sticking probability. A recent study [1] showed that aggregates (with radius from 0.2 to 2 mm) did not stick when collided at a speed of 0.15 to 4 m/s. Therefore, somewhere between 1 micrometer and 200 micrometers, sticking probabilities of fine particles change from nearly 1 to nearly 0. We have been studying [2,3] sticking probabilities of dust aggregates in this size range using an optical sizing method. The optical sizing method has been well established for spherical particles. This method utilizes the fact that the smaller the size, the larger the angle of the scattered light. For spheres with various sizes, the size distribution is determined by solving Y(i) = M(i,j)X(j), where Y(i) is the scattered light intensity at angle i, X(j) is the number density of spheres with size j, and M(i,j) is the scattering matrix, which is determined by Mie theory. Dust aggregates, which we expect to be present in the early solar nebula, are not solid spheres, but probably have a porous fractal structure. For such aggregates the scattering matrix M(i,j) must be determined by taking account of all the interaction among constituent particles (discrete dipole approximation). Such calculation is possible only for very small aggregates, and for larger aggregates we estimate the scattering matrix by extrapolation, assuming that the fractal nature of the aggregates allows such extrapolation. In the experiments using magnesium oxide fine particles floating in a chamber at ambient pressure, the size distribution (determined by

  4. Effect of Different Coarse Aggregate Sizes on the Strength Characteristics of Laterized Concrete

    NASA Astrophysics Data System (ADS)

    Salau, M. A.; Busari, A. O.

    2015-11-01

    The high cost of conventional concrete materials is a major factor affecting housing delivery in developing countries such as Nigeria. Since Nigeria is blessed with abundant locally available materials like laterite, researchers have conducted comprehensive studies on the use of laterite to replace river sand partially or fully in the concrete. However, the works did not consider the optimum use of coarse aggregate to possibly improve the strength of the laterized concrete, since it is normally lower than that of normal concrete. The results of the tests showed that workability, density and compressive strength at constant water-cement ratio increase with the increase in the coarse aggregate particle size and also with curing age. As the percentage of laterite increases, there was a reduction in all these characteristics even with the particle size of coarse aggregate reduction due to loss from the aggregate-paste interface zone. Also, when sand was replaced by 25% of laterite, the 19.5mm and 12.5mm coarse aggregate particle sizes gave satisfactory results in terms of workability and compressive strength respectively at 28 days of curing age, compared to normal concrete. However, in case of 50% up to 100% laterite contents, the workability and compressive strength values were very low.

  5. Class Size and Education in England Evidence Report. Research Report. DFE-RR169

    ERIC Educational Resources Information Center

    Department for Education, 2011

    2011-01-01

    This report gives an overview of the existing evidence base on class size and education in England. In particular, it considers how class sizes have changed over time; the impact of the increase in birth rate on pupil numbers and how this could affect the teacher requirement and class sizes; and the impact of class size on educational outcomes.…

  6. Crowding Peter to Educate Paul: Lessons from a Class Size Reduction Externality

    ERIC Educational Resources Information Center

    Sims, David P.

    2009-01-01

    This paper examines an increase in upper elementary class sizes in California associated with the K-3 class size reduction program. I also use the variation in fourth and fifth grade class size generated by idiosyncratic first and second grade reductions required to meet program rules to identify a negative impact of larger class sizes on…

  7. Connecting in Class? College Class Size and Inequality in Academic Social Capital

    ERIC Educational Resources Information Center

    Beattie, Irenee R.; Thiele, Megan

    2016-01-01

    College students who interact with professors and peers about academic matters have better college outcomes. Although institutional factors influence engagement, prior scholarship has not systematically examined whether class sizes affect students' academic interactions, nor whether race or first-generation status moderate such effects. We…

  8. Class Size: Can School Districts Capitalize on the Benefits of Smaller Classes?

    ERIC Educational Resources Information Center

    Hertling, Elizabeth; Leonard, Courtney; Lumsden, Linda; Smith, Stuart C.

    2000-01-01

    This report is intended to help policymakers understand the benefits of class-size reduction (CSR). It assesses the costs of CSR, considers some research-based alternatives, and explores strategies that will help educators realize the benefits of CSR when it is implemented. It examines how CSR enhances student achievement, such as when the…

  9. Diffusion limited aggregation of particles with different sizes: Fractal dimension change by anisotropic growth

    NASA Astrophysics Data System (ADS)

    Braga, F. L.; Mattos, O. A.; Amorin, V. S.; Souza, A. B.

    2015-07-01

    Clusters formation models have been extensively studied in literature, and one of the main task of this research area is the analysis of the particle aggregation processes. Some work support that the main characteristics of this processes are strictly correlated to the cluster morphology, for example in DLA. It is expected that in the DLA clusters formation with particles containing different sizes the modification of the aggregation processes can be responsible for changes in the DLA morphology. The present article is going to analyze the formation of DLA clusters of particles with different sizes and show that the aggregates obtained by this approach generate an angle selection mechanism on dendritic growth that influences the shielding effect of the DLA edge and affect the fractal dimension of the clusters.

  10. Ionic Liquid-Induced Unprecedented Size Enhancement of Aggregates within Aqueous Sodium Dodecylbenzene Sulfonate

    SciTech Connect

    Rai, Rewa; Baker, Gary A; Behera, Kamalakanta; Mohanty, Pravakar; Kurur, Narayanan; Pandey, Siddharth

    2010-01-01

    Physicochemical properties of aqueous micellar solutions may change in the presence of ionic liquids (ILs). Micelles help to increase the aqueous solubility of ILs. The average size of the micellar aggregates within aqueous sodium dodecylbenzene sulfonate (SDBS) is observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) to increase in a sudden and drastic fashion as the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) is added. Similar addition of [bmim][PF6] to aqueous sodium dodecyl sulfate (SDS) results in only a slow gradual increase in average aggregate size. While addition of the IL [bmim][BF4] also gives rise to sudden aggregate size enhancement within aqueous SDBS, the IL 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]), and inorganic salts NaPF6 and NaBF4, only gradually increase the assembly size upon their addition. Bulk dynamic viscosity, microviscosity, dipolarity (indicated by the fluorescent reporter pyrene), zeta potential, and electrical conductance measurements were taken to gain insight into this unusual size enhancement. It is proposed that bmim cations of the IL undergo Coulombic attractive interactions with anionic headgroups at the micellar surface at all [bmim][PF6] concentrations in aqueous SDS; in aqueous SDBS, beyond a critical IL concentration, bmim becomes involved in cation- interaction with the phenyl moiety of SDBS within micellar aggregates with the butyl group aligned along the alkyl chain of the surfactant. This relocation of bmim results in an unprecedented size increase in micellar aggregates. Aromaticity of the IL cation alongside the presence of sufficiently aliphatic (butyl or longer) alkyl chains on the IL appear to be essential for this dramatic critical expansion in self-assembly dimensions within aqueous SDBS.

  11. 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. PMID:22365838

  12. Significant effect of grain size distribution on compaction rates in granular aggregates

    NASA Astrophysics Data System (ADS)

    Niemeijer, André; Elsworth, Derek; Marone, Chris

    2009-07-01

    We investigate the role of pressure solution in deformation of upper- to mid-crustal rocks using aggregates of halite as a room temperature analog for fluid-assisted deformation processes in the Earth's crust. Experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution. We find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion-controlled pressure solution. Models typically assume mono-dispersed spherical particles in pseudo-regular packing. We infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental (and natural) samples from regular packs of mono-dispersed spherical particles. Moreover, we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size. Wider size distributions allow for higher initial compaction rates, increasing the macroscopic compaction rate with respect to more narrow grain size distributions. Grain sizes in rocks, fault gouges, and hydrocarbon reservoirs are typically log-normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions. Spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones, which could potentially focus deformation in these zones and produce pockets of high pore pressures, promoting nucleation of frictional instability and earthquake rupture.

  13. 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.

  14. Probing surface characteristics of diffusion-limited-aggregation clusters with particles of variable size

    NASA Astrophysics Data System (ADS)

    Menshutin, A. Yu.; Shchur, L. N.; Vinokur, V. M.

    2007-01-01

    We develop a technique for probing the harmonic measure of a diffusion-limited-aggregation (DLA) cluster surface with variable-size particles and generate 1000 clusters with 50×106 particles using an original off-lattice killing-free algorithm. Taking, in sequence, the limit of the vanishing size of the probing particles and then sending the growing cluster size to infinity, we achieve unprecedented accuracy in determining the fractal dimension D=1.7100(2) crucial to the characterization of the geometric properties of DLA clusters.

  15. Size-Resolved Density Measurements of Particulate Emissions from an Advanced Combustion Diesel Engine: Effect of Aggregate Morphology

    SciTech Connect

    Barone, Teresa L; Storey, John Morse; Prikhodko, Vitaly Y; Parks, II, James E

    2011-01-01

    We report the first in situ size-resolved density measurements of particles produced by premixed charge compression ignition (PCCI) and compare these with conventional diesel particles. The densities of size-classified particles were determined by measurements with a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). Particle masses of the different size classes were evaluated with a proposed DMA-APM response function for aggregates. Our results indicate that the effective densities of PCCI and conventional diesel particles were approximately the same for 50 and 100 nm electrical mobility diameters (0.9 and 0.6 g/cc, respectively), but the PCCI particle effective density (0.4 g/cc) was less than the conventional (0.5 g/cc) for 150 nm. The lowest effective particle densities were observed for exhaust gas recirculation (EGR) levels somewhat less than that required for PCCI operation. The inherent densities of conventional particles in the 50 and 100 nm size classes were 1.22 and 1.77 g/cc, which is in good agreement with Park et al. (2004). PCCI inherent particle densities for these same size classes were higher (1.27 and 2.10 g/cc), suggesting that there may have been additional adsorbed liquid hydrocarbons. For 150 nm particles, the inherent densities were nearly the same for PCCI and conventional particles at 2.20 g/cc. We expect that the lower effective density of PCCI particles may improve particulate emissions control with diesel particulate filters (DPFs). The presence of liquid hydrocarbons may also promote oxidation in DPFs.

  16. Effects of grid size and aggregation on regional scale landuse scenario calculations using SVAT schemes

    NASA Astrophysics Data System (ADS)

    Bormann, H.

    2006-09-01

    This paper analyses the effect of spatial input data resolution on the simulated effects of regional scale landuse scenarios using the TOPLATS model. A data set of 25 m resolution of the central German Dill catchment (693 km2) and three different landuse scenarios are used for the investigation. Landuse scenarios in this study are field size scenarios, and depending on a specific target field size (0.5 ha, 1.5 ha and 5.0 ha) landuse is determined by optimising economic outcome of agricultural used areas and forest. After an aggregation of digital elevation model, soil map, current landuse and landuse scenarios to 50 m, 75 m, 100 m, 150 m, 200 m, 300 m, 500 m, 1 km and 2 km, water balances and water flow components for a 20 years time period are calculated for the entire Dill catchment as well as for 3 subcatchments without any recalibration. Additionally water balances based on the three landuse scenarios as well as changes between current conditions and scenarios are calculated. The study reveals that both model performance measures (for current landuse) as well as water balances (for current landuse and landuse scenarios) almost remain constant for most of the aggregation steps for all investigated catchments. Small deviations are detected at the resolution of 50 m to 500 m, while significant differences occur at the resolution of 1 km and 2 km which can be explained by changes in the statistics of the input data. Calculating the scenario effects based on increasing grid sizes yields similar results. However, the change effects react more sensitive to data aggregation than simple water balance calculations. Increasing deviations between simulations based on small grid sizes and simulations using grid sizes of 300 m and more are observed. Summarizing, this study indicates that an aggregation of input data for the calculation of regional water balances using TOPLATS type models does not lead to significant errors up to a resolution of 500 m. Focusing on scenario

  17. Levitation, aggregation and separation of micro-sized particles in a Hydrodynamic Acoustic Sorter, HAS

    NASA Astrophysics Data System (ADS)

    Hoyos, Mauricio; Castro, Angelica; Bazou, Despina; Separation Collaboration

    2011-11-01

    Levitation, aggregation and separation of micron-sized particulate materials can be generated in a fluidic resonator by an ultrasonic standing wave field force. A piezoelectric transducer generates standing waves between the two walls of a parallel plate channel composing the resonator. The number of pressure nodes n is given by the relationship: w = nλ / 2 with λ the wavelength. The primary radiation force generated by the standing wave generates levitation of micron-sized particles driving them toward the nodal planes. An equilibrium position is reached in the channel thickness where the acoustic force balances the gravity force. The equilibrium position is independent on particle size but it depends on the acoustic properties. Once particles reach the equilibrium position, transversal secondary forces generate aggregation. We shall present the levitation and aggregation process of latex particles and cancer cells in a 2MHz resonator. We demonstrate the possibility of separating particles under flow in a Hydrodynamic Acoustic Sorter HAS, in function of their acoustic impedance and in function of their size using a programming field force.

  18. 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

  19. 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.

  20. 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.

  1. Class Size Effects on Mathematics Achievement in Cyprus: Evidence from TIMSS

    ERIC Educational Resources Information Center

    Konstantopoulos, Spyros; Shen, Ting

    2016-01-01

    Class size reduction has been viewed as one school mechanism that can improve student achievement. Nonetheless, the literature has reported mixed findings about class size effects. We used 4th- and 8th-grade data from TIMSS 2003 and 2007 to examine the association between class size and mathematics achievement in public schools in Cyprus. We…

  2. Review of "Class Size: What Research Says and What It Means for State Policy"

    ERIC Educational Resources Information Center

    Whitmore Schanzenbach, Diane

    2011-01-01

    "Class Size: What Research Says and What It Means for State Policy" argues that increasing average class size by one student will save about 2% of total education spending with negligible impact on academic achievement. It justifies this conclusion on the basis that Class-Size Reduction (CSR) is not particularly effective and is not as…

  3. Class Size: What Research Says and What It Means for State Policy

    ERIC Educational Resources Information Center

    Whitehurst, Grover J.; Chingos, Matthew M.

    2011-01-01

    Class size is one of the small number of variables in American K-12 education that are both thought to influence student learning and are subject to legislative action. Legislative mandates on maximum class size have been very popular at the state level. In recent decades, at least 24 states have mandated or incentivized class-size reduction…

  4. Why "Small" Can Be Better: An Exploration of the Relationships between Class Size and Pedagogical Practices

    ERIC Educational Resources Information Center

    Harfitt, Gary James

    2013-01-01

    A central issue in the class size debate is that while cutting class size might lead to improved teaching and learning, it is also possible that it may not if teachers do not seek to exploit the advantages of a smaller class size through an alternative pedagogy. Research suggests that teachers do not change their pedagogy when moving from large…

  5. Class Size Effects on Fourth-Grade Mathematics Achievement: Evidence from TIMSS 2011

    ERIC Educational Resources Information Center

    Li, Wei; Konstantopoulos, Spyros

    2016-01-01

    Class size reduction policies have been widely implemented around the world in recent years. However, findings about the effects of class size on student achievement have been mixed. This study examines class size effects on fourth-grade mathematics achievement in 14 European countries using data from TIMSS (Trends in International Mathematics and…

  6. Capitalizing on Small Class Size. ERIC Digest Number 136.

    ERIC Educational Resources Information Center

    O'Connell, Jessica; Smith, Stuart C.

    This Digest examines school districts' efforts to reap the greatest benefit from smaller classes. Although the report discusses teaching strategies that are most effective in small classes, research has shown that teachers do not significantly change their teaching practices when they move from larger to smaller classes. Smaller classes mean…

  7. Effect of biochar application and soil temperature on characteristics of organic matter associated with aggregate-size and density fractions

    NASA Astrophysics Data System (ADS)

    Kaiser, Michael; Grunwald, Dennis; Marhan, Sven; Poll, Christian; Bamminger, Chris; Ludwig, Bernard

    2016-04-01

    Potential increases in soil temperature due to climate change might result in intensified soil organic matter (SOM) decomposition and thus higher CO2 emissions. Management options to increase and stabilize SOM include the application of biochar. However, the effects of biochar amendments under elevated soil temperatures on SOM dynamics are largely unknown. The objective of this study was to analyze the effect of biochar application and elevated soil temperature on the amount and composition of OM associated with fractions of different turnover kinetics. Samples were taken from four treatments of the Hohenheim Climate Change Experiment with the factors temperature (ambient or elevated by 2.5 °C in 4 cm depth, six years before sampling) and biochar (control and 30 t / ha Miscanthus pyrolysis biochar, one year before sampling) in two depths (0 - 5 and 5 - 15 cm). Basal respiration and microbial biomass C were analyzed within an incubation experiment. Aggregate size-fractions were separated by wet-sieving and the free light, occluded light (oLF), and heavy fractions were isolated by density fractionation. All fractions were analyzed for organic C and δ13C as well as by infrared spectroscopy. Preliminary data suggest that biochar significantly increased basal respiration and that the microbial biomass C was significantly affected by elevated temperature. No biochar-C was found in the microbial biomass. Biochar and elevated temperature had only minor effects on the organic C associated with aggregate-size classes, although biochar was incorporated into all fractions already after one year of application. Biochar application significantly increased the organic C associated with oLF. In most samples affected by biochar, the proportion of C=O groups was significantly increased. The results suggest that already after one year, biochar-mineral interactions were formed leading to an aggregate occlusion of applied biochar. At least in the short-term, the effect of biochar on

  8. The Suborbital Particle Aggregation and Collision Experiment (SPACE): studying the collision behavior of submillimeter-sized dust aggregates on the suborbital rocket flight REXUS 12.

    PubMed

    Brisset, Julie; Heißelmann, Daniel; Kothe, Stefan; Weidling, René; Blum, Jürgen

    2013-09-01

    The Suborbital Particle Aggregation and Collision Experiment (SPACE) is a novel approach to study the collision properties of submillimeter-sized, highly porous dust aggregates. The experiment was designed, built, and carried out to increase our knowledge about the processes dominating the first phase of planet formation. During this phase, the growth of planetary precursors occurs by agglomeration of micrometer-sized dust grains into aggregates of at least millimeters to centimeters in size. However, the formation of larger bodies from the so-formed building blocks is not yet fully understood. Recent numerical models on dust growth lack a particular support by experimental studies in the size range of submillimeters, because these particles are predicted to collide at very gentle relative velocities of below 1 cm/s that can only be achieved in a reduced-gravity environment. The SPACE experiment investigates the collision behavior of an ensemble of silicate-dust aggregates inside several evacuated glass containers which are being agitated by a shaker to induce the desired collisions at chosen velocities. The dust aggregates are being observed by a high-speed camera, allowing for the determination of the collision properties of the protoplanetary dust analog material. The data obtained from the suborbital flight with the REXUS (Rocket Experiments for University Students) 12 rocket will be directly implemented into a state-of-the-art dust growth and collision model.

  9. Summary of an Analysis of Pupil-Teacher Ratio and Class Size: Differences That Make a Difference and Its Implications on Staffing for Class-Size Reduction.

    ERIC Educational Resources Information Center

    Sharp, Mark A.

    The purpose of this paper was to share findings from an earlier study and to provide a framework for administrators to use in the implementation of class-size reduction (CSR) in their buildings. The study examined actual and average class size (CS), pupil-teacher ratios (PTR), and their differences. A primary goal was to clarify the ramifications…

  10. Public School Education: The Case for Reduced Class Size. Why the Present Class Size is Not Working and What Can We Do about It?

    ERIC Educational Resources Information Center

    Graham, Evol

    2009-01-01

    By reducing class size we will close the achievement gap in public school education, caused by prior neglect especially since the civil rights era of the sixties. Additional, highly qualified and specialized teachers will more effectively manage a smaller class size and serve more individual student needs in the crucial early grades, where a solid…

  11. 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

  12. 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

  13. 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

  14. Influence of aggregate sizes and microstructures on bioremediation assessment of field-contaminated soils in pilot-scale biopiles

    NASA Astrophysics Data System (ADS)

    Chang, W.; Akbari, A.; Frigon, D.; Ghoshal, S.

    2011-12-01

    Petroleum hydrocarbon contamination of soils and groundwater is an environmental concern. Bioremediation has been frequently considered a cost-effective, less disruptive remedial technology. Formation of soil aggregate fractions in unsaturated soils is generally believed to hinder aerobic hydrocarbon biodegradation due to the slow intra-pore diffusion of nutrients and oxygen within the aggregate matrix and to the reduced bioavailability of hydrocarbons. On the other hand, soil aggregates may harbour favourable niches for indigenous bacteria, providing protective microsites against various in situ environmental stresses. The size of the soil aggregates is likely to be a critical factor for these processes and could be interpreted as a relevant marker for biodegradation assessment. There have been only limited attempts in the past to assess petroleum hydrocarbon biodegradation in unsaturated soils as a function of aggregate size. This study is aimed at investigating the roles of aggregate sizes and aggregate microstructures on biodegradation activity. Field-aged, contaminated, clayey soils were shipped from Norman Wells, Canada. Attempts were made to stimulate indigenous microbial activity by soil aeration and nutrient amendments in a pilot-scale biopile tank (1m L×0.65m W×0.3 m H). A control biopile was maintained without the nutrient amendment but was aerated. The initial concentrations of petroleum hydrocarbons in the field-contaminated soils increased with increasing aggregate sizes, which were classified in three fractions: micro- (<250 μm), meso- (>250-2000 μm) and macro-aggregates (>2000 μm). Compared to the TPH analyses at whole-soil level, the petroleum hydrocarbon analyses based on the aggregate-size levels demonstrated more clearly the extent of biodegradation of non-volatile, heavier hydrocarbons (C16-C34) in the soil. The removal of the C16-C34 hydrocarbons was 44% in macro-aggregates, but only 13% in meso-aggregates. The increased protein

  15. 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.

  16. Fate of Multimeric Oligomers, Submicron, and Micron Size Aggregates of Monoclonal Antibodies Upon Subcutaneous Injection in Mice.

    PubMed

    Kijanka, Grzegorz; Bee, Jared S; Bishop, Steven M; Que, Ivo; Löwik, Clemens; Jiskoot, Wim

    2016-05-01

    The aim of this study was to examine the fate of differently sized protein aggregates upon subcutaneous injection in mice. A murine and a human monoclonal immunoglobulin G 1 (IgG1) antibody were labeled with a fluorescent dye and subjected to stress conditions to create aggregates. Aggregates fractionated by centrifugation or gel permeation chromatography were administered subcutaneously into SKH1 mice. The biodistribution was measured by in vivo fluorescence imaging for up to 1 week post injection. At several time points, mice were sacrificed and selected organs and tissues were collected for ex vivo analysis. Part of injected aggregated IgGs persisted much longer at the injection site than unstressed controls. Aggregate fractions containing submicron (0.1-1 μm) or micron (1-100 μm) particles were retained to a similar extent. Highly fluorescent "hot-spots" were detected 24 h post injection in spleens of mice injected with submicron aggregates of murine IgG. Submicron aggregates of human IgG showed higher accumulation in draining lymph nodes 1 h post injection than unstressed controls or micron size aggregates. For both tested proteins, aggregated fractions seemed to be eliminated from circulation more rapidly than monomeric fractions. The biodistribution of monomers isolated from solutions subjected to stress conditions was similar to that of unstressed control. PMID:27044942

  17. Acceleration of Individual, Decimetre-sized Aggregates in the Lower Coma of Comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Agarwal, Jessica; A'Hearn, M. F.; Vincent, J.-B.; Güttler, C.; Höfner, S.; Sierks, H.; Tubiana, C.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco, M.; Deller, J.; Fornasier, S.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Hofmann, M.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Lopez Moreno, J. J.; Marzari, F.; Naletto, G.; Oklay, N.; Shi, X.; Thomas, N.

    2016-09-01

    We present OSIRIS/NAC observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained in January 2016 when the comet was at 2 AU from the Sun out-bound from perihelion. We measure the acceleration of individual aggregates through a two-hour image series. Approximately 50% of the aggregates are accelerated away from the nucleus, and 50% towards it, and likewise towards either horizontal direction. The accelerations are up to one order of magnitude stronger than local gravity, and are most simply explained by the combined effect of gas drag accelerating all aggregates upwards, and the recoil force from asymmetric outgassing, either from rotating aggregates with randomly oriented spin axes and sufficient thermal inertia to shift the temperature maximum away from an aggregate's subsolar region, or from aggregates with variable ice content. At least 10% of the aggregates will escape the gravity field of the nucleus and feed the comet's debris trail, while others may fall back to the surface and contribute to the deposits covering parts of the northern hemisphere. The rocket force plays a crucial role in pushing these aggregates back towards the surface. Our observations show the future back fall material in the process of ejection, and provide the first direct measurement of the acceleration of aggregates in the innermost coma (<2km) of a comet, where gas drag is still significant.

  18. Size of spawning population, residence time, and territory shifts of individuals in the spawning aggregation of a riverine catostomid

    USGS Publications Warehouse

    Grabowski, T.B.; Isely, J.J.

    2008-01-01

    Little is known about the behavior of individual fish in a spawning aggregation, specifically how long an individual remains in an aggregation. We monitored Moxostoma robustum (Cope) (Robust Redhorse) in a Savannah River spawning aggregation during spring 2004 and 2005 to provide an estimate of the total number of adults and the number of males comprising the aggregation and to determine male residence time and movements within a spawning aggregation. Robust Redhorse were captured using prepostioned grid electrofishers, identified to sex, weighed, measured, and implanted with a passive integrated transponder. Spawning aggregation size was estimated using a multiple census mark-and-recapture procedure. The spawning aggregation seemed to consist of approximately the same number of individuals (82-85) and males (50-56) during both years of this study. Individual males were present for a mean of 3.6 ?? 0.24 days (?? SE) during the 12-day spawning period. The mean distance between successive recaptures of individual males was 15.9 ?? 1.29 m (?? SE). We conclude that males establish spawning territories on a daily basis and are present within the spawning aggregation for at least 3-4 days. The relatively short duration of the aggregation may be the result of an extremely small population of adults. However, the behavior of individuals has the potential to influence population estimates made while fish are aggregated for spawning.

  19. Acceleration of individual, decimetre-sized aggregates in the lower coma of comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Agarwal, Jessica; A'Hearn, M. F.; Vincent, J.-B.; Güttler, C.; Höfner, S.; Sierks, H.; Tubiana, C.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco, M.; Deller, J.; Fornasier, S.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Hofmann, M.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Lopez Moreno, J. J.; Marzari, F.; Naletto, G.; Oklay, N.; Shi, X.; Thomas, N.

    2016-11-01

    We present OSIRIS/NAC observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained in January 2016 when the comet was at 2 AU from the Sun out-bound from perihelion. We measure the acceleration of individual aggregates through a two-hour image series. Approximately 50% of the aggregates are accelerated away from the nucleus, and 50% towards it, and likewise towards either horizontal direction. The accelerations are up to one order of magnitude stronger than local gravity, and are most simply explained by the combined effect of gas drag accelerating all aggregates upwards, and the recoil force from asymmetric outgassing, either from rotating aggregates with randomly oriented spin axes and sufficient thermal inertia to shift the temperature maximum away from an aggregate's subsolar region, or from aggregates with variable ice content. At least 10% of the aggregates will escape the gravity field of the nucleus and feed the comet's debris trail, while others may fall back to the surface and contribute to the deposits covering parts of the northern hemisphere. The rocket force plays a crucial role in pushing these aggregates back towards the surface. Our observations show the future back fall material in the process of ejection, and provide the first direct measurement of the acceleration of aggregates in the innermost coma (<2km) of a comet, where gas drag is still significant.

  20. How to form planetesimals from mm-sized chondrules and chondrule aggregates

    NASA Astrophysics Data System (ADS)

    Carrera, Daniel; Johansen, Anders; Davies, Melvyn B.

    2015-07-01

    The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than ~100 km in size. Instead, planetesimals appear to form top-down, with large 100-1000 km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found that particles down to millimeter sizes can form dense particle clouds through the run-away convergence of radial drift known as the streaming instability. We made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ~105 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (~106-107 years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn, reduces collision speeds and enhances coagulation. Future simulations should model coagulation and the streaming instability together to explore this feedback loop further. Appendices are available in electronic form at http://www.aanda.org

  1. "That's It for Today": Academic Lecture Closings and the Impact of Class Size

    ERIC Educational Resources Information Center

    Cheng, Stephanie W.

    2012-01-01

    The present study investigates the rhetorical structure of academic lecture closings, and the impact of class size on this part genre. A framework of "stages" and "strategies" is developed to analyze the rhetorical structure of lecture closings. Large and small classes are further compared to find how class size may influence the ways lecturers…

  2. Class Size Reduction in California: Summary of the 1998-99 Evaluation Findings.

    ERIC Educational Resources Information Center

    Stecher, Brian M.; Bohrnstedt, George W.

    This report discusses the results of the third year--1998-99--of California's Class Size Reduction (CSR) program. Assessments of the program show that CSR was almost fully implemented by 1998-99, with over 92 percent of students in K-3 in classes of 20 or fewer students. Those K-3 classes that had not been reduced in size were concentrated in…

  3. Class Size and Student Diversity: Two Sides of the Same Coin. Teacher Voice

    ERIC Educational Resources Information Center

    Froese-Germain, Bernie; Riel, Rick; McGahey, Bob

    2012-01-01

    Among Canadian teacher unions, discussions of class size are increasingly being informed by the importance of considering the diversity of student needs within the classroom (often referred to as class composition). For teachers, both class size and diversity matter. Teachers consistently adapt their teaching to address the individual needs of the…

  4. Bacterial diversity of soil aggregates of different sizes in various land use conditions

    NASA Astrophysics Data System (ADS)

    Ivanova, Ekaterina; Azida, Thakahova; Olga, Kutovaya

    2014-05-01

    The patterns of soil microbiome structure may be a universal and very sensitive indicator of soil quality (soil "health") used for optimization and biologization of agricultural systems. The understanding of how microbial diversity influenses, and is influenced by, the environment can only be attained by analyses at scales relevant to those at which processes influencing microbial diversity actually operate. The basic structural and functional unit of the soil is a soil aggregate, which is actually a microcosm of the associative co-existing groups of microorganisms that form characteristic ecological food chains. It is known that many important microbial processes occur in spatially segregated microenvironments in soil leading to a microscale biogeography. The Metagenomic library of typical chernozem in conditions of different land use systems was created. Total genomic DNA was extracted from 0.5 g of the frozen soil after mechanical destruction. Sample preparation and sequencing was performed on a GS Junior ("Roche»", Switzerland) according to manufacturer's recommendations, using the universal primers to the variable regions V4 gene 16S - rRNA - F515 (GTGCCAGCMGCCGCGGTAA) and R806 (GGACT-ACVSGGGTATCTAAT). It is shown that the system of land use is a stronger determinant of the taxonomic composition of the soil microbial community, rather than the size of the structural units. In soil samples from different land use systems the presence of accessory components was revealed. They may be used as indicators of processes of soil recovery, soil degradation or soil exhaustion processes occuring in the agroecosystems. The comparative analysis of microbial communities of chernozem aggregates investigated demonstrates the statistically valuable differences in the amount of bacterial phyla and Archean domain content as well as the species richness in aggregates of various size fractions. The occurrence of specific components in the taxonomic structure of micro-and macro-aggregates

  5. Size-Exclusion Chromatography for the Analysis of Protein Biotherapeutics and their Aggregates

    PubMed Central

    Hong, Paula; Koza, Stephan; Bouvier, Edouard S. P.

    2012-01-01

    In recent years, the use and number of biotherapeutics has increased significantly. For these largely protein-based therapies, the quantitation of aggregates is of particular concern given their potential effect on efficacy and immunogenicity. This need has renewed interest in size-exclusion chromatography (SEC). In the following review we will outline the history and background of SEC for the analysis of proteins. We will also discuss the instrumentation for these analyses, including the use of different types of detectors. Method development for protein analysis by SEC will also be outlined, including the effect of mobile phase and column parameters (column length, pore size). We will also review some of the applications of this mode of separation that are of particular importance to protein biopharmaceutical development and highlight some considerations in their implementation. PMID:23378719

  6. Effect Size, Statistical Power and Sample Size Requirements for the Bootstrap Likelihood Ratio Test in Latent Class Analysis

    PubMed Central

    Dziak, John J.; Lanza, Stephanie T.; Tan, Xianming

    2014-01-01

    Selecting the number of different classes which will be assumed to exist in the population is an important step in latent class analysis (LCA). The bootstrap likelihood ratio test (BLRT) provides a data-driven way to evaluate the relative adequacy of a (K −1)-class model compared to a K-class model. However, very little is known about how to predict the power or the required sample size for the BLRT in LCA. Based on extensive Monte Carlo simulations, we provide practical effect size measures and power curves which can be used to predict power for the BLRT in LCA given a proposed sample size and a set of hypothesized population parameters. Estimated power curves and tables provide guidance for researchers wishing to size a study to have sufficient power to detect hypothesized underlying latent classes. PMID:25328371

  7. Quality assessment for recycling aggregates from construction and demolition waste: An image-based approach for particle size estimation.

    PubMed

    Di Maria, Francesco; Bianconi, Francesco; Micale, Caterina; Baglioni, Stefano; Marionni, Moreno

    2016-02-01

    The size distribution of aggregates has direct and important effects on fundamental properties of construction materials such as workability, strength and durability. The size distribution of aggregates from construction and demolition waste (C&D) is one of the parameters which determine the degree of recyclability and therefore the quality of such materials. Unfortunately, standard methods like sieving or laser diffraction can be either very time consuming (sieving) or possible only in laboratory conditions (laser diffraction). As an alternative we propose and evaluate the use of image analysis to estimate the size distribution of aggregates from C&D in a fast yet accurate manner. The effectiveness of the procedure was tested on aggregates generated by an existing C&D mechanical treatment plant. Experimental comparison with manual sieving showed agreement in the range 81-85%. The proposed technique demonstrated potential for being used on on-line systems within mechanical treatment plants of C&D.

  8. Class Size Effects on Student Achievement: Heterogeneity across Abilities and Fields

    ERIC Educational Resources Information Center

    De Paola, Maria; Ponzo, Michela; Scoppa, Vincenzo

    2013-01-01

    In this paper, we analyze class size effects on college students exploiting data from a project offering special remedial courses in mathematics and language skills to freshmen enrolled at an Italian medium-sized public university. To estimate the effects of class size, we exploit the fact that students and teachers are virtually randomly assigned…

  9. The Relationship between Class Size and Online Activity Patterns in Asynchronous Computer Conferencing Environments

    ERIC Educational Resources Information Center

    Hewitt, Jim; Brett, Clare

    2007-01-01

    This study analyzes the relationship between class size and student online activity patterns in a series of 28 graduate level computer conferencing courses. Quantitative analyses of note production, average note size, note opening and note reading percentages found a significant positive correlation between class size and mean number of notes…

  10. Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution

    NASA Astrophysics Data System (ADS)

    Kostadinov, Tihomir S.; Milutinović, Svetlana; Marinov, Irina; Cabré, Anna

    2016-04-01

    Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth system models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing methods to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size - picophytoplankton (0.5-2 µm in diameter), nanophytoplankton (2-20 µm) and microphytoplankton (20-50 µm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global class="text">SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e., oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have high biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global climatological, spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield ˜ 0.25 Gt of C, consistent with analogous estimates from two other ocean color algorithms and several state-of-the-art Earth system models. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm. Uncertainty budget analyses indicate that absolute carbon concentration uncertainties are driven by the PSD parameter No which determines particle number concentration to first order, while uncertainties in PFTs' fractional contributions to total C biomass

  11. 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.

  12. Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry.

    PubMed

    Saha, Debashish; Babler, Matthaus U; Holzner, Markus; Soos, Miroslav; Lüthi, Beat; Liberzon, Alex; Kinzelbach, Wolfgang

    2016-01-12

    Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of ∼2.2, and their size is 1.4 ± 0.4 mm, which is large, compared to the Kolmogorov length scale (η = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., dfrag ∼ σ(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude. PMID:26646289

  13. Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry.

    PubMed

    Saha, Debashish; Babler, Matthaus U; Holzner, Markus; Soos, Miroslav; Lüthi, Beat; Liberzon, Alex; Kinzelbach, Wolfgang

    2016-01-12

    Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of ∼2.2, and their size is 1.4 ± 0.4 mm, which is large, compared to the Kolmogorov length scale (η = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., dfrag ∼ σ(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude.

  14. Influence of polydisperse distributions of both primary particle and aggregate size on soot temperature in low-fluence LII

    NASA Astrophysics Data System (ADS)

    Liu, F.; Yang, M.; Hill, F. A.; Snelling, D. R.; Smallwood, G. J.

    2006-06-01

    An improved aggregate-based low-fluence laser-induced incandescence (LII) model has been developed. The shielding effect in heat conduction between aggregated soot particles and the surrounding gas was modeled using the concept of the equivalent heat transfer sphere. The diameter of such an equivalent sphere was determined from direct simulation Monte Carlo calculations in the free molecular regime as functions of the aggregate size and the thermal accommodation coefficient of soot. Both the primary soot particle diameter and the aggregate size distributions are assumed to be lognormal. The effective temperature of a soot particle ensemble containing different primary particle diameters and aggregate sizes in the laser probe volume was calculated based on the ratio of the total thermal radiation intensities of soot particles at 400 and 780 nm to simulate the experimentally measured soot particle temperature using two-color optical pyrometry. The effect of primary particle diameter polydispersity is in general important and should be considered. The effect of aggregate size polydispersity is relatively unimportant when the heat conduction between the primary particles and the surrounding gas takes place in the free-molecular regime; however, it starts to become important when the heat conduction process occurs in the near transition regime. The model developed in this study was also applied to the re-determination of the thermal accommodation coefficient of soot in an atmospheric pressure laminar ethylene diffusion flame.

  15. Aggregate morphology of nano-TiO2: role of primary particle size, solution chemistry, and organic matter.

    PubMed

    Chowdhury, Indranil; Walker, Sharon L; Mylon, Steven E

    2013-01-01

    A systematic investigation was conducted to understand the role of aquatic conditions on the aggregate morphology of nano-TiO2, and the subsequent impact on their fate in the environment. In this study, three distinctly sized TiO2 nanoparticles (6, 13, and 23 nm) that had been synthesized with flame spray pyrolysis were employed. Nanoparticle aggregate morphology was measured using static light scattering (SLS) over a wide range of solution chemistry, and in the presence of natural organic matter (NOM). Results showed that primary nanoparticle size can significantly affect the fractal dimension of stable aggregates. A linear relationship was observed between surface areas of primary nanoparticles and fractal dimension indicating that smaller primary nanoparticles can form more compact aggregate in the aquatic environment. The pH, ionic strength, and ion valence also influenced the aggregate morphology of TNPs. Increased pH resulted a decrease in fractal dimension, whereas higher ionic strength resulted increased fractal dimension particularly for monovalent ions. When NOM was present, aggregate fractal dimension was also affected, which was also notably dependent on solution chemistry. Fractal dimension of aggregate increase for 6 nm system in the presence of NOM, whereas a drop in fractal dimension was observed for 13 nm and 23 nm aggregates. This effect was most profound for aggregates comprised of the smallest primary particles suggesting that interactions of NOM with smaller primary nanoparticles are more significant than those with larger ones. The findings from this study will be helpful for the prediction of nanoparticle aggregate fate in the aquatic environment. PMID:24592445

  16. Comminution and sizing processes of concrete block waste as recycled aggregates.

    PubMed

    Gomes, P C C; Ulsen, C; Pereira, F A; Quattrone, M; Angulo, S C

    2015-11-01

    Due to the environmental impact of construction and demolition waste (CDW), recycling is mandatory. It is also important that recycled concrete aggregates (RCA) are used in concrete to meet market demands. In the literature, the influence of RCAs on concrete has been investigated, but very limited studies have been conducted on how the origin of concrete waste and comminution processes influence RCA characteristics. This paper aims to investigate the influence of three different comminution and sizing processes (simple screening, crushing and grinding) on the composition, shape and porosity characteristics of RCA obtained from concrete block waste. Crushing and grinding implies a reduction of RCA porosity. However, due to the presence of coarse quartz rounded river pebbles in the original concrete block mixtures, the shape characteristics deteriorated. A large amount of powder (<0.15 mm) without detectable anhydrous cement was also generated. PMID:26168872

  17. Comminution and sizing processes of concrete block waste as recycled aggregates.

    PubMed

    Gomes, P C C; Ulsen, C; Pereira, F A; Quattrone, M; Angulo, S C

    2015-11-01

    Due to the environmental impact of construction and demolition waste (CDW), recycling is mandatory. It is also important that recycled concrete aggregates (RCA) are used in concrete to meet market demands. In the literature, the influence of RCAs on concrete has been investigated, but very limited studies have been conducted on how the origin of concrete waste and comminution processes influence RCA characteristics. This paper aims to investigate the influence of three different comminution and sizing processes (simple screening, crushing and grinding) on the composition, shape and porosity characteristics of RCA obtained from concrete block waste. Crushing and grinding implies a reduction of RCA porosity. However, due to the presence of coarse quartz rounded river pebbles in the original concrete block mixtures, the shape characteristics deteriorated. A large amount of powder (<0.15 mm) without detectable anhydrous cement was also generated.

  18. Setting limits for acceptable change in sediment particle size composition following marine aggregate dredging.

    PubMed

    Cooper, Keith M

    2012-08-01

    In the UK, Government policy requires marine aggregate extraction companies to leave the seabed in a similar physical condition after the cessation of dredging. This measure is intended to promote recovery, and the return of a similar faunal community to that which existed before dredging. Whilst the policy is sensible, and in line with the principles of sustainable development, the use of the word 'similar' is open to interpretation. There is, therefore, a need to set quantifiable limits for acceptable change in sediment composition. Using a case study site, it is shown how such limits could be defined by the range of sediment particle size composition naturally found in association with the faunal assemblages in the wider region. Whilst the approach offers a number of advantages over the present system, further testing would be required before it could be recommended for use in the regulatory context. PMID:22721693

  19. Inverting microwell array chip for the cultivation of human induced pluripotent stem cells with controlled aggregate size and geometrical arrangement

    PubMed Central

    Satoh, Taku; Sugiura, Shinji; Sumaru, Kimio; Ozaki, Shigenori; Gomi, Shinichi; Kurakazu, Tomoaki; Oshima, Yasuhiro; Kanamori, Toshiyuki

    2014-01-01

    We present a novel cell culture chip, namely, “inverting microwell array chip,” for cultivation of human induced pluripotent stem cells. The chip comprises a lower hydrogel microwell array and an upper polystyrene culture surface. We demonstrate the formation of uniform cellular aggregates in the microwell array, and after inversion, a culture with controlled aggregate size and geometrical arrangement on the polystyrene surface. Here, we report effects of cell concentrations on a cultivation sequence in the chip. PMID:24803961

  20. How Do the Size, Charge and Shape of Nanoparticles Affect Amyloid β Aggregation on Brain Lipid Bilayer?

    PubMed

    Kim, Yuna; Park, Ji-Hyun; Lee, Hyojin; Nam, Jwa-Min

    2016-01-01

    Here, we studied the effect of the size, shape, and surface charge of Au nanoparticles (AuNPs) on amyloid beta (Aβ) aggregation on a total brain lipid-based supported lipid bilayer (brain SLB), a fluid platform that facilitates Aβ-AuNP aggregation process. We found that larger AuNPs induce large and amorphous aggregates on the brain SLB, whereas smaller AuNPs induce protofibrillar Aβ structures. Positively charged AuNPs were more strongly attracted to Aβ than negatively charged AuNPs, and the stronger interactions between AuNPs and Aβ resulted in fewer β-sheets and more random coil structures. We also compared spherical AuNPs, gold nanorods (AuNRs), and gold nanocubes (AuNCs) to study the effect of nanoparticle shape on Aβ aggregation on the brain SLB. Aβ was preferentially bound to the long axis of AuNRs and fewer fibrils were formed whereas all the facets of AuNCs interacted with Aβ to produce the fibril networks. Finally, it was revealed that different nanostructures induce different cytotoxicity on neuroblastoma cells, and, overall, smaller Aβ aggregates induce higher cytotoxicity. The results offer insight into the roles of NPs and brain SLB in Aβ aggregation on the cell membrane and can facilitate the understanding of Aβ-nanostructure co-aggregation mechanism and tuning Aβ aggregate structures. PMID:26782664

  1. How Do the Size, Charge and Shape of Nanoparticles Affect Amyloid β Aggregation on Brain Lipid Bilayer?

    NASA Astrophysics Data System (ADS)

    Kim, Yuna; Park, Ji-Hyun; Lee, Hyojin; Nam, Jwa-Min

    2016-01-01

    Here, we studied the effect of the size, shape, and surface charge of Au nanoparticles (AuNPs) on amyloid beta (Aβ) aggregation on a total brain lipid-based supported lipid bilayer (brain SLB), a fluid platform that facilitates Aβ-AuNP aggregation process. We found that larger AuNPs induce large and amorphous aggregates on the brain SLB, whereas smaller AuNPs induce protofibrillar Aβ structures. Positively charged AuNPs were more strongly attracted to Aβ than negatively charged AuNPs, and the stronger interactions between AuNPs and Aβ resulted in fewer β-sheets and more random coil structures. We also compared spherical AuNPs, gold nanorods (AuNRs), and gold nanocubes (AuNCs) to study the effect of nanoparticle shape on Aβ aggregation on the brain SLB. Aβ was preferentially bound to the long axis of AuNRs and fewer fibrils were formed whereas all the facets of AuNCs interacted with Aβ to produce the fibril networks. Finally, it was revealed that different nanostructures induce different cytotoxicity on neuroblastoma cells, and, overall, smaller Aβ aggregates induce higher cytotoxicity. The results offer insight into the roles of NPs and brain SLB in Aβ aggregation on the cell membrane and can facilitate the understanding of Aβ-nanostructure co-aggregation mechanism and tuning Aβ aggregate structures.

  2. Class Size and Student Performance at a Public Research University: A Cross-Classified Model

    ERIC Educational Resources Information Center

    Johnson, Iryna Y.

    2010-01-01

    This study addresses several methodological problems that have confronted prior research on the effect of class size on student achievement. Unlike previous studies, this analysis accounts for the hierarchical data structure of student achievement, where grades are nested within classes and students, and considers a wide range of class sizes…

  3. A Survey of Selected Teachers Opinions to the Effects of Class Size on Student Achievement among Middle School Students

    ERIC Educational Resources Information Center

    Leahy, Sarah

    2006-01-01

    Researchers have studied the affects of class size on student achievement for years. Therefore, the size of classes presently is disturbing. In regards to class size reductions, Murphy, 1998 states that students enjoyed significantly greater improvements in test scores in reading, language arts, and math. A class size research study was conducted…

  4. Another Look at the Glass and Smith Study on Class Size

    ERIC Educational Resources Information Center

    Phelps, James L.

    2011-01-01

    One of the most influential studies affecting educational policy is Glass and Smith's 1978 study, "Meta-Analysis of Research on the Relationship of Class-Size and Achievement." Since its publication, educational policymakers have referenced it frequently as the justification for reducing class size. While teachers and the public had long believed…

  5. No Room To Learn: Crowded NYC Schools Jeopardize Smaller Class Size Plans

    ERIC Educational Resources Information Center

    Green, Mark; Doran, Helaine

    This report presents data collected from 43 over-capacity elementary schools in the New York City Public School system. The data give information about typical class sizes in the early grades and the cost of an initiative to reduce class size. Of the 1,722 classrooms examined, 56 percent are considered to be overcrowded, and 438 of the city's 723…

  6. Identifying Class Size Effects in Developing Countries: Evidence from Rural Schools in Bolivia.

    ERIC Educational Resources Information Center

    Urquiola, Miguel

    Although great interest surrounds class size as a policy instrument, inferences on its effects are controversial. Recent work highlights a particular way to consider the endogeneity issues that affect this variable: class size is often correlated with enrollment, which in turn may be related to socioeconomic status (SES). This paper shows why such…

  7. The Cost of Class Size Reduction: Advice for Policymakers. RAND Graduate School Dissertation.

    ERIC Educational Resources Information Center

    Reichardt, Robert E.

    This dissertation provides information to state-level policymakers that will help them avoid two implementation problems seen in the past in California's class-size-reduction (CSR) reform. The first problem was that flat, per student reimbursement did not adequately cover costs in districts with larger pre-CSR class-sizes or smaller schools. The…

  8. The Impact of a Universal Class-Size Reduction Policy: Evidence from Florida's Statewide Mandate

    ERIC Educational Resources Information Center

    Chingos, Matthew M.

    2012-01-01

    Class-size reduction (CSR) mandates presuppose that resources provided to reduce class size will have a larger impact on student outcomes than resources that districts can spend as they see fit. I estimate the impact of Florida's statewide CSR policy by comparing the deviations from prior achievement trends in districts that were required to…

  9. The Effects of Class Size on Student Grades at a Public University

    ERIC Educational Resources Information Center

    Kokkelenberg, Edward C.; Dillon, Michael; Christy, Sean M.

