Science.gov

Sample records for aggregate size classes

  1. Differences in SOM Decomposition and Temperature Sensitivity among Soil Aggregate Size Classes in a Temperate Grasslands

    PubMed Central

    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. PMID:25692291

  2. Class Size.

    ERIC Educational Resources Information Center

    Underwood, Siobhan; Lumsden, Linda S.

    1994-01-01

    The items featured in this annotated bibliography touch on several aspects of the multifaceted class-size debate. Allen Odden reviews the literature and contends that class-size reduction should be used "sparingly and strategically." C. M. Achilles and colleagues examines two different class-size situations and find student test performance in the…

  3. Class Size.

    ERIC Educational Resources Information Center

    Johnston, Holly R.

    Exploring the class-size issue, this paper focuses on the primary grades and asks questions such as "does a reduction in class size promote an increase in academic achievement?" and "how substantial does the reduction in numbers have to be in order for a significant increase to occur?" The paper surveys debates on class size and the social factors…

  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. 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

  8. 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…

  9. Phosphorus content as a function of soil aggregate size and paddy cultivation in highly weathered soils.

    PubMed

    Li, Baozhen; Ge, Tida; Xiao, Heai; Zhu, Zhenke; Li, Yong; Shibistova, Olga; Liu, Shoulong; Wu, Jinshui; Inubushi, Kazuyuki; Guggenberger, Georg

    2016-04-01

    Red soils are the major land resource in subtropical and tropical areas and are characterized by low phosphorus (P) availability. To assess the availability of P for plants and the potential stability of P in soil, two pairs of subtropical red soil samples from a paddy field and an adjacent uncultivated upland were collected from Hunan Province, China. Analysis of total P and Olsen P and sequential extraction was used to determine the inorganic and organic P fractions in different aggregate size classes. Our results showed that the soil under paddy cultivation had lower proportions of small aggregates and higher proportions of large aggregates than those from the uncultivated upland soil. The portion of >2-mm-sized aggregates increased by 31 and 20 % at Taoyuan and Guiyang, respectively. The total P and Olsen P contents were 50-150 and 50-300 % higher, respectively, in the paddy soil than those in the upland soil. Higher inorganic and organic P fractions tended to be enriched in both the smallest and largest aggregate size classes compared to the middle size class (0.02-0.2 mm). Furthermore, the proportion of P fractions was higher in smaller aggregate sizes (<2 mm) than in the higher aggregate sizes (>2 mm). In conclusion, soils under paddy cultivation displayed improved soil aggregate structure, altered distribution patterns of P fractions in different aggregate size classes, and to some extent had enhanced labile P pools. PMID:26728283

  10. 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

  11. 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…

  12. 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…

  13. 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…

  14. The "Why's" of Class Size: Student Behavior in Small Classes

    ERIC Educational Resources Information Center

    Finn, Jeremy D.; Pannozzo, Gina M.; Achilles, Charles M.

    2003-01-01

    Small classes in the elementary grades have been shown to boost students' academic performance. However, researchers continue to seek a consistent, integrated explanation of "why" small classes have positive effects. This article forwards the hypothesis that when class sizes are reduced, major changes occur in students' engagement in the…

  15. 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)

  16. 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…

  17. Additional Evidence on the Relationship between Class Size and Student Performance

    ERIC Educational Resources Information Center

    Arias, J. J.; Walker, Douglas M.

    2004-01-01

    Much of the economic education literature suggests that the principles of economics class size does not significantly affect student performance. However, study methods have varied in terms of the aggregation level (student or class), the measure of performance (TUCE or course letter grade), and the class size measure (e.g., students who completed…

  18. Self-aggregation and its dependence on domain size

    NASA Astrophysics Data System (ADS)

    Jeevanjee, N.; Romps, D. M.

    2012-12-01

    When evaluating a single-column model against a cloud-resolving model (CRM), the choice of CRM domain size can exert a substantial influence on the results. In particular, recent studies have shown that self-aggregation of convection in numerical models occurs only beyond a certain threshold domain size of about 200-300 km. We present evidence that, in the absence of cold pools, self-aggregation can actually occur in any size domain, implying that self-aggregation is a more universal tendency than previously thought. At small (~ 50 km) domains, however, the degree of aggregation (as measured by the precipitable water in the dry region) is quite small. As the domain size increases, though, the degree of aggregation increases as well, peaking in the same 200-300 km regime in which the transition from un-aggregated to self-aggregated convection (with cold pools) has been seen to occur. We will discuss some of the factors responsible for setting this scale. 2D horizontal plots of boundary-layer specific humidity for different domain sizes. The different degrees of aggregation are evident

  19. 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…

  20. 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.