    2008-01-01

    We model how class size affects the grade higher education students earn and we test the model using an ordinal logit with and without fixed effects on over 760,000 undergraduate observations from a northeastern public university. We find that class size negatively affects grades for a variety of specifications and subsets of the data, as well as…

  10. Class Size Reduction in Practice: Investigating the Influence of the Elementary School Principal

    ERIC Educational Resources Information Center

    Burch, Patricia; Theoharis, George; Rauscher, Erica

    2010-01-01

    Class size reduction (CSR) has emerged as a very popular, if not highly controversial, policy approach for reducing the achievement gap. This article reports on findings from an implementation study of class size reduction policy in Wisconsin entitled the Student Achievement Guarantee in Education (SAGE). Drawing on case studies of nine schools,…

  11. The Effects of Class Size on Student Achievement in Intermediate Level Elementary Students

    ERIC Educational Resources Information Center

    McInerney, Melissa

    2014-01-01

    Class size and student achievement have been debated for decades. The vast amount of research on this topic is either conflicting or inconclusive. There are large and small scale studies that support both sides of this dilemma (Achilles, Nye, Boyd-Zaharias, Fulton, & Cain, 1994; Glass & Smith, 1979; Slavin, 1989). Class size reduction is a…

  12. Reducing Class Size: A Smart Way To Improve America's Urban Schools. Second Edition.

    ERIC Educational Resources Information Center

    Naik, Manish; Casserly, Michael; Uro, Gabriela

    The Council of the Great City Schools, a coalition of the largest urban public schools in the United States, surveyed its membership to determine how they were using federal class size reduction funds in the 2000-2001 school year. Thirty-six major urban school systems responded. Results indicate that the federal class size reduction program is…

  13. Effects of Class Size and Attendance Policy on University Classroom Interaction in Taiwan

    ERIC Educational Resources Information Center

    Bai, Yin; Chang, Te-Sheng

    2016-01-01

    Classroom interaction experience is one of the main parts of students' learning lives. However, surprisingly little research has investigated students' perceptions of classroom interaction with different attendance policies across different class sizes in the higher education system. To elucidate the effects of class size and attendance policy on…

  14. Class Size Effects on Reading Achievement Using PIRLS Data: Evidence from Greece

    ERIC Educational Resources Information Center

    Konstantopoulos, Spyros; Traynor, Anne

    2014-01-01

    Background/Context: The effects of class size on student achievement have gained considerable attention in education research and policy, especially over the last 30 years. Perhaps the best evidence about the effects of class size thus far has been produced from analyses of Project STAR data, a large-scale experiment where students and teachers…

  15. What We Have Learned about Class Size Reduction in California. Capstone Report.

    ERIC Educational Resources Information Center

    Bohrnstedt, George W., Ed.; Stecher, Brian M., Ed.

    This final report on the California Class Size Reduction (CSR) initiative summarizes findings from three earlier reports dating back to 1997. Chapter 1 recaps the history of California's CSR initiative and includes a discussion of what state leaders' expectations were when CSR was passed. The chapter also describes research on class-size reduction…

  16. Class Size Reduction and Academic Achievement of Low-Socioeconomic Students

    ERIC Educational Resources Information Center

    Rollins, Sarah E.

    2013-01-01

    Concern about the academic and social well-being of public education in the United States has been at the forefront of education reform. Increased class sizes, amended curriculum standards, and accountability standards have guided the way toward ways to reduce class sizes to meet the demands put upon educators. This study investigated the…

  17. Willingness to Communicate in Iranian EFL Learners: The Effect of Class Size

    ERIC Educational Resources Information Center

    Khazaei, Zeinab Moradi; Zadeh, Ahmad Moin; Ketabi, Saeed

    2012-01-01

    Willingness to communicate can be considered as one of the important factors in modern language pedagogy which put emphasis on meaningful communication. The present study investigated the effect of class size on the Iranian EFL students' willingness to communicate among three different class sizes. The researcher collected the data through…

  18. Class Size: The Issue for Policy Makers in the State of Utah.

    ERIC Educational Resources Information Center

    Nishi, Shannon

    A review of literature on class size is the purpose of this report. Included are a summary of four meta analyses (Robinson and Wittebols 1986), (Cone 1978), and (Glass and Smith 1978 and 1979); a discussion of research methodologies; recommendations for policy makers; and alternative strategies for class size reduction. Appendices present…

  19. Cooperative Learning in Industrial-sized Biology Classes

    PubMed Central

    Chang, Shu-Mei; Brickman, Marguerite

    2007-01-01

    This study examined the impact of cooperative learning activities on student achievement and attitudes in large-enrollment (>250) introductory biology classes. We found that students taught using a cooperative learning approach showed greater improvement in their knowledge of course material compared with students taught using a traditional lecture format. In addition, students viewed cooperative learning activities highly favorably. These findings suggest that encouraging students to work in small groups and improving feedback between the instructor and the students can help to improve student outcomes even in very large classes. These results should be viewed cautiously, however, until this experiment can be replicated with additional faculty. Strategies for potentially improving the impact of cooperative learning on student achievement in large courses are discussed. PMID:17548878

  20. Structure−Activity Relationships in Peptide Modulators of β-Amyloid Protein Aggregation: Variation in α,α-Disubstitution Results in Altered Aggregate Size and Morphology

    PubMed Central

    2010-01-01

    Neuronal cytotoxicity observed in Alzheimer’s disease (AD) is linked to the aggregation of β-amyloid peptide (Aβ) into toxic forms. Increasing evidence points to oligomeric materials as the neurotoxic species, not Aβ fibrils; disruption or inhibition of Aβ self-assembly into oligomeric or fibrillar forms remains a viable therapeutic strategy to reduce Aβ neurotoxicity. We describe the synthesis and characterization of amyloid aggregation mitigating peptides (AAMPs) whose structure is based on the Aβ “hydrophobic core” Aβ17−20, with α,α-disubstituted amino acids (ααAAs) added into this core as potential disrupting agents of fibril self-assembly. The number, positional distribution, and side-chain functionality of ααAAs incorporated into the AAMP sequence were found to influence the resultant aggregate morphology as indicated by ex situ experiments using atomic force microscopy (AFM) and transmission electron microscopy (TEM). For instance, AAMP-5, incorporating a sterically hindered ααAA with a diisobutyl side chain in the core sequence, disrupted Aβ1−40 fibril formation. However, AAMP-6, with a less sterically hindered ααAA with a dipropyl side chain, altered fibril morphology, producing shorter and larger sized fibrils (compared with those of Aβ1−40). Remarkably, ααAA-AAMPs caused disassembly of existing Aβ fibrils to produce either spherical aggregates or protofibrillar structures, suggesting the existence of equilibrium between fibrils and prefibrillar structures. PMID:22778850

  1. Influence of soot aggregate structure on particle sizing using laser-induced incandescence: importance of bridging between primary particles

    NASA Astrophysics Data System (ADS)

    Johnsson, J.; Bladh, H.; Olofsson, N.-E.; Bengtsson, P.-E.

    2013-09-01

    Soot aggregates formed in combustion processes are often described as clusters of carbonaceous particles in random fractal structures. For theoretical studies of the physical properties of such aggregates, they have often been modelled as spherical primary particles in point contact. However, transmission electron microscopy (TEM) images show that the primary particles are more connected than in a single point; there is a certain amount of bridging between the primary particles. Particle sizing using the diagnostic technique laser-induced incandescence (LII) is crucially dependent on the heat conduction rate from the aggregate to the ambient gas, which depends on the amount of bridging. In this work, aggregates with bridging are modelled using overlapping spheres, and it is shown how such aggregates can be built to fulfil specific fractal parameters. Aggregates with and without bridging are constructed numerically, and it is investigated how the bridging influences the heat conduction rate in the free-molecular regime. The calculated heat conduction rates are then used in an LII model to show how LII particle sizing is influenced by different amounts of bridging. For realistic amounts of bridging (), the primary particle diameters were overestimated by up to 9 % if bridging was not taken into account.

  2. Drivers of aggregation in a novel arboreal parasite: the influence of host size and infra-populations.

    PubMed

    Yule, Kirsty J; Burns, Kevin C

    2015-02-01

    As a novel arboreal parasite, New Zealand's largest endemic moth, Aenetus virescens, is a biological oddity. With arguably the most unusual lepidopteran life history on earth, larvae grow to 100mm, spending ∼6 years as wood-boring parasites feeding on host tree phloem. Parasite fitness is a product of host suitability. Parasite discrimination between heterogeneous hosts in fragmented populations shapes parasite aggregation. We investigated whether A. virescens aggregation among hosts occurs randomly (target area effect), or if larvae select hosts based on host quality (ideal free distribution). Using long-term larval growth as an indicator of energy intake, we examined A. virescens aggregation in relation to host size and infra-population. Using a generalised linear model, the relationship between parasite intensity and host tree size was analysed. Reduced major axis regression was used to evaluate A. virescens growth after 1 year. Linear mixed-effects models inferred the influence of parasite infra-population on parasite growth, with host tree as a random factor. Results indicate parasite intensity scaled positively with host size. Furthermore, parasite growth remained consistent throughout ontogeny regardless of host size or parasite infra-population. Aenetus virescens aggregation among hosts violates the ideal free distribution hypothesis, occurring instead as a result of host size, supporting the target area effect.

  3. Do Reductions in Class Size Raise Students' Test Scores? Evidence from Population Variation in Minnesota's Elementary Schools

    ERIC Educational Resources Information Center

    Cho, Hyunkuk; Glewwe, Paul; Whitler, Melissa

    2012-01-01

    Many U.S. states and cities spend substantial funds to reduce class size, especially in elementary (primary) school. Estimating the impact of class size on learning is complicated, since children in small and large classes differ in many observed and unobserved ways. This paper uses a method of Hoxby (2000) to assess the impact of class size on…

  4. Sustainable management and supply of natural and recycled aggregates in a medium-size integrated plant.

    PubMed

    Faleschini, Flora; Zanini, Mariano Angelo; Pellegrino, Carlo; Pasinato, Stefano

    2016-03-01

    The consumption of natural aggregates in civil engineering applications can cause severe environmental impacts on a regional scale, depleting the stock of bulk resources within a territory. Several methods can improve the environmental sustainability of the whole aggregates' supply process, including natural and recycled aggregates' productive chains, for instance promoting the use of recycled aggregates (RA). However, when quarrying and recycling activities are considered as stand-alone processes, also the RA supply chain may not be as sustainable as expected, due to the high environmental loads associated to transportation, if high distances from the production to the use sites are involved. This work gives some insights on the environmental impact assessment of the aggregates' industry in the Italian context, through a comparative assessment of the environmental loads of natural and recycled aggregates' productive chains. An integrated plant for the extraction of virgin aggregates and recycling of construction and demolition waste (C&DW) was analyzed as significant case study, with the aim to identify the influence of sustainable solutions on the overall emissions of the facility. A Life Cycle Assessment (LCA) approach was used, using site-specific data and paying particular attention on transportation-related impacts, land use, avoided landfill and non-renewable resources preservation. From this work it was possible to evaluate the influence of transportation and PV energy use on the overall environmental emissions of natural and recycled aggregates' productive chains. PMID:26810029

  5. Sustainable management and supply of natural and recycled aggregates in a medium-size integrated plant.

    PubMed

    Faleschini, Flora; Zanini, Mariano Angelo; Pellegrino, Carlo; Pasinato, Stefano

    2016-03-01

    The consumption of natural aggregates in civil engineering applications can cause severe environmental impacts on a regional scale, depleting the stock of bulk resources within a territory. Several methods can improve the environmental sustainability of the whole aggregates' supply process, including natural and recycled aggregates' productive chains, for instance promoting the use of recycled aggregates (RA). However, when quarrying and recycling activities are considered as stand-alone processes, also the RA supply chain may not be as sustainable as expected, due to the high environmental loads associated to transportation, if high distances from the production to the use sites are involved. This work gives some insights on the environmental impact assessment of the aggregates' industry in the Italian context, through a comparative assessment of the environmental loads of natural and recycled aggregates' productive chains. An integrated plant for the extraction of virgin aggregates and recycling of construction and demolition waste (C&DW) was analyzed as significant case study, with the aim to identify the influence of sustainable solutions on the overall emissions of the facility. A Life Cycle Assessment (LCA) approach was used, using site-specific data and paying particular attention on transportation-related impacts, land use, avoided landfill and non-renewable resources preservation. From this work it was possible to evaluate the influence of transportation and PV energy use on the overall environmental emissions of natural and recycled aggregates' productive chains.

  6. Free collisions in a microgravity many-particle experiment. III. The collision behavior of sub-millimeter-sized dust aggregates

    NASA Astrophysics Data System (ADS)

    Kothe, Stefan; Blum, Jürgen; Weidling, René; Güttler, Carsten

    2013-07-01

    We conducted micro-gravity experiments to study the outcome of collisions between sub-mm-sized dust agglomerates consisting of μm-sized SiO2 monomer grains at velocities of several cm s-1. Prior to the experiments, we used X-ray computer tomography (nano-CT) imaging to study the internal structure of these dust agglomerates and found no rim compaction so that their collision behavior is not governed by preparation-caused artefacts. We found that collisions between these dust aggregates can lead either to sticking or to bouncing, depending mostly on the impact velocity. While previous collision models derived the transition between both regimes from contact physics, we used the available empirical data from these and earlier experiments to derive a power law relation between dust-aggregate mass and impact velocity for the threshold between the two collision outcomes. In agreement with earlier experiments, we show that the transition between both regimes is not sharp, but follows a shallower power law than predicted by previous models (Güttler, C., Blum, J., Zsom, A., Ormel, C.W., Dullemond, C.P. [2010]. Astron. Astrophys. 513, A56). Furthermore, we find that sticking between dust aggregates can lead to the formation of larger structures. Collisions between aggregates-of-aggregates can lead to growth at higher velocities than homogeneous dust agglomerates.

  7. Aggregates of nisin with various bactoprenol-containing cell wall precursors differ in size and membrane permeation capacity.

    PubMed

    Scherer, Katharina; Wiedemann, Imke; Ciobanasu, Corina; Sahl, Hans-Georg; Kubitscheck, Ulrich

    2013-11-01

    Many lantibiotics use the membrane bound cell wall precursor Lipid II as a specific target for killing Gram-positive bacteria. Binding of Lipid II usually impedes cell wall biosynthesis, however, some elongated lantibiotics such as nisin, use Lipid II also as a docking molecule for pore formation in bacterial membranes. Although the unique nisin pore formation can be analyzed in Lipid II-doped vesicles, mechanistic details remain elusive. We used optical sectioning microscopy to directly visualize the interaction of fluorescently labeled nisin with membranes of giant unilamellar vesicles containing Lipid II and its various bactoprenol precursors. We quantitatively analyzed the binding and permeation capacity of nisin when applied at nanomolar concentrations. Specific interactions with Lipid I, Lipid II and bactoprenol-diphosphate (C55-PP), but not bactoprenol-phosphate (C55-P), resulted in the formation of large molecular aggregates. For Lipid II, we demonstrated the presence of both nisin and Lipid II in these aggregates. Membrane permeation induced by nisin was observed in the presence of Lipid I and Lipid II, but not in the presence of C55-PP. Notably, the size of the C55-PP-nisin aggregates was significantly smaller than that of the aggregates formed with Lipid I and Lipid II. We conclude that the membrane permeation capacity of nisin is determined by the size of the bactoprenol-containing aggregates in the membrane. Notably, transmitted light images indicated that the formation of large aggregates led to a pinch-off of small vesicles, a mechanism, which probably limits the growth of aggregates and induces membrane leakage.

  8. Aggregate Size and Architecture Determine Microbial Activity Balance for One-Stage Partial Nitritation and Anammox ▿

    PubMed Central

    Vlaeminck, Siegfried E.; Terada, Akihiko; Smets, Barth F.; De Clippeleir, Haydée; Schaubroeck, Thomas; Bolca, Selin; Demeestere, Lien; Mast, Jan; Boon, Nico; Carballa, Marta; Verstraete, Willy

    2010-01-01

    Aerobic ammonium-oxidizing bacteria (AerAOB) and anoxic ammonium-oxidizing bacteria (AnAOB) cooperate in partial nitritation/anammox systems to remove ammonium from wastewater. In this process, large granular microbial aggregates enhance the performance, but little is known about granulation so far. In this study, three suspended-growth oxygen-limited autotrophic nitrification-denitrification (OLAND) reactors with different inoculation and operation (mixing and aeration) conditions, designated reactors A, B, and C, were used. The test objectives were (i) to quantify the AerAOB and AnAOB abundance and the activity balance for the different aggregate sizes and (ii) to relate aggregate morphology, size distribution, and architecture putatively to the inoculation and operation of the three reactors. A nitrite accumulation rate ratio (NARR) was defined as the net aerobic nitrite production rate divided by the anoxic nitrite consumption rate. The smallest reactor A, B, and C aggregates were nitrite sources (NARR, >1.7). Large reactor A and C aggregates were granules capable of autonomous nitrogen removal (NARR, 0.6 to 1.1) with internal AnAOB zones surrounded by an AerAOB rim. Around 50% of the autotrophic space in these granules consisted of AerAOB- and AnAOB-specific extracellular polymeric substances. Large reactor B aggregates were thin film-like nitrite sinks (NARR, <0.5) in which AnAOB were not shielded by an AerAOB layer. Voids and channels occupied 13 to 17% of the anoxic zone of AnAOB-rich aggregates (reactors B and C). The hypothesized granulation pathways include granule replication by division and budding and are driven by growth and/or decay based on species-specific physiology and by hydrodynamic shear and mixing. PMID:19948857

  9. Big Class Size Challenges: Teaching Reading in Primary Classes in Kampala, Uganda's Central Municipality

    ERIC Educational Resources Information Center

    Kewaza, Samuel; Welch, Myrtle I.

    2013-01-01

    Research on reading has established that reading is a pivotal discipline and early literacy development dictates later reading success. Therefore, the purpose of this study is to investigate challenges encountered with reading pedagogy, teaching materials, and teachers' attitudes towards teaching reading in crowded primary classes in Kampala,…

  10. Mapping Surface Cover Parameters Using Aggregation Rules and Remotely Sensed Cover Classes. Version 1.9

    NASA Technical Reports Server (NTRS)

    Arain, Altaf M.; Shuttleworth, W. James; Yang, Z-Liang; Michaud, Jene; Dolman, Johannes

    1997-01-01

    A coupled model, which combines the Biosphere-Atmosphere Transfer Scheme (BATS) with an advanced atmospheric boundary-layer model, was used to validate hypothetical aggregation rules for BATS-specific surface cover parameters. The model was initialized and tested with observations from the Anglo-Brazilian Amazonian Climate Observational Study and used to simulate surface fluxes for rain forest and pasture mixes at a site near Manaus in Brazil. The aggregation rules are shown to estimate parameters which give area-average surface fluxes similar to those calculated with explicit representation of forest and pasture patches for a range of meteorological and surface conditions relevant to this site, but the agreement deteriorates somewhat when there are large patch-to-patch differences in soil moisture. The aggregation rules, validated as above, were then applied to remotely sensed 1 km land cover data set to obtain grid-average values of BATS vegetation parameters for 2.8 deg x 2.8 deg and 1 deg x 1 deg grids within the conterminous United States. There are significant differences in key vegetation parameters (aerodynamic roughness length, albedo, leaf area index, and stomatal resistance) when aggregate parameters are compared to parameters for the single, dominant cover within the grid. However, the surface energy fluxes calculated by stand-alone BATS with the 2-year forcing, data from the International Satellite Land Surface Climatology Project (ISLSCP) CDROM were reasonably similar using aggregate-vegetation parameters and dominant-cover parameters, but there were some significant differences, particularly in the western USA.

  11. Biomass and productivity of three phytoplankton size classes in San Francisco Bay.

    USGS Publications Warehouse

    Cole, B.E.; Cloern, J.E.; Alpine, A.E.

    1986-01-01

    The 5-22 mu m size accounted for 40-50% of annual production in each embayment, but production by phytoplanton >22 mu m ranged from 26% in the S reach to 54% of total phytoplankton production in the landward embayment of the N reach. A productivity index is derived that predicts daily productivity for each size class as a function of ambient irradiance and integrated chlorophyll a in the photic zone. For the whole phytoplankton community and for each size class, this index was constant at approx= 0.76 g C m-2 (g chlorophyll a Einstein)-1. The annual means of maximum carbon assimilation numbers were usually similar for the three size classes. Spatial and temporal variations in size-fractionated productivity are primarily due to differences in biomass rather than size-dependent carbon assimilation rates. -from Authors

  12. Polymorphic mountain whitefish (Prosopium williamsoni) in a coastal riverscape: size class assemblages, distribution, and habitat associations

    USGS Publications Warehouse

    Starr, James C.; Torgersen, Christian

    2015-01-01

    We compared the assemblage structure, spatial distributions, and habitat associations of mountain whitefish (Prosopium williamsoni) morphotypes and size classes. We hypothesised that morphotypes would have different spatial distributions and would be associated with different habitat features based on feeding behaviour and diet. Spatially continuous sampling was conducted over a broad extent (29 km) in the Calawah River, WA (USA). Whitefish were enumerated via snorkelling in three size classes: small (10–29 cm), medium (30–49 cm), and large (≥50 cm). We identified morphotypes based on head and snout morphology: a pinocchio form that had an elongated snout and a normal form with a blunted snout. Large size classes of both morphotypes were distributed downstream of small and medium size classes, and normal whitefish were distributed downstream of pinocchio whitefish. Ordination of whitefish assemblages with nonmetric multidimensional scaling revealed that normal whitefish size classes were associated with higher gradient and depth, whereas pinocchio whitefish size classes were positively associated with pool area, distance upstream, and depth. Reach-scale generalised additive models indicated that normal whitefish relative density was associated with larger substrate size in downstream reaches (R2 = 0.64), and pinocchio whitefish were associated with greater stream depth in the reaches farther upstream (R2 = 0.87). These results suggest broad-scale spatial segregation (1–10 km), particularly between larger and more phenotypically extreme individuals. These results provide the first perspective on spatial distributions and habitat relationships of polymorphic mountain whitefish.

  13. Interpreting nanoscale size-effects in aggregated Fe-oxide suspensions: Reaction of Fe(II) with Goethite

    NASA Astrophysics Data System (ADS)

    Cwiertny, David M.; Handler, Robert M.; Schaefer, Michael V.; Grassian, Vicki H.; Scherer, Michelle M.

    2008-03-01

    The Fe(II)/Fe(III) redox couple plays an important role in both the subsurface fate and transport of groundwater pollutants and the global cycling of carbon and nitrogen in iron-limited marine environments. Iron oxide particles involved in these redox processes exhibit broad size distributions, and the recent demonstrations of dramatic nanoscale size-effects with various metal oxides has compelled us, as well as many others, to consider whether the rate and extent of Fe(II)/Fe(III) cycling depends upon oxide particle size in natural systems. Here, we investigated the reaction of Fe(II) with three different goethite particle sizes in pH 7.5 suspensions. Acicular goethite rods with primary particle dimensions ranging from 7 by 80 nm to 25 by 670 nm were studied. Similar behavior with respect to Fe(II) sorption, electron transfer and nitrobenzene reduction was observed on a mass-normalized basis despite almost a threefold difference in goethite specific surface areas. Scanning electron microscopy (SEM) images, dynamic light scattering (DLS) and sedimentation measurements all indicated that, at pH 7.5, significant aggregation occurred with all three sizes of goethite particles. SEM images further revealed that nanoscale particles formed dense aggregates on the order of several microns in diameter. The clear formation of particle aggregates in solution raises questions regarding the use of primary particle surface area as a basis for assessing nanoscale size-effects in iron oxide suspensions at circum-neutral pH values. In our case, normalizing the Fe(II) sorption densities and rate constants for nitrobenzene reduction by BET surface area implies that goethite nanoparticles are less reactive than larger particles. We suspect, however, that aggregation is responsible for this observed size-dependence, and argue that BET values should not be used to assess differences in surface site density or intrinsic surface reactivity in aggregated particle suspensions. In order to

  14. The Class-Size Effect upon Activity and Cognitive Dimensions of Lessons in Higher Education.

    ERIC Educational Resources Information Center

    Mahler, Sophia; And Others

    1986-01-01

    A study of the relationship of class size to the length, frequency, and cognitive level and diversity of both teacher and student verbalizations in medical instruction in an Israeli university is reported. (MSE)

  15. Utilizing Online Education in Florida to Meet Mandated Class Size Limitations

    ERIC Educational Resources Information Center

    Mattox, Kari Ann

    2012-01-01

    With the passage of a state constitutional amendment in 2002, Florida school districts faced the challenge of meeting class size mandates in core subjects, such as mathematics, English, and science by the 2010-2011 school year, or face financial penalties. Underpinning the amendment's goals was the argument that smaller classes are more effective…

  16. Teaching Large Class Sizes in Physical Education: Guidelines and Strategies. Guidance Document

    ERIC Educational Resources Information Center

    National Association for Sport and Physical Education, 2006

    2006-01-01

    The National Association for Sport and Physical Education (NASPE) recommends that the size of physical education class be consistent with those of other subject areas (e.g. maximum 1:25 for ES, 1:30 for MS, 1:35 for HS) for safe and effective instruction. When students with special needs are included in regular physical education classes, their…

  17. Experimental Estimates of the Impacts of Class Size on Test Scores: Robustness and Heterogeneity

    ERIC Educational Resources Information Center

    Ding, Weili; Lehrer, Steven F.

    2011-01-01

    Proponents of class size reductions (CSRs) draw heavily on the results from Project Student/Teacher Achievement Ratio to support their initiatives. Adding to the political appeal of these initiative are reports that minority and economically disadvantaged students received the largest benefits from smaller classes. We extend this research in two…

  18. Class Size Reduction: Lessons Learned from Experience. Policy Brief No. Twenty-Three.

    ERIC Educational Resources Information Center

    McRobbie, Joan; Finn, Jeremy D.; Harman, Patrick

    New federal proposals have fueled national interest in class-size reduction (CSR). However, CSR raises numerous concerns, some of which are addressed in this policy brief. The text draws on the experiences of states and districts that have implemented CSR. The brief addresses the following 15 concerns: Do small classes in and of themselves affect…

  19. A Descriptive Evaluation of the Federal Class-Size Reduction Program: Final Report

    ERIC Educational Resources Information Center

    Millsap, Mary Ann; Giancola, Jennifer; Smith, W. Carter; Hunt, Dana; Humphrey, Daniel C.; Wechsler, Marjorie E.; Riehl, Lori M.

    2004-01-01

    The federal Class-Size Reduction (CSR) Program, P.L. 105-277, begun in Fiscal Year 1999, represented a major federal commitment to help school districts hire additional qualified teachers, especially in the early elementary grades, so children would learn in smaller classes. The CSR program also allowed funds to be spent as professional…

  20. Class-Size Effects on Adolescents' Mental Health and Well-Being in Swedish Schools

    ERIC Educational Resources Information Center

    Jakobsson, Niklas; Persson, Mattias; Svensson, Mikael

    2013-01-01

    This paper analyzes whether class size has an effect on the prevalence of mental health problems and well-being among adolescents in Swedish schools. We use cross-sectional data collected in year 2008 covering 2755 Swedish adolescents in ninth grade from 40 schools and 159 classes. We utilize different econometric approaches to address potential…

  1. The Influence of Small Class Size, Duration, Intensity, and Heterogeneity on Head Start Fade

    ERIC Educational Resources Information Center

    Huss, Christopher D.

    2010-01-01

    The researcher conducted a nonexperimental study to investigate and analyze the influence of reduced class sizes, intensity (all day and every day), duration (five years), and heterogeneity (random class assignment) on the Head Start Fade effect. The researcher employed retrospective data analysis using a longitudinal explanatory design on data…

  2. Size Matters: An Exploratory Comparison of Small- and Large-Class University Lecture Introductions

    ERIC Educational Resources Information Center

    Lee, Joseph J.

    2009-01-01

    This exploratory study investigates the impact of class size on the rhetorical move structures and lexico-grammatical features of academic lecture introductions. From the MICASE corpus (The Michigan Corpus of Academic Spoken English), two small corpora of lecture introductions of small- and large-class lectures were compiled. Using a genre-based…

  3. Class-Size Reduction: Using What's Been Learned To Inform Educational Decisions. The Informed Educator Series.

    ERIC Educational Resources Information Center

    Boniface, Russell; Protheroe, Nancy

    Class-size reduction (CSR) has been a complex and contentious issue for the last quarter century. Although the small-class concept was adopted because it appealed to common sense, research over time has revealed a mix of confounding variables, instead of a definitive conclusion. Some CSR efforts, such as Tennessee's Project STAR and Wisconsin's…

  4. The Allocation of Teachers in Schools--An Alternative to the Class Size Dialogue.

    ERIC Educational Resources Information Center

    Loader, David N.

    1978-01-01

    This article looks beyond class size to such specifics as teachers' load, subject electives available, subject load, and different class groupings in developing a flow chart that gives added understanding and control over the variables relating to the deployment of teachers. (Author/IRT)

  5. The Non-Cognitive Returns to Class Size. NBER Working Paper No. 13994

    ERIC Educational Resources Information Center

    Dee, Thomas; West, Martin

    2008-01-01

    Although recent evidence suggests that non-cognitive skills such as engagement matter for academic and economic success, there is little evidence on how key educational inputs affect the development of these skills. We present a re-analysis of follow-up data from the Project STAR class-size experiment and find evidence that early-grade class-size…

  6. Longitudinal Effects of Class Size Reductions on Attainment: Results from Hong Kong Primary Classrooms

    ERIC Educational Resources Information Center

    Galton, Maurice; Pell, Tony

    2012-01-01

    In a four-year study of the effect of class size on pupil outcomes in a sample of 36 primary schools in Hong Kong, it has been found that there are few positive differences in attainment between classes set at less than 25 pupils and those of normal size averaging 38. Three cohorts of pupils were studied. In Cohort 1 pupils spent 3 years in small…

  7. 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

  8. 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

  9. A Revised Pilot Study Examining the Effects of the Timing and Size of Classes on Student Performance in Introductory Accounting Classes

    ERIC Educational Resources Information Center

    Morris, David E., Sr.; Scott, John

    2014-01-01

    The purpose of this pilot study is to examine the effects of the timing of classes and class size on student performance in introductory accounting courses. Factors affecting student success are important to all stakeholders in the academic community. Previous studies have shown mixed results regarding the effects of class size on student success…

  10. Linking Intra-Aggregate Pore Size Distribution with Organic Matter Decomposition Status, Evidence from FTIR and X-Ray Tomography

    NASA Astrophysics Data System (ADS)

    Toosi, E. R.; Quigley, M.; Kravchenko, A. N.

    2014-12-01

    It has been reported that conversion of intensively cultivated lands to less disturbed systems enhances soil OM storage capacity, primarily through OM stabilization in macroaggregates. We hypothesized that the potential for OM stabilization inside macro-aggregates is influenced by presence and abundance of intra-aggregate pores. Pores determine microbial access to OM and regulate diffusion of solution/gases within aggregates which drives microbial functioning. We investigated the influence of longterm disturbance intensity on soil OM composition and its relation to pore size distribution within macroaggregates. We used quantitative FTIR to determine OM decomposition status and X-ray micro-tomography to assess pore size distribution in macroaggregates as affected by management and landuse. Macroaggregates 4-6 mm in size where selected from topsoil under long term conventional tillage (CT), cover-crop (CC), and native succession vegetation (NS) treatments at Kellogg Biological Station, Michigan. Comparison of main soil OM functional groups suggested that with increasing disturbance intensity, the proportion of aromatic and carboxylic/carbohydrates associated compounds increased and it was concomitant with a decrease in the proportion of aliphatic associated compounds and lignin derivatives. Further, FTIR-based decomposition indices revealed that overall decomposition status of macroaggregates followed the pattern of CT > CC ≈ NS. X-ray micro-tomography findings suggested that greater OM decomposition within the macroaggregates was associated with i) greater percent of pores >13 micron in size within the aggregates, as well as ii) greater proportion of small to medium pores (13-110 micron). The results develop previous findings, suggesting that shift in landuse or management indirectly affects soil OM stabilization through alteration of pore size distribution within macroaggregates that itself, is coupled with OM decomposition status.

  11. Culling experiments demonstrate size-class specific biomass increases with mortality.

    PubMed

    Schröder, A; Persson, L; de Roos, A M

    2009-02-24

    Size-selective mortality inevitably leads to a decrease in population density and exerts a direct negative effect on targeted size classes. But density and population size structure are also shaped by food-dependent processes, such as individual growth, maturation, and reproduction. Mortality relaxes competition and thereby alters the dynamic interplay among these processes. As shown by the recently developed size-structured theory, which can account for food-dependent individual performance, this altered interplay can lead to overcompensatory responses in size class-specific biomass, with increasing mortality. We experimentally tested this theory by subjecting laboratory fish populations to a range of size-selective mortality rates. Overall, the results were in agreement with theoretical predictions. Biomass of the juvenile size class increased above control levels at intermediate adult mortality rates and thereafter declined at high mortality rates. Juvenile biomass also increased when juveniles themselves were subjected to intermediate mortality rates. Biomass in other size classes decreased with mortality. Such biomass overcompensation can have wide-ranging implications for communities and food webs, including a high sensitivity of top predators to irreversible catastrophic collapses, the establishment of alternative stable community states, and the promotion of coexistence and biodiversity. PMID:19193850

  12. Influence of aggregate size and free water on the dynamic behaviour of concrete subjected to impact loading

    NASA Astrophysics Data System (ADS)

    Erzar, B.; Forquin, P.; Pontiroli, C.; Buzaud, E.

    2010-06-01

    Concrete is a material widely used in civil engineering. Thus the knowledge of its mechanical behaviour is a major safety issue to evaluate the ability of a structure to resist to an intense dynamic loading. In this study, two experimental techniques have been applied to a micro-concrete and a common concrete to assess the influence of the aggregate size on the dynamic response. First, spalling tests on dry and wet specimens have been performed to characterize the tensile strength of concrete at strain rates in the range 30 - 150/s. Then, edge-on impact tests in sarcophagus configuration have been conducted. The cracking pattern of the micro-concrete and the concrete plates in wet and dry conditions have been compared to appraise the influence of aggregate size and free water on the damaging process.

  13. Microcystin distribution in physical size class separations of natural plankton communities

    USGS Publications Warehouse

    Graham, J.L.; Jones, J.R.

    2007-01-01

    Phytoplankton communities in 30 northern Missouri and Iowa lakes were physically separated into 5 size classes (>100 ??m, 53-100 ??m, 35-53 ??m, 10-35 ??m, 1-10 ??m) during 15-21 August 2004 to determine the distribution of microcystin (MC) in size fractionated lake samples and assess how net collections influence estimates of MC concentration. MC was detected in whole water (total) from 83% of takes sampled, and total MC values ranged from 0.1-7.0 ??g/L (mean = 0.8 ??g/L). On average, MC in the > 100 ??m size class comprised ???40% of total MC, while other individual size classes contributed 9-20% to total MC. MC values decreased with size class and were significantly greater in the >100 ??m size class (mean = 0.5 ??g /L) than the 35-53 ??m (mean = 0.1 ??g/L), 10-35 ??m (mean = 0.0 ??g/L), and 1-10 ??m (mean = 0.0 ??g/L) size classes (p < 0.01). MC values in nets with 100-??m, 53-??m, 35-??m, and 10-??m mesh were cumulatively summed to simulate the potential bias of measuring MC with various size plankton nets. On average, a 100-??m net underestimated total MC by 51%, compared to 37% for a 53-??m net, 28% for a 35-??m net, and 17% for a 10-??m net. While plankton nets consistently underestimated total MC, concentration of algae with net sieves allowed detection of MC at low levels (???0.01 ??/L); 93% of lakes had detectable levels of MC in concentrated samples. Thus, small mesh plankton nets are an option for documenting MC occurrence, but whole water samples should be collected to characterize total MC concentrations. ?? Copyright by the North American Lake Management Society 2007.

  14. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects

    NASA Astrophysics Data System (ADS)

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F.; Carroll, Natalie J.; Applegate, Bruce; Turco, Ronald F.

    2016-06-01

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials.

  15. The influence of coarse aggregate size and volume on the fracture behavior and brittleness of self-compacting concrete

    SciTech Connect

    Beygi, Morteza H.A.; Kazemi, Mohammad Taghi; Nikbin, Iman M.; Vaseghi Amiri, Javad; Rabbanifar, Saeed; Rahmani, Ebrahim

    2014-12-15

    This paper presents the results of an experimental investigation on fracture characteristics and brittleness of self-compacting concrete (SCC), involving the tests of 185 three point bending beams with different coarse aggregate size and content. Generally, the parameters were analyzed by the work of fracture method (WFM) and the size effect method (SEM). The results showed that with increase of size and content of coarse aggregate, (a) the fracture energy increases which is due to the change in fractal dimensions, (b) behavior of SCC beams approaches strength criterion, (c) characteristic length, which is deemed as an index of brittleness, increases linearly. It was found with decrease of w/c ratio that fracture energy increases which may be explained by the improvement in structure of aggregate-paste transition zone. Also, the results showed that there is a correlation between the fracture energy measured by WFM (G{sub F}) and the value measured through SEM (G{sub f}) (G{sub F} = 3.11G{sub f})

  16. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects.

    PubMed

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F; Carroll, Natalie J; Applegate, Bruce; Turco, Ronald F

    2016-01-01

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials. PMID:27306076

  17. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects

    PubMed Central

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F.; Carroll, Natalie J.; Applegate, Bruce; Turco, Ronald F.

    2016-01-01

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials. PMID:27306076

  18. Neutral hydrolysable sugars, OC and N content across soil aggregate size fractions, as an effect of two different crop rotations

    NASA Astrophysics Data System (ADS)

    Angeletti, Carlo; Giannetta, Beatrice; Kölbl, Angelika; Monaci, Elga; Kögel-Knabner, Ingrid; Vischetti, Costantino

    2016-04-01

    This paper presents the results regarding the effects of two 13 years long crop rotations, on the composition of mineral associated neutral sugars, organic carbon (OC) and N concentration, across different aggregate size fractions. The two cropping sequences were characterized by different levels of N input from plant residues and tillage frequency. We also analysed the changes that occurred in soil organic matter (SOM) chemical composition following the cultivation in the two soils of winter wheat and chickpea on the same soils. The analysis of OC and N content across soil aggregate fractions allowed getting an insight into the role played by SOM chemical composition in the formation of organo-mineral associations, while neutral sugars composition provided information on mineral associated SOM origin and decomposition processes, as pentoses derive mostly from plant tissues and hexoses are prevalently of microbial origin. Soil samples were collected from two adjacent fields, from the 0-10 cm layer, in November 2011 (T0). For 13 years before the beginning of the experiment, one soil was cultivated mostly with alfalfa (ALF), while a conventional cereal-sunflower-legume rotation (CON) was carried out on the other. Winter wheat and chickpea were sown on the two soils during the following 2 growing seasons and the sampling was repeated after 18 months (T1). A combination of aggregates size and density fractionation was used to isolate OM associated with mineral particles in: macro-aggregates (>212 μm), micro-aggregates (<200 μm, > 63 μm) and silt and clay size particles (<63 μm). For every fraction, OC and N contents were measured by means of elemental analysis, while the content of the following neutral hydrolysable sugar monomers was measured via GC-FID: rhamnose, fucose, ribose, arabinose, xylose, mannose, galactose, glucose. OC and N contents were higher in ALF as compared to CON for every aggregate fraction, both at T0 and T1. During the 18-months cultivation

  19. Does Size Matter? Size-class differences in Cornus drummondii physiology

    NASA Astrophysics Data System (ADS)

    O'Keefe, K.; O'Connor, R.; Nippert, J. B.

    2015-12-01

    Woody plants have expanded into grasslands over the last century, altering plant diversity, resource availability, and carbon and water fluxes in these systems. In the tallgrass prairies of northeastern Kansas, Cornus drummondii is a clonal C3 shrub that forms monospecific "islands" and is currently increasing in abundance and cover. Clonal expansion of C. drummondii may alter site ecohydrology in unpredictable ways, particularly if physiological characteristics vary throughout an island or change as island size increases. Here, we investigated the physiology of C. drummondii within individual islands and across islands of varying sizes in a mesic tallgrass prairie. We selected six C. drummondii islands of varying sizes at the Konza Prairie Long Term Ecological Research site near Manhattan, KS, USA. Within each island, we measured leaf-level gas exchange and leaf water potential at five ramets equidistant from the outer edge of the island to the center, bi-weekly during the 2015 growing season. Additionally, external heat pulse sap flow sensors were installed at three positions within each island that measured stem sap flow every 10 minutes. We found that leaf level gas exchange rates were consistently higher in the small islands than the medium and large islands, and that the outer most sampling location of the islands had higher net photosynthesis compared to the rest of the island. Conversely, leaf-water potential and stem sap flow rates did not differ between island sizes or within individual islands. These results suggest that carbon, not water flux dynamics, may vary as C. drummondii island size increases at the Konza Prairie. Additionally, these results will facilitate scaling water fluxes from individual shrub islands to watersheds that are encroached with C. drummondii and will ultimately improve our ability to predict changes in the water budget between woody encroached grasslands versus unencroached grasslands.

  20. Size-tunable copper nanocluster aggregates and their application in hydrogen sulfide sensing on paper-based devices

    NASA Astrophysics Data System (ADS)

    Chen, Po-Cheng; Li, Yu-Chi; Ma, Jia-Yin; Huang, Jia-Yu; Chen, Chien-Fu; Chang, Huan-Tsung

    2016-04-01

    Polystyrene sulfonate (PSS), a strong polyelectrolyte, was used to prepare red photoluminescent PSS-penicillamine (PA) copper (Cu) nanoclusters (NC) aggregates, which displayed high selectivity and sensitivity to the detection of hydrogen sulfide (H2S). The size of the PSS-PA-Cu NC aggregates could be readily controlled from 5.5 μm to 173 nm using different concentrations of PSS, which enabled better dispersity and higher sensitivity towards H2S. PSS-PA-Cu NC aggregates provided rapid H2S detection by using the strong Cu-S interaction to quench NC photoluminescence as a sensing mechanism. As a result, a detection limit of 650 nM, which is lower than the maximum level permitted in drinking water by the World Health Organization, was achieved for the analysis of H2S in spring-water samples. Moreover, highly dispersed PSS-PA-Cu NC aggregates could be incorporated into a plate-format paper-based analytical device which enables ultra-low sample volumes (5 μL) and feature shorter analysis times (30 min) compared to conventional solution-based methods. The advantages of low reagent consumption, rapid result readout, limited equipment, and long-term storage make this platform sensitive and simple enough to use without specialized training in resource constrained settings.

  1. Size-tunable copper nanocluster aggregates and their application in hydrogen sulfide sensing on paper-based devices

    PubMed Central

    Chen, Po-Cheng; Li, Yu-Chi; Ma, Jia-Yin; Huang, Jia-Yu; Chen, Chien-Fu; Chang, Huan-Tsung

    2016-01-01

    Polystyrene sulfonate (PSS), a strong polyelectrolyte, was used to prepare red photoluminescent PSS-penicillamine (PA) copper (Cu) nanoclusters (NC) aggregates, which displayed high selectivity and sensitivity to the detection of hydrogen sulfide (H2S). The size of the PSS-PA-Cu NC aggregates could be readily controlled from 5.5 μm to 173 nm using different concentrations of PSS, which enabled better dispersity and higher sensitivity towards H2S. PSS-PA-Cu NC aggregates provided rapid H2S detection by using the strong Cu-S interaction to quench NC photoluminescence as a sensing mechanism. As a result, a detection limit of 650 nM, which is lower than the maximum level permitted in drinking water by the World Health Organization, was achieved for the analysis of H2S in spring-water samples. Moreover, highly dispersed PSS-PA-Cu NC aggregates could be incorporated into a plate-format paper-based analytical device which enables ultra-low sample volumes (5 μL) and feature shorter analysis times (30 min) compared to conventional solution-based methods. The advantages of low reagent consumption, rapid result readout, limited equipment, and long-term storage make this platform sensitive and simple enough to use without specialized training in resource constrained settings. PMID:27113330

  2. Educational Practice for Small Size Class in Fundamental Education of Faculty of Engineering

    NASA Astrophysics Data System (ADS)

    Yokota, Mitsuhiro; Hirano, Kimitaka; Honda, Chikahisa

    An educational practice for small size class in fundamental education of our faculty has been carried out using a special fund from the Ministry of Education, Culture, Sports, Science and Technology since fiscal year 2005. The fundamental subjects such as Mathematics and Physics are very important for the students of Faculty of Engineering. In order to achieve the aim of each subject for students with insufficient understanding, we wrestle with the project of the education for small size class. Some projects are described in this paper.

  3. Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution

    NASA Astrophysics Data System (ADS)

    Kostadinov, T. S.; Milutinović, S.; Marinov, I.; Cabré, A.

    2015-05-01

    Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth System models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing algorithms to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size - picophytoplankton (0.5-2 μm in diameter), nanophytoplankton (2-20 μm) and microphytoplankton (20-50 μm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e. oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have large biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield on average ~0.2-0.3 Gt of C, consistent with analogous estimates from two other ocean color algorithms, and several state-of-the-art Earth System models. However, the range of phytoplankton C biomass spatial variability globally is larger than estimated by any other models considered here, because the PSD-based algorithm is not a priori empirically constrained and introduces improvement over the assumptions of the other approaches. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm

  4. Emergence of multicellularity in a model of cell growth, death and aggregation under size-dependent selection

    PubMed Central

    Duran-Nebreda, Salva; Solé, Ricard

    2015-01-01

    How multicellular life forms evolved from unicellular ones constitutes a major problem in our understanding of the evolution of our biosphere. A recent set of experiments involving yeast cell populations have shown that selection for faster sedimenting cells leads to the appearance of stable aggregates of cells that are able to split into smaller clusters. It was suggested that the observed evolutionary patterns could be the result of evolved programmes affecting cell death. Here, we show, using a simple model of cell–cell interactions and evolving adhesion rates, that the observed patterns in cluster size and localized mortality can be easily interpreted in terms of waste accumulation and toxicity-driven apoptosis. This simple mechanism would have played a key role in the early evolution of multicellular life forms based on both aggregative and clonal development. The potential extensions of this work and its implications for natural and synthetic multicellularity are discussed. PMID:25551152

  5. Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

    PubMed Central

    Green, Peter T.; Harms, Kyle E.; Connell, Joseph H.

    2014-01-01

    A variety of ecological processes influence diversity and species composition in natural communities. Most of these processes, whether abiotic or biotic, differentially filter individuals from birth to death, thereby altering species’ relative abundances. Nonrandom outcomes could accrue throughout ontogeny, or the processes that generate them could be particularly influential at certain stages. One long-standing paradigm in tropical forest ecology holds that patterns of relative abundance among mature trees are largely set by processes operating at the earliest life cycle stages. Several studies confirm filtering processes at some stages, but the longevity of large trees makes a rigorous comparison across size classes impossible without long-term demographic data. Here, we use one of the world’s longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and monitored in 13 mortality censuses over 42 y to 2013. Nonrandom mortality with respect to species identity occurred more often in the smaller rather than the larger size classes. Furthermore, observed nonrandom mortality in the smaller size classes had a diversifying influence; species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes. These results highlight the importance of early life cycle stages in tropical forest community dynamics. More generally, they add to an accumulating body of evidence for the importance of early-stage nonrandom outcomes to community structure in marine and terrestrial environments. PMID:25512498

  6. Do Class and School Size Matter? A Crucial Issue to School Improvement

    ERIC Educational Resources Information Center

    Cornelius, Elizabeth; Gaines, Raffaella; Gautney, Tara; Johnson, Gresha; Rainer, Robyn; Notar, Charles E.; Webb, Shelia A.

    2008-01-01

    Students in a first year Master's degree seminar were asked to find the answer to the question "Do Class and School Size Matter as A Crucial Issue to School Improvement?" The paper the students wrote is based on a review of the literature. The students determined that the question had several issues to be addressed before they could…

  7. Financing Public School Facilities under the Maximum Class Size Requirements in Texas.

    ERIC Educational Resources Information Center

    Haas, Debra Suzanne

    The inadequate financing of public school facilities under the maximum class size requirements in Texas public education raises issues of quality and equity. In six chapters, this thesis attempts to examine the costs of facilities needs and to evaluate the options available to state and to local school districts. Chapter 1 states the problem and…

  8. Class Size Reduction in a Large Urban School District: A Mixed Methodology Evaluation Research Study.

    ERIC Educational Resources Information Center

    Munoz, Marco A.

    This study evaluated the Class Size Reduction (CSR) program in 34 elementary schools in Kentucky's Jefferson County Public Schools. The CSR program is a federal initiative to help elementary schools improve student learning by hiring additional teachers. Qualitative data were collected using unstructured interviews, site observations, and document…

  9. Class Size Reduction or Rapid Formative Assessment?: A Comparison of Cost-Effectiveness

    ERIC Educational Resources Information Center

    Yeh, Stuart S.

    2009-01-01

    The cost-effectiveness of class size reduction (CSR) was compared with the cost-effectiveness of rapid formative assessment, a promising alternative for raising student achievement. Drawing upon existing meta-analyses of the effects of student-teacher ratio, evaluations of CSR in Tennessee, California, and Wisconsin, and RAND cost estimates, CSR…

  10. What the Research Tells Us: Class Size Reduction. Information Capsule. Volume 1001

    ERIC Educational Resources Information Center

    Romanik, Dale

    2010-01-01

    This Information Capsule examines the background and history in addition to research findings pertaining to class size reduction (CSR). This Capsule concludes that although educational researchers have not definitively agreed upon the effectiveness of CSR, given its almost universal public appeal, there is little doubt it is here to stay in some…

  11. Relationship between Class Size and Students' Opportunity to Learn Writing in Middle School

    ERIC Educational Resources Information Center

    Tienken, Christopher H.; Achilles, Charles M.

    2009-01-01

    Class-size reduction (CSR) initiatives have demonstrated positive short- and long-term effects in elementary grades. Less is known about CSR influence on achievement in middle grades. Thus, we conducted a non-experimental, longitudinal, explanatory study of CSR influence on writing achievement of 3 independent cohorts of students (n = 123) in…

  12. Smart Class-Size Policies for Lean Times. SREB Policy Brief

    ERIC Educational Resources Information Center

    Gagne, Jeff

    2012-01-01

    Most states nationwide have had policies for several decades that limit the number of students assigned to public K-12 classrooms. Southern Regional Education Board (SREB) states, led by Tennessee and Texas, spearheaded this effort in the 1980s, and SREB's own "Legislative Briefings" have marked the growth of class-size policies across the region.…

  13. A Study on the Effects of Smaller Class Size on Student Achievement

    ERIC Educational Resources Information Center

    Watts, Rebecca S.; Georgiou, Andrea

    2008-01-01

    Since the passage of No Child Left Behind, schools have been looking for resources that are proven, through research, to improve student achievement. The purpose of this article is to determine if there is a relationship between class size and student achievement among 137 school systems in Tennessee. The authors provide a review of the literature…

  14. A Plan for the Evaluation of California's Class Size Reduction Initiative.

    ERIC Educational Resources Information Center

    Kirst, Michael; Bomstedt, George; Stecher, Brian

    In July 1996, California began its Class Size Reduction (CSR) Initiative. To gauge the effectiveness of this initiative, an analysis of its objectives and an overview of proposed strategies for evaluating CSR are presented here. An outline of the major challenges that stand between CSR and its mission are provided. These include logistical…

  15. A Comparison of QEIA and Non-QEIA Schools: Implications of Class Size Reduction

    ERIC Educational Resources Information Center

    Platt, Louise Carolyn Sater

    2013-01-01

    The purpose of this research study is to compare student achievement changes between matched QEIA and non-QEIA schools in an effort to infer effects of the most significant feature of QEIA funding, class size reduction. The study addressed the critical question--are there demonstrated, significant differences in student achievement gains between…

  16. Class Size Reduction: A Review of the Literature. Research Watch. E&R Report.

    ERIC Educational Resources Information Center

    Scudder, David F.

    High quality evaluation research has demonstrated that smaller classes with a heterogeneous student composition can increase academic achievement and close the achievement gap. Research suggests that changes occur in the classroom naturally as a result of smaller size without efforts by teachers or students to do anything different. With fewer…

  17. Size-class effect contributes to tree species assembly through influencing dispersal in tropical forests.

    PubMed

    Hu, Yue-Hua; Kitching, Roger L; Lan, Guo-Yu; Zhang, Jiao-Lin; Sha, Li-Qing; Cao, Min

    2014-01-01

    We have investigated the processes of community assembly using size classes of trees. Specifically our work examined (1) whether point process models incorporating an effect of size-class produce more realistic summary outcomes than do models without this effect; (2) which of three selected models incorporating, respectively environmental effects, dispersal and the joint-effect of both of these, is most useful in explaining species-area relationships (SARs) and point dispersion patterns. For this evaluation we used tree species data from the 50-ha forest dynamics plot in Barro Colorado Island, Panama and the comparable 20 ha plot at Bubeng, Southwest China. Our results demonstrated that incorporating an size-class effect dramatically improved the SAR estimation at both the plots when the dispersal only model was used. The joint effect model produced similar improvement but only for the 50-ha plot in Panama. The point patterns results were not improved by incorporation of size-class effects using any of the three models. Our results indicate that dispersal is likely to be a key process determining both SARs and point patterns. The environment-only model and joint-effects model were effective at the species level and the community level, respectively. We conclude that it is critical to use multiple summary characteristics when modelling spatial patterns at the species and community levels if a comprehensive understanding of the ecological processes that shape species' distributions is sought; without this results may have inherent biases. By influencing dispersal, the effect of size-class contributes to species assembly and enhances our understanding of species coexistence. PMID:25251538

  18. Relationships among the abundances of plastic debris in different size classes on beaches in South Korea.

    PubMed

    Lee, Jongmyoung; Hong, Sunwook; Song, Young Kyung; Hong, Sang Hee; Jang, Yong Chang; Jang, Mi; Heo, Nak Won; Han, Gi Myung; Lee, Mi Jeong; Kang, Daeseok; Shim, Won Joon

    2013-12-15

    Plastic debris on six beaches near the Nakdong River Estuary, South Korea, was sampled in May and September 2012 and classified into three size classes, large microplastics (1-5 mm), mesoplastics (5-25 mm), and macroplastics (>25 mm). The relationships among the abundances of the size classes were then examined. The abundances of each size category in May (before rainy season) and in September (after rainy season) were 8205 and 27,606 particles/m(2) for large microplastics, 238 and 237 particles/m(2) for mesoplastics, and 0.97 and 1.03 particles/m(2) for macroplastics, respectively. Styrofoam was the most abundant item both in microplastic and mesoplastic debris, while intact plastics were most common in macroplastic debris. The abundances of meso- and micro-plastics were the most strongly correlated. There was a higher correlation between the abundances of macro- and meso-plastics than between macro- and micro-plastics. PMID:24054782

  19. Submillimetre-sized dust aggregate collision and growth properties. Experimental study of a multi-particle system on a suborbital rocket

    NASA Astrophysics Data System (ADS)

    Brisset, J.; Heißelmann, D.; Kothe, S.; Weidling, R.; Blum, J.

    2016-08-01

    Context. In the very first steps of the formation of a new planetary system, dust agglomerates grow inside the protoplanetary disk that rotates around the newly formed star. In this disk, collisions between the dust particles, induced by interactions with the surrounding gas, lead to sticking. Aggregates start growing until their sizes and relative velocities are high enough for collisions to result in bouncing or fragmentation. With the aim of investigating the transitions between sticking and bouncing regimes for colliding dust aggregates and the formation of clusters from multiple aggregates, the Suborbital Particle and Aggregation Experiment (SPACE) was flown on the REXUS 12 suborbital rocket. Aims: The collisional and sticking properties of sub-mm-sized aggregates composed of protoplanetary dust analogue material are measured, including the statistical threshold velocity between sticking and bouncing, their surface energy and tensile strength within aggregate clusters. Methods: We performed an experiment on the REXUS 12 suborbital rocket. The protoplanetary dust analogue materials were micrometre-sized monodisperse and polydisperse SiO2 particles prepared into aggregates with sizes around 120 μm and 330 μm, respectively and volume filling factors around 0.37. During the experimental run of 150 s under reduced gravity conditions, the sticking of aggregates and the formation and fragmentation of clusters of up to a few millimetres in size was observed. Results: The sticking probability of the sub-mm-sized dust aggregates could be derived for velocities decreasing from ~22 to 3 cm s-1. The transition from bouncing to sticking collisions happened at 12.7+2.1-1.4 cm s-1 for the smaller aggregates composed of monodisperse particles and at 11.5+1.9-1.3 and 11.7+1.9-1.3 cm s-1 for the larger aggregates composed of mono- and polydisperse dust particles, respectively. Using the pull-off force of sub-mm-sized dust aggregates from the clusters, the surface energy of the

  20. Response of microbial extracellular enzyme activities and r- vs. K- selected microorganisms to elevated atmospheric CO2 depends on soil aggregate size

    NASA Astrophysics Data System (ADS)

    Dorodnikov, Maxim; Blagodatskaya, Evgenia; Blagodatskiy, Sergey; Kuzyakov, Yakov

    2014-05-01

    Increased belowground carbon (C) transfer by plant roots under elevated atmospheric CO2 and the contrasting environment in soil macro- and microaggregates could affect properties of the microbial community in the rhizosphere. We evaluated the effect of 5 years of elevated CO2 (550 ppm) on four extracellular enzymes: ß-glucosidase, chitinase, phosphatase, and sulfatase along with the contribution of fast- (r-strategists) and slow-growing microorganisms (K-strategists) in soil aggregates. We fractionated the bulk soil from the ambient and elevated CO2 treatments of FACE-Hohenheim (Stuttgart) into large macro- (>2 mm), small macro- (0.25-2.00 mm), and microaggregates (<0.25 mm) using a modified dry sieving. Microbial biomass (C-mic by SIR), the maximal specific growth rate (µ), growing microbial biomass (GMB) and lag-period (t-lag) were estimated by the kinetics of CO2 emission from bulk soil and aggregates amended with glucose and nutrients. In the bulk soil and isolated aggregates before and after activation with glucose, the actual and the potential enzyme activities were measured. Although C-org and C-mic as well as the activities of ß-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO2, significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO2 were 1.2-1.9-fold higher than under ambient CO2. In addition, µ values were significantly higher under elevated than ambient CO2 for bulk soil, small macroaggregates, and microaggregates. Based on changes in µ, GMB, and lag-period, we conclude that elevated atmospheric CO2 stimulated the r-selected microorganisms, especially in soil microaggregates. In contrast, significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO2 revealed an increased contribution of fungi to turnover processes. We conclude that quantitative and

  1. Do Class Size Reductions Make a Difference to Classroom Practice? The Case of Hong Kong Primary Schools

    ERIC Educational Resources Information Center

    Galton, Maurice; Pell, Tony

    2012-01-01

    This paper describes changes which took place in 37 Hong Kong primary schools where class sizes were reduced from 38 to between 20 and 25. Chinese, English and mathematics classes were observed over three years from Primary 1 (aged 6) to Primary 3. For 75% of observations no child was the focus of the teacher's attention in large classes. Reducing…

  2. Does Class Size in First Grade Relate to Children's Academic and Social Performance or Observed Classroom Processes?

    ERIC Educational Resources Information Center

    Allhusen, Virginia; Belsky, Jay; Booth-LaForce, Cathryn L.; Bradley, Robert; Brownwell, Celia A; Burchinal, Margaret; Campbell, Susan B.; Clarke-Stewart, K. Alison; Cox, Martha; Friedman, Sarah L.; Hirsh-Pasek, Kathryn; Houts, Renate M.; Huston, Aletha; Jaeger, Elizabeth; Johnson, Deborah J.; Kelly, Jean F.; Knoke, Bonnie; Marshall, Nancy; McCartney, Kathleen; Morrison, Frederick J.; O'Brien, Marion; Tresch Owen, Margaret; Payne, Chris; Phillips, Deborah; Pianta, Robert; Randolph, Suzanne M.; Robeson, Wendy W.; Spieker, Susan; Lowe Vandell, Deborah; Weinraub, Marsha

    2004-01-01

    This study evaluated the extent to which first-grade class size predicted child outcomes and observed classroom processes for 651 children (in separate classrooms). Analyses examined observed child-adult ratios and teacher-reported class sizes. Smaller classrooms showed higher quality instructional and emotional support, although children were…

  3. The Empirical Case against Large Class Size: Adverse Effects on the Teaching, Learning, and Retention of First-Year Students

    ERIC Educational Resources Information Center

    Cuseo, Joe

    2007-01-01

    Budgetary constraints are creating a current climate of cost containment, within which increasing class size may be seen as a quick and convenient cost-cutting strategy. Empirical evidence suggests that there are eight deleterious outcomes associated with increasingly larger class size. This article synthesizes research relating to these eight…

  4. Estimation of size of red blood cell aggregates using backscattering property of high-frequency ultrasound: In vivo evaluation

    NASA Astrophysics Data System (ADS)

    Kurokawa, Yusaku; Taki, Hirofumi; Yashiro, Satoshi; Nagasawa, Kan; Ishigaki, Yasushi; Kanai, Hiroshi

    2016-07-01

    We propose a method for assessment of the degree of red blood cell (RBC) aggregation using the backscattering property of high-frequency ultrasound. In this method, the scattering property of RBCs is extracted from the power spectrum of RBC echoes normalized by that from the posterior wall of a vein. In an experimental study using a phantom, employing the proposed method, the sizes of microspheres 5 and 20 µm in diameter were estimated to have mean values of 4.7 and 17.3 µm and standard deviations of 1.9 and 1.4 µm, respectively. In an in vivo experimental study, we compared the results between three healthy subjects and four diabetic patients. The average estimated scatterer diameters in healthy subjects at rest and during avascularization were 7 and 28 µm, respectively. In contrast, those in diabetic patients receiving both antithrombotic therapy and insulin therapy were 11 and 46 µm, respectively. These results show that the proposed method has high potential for clinical application to assess RBC aggregation, which may be related to the progress of diabetes.

  5. Evidence of economic regularities and disparities of Italian regions from aggregated tax income size data

    NASA Astrophysics Data System (ADS)

    Cerqueti, Roy; Ausloos, Marcel

    2015-03-01

    This paper discusses the size distribution-in economic terms-of the Italian municipalities over the period 2007-2011. Yearly data are rather well fitted by a modified Lavalette law, while Zipf-Mandelbrot-Pareto law seems to fail in this doing. The analysis is performed either at a national as well as at a local (regional and provincial) level. Deviations are discussed as originating in so called king and vice-roy effects. Results confirm that Italy is shared among very different regional realities. The case of Lazio is puzzling.

  6. An interlaboratory comparison of sizing and counting of subvisible particles mimicking protein aggregates.

    PubMed

    Ripple, Dean C; Montgomery, Christopher B; Hu, Zhishang

    2015-02-01

    Accurate counting and sizing of protein particles has been limited by discrepancies of counts obtained by different methods. To understand the bias and repeatability of techniques in common use in the biopharmaceutical community, the National Institute of Standards and Technology has conducted an interlaboratory comparison for sizing and counting subvisible particles from 1 to 25 μm. Twenty-three laboratories from industry, government, and academic institutions participated. The circulated samples consisted of a polydisperse suspension of abraded ethylene tetrafluoroethylene particles, which closely mimic the optical contrast and morphology of protein particles. For restricted data sets, agreement between data sets was reasonably good: relative standard deviations (RSDs) of approximately 25% for light obscuration counts with lower diameter limits from 1 to 5 μm, and approximately 30% for flow imaging with specified manufacturer and instrument setting. RSDs of the reported counts for unrestricted data sets were approximately 50% for both light obscuration and flow imaging. Differences between instrument manufacturers were not statistically significant for light obscuration but were significant for flow imaging. We also report a method for accounting for differences in the reported diameter for flow imaging and electrical sensing zone techniques; the method worked well for diameters greater than 15 μm.

  7. A new series of C-6 unsubstituted tetrahydropyrimidines: convenient one-pot chemoselective synthesis, aggregation-induced and size-independent emission characteristics.

    PubMed

    Zhu, Qiuhua; Huang, Lan; Chen, Zhipeng; Zheng, Sichao; Lv, Longyun; Zhu, Zhibo; Cao, Derong; Jiang, Huanfeng; Liu, Shuwen

    2013-01-21

    A new series of C-6 unsubstituted tetrahydropyrimidines 6 have been directly synthesized via a convenient urea-catalyzed chemoselective five-component reaction (5CR) under mild conditions. Compounds 6 show typical aggregation-induced emission enhancement (AIEE) characteristics because they are practically no emissive in solution but emit blue or green fluorescence in aggregates with fluorescence yield up to 93%. One of the 5CR products, 6aa, exhibits blue- and green-fluorescence aggregates (bf- and gf-aggregates). The bf- and gf-aggregates are prepared under different conditions and proved to result from different J-aggregations by single-crystal X-ray analysis. In addition, the bf- and gf-aggregates of 6aa show unusual size-independent emission (SIE) characteristics because their maximum emission wavelengths in different sizes (suspension particles, film, powder and crystals) are the same, 434 and 484 nm, respectively. Based on the obtained experimental results, the 5CR mechanism, the origins of AIEE and SIE characteristics are discussed.

  8. Design and synthesis of micron-sized spherical aggregates composed of hollow Fe2O3 nanospheres for use in lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Cho, Jung Sang; Hong, Young Jun; Lee, Jong-Heun; Kang, Yun Chan

    2015-04-01

    A novel structure denoted a ``hollow nanosphere aggregate'' is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe2O3 nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe2O3 nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe2O3 nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe2O3 nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with various compositions for wide applications including energy storage can be prepared by the simple fabrication method introduced in this study.A novel structure denoted a ``hollow nanosphere aggregate'' is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe2O3 nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe2O3 nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe2O3 nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe2O3 nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with

  9. Optimal choice of species and size class for transplanting coral community.

    PubMed

    Muko, Soyoka; Iwasa, Yoh

    2011-03-21

    Transplantation of sessile organisms living in a planned destruction site to a safe site is an important means of restoration to mitigate biodiversity loss following anthropogenic developments. In particular, corals, which play fundamental roles in the coral reef ecosystem and contribute to biodiversity, are good candidates for transplantation. In this study, we investigate the optimal choice of species and size class to be used for coral transplantation. We first studied a case in which the objective function to evaluate the success of transplantation is the maximum total coverage. The optimal strategy is to choose the species and size class with higher net coverage gain per unit handling effort. It is often recommended to transplant only one or a few species and neglect others, even if the original community consists of many species. This may achieve high coverage in the restored coral community but cause loss of species diversity. To overcome this problem, we next study a case in which the objective of the transplantation operation is to maximize the "prosperity index", defined as the product of total coverage and species diversity. In this case, the optimal strategy depends on the species property, population size, and the limitation of total cost allowed for transplantation, but it tends to recommend more species to be transplanted than what is recommended by the coverage maximization criterion. We conclude that maximization of the prosperity index is a better criterion for transplantation than simple coverage maximization.

  10. Injectability of calcium phosphate pastes: Effects of particle size and state of aggregation of β-tricalcium phosphate powders.

    PubMed

    Torres, P M C; Gouveia, S; Olhero, S; Kaushal, A; Ferreira, J M F

    2015-07-01

    The present study discloses a systematic study about the influence of some relevant experimental variables on injectability of calcium phosphate cements. Non-reactive and reactive pastes were prepared, based on tricalcium phosphate doped with 5 mol% (Sr-TCP) that was synthesised by co-precipitation. The varied experimental parameters included: (i) the heat treatment temperature within the range of 800-1100°C; (ii) different milling extents of calcined powders; (iii) the liquid-to-powder ratio (LPR); (iv) the use of powder blends with different particle sizes (PS) and particle size distributions (PSD); (v) the partial replacement of fine powders by large spherical dense granules prepared via freeze granulation method to simulate coarse individual particles. The aim was contributing to better understanding of the effects of PS, PSD, morphology and state of aggregation of the starting powders on injectability of pastes produced thereof. Powders heat treated at 800 and 1000°C with different morphologies but with similar apparent PSD curves obtained by milling/blending originated completely injectable reactive cement pastes at low LPR. This contrasted with non-reactive systems prepared thereof under the same conditions. Hypotheses were put forward to explain why the injectability results collected upon extruding non-reactive pastes cannot be directly transposed to reactive systems. The results obtained underline the interdependent roles of the different powder features and ionic strength in the liquid media on determining the flow and injectability behaviours.

  11. Injectability of calcium phosphate pastes: Effects of particle size and state of aggregation of β-tricalcium phosphate powders.

    PubMed

    Torres, P M C; Gouveia, S; Olhero, S; Kaushal, A; Ferreira, J M F

    2015-07-01

    The present study discloses a systematic study about the influence of some relevant experimental variables on injectability of calcium phosphate cements. Non-reactive and reactive pastes were prepared, based on tricalcium phosphate doped with 5 mol% (Sr-TCP) that was synthesised by co-precipitation. The varied experimental parameters included: (i) the heat treatment temperature within the range of 800-1100°C; (ii) different milling extents of calcined powders; (iii) the liquid-to-powder ratio (LPR); (iv) the use of powder blends with different particle sizes (PS) and particle size distributions (PSD); (v) the partial replacement of fine powders by large spherical dense granules prepared via freeze granulation method to simulate coarse individual particles. The aim was contributing to better understanding of the effects of PS, PSD, morphology and state of aggregation of the starting powders on injectability of pastes produced thereof. Powders heat treated at 800 and 1000°C with different morphologies but with similar apparent PSD curves obtained by milling/blending originated completely injectable reactive cement pastes at low LPR. This contrasted with non-reactive systems prepared thereof under the same conditions. Hypotheses were put forward to explain why the injectability results collected upon extruding non-reactive pastes cannot be directly transposed to reactive systems. The results obtained underline the interdependent roles of the different powder features and ionic strength in the liquid media on determining the flow and injectability behaviours. PMID:25870171

  12. Using What We Know: A Review of the Research on Implementing Class-Size Reduction Initiatives for State and Local Policymakers.

    ERIC Educational Resources Information Center

    Laine, Sabrina W. M., Ed.; Ward, James G., Ed.

    This book contains a collection of essays involving new research on class-size reduction. Six chapters include: (1) "Reducing Class Size in Public Schools: Cost-Benefit Issues and Implications" (John F. Witte); (2) "Making Policy Choices: Is Class-Size Reduction the Best Alternative?" (Doug Harris and David N. Plank); (3) "Smaller Classes, Lower…

  13. Design and synthesis of micron-sized spherical aggregates composed of hollow Fe2O3 nanospheres for use in lithium-ion batteries.

    PubMed

    Cho, Jung Sang; Hong, Young Jun; Lee, Jong-Heun; Kang, Yun Chan

    2015-05-14

    A novel structure denoted a "hollow nanosphere aggregate" is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe2O3 nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe2O3 nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe2O3 nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe2O3 nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with various compositions for wide applications including energy storage can be prepared by the simple fabrication method introduced in this study.

  14. A Further Examination of the Big-Fish-Little-Pond Effect: Perceived Position in Class, Class Size, and Gender Comparisons

    ERIC Educational Resources Information Center

    Thijs, Jochem; Verkuyten, Maykel; Helmond, Petra

    2010-01-01

    Among early adolescents (10-12 years) in the Netherlands, this study examined the academic self-concept in terms of the big-fish-little-pond effect (BFLPE). The BFLPE implies that students in classes where the average achievement is low will have a higher academic self-concept than equally achieving students in classes where the average…

  15. Three Essays on the Economics of Education: Class-Size Reduction, Teacher Labor Markets, and Teacher Effectiveness

    ERIC Educational Resources Information Center

    Dieterle, Steven

    2012-01-01

    Prior research has established the potential for achievement gains from attending smaller classes. However, large statewide class-size reduction (CSR) policies have not been found to consistently realize such gains. A leading explanation for the disappointing performance of CSR policies is that schools are forced to hire additional teachers of…

  16. Global patterns of pelagic dinoflagellate diversity across protist size classes unveiled by metabarcoding.

    PubMed

    Le Bescot, Noan; Mahé, Frédéric; Audic, Stéphane; Dimier, Céline; Garet, Marie-José; Poulain, Julie; Wincker, Patrick; de Vargas, Colomban; Siano, Raffaele

    2016-02-01

    Dinoflagellates (Alveolata) are one of the ecologically most important groups of modern phytoplankton. Their biological complexity makes assessment of their global diversity and community structure difficult. We used massive V9 18S rDNA sequencing from 106 size-fractionated plankton communities collected across the world's surface oceans during the Tara Oceans expedition (2009-2012) to assess patterns of pelagic dinoflagellate diversity and community structuring over global taxonomic and ecological scales. Our data and analyses suggest that dinoflagellate diversity has been largely underestimated, representing overall ∼ 1/2 of protistan rDNA metabarcode richness assigned at ≥ 90% to a reference sequence in the world's surface oceans. Dinoflagellate metabarcode diversity and abundance display regular patterns across the global scale, with different order-level taxonomic compositions across organismal size fractions. While the pico to nano-planktonic communities are composed of an extreme diversity of metabarcodes assigned to Gymnodiniales or are simply undetermined, most micro-dinoflagellate metabarcodes relate to the well-referenced Gonyaulacales and Peridiniales orders, and a lower abundance and diversity of essentially symbiotic Peridiniales is unveiled in the meso-plankton. Our analyses could help future development of biogeochemical models of pelagic systems integrating the separation of dinoflagellates into functional groups according to plankton size classes.

  17. Sizing nanomaterials in bio-fluids by cFRAP enables protein aggregation measurements and diagnosis of bio-barrier permeability

    PubMed Central

    Xiong, Ranhua; Vandenbroucke, Roosmarijn E.; Broos, Katleen; Brans, Toon; Van Wonterghem, Elien; Libert, Claude; Demeester, Jo; De Smedt, Stefaan C.; Braeckmans, Kevin

    2016-01-01

    Sizing nanomaterials in complex biological fluids, such as blood, remains a great challenge in spite of its importance for a wide range of biomedical applications. In drug delivery, for instance, it is essential that aggregation of protein-based drugs is avoided as it may alter their efficacy or elicit immune responses. Similarly it is of interest to determine which size of molecules can pass through biological barriers in vivo to diagnose pathologies, such as sepsis. Here, we report on continuous fluorescence recovery after photobleaching (cFRAP) as a analytical method enabling size distribution measurements of nanomaterials (1–100 nm) in undiluted biological fluids. We demonstrate that cFRAP allows to measure protein aggregation in human serum and to determine the permeability of intestinal and vascular barriers in vivo. cFRAP is a new analytical technique that paves the way towards exciting new applications that benefit from nanomaterial sizing in bio-fluids. PMID:27653841

  18. Sizing nanomaterials in bio-fluids by cFRAP enables protein aggregation measurements and diagnosis of bio-barrier permeability

    NASA Astrophysics Data System (ADS)

    Xiong, Ranhua; Vandenbroucke, Roosmarijn E.; Broos, Katleen; Brans, Toon; van Wonterghem, Elien; Libert, Claude; Demeester, Jo; de Smedt, Stefaan C.; Braeckmans, Kevin

    2016-09-01

    Sizing nanomaterials in complex biological fluids, such as blood, remains a great challenge in spite of its importance for a wide range of biomedical applications. In drug delivery, for instance, it is essential that aggregation of protein-based drugs is avoided as it may alter their efficacy or elicit immune responses. Similarly it is of interest to determine which size of molecules can pass through biological barriers in vivo to diagnose pathologies, such as sepsis. Here, we report on continuous fluorescence recovery after photobleaching (cFRAP) as a analytical method enabling size distribution measurements of nanomaterials (1-100 nm) in undiluted biological fluids. We demonstrate that cFRAP allows to measure protein aggregation in human serum and to determine the permeability of intestinal and vascular barriers in vivo. cFRAP is a new analytical technique that paves the way towards exciting new applications that benefit from nanomaterial sizing in bio-fluids.

  19. Pre-study and in-study validation of a size-exclusion chromatography method with different detection modes for the analysis of monoclonal antibody aggregates.

    PubMed

    Oliva, Alexis; Fariña, Jose B; Llabrés, Matías

    2016-06-01

    Size exclusion chromatography (SEC) with different detection modes was assessed as a means to characterize the type of bevacizumab aggregate that forms under thermal stress, quantitatively monitoring the aggregation kinetics. The combination of SEC with light-scattering (SEC/LS) detection was validated using in-study validation process. This was performed by applying a strategy based on a control chart to monitor the process parameters and by inserting quality control samples in routine runs. The SEC coupled with a differential refractive-index detector (SEC/RI) was validated using a pre-study validation process in accordance with the ICH-Q2 (R1) guidelines and in-study monitoring in accordance with the Analytical Target Profile (ATP) criteria. The total error and β-expectation tolerance interval rules were used to assess method suitability and control the risk of incorrectly accepting unsuitable analytical methods. The aggregation kinetics data were interpreted using a modified Lumry-Eyring model. The true order of the reaction was determined using the initial-rate approach. All the kinetic data show a linear Arrhenius dependence within the studied temperature range. The Arrhenius approach over-predicted the aggregation rate for 5°C, but provides an idea of the aggregation process and amount of aggregate formed. In any case, real-time stability data are necessary to establish the product shelf-life.

  20. Scales and processes in the aggregation of diatom blooms: high time resolution and wide size range records in a mesocosm study

    NASA Astrophysics Data System (ADS)

    Prieto, L.; Ruiz, J.; Echevarría, F.; García, C. M.; Bartual, A.; Gálvez, J. A.; Corzo, A.; Macías, D.

    2002-07-01

    Diatoms and the large, fast-sinking aggregates they form during blooms play an important role in downward flux of particles in the ocean. To study how the aggregation process operates on particle dynamics, diatom blooms were generated and followed under controlled conditions in nutrient-enriched laboratory mesocosm where a homogeneous mixed surface layer was emulated. The size spectrum of particles (from 12 μm to several mm) was recorded each hour during the 1 month span of the experiment by a non-intrusive image analysis system with two CCD cameras. Beam attenuation was continuously recorded as an additional estimator for particle abundance. The high time resolution and wide size range of the records obtained with this design were able to resolve the time scale for coagulation as well as to determine the lowest time resolution needed to sample any experiment aimed to study aggregation of diatoms. Our results narrow previous theoretical time scales to the order of hours to days for the process of mass transfer from small particles to marine snow. Also, daily analyses of a broad range of biological and chemical variables permitted to link phytoplankton succession to the aggregation process. Finally, the evaluated role of different copious exopolymers suggested a lower implication of Coomassie stained particles (CSP) than transparent exopolymeric particles (TEP) in the formation of marine aggregates.

  1. Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta.

    PubMed

    Kleier, Catherine; Trenary, Tim; Graham, Eric A; Stenzel, William; Rundel, Philip W

    2015-01-01

    Azorella compacta (llareta; Apiaceae) forms dense, woody, cushions and characterizes the high elevation rocky slopes of the central Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National Park in northern Chile found a reverse J-shape distribution of size classes of individuals with abundant small plants at all elevations. A new elevational limit for A. compacta was established at 5,250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small degrees of growth up to 2.2 cm yr(-1). Despite their irregularity in growth, cushions of A. compacta show a strong orientation, centered on a north-facing aspect and angle of about 20° from horizontal. This exposure to maximize solar irradiance closely matches previous observations of a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear to be stable, or even expanding, with young plants abundant.

  2. Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta

    PubMed Central

    Trenary, Tim; Graham, Eric A.; Stenzel, William; Rundel, Philip W.

    2015-01-01

    Azorella compacta (llareta; Apiaceae) forms dense, woody, cushions and characterizes the high elevation rocky slopes of the central Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National Park in northern Chile found a reverse J-shape distribution of size classes of individuals with abundant small plants at all elevations. A new elevational limit for A. compacta was established at 5,250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small degrees of growth up to 2.2 cm yr−1. Despite their irregularity in growth, cushions of A. compacta show a strong orientation, centered on a north-facing aspect and angle of about 20° from horizontal. This exposure to maximize solar irradiance closely matches previous observations of a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear to be stable, or even expanding, with young plants abundant. PMID:25802811

  3. The effect of small class sizes on mortality through age 29 years: evidence from a multicenter randomized controlled trial.

    PubMed

    Muennig, Peter; Johnson, Gretchen; Wilde, Elizabeth Ty

    2011-06-15

    Limiting the number of students per classroom in the early years has been shown to improve educational outcomes. Improved education is, in turn, hypothesized to improve health. The authors examined whether smaller class sizes affect mortality through age 29 years and whether cognitive factors play a role. They used data from the Project Student Teacher Achievement Ratio, a 4-year multicenter randomized controlled trial of reduced class sizes in Tennessee involving 11,601 students between 1985 and 1989. Children randomized to small classes (13-17 students) experienced improved measures of cognition and academic performance relative to those assigned to regular classes (22-25 students). As expected, these cognitive measures were significantly inversely associated with mortality rates (P < 0.05). However, through age 29 years, students randomized to small class size nevertheless experienced higher mortality rates than those randomized to regular size classes (hazard ratio (HR) = 1.58, 95% confidence interval (CI): 1.07, 2.32). The groups at risk included males (HR = 1.73, 95% CI: 1.05, 2.85), whites/Asians (HR = 1.68, 95% CI: 1.04, 2.72), and higher income students (HR = 2.20, 95% CI: 1.06, 4.57). The authors speculate that small classes might produce behavior changes that increase mortality through young adulthood that are stronger than the protective effects of enhanced cognition. PMID:21540326

  4. The effect of small class sizes on mortality through age 29 years: evidence from a multicenter randomized controlled trial.

    PubMed

    Muennig, Peter; Johnson, Gretchen; Wilde, Elizabeth Ty

    2011-06-15

    Limiting the number of students per classroom in the early years has been shown to improve educational outcomes. Improved education is, in turn, hypothesized to improve health. The authors examined whether smaller class sizes affect mortality through age 29 years and whether cognitive factors play a role. They used data from the Project Student Teacher Achievement Ratio, a 4-year multicenter randomized controlled trial of reduced class sizes in Tennessee involving 11,601 students between 1985 and 1989. Children randomized to small classes (13-17 students) experienced improved measures of cognition and academic performance relative to those assigned to regular classes (22-25 students). As expected, these cognitive measures were significantly inversely associated with mortality rates (P < 0.05). However, through age 29 years, students randomized to small class size nevertheless experienced higher mortality rates than those randomized to regular size classes (hazard ratio (HR) = 1.58, 95% confidence interval (CI): 1.07, 2.32). The groups at risk included males (HR = 1.73, 95% CI: 1.05, 2.85), whites/Asians (HR = 1.68, 95% CI: 1.04, 2.72), and higher income students (HR = 2.20, 95% CI: 1.06, 4.57). The authors speculate that small classes might produce behavior changes that increase mortality through young adulthood that are stronger than the protective effects of enhanced cognition.

  5. Combined Protein A and size exclusion high performance liquid chromatography for the single-step measurement of mAb, aggregates and host cell proteins.

    PubMed

    Gjoka, Xhorxhi; Schofield, Mark; Cvetkovic, Aleksandar; Gantier, Rene

    2014-12-01

    Quantification of monoclonal antibody (mAb) monomer, mAb aggregates, and host cell proteins (HCPs) is critical for the optimization of the mAb production process. The present work describes a single high throughput analytical tool capable of tracking the concentration of mAb, mAb aggregate and HCPs in a growing cell culture batch. By combining two analytical HPLC methods, Protein A affinity and size-exclusion chromatography (SEC), it is possible to detect a relative increase or decrease in the concentration of all three entities simultaneously. A comparison of the combined Protein A-SEC assay to SEC alone was performed, demonstrating that it can be useful tool for the quantification of mAb monomer along with trending data for mAb aggregate and HCP. Furthermore, the study shows that the Protein A-SEC method is at least as accurate as other commonly used analytical methods such as ELISA and Bradford.

  6. Classification and Characterization of Therapeutic Antibody Aggregates

    PubMed Central

    Joubert, Marisa K.; Luo, Quanzhou; Nashed-Samuel, Yasser; Wypych, Jette; Narhi, Linda O.

    2011-01-01

    A host of diverse stress techniques was applied to a monoclonal antibody (IgG2) to yield protein particles with varying attributes and morphologies. Aggregated solutions were evaluated for percent aggregation, particle counts, size distribution, morphology, changes in secondary and tertiary structure, surface hydrophobicity, metal content, and reversibility. Chemical modifications were also identified in a separate report (Luo, Q., Joubert, M. K., Stevenson, R., Narhi, L. O., and Wypych, J. (2011) J. Biol. Chem. 286, 25134–25144). Aggregates were categorized into seven discrete classes, based on the traits described. Several additional molecules (from the IgG1 and IgG2 subtypes as well as intravenous IgG) were stressed and found to be defined with the same classification system. The mechanism of protein aggregation and the type of aggregate formed depends on the nature of the stress applied. Different IgG molecules appear to aggregate by a similar mechanism under the same applied stress. Aggregates created by harsh mechanical stress showed the largest number of subvisible particles, and the class generated by thermal stress displayed the largest number of visible particles. Most classes showed a disruption of the higher order structure, with the degree of disorder depending on the stress process. Particles in all classes (except thermal stress) were at least partially reversible upon dilution in pH 5 buffer. High copper content was detected in isolated metal-catalyzed aggregates, a stress previously shown to produce immunogenic aggregates. In conclusion, protein aggregates can be a very heterogeneous population, whose qualities are the result of the type of stress that was experienced. PMID:21454532

  7. Class size as related to the use of technology, educational practices, and outcomes in Web-based nursing courses.

    PubMed

    Burruss, Nancy M; Billings, Diane M; Brownrigg, Vicki; Skiba, Diane J; Connors, Helen R

    2009-01-01

    With the expanding numbers of nursing students enrolled in Web-based courses and the shortage of faculty, class sizes are increasing. This exploratory descriptive study examined class size in relation to the use of technology and to particular educational practices and outcomes. The sample consisted of undergraduate (n = 265) and graduate (n = 863) students enrolled in fully Web-based nursing courses. The Evaluating Educational Uses of Web-based Courses in Nursing survey (Billings, D., Connors, H., Skiba, D. (2001). Benchmarking best practices in Web-based nursing courses. Advances in Nursing Science, 23, 41--52) and the Social Presence Scale (Gunawardena, C. N., Zittle, F. J. (1997). Social presence as a predictor of satisfaction within a computer-mediated conferencing environment. The American Journal of Distance Education, 11, 9-26.) were used to gather data about the study variables. Class sizes were defined as very small (1 to 10 students), small (11 to 20 students), medium (21 to 30 students), large (31 to 40 students), and very large (41 students and above). Descriptive and inferential statistics were used to analyze the data. There were significant differences by class size in students' perceptions of active participation in learning, student-faculty interaction, peer interaction, and connectedness. Some differences by class size between undergraduate and graduate students were also found, and these require further study.

  8. Relationship between different size classes of particulate matter and meteorology in three European cities.

    PubMed

    de Hartog, Jeroen J; Hoek, Gerard; Mirme, Aadu; Tuch, Thomas; Kos, Gerard P A; ten Brink, Harry M; Brunekreef, Bert; Cyrys, Josef; Heinrich, Joachim; Pitz, Mike; Lanki, Timo; Vallius, Marko; Pekkanen, Juha; Kreyling, Wolfgang G

    2005-04-01

    Evidence on the correlation between particle mass and (ultrafine) particle number concentrations is limited. Winter- and spring-time measurements of urban background air pollution were performed in Amsterdam (The Netherlands), Erfurt (Germany) and Helsinki (Finland), within the framework of the EU funded ULTRA study. Daily average concentrations of ambient particulate matter with a 50% cut off of 2.5 microm (PM2.5), total particle number concentrations and particle number concentrations in different size classes were collected at fixed monitoring sites. The aim of this paper is to assess differences in particle concentrations in several size classes across cities, the correlation between different particle fractions and to assess the differential impact of meteorological factors on their concentrations. The medians of ultrafine particle number concentrations were similar across the three cities (range 15.1 x 10(3)-18.3 x 10(3) counts cm(-3)). Within the ultrafine particle fraction, the sub fraction (10-30 nm) made a higher contribution to particle number concentrations in Erfurt than in Helsinki and Amsterdam. Larger differences across the cities were found for PM2.5(range 11-17 microg m(-3)). PM2.5 and ultrafine particle concentrations were weakly (Amsterdam, Helsinki) to moderately (Erfurt) correlated. The inconsistent correlation for PM2.5 and ultrafine particle concentrations between the three cities was partly explained by the larger impact of more local sources from the city on ultrafine particle concentrations than on PM2.5, suggesting that the upwind or downwind location of the measuring site in regard to potential particle sources has to be considered. Also, relationship with wind direction and meteorological data differed, suggesting that particle number and particle mass are two separate indicators of airborne particulate matter. Both decreased with increasing wind speed, but ultrafine particle number counts consistently decreased with increasing

  9. 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

  10. Meteorological influences on stemflow generation across diameter size classes of two morphologically distinct deciduous species.

    PubMed

    Van Stan, John T; Van Stan, Jarrad H; Levia, Delphis F

    2014-12-01

    Many tree species have been shown to funnel substantial rainfall to their stem base as stemflow flux, given a favorable stand structure and storm conditions. As stemflow is a spatially concentrated flux, prior studies have shown its impact on ecohydrological and biogeochemical processes can be significant. Less work has been performed examining stemflow variability from meteorological conditions compared to canopy structural traits. As such, this study performs multiple regressions: (1) to examine stemflow variability due to event-based rainfall amount, intensity, mean wind speeds, and vapor pressure deficit; (2) across three diameter size classes (10-20, 21-40, and >41 cm DBH); and (3) for two common tree species in the northeastern USA of contrasting canopy morphology--Liriodendron tulipifera L. (yellow poplar) versus Fagus grandifolia Ehrh. (American beech). On the whole, multiple regression results yielded significant positive correlations with stemflow for rainfall amount, intensity, and mean wind speed and a significant negative correlation for vapor pressure deficit (VPD). Tree size altered stemflow-meteorological condition relationships, where larger trees strengthened indirect stemflow-VPD and direct stemflow-rainfall and stemflow-intensity associations. Canopies of rougher bark and lower branch angle (represented by L. tulipifera) enhanced correlations for nearly all meteorological conditions via greater stemflow residence time (and longer exposure to meteorological conditions). Multiple regressions performed on leafless canopy stemflow resulted in an inverse relationship with wind speeds, likely decoupling stemflow sheltered solely on bark surfaces from VPD influences. Leaf presence generally increased direct stemflow associations with rainfall intensity, yet diminished stemflow-rainfall relationships. F. grandifolia canopies (exemplifying structures of smoother bark and greater branch angle) strengthened differences in stemflow associations with

  11. Meteorological influences on stemflow generation across diameter size classes of two morphologically distinct deciduous species

    NASA Astrophysics Data System (ADS)

    Van Stan, John T.; Van Stan, Jarrad H.; Levia, Delphis F.

    2014-12-01

    Many tree species have been shown to funnel substantial rainfall to their stem base as stemflow flux, given a favorable stand structure and storm conditions. As stemflow is a spatially concentrated flux, prior studies have shown its impact on ecohydrological and biogeochemical processes can be significant. Less work has been performed examining stemflow variability from meteorological conditions compared to canopy structural traits. As such, this study performs multiple regressions: (1) to examine stemflow variability due to event-based rainfall amount, intensity, mean wind speeds, and vapor pressure deficit; (2) across three diameter size classes (10-20, 21-40, and >41 cm DBH); and (3) for two common tree species in the northeastern USA of contrasting canopy morphology— Liriodendron tulipifera L. (yellow poplar) versus Fagus grandifolia Ehrh. (American beech). On the whole, multiple regression results yielded significant positive correlations with stemflow for rainfall amount, intensity, and mean wind speed and a significant negative correlation for vapor pressure deficit (VPD). Tree size altered stemflow-meteorological condition relationships, where larger trees strengthened indirect stemflow-VPD and direct stemflow-rainfall and stemflow-intensity associations. Canopies of rougher bark and lower branch angle (represented by L. tulipifera) enhanced correlations for nearly all meteorological conditions via greater stemflow residence time (and longer exposure to meteorological conditions). Multiple regressions performed on leafless canopy stemflow resulted in an inverse relationship with wind speeds, likely decoupling stemflow sheltered solely on bark surfaces from VPD influences. Leaf presence generally increased direct stemflow associations with rainfall intensity, yet diminished stemflow-rainfall relationships. F. grandifolia canopies (exemplifying structures of smoother bark and greater branch angle) strengthened differences in stemflow associations with

  12. Capitalizando en los cursos pequenos (Capitalizing on Small Class Size). ERIC Digest.

    ERIC Educational Resources Information Center

    O'Connell, Jessica; Smith, Stuart C.

    This digest in Spanish examines school districts' efforts to reap the greatest benefit from smaller classes. Although the report discusses teaching strategies that are most effective in small classes, research has shown that teachers do not significantly change their teaching practices when they move from larger to smaller classes. Although…

  13. Improved particle counting and size distribution determination of aggregated virus populations by asymmetric flow field-flow fractionation and multiangle light scattering techniques.

    PubMed

    McEvoy, Matt; Razinkov, Vladimir; Wei, Ziping; Casas-Finet, Jose R; Tous, Guillermo I; Schenerman, Mark A

    2011-01-01

    A method using a combination of asymmetric flow field-flow fractionation (AFFFF) and multiangle light scattering (MALS) techniques has been shown to improve the estimation of virus particle counts and the amount of aggregated virus in laboratory samples. The method is based on the spherical particle counting approach given by Wyatt and Weida in 2004, with additional modifications. The new method was tested by analyzing polystyrene beads and adenovirus samples, both having a well-characterized particle size and concentration. Influenza virus samples were analyzed by the new AFFFF-MALS technique, and particle size and aggregate state were compared with results from atomic force microscopy analysis. The limitations and source of possible errors for the new AFFFF-MALS analysis are discussed.

  14. Temperature-dependent toxicities of nano zinc oxide to marine diatom, amphipod and fish in relation to its aggregation size and ion dissolution.

    PubMed

    Wong, Stella W Y; Leung, Kenneth M Y

    2014-08-01

    This study, for the first time, concurrently investigated the influence of seawater temperature, exposure concentration and time on the aggregation size and ion dissolution of nano zinc oxides (nZnO) in seawater, and the interacting effect of temperature and waterborne exposure of nZnO to the marine diatom Skeletonema costatum, amphipod Melita longidactyla and fish Oryzias melastigma, respectively. Our results showed that aggregate size was jointly affected by seawater temperature, nZnO concentration and exposure time. Among the three factors, the concentration of nZnO was the most important and followed by exposure time, whereas temperature was less important as reflected by their F values in the three-way analysis of variance (concentration: F3, 300 = 247.305; time: F2, 300 = 20.923 and temperature: F4, 300 = 4.107; All p values <0.001). The aggregate size generally increased with increasing nZnO concentration and exposure time. The release of Zn ions from nZnO was significantly influenced by seawater temperature and exposure time; the ion dissolution rate generally increased with decreasing temperature and increasing exposure time. Growth inhibition of diatoms increased with increasing temperature, while temperature and nZnO had an interactional effect on their photosynthesis. For the amphipod, mortality was positively correlated with temperature. Fish larvae growth rate was only affected by temperature but not nZnO, while the two factors interactively modulated the expression of heat shock and metallothionein proteins. Evidently, temperature can influence aggregate size and ion dissolution and thus toxicity of nZnO to the marine organisms in a species-specific manner. PMID:24219175

  15. 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.

  16. An atypical IgM class platelet cold agglutinin induces GPVI-dependent aggregation of human platelets.

    PubMed

    Sánchez Guiu, I M; Martínez-Martinez, I; Martínez, C; Navarro-Fernandez, J; García-Candel, F; Ferrer-Marín, F; Vicente, V; Watson, S P; Andrews, R K; Gardiner, E E; Lozano, M L; Rivera, J

    2015-08-01

    Platelet cold agglutinins (PCA) cause pseudothrombocytopenia, spurious thrombocytopenia due to ex vivo platelet clumping, complicating clinical diagnosis, but mechanisms and consequences of PCA are not well defined. Here, we characterised an atypical immunoglobulin (Ig)M PCA in a 37-year-old woman with lifelong bleeding and chronic moderate thrombocytopenia, that induces activation and aggregation of autologous or allogeneic platelets via interaction with platelet glycoprotein (GP)VI. Patient temperature-dependent pseudothrombocytopenia was EDTA-independent, but was prevented by integrin αIIbβ3 blockade. Unstimulated patient platelets revealed elevated levels of bound IgM, increased expression of activation markers (P-selectin and CD63), low GPVI levels and abnormally high thromboxane (TX)A2 production. Patient serum induced temperature- and αIIbβ3-dependent decrease of platelet count in allogeneic donor citrated platelet-rich plasma (PRP), but not in PRP from Glanzmann's thrombasthenia or afibrinogenaemia patients. In allogeneic platelets, patient plasma induced shape change, P-selectin and CD63 expression, (14)C-serotonin release, and TXA2 production. Activation was not inhibited by aspirin, cangrelor or blocking anti-Fc receptor (FcγRIIA) antibody, but was abrogated by inhibitors of Src and Syk, and by a soluble GPVI-Fc fusion protein. GPVI-deficient platelets were not activated by patient plasma. These data provide the first evidence for an IgM PCA causing platelet activation/aggregation via GPVI. The PCA activity persisted over a five-year follow-up period, supporting a causative role in patient chronic thrombocytopenia and bleeding. PMID:25994029

  17. An atypical IgM class platelet cold agglutinin induces GPVI-dependent aggregation of human platelets.

    PubMed

    Sánchez Guiu, I M; Martínez-Martinez, I; Martínez, C; Navarro-Fernandez, J; García-Candel, F; Ferrer-Marín, F; Vicente, V; Watson, S P; Andrews, R K; Gardiner, E E; Lozano, M L; Rivera, J

    2015-08-01

    Platelet cold agglutinins (PCA) cause pseudothrombocytopenia, spurious thrombocytopenia due to ex vivo platelet clumping, complicating clinical diagnosis, but mechanisms and consequences of PCA are not well defined. Here, we characterised an atypical immunoglobulin (Ig)M PCA in a 37-year-old woman with lifelong bleeding and chronic moderate thrombocytopenia, that induces activation and aggregation of autologous or allogeneic platelets via interaction with platelet glycoprotein (GP)VI. Patient temperature-dependent pseudothrombocytopenia was EDTA-independent, but was prevented by integrin αIIbβ3 blockade. Unstimulated patient platelets revealed elevated levels of bound IgM, increased expression of activation markers (P-selectin and CD63), low GPVI levels and abnormally high thromboxane (TX)A2 production. Patient serum induced temperature- and αIIbβ3-dependent decrease of platelet count in allogeneic donor citrated platelet-rich plasma (PRP), but not in PRP from Glanzmann's thrombasthenia or afibrinogenaemia patients. In allogeneic platelets, patient plasma induced shape change, P-selectin and CD63 expression, (14)C-serotonin release, and TXA2 production. Activation was not inhibited by aspirin, cangrelor or blocking anti-Fc receptor (FcγRIIA) antibody, but was abrogated by inhibitors of Src and Syk, and by a soluble GPVI-Fc fusion protein. GPVI-deficient platelets were not activated by patient plasma. These data provide the first evidence for an IgM PCA causing platelet activation/aggregation via GPVI. The PCA activity persisted over a five-year follow-up period, supporting a causative role in patient chronic thrombocytopenia and bleeding.

  18. Effects of particle size distribution, shape and volume fraction of aggregates on the wall effect of concrete via random sequential packing of polydispersed ellipsoidal particles

    NASA Astrophysics Data System (ADS)

    Xu, W. X.; Lv, Z.; Chen, H. S.

    2013-02-01

    Concrete can be viewed as granular materials at the mesoscopic level. A specific distribution of aggregate particles in boundary layers, known as the wall effect, plays an important role in the mechanical properties and durability of concrete. However, the detailed and systematic experimental and simulated data about the wall effect of concrete is hardly adequate yet. Specially, the modeling study of spherical and two-dimensional (2D) elliptical aggregates distribution for the wall effect has been focused on in previous work, little is known about three-dimensional (3D) ellipsoidal aggregates. In the present work, based on a mesostructure model of concrete, the wall effect of concrete is quantified by configuration parameters such as the volume fraction, the specific surface area and the meaning free spacing of the solid phase. In addition, the influences of ellipsoidal particle size distribution (EPSD), shape and volume fraction (Vf) of ellipsoidal aggregates on the configuration parameters are evaluated by stereological methods and serial section analysis technique. Furthermore, the effect mechanisms of EPSD, shape and Vf are analyzed and discussed in this paper. The reliability of the statistical results is verified by experimental data and theoretical analytical results.

  19. Sequence relationships between adenovirus 2 early RNA and viral RNA size classes synthesized at 18 hours after infection.