  1. 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…

  2. 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.

  3. 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.

  4. 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…

  5. Class Size and Public Policy: Politics and Panaceas.

    ERIC Educational Resources Information Center

    Tomlinson, Tommy M.

    This document reviews the issue of class size reduction, analyzes the evidence from research on the relationship between class size and educational improvement, and cites findings supporting the view that the costs of class size reduction outweigh the benefits and that reducing class size to improve student achievement is inconsistent with the…

  6. Class Size and Student Success: Comparing the Results of Five Elementary Schools Using Small Class Sizes.

    ERIC Educational Resources Information Center

    Haenn, Joseph F.

    Three "Lab" schools were established in 1994-1995 in Durham, North Carolina public schools solely to provide smaller classes for disadvantaged inner-city students. In addition, smaller class sizes were achieved in two additional elementary schools by "cashing in" teacher aides and other more judicious use of available funds. These two schools were…

  7. 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

  8. 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...

  9. 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

  10. Measurement of aggregates' size distribution by angular light scattering

    NASA Astrophysics Data System (ADS)

    Caumont-Prim, Chloé; Yon, Jérôme; Coppalle, Alexis; Ouf, François-Xavier; Fang Ren, Kuan

    2013-09-01

    A novel method is introduced for in situ determination of the size distribution of submicronic fractal aggregate particles by unique measurement of angular scattering of light. This method relies on the dependence of a new defined function Rg⋆ on the polydispersity of the aggregates' size distribution. The function Rg⋆ is then interpreted by the use of iso-level charts to determine the parameters of the log-normal soot size distribution. The main advantage of this method is its independence of the particle optical properties and primary sphere diameter. Moreover, except for the knowledge of fractal dimension, this method does not require any additional measurement. It is validated on monodisperse particles selected by a differential mobility analyzer and polydisperse soot from ethylene diffusion flame whose size distribution is independently determined by Transmission Electron Microscopy. Finally, the size distribution of soot generated by a commercial apparatus is measured by the proposed method and the comparison to that given by a commercial granulometer shows a good agreement.

  11. 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

  12. 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.

  13. 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

  14. 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…

  15. 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. PMID:26742959

  16. 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…

  17. Online Courses and Optimal Class Size: A Complex Formula

    ERIC Educational Resources Information Center

    Arzt, Judy

    2011-01-01

    The purpose of this study was to conduct descriptive, exploratory research to answer the questions: What is the ideal class size for online courses? What are the variables that affect optimal class size in this environment? As a study of the literature, the goal was to collect research-based evidence supporting optimal class size. The initial…

  18. The Paradox of Reducing Class Size and Improving Learning Outcomes

    ERIC Educational Resources Information Center

    Hattie, John

    2005-01-01

    This paper addresses four questions: What are the effects of reducing class size? How important are these effects? How can we explain these effects? and How can we improve the outcomes when class sizes are reduced? A major aim is to provide directions for resolving the paradox as to "Why reducing class size has not led to major improvements in…

  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. 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…

  1. High School Class-Size and College Performance in Science

    ERIC Educational Resources Information Center

    Wyss, Vanessa L.; Tai, Robert H.; Sadler, Philip M.

    2007-01-01

    This paper focuses on the influence of high school science class size on students' achievement in introductory college science courses and on the variation of teacher practice across class size. Surveys collected information about high school science class experiences from 2754 biology, 3521 chemistry, and 1903 physics students across 36 public…

  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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

    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-1 and 2 m s-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-1 was significantly lower than expected. We present the critical energy for disruptive collisions Q sstarf, 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. Finite Size Effects in Simulations of Protein Aggregation

    PubMed Central

    Pawar, Amol; Favrin, Giorgio

    2008-01-01

    It is becoming increasingly clear that the soluble protofibrillar species that proceed amyloid fibril formation are associated with a range of neurodegenerative disorders such as Alzheimer's and Parkinson diseases. Computer simulations of the processes that lead to the formation of these oligomeric species are starting to make significant contributions to our understanding of the determinants of protein aggregation. We simulate different systems at constant concentration but with a different number of peptides and we study the how the finite number of proteins affects the underlying free energy of the system and therefore the relative stability of the species involved in the process. If not taken into account, this finite size effect can undermine the validity of theoretical predictions regarding the relative stability of the species involved and the rates of conversion from one to the other. We discuss the reasons that give rise to this finite size effect form both a probabilistic and energy fluctuations point of view and also how this problem can be dealt by a finite size scaling analysis. PMID:18612385

  5. School Facility Recommendations for Class Size Reduction.

    ERIC Educational Resources Information Center

    Evans, Ann M.