    PubMed Central

    Tal, J; Craig, E A; Raskas, H J

    1975-01-01

    Synthesis of cytoplasmic viral RNA was studied during infection of cultured human (KB) cells with adenovirus 2. At 6 h, before viral DNA synthesis began 5% of the poly(A)-containing RNA hybridized to viral DNA; by 12 h and at later times more than 80% was virus specified. At 18 h after infection, four major size classes of cytoplasmic viral RNA were identified among the poly(A)-containing molecules. These size classes migrated as 27S, 24S, 19S, and 12 to 15S in polyacrylamide gels. The three larger size classes could also be identified in denaturing formamide gels. Hybridization of the 27S, 24S, and 19S viral RNAs was not inhibited by RNA harvested from cells at early times in infection. Therefore, these three major RNAs must code for late viral proteins. Hybridization of the 12 to 15S RNA was partially inhibited by RNA from cultures harvested at early times, suggesting that in this size class some of the RNA labeled at 18 h codes for early viral proteins. PMID:1113370

  20. Student/Teacher Achievement Ratio (STAR) Tennessee's K-3 Class Size Study. Final Summary Report 1985-1990.

    ERIC Educational Resources Information Center

    Word, Elizabeth; And Others

    This document provides the final summary report of Tennessee's primary school class size study, called Project STAR. Sections of the report concern: (1) background; (2) organization to conduct the study; (3) sample selection; (4) data collection plan and data base; (5) general operating guidelines; (6) teacher orientation; (7) study design; (8)…

  1. Principals as Middle Managers: School Leadership during the Implementation of Primary Class Size Reduction Policy in Ontario

    ERIC Educational Resources Information Center

    Flessa, Joseph J.

    2012-01-01

    Previous work on policy implementation has often suggested that schools leave their "thumbprints" on policies received from above. During the implementation of Primary Class Size Reduction (PCS) Initiative in Ontario, Canada, however, school principals spoke with remarkable uniformity about the ways PCS affected their work. This article reports…

  2. The Impact of California's Class Size Reduction Initiative on Student Achievement: Detailed Findings from Eight School Districts.

    ERIC Educational Resources Information Center

    Mitchell, Douglas E.; Mitchell, Ross E.

    This report presents a comprehensive preliminary analysis of how California's Class Size Reduction (CSR) initiative has impacted student achievement during the first 2 years of implementation. The analysis is based on complete student, classroom, and teacher records from 26,126 students in 1,174 classrooms from 83 schools in 8 Southern California…

  3. 40 CFR 113.4 - Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. 113.4 Section 113.4... SMALL ONSHORE STORAGE FACILITIES Oil Storage Facilities § 113.4 Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. Unless the United...

  4. 40 CFR 113.4 - Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. 113.4 Section 113.4... SMALL ONSHORE STORAGE FACILITIES Oil Storage Facilities § 113.4 Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. Unless the United...

  5. 40 CFR 113.4 - Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. 113.4 Section 113.4... SMALL ONSHORE STORAGE FACILITIES Oil Storage Facilities § 113.4 Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. Unless the United...

  6. 40 CFR 113.4 - Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. 113.4 Section 113.4... SMALL ONSHORE STORAGE FACILITIES Oil Storage Facilities § 113.4 Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. Unless the United...

  7. 40 CFR 113.4 - Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. 113.4 Section 113.4... SMALL ONSHORE STORAGE FACILITIES Oil Storage Facilities § 113.4 Size classes and associated liability limits for fixed onshore oil storage facilities, 1,000 barrels or less capacity. Unless the United...

  8. The Perceptions of Student Teachers about the Effects of Class Size with Regard to Effective Teaching Process

    ERIC Educational Resources Information Center

    Cakmak, Melek

    2009-01-01

    The main purpose of this study was to determine student teachers' perceptions concerning the effects of class size with regard to the teaching process. A total of 41 fourth-year student teachers participated in the study. A questionnaire including open-ended items was used for data collection. The study revealed that there is a direct relationship…

  9. The View from the Lighted Schoolhouse: Conceptualizing Home-School Relations within a Class Size Reduction Reform

    ERIC Educational Resources Information Center

    Graue, M. Elizabeth; Sherfinski, Melissa

    2011-01-01

    In this essay we examine how educators work within a component of a class size reduction reform designed to strengthen the connections between families' home and school lives. We describe the accomplishments and struggles experienced by educators enacting this "lighted schoolhouse" based on our research in nine schools over three years.…

  10. You Just Feed Them with a Long-Handled Spoon: Families Evaluate Their Experiences in a Class Size Reduction Reform

    ERIC Educational Resources Information Center

    Graue, M. Elizabeth; Oen, Denise

    2009-01-01

    Emerging from an evaluation of Wisconsin's Student Achievement Guarantee in Education program (SAGE), a multidimensional program popularly known for its class size reduction component, this article examines SAGE's "lighted schoolhouse" initiative aimed to strengthen links between home and school. Drawing on family focus groups held at nine SAGE…

  11. An Evaluation of the Federal Class-Size Reduction Program in Wake County, North Carolina--1999-2000.

    ERIC Educational Resources Information Center

    Scudder, David F.

    An empirical evaluation of the federal class-size reduction (CSR) program in Wake County, North Carolina, during the 1999-2000 school year is presented. The qualitative process evaluation showed implementation issues involving the mechanics and the meaning of CSR. Often, schools did not understand where CSR occurred because of changing enrollment…

  12. The Causal Effect of Class Size on Academic Achievement: Multivariate Instrumental Variable Estimators with Data Missing at Random

    ERIC Educational Resources Information Center

    Shin, Yongyun; Raudenbush, Stephen W.

    2011-01-01

    This article addresses three questions: Does reduced class size cause higher academic achievement in reading, mathematics, listening, and word recognition skills? If it does, how large are these effects? Does the magnitude of such effects vary significantly across schools? The authors analyze data from Tennessee's Student/Teacher Achievement Ratio…

  13. The Political and Institutional Origins of a Randomized Controlled Trial on Elementary School Class Size: Tennessee's Project STAR.

    ERIC Educational Resources Information Center

    Ritter, Gary W.; Boruch, Robert F.

    1999-01-01

    Examines the origins of Tennessee's Project Student/Teacher Achievement Ratio (STAR) and explores what it was about Tennessee in the mid-1980s that fostered the development of this experimental approach to class size. Highlights the connection between the research world and the political world that resulted in the STAR project. (SLD)

  14. District Resource Capacity and the Effects of Educational Policy: The Case of Primary Class Size Reduction in Ontario

    ERIC Educational Resources Information Center

    Mascall, Blair; Leung, Joannie

    2012-01-01

    In a study of Ontario, Canada's province-wide Primary Class Size Reduction (PCS) Initiative, school districts' ability to direct and support schools was related to their experience with planning and monitoring, interest in innovation, and its human and fiscal resource base. Districts with greater "resource capacity" were able to coordinate local…

  15. The Cumulative Effects of Indiana PRIME TIME: A State Sponsored Reduced Class Size Program, on Basic Skills Achievement.

    ERIC Educational Resources Information Center

    Malloy, Leanne; Gilman, David

    The purpose of this paper was to analyze the initial results of statewide implementation of the PRIME TIME program in Indiana. PRIME TIME is a state-wide program to reduce class size in the primary grades. Mean scores from 65,911 third graders who had completed the Indiana Competency Test in the spring of 1987 after completing 3 years of the…

  16. Perception of Business Studies Teachers on the Infuence of Large Class Size in Public Secondary Schools in Yobe State, Nigeria

    ERIC Educational Resources Information Center

    Mamman, Jummai; Chadi, Aishatu Mohammad; Jirgi, Ibrahim

    2015-01-01

    This is a survey study conducted to determine the perception of business studies teacher's on the influence of large class size in Yobe state public secondary school. Three research questions were raised to guide the study. The population comprised of one hundred and twenty (120) business studies teachers from one hundred and five (105) Secondary…

  17. Scaling Up: Faculty Workload, Class Size, and Student Satisfaction in a Distance Learning Course on Geographic Information Science.

    ERIC Educational Resources Information Center

    Dibiase, David; Rademacher, Henry J.

    2005-01-01

    This article explores issues of scalability and sustainability in distance learning. The authors kept detailed records of time they spent teaching a course in geographic information science via the World Wide Web over a six-month period, during which class sizes averaged 49 students. The authors also surveyed students' satisfaction with the…

  18. Method for relating suspended-chemical concentrations to suspended-sediment particle-size classes in storm-water runoff

    USGS Publications Warehouse

    Rinella, Joseph F.; McKenzie, Stuart W.

    1982-01-01

    A method has been developed to relate suspended-chemical concentrations (associated with suspended sediments) in storm-water runoff to suspended-sediment particle-size classes. These classes are based on settling velocities in quiescent native water. This method requires processing 20 liters of water having a suspended-sediment concentration greater than 500 milligrams per liter. However, samples with suspended-sediment concentrations as low as 250 milligrams per liter may be analyzed, if sample volumes are increased to 50 liters. The time required for one person to separate suspended sediments into particle-size classes ranges from 6 to 14 hours. This report outlines procedures for processing metal, nutrient, and organic samples.

  19. Comparative analysis of the particle size and shape of commercially available mineral trioxide aggregates and Portland cement: a study with a flow particle image analyzer.

    PubMed

    Komabayashi, Takashi; Spångberg, Larz S W

    2008-01-01

    The aim of this study is to characterize the particle size distribution and circularity of various Mineral Trioxide Aggregates (MTA) (ProRoot MTA/ MTA Angelus/Gray and White) and Portland cements with effective size ranges of 1.5-160 microm using a flow particle analyzer (Sysmex FPIA-3000, Kobe, Japan). Cumulative percentage of particles between 6 and 10 microm were, 65, 73, 48, 53, and 70 %, for Gray ProRoot MTA, White ProRoot MTA, Gray MTA Angelus, White MTA Angelus, and Portland cement, respectively. ProRoot MTA contains fewer large particles than MTA Angelus. MTA Angelus contains a higher number of small particles than ProRoot MTA. White MTA contains smaller particles with a narrower range of size distribution than Gray MTA. MTA Angelus particles have relatively low circularity and wide size distribution and are less homogeneous than ProRoot MTA.

  20. Laser Particle Diffraction: A Novel Approach to Quantify In-Situ Suspended Sediment Particle Size Class Concentrations

    NASA Astrophysics Data System (ADS)

    Freeman, G. W.; Hubbart, J. A.; Chinnasamy, P.; Bulliner, E. A.; Schulz, J.

    2010-12-01

    Hydrologic modification exacted by development can variably increase or decreases diffuse pollution loads, and sediment particle class concentrations. For example, larger particle classes may originate primarily from agricultural and localized riparian development or in-stream hydrogeomorphological processes, while smaller particle size class concentrations may increase in urban environments. These distinctions are critical since fine sediments can transport greater quantities of adsorbed chemicals, nutrients and pollutants, fill interstitial spaces of gravel in spawning beds, and detrimentally affect aquatic biota (e.g. invertebrates and fish). Laser Diffraction (LD) instruments measure optical scattering with specially constructed detectors to detect light diffraction effects of particles of individual size classes. The Streamside Laser In-Situ Scattering and Transmissometry (LISST, Sequoia Scientific, Inc) LD instrument was designed for monitoring suspended sediment in shallow rivers, streams, and ponds sensing particle sizes ranging from 1.9 to 387 um (accuracy ± 10 to 20%). Multiple on-going studies in central Missouri, USA are utilizing LD instruments to better understand anthropogenic diffuse sediment pollution. Three LD units were deployed in a central Missouri stream during spring 2010. In an Urban environment, after a single precipitation event the largest particle class bin (356.79 um) comprised almost 50% of the total concentration of suspended sediments in pre-event flow conditions, whereas in the post-precipitation flow event conditions it comprised nearly 44%, a 12.5% difference. The smallest particle class (2.06 um) concentrations in pre and post-precipitation event conditions was 0.8 and 3.4% respectively reflecting more than 450% increased concentration in post flow conditions after a 13.2 mm (0.52 in) precipitation event. During the month of March 2010 average total concentration of sediment (μl/l) in forested, agricultural, and urban

  1. Effect of water deficit and domestic storage on the procyanidin profile, size, and aggregation process in pear-jujube (Z. jujuba) fruits.

    PubMed

    Collado-González, J; Cruz, Z N; Rodríguez, P; Galindo, A; Díaz-Baños, F G; García de la Torre, J; Ferreres, F; Medina, S; Torrecillas, A; Gil-Izquierdo, A

    2013-07-01

    No information exists on the proanthocyanidin content of pear-jujube (Ziziphus jujuba Mill) fruit, their polymeric types and sizes, and their self-aggregation, or on the effect of different water deficit levels during the fruit maturation period on these compounds. Two trimers, two tetramers, and six B type procyanidin pentamers were identified and quantified for the first time. Water deficit increased the content of procyanidins of low molecular mass, improving their potential bioavailability and possible physiological effects on human health. The tendency of procyanidins to self-aggregate was similar in the edible portion and pit, and was not affected by water deficit. The procyanidin content of fruit from well watered trees increased during domestic cold storage, whereas the fruits from trees suffering severe water stress lost some of their procyanidin content. PMID:23750994

  2. Effect of water deficit and domestic storage on the procyanidin profile, size, and aggregation process in pear-jujube (Z. jujuba) fruits.

    PubMed

    Collado-González, J; Cruz, Z N; Rodríguez, P; Galindo, A; Díaz-Baños, F G; García de la Torre, J; Ferreres, F; Medina, S; Torrecillas, A; Gil-Izquierdo, A

    2013-07-01

    No information exists on the proanthocyanidin content of pear-jujube (Ziziphus jujuba Mill) fruit, their polymeric types and sizes, and their self-aggregation, or on the effect of different water deficit levels during the fruit maturation period on these compounds. Two trimers, two tetramers, and six B type procyanidin pentamers were identified and quantified for the first time. Water deficit increased the content of procyanidins of low molecular mass, improving their potential bioavailability and possible physiological effects on human health. The tendency of procyanidins to self-aggregate was similar in the edible portion and pit, and was not affected by water deficit. The procyanidin content of fruit from well watered trees increased during domestic cold storage, whereas the fruits from trees suffering severe water stress lost some of their procyanidin content.

  3. Construction aggregates

    USGS Publications Warehouse

    Nelson, T.I.; Bolen, W.P.

    2007-01-01

    Construction aggregates, primarily stone, sand and gravel, are recovered from widespread naturally occurring mineral deposits and processed for use primarily in the construction industry. They are mined, crushed, sorted by size and sold loose or combined with portland cement or asphaltic cement to make concrete products to build roads, houses, buildings, and other structures. Much smaller quantities are used in agriculture, cement manufacture, chemical and metallurgical processes, glass production and many other products.

  4. Cryopreservation of embryonic stem cell-derived multicellular neural aggregates labeled with micron-sized particles of iron oxide for magnetic resonance imaging.

    PubMed

    Yan, Yuanwei; Sart, Sébastien; Calixto Bejarano, Fabian; Muroski, Megan E; Strouse, Geoffrey F; Grant, Samuel C; Li, Yan

    2015-01-01

    Magnetic resonance imaging (MRI) provides an effective approach to track labeled pluripotent stem cell (PSC)-derived neural progenitor cells (NPCs) for neurological disorder treatments after cell labeling with a contrast agent, such as an iron oxide derivative. Cryopreservation of pre-labeled neural cells, especially in three-dimensional (3D) structure, can provide a uniform cell population and preserve the stem cell niche for the subsequent applications. In this study, the effects of cryopreservation on PSC-derived multicellular NPC aggregates labeled with micron-sized particles of iron oxide (MPIO) were investigated. These NPC aggregates were labeled prior to cryopreservation because labeling thawed cells can be limited by inefficient intracellular uptake, variations in labeling efficiency, and increased culture time before use, minimizing their translation to clinical settings. The results indicated that intracellular MPIO incorporation was retained after cryopreservation (70-80% labeling efficiency), and MPIO labeling had little adverse effects on cell recovery, proliferation, cytotoxicity and neural lineage commitment post-cryopreservation. MRI analysis showed comparable detectability for the MPIO-labeled cells before and after cryopreservation indicated by T2 and T2* relaxation rates. Cryopreserving MPIO-labeled 3D multicellular NPC aggregates can be applied in in vivo cell tracking studies and lead to more rapid translation from preservation to clinical implementation. PMID:25905549

  5. Stable and Size-Tunable Aggregation-Induced Emission Nanoparticles Encapsulated with Nanographene Oxide and Applications in Three-Photon Fluorescence Bioimaging.

    PubMed

    Zhu, Zhenfeng; Qian, Jun; Zhao, Xinyuan; Qin, Wei; Hu, Rongrong; Zhang, Hequn; Li, Dongyu; Xu, Zhengping; Tang, Ben Zhong; He, Sailing

    2016-01-26

    Organic fluorescent dyes with high quantum yield are widely applied in bioimaging and biosensing. However, most of them suffer from a severe effect called aggregation-caused quenching (ACQ), which means that their fluorescence is quenched at high molecular concentrations or in the aggregation state. Aggregation-induced emission (AIE) is a diametrically opposite phenomenon to ACQ, and luminogens with this feature can effectively solve this problem. Graphene oxide has been utilized as a quencher for many fluorescent dyes, based on which biosensing can be achieved. However, using graphene oxide as a surface modification agent of fluorescent nanoparticles is seldom reported. In this article, we used nanographene oxide (NGO) to encapsulate fluorescent nanoparticles, which consisted of a type of AIE dye named TPE-TPA-FN (TTF). NGO significantly improved the stability of nanoparticles in aqueous dispersion. In addition, this method could control the size of nanoparticles' flexibly as well as increase their emission efficiency. We then used the NGO-modified TTF nanoparticles to achieve three-photon fluorescence bioimaging. The architecture of ear blood vessels in mice and the distribution of nanoparticles in zebrafish could be observed clearly. Furthermore, we extended this method to other AIE luminogens and showed it was widely feasible.

  6. A Program for Partitioning Shifted Truncated Lognormal Distributions into Size-Class Bins

    USGS Publications Warehouse

    Attanasi, E.D.; Charpentier, Ronald R.

    2007-01-01

    In recent years, oil and gas accumulation-size frequency distributions have become a standard way to characterize undiscovered conventional oil and gas resources that have been postulated by geologic assessments. The preparation of such distributions requires the assessment geologists to explicitly choose parameters for the probability distribution for the sizes of undiscovered accumulations. The purpose of this report is to present a computational scheme for obtaining a binned size frequency distribution of undiscovered accumulations when the undiscovered accumulation size distribution is shifted truncated lognormal.

  7. Biodegradation of petroleum hydrocarbons in contaminated clayey soils from a sub-arctic site: the role of aggregate size and microstructure.

    PubMed

    Chang, Wonjae; Akbari, Ali; Snelgrove, Jessica; Frigon, Dominic; Ghoshal, Subhasis

    2013-06-01

    This study investigates the extent of biodegradation of non-volatile petroleum hydrocarbons (C16-C34) and the associated microbial activity in predominant aggregate sizes during a pilot-scale biopile experiment conducted at 15 °C, with a clayey soil, from a crude oil-impacted site in northern Canada. The in situ aggregate microstructure was characterized by N2 adsorption and X-ray CT scanning. The soils in the nutrient (N)-amended and unamended biopile tanks were comprised of macroaggregates (>2 mm) and mesoaggregates (0.25-2 mm). Nutrient addition significantly enhanced petroleum hydrocarbon biodegradation in macroaggregates, but not in mesoaggregates. At the end of 65-d biopile experiment, 42% of the C16-C34 hydrocarbons were degraded in the nutrient-amended macroaggregates, compared to 13% in the mesoaggregates. Higher microbial activity in the macroaggregates of the nutrient amended biopile was inferred from a larger increase in extractable protein concentrations, compared to the other aggregates. Terminal Restriction Fragment Length Polymorphism (T-RFLP) of 16S rRNA genes showed that there was no selection of bacterial populations in any of the aggregates during biopile treatment, suggesting that the enhanced biodegradation in nutrient-amended macroaggregates was likely due to metabolic stimulation. X-ray micro CT scanning revealed that the number of pores wider than 4 μm, which would be easily accessible by bacteria, were an order of magnitude higher in macroaggregates. Also, N2 adsorption analyses showed that pore surface areas and pore volumes per unit weight were four to five-times larger, compared to the mesoaggregates. Thus the higher porosity microstructure in macroaggregates allowed greater hydrocarbon degradation upon biostimulation by nutrient addition and aeration.

  8. Development and testing of a genetic marker-based pedigree reconstruction system 'PR-genie' incorporating size-class data.

    PubMed

    Cope, Robert C; Lanyon, Janet M; Seddon, Jennifer M; Pollett, Philip K

    2014-07-01

    For wildlife populations, it is often difficult to determine biological parameters that indicate breeding patterns and population mixing, but knowledge of these parameters is essential for effective management. A pedigree encodes the relationship between individuals and can provide insight into the dynamics of a population over its recent history. Here, we present a method for the reconstruction of pedigrees for wild populations of animals that live long enough to breed multiple times over their lifetime and that have complex or unknown generational structures. Reconstruction was based on microsatellite genotype data along with ancillary biological information: sex and observed body size class as an indicator of relative age of individuals within the population. Using body size-class data to infer relative age has not been considered previously in wildlife genealogy and provides a marked improvement in accuracy of pedigree reconstruction. Body size-class data are particularly useful for wild populations because it is much easier to collect noninvasively than absolute age data. This new pedigree reconstruction system, PR-genie, performs reconstruction using maximum likelihood with optimization driven by the cross-entropy method. We demonstrated pedigree reconstruction performance on simulated populations (comparing reconstructed pedigrees to known true pedigrees) over a wide range of population parameters and under assortative and intergenerational mating schema. Reconstruction accuracy increased with the presence of size-class data and as the amount and quality of genetic data increased. We provide recommendations as to the amount and quality of data necessary to provide insight into detailed familial relationships in a wildlife population using this pedigree reconstruction technique. PMID:24373173

  9. Development and testing of a genetic marker-based pedigree reconstruction system 'PR-genie' incorporating size-class data.

    PubMed

    Cope, Robert C; Lanyon, Janet M; Seddon, Jennifer M; Pollett, Philip K

    2014-07-01

    For wildlife populations, it is often difficult to determine biological parameters that indicate breeding patterns and population mixing, but knowledge of these parameters is essential for effective management. A pedigree encodes the relationship between individuals and can provide insight into the dynamics of a population over its recent history. Here, we present a method for the reconstruction of pedigrees for wild populations of animals that live long enough to breed multiple times over their lifetime and that have complex or unknown generational structures. Reconstruction was based on microsatellite genotype data along with ancillary biological information: sex and observed body size class as an indicator of relative age of individuals within the population. Using body size-class data to infer relative age has not been considered previously in wildlife genealogy and provides a marked improvement in accuracy of pedigree reconstruction. Body size-class data are particularly useful for wild populations because it is much easier to collect noninvasively than absolute age data. This new pedigree reconstruction system, PR-genie, performs reconstruction using maximum likelihood with optimization driven by the cross-entropy method. We demonstrated pedigree reconstruction performance on simulated populations (comparing reconstructed pedigrees to known true pedigrees) over a wide range of population parameters and under assortative and intergenerational mating schema. Reconstruction accuracy increased with the presence of size-class data and as the amount and quality of genetic data increased. We provide recommendations as to the amount and quality of data necessary to provide insight into detailed familial relationships in a wildlife population using this pedigree reconstruction technique.

  10. Class-Size Reduction: Policy, Politics, and Implications for Equity. Equity Matters. Research Review No. 2

    ERIC Educational Resources Information Center

    Ready, Douglas D.

    2008-01-01

    Over the past several decades, researchers, politicians, and corporate leaders have focused reform efforts on the size of educational contexts. Hundreds of billions of public and private dollars have been invested to reduce the size and scope of both classrooms and schools (Lee & Ready, 2007). Unlike many education reforms, these downsizing plans…

  11. Leveraging Innovation in Science Education: Using Writing and Assessment to Decode the Class Size Conundrum

    ERIC Educational Resources Information Center

    Camfield, Eileen Kogl; McFall, Eileen Eckert; Land, Kirkwood M.

    2016-01-01

    Introductory biology courses are supposed to serve as gateways for many majors, but too often they serve instead as gatekeepers. Reliance on lectures, large classes, and multiple-choice tests results in high drop and failure rates. Critiques of undergraduate science education are clear about the problems with conventional introductory science…

  12. THE PHYSICS OF PROTOPLANETESIMAL DUST AGGLOMERATES. VI. EROSION OF LARGE AGGREGATES AS A SOURCE OF MICROMETER-SIZED PARTICLES

    SciTech Connect

    Schraepler, Rainer; Blum, Juergen

    2011-06-20

    Observed protoplanetary disks consist of a large amount of micrometer-sized particles. Dullemond and Dominik pointed out for the first time the difficulty in explaining the strong mid-infrared excess of classical T Tauri stars without any dust-retention mechanisms. Because high relative velocities in between micrometer-sized and macroscopic particles exist in protoplanetary disks, we present experimental results on the erosion of macroscopic agglomerates consisting of micrometer-sized spherical particles via the impact of micrometer-sized particles. We find that after an initial phase, in which an impacting particle erodes up to 10 particles of an agglomerate, the impacting particles compress the agglomerate's surface, which partly passivates the agglomerates against erosion. Due to this effect, the erosion halts for impact velocities up to {approx}30 m s{sup -1} within our error bars. For higher velocities, the erosion is reduced by an order of magnitude. This outcome is explained and confirmed by a numerical model. In a next step, we build an analytical disk model and implement the experimentally found erosive effect. The model shows that erosion is a strong source of micrometer-sized particles in a protoplanetary disk. Finally, we use the stationary solution of this model to explain the amount of micrometer-sized particles in the observational infrared data of Furlan et al.

  13. An Analysis of the Effects of Class Size on Student Achievement in Selected Middle Schools in the Sandhills Region of North Carolina

    ERIC Educational Resources Information Center

    Maples, Jeffrey B.

    2009-01-01

    The purpose of this study was to analyze the effects of class size and student achievement in mathematics and reading. The study focused on grades 6 through 8 and used the results of the North Carolina EOG tests in mathematics and reading for the academic year 2006-2007. This study examined the effects of class size and student achievement in…

  14. The Impact of a Universal Class-Size Reduction Policy: Evidence from Florida's Statewide Mandate. Program on Education Policy and Governance Working Papers Series. PEPG 10-03

    ERIC Educational Resources Information Center

    Chingos, Matthew M.

    2010-01-01

    Class-size reduction (CSR) mandates presuppose that resources provided to reduce class size will have a larger impact on student outcomes than resources that districts can spend as they see fit. I estimate the impact of Florida's statewide CSR policy by comparing the deviations from prior achievement trends in districts that were required to…

  15. Some Analyses of Kindergarten Results in a Statewide Study of Class Size: Project ST*R, Tennessee, 1985-86. (Draft).

    ERIC Educational Resources Information Center

    Achilles, C. M.

    Reported are background information and initial analyses of Tennessee's Project STAR, a legislatively authorized study of class size. The aim of the project was to identify causes and effects of differences in elementary school class size. Primary analyses were conducted on kindergarten data for 1985-1986. During that year, 42 school districts and…

  16. Size Determination of Aqueous C60 by Asymmetric Flow Field-Flow Fractionation (AF4) and in-Line Dynamic Light Scattering

    EPA Science Inventory

    To date, studies on the environmental behaviour of aggregated aqueous fullerene nanomaterials have used the entire size distribution of fullerene aggregates and do not distinguish between different aggregate size classes. This is a direct result of the lack of analytical methods ...

  17. Linkage disequilibrium in the insulin gene region: size variation at the 5' flanking polymorphism and bimodality among "class I" alleles.

    PubMed Central

    McGinnis, R. E.; Spielman, R. S.

    1994-01-01

    The 5' flanking polymorphism (5'FP), a hypervariable region at the 5' end of the insulin gene, has "class 1" alleles (650-900 bp long) that are in positive linkage disequilibrium with insulin-dependent diabetes mellitus (IDDM). We report that precise sizing of the 5'FP yields a bimodal frequency distribution of class 1 allele lengths. Class 1 alleles belonging to the lower component (650-750 bp) of the bimodal distribution were somewhat more highly associated with IDDM than were alleles from the upper component (760-900 bp), but the difference was not statistically significant. We also examined 5'FP length variation in relation to allelic variation at nearby polymorphisms. At biallelic RFLPs on both sides of the 5'FP, we found that one allele exhibits near-total association with the upper component of the 5'FP class 1 distribution. Such associations represent a little-known but potentially widespread form of linkage disequilibrium. In this type of disequilibrium, a flanking allele has near-complete association with a single mode of VNTR alleles whose lengths represent consecutive numbers of tandem repeats (CNTR). Such extreme disequilibrium between a CNTR mode and flanking alleles may originate and persist because length mutations at some VNTR loci usually add or delete only one or two repeat units. PMID:7915880

  18. Dynamics of noncovalent interactions in all-α and all-β class proteins: implications for the stability of amyloid aggregates.

    PubMed

    Jain, Alok; Sankararamakrishnan, Ramasubbu

    2011-12-27

    results clearly indicate that the weak C-H···O interactions between the main-chain atoms are the distinguishing factor between the all-α and all-β class of proteins, and these interstrand interactions can provide additional stability to all-β protein structures. Based on these results, we hypothesize that such weak C-H···O interstrand interactions could play a major role in providing stability to amyloid type of aggregates that are responsible for the pathological state of many proteins.

  19. Crop size, plant aggregation, and microhabitat type affect fruit removal by birds from individual melastome plants in the Upper Amazon.

    PubMed

    Blendinger, Pedro G; Loiselle, Bette A; Blake, John G

    2008-11-01

    We studied the efficiency (proportion of the crop removed) and quantitative effectiveness (number of fruits removed) of dispersal of Miconia fosteri and M. serrulata (Melastomataceae) seeds by birds in lowland tropical wet forest of Ecuador. Specifically, we examined variation in fruit removal in order to reveal the spatial scale at which crop size influences seed dispersal outcome of individual plants, and to evaluate how the effect of crop size on plant dispersal success may be affected by conspecific fruit abundance and by the spatial distribution of frugivore abundance. We established two 9-ha plots in undisturbed terra-firme understory, where six manakin species (Pipridae) disperse most seeds of these two plant species. Mean levels of fruit removal were low for both species, with high variability among plants. In general, plants with larger crop sizes experienced greater efficiency and effectiveness of fruit removal than plants with smaller crops. Fruit removal, however, was also influenced by microhabitat, such as local topography and local neighborhood. Fruit-rich and disperser-rich patches overlapped spatially for M. fosteri but not M. serrulata, nonetheless fruit removal of M. serrulata was still much greater in fruit-rich patches. Fruit removal from individual plants did not decrease in patches with many fruiting conspecifics and, in fact, removal effectiveness was enhanced for M. fosteri with small crop sizes when such plants were in patches with more conspecifics. These results suggest that benefits of attracting dispersers to a patch balanced or outweighed the costs of competition for dispersers. Spatial pattern of fruit removal, a measure of plant fitness, depended on a complex interaction among plant traits, spatial patterns of plant distribution, and disperser behavior. PMID:18810498

  20. Surfactant adsorption and aggregate structure of silica nanoparticles: a versatile stratagem for the regulation of particle size and surface modification

    NASA Astrophysics Data System (ADS)

    Chaudhary, Savita; Rohilla, Deepak; Mehta, S. K.

    2014-03-01

    The area of silica nanoparticles is incredibly polygonal. Silica particles have aroused exceptional deliberation in bio-analysis due to great progress in particular arenas, for instance, biocompatibility, unique properties of modifiable pore size and organization, huge facade areas and pore volumes, manageable morphology and amendable surfaces, elevated chemical and thermal stability. Currently, silica nanoparticles participate in crucial utilities in daily trade rationales such as power storage, chemical and genetic sensors, groceries dispensation and catalysis. Herein, the size-dependent interfacial relation of anionic silica nanoparticles with twelve altered categories of cationic surfactants has been carried out in terms of the physical chemical facets of colloid and interface science. The current analysis endeavours to investigate the virtual consequences of different surfactants through the development of the objective composite materials. The nanoparticle size controls, the surface-to-volume ratio and surface bend relating to its interaction with surfactant will also be addressed in this work. More importantly, the simulated stratagem developed in this work can be lengthened to formulate core-shell nanostructures with functional nanoparticles encapsulated in silica particles, making this approach valuable and extensively pertinent for employing sophisticated materials for catalysis and drug delivery.

  1. QTL mapping in multiple populations and development stages reveals dynamic quantitative trait loci for fruit size in cucumbers of different market classes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Fruit size is an important quality trait in cucumber of different market classes. The genetic and molecular basis of fruit size variations in cucumber is not well understood. In this study, we conducted QTL mapping of fruit size in cucumber using three mapping populations developed from cross betwee...

  2. On Determining the Rise, Size, and Duration Classes of a Sunspot Cycle

    NASA Technical Reports Server (NTRS)

    Wilson, Robert M.; Hathaway, David H.; Reichmann, Edwin J.

    1996-01-01

    The behavior of ascent duration, maximum amplitude, and period for cycles 1 to 21 suggests that they are not mutually independent. Analysis of the resultant three-dimensional contingency table for cycles divided according to rise time (ascent duration), size (maximum amplitude), and duration (period) yields a chi-square statistic (= 18.59) that is larger than the test statistic (= 9.49 for 4 degrees-of-freedom at the 5-percent level of significance), thereby, inferring that the null hypothesis (mutual independence) can be rejected. Analysis of individual 2 by 2 contingency tables (based on Fisher's exact test) for these parameters shows that, while ascent duration is strongly related to maximum amplitude in the negative sense (inverse correlation) - the Waldmeier effect, it also is related (marginally) to period, but in the positive sense (direct correlation). No significant (or marginally significant) correlation is found between period and maximum amplitude. Using cycle 22 as a test case, we show that by the 12th month following conventional onset, cycle 22 appeared highly likely to be a fast-rising, larger-than-average-size cycle. Because of the inferred correlation between ascent duration and period, it also seems likely that it will have a period shorter than average length.

  3. Overwinter body condition, mortality and parasite infection in two size classes of 0+ year juvenile European bitterling Rhodeus amarus.

    PubMed

    Francová, K; Ondračková, M

    2013-02-01

    Body condition and parasite abundance were examined in two size classes of European bitterling Rhodeus amarus during the first overwintering period in two seasons (2007-2008 and 2009-2010). Body condition of large fish did not change during winter, and increased significantly in March. From November to February, small fish showed a decreasing trend in condition. Despite a significant increase in March condition of small fish only reached the same level as before winter. Total parasite abundance increased significantly in winter in both fish size classes, reflecting a seasonal increase in monogenean infection. Large fish were parasitized significantly more than small fish during winter, but only in small fish was a negative correlation between parasite infection and condition found and a significant decrease in parasite abundance recorded after wintering, indicating mortality of heavily infected individuals with low condition during the winter. A trend for higher overwinter mortality in small fish was found under semi-experimental conditions. The decrease in condition during the winter period in small fish may reflect faster energy depletion generally expected in smaller individuals. The results indicate that parasite infection may contribute to the overwinter mortality of 0+ year R. amarus, with a stronger effect in smaller individuals.

  4. CD40-induced aggregation of MHC class II and CD80 on the cell surface leads to an early enhancement in antigen presentation.

    PubMed

    Clatza, Abigail; Bonifaz, Laura C; Vignali, Dario A A; Moreno, José

    2003-12-15

    Ligation of CD40 on B cells increases their ability to present Ag and to activate MHC class II (MHC-II)-restricted T cells. How this occurs is not entirely clear. In this study we demonstrate that CD40 ligation on Ag-presenting B cells (APC) for a short period between 30 min and 3 h has a rapid, augmenting effect on the ability of a B cell line and normal B cells to activate T cells. This is not due to alterations in Ag processing or to an increase in surface expression of CD80, CD86, ICAM-1, or MHC-II. This effect is particularly evident with naive, resting T lymphocytes and appears to be more pronounced under limiting Ag concentrations. Shortly after CD40 ligation on a B cell line, MHC-II and CD80 progressively accumulated in cholesterol-enriched microdomains on the cell surface, which correlated with an initial enhancement in their Ag presentation ability. Moreover, CD40 ligation induced a second, late, more sustained enhancement of Ag presentation, which correlates with a significant increase in CD80 expression by APC. Thus, CD40 signaling enhances the efficiency with which APC activate T cells by at least two related, but distinct, mechanisms: an early stage characterized by aggregation of MHC-II and CD80 clusters, and a late stage in which a significant increase in CD80 expression is observed. These results raise the possibility that one important role of CD40 is to contribute to the formation of the immunological synapse on the APC side.

  5. Techniques for Accurate Sizing of Gold Nanoparticles Using Dynamic Light Scattering with Particular Application to Chemical and Biological Sensing Based on Aggregate Formation.

    PubMed

    Zheng, Tianyu; Bott, Steven; Huo, Qun

    2016-08-24

    Gold nanoparticles (AuNPs) have found broad applications in chemical and biological sensing, catalysis, biomolecular imaging, in vitro diagnostics, cancer therapy, and many other areas. Dynamic light scattering (DLS) is an analytical tool used routinely for nanoparticle size measurement and analysis. Due to its relatively low cost and ease of operation in comparison to other more sophisticated techniques, DLS is the primary choice of instrumentation for analyzing the size and size distribution of nanoparticle suspensions. However, many DLS users are unfamiliar with the principles behind the DLS measurement and are unware of some of the intrinsic limitations as well as the unique capabilities of this technique. The lack of sufficient understanding of DLS often leads to inappropriate experimental design and misinterpretation of the data. In this study, we performed DLS analyses on a series of citrate-stabilized AuNPs with diameters ranging from 10 to 100 nm. Our study shows that the measured hydrodynamic diameters of the AuNPs can vary significantly with concentration and incident laser power. The scattered light intensity of the AuNPs has a nearly sixth order power law increase with diameter, and the enormous scattered light intensity of AuNPs with diameters around or exceeding 80 nm causes a substantial multiple scattering effect in conventional DLS instruments. The effect leads to significant errors in the reported average hydrodynamic diameter of the AuNPs when the measurements are analyzed in the conventional way, without accounting for the multiple scattering. We present here some useful methods to obtain the accurate hydrodynamic size of the AuNPs using DLS. We also demonstrate and explain an extremely powerful aspect of DLS-its exceptional sensitivity in detecting gold nanoparticle aggregate formation, and the use of this unique capability for chemical and biological sensing applications. PMID:27472008

  6. Effects of Large Class Size on Effective Teaching and Learning at the Winneba Campus of the UEW (University of Education, Winneba), Ghana

    ERIC Educational Resources Information Center

    Yelkpieri, Daniel; Namale, Matthew; Esia-Donkoh, Kweku; Ofosu-Dwamena, Eric

    2012-01-01

    Large class size is one of the problems in the educational sector that developing nations have been grappling with. Ghana as a developing nation is no exception and has its own fair share of this problem at the pre-tertiary and tertiary levels of education. The sight of large class at the tertiary level is appalling and a headache to teachers at…

  7. Voices from the Field: The Perceptions of Teachers and Principals on the Class Size Reduction Program in a Large Urban School District.

    ERIC Educational Resources Information Center

    Munoz, Marco A.; Portes, Pedro R.

    A class size reduction (CSR) program was implemented in a large low-performing urban elementary school district. The CSR program helps schools improve student learning by hiring additional teachers so that children in the early elementary grades can attend smaller classes. This study used a participant-oriented evaluation model to examine the…

  8. Low-velocity collisions between centimeter-sized snowballs: Porosity dependence of coefficient of restitution for ice aggregates analogues in the Solar System

    NASA Astrophysics Data System (ADS)

    Shimaki, Yuri; Arakawa, Masahiko

    2012-09-01

    Understanding the collisional behavior of ice dust aggregates at low velocity is a key to determining the formation process of small icy bodies such as icy planetesimals, comets and icy satellites, and this collisional behavior is also closely related to the energy dissipation mechanism in Saturn’s rings. We performed head-on collision experiments in air by means of free-falling centimeter-sized sintered snowballs with porosities from 44% to 80% at impact velocities from 0.44 m s-1 to 4.12 m s-1 at -10 °C. In cases of porosity larger than 70%, impact sticking was the dominant collision outcome, while bouncing was dominant at lower porosity. Coefficients of restitution of snow in this velocity range were found to depend strongly on the porosity rather than the impact velocity and to decrease with the increase of the porosity. We successfully measured the compaction volume of snowballs after the impact, and it enabled us to estimate the dynamic compressive strength of snow with the assumption of the energy conservation between kinetic energy and work for deformation, which was found to be consistent with the upper limit of static compressive strength. The velocity dependence of coefficients of restitution of snow was analyzed using a Johnson’s model, and a diagram for collision outcomes among equal-sized sintered snowballs was successfully drawn as a function of porosity and impact velocity.

  9. Behavior and finite-size effects of the sixth order cumulant in the three-dimensional Ising universality class

    NASA Astrophysics Data System (ADS)

    Pan, Xue; Chen, Li-Zhu; Wu, Yuan-Fang

    2016-09-01

    The high-order cumulants of conserved charges are suggested to be sensitive observables to search for the critical point of Quantum Chromodynamics (QCD). This has been calculated to the sixth order in experiments. Corresponding theoretical studies on the sixth order cumulant are necessary. Based on the universality of the critical behavior, we study the temperature dependence of the sixth order cumulant of the order parameter using the parametric representation of the three-dimensional Ising model, which is expected to be in the same universality class as QCD. The density plot of the sign of the sixth order cumulant is shown on the temperature and external magnetic field plane. We found that at non-zero external magnetic field, when the critical point is approached from the crossover side, the sixth order cumulant has a negative valley. The width of the negative valley narrows with decreasing external field. Qualitatively, the trend is similar to the result of Monte Carlo simulation on a finite-size system. Quantitatively, the temperature of the sign change is different. Through Monte Carlo simulation of the Ising model, we calculated the sixth order cumulant of different sizes of systems. We discuss the finite-size effects on the temperature at which the cumulant changes sign. Supported by Fund Project of Sichuan Provincial Department of Education (16ZB0339), Fund Project of Chengdu Technological University for Doctor (2016RC004), Major State Basic Research Development Program of China (2014CB845402) and National Natural Science Foundation of China (11405088, 11221504)

  10. 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

    intensity of WR in aggregates of different sizes. [ii] the intra-aggregate distribution of OC and the intensity of WR and [iii] the structural stability of soil aggregates relative to the OC content and the intensity of WR in soils under different crops (apricot, citrus and wheat) and different treatments (conventional tilling and mulching). Soil samples were collected from an experimental area (Luvic Calcisols and Calcic Luvisols) in the province of Sevilla (Southern Spain) under different crops (apricot, citrus and wheat) and different management types (conventional tillage with moldboard plow) and mulching (no-tilling and addition of wheat residues at rates varying between 5 and 8 Mg/ha/year). At each sampling site, soil blocks (50 cm long × 50 cm wide × 10 cm deep) were carefully collected to avoid disturbance of aggregates as much as possible and transported to the laboratory. At field moist condition, undisturbed soil aggregates were separated by hand. In order to avoid possible interferences due to disturbance by handling, aggregates broken during this process were discarded. Individual aggregates were arranged in paper trays and air-dried during 7 days under laboratory standard conditions. After air-drying, part of each sample was carefully divided for different analyses: [i] part of the original samples was sieved (2 mm) to eliminate coarse soil particles and homogenized for characterization of OC and N contents, C/N ratio and texture; [ii] part of the aggregates were dry-sieved (0.25-0.5, 0.5-1 and 1-2 mm) or measured with a caliper (2-5, 5-10 and 10-15 mm) and separated in different sieve-size classes for determination of WR and OC content; [iii] aggregates 10-15 mm in size were selected for obtaining aggregate layers using a soil aggregate erosion (SAE) apparatus and WR and OC content were determined at each layer; finally, [iv] in order to study the relation between stability to slaking, WR and OC, these properties were determined in 90 air-dried aggregates

  11. Social class and family size as determinants of attributed machismo, femininity, and family planning: a field study in two South American communities.

    PubMed

    Nicassio, P M

    1977-12-01

    A study was conducted to determine the way in which stereotypes of machismo and femininity are associated with family size and perceptions of family planning. A total of 144 adults, male and female, from a lower class and an upper middle class urban area in Colombia were asked to respond to photographs of Colombian families varying in size and state of completeness. The study illustrated the critical role of sex-role identity and sex-role organization as variables having an effect on fertility. The lower-class respondents described parents in the photographs as significantly more macho or feminine because of their children than the upper-middle-class subjects did. Future research should attempt to measure when this drive to sex-role identity is strongest, i.e., when men and women are most driven to reproduce in order to "prove" themselves. Both lower- and upper-middle-class male groups considered male dominance in marriage to be directly linked with family size. Perceptions of the use of family planning decreased linearly with family size for both social groups, although the lower-class females attributed more family planning to spouses of large families than upper-middle-class females. It is suggested that further research deal with the ways in which constructs of machismo and male dominance vary between the sexes and among socioeconomic groups and the ways in which they impact on fertility.

  12. Application of a kosmotrope-based solubility assay to multiple protein therapeutic classes indicates broad use as a high-throughput screen for protein therapeutic aggregation propensity.

    PubMed

    Yamniuk, Aaron P; Ditto, Noah; Patel, Mehul; Dai, Jun; Sejwal, Preeti; Stetsko, Paul; Doyle, Michael L

    2013-08-01

    Aggregation propensity is a critical attribute of protein therapeutics that can influence production, manufacturing, delivery, and potential activity and safety (immunogenicity). It is therefore imperative to select molecules with low aggregation propensity in the early stages of drug discovery to mitigate the risk of delays or failure in clinical development. Although many biophysical methods have been developed to characterize protein aggregation, most established methods are low-throughput, requiring large quantities of protein, lengthy assay times, and/or significant upstream sample preparation, which can limit application in early candidate screening. To avoid these limitations, we developed a reliable method to characterize aggregation propensity, by measuring the relative solubility of protein therapeutic candidates in the presence of the kosmotropic salt ammonium sulfate. Manual bench-scale and automated plate-based methods were applied to different protein therapeutic formats including Adnectins, domain antibodies, PEGylated Adnectins, Fc fusion proteins, and monoclonal antibodies. The kosmotrope solubility data agreed well with the aggregation propensity observed by established methods, while being amenable to high-throughput screening because of speed, simplicity, versatility and low protein material requirements. The results suggest that kosmotrope-based solubility assessment has broad applicability to selecting protein therapeutic candidates with low aggregation propensity and high "developability" to progress into development.

  13. Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea.

    PubMed

    Lin, Junfang; Cao, Wenxi; Wang, Guifen; Hu, Shuibo

    2014-06-15

    Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity.

  14. 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.

  15. Synthesis of Phenylene Vinylene Macrocycles through Acyclic Diene Metathesis Macrocyclization and Their Aggregation Behavior.

    PubMed

    Zhang, Chenxi; Yu, Chao; Long, Hai; Denman, Ryan J; Jin, Yinghua; Zhang, Wei

    2015-11-16

    A series of phenylene vinylene macrocycles (PVMs) bearing substituents with various sizes and electronic properties have been synthesized through a one-step acyclic diene metathesis macrocyclization approach and their aggregation behaviors have been investigated. In great contrast to the aggregation of the analogous phenylene ethynylene macrocycles, which aggregate only when substituted with electron-withdrawing groups, these PVMs undergo exceptionally strong aggregation, regardless of the electron-donating or -withdrawing characters of the substituents. The unusual aggregation behavior of the PVMs is further investigated with thermodynamic and computer modeling studies, which show a good agreement with the recently proposed direct through-space interaction model, rather than the polar/π model. The high aggregation tendency of PVMs suggests the great potential of this novel class of shape-persistent macrocycles in a variety of applications, such as ion channels, host-guest recognition, and catalysis. PMID:26420443

  16. Analysis of phytoplankton distribution and community structure in the German Bight with respect to the different size classes

    NASA Astrophysics Data System (ADS)

    Wollschläger, Jochen; Wiltshire, Karen Helen; Petersen, Wilhelm; Metfies, Katja

    2015-05-01

    Investigation of phytoplankton biodiversity, ecology, and biogeography is crucial for understanding marine ecosystems. Research is often carried out on the basis of microscopic observations, but due to the limitations of this approach regarding detection and identification of picophytoplankton (0.2-2 μm) and nanophytoplankton (2-20 μm), these investigations are mainly focused on the microphytoplankton (20-200 μm). In the last decades, various methods based on optical and molecular biological approaches have evolved which enable a more rapid and convenient analysis of phytoplankton samples and a more detailed assessment of small phytoplankton. In this study, a selection of these methods (in situ fluorescence, flow cytometry, genetic fingerprinting, and DNA microarray) was placed in complement to light microscopy and HPLC-based pigment analysis to investigate both biomass distribution and community structure of phytoplankton. As far as possible, the size classes were analyzed separately. Investigations were carried out on six cruises in the German Bight in 2010 and 2011 to analyze both spatial and seasonal variability. Microphytoplankton was identified as the major contributor to biomass in all seasons, followed by the nanophytoplankton. Generally, biomass distribution was patchy, but the overall contribution of small phytoplankton was higher in offshore areas and also in areas exhibiting higher turbidity. Regarding temporal development of the community, differences between the small phytoplankton community and the microphytoplankton were found. The latter exhibited a seasonal pattern regarding number of taxa present, alpha- and beta-diversity, and community structure, while for the nano- and especially the picophytoplankton, a general shift in the community between both years was observable without seasonality. Although the reason for this shift remains unclear, the results imply a different response of large and small phytoplankton to environmental influences.

  17. Nevada's Class-Size Reduction Program. Nevada Revised Statutes 388.700-388.730: "Program To Reduce the Pupil-Teacher Ratio." Background Paper 97-7.

    ERIC Educational Resources Information Center

    Sturm, H. Pepper

    In 1989, the Nevada Legislature enacted the Class-Size Reduction (CSR) Act. The measure was designed to reduce the pupil-teacher ratio in the public schools, particularly in the earliest grades. The program was scheduled to proceed in several phases. The first step reduced the student-teacher ratio in selected kindergartens and first grade classes…

  18. Planning and Delivering Instruction with Increasing Class Sizes in Educational Administration Program Coursework: Modeling Leadership Skills for New Professors Transitioning from K-12 Administration

    ERIC Educational Resources Information Center

    Stebbins, Gary

    2009-01-01

    Increased class sizes and advising responsibilities are the new realities in California's graduate programs of Educational Administration. In order to effectively meet new challenges, professors must make adjustments in venue, plan meticulously, utilize technology, distribute leadership, and implement alternative grading systems. This is a…

  19. Examining the Effect of Class Size on Classroom Engagement and Teacher-Pupil Interaction: Differences in Relation to Pupil Prior Attainment and Primary vs. Secondary Schools

    ERIC Educational Resources Information Center

    Blatchford, Peter; Bassett, Paul; Brown, Penelope

    2011-01-01

    It is widely recognized that we need to know more about effects of class size on classroom interactions and pupil behavior. This paper extends research by comparing effects on pupil classroom engagement and teacher-pupil interaction, and examining if effects vary by pupil attainment level and between primary and secondary schools. Systematic…

  20. Approximate formulas for the mean dry size and the size-class fractions of cloud condensation nuclei as a function of supersaturation

    SciTech Connect

    Rivera-Carpio, C.A.; Novakov, T.

    1995-12-31

    Approximate formulas are presented for the mean dry size and the submicron and Aitken-size fractions of cloud condensation nuclei (CCN) as function of supersaturation. The expressions allow to estimate these CCN size-related characteristics, at the supersaturation levels reached during cloud formation, from aerosol size distribution and activation parametric data. The proposed formulas are derived based on approximations inferred from the very good agreement observed between measured and predicted slopes of CCN supersaturation activation spectra. Their application to the problem of assessing the physico-chemical characteristics of CCN-active aerosol particles in marine and continental air masses is illustrated.

  1. Prediction of reversible IgG1 aggregation occurring in a size exclusion chromatography column is enabled through a model based approach.

    PubMed

    Ojala, Frida; Sellberg, Anton; Hansen, Thomas Budde; Hansen, Ernst Broberg; Nilsson, Bernt

    2015-09-01

    One important aspect of antibody separation being studied today is aggregation, as this not only leads to a loss in yield, but aggregates can also be hazardous if injected into the body. The aim of this study was to determine whether the methodology applied in the previous study could be used to predict the aggregation of a different batch of IgG1, and to model the aggregation occurring in a SEC column. Aggregation was found to be reversible. The equilibrium parameter was found to be 272 M(-1) and the reaction kinetic parameter 1.33 × 10(-5) s(-1) , both within the 95% confidence interval of the results obtained in the previous work. The effective diffusivities were estimated to be 1.45 × 10(-13) and 1.90 10(-14) m(2) /s for the monomers and dimers, respectively. Good agreement was found between the new model and the chromatograms obtained in the SEC experiments. The model was also able to predict the decrease of dimers due to the dilution and separation in the SEC column during long retention times.

  2. Performance of Factor Mixture Models as a Function of Model Size, Covariate Effects, and Class-Specific Parameters

    ERIC Educational Resources Information Center

    Lubke, Gitta; Muthen, Bengt O.

    2007-01-01

    Factor mixture models are designed for the analysis of multivariate data obtained from a population consisting of distinct latent classes. A common factor model is assumed to hold within each of the latent classes. Factor mixture modeling involves obtaining estimates of the model parameters, and may also be used to assign subjects to their most…

  3. Release of leukotrienes C4 and B4 (LTC4, LTB4) and prostaglandin E2 (PGE2) from human monocytes (M phi) induced with aggregated immunoglobulins (Ig) of different classes

    SciTech Connect

    Ferreri, N.R.; Howland, W.C.; Spiegelberg, H.L.

    1986-03-01

    Purified human peripheral blood monocytes were stimulated with aggregated human myeloma proteins or the calcium ionophore A23187. Release of LTC4, LTB4 and PGE2 into the supernate was determined by radioimmunoassay and high performance liquid chromatography. The ionophore induced release of 10 +/- 5 ng LTC4 and 25 +/- 8 ng LTB4/10/sup 6/ M phi. Aggregated IgG, IgA and IgE but not IgM or monomeric Ig induced release of LTC4 and LTB4 that was approximately 10-20% of that induced by ionophore. Similarly, IgG, IgA and IgE but not IgM induced release of PGE2 (range 0.015-0.22 ng/10/sup 6/ M phi). Absence of calcium or preincubation with nordihydroguaiaretic acid (10/sup -6/ M) inhibited Ig-induced LTC4 and LTB4 release and indomethacin (10/sup -6/ M) inhibited PGE2 release. Phagocytosis of the Ig aggregates was not required since release was not inhibited by cytochalasin B. Release of PGE2 and LTC4/LTB4 induced by all classes except IgM correlated with the presence or absence of M phi Fc receptors (FcR) for each class as determined by rosette assay. The data indicate that IgG, IgA and IgE immune complexes can induce M phi arachidonic acid metabolism via interaction with FcR despite inhibition of phagocytosis. Such a mechanism may contribute to inflammatory reactions characterized by mononuclear cell infiltrates.

  4. Ising universality class for the liquid-liquid critical point of a one component fluid: a finite-size scaling test.

    PubMed

    Gallo, Paola; Sciortino, Francesco

    2012-10-26

    We present a finite-size scaling study of the liquid-liquid critical point in the Jagla model, a prototype model for liquids that present the same thermodynamic anomalies which characterize liquid water. Performing successive umbrella sampling grand canonical Monte Carlo simulations, we evaluate an accurate density of states for different system sizes and determine the size-dependent critical parameters. Extrapolation to infinite size provides estimates of the bulk critical values for this model. The finite-size study allows us to establish that critical fluctuations are consistent with the Ising universality class and to provide definitive evidence for the existence of a liquid-liquid critical point in the Jagla potential. This finding supports the possibility of the existence of a genuine liquid-liquid critical point in anomalous one-component liquids like water. PMID:23215223

  5. Holographic characterization of protein aggregates

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Zhong, Xiao; Ruffner, David; Stutt, Alexandra; Philips, Laura; Ward, Michael; Grier, David

    Holographic characterization directly measures the size distribution of subvisible protein aggregates in suspension and offers insights into their morphology. Based on holographic video microscopy, this analytical technique records and interprets holograms of individual aggregates in protein solutions as they flow down a microfluidic channel, without requiring labeling or other exceptional sample preparation. The hologram of an individual protein aggregate is analyzed in real time with the Lorenz-Mie theory of light scattering to measure that aggregate's size and optical properties. Detecting, counting and characterizing subvisible aggregates proceeds fast enough for time-resolved studies, and lends itself to tracking trends in protein aggregation arising from changing environmental factors. No other analytical technique provides such a wealth of particle-resolved characterization data in situ. Holographic characterization promises accelerated development of therapeutic protein formulations, improved process control during manufacturing, and streamlined quality assurance during storage and at the point of use. Mrsec and MRI program of the NSF, Spheryx Inc.

  6. Construction aggregates

    USGS Publications Warehouse

    Langer, W.H.; Tepordei, V.V.; Bolen, W.P.

    2000-01-01

    Construction aggregates consist primarily of crushed stone and construction sand and gravel. Total estimated production of construction aggregates increased in 1999 by about 2% to 2.39 Gt (2.64 billion st) compared with 1998. This record production level continued an expansion that began in 1992. By commodities, crushed stone production increased 3.3%, while sand and gravel production increased by about 0.5%.

  7. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1994-01-01

    Part of a special section on industrial minerals in 1993. The 1993 production of construction aggregates increased 6.3 percent over the 1992 figure, to reach 2.01 Gt. This represents the highest estimated annual production of combined crushed stone and construction sand and gravel ever recorded in the U.S. The outlook for construction aggregates and the issues facing the industry are discussed.

  8. Application of DNA barcoding for identification of freshwater carnivorous fish diets: Is number of prey items dependent on size class for Micropterus salmoides?

    PubMed Central

    Jo, Hyunbin; Gim, Jeong-An; Jeong, Kwang-Seuk; Kim, Heui-Soo; Joo, Gea-Jae

    2014-01-01

    Understanding predator–prey interactions is a major challenge in ecological studies. In particular, the accurate identification of prey is a fundamental requirement in elucidating food-web structure. This study took a molecular approach in determining the species identity of consumed prey items of a freshwater carnivorous fish (largemouth bass, Micropterus salmoides), according to their size class. Thirty randomly selected gut samples were categorized into three size classes, based on the total length of the bass. Using the universal primer for the mtDNA cytochrome oxidase I (COI) region, polymerase chain reaction (PCR) amplification was performed on unidentified gut contents and then sequenced after cloning. Two gut samples were completely empty, and DNA materials from 27 of 28 gut samples were successfully amplified by PCR (success rate: 96.4%). Sequence database navigation yielded a total of 308 clones, containing DNA from 26 prey items. They comprised four phyla, including seven classes, 12 orders, and 12 families based on BLAST and BOLD database searches. The results indicate that largemouth bass show selective preferences in prey item consumption as they mature. These results corroborate a hypothesis, presence of ontogenetic diet shift, derived through other methodological approaches. Despite the practical limitations inherent in DNA barcoding analysis, high-resolution (i.e., species level) identification was possible, and the predation patterns of predators of different sizes were identifiable. The utilization of this method is strongly recommended for determining specific predator–prey relationships in complex freshwater ecosystems. PMID:24558577

  9. Application of DNA barcoding for identification of freshwater carnivorous fish diets: Is number of prey items dependent on size class for Micropterus salmoides?

    PubMed

    Jo, Hyunbin; Gim, Jeong-An; Jeong, Kwang-Seuk; Kim, Heui-Soo; Joo, Gea-Jae

    2014-01-01

    Understanding predator-prey interactions is a major challenge in ecological studies. In particular, the accurate identification of prey is a fundamental requirement in elucidating food-web structure. This study took a molecular approach in determining the species identity of consumed prey items of a freshwater carnivorous fish (largemouth bass, Micropterus salmoides), according to their size class. Thirty randomly selected gut samples were categorized into three size classes, based on the total length of the bass. Using the universal primer for the mtDNA cytochrome oxidase I (COI) region, polymerase chain reaction (PCR) amplification was performed on unidentified gut contents and then sequenced after cloning. Two gut samples were completely empty, and DNA materials from 27 of 28 gut samples were successfully amplified by PCR (success rate: 96.4%). Sequence database navigation yielded a total of 308 clones, containing DNA from 26 prey items. They comprised four phyla, including seven classes, 12 orders, and 12 families based on BLAST and BOLD database searches. The results indicate that largemouth bass show selective preferences in prey item consumption as they mature. These results corroborate a hypothesis, presence of ontogenetic diet shift, derived through other methodological approaches. Despite the practical limitations inherent in DNA barcoding analysis, high-resolution (i.e., species level) identification was possible, and the predation patterns of predators of different sizes were identifiable. The utilization of this method is strongly recommended for determining specific predator-prey relationships in complex freshwater ecosystems. PMID:24558577

  10. Application of DNA barcoding for identification of freshwater carnivorous fish diets: Is number of prey items dependent on size class for Micropterus salmoides?

    PubMed

    Jo, Hyunbin; Gim, Jeong-An; Jeong, Kwang-Seuk; Kim, Heui-Soo; Joo, Gea-Jae

    2014-01-01

    Understanding predator-prey interactions is a major challenge in ecological studies. In particular, the accurate identification of prey is a fundamental requirement in elucidating food-web structure. This study took a molecular approach in determining the species identity of consumed prey items of a freshwater carnivorous fish (largemouth bass, Micropterus salmoides), according to their size class. Thirty randomly selected gut samples were categorized into three size classes, based on the total length of the bass. Using the universal primer for the mtDNA cytochrome oxidase I (COI) region, polymerase chain reaction (PCR) amplification was performed on unidentified gut contents and then sequenced after cloning. Two gut samples were completely empty, and DNA materials from 27 of 28 gut samples were successfully amplified by PCR (success rate: 96.4%). Sequence database navigation yielded a total of 308 clones, containing DNA from 26 prey items. They comprised four phyla, including seven classes, 12 orders, and 12 families based on BLAST and BOLD database searches. The results indicate that largemouth bass show selective preferences in prey item consumption as they mature. These results corroborate a hypothesis, presence of ontogenetic diet shift, derived through other methodological approaches. Despite the practical limitations inherent in DNA barcoding analysis, high-resolution (i.e., species level) identification was possible, and the predation patterns of predators of different sizes were identifiable. The utilization of this method is strongly recommended for determining specific predator-prey relationships in complex freshwater ecosystems.

  11. A new class of cyclin dependent kinase in Chlamydomonas is required for coupling cell size to cell division

    PubMed Central

    Li, Yubing; Liu, Dianyi; López-Paz, Cristina; Olson, Bradley JSC; Umen, James G

    2016-01-01

    Proliferating cells actively control their size by mechanisms that are poorly understood. The unicellular green alga Chlamydomonas reinhardtii divides by multiple fission, wherein a ‘counting’ mechanism couples mother cell-size to cell division number allowing production of uniform-sized daughters. We identified a sizer protein, CDKG1, that acts through the retinoblastoma (RB) tumor suppressor pathway as a D-cyclin-dependent RB kinase to regulate mitotic counting. Loss of CDKG1 leads to fewer mitotic divisions and large daughters, while mis-expression of CDKG1 causes supernumerous mitotic divisions and small daughters. The concentration of nuclear-localized CDKG1 in pre-mitotic cells is set by mother cell size, and its progressive dilution and degradation with each round of cell division may provide a link between mother cell-size and mitotic division number. Cell-size-dependent accumulation of limiting cell cycle regulators such as CDKG1 is a potentially general mechanism for size control. DOI: http://dx.doi.org/10.7554/eLife.10767.001 PMID:27015111

  12. The effects of overwinter flowson the spring condition of rainbow and brown trout size classes in the Green River downstream of Flaming Gorge Dam, Utah.

    SciTech Connect

    Magnusson, A. K.; LaGory, K. E.; Hayse, J. W.; Environmental Science Division

    2010-06-25

    Flaming Gorge Dam, a hydroelectric facility operated by the Bureau of Reclamation (Reclamation), is located on the Green River in Daggett County, northeastern Utah. Until recently, and since the early 1990s, single daily peak releases or steady flows have been the operational pattern of the dam during the winter period. However, releases from Flaming Gorge Reservoir followed a double-peak pattern (two daily flow peaks) during the winters of 2006-2007 and 2008-2009. Because there is little recent long-term history of double-peaking at Flaming Gorge Dam, the potential effects of double-peaking operations on trout body condition in the dam's tailwater are not known. A study plan was developed that identified research activities to evaluate potential effects from winter double-peaking operations (Hayse et al. 2009). Along with other tasks, the study plan identified the need to conduct a statistical analysis of historical trout condition and macroinvertebrate abundance to evaluate the potential effects of hydropower operations. The results from analyses based on the combined size classes of trout (85-630 mm) were presented in Magnusson et al. (2008). The results of this earlier analysis suggested possible relationships between trout condition and flow, but concern that some of the relationships resulted from size-based effects (e.g., apparent changes in condition may have been related to concomitant changes in size distribution, because small trout may have responded differently to flow than large trout) prompted additional analysis of within-size class relationships. This report presents the results of analyses of three different size classes of trout (small: 200-299 mm, medium: 300-399 mm, and large: {ge}400 mm body length). We analyzed historical data to (1) describe temporal patterns and relationships among flows, benthic macroinvertebrate abundance, and condition of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) in the tailwaters of Flaming

  13. Biochemical distributions (amino acids, neutral sugars, and lignin phenols) among size-classes of modern marine sediments from the Washington coast

    NASA Astrophysics Data System (ADS)

    Keil, Richard G.; Tsamakis, Elizabeth; Giddings, J. Calvin; Hedges, John I.

    1998-04-01

    lignin phenol yields and low acid/aldehyde ratios. Clay-size fractions are enriched in nitrogenous components, as reflected by elevated yields of total and basic amino acids (especially lysine). Silt- and sand-size fractions rich in quartz and albite show slightly higher yields of neutral amino acids. Consistent trends across all size classes and among the different depositional settings illustrates that only a small portion of the organic matter is present as distinct organic debris (e.g. pollen, vascular plant tissues, etc.), but that this debris can be isolated in specific size classes. The data for surface-associated organic matter are consistent with, but not conclusive of, selective partitioning of some organic matter to specific mineral surfaces. The dominant size class-specific trends in organic matter composition are due to changes in both source and diagenetic alteration.

  14. Impacts of Cropping Systems on Aggregates Associated Organic Carbon and Nitrogen in a Semiarid Highland Agroecosystem

    PubMed Central

    Chu, Jiashu; Zhang, Tianzhe; Chang, Weidong; Zhang, Dan; Zulfiqar, Saman; Fu, Aigen; Hao, Yaqi

    2016-01-01

    The effect of cropping system on the distribution of organic carbon (OC) and nitrogen (N) in soil aggregates has not been well addressed, which is important for understanding the sequestration of OC and N in agricultural soils. We analyzed the distribution of OC and N associated with soil aggregates in three unfertilized cropping systems in a 27-year field experiment: continuously cropped alfalfa, continuously cropped wheat and a legume-grain rotation. The objectives were to understand the effect of cropping system on the distribution of OC and N in aggregates and to examine the relationships between the changes in OC and N stocks in total soils and in aggregates. The cropping systems increased the stocks of OC and N in total soils (0–40 cm) at mean rates of 15.6 g OC m-2 yr-1 and 1.2 g N m-2 yr-1 relative to a fallow control. The continuous cropping of alfalfa produced the largest increases at the 0–20 cm depth. The OC and N stocks in total soils were significantly correlated with the changes in the >0.053 mm aggregates. 27-year of cropping increased OC stocks in the >0.053 mm size class of aggregates and N stocks in the >0.25 mm size class but decreased OC stocks in the <0.053 mm size class and N stocks in the <0.25 mm size class. The increases in OC and N stocks in these aggregates accounted for 99.5 and 98.7% of the total increases, respectively, in the continuous alfalfa system. The increases in the OC and N stocks associated with the >0.25 mm aggregate size class accounted for more than 97% of the total increases in the continuous wheat and the legume-grain rotation systems. These results suggested that long-term cropping has the potential to sequester OC and N in soils and that the increases in soil OC and N stocks were mainly due to increases associated with aggregates >0.053 mm. PMID:27764209

  15. Near-infrared excited state dynamics of melanins: the effects of iron content, photo-damage, chemical oxidation, and aggregate size.

    PubMed

    Simpson, Mary Jane; Wilson, Jesse W; Robles, Francisco E; Dall, Christopher P; Glass, Keely; Simon, John D; Warren, Warren S

    2014-02-13

    Ultrafast pump-probe measurements can discriminate the two forms of melanin found in biological tissue (eumelanin and pheomelanin), which may be useful for diagnosing and grading melanoma. However, recent work has shown that bound iron content changes eumelanin's pump-probe response, making it more similar to that of pheomelanin. Here we record the pump-probe response of these melanins at a wider range of wavelengths than previous work and show that with shorter pump wavelengths the response crosses over from being dominated by ground-state bleaching to being dominated by excited-state absorption. The crossover wavelength is different for each type of melanin. In our analysis, we found that the mechanism by which iron modifies eumelanin's pump-probe response cannot be attributed to Raman resonances or differences in melanin aggregation and is more likely caused by iron acting to broaden the unit spectra of individual chromophores in the heterogeneous melanin aggregate. We analyze the dependence on optical intensity, finding that iron-loaded eumelanin undergoes irreversible changes to the pump-probe response after intense laser exposure. Simultaneously acquired fluorescence data suggest that the previously reported "activation" of eumelanin fluorescence may be caused in part by the dissociation of metal ions or the selective degradation of iron-containing melanin.

  16. Near-Infrared Excited State Dynamics of Melanins: The Effects of Iron Content, Photo-Damage, Chemical Oxidation, and Aggregate Size

    PubMed Central

    2015-01-01

    Ultrafast pump–probe measurements can discriminate the two forms of melanin found in biological tissue (eumelanin and pheomelanin), which may be useful for diagnosing and grading melanoma. However, recent work has shown that bound iron content changes eumelanin’s pump–probe response, making it more similar to that of pheomelanin. Here we record the pump–probe response of these melanins at a wider range of wavelengths than previous work and show that with shorter pump wavelengths the response crosses over from being dominated by ground-state bleaching to being dominated by excited-state absorption. The crossover wavelength is different for each type of melanin. In our analysis, we found that the mechanism by which iron modifies eumelanin’s pump–probe response cannot be attributed to Raman resonances or differences in melanin aggregation and is more likely caused by iron acting to broaden the unit spectra of individual chromophores in the heterogeneous melanin aggregate. We analyze the dependence on optical intensity, finding that iron-loaded eumelanin undergoes irreversible changes to the pump–probe response after intense laser exposure. Simultaneously acquired fluorescence data suggest that the previously reported “activation” of eumelanin fluorescence may be caused in part by the dissociation of metal ions or the selective degradation of iron-containing melanin. PMID:24446774

  17. Euphausiid distribution along the Western Antarctic Peninsula—Part A: Development of robust multi-frequency acoustic techniques to identify euphausiid aggregations and quantify euphausiid size, abundance, and biomass

    NASA Astrophysics Data System (ADS)

    Lawson, Gareth L.; Wiebe, Peter H.; Stanton, Timothy K.; Ashjian, Carin J.

    2008-02-01

    Methods were refined and tested for identifying the aggregations of Antarctic euphausiids ( Euphausia spp.) and then estimating euphausiid size, abundance, and biomass, based on multi-frequency acoustic survey data. A threshold level of volume backscattering strength for distinguishing euphausiid aggregations from other zooplankton was derived on the basis of published measurements of euphausiid visual acuity and estimates of the minimum density of animals over which an individual can maintain visual contact with its nearest neighbor. Differences in mean volume backscattering strength at 120 and 43 kHz further served to distinguish euphausiids from other sources of scattering. An inversion method was then developed to estimate simultaneously the mean length and density of euphausiids in these acoustically identified aggregations based on measurements of mean volume backscattering strength at four frequencies (43, 120, 200, and 420 kHz). The methods were tested at certain locations within an acoustically surveyed continental shelf region in and around Marguerite Bay, west of the Antarctic Peninsula, where independent evidence was also available from net and video systems. Inversion results at these test sites were similar to net samples for estimated length, but acoustic estimates of euphausiid density exceeded those from nets by one to two orders of magnitude, likely due primarily to avoidance and to a lesser extent to differences in the volumes sampled by the two systems. In a companion study, these methods were applied to the full acoustic survey data in order to examine the distribution of euphausiids in relation to aspects of the physical and biological environment [Lawson, G.L., Wiebe, P.H., Ashjian, C.J., Stanton, T.K., 2008. Euphausiid distribution along the Western Antarctic Peninsula—Part B: Distribution of euphausiid aggregations and biomass, and associations with environmental features. Deep-Sea Research II, this issue [doi:10.1016/j.dsr2.2007.11.014

  18. Linkage disequilibrium in the insulin gene region: Size variation at the 5{prime} flanking polymorphism and bimodality among {open_quotes}Class I{close_quotes} alleles

    SciTech Connect

    McGinnis, R.E.; Spielman, R.S.

    1994-09-01

    The 5{prime} flanking polymorphism (5{prime}FP), a hypervariable region at the 5{prime} end of the insulin gene, has {open_quotes}class 1{close_quotes} alleles (650-900 bp long) that are in positive linkage disequilibrium with insulin-dependent diabetes mellitus (IDDM). The authors report that precise sizing of the 5{prime}FP yields a bimodal frequency distribution of class 1 allele lengths. Class 1 alleles belonging to the lower component (650-750 bp) of the bimodal distribution were somewhat more highly associated with IDDM than were alleles from the upper component (760-900 bp), but the difference was not statistically significant. They also examined 5{prime}FP length variation in relation to allelic variation at nearby polymorphisms. At biallelic RFLPs on both sides of the 5{prime}FP, they found that one allele exhibits near-total association with the upper component of the 5FP class 1 distribution. Such associations represent a little-known but potentially wide-spread form of linkage disequilibrium. In this type of disequilibrium, a flanking allele has near-complete association with a single mode of VNTR alleles whose lengths represent consecutive numbers of tandem repeats (CNTR). Such extreme disequilibrium between a CNTR mode and flanking alleles may originate and persist because length mutations at some VNTR loci usually add or delete only one or two repeat units. 22 refs., 5 figs., 6 tabs.

  19. Virtual Class: Distance Learning for Small and Medium Sized Enterprises in the Spanish Region of Castilla y Leon.

    ERIC Educational Resources Information Center

    Rodriguez, Blanca; Perez, Maria Angeles; Verdu, Maria Jesus; Navazo, Maria Agustina; Lopez, Ricardo; Mompo, Rafael; Garcia, Joaquin

    Lifelong learning is becoming a necessity in the new Information Society where everyone, particularly small and medium sized enterprises (SMEs), must keep up with new technologies. Education and training are of the most importance in this updating. An interdisciplinary and inter-university work group called "Canalejas" (Spain) has developed a…

  20. Asymmetric Flow-Field Flow Fractionation (AF4) of Aqueous C60 Aggregates with Dynamic Light Scattering Size and LC-MS

    EPA Science Inventory

    Current methods for the size determination of nanomaterials in aqueous suspension include dynamic or static light scattering and electron or atomic force microscopy techniques. Light scattering techniques are limited by poor resolution and the scattering intensity dependence on p...

  1. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1996-01-01

    Part of the Annual Commodities Review 1995. Production of construction aggregates such as crushed stone and construction sand and gravel showed a marginal increase in 1995. Most of the 1995 increases were due to funding for highway construction work. The major areas of concern to the industry included issues relating to wetlands classification and the classification of crystalline silica as a probable human carcinogen. Despite this, an increase in demand is anticipated for 1996.

  2. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1993-01-01

    Part of a special section on the market performance of industrial minerals in 1992. Production of construction aggregates increased by 4.6 percent in 1992. This increase was due, in part, to the increased funding for transportation and infrastructure projects. The U.S. produced about 1.05 Gt of crushed stone and an estimated 734 Mt of construction sand and gravel in 1992. Demand is expected to increase by about 5 percent in 1993.

  3. HecA, a member of a class of adhesins produced by diverse pathogenic bacteria, contributes to the attachment, aggregation, epidermal cell killing, and virulence phenotypes of Erwinia chrysanthemi EC16 on Nicotiana clevelandii seedlings

    PubMed Central

    Rojas, Clemencia M.; Ham, Jong Hyun; Deng, Wen-Ling; Doyle, Jeff J.; Collmer, Alan

    2002-01-01

    Erwinia chrysanthemi is representative of a broad class of bacterial pathogens that are capable of inducing necrosis in plants. The E. chrysanthemi EC16 hecA gene predicts a 3,850-aa member of the Bordetella pertussis filamentous hemagglutinin family of adhesins. A hecA∷Tn7 mutant was reduced in virulence on Nicotiana clevelandii seedlings after inoculation without wounding. Epifluorescence and confocal laser-scanning microscopy observations of hecA and wild-type cells expressing the green fluorescent protein revealed that the mutant is reduced in its ability to attach and then form aggregates on leaves and to cause an aggregate-associated killing of epidermal cells. Cell killing also depended on production of the major pectate lyase isozymes and the type II, but not the type III, secretion pathway in E. chrysanthemi. HecA homologs were found in bacterial pathogens of plants and animals and appear to be unique to pathogens and universal in necrogenic plant pathogens. Phylogenetic comparison of the conserved two-partner secretion domains in the proteins and the 16S rRNA sequences in respective bacteria revealed the two datasets to be fundamentally incongruent, suggesting horizontal acquisition of these genes. Furthermore, hecA and its two homologs in Yersinia pestis had a G+C content that was 10% higher than that of their genomes and similar to that of plant pathogenic Ralstonia, Xylella, and Pseudomonas spp. Our data suggest that filamentous hemagglutinin-like adhesins are broadly important virulence factors in both plant and animal pathogens. PMID:12271135

  4. Pigments and plastic in limnetic ecosystems: A qualitative and quantitative study on microparticles of different size classes.

    PubMed

    Imhof, Hannes K; Laforsch, Christian; Wiesheu, Alexandra C; Schmid, Johannes; Anger, Philipp M; Niessner, Reinhard; Ivleva, Natalia P

    2016-07-01

    Recently, macroplastic (>5 mm) and especially microplastic (<5 mm) particles have been reported as emerging contaminants in marine and limnetic ecosystems. Their coloration is gained by the addition of pigments to the polymer blend which is the major component of the respective product. However, color is also a feature of paint and coatings whereby the pigment is the major component. Once abraded from a surface, paint particles may enter the environment via similar pathways as microplastic particles. So far no detailed studies of microplastic particles (pigmented and non-pigmented) as well as paint particles have been performed focusing on very small microparticles (1-50 μm), in either marine or limnetic ecosystems. Using Raman microspectroscopy with a spatial resolution down to 1 μm, we report a remarkable increase in the occurrence of (pigmented) microplastic particles below 500 μm. Among those, most particles were found at a size of ∼130 μm in a freshwater ecosystem (subalpine Lake Garda, Italy). Moreover, our qualitative and quantitative analyses revealed that the number of paint microparticles significantly increased below the size range of 50 μm due to their brittleness (the smallest detected paint particle had a size of 4 μm). Inductively coupled plasma mass spectrometry measurements showed that both colored particles found in nature as well as virgin particles contain a high variety of metals such as cadmium, lead and copper. These additives may elicit adverse effects in biota ingesting these microparticles, thus paints and associated compounds may act as formerly overlooked contaminants in freshwater ecosystems.

  5. Pigments and plastic in limnetic ecosystems: A qualitative and quantitative study on microparticles of different size classes.

    PubMed

    Imhof, Hannes K; Laforsch, Christian; Wiesheu, Alexandra C; Schmid, Johannes; Anger, Philipp M; Niessner, Reinhard; Ivleva, Natalia P

    2016-07-01

    Recently, macroplastic (>5 mm) and especially microplastic (<5 mm) particles have been reported as emerging contaminants in marine and limnetic ecosystems. Their coloration is gained by the addition of pigments to the polymer blend which is the major component of the respective product. However, color is also a feature of paint and coatings whereby the pigment is the major component. Once abraded from a surface, paint particles may enter the environment via similar pathways as microplastic particles. So far no detailed studies of microplastic particles (pigmented and non-pigmented) as well as paint particles have been performed focusing on very small microparticles (1-50 μm), in either marine or limnetic ecosystems. Using Raman microspectroscopy with a spatial resolution down to 1 μm, we report a remarkable increase in the occurrence of (pigmented) microplastic particles below 500 μm. Among those, most particles were found at a size of ∼130 μm in a freshwater ecosystem (subalpine Lake Garda, Italy). Moreover, our qualitative and quantitative analyses revealed that the number of paint microparticles significantly increased below the size range of 50 μm due to their brittleness (the smallest detected paint particle had a size of 4 μm). Inductively coupled plasma mass spectrometry measurements showed that both colored particles found in nature as well as virgin particles contain a high variety of metals such as cadmium, lead and copper. These additives may elicit adverse effects in biota ingesting these microparticles, thus paints and associated compounds may act as formerly overlooked contaminants in freshwater ecosystems. PMID:27082693

  6. Role of streams in myxobacteria aggregate formation

    NASA Astrophysics Data System (ADS)

    Kiskowski, Maria A.; Jiang, Yi; Alber, Mark S.

    2004-10-01

    Cell contact, movement and directionality are important factors in biological development (morphogenesis), and myxobacteria are a model system for studying cell-cell interaction and cell organization preceding differentiation. When starved, thousands of myxobacteria cells align, stream and form aggregates which later develop into round, non-motile spores. Canonically, cell aggregation has been attributed to attractive chemotaxis, a long range interaction, but there is growing evidence that myxobacteria organization depends on contact-mediated cell-cell communication. We present a discrete stochastic model based on contact-mediated signaling that suggests an explanation for the initialization of early aggregates, aggregation dynamics and final aggregate distribution. Our model qualitatively reproduces the unique structures of myxobacteria aggregates and detailed stages which occur during myxobacteria aggregation: first, aggregates initialize in random positions and cells join aggregates by random walk; second, cells redistribute by moving within transient streams connecting aggregates. Streams play a critical role in final aggregate size distribution by redistributing cells among fewer, larger aggregates. The mechanism by which streams redistribute cells depends on aggregate sizes and is enhanced by noise. Our model predicts that with increased internal noise, more streams would form and streams would last longer. Simulation results suggest a series of new experiments.

  7. Nanoparticle aggregation: principles and modeling.

    PubMed

    Zhang, Wen

    2014-01-01

    The high surface area to volume ratio of nanoparticles usually results in highly reactive and colloidal instability compared to their bulk counterparts. Aggregation as well as many other transformations (e.g., dissolution) in the environment may alter the physiochemical properties, reactivity, fate, transport, and biological interactions (e.g., bioavailability and uptake) of nanoparticles. The unique properties pertinent to nanoparticles, such as shape, size, surface characteristics, composition, and electronic structures, greatly challenge the ability of colloid science to understand nanoparticle aggregation and its environmental impacts. This review briefly introduces fundamentals about aggregation, fractal dimensions, classic and extended Derjaguin-Landau-Verwey-Overbeak (DLVO) theories, aggregation kinetic modeling, experimental measurements, followed by detailed discussions on the major factors on aggregation and subsequent effects on nanomaterial transport and reactivity.

  8. Construction aggregates

    USGS Publications Warehouse

    Bolen, W.P.; Tepordei, V.V.

    2001-01-01

    The estimated production during 2000 of construction aggregates, crushed stone, and construction sand and gravel increased by about 2.6% to 2.7 Gt (3 billion st), compared with 1999. The expansion that started in 1992 continued with record production levels for the ninth consecutive year. By commodity, construction sand and gravel production increased by 4.5% to 1.16 Gt (1.28 billion st), while crushed stone production increased by 1.3% to 1.56 Gt (1.72 billion st).

  9. Differential regulation of meristem size, morphology and organization by the ERECTA, CLAVATA and class III HD-ZIP pathways

    PubMed Central

    Mandel, Tali; Candela, Héctor; Landau, Udi; Asis, Lior; Zelinger, Einat; Carles, Cristel C.; Williams, Leor Eshed

    2016-01-01

    ABSTRACT The shoot apical meristem (SAM) of angiosperm plants is a small, highly organized structure that gives rise to all above-ground organs. The SAM is divided into three functional domains: the central zone (CZ) at the SAM tip harbors the self-renewing pluripotent stem cells and the organizing center, providing daughter cells that are continuously displaced into the interior rib zone (RZ) or the surrounding peripheral zone (PZ), from which organ primordia are initiated. Despite the constant flow of cells from the CZ into the RZ or PZ, and cell recruitment for primordium formation, a stable balance is maintained between the distinct cell populations in the SAM. Here we combined an in-depth phenotypic analysis with a comparative RNA-Seq approach to characterize meristems from selected combinations of clavata3 (clv3), jabba-1D (jba-1D) and erecta (er) mutants of Arabidopsis thaliana. We demonstrate that CLV3 restricts meristem expansion along the apical-basal axis, whereas class III HD-ZIP and ER pathways restrict meristem expansion laterally, but in distinct and possibly perpendicular orientations. Our k-means analysis reveals that clv3, jba-1D/+ and er lead to meristem enlargement by affecting different aspects of meristem function; for example, clv3 displays an increase in the stem cell population, whereas jba-1D/+ er exhibits an increase in mitotic activity and in the meristematic cell population. Our analyses demonstrate that a combined genetic and mRNA-Seq comparative approach provides a precise and sensitive method to identify cell type-specific transcriptomes in a small structure, such as the SAM. PMID:26989178

  10. Maternal-fetal interactions and birth order influence insulin variable number of tandem repeats allele class associations with head size at birth and childhood weight gain.

    PubMed

    Ong, Ken K; Petry, Clive J; Barratt, Bryan J; Ring, Susan; Cordell, Heather J; Wingate, Diane L; Pembrey, Marcus E; Todd, John A; Dunger, David B

    2004-04-01

    Polymorphism of the insulin gene (INS) variable number of tandem repeats (VNTR; class I or class III alleles) locus has been associated with adult diseases and with birth size. Therefore, this variant is a potential contributory factor to the reported fetal origins of adult disease. In the population-based Avon Longitudinal Study of Pregnancy and Childhood birth cohort, we have confirmed in the present study the association between the INS VNTR III/III genotype and larger head circumference at birth (odds ratio [OR] 1.92, 95% CI 1.23-3.07; P = 0.004) and identified an association with higher cord blood IGF-II levels (P = 0.05 to 0.0001). The genotype association with head circumference was influenced by maternal parity (birth order): the III/III OR for larger head circumference was stronger in second and subsequent pregnancies (OR 5.0, 95% CI 2.2-11.5; P = 0.00003) than in first pregnancies (1.2, 0.6-2.2; P = 0.8; interaction with birth order, P = 0.02). During childhood, the III/III genotype remained associated with larger head circumference (P = 0.004) and was also associated with greater BMI (P = 0.03), waist circumference (P = 0.03), and higher fasting insulin levels in girls (P = 0.02). In addition, there were interactions between INS VNTR genotype and early postnatal weight gain in determining childhood BMI (P = 0.001 for interaction), weight (P = 0.005), and waist circumference (P = 0.0005), such that in the approximately 25% of children (n = 286) with rapid early postnatal weight gain, class III genotype-negative children among this group gained weight more rapidly. Our results indicate that complex prenatal and postnatal gene-maternal/fetal interactions influence size at birth and childhood risk factors for adult disease. PMID:15047631

  11. The aggregation efficiency of very fine volcanic ash

    NASA Astrophysics Data System (ADS)

    Del Bello, E.; Taddeucci, J.; Scarlato, P.

    2013-12-01

    Explosive volcanic eruptions can discharge large amounts of very small sized pyroclasts (under 0.090 mm) into the atmosphere that may cause problems to people, infrastructures and environment. The transport and deposition of fine ash are ruled by aggregation that causes premature settling of fine ash and, as consequence, significantly reduces the concentration of airborne material over long distances. Parameterizing the aggregation potential of fine ash is then needed to provide accurate modelling of ash transport and deposition from volcanic plumes. Here we present the first results of laboratory experiments investigating the aggregation efficiency of very fine volcanic particles. Previous laboratory experiments have shown that collision kinetic and relative humidity provide the strongest effect on aggregation behaviour but were only limited to particles with size > 0.125 mm. In our work, we focus on natural volcanic ash at ambient humidity with particles size < 0.090 mm, by taking into account the effect of grain size distribution on aggregation potential. Two types of ash were used in our experiments: fresh ash, collected during fall-out from a recent plume-forming eruption at Sakurajima (Japan -July 2013) and old ash, collected from fall-out tephra deposits at Campi Flegrei (Italy, ca. 10 ka), to account for the different chemical composition and morphoscopic effects of altered ash on aggregation efficiency. Total samples were hand sieved to obtain three classes with unimodal grain size distributions (<0.090 mm, <0.063 mm, <0.032 mm). Bimodal grain size distributions were also obtained by mixing the three classes in different proportions. During each experiments, particles were sieved from the top of a transparent tank where a fan, placed at the bottom, allows turbulent dispersion of particles. Collision and sticking of particles on a vertical glass slide were filmed with a high speed cameras at 6000 fps. Our lenses arrangement provide high image resolution

  12. Sequence-dependent Internalization of Aggregating Peptides*

    PubMed Central

    Couceiro, José R.; Gallardo, Rodrigo; De Smet, Frederik; De Baets, Greet; Baatsen, Pieter; Annaert, Wim; Roose, Kenny; Saelens, Xavier; Schymkowitz, Joost; Rousseau, Frederic

    2015-01-01

    Recently, a number of aggregation disease polypeptides have been shown to spread from cell to cell, thereby displaying prionoid behavior. Studying aggregate internalization, however, is often hampered by the complex kinetics of the aggregation process, resulting in the concomitant uptake of aggregates of different sizes by competing mechanisms, which makes it difficult to isolate pathway-specific responses to aggregates. We designed synthetic aggregating peptides bearing different aggregation propensities with the aim of producing modes of uptake that are sufficiently distinct to differentially analyze the cellular response to internalization. We found that small acidic aggregates (≤500 nm in diameter) were taken up by nonspecific endocytosis as part of the fluid phase and traveled through the endosomal compartment to lysosomes. By contrast, bigger basic aggregates (>1 μm) were taken up through a mechanism dependent on cytoskeletal reorganization and membrane remodeling with the morphological hallmarks of phagocytosis. Importantly, the properties of these aggregates determined not only the mechanism of internalization but also the involvement of the proteostatic machinery (the assembly of interconnected networks that control the biogenesis, folding, trafficking, and degradation of proteins) in the process; whereas the internalization of small acidic aggregates is HSF1-independent, the uptake of larger basic aggregates was HSF1-dependent, requiring Hsp70. Our results show that the biophysical properties of aggregates determine both their mechanism of internalization and proteostatic response. It remains to be seen whether these differences in cellular response contribute to the particular role of specific aggregated proteins in disease. PMID:25391649

  13. 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

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

    PubMed

    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

  15. Diffusion Limited Aggregation: Algorithm optimization revisited

    NASA Astrophysics Data System (ADS)

    Braga, F. L.; Ribeiro, M. S.

    2011-08-01

    The Diffusion Limited Aggregation (DLA) model developed by Witten and Sander in 1978 is useful in modeling a large class of growth phenomena with local dependence. Besides its simplicity this aggregation model has a complex behavior that can be observed at the patterns generated. We propose on this work a brief review of some important proprieties of this model and present an algorithm to simulate a DLA aggregates that simpler and efficient compared to others found in the literature.

  16. Fractal aggregates in Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Cabane, M.; Rannou, P.; Chassefiere, E.; Israel, G.

    1993-04-01

    The cluster structure of Titan's atmosphere was modeled by using an Eulerian microphysical model with the specific formulation of microphysical laws applying to fractal particles. The growth of aggregates in the settling phase was treated by introducing the fractal dimension as a parameter of the model. The model was used to obtain a vertical distribution of size and number density of the aggregates for different production altitudes. Results confirm previous estimates of the formation altitude of photochemical aerosols. The vertical profile of the effective radius of aggregates was calculated as a function of the visible optical depth.

  17. 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

    intensity of WR in aggregates of different sizes. [ii] the intra-aggregate distribution of OC and the intensity of WR and [iii] the structural stability of soil aggregates relative to the OC content and the intensity of WR in soils under different crops (apricot, citrus and wheat) and different treatments (conventional tilling and mulching). Soil samples were collected from an experimental area (Luvic Calcisols and Calcic Luvisols) in the province of Sevilla (Southern Spain) under different crops (apricot, citrus and wheat) and different management types (conventional tillage with moldboard plow) and mulching (no-tilling and addition of wheat residues at rates varying between 5 and 8 Mg/ha/year). At each sampling site, soil blocks (50 cm long × 50 cm wide × 10 cm deep) were carefully collected to avoid disturbance of aggregates as much as possible and transported to the laboratory. At field moist condition, undisturbed soil aggregates were separated by hand. In order to avoid possible interferences due to disturbance by handling, aggregates broken during this process were discarded. Individual aggregates were arranged in paper trays and air-dried during 7 days under laboratory standard conditions. After air-drying, part of each sample was carefully divided for different analyses: [i] part of the original samples was sieved (2 mm) to eliminate coarse soil particles and homogenized for characterization of OC and N contents, C/N ratio and texture; [ii] part of the aggregates were dry-sieved (0.25-0.5, 0.5-1 and 1-2 mm) or measured with a caliper (2-5, 5-10 and 10-15 mm) and separated in different sieve-size classes for determination of WR and OC content; [iii] aggregates 10-15 mm in size were selected for obtaining aggregate layers using a soil aggregate erosion (SAE) apparatus and WR and OC content were determined at each layer; finally, [iv] in order to study the relation between stability to slaking, WR and OC, these properties were determined in 90 air-dried aggregates

  18. To what extent clay mineralogy affects soil aggregation? Consequences for soil organic matter stabilization

    NASA Astrophysics Data System (ADS)

    Fernandez-Ugalde, O.; Barré, P.; Hubert, F.; Virto, I.; Chenu, C.; Ferrage, E.; Caner, L.

    2012-12-01

    Aggregation is a key process for soil functioning as it influences C storage, vulnerability to erosion and water holding capacity. While the influence of soil organic C on aggregation has been documented, much less is known about the role of soil mineralogy. Soils usually contain a mixture of clay minerals with contrasted surface properties, which should result on different abilities of clay minerals to aggregation. We took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals (illite, smectite, kaolinite, and mixed-layer illite-smectite) in aggregation. In a first step, grassland and tilled soil samples were fractionated in water in aggregate-size classes according to the hierarchical model of aggregation (Tisdall and Oades, 1982). Clay mineralogy and organic C in the aggregate-size classes were analyzed. The results showed that interstratified minerals containing swelling phases accumulated in aggregated fractions (>2 μm) compared to free clay fractions (<2 μm) in the two land-uses. The accumulation increased from large macro-aggregates (>500 μm) to micro-aggregates (50-250 μm). C concentration and C/N ratio followed the opposite trend. These results constitute a clay mineral-based evidence for the hierarchical model of aggregation, which postulates an increasing importance of the reactivity of clay minerals in the formation of micro-aggregates compared to larger aggregates. In the latter aggregates, formation relies on the physical enmeshment of particles by fungal hyphae, and root and microbial exudates. In a second step, micro-aggregates from the tilled soil samples were submitted to increasingly disaggregating treatments by sonication to evaluate the link between their water stability and clay mineralogy. Micro-aggregates with increasing stability showed an increase of interstratified minerals containing swelling phases and C concentration for low intensities of disaggregation (from 0 to 5 J mL-1

  19. Changes in fractal dimension during aggregation.

    PubMed

    Chakraborti, Rajat K; Gardner, Kevin H; Atkinson, Joseph F; Van Benschoten, John E

    2003-02-01

    Experiments were performed to evaluate temporal changes in the fractal dimension of aggregates formed during flocculation of an initially monodisperse suspension of latex microspheres. Particle size distributions and aggregate geometrical information at different mixing times were obtained using a non-intrusive optical sampling and digital image analysis technique, under variable conditions of mixing speed, coagulant (alum) dose and particle concentration. Pixel resolution required to determine aggregate size and geometric measures including the fractal dimension is discussed and a quantitative measure of accuracy is developed. The two-dimensional fractal dimension was found to range from 1.94 to 1.48, corresponding to aggregates that are either relatively compact or loosely structured, respectively. Changes in fractal dimension are explained using a conceptual model, which describes changes in fractal dimension associated with aggregate growth and changes in aggregate structure. For aggregation of an initially monodisperse suspension, the fractal dimension was found to decrease over time in the initial stages of floc formation.

  20. Titan's aerosols. I - Laboratory investigations of shapes, size distributions, and aggregation of particles produced by UV photolysis of model Titan atmospheres

    NASA Technical Reports Server (NTRS)

    Scattergood, Thomas W.; Lau, Edmond Y.; Stone, Bradley M.

    1992-01-01

    Experiments in which C2H2, C2H4, and HCN were photolyzed separately and as a mixture in UV light have been conducted in order to ascertain the physical properties of model Titan atmosphere aerosols. Aerosols formed from photolysis of C2H4 were physically similar to those formed from C2H2; protolysis of HCN rapidly generated particles that did not grow to sizes greater than 0.09 microns. While the formation of particles from C4H2 was observed within minutes, formation was slowed by a factor of 4 when C2H2 and HCN were added.

  1. Dynamic, self-assembled aggregates of magnetized, millimeter-sized objects rotating at the liquid-air interface: macroscopic, two-dimensional classical artificial atoms and molecules.

    PubMed

    Grzybowski, B A; Jiang, X; Stone, H A; Whitesides, G M

    2001-07-01

    This paper describes self-assembly of millimeter-sized, magnetized disks floating on a liquid-air interface, and rotating under the influence of a rotating external magnetic field. Spinning of the disks results in hydrodynamic repulsion between them, while the rotating magnetic field produces an average confining potential acting on all disks. The interplay between hydrodynamic and magnetic interactions leads to the formation of patterns. Theoretical analysis of hydrodynamic and magnetic forces indicates that the interactions in this system are similar to those acting in systems of finite numbers of particles behaving classically ("classical artificial atoms"). Macroscopic artificial atoms and molecules are described, and the rules governing their morphologies outlined.

  2. A review of volcanic ash aggregation

    NASA Astrophysics Data System (ADS)

    Brown, R. J.; Bonadonna, C.; Durant, A. J.

    2012-01-01

    Most volcanic ash particles with diameters <63 μm settle from eruption clouds as particle aggregates that cumulatively have larger sizes, lower densities, and higher terminal fall velocities than individual constituent particles. Particle aggregation reduces the atmospheric residence time of fine ash, which results in a proportional increase in fine ash fallout within 10-100 s km from the volcano and a reduction in airborne fine ash mass concentrations 1000 s km from the volcano. Aggregate characteristics vary with distance from the volcano: proximal aggregates are typically larger (up to cm size) with concentric structures, while distal aggregates are typically smaller (sub-millimetre size). Particles comprising ash aggregates are bound through hydro-bonds (liquid and ice water) and electrostatic forces, and the rate of particle aggregation correlates with cloud liquid water availability. Eruption source parameters (including initial particle size distribution, erupted mass, eruption column height, cloud water content and temperature) and the eruption plume temperature lapse rate, coupled with the environmental parameters, determines the type and spatiotemporal distribution of aggregates. Field studies, lab experiments and modelling investigations have already provided important insights on the process of particle aggregation. However, new integrated observations that combine remote sensing studies of ash clouds with field measurement and sampling, and lab experiments are required to fill current gaps in knowledge surrounding the theory of ash aggregate formation.

  3. Aggregation-induced reversal of transport distances of soil organic matter: are our balances correct?

    NASA Astrophysics Data System (ADS)

    Hu, Yaxian; Kuhn, Nikolaus

    2014-05-01

    The effect of soil erosion on global carbon cycling, especially as a source or sink of green-house gases (GHGs), is the subject of intense debate. The controversy arises mostly from the lack of information on the fate of eroded soil organic carbon (SOC) as it moves from the site of erosion to the site of longer-term deposition. This requires improved understanding the transport distances of eroded SOC, which is principally related to the settling velocities of sediment fractions that carry the eroded SOC. For aggregated soils, settling velocities are affected by their actual aggregate size rather than the mineral grain size distribution. Aggregate stability is, in turn, strongly influenced by soil organic matter. This study aims at identifying the effect of aggregation on the transport distances of eroded SOC and its susceptibility to mineralization after transport and deposition. A rainfall simulation was carried out on a silty loam soil. The eroded sediments were fractionated by a settling tube apparatus into six different size classes according to their settling velocities and likely transport distances. Weight, SOC concentration and instantaneous respiration rates of the fractions of the six classes were measured. Our results show that: 1) 41% of the eroded SOC was transported with coarse aggregates that would be likely re-distributed across landscapes; 2) erosion was prone to accelerate the mineralization of eroded organic carbon immediately after erosion, compared to undisturbed aggregates; 3) erosion might make a higher contribution to atmospheric CO2 than the estimation made without considering the effects of aggregation and extra SOC mineralization during transport.

  4. Morphological diagram of diffusion driven aggregate growth in plane: Competition of anisotropy and adhesion

    NASA Astrophysics Data System (ADS)

    Menshutin, A. Yu.; Shchur, L. N.

    2011-09-01

    Two-dimensional structures grown with Witten and Sander algorithm are investigated. We analyze clusters grown off-lattice and clusters grown with antenna method with N=3,4,5,6,7 and 8 allowed growth directions. With the help of variable probe particles technique we measure fractal dimension of such clusters D(N) as a function of their size N. We propose that in the thermodynamic limit of infinite cluster size the aggregates grown with high degree of anisotropy ( N=3,4,5) tend to have fractal dimension D equal to 3/2, while off-lattice aggregates and aggregates with lower anisotropy ( N>6) have D≈1.710. Noise-reduction procedure results in the change of universality class for DLA. For high enough noise-reduction value clusters with N⩾6 have fractal dimension going to 3/2 when N→∞.

  5. Aggregate breakdown of nanoparticulate titania

    NASA Astrophysics Data System (ADS)

    Venugopal, Navin

    Six nanosized titanium dioxide powders synthesized from a sulfate process were investigated. The targeted end-use of this powder was for a de-NOx catalyst honeycomb monolith. Alteration of synthesis parameters had resulted principally in differences in soluble ion level and specific surface area of the powders. The goal of this investigation was to understand the role of synthesis parameters in the aggregation behavior of these powders. Investigation via scanning electron microscopy of the powders revealed three different aggregation iterations at specific length scales. Secondary and higher order aggregate strength was investigated via oscillatory stress rheometry as a means of simulating shear conditions encountered during extrusion. G' and G'' were measured as a function of the applied oscillatory stress. Oscillatory rheometry indicated a strong variation as a function of the sulfate level of the particles in the viscoelastic yield strengths. Powder yield stresses ranged from 3.0 Pa to 24.0 Pa of oscillatory stress. Compaction curves to 750 MPa found strong similarities in extrapolated yield point of stage I and II compaction for each of the powders (at approximately 500 MPa) suggesting that the variation in sulfate was greatest above the primary aggregate level. Scanning electron microscopy of samples at different states of shear in oscillatory rheometry confirmed the variation in the linear elastic region and the viscous flow regime. A technique of this investigation was to approach aggregation via a novel perspective: aggregates are distinguished as being loose open structures that are highly disordered and stochastic in nature. The methodology used was to investigate the shear stresses required to rupture the various aggregation stages encountered and investigate the attempt to realign the now free-flowing constituents comprising the aggregate into a denser configuration. Mercury porosimetry was utilized to measure the pore size of the compact resulting from

  6. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size.

  7. Convex aggregative modelling of infinite memory nonlinear systems

    NASA Astrophysics Data System (ADS)

    Wachel, Paweł

    2016-08-01

    The convex aggregation technique is applied for modelling general class of nonlinear systems with unknown structure and infinite memory. The finite sample size properties of the algorithm are formally established and compared to the standard least-squares counterpart of the method. The proposed algorithm demonstrates its advantages when the a-priori knowledge and the measurement data are both scarce, that is, when the information about the actual system structure is unknown or uncertain and the measurement set is small and disturbed by a noise. Numerical experiments illustrate application and practical benefits of the method for various nonlinear systems.

  8. What favors convective aggregation and why?

    NASA Astrophysics Data System (ADS)

    Muller, Caroline; Bony, Sandrine

    2015-07-01

    The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self-aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self-aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a "radiative aggregation." In that case, sufficient spatial variability of radiative cooling rates yields a low-level circulation, which induces the upgradient energy transport and radiative-convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak ("moisture-memory aggregation"), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self-aggregation to various parameters, including resolution or domain size.

  9. Fractal dimension of soil aggregates as an index of soil erodibility

    NASA Astrophysics Data System (ADS)

    Ahmadi, Abbas; Neyshabouri, Mohammad-Reza; Rouhipour, Hassan; Asadi, Hossein

    2011-04-01

    SummaryAggregate stability is an influential factor governing soil erodibility. The fractal dimension of soil aggregates has been related to their size distributions and stabilities. Several fractal models have been proposed for estimating fractal dimension of soil aggregates. This study was conducted to investigate how closely the soil interrill erodibility factor in WEPP model can be correlated to and predicted from soil aggregate size distribution or from their fractal dimensions. Samples from 36 soil series with contrasting properties were collected from northwest of Iran. The fractal dimensions of soil aggregates were calculated from Rieu and Sposito ( D n), Tyler and Wheatcraft ( D mT), and Young and Crawford ( D mY) models using aggregate size distribution (ASD) data. A rainfall simulator with drainable tilting flume (1 × 0.5 m) at slope of 9% was employed and total interrill erosion ( TIE), total splashed soil ( TS) and interrill erodibility factor ( K i) were calculated for 20, 37, and 47 mm h -1 rainfall intensities. Results showed that both D n and D mT estimated from aggregate wet-sieving data characterized ASD of the examined soils and significantly ( p < 0.01) correlated to TS, TIE and K i. Values of D n and D mT estimated from dry-sieving data only correlated to TS but not to TIE and K i. Using air-dried aggregates of 4.75-8 mm size range, instead of aggregates <4.75 mm, in wet-sieving was better for estimating D n as an index for the predication of TIE, TS and K i. Correction of ASD for the particle fraction greater than lower sieve mesh size in each size class decreased the correlation coefficient between TIE, TS or K i and D n or D mT. The values of D mY were not correlated to TS, TIE and K i. The correlation coefficient TIE and K i with D n and D mT derived from wet-sieving data, were higher than those with wet-aggregate stability (WAS), mean weight diameter (MWD) and geometric mean diameter (GMD), implying that D n and D mT may be better

  10. Taurine and platelet aggregation

    SciTech Connect

    Nauss-Karol, C.; VanderWende, C.; Gaut, Z.N.

    1986-03-01

    Taurine is a putative neurotransmitter or neuromodulator. The endogenous taurine concentration in human platelets, determined by amino acid analysis, is 15 ..mu..M/g. In spite of this high level, taurine is actively accumulated. Uptake is saturable, Na/sup +/ and temperature dependent, and suppressed by metabolic inhibitors, structural analogues, and several classes of centrally active substances. High, medium and low affinity transport processes have been characterized, and the platelet may represent a model system for taurine transport in the CNS. When platelets were incubated with /sup 14/C-taurine for 30 minutes, then resuspended in fresh medium and reincubated for one hour, essentially all of the taurine was retained within the cells. Taurine, at concentrations ranging from 10-1000 ..mu..M, had no effect on platelet aggregation induced by ADP or epinephrine. However, taurine may have a role in platelet aggregation since 35-39% of the taurine taken up by human platelets appears to be secreted during the release reaction induced by low concentrations of either epinephrine or ADP, respectively. This release phenomenon would imply that part of the taurine taken up is stored directly in the dense bodies of the platelet.

  11. Ash Aggregates in Proximal Settings

    NASA Astrophysics Data System (ADS)

    Porritt, L. A.; Russell, K.

    2012-12-01

    early pyroclastic phase of the formation of Kima'Kho, a tuya in northern B.C., Canada produced a subaqueous pyroclastic cone which became emergent during the latter stages of formation. Armoured lapilli are pervasive within the emergent upper third of the sequence. No other types of ash aggregates have been observed. Petrographic and textural analysis of the armoured lapilli shows them to comprise a central 2-30 mm-sized, juvenile, vesiculated pyroclast, concentrically coated by mm-scale layers of 10-250 μm sized ash particles. At Kima'Kho, the armoured lapilli are shown to be a direct indicator of fallout from a sustained plume attended by concomitant production of pyroclastic density currents. The size and internal structure of the armoured lapilli provide constraints on the nature of the initial explosive phase of eruption at Kima'Kho. Their proximity to the vent also indicates rapid aggregation within the eruption plume. Within both sequences rapid aggregation of ash particles occurred in proximity to the vent. However, the conditions were substantially different leading to the production of armoured lapilli (no accretionary lapilli) at Kima'Kho and diverse ash aggregates but no armoured lapilli at A418. Here we investigate vent-proximal ash aggregation and the specific conditions which lead to the formation of coated ash pellets and armoured lapilli.

  12. Does lake size matter? Combining morphology and process modeling to examine the contribution of lake classes to population-scale processes

    USGS Publications Warehouse

    Winslow, Luke A.; Read, Jordan S.; Hanson, Paul C.; Stanley, Emily H.

    2014-01-01

    With lake abundances in the thousands to millions, creating an intuitive understanding of the distribution of morphology and processes in lakes is challenging. To improve researchers’ understanding of large-scale lake processes, we developed a parsimonious mathematical model based on the Pareto distribution to describe the distribution of lake morphology (area, perimeter and volume). While debate continues over which mathematical representation best fits any one distribution of lake morphometric characteristics, we recognize the need for a simple, flexible model to advance understanding of how the interaction between morphometry and function dictates scaling across large populations of lakes. These models make clear the relative contribution of lakes to the total amount of lake surface area, volume, and perimeter. They also highlight the critical thresholds at which total perimeter, area and volume would be evenly distributed across lake size-classes have Pareto slopes of 0.63, 1 and 1.12, respectively. These models of morphology can be used in combination with models of process to create overarching “lake population” level models of process. To illustrate this potential, we combine the model of surface area distribution with a model of carbon mass accumulation rate. We found that even if smaller lakes contribute relatively less to total surface area than larger lakes, the increasing carbon accumulation rate with decreasing lake size is strong enough to bias the distribution of carbon mass accumulation towards smaller lakes. This analytical framework provides a relatively simple approach to upscaling morphology and process that is easily generalizable to other ecosystem processes.

  13. Stoichiometry and Physical Chemistry of Promiscuous Aggregate-Based Inhibitors

    PubMed Central

    Coan, Kristin E. D.

    2009-01-01

    Many false positives in early drug discovery owe to nonspecific inhibition by colloid-like aggregates of organic molecules. Despite their prevalence, little is known about aggregate concentration, structure, or dynamic equilibrium; the binding mechanism, stoichiometry with, and affinity for enzymes remain uncertain. To investigate the elementary question of concentration, we counted aggregate particles using flow cytometry. For seven aggregate-forming molecules, aggregates were not observed until the concentration of monomer crossed a threshold, indicating a “critical aggregation concentration” (CAC). Above the CAC, aggregate count increased linearly with added organic material, while the particles dispersed when diluted below the CAC. The concentration of monomeric organic molecule is constant above the CAC, as is the size of the aggregate particles. For two compounds that form large aggregates, nicardipine and miconazole, we measured particle numbers directly by flow cytometry, determining that the aggregate concentration just above the CAC ranged from 5 to 30 fM. By correlating inhibition of an enzyme with aggregate count for these two drugs, we determined that the stoichiometry of binding is about 10 000 enzyme molecules per aggregate particle. Using measured volumes for nicardipine and miconazole aggregate particles (2.1 × 1011 and 4.7 × 1010 Å3, respectively), computed monomer volumes, and the observation that past the CAC all additional monomer forms aggregate particles, we find that aggregates are densely packed particles. Finally, given their size and enzyme stoichiometry, all sequestered enzyme can be comfortably accommodated on the surface of the aggregate. PMID:18588298

  14. Novel insights into amylin aggregation

    PubMed Central

    Pillay, Karen; Govender, Patrick

    2014-01-01

    Amylin is a peptide that aggregates into species that are toxic to pancreatic beta cells, leading to type II diabetes. This study has for the first time quantified amylin association and dissociation kinetics (association constant (ka) = 28.7 ± 5.1 L mol−1 s−1 and dissociation constant (kd) = 2.8 ± 0.6 ×10−4 s−1) using surface plasmon resonance (SPR). Thus far, techniques used for the sizing of amylin aggregates do not cater for the real-time monitoring of unconstrained amylin in solution. In this regard we evaluated recently innovated nanoparticle tracking analysis (NTA). In addition, both SPR and NTA were used to study the effect of previously synthesized amylin derivatives on amylin aggregation and to evaluate their potential as a cell-free system for screening potential inhibitors of amylin-mediated cytotoxicity. Results obtained from NTA highlighted a predominance of 100–300 nm amylin aggregates and correlation to previously published cytotoxicity results suggests the toxic species of amylin to be 200–300 nm in size. The results seem to indicate that NTA has potential as a new technique to monitor the aggregation potential of amyloid peptides in solution and also to screen potential inhibitors of amylin-mediated cytotoxicity. PMID:26019498

  15. Can intra-aggregate pore structures affect the aggregate's effectiveness in protecting carbon?

    SciTech Connect

    Ananyeva, K; Wang, W; Smucker, A J.M.; Rivers, M L; Kravchenko, A N

    2012-11-15

    Aggregates are known to provide physical protection to soil organic matter shielding it from rapid decomposition. Spatial arrangement and size distribution of intra-aggregate pores play an important role in this process. This study examined relationships between intra-aggregate pores measured using X-ray computed micro-tomography images and concentrations of total C in 4–6 mm macro-aggregates from two contrasting land use and management practices, namely, conventionally tilled and managed row crop agricultural system (CT) and native succession vegetation converted from tilled agricultural land in 1989 (NS). Previous analyses of these aggregates indicated that small (<15 μm) and large (>100 μm) pores prevail in NS aggregates while medium (30–90 μm) pores are more abundant in CT aggregates (Kravchenko et al., 2011; Wang et al., 2012). We hypothesized that these differences in pore size distributions affect the ability of macro-aggregates to protect C. The results of this study supported this hypothesis. Consistent with greater heterogeneity of pore distributions within NS aggregates we observed higher total C and greater intra-aggregate C variability in NS as compared with CT aggregates. Total C concentrations and intra-aggregate C standard deviations were negatively correlated with fractions of medium sized pores, indicating that presence of such pores was associated with lower but more homogeneously distributed total C. While total C was positively correlated with presence of small and large pores. The results suggest that because of their pore structure NS macro-aggregates provide more effective physical protection to C than CT aggregates.

  16. Bouncing behavior of microscopic dust aggregates

    NASA Astrophysics Data System (ADS)

    Seizinger, A.; Kley, W.

    2013-03-01

    Context. Bouncing collisions of dust aggregates within the protoplanetary disk may have a significant impact on the growth process of planetesimals. Yet, the conditions that result in bouncing are not very well understood. Existing simulations studying the bouncing behavior used aggregates with an artificial, very regular internal structure. Aims: Here, we study the bouncing behavior of sub-mm dust aggregates that are constructed applying different sample preparation methods. We analyze how the internal structure of the aggregate alters the collisional outcome and we determine the influence of aggregate size, porosity, collision velocity, and impact parameter. Methods: We use molecular dynamics simulations where the individual aggregates are treated as spheres that are made up of several hundred thousand individual monomers. The simulations are run on graphic cards (GPUs). Results: Statistical bulk properties and thus bouncing behavior of sub-mm dust aggregates depend heavily on the preparation method. In particular, there is no unique relation between the average volume filling factor and the coordination number of the aggregate. Realistic aggregates bounce only if their volume filling factor exceeds 0.5 and collision velocities are below 0.1 ms-1. Conclusions: For dust particles in the protoplanetary nebula we suggest that the bouncing barrier may not be such a strong handicap in the growth phase of dust agglomerates, at least in the size range of ≈100 μm.

  17. Acetylcholinesterase triggers the aggregation of PrP 106-126

    SciTech Connect

    Pera, M.; Roman, S.; Ratia, M.; Camps, P.; Munoz-Torrero, D.; Colombo, L.; Manzoni, C.; Salmona, M.; Badia, A.; Clos, M.V. . E-mail: Victoria.Clos@uab.es

    2006-07-21

    Acetylcholinesterase (AChE), a senile plaque component, promotes amyloid-{beta}-protein (A{beta}) fibril formation in vitro. The presence of prion protein (PrP) in Alzheimer's disease (AD) senile plaques prompted us to assess if AChE could trigger the PrP peptides aggregation as well. Consequently, the efficacy of AChE on the PrP peptide spanning-residues 106-126 aggregation containing a coumarin fluorescence probe (coumarin-PrP 106-126) was studied. Kinetics of coumarin-PrP 106-126 aggregation showed a significant increase of maximum size of aggregates (MSA), which was dependent on AChE concentration. AChE-PrP 106-126 aggregates showed the tinctorial and optical amyloid properties as determined by polarized light and electronic microscopy analysis. A remarkable inhibition of MSA was obtained with propidium iodide, suggesting that AChE triggers PrP 106-126 and A{beta} aggregation through a similar mechanism. Huprines (AChE inhibitors) also significantly decreased MSA induced by AChE as well, unveiling the potential interest for some AChE inhibitors as a novel class of potential anti-prion drugs.

  18. CHARGING OF AGGREGATE GRAINS IN ASTROPHYSICAL ENVIRONMENTS

    SciTech Connect

    Ma, Qianyu; Matthews, Lorin S.; Hyde, Truell W.; Land, Victor

    2013-02-15

    The charging of dust grains in astrophysical environments has been investigated with the assumption that these grains are homogeneous spheres. However, there is evidence which suggests that many grains in astrophysical environments are irregularly shaped aggregates. Recent studies have shown that aggregates acquire higher charge-to-mass ratios due to their complex structures, which in turn may alter their subsequent dynamics and evolution. In this paper, the charging of aggregates is examined including secondary electron emission and photoemission in addition to primary plasma currents. The results show that the equilibrium charge on aggregates can differ markedly from spherical grains with the same mass, but that the charge can be estimated for a given environment based on structural characteristics of the grain. The 'small particle effect' due to secondary electron emission is also important for de terming the charge of micron-sized aggregates consisting of nano-sized particles.

  19. Equilibrium structure of ferrofluid aggregates

    SciTech Connect

    Yoon, Mina; Tomanek, David

    2010-01-01

    We study the equilibrium structure of large but finite aggregates of magnetic dipoles, representing a colloidal suspension of magnetite particles in a ferrofluid. With increasing system size, the structural motif evolves from chains and rings to multi-chain and multi-ring assemblies. Very large systems form single- and multi-wall coils, tubes and scrolls. These structural changes result from a competition between various energy terms, which can be approximated analytically within a continuum model. We also study the effect of external parameters such as magnetic field on the relative stability of these structures. Our results may give insight into experimental data obtained during solidification of ferrofluid aggregates at temperatures where thermal fluctuations become negligible in comparison to inter-particle interactions. These data may also help to experimentally control the aggregation of magnetic particles.

  20. What the Research Says about Class Size, Professional Development, and Recruitment, Induction, and Retention of Highly Qualified Teachers: A Compendium of the Evidence on Title II, Part A, Program-Funded Strategies

    ERIC Educational Resources Information Center

    Krasnoff, Basha

    2015-01-01

    States and districts have the flexibility to creatively use Title II, Part A funds to address teacher quality issues. Currently, three strategies predominate--class size reduction, professional development, and recruitment, induction, and retention of highly qualified teachers. Each strategy is implemented with the intention of improving teaching…

  1. Aggregation of ice crystals in cirrus

    NASA Technical Reports Server (NTRS)

    Kajikawa, Masahiro; Heymsfield, Andrew J.

    1989-01-01

    Results are given from analysis of the aggregation of thick plate, columnar, and bullet rosette ice crystals in cirrus. Data were obtained from PMS 2D-C images, oil coated slides, and aircraft meteorological measurements. Crystal size ranged from 100 to 900 microns in temperatures from -30 to -45 C. The results indicate that the ratio of the sizes of aggregating crystals and the difference of their terminal velocities are important in aggregation. The collection efficiency was calculated for the thick plate crystals from the same data.

  2. Impact of Particle Aggregation on Nanoparticle Reactivity

    NASA Astrophysics Data System (ADS)

    Jassby, David

    2011-12-01

    The prevalence of nanoparticles in the environment is expected to grow in the coming years due to their increasing pervasiveness in consumer and industrial applications. Once released into the environment, nanoparticles encounter conditions of pH, salinity, UV light, and other solution conditions that may alter their surface characteristics and lead to aggregation. The unique properties that make nanoparticles desirable are a direct consequence of their size and increased surface area. Therefore, it is critical to recognize how aggregation alters the reactive properties of nanomaterials, if we wish to understand how these properties are going to behave once released into the environment. The size and structure of nanoparticle aggregates depend on surrounding conditions, including hydrodynamic ones. Depending on these conditions, aggregates can be large or small, tightly packed or loosely bound. Characterizing and measuring these changes to aggregate morphology is important to understanding the impact of aggregation on nanoparticle reactive properties. Examples of decreased reactivity due to aggregation include the case where tightly packed aggregates have fewer available surface sites compared to loosely packed ones; also, photocatalytic particles embedded in the center of large aggregates will experience less light when compared to particles embedded in small aggregates. However, aggregation also results in an increase in solid-solid interfaces between nanoparticles. This can result in increased energy transfer between neighboring particles, surface passivation, and altered surface tension. These phenomena can lead to an increase in reactivity. The goal of this thesis is to examine the impacts of aggregation on the reactivity of a select group of nanomaterials. Additionally, we examined how aggregation impacts the removal efficiency of fullerene nanoparticles using membrane filtration. The materials we selected to study include ZnS---a metal chalcogenide

  3. When One-Size Methods Class Doesn't Fit All: A Self-Study of Teaching Traditional and Alternative Licensure Students Together

    ERIC Educational Resources Information Center

    Journell, Wayne; Webb, Angela W.

    2013-01-01

    This article uses a narrative approach to start a dialogue about the challenges of teaching blended methods classes that contain traditional and alternative licensure students. Many alternative licensure students enter their methods classes as lateral-entry teachers who must balance their licensure requirements with the demands associated with…

  4. A comparison of metropolitan and non-metropolitan employment characteristics: Indications of the size of non-metropolitan mobile communication services user classes

    NASA Technical Reports Server (NTRS)

    Wilcox, R. E.

    1985-01-01

    The similarities and differences between areas inside and outside U.S. metropolitan areas were evaluated in terms of their commercial/industrial and government employment characteristics. The comparison focuses on the levels, shares, and composition of employment in the commercial/industrial and government sectors that represent potential classes of land mobile communications users. The major findings of the analysis are as follows: (1) non-metropolitan commercial/industrial user classes of land mobile communication services exist in significant numbers; (2) the compositions of non-metropolitan and metropolitan commercial/industrial user classes of land mobile communication services closely resemble each other; (3) non-metropolitan areas have significant levels of the government user classes that represent potential markets for land mobile communication services; and (4) non-metropolitan local governments have a significantly larger proportion of their employment in the primary user classes of private land mobile radio service than do metropolitan local governments.

  5. Enhancing Therapeutic Efficacy through Designed Aggregation of Nanoparticles

    PubMed Central

    Sadhukha, Tanmoy; Wiedmann, Timothy Scott; Panyama, Jayanth

    2015-01-01

    Particle size is a key determinant of biological performance of sub-micron size delivery systems. Previous studies investigating the effect of particle size have primarily focused on well-dispersed nanoparticles. However, inorganic nanoparticles are prone to aggregation in biological environments. In our studies, we examined the consequence of aggregation on superparamagnetic iron oxide (SPIO) nanoparticle-induced magnetic hyperthermia. Here we show that the extent and mechanism of hyperthermia-induced cell kill is highly dependent on the aggregation state of SPIO nanoparticles. Well-dispersed nanoparticles induced apoptosis, similar to that observed with conventional hyperthermia. Sub-micron size aggregates, on the other hand, induced temperature-dependent autophagy through generation of oxidative stress. Micron size aggregates caused rapid membrane damage, resulting in acute cell kill. Overall, this work highlights the potential for developing highly effective anticancer therapeutics through designed aggregation of nano delivery systems. PMID:24947232

  6. Enhancing therapeutic efficacy through designed aggregation of nanoparticles.

    PubMed

    Sadhukha, Tanmoy; Wiedmann, Timothy S; Panyam, Jayanth

    2014-09-01

    Particle size is a key determinant of biological performance of sub-micron size delivery systems. Previous studies investigating the effect of particle size have primarily focused on well-dispersed nanoparticles. However, inorganic nanoparticles are prone to aggregation in biological environments. In our studies, we examined the consequence of aggregation on superparamagnetic iron oxide (SPIO) nanoparticle-induced magnetic hyperthermia. Here we show that the extent and mechanism of hyperthermia-induced cell kill is highly dependent on the aggregation state of SPIO nanoparticles. Well-dispersed nanoparticles induced apoptosis, similar to that observed with conventional hyperthermia. Sub-micron size aggregates, on the other hand, induced temperature-dependent autophagy through generation of oxidative stress. Micron size aggregates caused rapid membrane damage, resulting in acute cell kill. Overall, this work highlights the potential for developing highly effective anticancer therapeutics through designed aggregation of nano delivery systems.

  7. Thermodynamics of Protein Aggregation

    NASA Astrophysics Data System (ADS)

    Osborne, Kenneth L.; Barz, Bogdan; Bachmann, Michael; Strodel, Birgit

    Amyloid protein aggregation characterizes many neurodegenerative disorders, including Alzheimer's, Parkinson's, and Creutz- feldt-Jakob disease. Evidence suggests that amyloid aggregates may share similar aggregation pathways, implying simulation of full-length amyloid proteins is not necessary for understanding amyloid formation. In this study we simulate GNNQQNY, the N-terminal prion-determining domain of the yeast protein Sup35 to investigate the thermodynamics of structural transitions during aggregation. We use a coarse-grained model with replica-exchange molecular dynamics to investigate the association of 3-, 6-, and 12-chain GNNQQNY systems and we determine the aggregation pathway by studying aggregation states of GN- NQQNY. We find that the aggregation of the hydrophilic GNNQQNY sequence is mainly driven by H-bond formation, leading to the formation of /3-sheets from the very beginning of the assembly process. Condensation (aggregation) and ordering take place simultaneously, which is underpinned by the occurrence of a single heat capacity peak only.

  8. Succession of Protists on Estuarine Aggregates.

    PubMed

    Wörner; Zimmerman-Timm; Kausch

    2000-08-01

    Colonization by and succession of bacteria and bacterivorous protists on laboratory-made aggregates were determined over a period of 14 days during winter and spring in 1997. Aggregates were generated from natural water from the limnetic zone of the Elbe Estuary using a tilting tube roller system. Within 1 h after the beginning of the experiments, macroaggregates started to form. Aggregates reached a maximum size of 1 mm with a tendency toward large sizes at the end of the experiment after the 10th day. On the first day, high bacterial densities of more than 10(9) cells ml(-1) were detected within the aggregates. The abundances of flagellates and ciliates within aggregates were also two or three orders of magnitude higher than in the surrounding water. Densities of aggregate associated organisms are comparable to those occuring in sediments. The first protistan colonizers on the aggregates were small heterotrophic flagellates, such as choanoflagellates and small euglenids. Later, beginning on the 4th day, small sarcodines and ciliates became abundant. The most abundant ciliates associated with aggregates were small species of the Hypotrichia, Cyrtophorida, and Hymenostomata. After 9 days, large omnivorous and carnivorous ciliates, such as large members of the Hypotrichia and the Pleurostomatida, occurred. In spring, large heterotrophic flagellates and amebae also appeared at this time. These findings indicated the existence of a succession of protists on newly formed aggregates and a microbial food net within the aggregates based on bacterial production. Additionally, most of the species observed during this study were adapted for living on surfaces. In natural environments they are more common in benthic than in pelagic environments. For them, aggregates are havens in the water column comparable to sediment communities.

  9. Laser light scattering as a probe of fractal colloid aggregates

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Lin, M. Y.

    1989-01-01

    The extensive use of laser light scattering is reviewed, both static and dynamic, in the study of colloid aggregation. Static light scattering enables the study of the fractal structure of the aggregates, while dynamic light scattering enables the study of aggregation kinetics. In addition, both techniques can be combined to demonstrate the universality of the aggregation process. Colloidal aggregates are now well understood and therefore represent an excellent experimental system to use in the study of the physical properties of fractal objects. However, the ultimate size of fractal aggregates is fundamentally limited by gravitational acceleration which will destroy the fractal structure as the size of the aggregates increases. This represents a great opportunity for spaceborne experimentation, where the reduced g will enable the growth of fractal structures of sufficient size for many interesting studies of their physical properties.

  10. Aggregate structure, morphology and the effect of aggregation mechanisms on viscosity at elevated protein concentrations.

    PubMed

    Barnett, Gregory V; Qi, Wei; Amin, Samiul; Neil Lewis, E; Roberts, Christopher J

    2015-12-01

    Non-native aggregation is a common issue in a number of degenerative diseases and during manufacturing of protein-based therapeutics. There is a growing interest to monitor protein stability at intermediate to high protein concentrations, which are required for therapeutic dosing of subcutaneous injections. An understanding of the impact of protein structural changes and interactions on the protein aggregation mechanisms and resulting aggregate size and morphology may lead to improved strategies to reduce aggregation and solution viscosity. This report investigates non-native aggregation of a model protein, α-chymotrypsinogen, under accelerated conditions at elevated protein concentrations. Far-UV circular dichroism and Raman scattering show structural changes during aggregation. Size exclusion chromatography and laser light scattering are used to monitor the progression of aggregate growth and monomer loss. Monomer loss is concomitant with increased β-sheet structures as monomers are added to aggregates, which illustrate a transition from a native monomeric state to an aggregate state. Aggregates grow predominantly through monomer-addition, resulting in a semi-flexible polymer morphology. Analysis of aggregation growth kinetics shows that pH strongly affects the characteristic timescales for nucleation (τn) and growth (τg), while the initial protein concentration has only minor effects on τn or τg. Low-shear viscosity measurements follow a common scaling relationship between average aggregate molecular weight (Mw(agg)) and concentration (σ), which is consistent with semi-dilute polymer-solution theory. The results establish a link between aggregate growth mechanisms, which couple Mw(agg) and σ, to increases in solution viscosity even at these intermediate protein concentrations (less than 3w/v %).

  11. Flow Partitioning in Fully Saturated Soil Aggregates

    SciTech Connect

    Yang, Xiaofan; Richmond, Marshall C.; Scheibe, Timothy D.; Perkins, William A.; Resat, Haluk

    2014-03-30

    Microbes play an important role in facilitating organic matter decomposition in soils, which is a major component of the global carbon cycle. Microbial dynamics are intimately coupled to environmental transport processes, which control access to labile organic matter and other nutrients that are needed for the growth and maintenance of microorganisms. Transport of soluble nutrients in the soil system is arguably most strongly impacted by preferential flow pathways in the soil. Since the physical structure of soils can be characterized as being formed from constituent micro aggregates which contain internal porosity, one pressing question is the partitioning of the flow among the “inter-aggregate” and “intra-aggregate” pores and how this may impact overall solute transport within heterogeneous soil structures. The answer to this question is particularly important in evaluating assumptions to be used in developing upscaled simulations based on highly-resolved mechanistic models. We constructed a number of diverse multi-aggregate structures with different packing ratios by stacking micro-aggregates containing internal pores and varying the size and shape of inter-aggregate pore spacing between them. We then performed pore-scale flow simulations using computational fluid dynamics methods to determine the flow patterns in these aggregate-of-aggregates structures and computed the partitioning of the flow through intra- and inter-aggregate pores as a function of the spacing between the aggregates. The results of these numerical experiments demonstrate that soluble nutrients are largely transported via flows through inter-aggregate pores. Although this result is consistent with intuition, we have also been able to quantify the relative flow capacity of the two domains under various conditions. For example, in our simulations, the flow capacity through the aggregates (intra-aggregate flow) was less than 2% of the total flow when the spacing between the aggregates

  12. Imbibition kinetics of spherical colloidal aggregates.

    PubMed

    Debacker, A; Makarchuk, S; Lootens, D; Hébraud, P

    2014-07-11

    The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by a wetting pure solvent is studied. Three successive regimes are observed. First, the imbibition proceeds by compressing the air inside the aggregate. Next, the solvent stops when the pressure of the compressed air is equal to the excess of capillary pressure at the meniscus of the wetting solvent in the porous aggregate. The interface is pinned and the aggregate slowly degases up to the point where the pressure of the entrapped air stops decreasing and is controlled by the capillary pressure. Finally, the imbibition starts again at a constant excess of pressure, smaller than the capillary pressure but larger than the one of the atmosphere. This last stage leads to the complete infiltration of the aggregate. PMID:25062241

  13. 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

  14. Dynamics of proteins aggregation. I. Universal scaling in unbounded media

    NASA Astrophysics Data System (ADS)

    Zheng, Size; Javidpour, Leili; Shing, Katherine S.; Sahimi, Muhammad

    2016-10-01

    It is well understood that in some cases proteins do not fold correctly and, depending on their environment, even properly-folded proteins change their conformation spontaneously, taking on a misfolded state that leads to protein aggregation and formation of large aggregates. An important factor that contributes to the aggregation is the interactions between the misfolded proteins. Depending on the aggregation environment, the aggregates may take on various shapes forming larger structures, such as protein plaques that are often toxic. Their deposition in tissues is a major contributing factor to many neuro-degenerative diseases, such as Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, and prion. This paper represents the first part in a series devoted to molecular simulation of protein aggregation. We use the PRIME, a meso-scale model of proteins, together with extensive discontinuous molecular dynamics simulation to study the aggregation process in an unbounded fluid system, as the first step toward MD simulation of the same phenomenon in crowded cellular environments. Various properties of the aggregates have been computed, including dynamic evolution of aggregate-size distribution, mean aggregate size, number of peptides that contribute to the formation of β sheets, number of various types of hydrogen bonds formed in the system, radius of gyration of the aggregates, and the aggregates' diffusivity. We show that many of such quantities follow dynamic scaling, similar to those for aggregation of colloidal clusters. In particular, at long times the mean aggregate size S(t) grows with time as, S(t) ˜ tz, where z is the dynamic exponent. To our knowledge, this is the first time that the qualitative similarity between aggregation of proteins and colloidal aggregates has been pointed out.

  15. Nanoscale Ionic Aggregate Morphology in Zwitterionic Copolymers

    NASA Astrophysics Data System (ADS)

    Choi, Jae-Hong; Huyck, Rebecca; Salas-de La Cruz, David; Long, Timothy E.; Winey, Karen I.

    2009-03-01

    The morphology of two different zwitterionic copolymers, poly(sulfobetaine methacrylate-ran-butyl acrylate), and poly(sulfobetaine methacrylamide-ran-butyl acrylate) are investigated as a function of the mol % content of SBMA (7 and 9 mol %) and SBMAm (6, 10 and 13 mol %), respectively. In both copolymers, X-ray scattering results show a new structure in the material arising from ionic aggregates. The sizes of the ionic aggregates are obtained through the scattering model. The sizes of the ionic aggregates increase as the ion content increases. The application of scanning transmission electron microscopy to the study of ionomer morphology has enabled direct, model-independent visualization of the ionic aggregates. The correlation between X-ray scattering results and the real space imaging for morphology of these zwitterionic copolymers will be presented.

  16. Silt-clay aggregates on Mars

    NASA Technical Reports Server (NTRS)

    Greeley, R.

    1979-01-01

    Viking observations suggest abundant silt and clay particles on Mars. It is proposed that some of these particles agglomerate to form sand size aggregates that are redeposited as sandlike features such as drifts and dunes. Although the binding for the aggregates could include salt cementation or other mechanisms, electrostatic bonding is considered to be a primary force holding the aggregates together. Various laboratory experiments conducted since the 19th century, and as reported here for simulated Martian conditions, show that both the magnitude and sign of electrical charges on windblown particles are functions of particle velocity, shape and composition, atmospheric pressure, atmospheric composition and other factors. Electrical charges have been measured for saltating particles in the wind tunnel and in the field, on the surfaces of sand dunes, and within dust clouds on earth. Similar, and perhaps even greater, charges are proposed to occur on Mars, which could form aggregates of silt and clay size particles

  17. Blood viscosity: influence of erythrocyte aggregation.

    PubMed

    Chien, S; Usami, S; Dellenback, R J; Gregersen, M I; Nanninga, L B; Guest, M M

    1967-08-18

    The addition of purified canine or bovine fibrinogen to suspensions of canine erythocytes in Ringer solution caused an increase in viscosity and the formation of aggregates of erythocytes. Both of these effects became increasingly pronounced as the fibrinogen concentration was raised, and they approached plateaus with 1 gram of fibrinogen per 100 milliliters. An increase in shear rate (or shear stress) reduced both the effect on viscosity and the aggregate size. The data suggest that fibrinogen causes an increase in blood viscosity and a departure from Newtonian behavior by interacting with erythrocytes to form cell aggregates which can be dispersed by shear stress. PMID:17842794

  18. Meaningful Effect Sizes, Intra-Class Correlations, and Proportions of Variance Explained by Covariates for Planning 3 Level Cluster Randomized Experiments in Prevention Science

    ERIC Educational Resources Information Center

    Dong, Nianbo; Reinke, Wendy M.; Herman, Keith C.; Bradshaw, Catherine P.; Murray, Desiree W.

    2015-01-01

    Cluster randomized experiments are now widely used to examine intervention effects in prevention science. It is meaningful to use empirical benchmarks for interpreting effect size in prevention science. The effect size (i.e., the standardized mean difference, calculated by the difference of the means between the treatment and control groups,…

  19. 17 CFR Appendix F to Part 43 - Initial Appropriate Minimum Block Sizes by Asset Class for Block Trades and Large Notional Off...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... (ICE and NYMEX) 25,000 bbl. Cheese (CME) 400,000 lbs. Class III Milk (CME) NO BLOCKS. Cocoa (ICE and... lbs. Corn (CBOT) NO BLOCKS. bushels. Cotton No. 2 (ICE and NYMEX) 5,000,000 lbs. Distillers' Dried.... Light Sweet Crude Oil (NYMEX) 50,000 bbl. Live Cattle (CME) NO BLOCKS. Mid-Columbia Day-Ahead...

  20. Kinetics of Thermal Denaturation and Aggregation of Bovine Serum Albumin

    PubMed Central

    Borzova, Vera A.; Markossian, Kira A.; Chebotareva, Natalia A.; Kleymenov, Sergey Yu.; Poliansky, Nikolay B.; Muranov, Konstantin O.; Stein-Margolina, Vita A.; Shubin, Vladimir V.; Markov, Denis I.; Kurganov, Boris I.

    2016-01-01

    Thermal aggregation of bovine serum albumin (BSA) has been studied using dynamic light scattering, asymmetric flow field-flow fractionation and analytical ultracentrifugation. The studies were carried out at fixed temperatures (60°C, 65°C, 70°C and 80°C) in 0.1 M phosphate buffer, pH 7.0, at BSA concentration of 1 mg/ml. Thermal denaturation of the protein was studied by differential scanning calorimetry. Analysis of the experimental data shows that at 65°C the stage of protein unfolding and individual stages of protein aggregation are markedly separated in time. This circumstance allowed us to propose the following mechanism of thermal aggregation of BSA. Protein unfolding results in the formation of two forms of the non-native protein with different propensity to aggregation. One of the forms (highly reactive unfolded form, Uhr) is characterized by a high rate of aggregation. Aggregation of Uhr leads to the formation of primary aggregates with the hydrodynamic radius (Rh,1) of 10.3 nm. The second form (low reactive unfolded form, Ulr) participates in the aggregation process by its attachment to the primary aggregates produced by the Uhr form and possesses ability for self-aggregation with formation of stable small-sized aggregates (Ast). At complete exhaustion of Ulr, secondary aggregates with the hydrodynamic radius (Rh,2) of 12.8 nm are formed. At 60°C the rates of unfolding and aggregation are commensurate, at 70°C the rates of formation of the primary and secondary aggregates are commensurate, at 80°C the registration of the initial stages of aggregation is complicated by formation of large-sized aggregates. PMID:27101281

  1. Effect of additives on protein aggregation.

    PubMed

    Hamada, Hiroyuki; Arakawa, Tsutomu; Shiraki, Kentaro

    2009-06-01

    This paper overviews solution additives that affect protein stability and aggregation during refolding, heating, and freezing processes. Solution additives are mainly grouped into two classes, i.e., protein denaturants and stabilizers. The former includes guanidine, urea, strong ionic detergents, and certain chaotropic salts; the latter includes certain amino acids, sugars, polyhydric alcohols, osmolytes, and kosmotropic salts. However, there are solution additives that are not unambiguously placed into these two classes, including arginine, certain divalent cation salts (e.g., MgCl(2)) and certain polyhydric alcohols (e.g., ethylene glycol). Certain non-ionic or non-detergent surfactants, ionic liquids, amino acid derivatives, polyamines, and certain amphiphilic polymers may belong to this class. They have marginal effects on protein structure and stability, but are able to disrupt protein interactions. Information on additives that do not catalyze chemical reactions nor affect protein functions helps us to design protein solutions for increased stability or reduced aggregation. PMID:19519415

  2. Biological framework for soil aggregation: Implications for ecological functions.

    NASA Astrophysics Data System (ADS)

    Ghezzehei, Teamrat; Or, Dani

    2016-04-01

    Soil aggregation is heuristically understood as agglomeration of primary particles bound together by biotic and abiotic cementing agents. The organization of aggregates is believed to be hierarchical in nature; whereby primary particles bond together to form secondary particles and subsequently merge to form larger aggregates. Soil aggregates are not permanent structures, they continuously change in response to internal and external forces and other drivers, including moisture, capillary pressure, temperature, biological activity, and human disturbances. Soil aggregation processes and the resulting functionality span multiple spatial and temporal scales. The intertwined biological and physical nature of soil aggregation, and the time scales involved precluded a universally applicable and quantifiable framework for characterizing the nature and function of soil aggregation. We introduce a biophysical framework of soil aggregation that considers the various modes and factors of the genesis, maturation and degradation of soil aggregates including wetting/drying cycles, soil mechanical processes, biological activity and the nature of primary soil particles. The framework attempts to disentangle mechanical (compaction and soil fragmentation) from in-situ biophysical aggregation and provides a consistent description of aggregate size, hierarchical organization, and life time. It also enables quantitative description of biotic and abiotic functions of soil aggregates including diffusion and storage of mass and energy as well as role of aggregates as hot spots of nutrient accumulation, biodiversity, and biogeochemical cycles.

  3. Reconsidering the mechanism of polyglutamine peptide aggregation.

    PubMed

    Lee, Christine C; Walters, Robert H; Murphy, Regina M

    2007-11-01

    There are at least nine neurodegenerative diseases associated with proteins that contain an unusually expanded polyglutamine domain, the best known of which is Huntington's disease. In all of these diseases, the mutant protein aggregates into neuronal inclusions; it is generally, although not universally, believed that protein aggregation is an underlying cause of the observed neuronal degeneration. In an effort to examine the role of polyglutamine in facilitating protein aggregation, investigators have used synthetic polyglutamine peptides as model systems. Analysis of kinetic data led to the conclusions that aggregation follows a simple nucleation-elongation mechanism characterized by a significant lag time, during which the peptide is monomeric, and that the nucleus is a monomer in a thermodynamically unfavorable conformation [Chen, S. M., et al. (2002) Proc. Natl. Acad. Sci. U.S.A. 99, 11884-11889]. We re-examined this hypothesis by measuring the aggregation kinetics of the polyglutamine peptide K2Q23K2, using sedimentation, static and dynamic light scattering, and size exclusion chromatography. Our data show that during the lag time in sedimentation kinetics, there is substantial organization of the peptide into soluble linear aggregates. These aggregates have no regular secondary structure as measured by circular dichroism but have particle dimensions and morphologies similar to those of mature insoluble aggregates. The soluble aggregates constitute approximately 30% of the total peptide mass, form rapidly, and continue to grow over a period of hours to days, eventually precipitating. Once insoluble aggregates form, loss of monomer from the solution phase continues. Our data support an assembly mechanism for polyglutamine peptide more complex than that previously proposed.

  4. Thermal Aggregation of Recombinant Protective Antigen: Aggregate Morphology and Growth Rate

    PubMed Central

    Belton, Daniel J.; Miller, Aline F.

    2013-01-01

    The thermal aggregation of the biopharmaceutical protein recombinant protective antigen (rPA) has been explored, and the associated kinetics and thermodynamic parameters have been extracted using optical and environmental scanning electron microscopies (ESEMs) and ultraviolet light scattering spectroscopy (UV-LSS). Visual observations and turbidity measurements provided an overall picture of the aggregation process, suggesting a two-step mechanism. Microscopy was used to examine the structure of aggregates, revealing an open morphology formed by the clustering of the microscopic aggregate particles. UV-LSS was used and developed to elucidate the growth rate of these particles, which formed in the first stage of the aggregation process. Their growth rate is observed to be high initially, before falling to converge on a final size that correlates with the ESEM data. The results suggest that the particle growth rate is limited by rPA monomer concentration, and by obtaining data over a range of incubation temperatures, an approach was developed to model the aggregation kinetics and extract the rate constants and the temperature dependence of aggregation. In doing so, we quantified the susceptibility of rPA aggregation under different temperature and environmental conditions and moreover demonstrated a novel use of UV spectrometry to monitor the particle aggregation quantitatively, in situ, in a nondestructive and time-resolved manner. PMID:23476645

  5. A comparison of 15 year old children with excellent occlusion and with crowding of the teeth, Angle Class I malocclusion, in respect of face size and shape and tooth size.

    PubMed

    Adams, C P

    1982-01-01

    The biological conflict that manifests itself in crowding of the teeth in man has fascinated orthodontists for generations. Correlations between tooth size and tooth arrangement can be shown, but such correlations tend to leave much unexplained in practical terms. The present report presents data from a preliminary examination of face size and shape and tooth size in boys and girls of 15-16 years, of which 47 had excellently arranged teeth and 91 showed crowding. Measurements were taken from lateral and posteroanterior cephalometric X-ray films and from dental casts. The statistical test used was the standard student t-test. Girls' faces were found to be on average significantly smaller than boys' whether the teeth were well arranged or were crowded. The comparisons of face size and shape of boys and girls with well arranged teeth with the faces of those with crowded teeth was less definite in its outcome. Girls' total tooth substance was on average significantly smaller than boys' whether the teeth were well arranged or crowded. Boys and girls with crowded teeth had a larger mean total tooth size than boys and girls with well arranged teeth.

  6. Aggregations in Flatworms.

    ERIC Educational Resources Information Center

    Liffen, C. L.; Hunter, M.

    1980-01-01

    Described is a school project to investigate aggregations in flatworms which may be influenced by light intensity, temperature, and some form of chemical stimulus released by already aggregating flatworms. Such investigations could be adopted to suit many educational levels of science laboratory activities. (DS)

  7. An energy landscape approach to protein aggregation

    NASA Astrophysics Data System (ADS)

    Buell, Alexander; Knowles, Tuomas

    2012-02-01

    Protein aggregation into ordered fibrillar structures is the hallmark of a class of diseases, the most prominent examples of which are Alzheimer's and Parkinson's disease. Recent results (e.g. Baldwin et al. J. Am. Chem. Soc. 2011) suggest that the aggregated state of a protein is in many cases thermodynamically more stable than the soluble state. Therefore the solubility of proteins in a cellular context appears to be to a large extent under kinetic control. Here, we first present a conceptual framework for the description of protein aggregation ( see AK Buell et al., Phys. Rev. Lett. 2010) that is an extension to the generally accepted energy landscape model for protein folding. Then we apply this model to analyse and interpret a large set of experimental data on the kinetics of protein aggregation, acquired mainly with a novel biosensing approach (see TPJK Knowles et al, Proc. Nat. Acad. Sc. 2007). We show how for example the effect of sequence modifications on the kinetics and thermodynamics of human lysozyme aggregation can be understood and quantified (see AK Buell et al., J. Am. Chem. Soc. 2011). These results have important implications for therapeutic strategies against protein aggregation disorders, in this case lysozyme systemic amyloidosis.

  8. Identification of particle size classes inhibiting protozoan recovery from surface water samples via U.S. Environmental Protection Agency method 1623.

    PubMed

    Krometis, Leigh-Anne H; Characklis, Gregory W; Sobsey, Mark D

    2009-10-01

    Giardia species recovery by U.S. Environmental Protection Agency method 1,623 appears significantly impacted by a wide size range (2 to 30 microm) of particles in water and organic matter. Cryptosporidium species recovery seems negatively correlated only with smaller (2 to 10 microm), presumably inorganic particles. Results suggest constituents and mechanisms interfering with method performance may differ by protozoan type.

  9. [Theory and practice of electrospray crystallization in particle size reduction].

    PubMed

    Szunyogh, Tímea; Ambrus, Rita; Szabóné Révész, Piroska

    2015-01-01

    Nowdays, one of the most challenges for the researchers is the formulation of poorly water soluble drugs. Reduction of particle size of active agents to submicron range could result in a faster dissolution rate and higher bioavailability. Integration as crystallization process is an often used particle size decreasing technique. The aim of this study was to show the theoretical background and practical application of the electros pray crystallization as an innovative particle size decreasing technique. Our model drug was the niflumic acid (NIF), which belongs to the BCS Class II. After the optimization of the process parameters, the physico-chemical properties of the samples were characterized. Particle size and shape were visualized by scanning electron microscopy (SEM). Crystalline state of NIF and the samples were investigated using differential scanning calorimetry (DSC) and X-ray powder diffraction. Physico-chemical properties were determined using dissolution test from simulated media. The electrospray crytallization resulted in particle size reduction but the aggregation of nanonized NIF crystals (NIF-nano) could not avoid without excipient. Aggregates with poor secondary forces are suitable for production of the interactive physical mixture. It was found that NIF-nano could be well distributed on the surface of the mannitol as carrier and the Poloxamer R protected the NIF-nano crystals (320 nm)from aggregation. Consequently, the physical mixture resulted in product with higher polarity, better wettability and faster dissolution rate of NIF as raw NIF or NIF-nano.

  10. [Theory and practice of electrospray crystallization in particle size reduction].

    PubMed

    Szunyogh, Tímea; Ambrus, Rita; Szabóné Révész, Piroska

    2015-01-01

    Nowdays, one of the most challenges for the researchers is the formulation of poorly water soluble drugs. Reduction of particle size of active agents to submicron range could result in a faster dissolution rate and higher bioavailability. Integration as crystallization process is an often used particle size decreasing technique. The aim of this study was to show the theoretical background and practical application of the electros pray crystallization as an innovative particle size decreasing technique. Our model drug was the niflumic acid (NIF), which belongs to the BCS Class II. After the optimization of the process parameters, the physico-chemical properties of the samples were characterized. Particle size and shape were visualized by scanning electron microscopy (SEM). Crystalline state of NIF and the samples were investigated using differential scanning calorimetry (DSC) and X-ray powder diffraction. Physico-chemical properties were determined using dissolution test from simulated media. The electrospray crytallization resulted in particle size reduction but the aggregation of nanonized NIF crystals (NIF-nano) could not avoid without excipient. Aggregates with poor secondary forces are suitable for production of the interactive physical mixture. It was found that NIF-nano could be well distributed on the surface of the mannitol as carrier and the Poloxamer R protected the NIF-nano crystals (320 nm)from aggregation. Consequently, the physical mixture resulted in product with higher polarity, better wettability and faster dissolution rate of NIF as raw NIF or NIF-nano. PMID:26390735

  11. Diffusion-limited aggregation on curved surfaces

    NASA Astrophysics Data System (ADS)

    Choi, J.; Crowdy, D.; Bazant, M. Z.

    2010-08-01

    We develop a general theory of transport-limited aggregation phenomena occurring on curved surfaces, based on stochastic iterated conformal maps and conformal projections to the complex plane. To illustrate the theory, we use stereographic projections to simulate diffusion-limited aggregation (DLA) on surfaces of constant Gaussian curvature, including the sphere (K>0) and the pseudo-sphere (K<0), which approximate "bumps" and "saddles" in smooth surfaces, respectively. Although the curvature affects the global morphology of the aggregates, the fractal dimension (in the curved metric) is remarkably insensitive to curvature, as long as the particle size is much smaller than the radius of curvature. We conjecture that all aggregates grown by conformally invariant transport on curved surfaces have the same fractal dimension as DLA in the plane. Our simulations suggest, however, that the multifractal dimensions increase from hyperbolic (K<0) to elliptic (K>0) geometry, which we attribute to curvature-dependent screening of tip branching.

  12. "Racializing" Class

    ERIC Educational Resources Information Center

    Hatt-Echeverria, Beth; Urrieta, Luis, Jr.

    2003-01-01

    In an effort to explore how racial and class oppressions intersect, the authors use their autobiographical narratives to depict cultural and experiential continuity and discontinuity in growing up white working class versus Chicano working class. They specifically focus on "racializing class" due to the ways class is often used as a copout by…

  13. Ion-specific aggregation of hydrophobic particles.

    PubMed

    López-León, Teresa; Ortega-Vinuesa, Juan Luis; Bastos-González, Delfina

    2012-06-18

    This work shows that colloidal stability and aggregation kinetics of hydrophobic polystyrene (PS) nanospheres are extremely sensitive to the nature of the salt used to coagulate them. Three PS latices and four aggregating electrolytes, which all share the same cation (Na(+)) but have various anions located at different positions in the classical Hofmeister series depending on their kosmotropic or chaotropic character, are used. The present study focuses on analyzing different aggregating parameters, such as critical coagulation concentrations (CCC), cluster size distributions (CSD), initial kinetic constants K(11), and fractal dimensions of the aggregates d(f). While aggregation induced by SO(4)(2-) and Cl(-) behaved according to the predictions of the classical Derjaguin-Landau-Verwey-Overbeek theory, important discrepancies are found with NO(3)(-), which become dramatic when using SCN(-). These discrepancies among the anions were far more significant when they acted as counterions rather than as co-ions. While SO(4)(2-) and Cl(-) trigger fast diffusion-limited aggregation, SCN(-) gives rise to a stationary cluster size distribution in a few aggregation times when working with cationic PS particles. Clear differences are found among all analyzed parameters (CCC, CSD, K(11), and d(f)), and the experimental findings show that particles aggregate in potential wells whose depth is controlled by the chaotropic character of the anion. This paper presents new experimental evidence that may help to understand the microscopic origin of Hofmeister effects, as the observations are consistent with appealing theoretical models developed in the last few years. PMID:22556130

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  15. Kepler Mission: a Discovery-Class Mission Designed to Determine the Frequency of Earth-Size and Larger Planets Around Solar-Like Stars

    NASA Technical Reports Server (NTRS)

    Borucki, William; Koch, David; Lissauer, Jack; Basri, Gibor; Caldwell, John; Cochran, William; Dunham, Edward W.; Gilliland, Ronald; Caldwell, Douglas; Kondo, Yoji; DeVincenzi, Donald (Technical Monitor)

    2002-01-01

    The first step in discovering the extent of life in our galaxy is to determine the number of terrestrial planets in the habitable zone (HZ). The Kepler Mission is designed around a 0.95 in aperture Schmidt-type telescope with an array of 42 CCDs designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. The photometer is scheduled to be launched into heliocentric orbit in 2007. Measurements of the depth and repetition time of transits provide the size of the planet relative to the star and its orbital period. When combined with ground-based spectroscopy of these stars to fix the stellar parameters, the true planet radius and orbit scale, hence the position relative to the HZ are determined. These spectra are also used to discover the relationships between the characteristics of planets and the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. At the end of the four year mission, hundreds of terrestrial planets should be discovered in and near the HZ of their stars if such planets are common. Extending the mission to six years doubles the expected number of Earth-size planets in the HZ. A null result would imply that terrestrial planets in the HZ occur in less than 1% of the stars and that life might be quite rare. Based on the results of the current Doppler-velocity discoveries, detection of a thousand giant planets is expected. Information on their albedos and densities of those giants showing transits will be obtained.

  16. Aggregate and the environment

    USGS Publications Warehouse

    Langer, William H.; Drew, Lawrence J.; Sachs, J.S.

    2004-01-01

    This book is designed to help you understand our aggregate resources-their importance, where they come from, how they are processed for our use, the environmental concerns related to their mining and processing, how those concerns are addressed, and the policies and regulations designed to safeguard workers, neighbors, and the environment from the negative impacts of aggregate mining. We hope this understanding will help prepare you to be involved in decisions that need to be made-individually and as a society-to be good stewards of our aggregate resources and our living planet.

  17. Aggregation kinetics and shear rheology of aqueous silica suspensions

    NASA Astrophysics Data System (ADS)

    Metin, Cigdem O.; Bonnecaze, Roger T.; Lake, Larry W.; Miranda, Caetano R.; Nguyen, Quoc P.

    2012-12-01

    The kinetics of aggregation of silica nanoparticle solutions as a function of NaCl and silica concentrations is studied experimentally and theoretically. Silica nanoparticles form fractal aggregates due to the collapse of the electrical double layer at high salt concentrations and resulting reduction in stabilizing repulsive force. We propose a convenient model to describe the aggregation of silica nanoparticles and the growth of their aggregate size that depends on particle size and concentration and salt concentration. The model agrees well with experimental data. The aggregation of silica nanoparticles also affects the rheology of the suspension. We propose an equilibrium approach for sediment volume fraction to determine the maximum effective packing fraction. The results for the relative viscosity of silica aggregates agree well with the proposed viscosity model, which also collapses onto a single master curve.

  18. Extraction of TNT from aggregate soil fractions.

    PubMed

    Williford, C W; Mark Bricka, R

    1999-04-23

    Past explosives manufacture, disposal, and training activities have contaminated soil at many military facilities, posing health and environmental risks through contact, potential detonation, and leaching into ground water. While methods have been confirmed for extraction and measuring explosives concentration in soil, no work has addressed aggregate size material (the >2 mm gravel and cobbles) that often occurs with the smaller soil fractions. This paper describes methods and results for extraction and measurement of TNT (2,4,6-trinitrotoluene) in aggregate material from 1/2 to 2-1/1 from a WWII era ammunition plant. TNT was extracted into acetonitrile by both Soxhlet and ultrasonic extraction methods. High pressure liquid chromatography analyses of extracts showed expected variation among samples. Also effective extraction and determination of TNT concentration for each aggregate size fraction was achieved.

  19. Protein aggregation and lyophilization: Protein structural descriptors as predictors of aggregation propensity

    PubMed Central

    Roughton, Brock C.; Iyer, Lavanya K.; Bertelsen, Esben; Topp, Elizabeth M.; Camarda, Kyle V.

    2014-01-01

    Lyophilization can induce aggregation in therapeutic proteins, but the relative importance of protein structure, formulation and processing conditions are poorly understood. To evaluate the contribution of protein structure to lyophilization-induced aggregation, fifteen proteins were co-lyophilized with each of five excipients. Extent of aggregation following lyophilization, measured using size-exclusion chromatography, was correlated with computational and biophysical protein structural descriptors via multiple linear regression. Descriptor selection was performed using exhaustive search and forward selection. The results demonstrate that, for a given excipient, extent of aggregation is highly correlated by eight to twelve structural descriptors. Leave-one-out cross validation showed that the correlations were able to successfully predict the aggregation for a protein “left out” of the data set. Selected descriptors varied with excipient, indicating both protein structure and excipient type contribute to lyophilization-induced aggregation. The results show some descriptors used to predict protein aggregation in solution are useful in predicting lyophilized protein aggregation. PMID:24516290

  20. Protein Colloidal Aggregation Project

    NASA Technical Reports Server (NTRS)

    Oliva-Buisson, Yvette J. (Compiler)

    2014-01-01

    To investigate the pathways and kinetics of protein aggregation to allow accurate predictive modeling of the process and evaluation of potential inhibitors to prevalent diseases including cataract formation, chronic traumatic encephalopathy, Alzheimer's Disease, Parkinson's Disease and others.

  1. Cell aggregation and sedimentation.

    PubMed

    Davis, R H

    1995-01-01

    The aggregation of cells into clumps or flocs has been exploited for decades in such applications as biological wastewater treatment, beer brewing, antibiotic fermentation, and enhanced sedimentation to aid in cell recovery or retention. More recent research has included the use of cell aggregation and sedimentation to selectively separate subpopulations of cells. Potential biotechnological applications include overcoming contamination, maintaining plasmid-bearing cells in continuous fermentors, and selectively removing nonviable hybridoma cells from perfusion cultures.

  2. In vitro refolding with simultaneous purification of recombinant human parathyroid hormone (rhPTH 1-34) from Escherichia coli directed by protein folding size exclusion chromatography (PF-SEC): implication of solution additives and their role on aggregates and renaturation.

    PubMed

    Vemula, Sandeep; Vemula, Sushma; Dedaniya, Akshay; Ronda, Srinivasa Reddy

    2016-01-01

    Recombinant proteins are frequently hampered by aggregation during the refolding and purification process. A simple and rapid method for in vitro refolding and purification of recombinant human parathyroid hormone (rhPTH 1-34) expressed in Escherichia coli with protein folding size exclusion chromatography (PF-SEC) was developed in the present work. Discrete effects of potential solution additives such as urea, polypolyethylene glycol, proline, and maltose on the refolding with simultaneous purification of rhPTH were investigated. The results of individual additives indicated that both maltose and proline had remarkable influences on the efficiency of refolding with a recovery yield of 65 and 66% respectively. Further, the synergistic effect of these additives on refolding was also explored. These results demonstrate that the additive combinations are more effective for inhibiting protein aggregation during purification of rhPTH in terms of recovery yield, purity, and specific activity. The maltose and proline combination system achieved the highest renatured rhPTH having a recovery yield of 78%, a purity of ≥99%, and a specific activity of 3.31 × 10(3) cAMP pM/cell respectively, when compared to the classical dilution method yield (41%) and purity (97%). In addition, the role of maltose and proline in a combined system on protein aggregation and refolding has been explained. The molecular docking (in silico) scores of maltose (-10.91) and proline (-9.0) support the in vitro results.

  3. Morphological classification of nanoceramic aggregates

    NASA Astrophysics Data System (ADS)

    Crosta, Giovanni F.; Kang, Bongwoo; Ospina, Carolina; Sung, Changmo

    2005-01-01

    Aluminum silicate nanoaggregates grown at near-room temperature on an organic template under a variety of experimental conditions have been imaged by transmission electron microscopy. Images have been automatically classified by an algorithm based on "spectrum enhancement", multivariate statistics and supervised optimization. Spectrum enhancement consists of subtracting, in the log scale, a known function of wavenumber from the angle averaged power spectral density of the image. Enhanced spectra of each image, after polynomial interpolation, have been regarded as morphological descriptors and as such submitted to principal components analysis nested with a multiobjective parameter optimization algorithm. The latter has maximized pairwise discrimination between classes of materials. The role of the organic template and of a reaction parameter on aggregate morphology has been assessed at two magnification scales. Classification results have also been related to crystal structure data derived from selected area electron diffraction patterns.

  4. On the behavior of mud floc size distribution: model calibration and model behavior

    NASA Astrophysics Data System (ADS)

    Mietta, Francesca; Chassagne, Claire; Verney, Romaric; Winterwerp, Johan C.

    2011-03-01

    In this paper, we study a population balance equation (PBE) where flocs are distributed into classes according to their mass. Each class i contains i primary particles with mass m p and size L p. All differently sized flocs can aggregate, binary breakup into two equally sized flocs is used, and the floc's fractal dimension is d 0 = 2, independently of their size. The collision efficiency is kept constant, and the collision frequency derived by Saffman and Turner (J Fluid Mech 1:16-30, 1956) is used. For the breakup rate, the formulation by Winterwerp (J Hydraul Eng Res 36(3):309-326, 1998), which accounts for the porosity of flocs, is used. We show that the mean floc size computed with the PBE varies with the shear rate as the Kolmogorov microscale, as observed both in laboratory and in situ. Moreover, the equilibrium mean floc size varies linearly with a global parameter P which is proportional to the ratio between the rates of aggregation and breakup. The ratio between the parameters of aggregation and breakup can therefore be estimated analytically from the observed equilibrium floc size. The parameter for aggregation can be calibrated from the temporal evolution of the mean floc size. We calibrate the PBE model using mixing jar flocculation experiments, see Mietta et al. (J Colloid Interface Sci 336(1):134-141, 2009a, Ocean Dyn 59:751-763, 2009b) for details. We show that this model can reproduce the experimental data fairly accurately. The collision efficiency α and the ratio between parameters for aggregation and breakup α and E are shown to decrease linearly with increasing absolute value of the ζ-potential, both for mud and kaolinite suspensions. Suspensions at high pH and different dissolved salt type and concentration have been used. We show that the temporal evolution of the floc size distribution computed with this PBE is very similar to that computed with the PBE developed by Verney et al. (Cont Shelf Res, 2010) where classes are distributed

  5. Phase transition in diffusion limited aggregation with patchy particles in two dimensions

    NASA Astrophysics Data System (ADS)

    Kartha, Moses J.; Sayeed, Ahmed

    2016-08-01

    The influence of patchy interactions on diffusion-limited aggregation (DLA) has been investigated by computer simulations. In this model, the adsorption of the particle is irreversible, but the adsorption occurs only when the 'sticky patch' makes contact with the sticky patch of a previously adsorbed particle. As we vary the patch size, growth rate of the cluster decreases, and below a well-defined critical patch size, pc the steady state growth rate goes to zero. The system reaches an absorbing phase producing a non-equilibrium continuous phase transition. The order parameter close to the critical value of the patch size shows a power law behavior ρ (∞) ∼(p -pc) β, where β = 0.2840. We have found that the value of the critical exponent convincingly shows that this transition in patchy DLA belongs to the directed percolation universality class.

  6. Fractal dimension and mechanism of aggregation of apple juice particles.

    PubMed

    Benítez, E I; Lozano, J E; Genovese, D B

    2010-04-01

    Turbidity of freshly squeezed apple juice is produced by a polydisperse suspension of particles coming from the cellular tissue. After precipitation of coarse particles by gravity, only fine-colloidal particles remain in suspension. Aggregation of colloidal particles leads to the formation of fractal structures. The fractal dimension is a measure of the internal density of these aggregates and depends on their mechanism of aggregation. Digitized images of primary particles and aggregates of depectinized, diafiltered cloudy apple juice were obtained by scanning electron microscopy (SEM). Average radius of the primary particles was found to be a = 40 ± 11 nm. Maximum radius of the aggregates, R(L), ranged between 250 and 7750 nm. Fractal dimension of the aggregates was determined by analyzing SEM images with the variogram method, obtaining an average value of D(f) = 2.3 ± 0.1. This value is typical of aggregates formed by rapid flocculation or diffusion limited aggregation. Diafiltration process was found to reduce the average size and polydispersity of the aggregates, determined by photon correlation spectroscopy. Average gyration radius of the aggregates before juice diafiltration was found to be R(g) = 629 ± 87 nm. Average number of primary particles per aggregate was calculated to be N = 1174. PMID:21339133

  7. Fibronectin Aggregation and Assembly

    PubMed Central

    Ohashi, Tomoo; Erickson, Harold P.

    2011-01-01

    The mechanism of fibronectin (FN) assembly and the self-association sites are still unclear and contradictory, although the N-terminal 70-kDa region (I1–9) is commonly accepted as one of the assembly sites. We previously found that I1–9 binds to superfibronectin, which is an artificial FN aggregate induced by anastellin. In the present study, we found that I1–9 bound to the aggregate formed by anastellin and a small FN fragment, III1–2. An engineered disulfide bond in III2, which stabilizes folding, inhibited aggregation, but a disulfide bond in III1 did not. A gelatin precipitation assay showed that I1–9 did not interact with anastellin, III1, III2, III1–2, or several III1–2 mutants including III1–2KADA. (In contrast to previous studies, we found that the III1–2KADA mutant was identical in conformation to wild-type III1–2.) Because I1–9 only bound to the aggregate and the unfolding of III2 played a role in aggregation, we generated a III2 domain that was destabilized by deletion of the G strand. This mutant bound I1–9 as shown by the gelatin precipitation assay and fluorescence resonance energy transfer analysis, and it inhibited FN matrix assembly when added to cell culture. Next, we introduced disulfide mutations into full-length FN. Three disulfide locks in III2, III3, and III11 were required to dramatically reduce anastellin-induced aggregation. When we tested the disulfide mutants in cell culture, only the disulfide bond in III2 reduced the FN matrix. These results suggest that the unfolding of III2 is one of the key factors for FN aggregation and assembly. PMID:21949131

  8. Low aggregation state diminishes ferrihydrite reactivity

    NASA Astrophysics Data System (ADS)

    Braunschweig, Juliane; Heister, Katja; Meckenstock, Rainer U.

    2013-04-01

    Ferrihydrite is an abundant iron(oxy)hydroxide in soils and sediments and plays an important role in microbial iron cycling due to its high reactivity. Therefore, it is often synthesized and used in geomicrobiological and mineralogical studies. The reactivities of synthetic ferrihydrites vary between different studies and synthesis protocols. Hence, we synthesized five different ferrihydrites and characterized them with XRD, FTIR, XPS, and BET specific surface area. The reactivity of the ferrihydrite samples towards ascorbic acid was examined and compared with microbial reduction rates by Geobacter sulfurreducens. FTIR and XRD results show the presence of secondary, higher crystalline iron oxide phases like goethite and akaganeite for two samples. Consequently, those samples revealed lower biotic and abiotic reduction rates compared to pure ferrihydrite. Comparison of reduction rates with the specific surface area of all ferrihydrites showed neither correlation with abiotic reductive dissolution nor with microbial reduction. Especially one sample, characterized by a very low aggregation state and presence of secondary minerals, revealed a poor reactivity. We speculate that apart from the occurring secondary minerals also the low aggregation state played an important role. Decreasing aggregation diminishes the amount of kinks and edges on the surfaces, which are produced at contact sites in aggregates. According to dissolution theories, dissolution mainly starts at those surface defects and slows down with decreasing amount of defects. Furthermore, the non-aggregated ferrihydrite is free of micropores, a further stimulant for dissolution. Independent repetitions of experiments and syntheses according to the same protocol but without formation of secondary minerals, confirmed the low reactivity of the non-aggregated ferrihydrite. In summary, our results indicate that a decreasing aggregation state of ferrihydrite to a certain size does increase the reactivity

  9. A population balance equation model of aggregation dynamics in Taxus suspension cell cultures.

    PubMed

    Kolewe, Martin E; Roberts, Susan C; Henson, Michael A

    2012-02-01

    The nature of plant cells to grow as multicellular aggregates in suspension culture has profound effects on bioprocess performance. Recent advances in the measurement of plant cell aggregate size allow for routine process monitoring of this property. We have exploited this capability to develop a conceptual model to describe changes in the aggregate size distribution that are observed over the course of a Taxus cell suspension batch culture. We utilized the population balance equation framework to describe plant cell aggregates as a particulate system, accounting for the relevant phenomenological processes underlying aggregation, such as growth and breakage. We compared model predictions to experimental data to select appropriate kernel functions, and found that larger aggregates had a higher breakage rate, biomass was partitioned asymmetrically following a breakage event, and aggregates grew exponentially. Our model was then validated against several datasets with different initial aggregate size distributions and was able to quantitatively predict changes in total biomass and mean aggregate size, as well as actual size distributions. We proposed a breakage mechanism where a fraction of biomass was lost upon each breakage event, and demonstrated that even though smaller aggregates have been shown to produce more paclitaxel, an optimum breakage rate was predicted for maximum paclitaxel accumulation. We believe this is the first model to use a segregated, corpuscular approach to describe changes in the size distribution of plant cell aggregates, and represents an important first step in the design of rational strategies to control aggregation and optimize process performance.

  10. 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

  11. Survivorship and feeding preferences among size classes of outplanted sea urchins, Tripneustes gratilla, and possible use as biocontrol for invasive alien algae

    PubMed Central

    Ringang, Rory R.; Cantero, Sean Michael A.; Toonen, Robert J.

    2015-01-01

    We investigate the survivorship, growth and diet preferences of hatchery-raised juvenile urchins, Tripneustes gratilla, to evaluate the efficacy of their use as biocontrol agents in the efforts to reduce alien invasive algae. In flow-through tanks, we measured urchin growth rates, feeding rates and feeding preferences among diets of the most common invasive algae found in Kāneʻohe Bay, Hawaiʻi: Acanthophora spicifera, Gracilaria salicornia, Eucheuma denticulatum and Kappaphycus clade B. Post-transport survivorship of outplanted urchins was measured in paired open and closed cages in three different reef environments (lagoon, reef flat and reef slope) for a month. Survivorship in closed cages was highest on the reef flat (∼75%), and intermediate in the lagoon and reef slope (∼50%). In contrast, open cages showed similar survivorship on the reef flat and in the lagoon, but only 20% of juvenile urchins survived in open cages placed on the reef slope. Urchins grew significantly faster on diets of G. salicornia (1.58 mm/week ± 0.14 SE) and Kappaphycus clade B (1.69 ± 0.14 mm/wk) than on E. denticulatum (0.97 ± 0.14 mm/wk), with intermediate growth when fed on A. spicifera (1.23 ± 0.11 mm/wk). Interestingly, urchins display size-specific feeding preferences. In non-choice feeding trials, small urchins (17.5–22.5 mm test diameter) consumed G. salicornia fastest (6.08 g/day ± 0.19 SE), with A. spicifera (4.25 ± 0.02 g/day) and Kappaphycus clade B (3.83 ± 0.02 g/day) intermediate, and E. denticulatum was clearly the least consumed (2.32 ± 0.37 g/day). Medium-sized (29.8–43.8 mm) urchins likewise preferentially consumed G. salicornia (12.60 ± 0.08 g/day), with less clear differences among the other species in which E. denticulatum was still consumed least (9.35 ± 0.90 g/day). In contrast, large urchins (45.0–65.0 mm) showed no significant preferences among the different algae species at all (12.43–15.24 g/day). Overall consumption rates in non

  12. Survivorship and feeding preferences among size classes of outplanted sea urchins, Tripneustes gratilla, and possible use as biocontrol for invasive alien algae.

    PubMed

    Westbrook, Charley E; Ringang, Rory R; Cantero, Sean Michael A; Toonen, Robert J

    2015-01-01

    We investigate the survivorship, growth and diet preferences of hatchery-raised juvenile urchins, Tripneustes gratilla, to evaluate the efficacy of their use as biocontrol agents in the efforts to reduce alien invasive algae. In flow-through tanks, we measured urchin growth rates, feeding rates and feeding preferences among diets of the most common invasive algae found in Kāne'ohe Bay, Hawai'i: Acanthophora spicifera, Gracilaria salicornia, Eucheuma denticulatum and Kappaphycus clade B. Post-transport survivorship of outplanted urchins was measured in paired open and closed cages in three different reef environments (lagoon, reef flat and reef slope) for a month. Survivorship in closed cages was highest on the reef flat (∼75%), and intermediate in the lagoon and reef slope (∼50%). In contrast, open cages showed similar survivorship on the reef flat and in the lagoon, but only 20% of juvenile urchins survived in open cages placed on the reef slope. Urchins grew significantly faster on diets of G. salicornia (1.58 mm/week ± 0.14 SE) and Kappaphycus clade B (1.69 ± 0.14 mm/wk) than on E. denticulatum (0.97 ± 0.14 mm/wk), with intermediate growth when fed on A. spicifera (1.23 ± 0.11 mm/wk). Interestingly, urchins display size-specific feeding preferences. In non-choice feeding trials, small urchins (17.5-22.5 mm test diameter) consumed G. salicornia fastest (6.08 g/day ± 0.19 SE), with A. spicifera (4.25 ± 0.02 g/day) and Kappaphycus clade B (3.83 ± 0.02 g/day) intermediate, and E. denticulatum was clearly the least consumed (2.32 ± 0.37 g/day). Medium-sized (29.8-43.8 mm) urchins likewise preferentially consumed G. salicornia (12.60 ± 0.08 g/day), with less clear differences among the other species in which E. denticulatum was still consumed least (9.35 ± 0.90 g/day). In contrast, large urchins (45.0-65.0 mm) showed no significant preferences among the different algae species at all (12.43-15.24 g/day). Overall consumption rates in non-choice trials

  13. Survivorship and feeding preferences among size classes of outplanted sea urchins, Tripneustes gratilla, and possible use as biocontrol for invasive alien algae.

    PubMed

    Westbrook, Charley E; Ringang, Rory R; Cantero, Sean Michael A; Toonen, Robert J

    2015-01-01

    We investigate the survivorship, growth and diet preferences of hatchery-raised juvenile urchins, Tripneustes gratilla, to evaluate the efficacy of their use as biocontrol agents in the efforts to reduce alien invasive algae. In flow-through tanks, we measured urchin growth rates, feeding rates and feeding preferences among diets of the most common invasive algae found in Kāne'ohe Bay, Hawai'i: Acanthophora spicifera, Gracilaria salicornia, Eucheuma denticulatum and Kappaphycus clade B. Post-transport survivorship of outplanted urchins was measured in paired open and closed cages in three different reef environments (lagoon, reef flat and reef slope) for a month. Survivorship in closed cages was highest on the reef flat (∼75%), and intermediate in the lagoon and reef slope (∼50%). In contrast, open cages showed similar survivorship on the reef flat and in the lagoon, but only 20% of juvenile urchins survived in open cages placed on the reef slope. Urchins grew significantly faster on diets of G. salicornia (1.58 mm/week ± 0.14 SE) and Kappaphycus clade B (1.69 ± 0.14 mm/wk) than on E. denticulatum (0.97 ± 0.14 mm/wk), with intermediate growth when fed on A. spicifera (1.23 ± 0.11 mm/wk). Interestingly, urchins display size-specific feeding preferences. In non-choice feeding trials, small urchins (17.5-22.5 mm test diameter) consumed G. salicornia fastest (6.08 g/day ± 0.19 SE), with A. spicifera (4.25 ± 0.02 g/day) and Kappaphycus clade B (3.83 ± 0.02 g/day) intermediate, and E. denticulatum was clearly the least consumed (2.32 ± 0.37 g/day). Medium-sized (29.8-43.8 mm) urchins likewise preferentially consumed G. salicornia (12.60 ± 0.08 g/day), with less clear differences among the other species in which E. denticulatum was still consumed least (9.35 ± 0.90 g/day). In contrast, large urchins (45.0-65.0 mm) showed no significant preferences among the different algae species at all (12.43-15.24 g/day). Overall consumption rates in non-choice trials

  14. Differences in extreme low salinity timing and duration differentially affect eastern oyster (Crassostrea virginica) size class growth and mortality in Breton Sound, LA

    USGS Publications Warehouse

    LaPeyre, Megan K.; Eberline, Benjamin S.; Soniat, Thomas M.; La Peyre, Jerome F.

    2013-01-01

    Understanding how different life history stages are impacted by extreme or stochastic environmental variation is critical for predicting and modeling organism population dynamics. This project examined recruitment, growth, and mortality of seed (25–75 mm) and market (>75 mm) sized oysters along a salinity gradient over two years in Breton Sound, LA. In April 2010, management responses to the Deepwater Horizon oil spill resulted in extreme low salinity (<5) at all sites through August 2010; in 2011, a 100-year Mississippi River flood event resulted in low salinity in late spring. Extended low salinity (<5) during hot summer months (>25 °C) significantly and negatively impacted oyster recruitment, survival and growth in 2010, while low salinity (<5) for a shorter period that did not extend into July (<25 °C) in 2011 had minimal impacts on oyster growth and mortality. In 2011, recruitment was limited, which may be due to a combination of low spring time salinities, high 2010 oyster mortality, minimal 2010 recruitment, cumulative effects from 10 years of declining oyster stock in the area, and poor cultch quality. In both 2010 and 2011, Perkinsus marinusinfection prevalence remained low throughout the year at all sites and almost all infection intensities were light. Oyster plasma osmolality failed to match surrounding low salinity waters in 2010, while oysters appeared to osmoconform throughout 2011 indicating that the high mortality in 2010 may be due to extended valve closing and resulting starvation or asphyxiation in response to the combination of low salinity during high temperatures (>25 °C). With increasing management of our freshwater inputs to estuaries combined with predicted climate changes, how extreme events affect different life history stages is key to understanding variation in population demographics of commercially important species and predicting future populations.

  15. Differences in extreme low salinity timing and duration differentially affect eastern oyster (Crassostrea virginica) size class growth and mortality in Breton Sound, LA

    NASA Astrophysics Data System (ADS)

    La Peyre, Megan K.; Eberline, Benjamin S.; Soniat, Thomas M.; La Peyre, Jerome F.

    2013-12-01

    Understanding how different life history stages are impacted by extreme or stochastic environmental variation is critical for predicting and modeling organism population dynamics. This project examined recruitment, growth, and mortality of seed (25-75 mm) and market (>75 mm) sized oysters along a salinity gradient over two years in Breton Sound, LA. In April 2010, management responses to the Deepwater Horizon oil spill resulted in extreme low salinity (<5) at all sites through August 2010; in 2011, a 100-year Mississippi River flood event resulted in low salinity in late spring. Extended low salinity (<5) during hot summer months (>25 °C) significantly and negatively impacted oyster recruitment, survival and growth in 2010, while low salinity (<5) for a shorter period that did not extend into July (<25 °C) in 2011 had minimal impacts on oyster growth and mortality. In 2011, recruitment was limited, which may be due to a combination of low spring time salinities, high 2010 oyster mortality, minimal 2010 recruitment, cumulative effects from 10 years of declining oyster stock in the area, and poor cultch quality. In both 2010 and 2011, Perkinsus marinus infection prevalence remained low throughout the year at all sites and almost all infection intensities were light. Oyster plasma osmolality failed to match surrounding low salinity waters in 2010, while oysters appeared to osmoconform throughout 2011 indicating that the high mortality in 2010 may be due to extended valve closing and resulting starvation or asphyxiation in response to the combination of low salinity during high temperatures (>25 °C). With increasing management of our freshwater inputs to estuaries combined with predicted climate changes, how extreme events affect different life history stages is key to understanding variation in population demographics of commercially important species and predicting future populations.

  16. The Stability of Student Ratings of the Class Environment

    ERIC Educational Resources Information Center

    Nelson, Peter M.; Hall, Gordon; Christ, Theodore J.

    2016-01-01

    The present study used data for 30 classes across 10 middle and high school teachers to evaluate the stability of class-level ratings on the Responsive Environmental Assessment for Classroom Teaching across time. Teachers collected data on 2 occasions and students' ratings (N = 806) were aggregated to the class-level. Classes were arranged into 2…

  17. Colloidal aggregation and dynamics in anisotropic fluids

    PubMed Central

    Mondiot, Frédéric; Botet, Robert; Snabre, Patrick; Mondain-Monval, Olivier; Loudet, Jean-Christophe

    2014-01-01

    We present experiments and numerical simulations to investigate the collective behavior of submicrometer-sized particles immersed in a nematic micellar solution. We use latex spheres with diameters ranging from 190 to 780 nm and study their aggregation properties due to the interplay of the various colloidal forces at work in the system. We found that the morphology of aggregates strongly depends on the particle size, with evidence for two distinct regimes: the biggest inclusions clump together within minutes into either compact clusters or V-like structures that are completely consistent with attractive elastic interactions. On the contrary, the smallest particles form chains elongated along the nematic axis, within comparable timescales. In this regime, Monte Carlo simulations, based on a modified diffusion-limited cluster aggregation model, strongly suggest that the anisotropic rotational Brownian motion of the clusters combined with short-range depletion interactions dominate the system coarsening; elastic interactions no longer prevail. The simulations reproduce the sharp transition between the two regimes on increasing the particle size. We provide reasonable estimates to interpret our data and propose a likely scenario for colloidal aggregation. These results emphasize the growing importance of the diffusion of species at suboptical-wavelength scales and raise a number of fundamental issues. PMID:24715727

  18. Kinetics of aggregation in liquids with dispersed nanoparticles.

    PubMed

    Jeżewski, Wojciech

    2015-04-14

    The process of attaching molecules of liquid media by dispersed nanoparticles is modeled and numerically studied. The growth rate of the resulting nanoparticle-induced aggregates is determined by assuming the preferential attachment rule according to which the effectiveness of the connection of a new molecular unit to aggregates is determined by their size. It is shown that, depending on a specific functional form of the growth rate, the size distribution of aggregates can display very different shapes, including various multimodal structures. This can explain experimentally obtained complex size distributions of inhomogeneous aggregates appearing as a consequence of the adsorption of molecules by nanoparticles or as a consequence of the self-assembling of active dispersants on surfaces of nanoparticles. The time evolution and the stationarity of the size distribution are also analyzed, gaining an insight into the long-time behavior of systems with dispersed nanoparticles. PMID:25745674

  19. Technology meets aggregate

    SciTech Connect

    Wilson, C.; Swan, C.

    2007-07-01

    New technology carried out at Tufts University and the University of Massachusetts on synthetic lightweight aggregate has created material from various qualities of fly ash from coal-fired power plants for use in different engineered applications. In pilot scale manufacturing tests an 'SLA' containing 80% fly ash and 20% mixed plastic waste from packaging was produced by 'dry blending' mixed plastic with high carbon fly ash. A trial run was completed to produce concrete masonry unit (CMU) blocks at a full-scale facility. It has been shown that SLA can be used as a partial substitution of a traditional stone aggregate in hot asphalt mix. 1 fig., 2 photos.

  20. Aggregation and sinking behaviour of resuspended fluffy layer material

    NASA Astrophysics Data System (ADS)

    Ziervogel, Kai; Forster, Stefan

    2005-09-01

    The influence of pelagic diatom addition ( Skeletonema costatum) on aggregation dynamics of resuspended fluffy layer material containing natural microorganism assemblages (bacteria and pennate diatoms) was studied during two roller table experiments. Sediment samples were taken at a fine sand site (16 m water depth) located in Mecklenburg Bight, south-western Baltic Sea. Fluff was experimentally resuspended from sediment cores and aggregation processes with and without S. costatum were studied in rotating tanks. Total particulate matter was incorporated into artificial aggregates in equal shares after both roller table experiments. However, biogenic parameters (particulate organic carbon, particulate organic nitrogen, and carbohydrate equivalents), as well as cell numbers of bacteria and pennate diatoms were found in higher percentages in S. costatum aggregates compared to aggregates without S. costatum. Transparent exopolymer particles were apparently irrelevant in the aggregation process during both experiments. Settling velocities of S. costatum aggregates exceeding 1000 μm in diameter showed a significantly higher mean settling velocity compared to aggregates without S. costatum of the same size. The pronounced effect of pelagic diatoms on aggregation processes of fluff in terms of particle attributes, size, and therewith sinking velocities could be demonstrated and may lead to further insight into near bed particle transport in coastal waters.

  1. Asphaltene Aggregation and Fouling Behavior

    NASA Astrophysics Data System (ADS)

    Derakhshesh, Marzie

    This thesis explored the properties of asphaltene nano-aggregates in crude oil and toluene based solutions and fouling at process furnace temperatures, and the links between these two phenomena. The link between stability of asphaltenes at ambient conditions and fouling at the conditions of a delayed coker furnace, at over 450 °C, was examined by blending crude oil with an aliphatic diluent in different ratios. The stability of the blends were measured using a S-value analyzer, then fouling rates were measured on electrically heated stainless steel 316 wires in an autoclave reactor. The less stable the blend, the greater the rate and extent of fouling. The most severe fouling occurred with the unstable asphaltenes. SEM imaging of the foulant illustrates very different textures, with the structure becoming more porous with lower stability. Under cross-polarized light, the coke shows the presence of mesophase in the foulant layer. These data suggest a correlation between the fouling rate at high temperature furnace conditions and the stability index of the crude oil. Three organic polysulfides were introduced to the crude oil to examine their effect on fouling. The polysulfides are able to reduce coking and carbon monoxide generation in steam crackers. The fouling results demonstrated that polysulfide with more sulfur content increased the amount of corrosion-fouling of the wire. Various additives, solvents, ultrasound, and heat were employed to attempt to completely disaggregate the asphaltene nano-aggregates in solution at room temperature. The primary analytical technique used to monitor the nano-aggregation state of the asphaltenes in solution was the UV-visible spectroscopy. The results indicate that stronger solvents, such as pyridine and quinoline, combined with ionic liquids yield a slight reduction in the apparent absorbance at longer wavelengths, indicative of a decrease in the nano-aggregate size although the magnitude of the decrease is not significant

  2. Multiple discrete soluble aggregates influence polyglutamine toxicity in a Huntington’s disease model system

    PubMed Central

    Xi, Wen; Wang, Xin; Laue, Thomas M.; Denis, Clyde L.

    2016-01-01

    Huntington’s disease (HD) results from expansions of polyglutamine stretches (polyQ) in the huntingtin protein (Htt) that promote protein aggregation, neurodegeneration, and death. Since the diversity and sizes of the soluble Htt-polyQ aggregates that have been linked to cytotoxicity are unknown, we investigated soluble Htt-polyQ aggregates using analytical ultracentrifugation. Soon after induction in a yeast HD model system, non-toxic Htt-25Q and cytotoxic Htt-103Q both formed soluble aggregates 29S to 200S in size. Because current models indicate that Htt-25Q does not form soluble aggregates, reevaluation of previous studies may be necessary. Only Htt-103Q aggregation behavior changed, however, with time. At 6 hr mid-sized aggregates (33S to 84S) and large aggregates (greater than 100S) became present while at 24 hr primarily only mid-sized aggregates (20S to 80S) existed. Multiple factors that decreased cytotoxicity of Htt-103Q (changing the length of or sequences adjacent to the polyQ, altering ploidy or chaperone dosage, or deleting anti-aging factors) altered the Htt-103Q aggregation pattern in which the suite of mid-sized aggregates at 6 hr were most correlative with cytotoxicity. Hence, the amelioration of HD and other neurodegenerative diseases may require increased attention to and discrimination of the dynamic alterations in soluble aggregation processes. PMID:27721444

  3. Reduction in soil aggregation in response to dust emission processes

    NASA Astrophysics Data System (ADS)

    Swet, Nitzan; Katra, Itzhak

    2016-09-01

    Dust emission by aeolian (wind) soil erosion depends on the topsoil properties of the source area, especially on the nature of the aggregates where most dust particles are held. Although the key role of soil aggregates in dust emission, the response of soil aggregation to aeolian processes and its implications for dust emission remain unknown. This study focuses on aggregate size distribution (ASD) analyses before and after in-situ aeolian experiments in semiarid loess soils that are associated with dust emission. Wind tunnel simulations show that particulate matter (PM) emission and saltation rates depend on the initial ASD and shear velocity. Under all initial ASD conditions, the content of saltator-sized aggregates (63-250 μm) increased by 10-34% due to erosion of macro-aggregates (> 500 μm), resulting in a higher size ratio (SR) between the saltators and macro-aggregates following the aeolian erosion. The results revealed that the saltator production increases significantly for soils that are subjected to short-term (anthropogenic) disturbance of the topsoil. The findings highlight a decrease in soil aggregation for all initial ASD's in response to aeolian erosion, and consequently its influence on the dust emission potential. Changes in ASD should be considered as a key parameter in dust emission models of complex surfaces.

  4. Planktonic Aggregates of Staphylococcus aureus Protect against Common Antibiotics

    PubMed Central

    Haaber, Jakob; Cohn, Marianne Thorup; Frees, Dorte; Andersen, Thorbjørn Joest; Ingmer, Hanne

    2012-01-01

    Bacterial cells are mostly studied during planktonic growth although in their natural habitats they are often found in communities such as biofilms with dramatically different physiological properties. We have examined another type of community namely cellular aggregates observed in strains of the human pathogen Staphylococcus aureus. By laser-diffraction particle–size analysis (LDA) we show, for strains forming visible aggregates, that the aggregation starts already in the early exponential growth phase and proceeds until post-exponential phase where more than 90% of the population is part of the aggregate community. Similar to some types of biofilm, the structural component of S. aureus aggregates is the polysaccharide intercellular adhesin (PIA). Importantly, PIA production correlates with the level of aggregation whether altered through mutations or exposure to sub-inhibitory concentrations of selected antibiotics. While some properties of aggregates resemble those of biofilms including increased mutation frequency and survival during antibiotic treatment, aggregated cells displayed higher metabolic activity than planktonic cells or cells in biofilm. Thus, our data indicate that the properties of cells in aggregates differ in some aspects from those in biofilms. It is generally accepted that the biofilm life style protects pathogens against antibiotics and the hostile environment of the host. We speculate that in aggregate communities S. aureus increases its tolerance to hazardous environments and that the combination of a biofilm-like environment with mobility has substantial practical and clinical importance. PMID:22815921

  5. Structure and aggregation in model tetramethylurea solutions

    SciTech Connect

    Gupta, Rini; Patey, G. N.

    2014-08-14

    The structure of model aqueous tetramethylurea (TMU) solutions is investigated employing large-scale (32 000, 64 000 particles) molecular dynamics simulations. Results are reported for TMU mole fractions, X{sub t}, ranging from infinite dilution up to 0.07, and for two temperatures, 300 and 330 K. Two existing force fields for TMU-water solutions are considered. These are the GROMOS 53A6 united-atom TMU model combined with SPC/E water [TMU(GROMOS-UA)/W(SPC/E)], and the more frequently employed AMBER03 all-atom force field for TMU combined with the TIP3P water model [TMU(AMBER-AA)/W(TIP3P)]. It is shown that TMU has a tendency towards aggregation for both models considered, but the tendency is significantly stronger for the [TMU(AMBER-AA)/W(TIP3P)] force field. For this model signs of aggregation are detected at X{sub t} = 0.005, aggregation is a well established feature of the solution at X{sub t} = 0.02, and the aggregates increase further in size with increasing concentration. This is in agreement with at least some experimental studies, which report signals of aggregation in the low concentration regime. The TMU aggregates exhibit little structure and are simply loosely ordered, TMU-rich regions of solution. The [TMU(GROMOS-UA)/W(SPC/E)] model shows strong signs of aggregation only at higher concentrations (X{sub t} ≳ 0.04), and the aggregates appear more loosely ordered, and less well-defined than those occurring in the [TMU(AMBER-AA)/W(TIP3P)] system. For both models, TMU aggregation increases when the temperature is increased from 300 to 330 K, consistent with an underlying entropy driven, hydrophobic interaction mechanism. At X{sub t} = 0.07, the extra-molecular correlation length expected for microheterogeneous solutions has become comparable with the size of the simulation cell for both models considered, indicating that even the systems simulated here are sufficiently large only at low concentrations.

  6. Aggregates, broccoli and cauliflower

    NASA Astrophysics Data System (ADS)

    Grey, Francois; Kjems, Jørgen K.

    1989-09-01

    Naturally grown structures with fractal characters like broccoli and cauliflower are discussed and compared with DLA-type aggregates. It is suggested that the branching density can be used to characterize the growth process and an experimental method to determine this parameter is proposed.

  7. Class Size, Class Composition, and the Distribution of Student Achievement

    ERIC Educational Resources Information Center

    Bosworth, Ryan

    2014-01-01

    Using richly detailed data on fourth- and fifth-grade students in the North Carolina public school system, I find evidence that students are assigned to classrooms in a non-random manner based on observable characteristics for a substantial portion of classrooms. Moreover, I find that this non-random assignment is statistically related to class…

  8. Class Matters

    ERIC Educational Resources Information Center

    Valdata, Patricia

    2005-01-01

    Ever since George Washington opted for the title of president rather than king, Americans have been uncomfortable with the idea of class distinctions. This article presents an interview with Dr. Janet Galligani Casey regarding the idea of class distinctions. Galligani Casey, who grew up in a working-class neighborhood in Somerville, Massachusetts,…

  9. Characterization of Ovine Dermal Papilla Cell Aggregation

    PubMed Central

    Sari, Agnes Rosarina Prita; Rufaut, Nicholas Wolfgang; Jones, Leslie Norman; Sinclair, Rodney Daniel

    2016-01-01

    Context: The dermal papilla (DP) is a condensation of mesenchymal cells at the proximal end of the hair follicle, which determines hair shaft size and regulates matrix cell proliferation and differentiation. DP cells have the ability to regenerate new hair follicles. These cells tend to aggregate both in vitro and in vivo. This tendency is associated with the ability of papilla cells to induce hair growth. However, human papilla cells lose their hair-inducing activity in later passage number. Ovine DP cells are different from human DP cells since they do not lose their aggregative behavior or hair-inducing activity in culture. Nonetheless, our understanding of ovine DP cells is still limited. Aim: The aim of this study was to observe the expression of established DP markers in ovine cells and their association with aggregation. Subjects and Methods: Ovine DP cells from three different sheep were compared. Histochemistry, immunoflourescence, and polymerase chain reaction experiments were done to analyze the DP markers. Results: We found that ovine DP aggregates expressed all the 16 markers evaluated, including alkaline phosphatase and versican. Expression of the versican V0 and V3 isoforms, neural cell adhesion molecule, and corin was increased significantly with aggregation, while hey-1 expression was significantly decreased. Conclusions: Overall, the stable expression of numerous markers suggests that aggregating ovine DP cells have a similar phenotype to papillae in vivo. The stability of their molecular phenotype is consistent with their robust aggregative behavior and retained follicle-inducing activity after prolonged culture. Their phenotypic stability in culture contrasts with DP cells from other species, and suggests that a better understanding of ovine DP cells might provide opportunities to improve the hair-inducing activity and therapeutic potential of human cells. PMID:27625564

  10. Characterization of Ovine Dermal Papilla Cell Aggregation

    PubMed Central

    Sari, Agnes Rosarina Prita; Rufaut, Nicholas Wolfgang; Jones, Leslie Norman; Sinclair, Rodney Daniel

    2016-01-01

    Context: The dermal papilla (DP) is a condensation of mesenchymal cells at the proximal end of the hair follicle, which determines hair shaft size and regulates matrix cell proliferation and differentiation. DP cells have the ability to regenerate new hair follicles. These cells tend to aggregate both in vitro and in vivo. This tendency is associated with the ability of papilla cells to induce hair growth. However, human papilla cells lose their hair-inducing activity in later passage number. Ovine DP cells are different from human DP cells since they do not lose their aggregative behavior or hair-inducing activity in culture. Nonetheless, our understanding of ovine DP cells is still limited. Aim: The aim of this study was to observe the expression of established DP markers in ovine cells and their association with aggregation. Subjects and Methods: Ovine DP cells from three different sheep were compared. Histochemistry, immunoflourescence, and polymerase chain reaction experiments were done to analyze the DP markers. Results: We found that ovine DP aggregates expressed all the 16 markers evaluated, including alkaline phosphatase and versican. Expression of the versican V0 and V3 isoforms, neural cell adhesion molecule, and corin was increased significantly with aggregation, while hey-1 expression was significantly decreased. Conclusions: Overall, the stable expression of numerous markers suggests that aggregating ovine DP cells have a similar phenotype to papillae in vivo. The stability of their molecular phenotype is consistent with their robust aggregative behavior and retained follicle-inducing activity after prolonged culture. Their phenotypic stability in culture contrasts with DP cells from other species, and suggests that a better understanding of ovine DP cells might provide opportunities to improve the hair-inducing activity and therapeutic potential of human cells.

  11. Digital image processing of nanometer-size metal particles on amorphous substrates

    NASA Technical Reports Server (NTRS)

    Soria, F.; Artal, P.; Bescos, J.; Heinemann, K.

    1989-01-01

    The task of differentiating very small metal aggregates supported on amorphous films from the phase contrast image features inherently stemming from the support is extremely difficult in the nanometer particle size range. Digital image processing was employed to overcome some of the ambiguities in evaluating such micrographs. It was demonstrated that such processing allowed positive particle detection and a limited degree of statistical size analysis even for micrographs where by bare eye examination the distribution between particles and erroneous substrate features would seem highly ambiguous. The smallest size class detected for Pd/C samples peaks at 0.8 nm. This size class was found in various samples prepared under different evaporation conditions and it is concluded that these particles consist of 'a magic number' of 13 atoms and have cubooctahedral or icosahedral crystal structure.

  12. Microbial community dynamics in soil aggregates shape biogeochemical gas fluxes from soil profiles - upscaling an aggregate biophysical model.

    PubMed

    Ebrahimi, Ali; Or, Dani

    2016-09-01

    Microbial communities inhabiting soil aggregates dynamically adjust their activity and composition in response to variations in hydration and other external conditions. These rapid dynamics shape signatures of biogeochemical activity and gas fluxes emitted from soil profiles. Recent mechanistic models of microbial processes in unsaturated aggregate-like pore networks revealed a highly dynamic interplay between oxic and anoxic microsites jointly shaped by hydration conditions and by aerobic and anaerobic microbial community abundance and self-organization. The spatial extent of anoxic niches (hotspots) flicker in time (hot moments) and support substantial anaerobic microbial activity even in aerated soil profiles. We employed an individual-based model for microbial community life in soil aggregate assemblies represented by 3D angular pore networks. Model aggregates of different sizes were subjected to variable water, carbon and oxygen contents that varied with soil depth as boundary conditions. The study integrates microbial activity within aggregates of different sizes and soil depth to obtain estimates of biogeochemical fluxes from the soil profile. The results quantify impacts of dynamic shifts in microbial community composition on CO2 and N2 O production rates in soil profiles in good agreement with experimental data. Aggregate size distribution and the shape of resource profiles in a soil determine how hydration dynamics shape denitrification and carbon utilization rates. Results from the mechanistic model for microbial activity in aggregates of different sizes were used to derive parameters for analytical representation of soil biogeochemical processes across large scales of practical interest for hydrological and climate models. PMID:27152862

  13. Regulation and aggregation of intrinsically disordered peptides.

    PubMed

    Levine, Zachary A; Larini, Luca; LaPointe, Nichole E; Feinstein, Stuart C; Shea, Joan-Emma

    2015-03-01

    Intrinsically disordered proteins (IDPs) are a unique class of proteins that have no stable native structure, a feature that allows them to adopt a wide variety of extended and compact conformations that facilitate a large number of vital physiological functions. One of the most well-known IDPs is the microtubule-associated tau protein, which regulates microtubule growth in the nervous system. However, dysfunctions in tau can lead to tau oligomerization, fibril formation, and neurodegenerative disease, including Alzheimer's disease. Using a combination of simulations and experiments, we explore the role of osmolytes in regulating the conformation and aggregation propensities of the R2/wt peptide, a fragment of tau containing the aggregating paired helical filament (PHF6*). We show that the osmolytes urea and trimethylamine N-oxide (TMAO) shift the population of IDP monomer structures, but that no new conformational ensembles emerge. Although urea halts aggregation, TMAO promotes the formation of compact oligomers (including helical oligomers) through a newly proposed mechanism of redistribution of water around the perimeter of the peptide. We put forth a "superposition of ensembles" hypothesis to rationalize the mechanism by which IDP structure and aggregation is regulated in the cell.

  14. Sizing Up What Matters.

    ERIC Educational Resources Information Center

    McCluskey, Neal

    "Smaller is better" is often the mantra of school leaders with regard to class size, while the benefits of smaller schools are ignored. Benefits of small classes seem obvious--teachers with fewer students could devote more time to each student. Conducted in 1985-89, Tennessee's Project STAR (Student/Teacher Achievement Ratio) found that students…

  15. Comparison of heat-induced aggregation of globular proteins.

    PubMed

    Delahaije, Roy J B M; Wierenga, Peter A; Giuseppin, Marco L F; Gruppen, Harry

    2015-06-01

    Typically, heat-induced aggregation of proteins is studied using a single protein under various conditions (e.g., temperature). Because different studies use different conditions and methods, a mechanistic relationship between molecular properties and the aggregation behavior of proteins has not been identified. Therefore, this study investigates the kinetics of heat-induced aggregation and the size/density of formed aggregates for three different proteins (ovalbumin, β-lactoglobulin, and patatin) under various conditions (pH, ionic strength, concentration, and temperature). The aggregation rate of β-lactoglobulin was slower (>10 times) than that of ovalbumin and patatin. Moreover, the conditions (pH, ionic strength, and concentration) affected the aggregation kinetics of β-lactoglobulin more strongly than for ovalbumin and patatin. In contrast to the kinetics, for all proteins the aggregate size/density increased with decreasing electrostatic repulsion. By comparing these proteins under these conditions, it became clear that the aggregation behavior cannot easily be correlated to the molecular properties (e.g., charge and exposed hydrophobicity). PMID:25965109

  16. Proteins aggregation and human diseases

    NASA Astrophysics Data System (ADS)

    Hu, Chin-Kun

    2015-04-01

    Many human diseases and the death of most supercentenarians are related to protein aggregation. Neurodegenerative diseases include Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), frontotemporallobar degeneration, etc. Such diseases are due to progressive loss of structure or function of neurons caused by protein aggregation. For example, AD is considered to be related to aggregation of Aβ40 (peptide with 40 amino acids) and Aβ42 (peptide with 42 amino acids) and HD is considered to be related to aggregation of polyQ (polyglutamine) peptides. In this paper, we briefly review our recent discovery of key factors for protein aggregation. We used a lattice model to study the aggregation rates of proteins and found that the probability for a protein sequence to appear in the conformation of the aggregated state can be used to determine the temperature at which proteins can aggregate most quickly. We used molecular dynamics and simple models of polymer chains to study relaxation and aggregation of proteins under various conditions and found that when the bending-angle dependent and torsion-angle dependent interactions are zero or very small, then protein chains tend to aggregate at lower temperatures. All atom models were used to identify a key peptide chain for the aggregation of insulin chains and to find that two polyQ chains prefer anti-parallel conformation. It is pointed out that in many cases, protein aggregation does not result from protein mis-folding. A potential drug from Chinese medicine was found for Alzheimer's disease.

  17. Packing density of rigid aggregates is independent of scale.

    PubMed

    Zangmeister, Christopher D; Radney, James G; Dockery, Lance T; Young, Jessica T; Ma, Xiaofei; You, Rian; Zachariah, Michael R

    2014-06-24

    Large planetary seedlings, comets, microscale pharmaceuticals, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (θf) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction. The θf of rigid aggregated structures across six orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ∼ 17-nm monomeric subunits and aggregates made from uniform monomeric 6-mm spherical subunits at the macroscale. We find θf = 0.36 ± 0.02 at both dimensions. These values are remarkably similar to θf observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that θf is independent of both monomer and aggregate size. These observations suggest that the θf of rigid aggregates subject to weak compaction forces is independent of spatial dimension across varied formative conditions. PMID:24927577

  18. Packing density of rigid aggregates is independent of scale

    PubMed Central

    Zangmeister, Christopher D.; Radney, James G.; Dockery, Lance T.; Young, Jessica T.; Ma, Xiaofei; You, Rian; Zachariah, Michael R.

    2014-01-01

    Large planetary seedlings, comets, microscale pharmaceuticals, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (θf) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction. The θf of rigid aggregated structures across six orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ∼17-nm monomeric subunits and aggregates made from uniform monomeric 6-mm spherical subunits at the macroscale. We find θf = 0.36 ± 0.02 at both dimensions. These values are remarkably similar to θf observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that θf is independent of both monomer and aggregate size. These observations suggest that the θf of rigid aggregates subject to weak compaction forces is independent of spatial dimension across varied formative conditions. PMID:24927577

  19. Increased cytoplasm viscosity hampers aggregate polar segregation in Escherichia coli.

    PubMed

    Oliveira, Samuel M D; Neeli-Venkata, Ramakanth; Goncalves, Nadia S M; Santinha, João A; Martins, Leonardo; Tran, Huy; Mäkelä, Jarno; Gupta, Abhishekh; Barandas, Marilia; Häkkinen, Antti; Lloyd-Price, Jason; Fonseca, José M; Ribeiro, Andre S

    2016-02-01

    In Escherichia coli, under optimal conditions, protein aggregates associated with cellular aging are excluded from midcell by the nucleoid. We study the functionality of this process under sub-optimal temperatures from population and time lapse images of individual cells and aggregates and nucleoids within. We show that, as temperature decreases, aggregates become homogeneously distributed and uncorrelated with nucleoid size and location. We present evidence that this is due to increased cytoplasm viscosity, which weakens the anisotropy in aggregate displacements at the nucleoid borders that is responsible for their preference for polar localisation. Next, we show that in plasmolysed cells, which have increased cytoplasm viscosity, aggregates are also not preferentially located at the poles. Finally, we show that the inability of cells with increased viscosity to exclude aggregates from midcell results in enhanced aggregate concentration in between the nucleoids in cells close to dividing. This weakens the asymmetries in aggregate numbers between sister cells of subsequent generations required for rejuvenating cell lineages. We conclude that the process of exclusion of protein aggregates from midcell is not immune to stress conditions affecting the cytoplasm viscosity. The findings contribute to our understanding of E. coli's internal organisation and functioning, and its fragility to stressful conditions. PMID:26507787

  20. Scaling laws in the diffusion limited aggregation of persistent random walkers

    NASA Astrophysics Data System (ADS)

    Nogueira, Isadora R.; Alves, Sidiney G.; Ferreira, Silvio C.

    2011-11-01

    We investigate the diffusion limited aggregation of particles executing persistent random walks. The scaling properties of both random walks and large aggregates are presented. The aggregates exhibit a crossover between ballistic and diffusion limited aggregation models. A non-trivial scaling relation ξ∼ℓ1.25 between the characteristic size ξ, in which the cluster undergoes a morphological transition, and the persistence length ℓ, between ballistic and diffusive regimes of the random walk, is observed.

  1. Structure and flow of dense suspensions of protein fractal aggregates in comparison with microgels.

    PubMed

    Inthavong, Walailuk; Kharlamova, Anna; Chassenieux, Christophe; Nicolai, Taco

    2016-03-14

    Solutions of the globular whey protein β-lactoglobulin (β-lg) were heated at different protein concentrations leading to the formation of polydisperse fractal aggregates with different average sizes. The structure of the solutions was analyzed with light scattering as a function of the protein concentration. The osmotic compressibility and the dynamic correlation length decreased with increasing concentration and became independent of the aggregate size in dense suspensions. The results obtained for different aggregate sizes could be superimposed after normalizing the concentration with the overlap concentration. Dense suspensions of fractal protein aggregates are strongly interpenetrated and can be visualized as an ensemble of fractal 'blobs'. The viscosity of the heated β-lg solutions increased extremely sharply above 80 g L(-1) and diverged at 98 g L(-1), mainly due to the sharply increasing aggregate size. At a fixed aggregate size, the viscosity increased initially exponentially with increasing concentration and then diverged. The increase was stronger when the aggregates were larger, but the dependence of the viscosity on the aggregate size was weaker than that of the osmotic compressibility and the dynamic correlation length. The concentration dependence of the viscosity of solutions of fractal β-lg aggregates is much stronger than that of homogeneous β-lg microgels. The behavior of fractal aggregates formed by whey protein isolates was similar. PMID:26864954

  2. Solute effects on the irreversible aggregation of serum albumin.

    PubMed

    Bagger, Heidi L; Øgendal, Lars H; Westh, Peter

    2007-10-01

    Thermal stress on bovine serum albumin (BSA) promotes protein aggregation through the formation of intermolecular beta-sheets. We have used light scattering and chromatography to study effects of (<1 M) Na(2)SO(4), NaSCN, sucrose, sorbitol and urea on the rate of the thermal aggregation. Both salts were strong inhibitors of BSA aggregation and they reduced both the size and number (concentration) of aggregate particles compared to non-ionic solutes (or pure buffer). Hence, the salts appear to suppress both nucleation- and growth rate. The non-electrolyte additives reduced the initial aggregation rate (compared to pure buffer), but did not significantly limit the extent of aggregation in samples quenched after 27 min. heat exposure (40-50% aggregation in all samples). The non-electrolytes did, however, modify the aggregation process as they consistently brought about smaller but more concentrated aggregates than pure buffer. The results are discussed along the lines of linkage- and transition state theories. In this framework, the rate of the aggregation process is governed by the equilibrium between a thermally denatured state (D) and the transition state D( not equal). Thus, the effect of a solute relies on its preferential interactions with respectively D and D( not equal). The current results do not show any correlation between the solutes' preferential interactions with native BSA and their effect on the rate of aggregation. This suggests that non-specific, "Hofmeister-type" interactions, which scale with the solvent accessible surface area, are of minor importance. Rather, salt induced suppression of aggregation is suggested to depend on the modulation of specific electrostatic forces in the D( not equal) state.

  3. Dynamics of fire ant aggregations

    NASA Astrophysics Data System (ADS)

    Tennenbaum, Michael; Hu, David; Fernandez-Nieves, Alberto

    Fire ant aggregations are an inherently active system. Each ant harvests its own energy and can convert it into motion. The motion of individual ants contributes non-trivially to the bulk material properties of the aggregation. We have measured some of these properties using plate-plate rheology, where the response to an applied external force or deformation is measured. In this talk, we will present data pertaining to the aggregation behavior in the absence of any external force. We quantify the aggregation dynamics by monitoring the rotation of the top plate and by measuring the normal force. We then compare the results with visualizations of 2D aggregations.

  4. Sans study of asphaltene aggregation

    SciTech Connect

    Overfield, R.E.; Sheu, E.Y.; Sinha, S.K.; Liang, K.S. )

    1988-06-01

    The colloidal properties of asphaltenes have long been recognized from peculiarities in their solubility and colligative properties. A layered micellar model or asphaltenes was proposed by others in which a highly condensed alkyl aromatic formed the central part, and molecules of decreasingly aromatic character (resins) clustered around them. Numerous studies, based on a variety of techniques such as ultracentrifugation and electron microscopy indicated a particulate nature for asphaltenes with size 20-40 A diameter. Others have proposed a refined model based on x-ray diffraction and small angle scattering. In this model, interactions between flat sheets of condensed aromatic rings form the central ''crystallite'' part of a spherical particle with the outer part being comprised of the aliphatic positions of the same molecules. These particles are bunched together with some degree of entanglement into ''micelles''. Concentration and solvent dependent radii of gyration, ranging from 30-50 A were reported. The aggregation creates a good deal of uncertainty as to the true molecular size or weight of asphaltenes. Neutron scattering offers novel contrast relative to light scattering (refractive index) and x-ray scattering (electron density). This is because the scattering length of proton is negative, whereas that from deuterium and other nuclei such as C, S, O, and N are positive. Thus by replacing hydrogen with deuterium in either the solvent or the scatterer the contrast can be varied, and different parts of the molecule can be highlighted.

  5. Economic performance and public concerns about social class in twentieth-century books.

    PubMed

    Chen, Yunsong; Yan, Fei

    2016-09-01

    What is the association between macroeconomic conditions and public perceptions of social class? Applying a novel approach based on the Google Books N-gram corpus, this study addresses the relationship between public concerns about social class and economic conditions throughout the twentieth century. The usage of class-related words/phrases, or "literary references to class," in American English-language books is related to US economic performance and income inequality. The findings of this study demonstrate that economic conditions play a significant role in literary references to class throughout the century, whereas income inequality does not. Similar results are obtained from further analyses using alternative measures of class concerns as well as different corpora of English Fiction and the New York Times. We add to the social class literature by showing that the long-term temporal dynamics of an economy can be exhibited by aggregate class concerns. The application of massive culture-wide content analysis using data of unprecedented size also represents a contribution to the literature. PMID:27480370

  6. Economic performance and public concerns about social class in twentieth-century books.

    PubMed

    Chen, Yunsong; Yan, Fei

    2016-09-01

    What is the association between macroeconomic conditions and public perceptions of social class? Applying a novel approach based on the Google Books N-gram corpus, this study addresses the relationship between public concerns about social class and economic conditions throughout the twentieth century. The usage of class-related words/phrases, or "literary references to class," in American English-language books is related to US economic performance and income inequality. The findings of this study demonstrate that economic conditions play a significant role in literary references to class throughout the century, whereas income inequality does not. Similar results are obtained from further analyses using alternative measures of class concerns as well as different corpora of English Fiction and the New York Times. We add to the social class literature by showing that the long-term temporal dynamics of an economy can be exhibited by aggregate class concerns. The application of massive culture-wide content analysis using data of unprecedented size also represents a contribution to the literature.

  7. Aggregating tags for column-free protein purification.

    PubMed

    Lin, Zhanglin; Zhao, Qing; Xing, Lei; Zhou, Bihong; Wang, Xu

    2015-12-01

    Protein purification remains a central need for biotechnology. In recent years, a class of aggregating tags has emerged, which offers a quick, cost-effective and column-free alternative for producing recombinant proteins (and also peptides) with yield and purity comparable to that of the popular His-tag. These column-free tags induce the formation of aggregates (during or after expression) when fused to a target protein or peptide, and upon separation from soluble impurities, the target protein or peptide is subsequently released via a cleavage site. In this review, we categorize these tags as follows: (i) tags that induce inactive protein aggregates in vivo; (ii) tags that induce active protein aggregates in vivo; and (iii) tags that induce soluble expression in vivo, but aggregates in vitro. The respective advantages and disadvantages of these tags are discussed, and compared to the three conventional tags (His-tag, maltose-binding protein [MBP] tag, and intein-mediated purification with a chitin-binding tag [IMPACT-CN]). While this new class of aggregating tags is promising, more systematic tests are required to further the use. It is conceivable, however, that the combination of these tags and the more traditional columns may significantly reduce the costs for resins and columns, particularly for the industrial scale.

  8. Self assembled nanoparticle aggregates from line focused femtosecond laser ablation.

    PubMed

    Zuhlke, Craig A; Alexander, Dennis R; Bruce, John C; Ianno, Natale J; Kamler, Chad A; Yang, Weiqing

    2010-03-01

    In this paper we present the use of a line focused femtosecond laser beam that is rastered across a 2024 T3 aluminum surface to produce nanoparticles that self assemble into 5-60 micron diameter domed and in some cases sphere-shaped aggregate structures. Each time the laser is rastered over initial aggregates their diameter increases as new layers of nanoparticles self assemble on the surface. The aggregates are thus composed of layers of particles forming discrete layered shells inside of them. When micron size aggregates are removed, using an ultrasonic bath, rings are revealed that have been permanently formed in the sample surface. These rings appear underneath, and extend beyond the physical boundary of the aggregates. The surface is blackened by the formation of these structures and exhibits high light absorption. PMID:20389444

  9. Artificial aggregate made from waste stone sludge and waste silt.

    PubMed

    Chang, Fang-Chih; Lee, Ming-Yu; Lo, Shang-Lien; Lin, Jyh-Dong

    2010-11-01

    In this research, waste stone sludge obtained from slab stone processing and waste silt from aggregate washing plants were recycled to manufacture artificial aggregate. Fine-powdered stone sludge was mixed with waste silt of larger particle size; vibratory compaction was applied for good water permeability, resulting in a smaller amount of solidifying agent being used. For the densified packing used in this study, the mix proportion of waste stone sludge to waste silt was 35:50, which produced artificial aggregate of more compact structure with water absorption rate below 0.1%. In addition, applying vibratory compaction of 33.3 Hz to the artificial aggregate and curing for 28 days doubled the compressive strength to above 29.4 MPa. Hence, recycling of waste stone sludge and waste silt for the production of artificial aggregate not only offers a feasible substitute for sand and stone, but also an ecological alternative to waste management of sludge and silt.

  10. Kinetics of protein aggregation

    NASA Astrophysics Data System (ADS)

    Knowles, Tuomas

    2015-03-01

    Aggregation into linear nanostructures, notably amyloid and amyloid-like fibrils, is a common form of behaviour exhibited by a range of peptides and proteins. This process was initially discovered in the context of the aetiology of a range of neurodegenerative diseases, but has recently been recognised to of general significance and has been found at the origin of a number of beneficial functional roles in nature, including as catalytic scaffolds and functional components in biofilms. This talk discusses our ongoing efforts to study the kinetics of linear protein self-assembly by using master equation approaches combined with global analysis of experimental data.

  11. Structure of Viral Aggregates

    NASA Astrophysics Data System (ADS)

    Barr, Stephen; Luijten, Erik

    2010-03-01

    The aggregation of virus particles is a particular form of colloidal self-assembly, since viruses of a give type are monodisperse and have identical, anisotropic surface charge distributions. In small-angle X-ray scattering experiments, the Qbeta virus was found to organize in different crystal structures in the presence of divalent salt and non-adsorbing polymer. Since a simple isotropic potential cannot explain the occurrence of all observed phases, we employ computer simulations to investigate how the surface charge distribution affects the virus interactions. Using a detailed model of the virus particle, we find an asymmetric ion distribution around the virus which gives rise to the different phases observed.

  12. Reversible NaCl-induced aggregation of a monoclonal antibody at low pH: Characterization of aggregates and factors affecting aggregation.

    PubMed

    Bickel, Fabian; Herold, Eva Maria; Signes, Alba; Romeijn, Stefan; Jiskoot, Wim; Kiefer, Hans

    2016-10-01

    We investigated the influence of pH and sodium chloride concentration on aggregation kinetics of a monoclonal antibody. Aggregation was induced by sodium chloride addition at low pH. Protein conformation before and after salt addition was determined as well as the reversibility of aggregation. Aggregation was monitored at pH values between 2 and 7 with NaCl up to 1.5M by turbidity measurement and size-exclusion chromatography. Particle size distribution was assessed by using size-exclusion chromatography as well as nanoparticle tracking analysis and flow imaging microscopy. Structural changes were monitored by circular dichroism, Fourier transform infrared and fluorescence spectroscopy. Thermal stability was measured by differential scanning fluorimetry. Aggregation propensity was maximal at low pH and high ionic strength. While thermal stability decreased with pH, the secondary structure remained unchanged down to pH 3.5 and up to 1.5M NaCl. Precipitated protein could be largely reverted to monomers by dilution into salt-free buffer. The re-solubilized antibody was indistinguishable in structure, solubility and monodispersity from the unstressed protein. Also, binding to Protein A was steady. Aggregation could be reduced in the presence of trehalose. The results suggest a reversible aggregation mechanism characterized by a limited change in tertiary structure at low pH and a subsequent loss of colloidal stability resulting from electrostatic repulsion once salt is added to the sample. The experimental setup is robust and allows high-throughput quantification of the effect of additives on aggregation kinetics. PMID:27449627

  13. Reversible NaCl-induced aggregation of a monoclonal antibody at low pH: Characterization of aggregates and factors affecting aggregation.

    PubMed

    Bickel, Fabian; Herold, Eva Maria; Signes, Alba; Romeijn, Stefan; Jiskoot, Wim; Kiefer, Hans

    2016-10-01

    We investigated the influence of pH and sodium chloride concentration on aggregation kinetics of a monoclonal antibody. Aggregation was induced by sodium chloride addition at low pH. Protein conformation before and after salt addition was determined as well as the reversibility of aggregation. Aggregation was monitored at pH values between 2 and 7 with NaCl up to 1.5M by turbidity measurement and size-exclusion chromatography. Particle size distribution was assessed by using size-exclusion chromatography as well as nanoparticle tracking analysis and flow imaging microscopy. Structural changes were monitored by circular dichroism, Fourier transform infrared and fluorescence spectroscopy. Thermal stability was measured by differential scanning fluorimetry. Aggregation propensity was maximal at low pH and high ionic strength. While thermal stability decreased with pH, the secondary structure remained unchanged down to pH 3.5 and up to 1.5M NaCl. Precipitated protein could be largely reverted to monomers by dilution into salt-free buffer. The re-solubilized antibody was indistinguishable in structure, solubility and monodispersity from the unstressed protein. Also, binding to Protein A was steady. Aggregation could be reduced in the presence of trehalose. The results suggest a reversible aggregation mechanism characterized by a limited change in tertiary structure at low pH and a subsequent loss of colloidal stability resulting from electrostatic repulsion once salt is added to the sample. The experimental setup is robust and allows high-throughput quantification of the effect of additives on aggregation kinetics.

  14. New Insights Into Carbon Sequestration of Steppe Soils - Composition and Turnover of Soil Organic Matter Fractions and Aggregation

    NASA Astrophysics Data System (ADS)

    Steffens, M.; Koelbl, A.; Koegel-Knabner, I.

    2008-12-01

    Grazing is one of the most important factors that may reduce soil organic carbon (SOC) stocks and subsequently aggregate stability in grassland topsoils. Improvements of land use management and 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 aim of this study was to analyse the quantity and quality of SOC fractions and their contribution to aggregate formation, stability and carbon sequestration as affected by increased inputs of organic matter due to grazing exclusion. We applied a combined aggregate size, density and particle size fractionation procedure and aggregate stability measurements to sandy steppe topsoils with different organic matter inputs due to different grazing intensities (continuously grazed = Cg, winter grazing = Wg, ungrazed since 1999 = Ug99, ungrazed since 1979 = Ug79). Higher inputs of organic matter led to higher amounts of OC in coarse aggregate size classes (ASC) and especially in particulate organic matter (POM) fractions. We found no grazing-induced changes of soil organic matter (SOM) quantity in fine ASC and mineral fractions. SOM quality (13C CPMAS-NMR spectroscopy, neutral sugars analyses) was comparable between different grazing intensities, but SOM in ungrazed plots was more decomposed across all fractions. We found generally higher radiocarbon activities in Ug79 compared to Cg. Aggregate stability, analysed as resistance to sonication, was higher in Ug79 compared to Cg. Higher litter inputs in grazing exclosures increased POM quantity, led to faster SOM turnover and resulted in the formation and stabilisation of coarse aggregates. Organo-mineral associations were affected by higher turnover times as radiocarbon activities increased, but OC saturation of this pool did not change. To summarise, additional litter inputs following grazing exclusion were mainly sequestered in the intermediate POM pool while the long-term pool of

  15. Interactions and Aggregation of Charged Nanoparticles in Uncharged Polymer Solutions.

    PubMed

    Pandav, Gunja; Pryamitsyn, Victor; Ganesan, Venkat

    2015-11-17

    We employ an extension of the single chain in mean field simulation method to study mixtures of charged particles and uncharged polymers. We examine the effect of particle charge, polymer concentration, and particle volume fraction on the resulting particle aggregates. The structures of aggregates were characterized using particle-particle radial distribution functions and cluster size distributions. We observe that the level of aggregation between particles increases with increasing particle volume fraction and polymer concentration and decreasing particle charge. At intermediate regimes of particle volume fraction and polymer concentrations, we observe the formation of equilibrium clusters with a preferred size. We also examined the influence of manybody effects on the structure of a charged particle-polymer system. Our results indicate that the effective two-body approximation overpredicts the aggregation between particles even at dilute particle concentrations. Such effects are thought to be a consequence of the interplay between the respective manybody effects on the depletion and electrostatic interactions.

  16. 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.

  17. Total organic carbon in aggregates as a soil recovery indicator

    NASA Astrophysics Data System (ADS)

    Luciene Maltoni, Katia; Rodrigues Cassiolato, Ana Maria; Amorim Faria, Glaucia; Dubbin, William

    2015-04-01

    The soil aggregation promotes physical protection of organic matter, preservation of which is crucial to improve soil structure, fertility and ensure the agro-ecosystems sustainability. The no-tillage cultivation system has been considered as one of the strategies to increase total soil organic carbono (TOC) contents and soil aggregation, both are closely related and influenced by soil management systems. The aim of this study was to evaluate the distribution of soil aggregates and the total organic carbon inside aggregates, with regard to soil recovery, under 3 different soil management systems, i.e. 10 and 20 years of no-tillage cultivation as compared with soil under natural vegetation (Cerrado). Undisturbed soils (0-5; 5-10; and 10-20 cm depth) were collected from Brazil, Central Region. The soils, Oxisols from Cerrado, were collected from a field under Natural Vegetation-Cerrado (NV), and from fields that were under conventional tillage since 1970s, and 10 and 20 years ago were changed to no-tillage cultivation system (NT-10; NT-20 respectively). The undisturbed samples were sieved (4mm) and the aggregates retained were further fractionated by wet sieving through five sieves (2000, 1000, 500, 250, and 50 μm) with the aggregates distribution expressed as percentage retained by each sieve. The TOC was determined, for each aggregate size, by combustion (Thermo-Finnigan). A predominance of aggregates >2000 μm was observed under NV treatment (92, 91, 82 %), NT-10 (64, 73, 61 %), and NT-20 (71, 79, 63 %) for all three depths (0-5; 5-10; 10-20 cm). In addition greater quantities of aggregates in sizes 1000, 500, 250 and 50 μm under NT-10 and NT-20 treatments, explain the lower aggregate stability under these treatments compared to the soil under NV. The organic C concentration for NV in aggregates >2000 μm was 24,4; 14,2; 8,7 mg/g for each depth (0-5; 5-10; 10-20 cm, respectively), higher than in aggregates sized 250-50 μm (7,2; 5,5; 4,4 mg/g) for all depths

  18. Topography of samples with variably aggregated metal particles

    NASA Astrophysics Data System (ADS)

    Schönauer, D.; Kreibig, U.

    1985-06-01

    A proper description of the optical (and other) properties of small particle samples containing clusters of interacting particles requires detailed information on the cluster topography. We present such an investigation performed on samples which were prepared from Au particle hydrosols, the clustering being controlled by addition of stabilizing agents. Numerical results are submitted for interdependencies between the number, the size and shape of aggregates and a Hausdorff dimension of 1.7 ± 0.2 is determined. Proper quantities are given, to detect even very low amounts of aggregation. There are indications that such samples may be modeled by introducing a few prototypic aggregates.

  19. Aggregates and Superaggregates of Soot with Four Distinct Fractal Morphologies

    NASA Technical Reports Server (NTRS)

    Sorensen, C. M.; Kim, W.; Fry, D.; Chakrabarti, A.

    2004-01-01

    Soot formed in laminar diffusion flames of heavily sooting fuels evolves through four distinct growth stages which give rise to four distinct aggregate fractal morphologies. These results were inferred from large and small angle static light scattering from the flames, microphotography of the flames, and analysis of soot sampled from the flames. The growth stages occur approximately over four successive orders of magnitude in aggregate size. Comparison to computer simulations suggests that these four growth stages involve either diffusion limited cluster aggregation or percolation in either three or two dimensions.

  20. Ru(II)-based metallosurfactant forming inverted aggregates.

    PubMed

    Domínguez-Gutiérrez, David; Surtchev, Marko; Eiser, Erika; Elsevier, Cornelis J

    2006-02-01

    Knowing the advantages of incorporating a transition metal into interfaces, we report on the first inverted aggregates formed using metallosurfactants. The metallosurfactant possesses four long linear tails that account for the shielding of the polar headgroup in apolar solvents. The nature of the so-formed aggregates changes dramatically from inverted vesicles (toluene) to inverted micelles (hexane). The size of the aggregates was determined using dynamic light scattering. Atomic force microscopy allowed us to study the dry structure of the vesicles on a glass surface.

  1. [Physico-chemical methods for studing β-amyloid aggregation].

    PubMed

    Radko, S P; Khmeleva, S A; Suprun, E V; Kozin, S A; Bodoev, N V; Makarov, A A; Archakov, A I; Shumyantseva, V V

    2015-01-01

    Alzheimer's disease is the most prevalent neurodegenerative pathology. According to the amyloid cascade hypothesis, a key event of the Alzheimer's disease pathogenesis is a transition of the β-amyloid peptide (Аβ) from the monomeric form to the aggregated state. The mechanism of Аβ aggregation is intensively studied in vitro, by means of synthetic peptides and various physico-chemical methods allowing evaluation of size, molecular structure, and morphology of the formed aggregates. The paper reviews both the well-known and recently introduced physico-chemical methods for analysis of Аβ aggregation, including microscopу, optical and fluorescent methods, method of electron paramagnetic resonance, electrochemical and electrophoretic methods, gel-filtration, and mass spectrometric methods. Merits and drawbacks of the methods are discussed. The unique possibility to simultaneously observe Аβ monomers as well oligomers and large aggregates by means of atomic force microscopy or fluorescence correlation spectroscopy is emphasized. The high detection sensitivity of the latter method, monitoring the aggregation process in Аβ solutions at low peptide concentrations is underlined. Among mass spectrometric methods, the ion mobility mass spectrometry is marked out as a method enabling to obtain information about both the spectrum of Аβ oligomers and their structure. It is pointed out that the use of several methods giving the complementary data about Аβ aggregates is the best experimental approach to studying the process of b-amyloid peptide aggregation in vitro.

  2. From Objects to Quantities: Developments in Preschool Children's Judgments about Aggregate Amount.

    ERIC Educational Resources Information Center

    Sophian, Catherine

    2000-01-01

    Examined the impact of object boundaries on 3-, 4-, and 5-year-olds' quantitative reasoning. Asked subjects to choose between alternative collections that differed in number and size of cookies and in aggregate amount. Found that children were influenced by size of individual cookies at 3 years but were generally unsuccessful in aggregating size…

  3. Aggregation behavior of a tetrameric cationic surfactant in aqueous solution.

    PubMed

    Hou, Yanbo; Han, Yuchun; Deng, Manli; Xiang, Junfen; Wang, Yilin

    2010-01-01

    A star-shaped tetrameric quaternary ammonium surfactant PATC, which has four hydrophobic chains and charged hydrophilic headgroups connected by amide-type spacer group, has been synthesized in this work. Surface tension, electrical conductivity, ITC, DLS, and NMR have been used to investigate the relationship between its chemical structure and its aggregation properties. Interestingly, a large size distribution around 75 nm is observed below the critical micelle concentration (cmc) of PATC, and the large size distribution starts to decrease beyond the cmc and finally transfers to a small size distribution. It is proved that the large size premicellar aggregates may display network-like structure, and the size decrease beyond the cmc is the transition of the network-like aggregates to micelles. The possible reason is that intramolecular electrostatic repulsion among the charged headgroups below the cmc leads to a star-shaped molecular configuration, which may form the network-like aggregates through intermolecular hydrophobic interaction between hydrocarbon chains, while the hydrophobic effect becomes strong enough to turn the molecular configuration into pyramid-like shape beyond the cmc, which make the transition of network-like aggregates to micelles available. PMID:19947615

  4. A computational model of chemotaxis-based cell aggregation.

    PubMed

    Eyiyurekli, Manolya; Manley, Prakash; Lelkes, Peter I; Breen, David E

    2008-09-01

    We present a computational model that successfully captures the cell behaviors that play important roles in 2-D cell aggregation. A virtual cell in our model is designed as an independent, discrete unit with a set of parameters and actions. Each cell is defined by its location, size, rates of chemoattractant emission and response, age, life cycle stage, proliferation rate and number of attached cells. All cells are capable of emitting and sensing a chemoattractant chemical, moving, attaching to other cells, dividing, aging and dying. We validated and fine-tuned our in silico model by comparing simulated 24-h aggregation experiments with data derived from in vitro experiments using PC12 pheochromocytoma cells. Quantitative comparisons of the aggregate size distributions from the two experiments are produced using the Earth Mover's Distance (EMD) metric. We compared the two size distributions produced after 24 h of in vitro cell aggregation and the corresponding computer simulated process. Iteratively modifying the model's parameter values and measuring the difference between the in silico and in vitro results allow us to determine the optimal values that produce simulated aggregation outcomes closely matched to the PC12 experiments. Simulation results demonstrate the ability of the model to recreate large-scale aggregation behaviors seen in live cell experiments.

  5. Interfacial adsorption and aggregation of amphiphilic proteins

    NASA Astrophysics Data System (ADS)

    Cheung, David

    2012-02-01

    The adsorption and aggregation on liquid interfaces of proteins is important in many biological contexts, such as the formation of aerial structures, immune response, and catalysis. Likewise the adsorption of proteins onto interfaces has applications in food technology, drug delivery, and in personal care products. As such there has been much interest in the study of a wide range of biomolecules at liquid interfaces. One class of proteins that has attracted particular attention are hydrophobins, small, fungal proteins with a distinct, amphiphilic surface structure. This makes these proteins highly surface active and they recently attracted much interest. In order to understand their potential applications a microscopic description of their interfacial and self-assembly is necessary and molecular simulation provides a powerful tool for providing this. In this presentation I will describe some recent work using coarse-grained molecular dynamics simulations to study the interfacial and aggregation behaviour of hydrophobins. Specifically this will present the calculation of their adsorption strength at oil-water and air-water interfaces, investigate the stability of hydrophobin aggregates in solution and their interaction with surfactants.

  6. Explaining the length threshold of polyglutamine aggregation

    NASA Astrophysics Data System (ADS)

    De Los Rios, Paolo; Hafner, Marc; Pastore, Annalisa

    2012-06-01

    The existence of a length threshold, of about 35 residues, above which polyglutamine repeats can give rise to aggregation and to pathologies, is one of the hallmarks of polyglutamine neurodegenerative diseases such as Huntington’s disease. The reason why such a minimal length exists at all has remained one of the main open issues in research on the molecular origins of such classes of diseases. Following the seminal proposals of Perutz, most research has focused on the hunt for a special structure, attainable only above the minimal length, able to trigger aggregation. Such a structure has remained elusive and there is growing evidence that it might not exist at all. Here we review some basic polymer and statistical physics facts and show that the existence of a threshold is compatible with the modulation that the repeat length imposes on the association and dissociation rates of polyglutamine polypeptides to and from oligomers. In particular, their dramatically different functional dependence on the length rationalizes the very presence of a threshold and hints at the cellular processes that might be at play, in vivo, to prevent aggregation and the consequent onset of the disease.

  7. Huntingtin aggregation kinetics and their pathological role in a Drosophila Huntington's disease model.

    PubMed

    Weiss, Kurt R; Kimura, Yoko; Lee, Wyan-Ching Mimi; Littleton, J Troy

    2012-02-01

    Huntington's disease is a neurodegenerative disorder resulting from expansion of a polyglutamine tract in the Huntingtin protein. Mutant Huntingtin forms intracellular aggregates within neurons, although it is unclear whether aggregates or more soluble forms of the protein represent the pathogenic species. To examine the link between aggregation and neurodegeneration, we generated Drosophila melanogaster transgenic strains expressing fluorescently tagged human huntingtin encoding pathogenic (Q138) or nonpathogenic (Q15) proteins, allowing in vivo imaging of Huntingtin expression and aggregation in live animals. Neuronal expression of pathogenic Huntingtin leads to pharate adult lethality, accompanied by formation of large aggregates within the cytoplasm of neuronal cell bodies and neurites. Live imaging and Fluorescence Recovery After Photobleaching (FRAP) analysis of pathogenic Huntingtin demonstrated that new aggregates can form in neurons within 12 hr, while preexisting aggregates rapidly accumulate new Huntingtin protein within minutes. To examine the role of aggregates in pathology, we conducted haplo-insufficiency suppressor screens for Huntingtin-Q138 aggregation or Huntingtin-Q138-induced lethality, using deficiencies covering ~80% of the Drosophila genome. We identified two classes of interacting suppressors in our screen: those that rescue viability while decreasing Huntingtin expression and aggregation and those that rescue viability without disrupting Huntingtin aggregation. The most robust suppressors reduced both soluble and aggregated Huntingtin levels, suggesting toxicity is likely to be associated with both forms of the mutant protein in Huntington's disease.

  8. Structural Transitions and Aggregation in Amyloidogenic Proteins

    NASA Astrophysics Data System (ADS)

    Steckmann, Timothy; Chapagain, Prem; Gerstman, Bernard; Computational and Theoretical Biophysics Group at Florida International University Team

    2014-03-01

    Amyloid fibrils are a common component in many debilitating human neurological diseases such as Alzheimer's and Parkinson's. A detailed molecular-level understanding of the formation process of amyloid fibrils is crucial for developing methods to slow down or prevent these horrific diseases. Alpha-helix to beta-sheet structural transformation is commonly observed in the process of fibril formation. We performed replica-exchange molecular dynamics simulations of structural transformations in an engineered model peptide cc-beta. Several sets of simulations with different number of cc-beta monomers were considered. Conversion of alpha-helix monomers to beta strands and the aggregation of beta strand monomers into sheets were analyzed as a function of the system size. Hydrogen bond analysis was performed and the beta-aggregate structures were characterized by a nematic order parameter.

  9. COSMIC DUST AGGREGATION WITH STOCHASTIC CHARGING

    SciTech Connect

    Matthews, Lorin S.; Hyde, Truell W.; Shotorban, Babak

    2013-10-20

    The coagulation of cosmic dust grains is a fundamental process which takes place in astrophysical environments, such as presolar nebulae and circumstellar and protoplanetary disks. Cosmic dust grains can become charged through interaction with their plasma environment or other processes, and the resultant electrostatic force between dust grains can strongly affect their coagulation rate. Since ions and electrons are collected on the surface of the dust grain at random time intervals, the electrical charge of a dust grain experiences stochastic fluctuations. In this study, a set of stochastic differential equations is developed to model these fluctuations over the surface of an irregularly shaped aggregate. Then, employing the data produced, the influence of the charge fluctuations on the coagulation process and the physical characteristics of the aggregates formed is examined. It is shown that dust with small charges (due to the small size of the dust grains or a tenuous plasma environment) is affected most strongly.

  10. A nonlocal continuum model for biological aggregation.

    PubMed

    Topaz, Chad M; Bertozzi, Andrea L; Lewis, Mark A

    2006-10-01

    We construct a continuum model for biological aggregations in which individuals experience long-range social attraction and short-range dispersal. For the case of one spatial dimension, we study the steady states analytically and numerically. There exist strongly nonlinear states with compact support and steep edges that correspond to localized biological aggregations, or clumps. These steady-state clumps are reached through a dynamic coarsening process. In the limit of large population size, the clumps approach a constant density swarm with abrupt edges. We use energy arguments to understand the nonlinear selection of clump solutions, and to predict the internal density in the large population limit. The energy result holds in higher dimensions as well, and is demonstrated via numerical simulations in two dimensions.

  11. SERS-active nanoparticle aggregate technology for tags and seals

    SciTech Connect

    Brown, Leif O; Montoya, Velma M; Havrilla, George J; Doorn, Stephen K

    2010-06-03

    In this paper, we describe our efforts to create a modern tagging and sealing technology for international safeguards application. Our passive tagging methods are based on SANAs (SERS-Active Nanoparticle Aggregates; SERS: Surface Enhanced Raman Scattering). These SANAs offer robust spectral barcoding capability in an inexpensive tag/seal, with the possibility of rapid in-field verification that requires no human input. At INMM 2009, we introduced SANAs, and showed approaches to integrating our technology with tags under development at Sandia National Laboratories (SNL). Here, we will focus on recent LANL development work, as well as adding additional dimensionality to the barcoding technique. The field of international safeguards employs a broad array of tags, seals, and tamper-indicating devices to assist with identification, tracking, and verification of components and materials. These devices each have unique strengths suited to specific applications, and span a range of technologies from passive metal cup seals and adhesive seals to active, remotely monitored fiber optic seals. Regardless of the technology employed, essential characteristics center around security, environmental and temporal stability, ease of use, and the ability to provide confidence to all parties. Here, we present a new inexpensive tagging technology that will deliver these attributes, while forming the basis of either a new seal, or as a secure layer added to many existing devices. Our approach uses the Surface Enhanced Raman Scattering (SERS) response from SANAs (SERS-Active Nanoparticle Aggregates, Figure 1) to provide a unique identifier or signature for tagging applications. SANAs are formed from gold or silver nanoparticles in the 40-80 nm size range. A chemical dye is installed on the nanoparticle surface, and the nanoparticles are then aggregated into ensembles of {approx}100 to 500 nm diameter, prior to being coated with silica. The silica shell protects the finished SANA from

  12. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences.

  13. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences. PMID:27588427

  14. Temporal changes in aggregation: a laboratory study.

    PubMed

    Scott, M E

    1987-06-01

    Changes in the variance to mean ratio and the parameter k of the negative binomial distribution were used to study temporal changes in the degree of aggregation of the monogenean parasite, Gyrodactylus turnbulli in free-running laboratory populations of the guppy, Poecilia reticulata. The parasite undergoes recurrent epidemic cycles in the host population under conditions of regular immigration of uninfected guppies. During the early phase of the epidemic, heterogeneity among fish together with direct reproduction are thought to contribute to the increasing degree of aggregation. During the increasing phase of the epidemic cycle, parasites become increasingly aggregated in the host population, presumably because of the direct reproduction of the parasite on the surface of a single host. As the peak prevalance and abundance are approached, the parasites become less aggregated with lowest clumping occurring during the declining phase of the cycle. This is thought to be a function of density-dependent death of infected hosts, and density-dependent reduction in parasite survival and reproduction on hosts that recover from infection. This study clearly indicates that the variance to mean ratio and the parameter k of the negative binomial distribution do not quantify the same aspect of the frequency distribution. It is suggested that the variance to mean ratio is a better measure when the prevalence and/or mean burden are changing and when the tail of the distribution is of particular interest, and that k may be a preferred parameter when the zero class or the lightly infected hosts are of primary interest. PMID:3614993

  15. The acoustic spectroscopy of asphaltene aggregation in petroleum

    NASA Astrophysics Data System (ADS)

    Abbott, G. D.; Povey, M. J. W.

    2012-12-01

    A sphaltenes are well known to be important in causing blockages during production, transportation and refining. They are also responsible for the formation of tar mats in petroleum reservoirs, which can impede crude oil recovery. Acoustic spectroscopy in the frequency range 2 - 120 MHz was used to detect the aggregation of asphaltenes in a North Sea crude oil (UK continental shelf). In the absence of aggregation, both the toluene solvent and the maltenes isolated from the oil exhibit a power law dependence which is a function of the continuous phase. In contrast the crude oil itself showed clear signs of a changing size of the scattering entities. With sufficient information, it may in future be possible to determine the size of the scattering particles from the acoustic spectrum including the changing size of the asphaltene particles during aggregation.

  16. Peptide aggregation in neurodegenerative disease.

    PubMed

    Murphy, Regina M

    2002-01-01

    In the not-so-distant past, insoluble aggregated protein was considered as uninteresting and bothersome as yesterday's trash. More recently, protein aggregates have enjoyed considerable scientific interest, as it has become clear that these aggregates play key roles in many diseases. In this review, we focus attention on three polypeptides: beta-amyloid, prion, and huntingtin, which are linked to three feared neurodegenerative diseases: Alzheimer's, "mad cow," and Huntington's disease, respectively. These proteins lack any significant primary sequence homology, yet their aggregates possess very similar features, specifically, high beta-sheet content, fibrillar morphology, relative insolubility, and protease resistance. Because the aggregates are noncrystalline, secrets of their structure at nanometer resolution are only slowly yielding to X-ray diffraction, solid-state NMR, and other techniques. Besides structure, the aggregates may possess similar pathways of assembly. Two alternative assembly pathways have been proposed: the nucleation-elongation and the template-assisted mode. These two modes may be complementary, not mutually exclusive. Strategies for interfering with aggregation, which may provide novel therapeutic approaches, are under development. The structural similarities between protein aggregates of dissimilar origin suggest that therapeutic strategies successful against one disease may have broad utility in others. PMID:12117755

  17. Topics in Probabilistic Judgment Aggregation

    ERIC Educational Resources Information Center

    Wang, Guanchun

    2011-01-01

    This dissertation is a compilation of several studies that are united by their relevance to probabilistic judgment aggregation. In the face of complex and uncertain events, panels of judges are frequently consulted to provide probabilistic forecasts, and aggregation of such estimates in groups often yield better results than could have been made…

  18. Mineral of the month: aggregates

    USGS Publications Warehouse

    Tepordei, Valentin V.

    2005-01-01

    Natural aggregates, consisting of crushed stone, and sand and gravel, are a major contributor to economic health, and have an amazing variety of uses. Aggregates are among the most abundant mineral resources and are major basic raw materials used by construction, agriculture and other industries that employ complex chemical and metallurgical processes.

  19. Hydrophobically modified polyelectrolytes: Characterization, aggregation and adsorption

    NASA Astrophysics Data System (ADS)

    Islam, Mohammad Ferdous

    large hydrophobe (C20) had a globular configuration, whereas the HASE polymers with smaller hydrophobes (C8 or C16) formed branch like configurations. The difference in the aggregate configurations of different HASE polymers explained why the solution viscosities in the dilute polymer concentration regime were found to increase with a decrease in the hydrophobe size. The adsorption study of the HASE polymers onto negatively charged polystyrene latex found that the adsorbed amount and the layer height, determined from DLS and SLS, increased with an increase in the salt concentration. At very high salt concentrations, the adsorbed layer height of the HASE polymer with large hydrophobes (C20) showed stronger dependence on the surface coverage compared to the dependence of the layer height on the surface coverage of the HASE polymers with weaker hydrophobes (C8 or C16). When no salt was added to the system, the layer height was independent of the surface coverage. The behavior of the adsorbed layer of the HASE polymers in the high and no salt regime was analogous to the behavior of the adsorbed layer formed by simple end-grafted polyelectrolytes. In conclusion, by disrupting the hydrophobic association in the HASE polymers, we determined their molecular weight and their molecular architecture. The aggregation phenomena of the HASE polymers were found to be rich. The interplay between hydrophobic association and electrostatic repulsion gave rise to different aggregate configurations such as linear string, branch, or globule. Our adsorption studies demonstrated the possibility of explaining the adsorption phenomena of the HASE polymers in terms of simple end-grafted polyelectrolytes.

  20. Molecular aggregation of humic substances

    USGS Publications Warehouse

    Wershaw, R. L.

    1999-01-01

    Humic substances (HS) form molecular aggregates in solution and on mineral surfaces. Elucidation of the mechanism of formation of these aggregates is important for an understanding of the interactions of HS in soils arid natural waters. The HS are formed mainly by enzymatic depolymerization and oxidation of plant biopolymers. These reactions transform the aromatic and lipid plant components into amphiphilic molecules, that is, molecules that consist of separate hydrophobic (nonpolar) and hydrophilic (polar) parts. The nonpolar parts of the molecules are composed of relatively unaltered segments of plant polymers and the polar parts of carboxylic acid groups. These amphiphiles form membrane-like aggregates on mineral surfaces and micelle-like aggregates in solution. The exterior surfaces of these aggregates are hydrophilic, and the interiors constitute separate hydrophobic liquid-like phases.