    The California Department of Education encourages its school districts to make every effort to reduce classroom size and maintain the physical size of 960 square feet for elementary schools and 1,350 square feet for kindergartens. This report examines the Code of Regulations relative to classroom size in elementary, kindergarten, and special…

  6. 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)

  7. 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…

  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. Competing Explanations of Class Size Reduction Effects: The California Case.

    ERIC Educational Resources Information Center

    Mitchell, Douglas E.; Mitchell, Ross E.

    Competing explanations of class size reduction effects on student academic achievement were tested using student, teacher, and school data collected from nearly 700 classrooms in over 70 schools during the first 3 years of implementation of California's (K-3) Class Size Reduction Program. Five major hypotheses were tested: (1) overall impact of…

  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. Effects of Particle Size and Shape, and Soil Structure on Thermal Properties of Non-aggregated and Aggregated Soils

    NASA Astrophysics Data System (ADS)

    Kamoshida, T.; Hamamoto, S.; Kawamoto, K.; Sakaki, T.; Komatsu, T.; Hu, Q.

    2012-12-01

    Thermal properties including thermal conductivity and heat capacity are very important for understanding heat transport processes in landfill site cover soil to control the microbial processes in the cover soil. Previous studies have shown effects of soil conditions such as moisture content and degree of compaction on the thermal properties for differently-textured soils. However, there are few studies on the relations between the thermal properties and micro-scale soil information such as particle size and shape although the size and shape of soil particles highly affect soil packing configuration. In addition, it is not fully understood that soil structure (i.e., aggregate structure) affects behaviors of thermal properties. In this study, non-aggregated (sandy) and aggregated soils with different size fractions at variably-saturated conditions were used for measuring thermal properties. Micro-scale characterizations of soil-pore structure and soil particle configuration using a X-ray CT device were also performed for sandy soils. For sandy soils, the relation between measured thermal properties and mineral composition (i.e., quartz content), roundness/sphericity of soil particles, and particle size, and solid-phase tortuosity based on X-ray CT images, were investigated. For aggregated soils, the measured thermal conductivities at variably-saturated conditions were discussed based on the water retention characteristics and pore-size distribution in inter- and intra-aggregate pore regions.

  15. 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.

  16. 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.

  17. 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

  18. Frequency, Size, and Localization of Bacterial Aggregates on Bean Leaf Surfaces

    PubMed Central

    Monier, J.-M.; Lindow, S. E.

    2004-01-01

    Using epifluorescence microscopy and image analysis, we have quantitatively described the frequency, size, and spatial distribution of bacterial aggregates on leaf surfaces of greenhouse-grown bean plants inoculated with the plant-pathogenic bacterium Pseudomonas syringae pv. syringae strain B728a. Bacterial cells were not randomly distributed on the leaf surface but occurred in a wide range of cluster sizes, ranging from single cells to over 104 cells per aggregate. The average cluster size increased through time, and aggregates were more numerous and larger when plants were maintained under conditions of high relative humidity levels than under dry conditions. The large majority of aggregates observed were small (less than 100 cells), and aggregate sizes exhibited a strong right-hand-skewed frequency distribution. While large aggregates are not frequent on a given leaf, they often accounted for the majority of cells present. We observed that up to 50% of cells present on a leaf were located in aggregates containing 103 cells or more. Aggregates were associated with several different anatomical features of the leaf surface but not with stomates. Aggregates were preferentially associated with glandular trichomes and veins. The biological and ecological significance of aggregate formation by epiphytic bacteria is discussed. PMID:14711662

  19. 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…

  20. Correlation of Red Blood Cell Aggregate Size with Transmitted Light Intensity Distributions

    NASA Astrophysics Data System (ADS)

    Hitt, Darren L.

    1998-11-01

    Under sufficiently low shear rates, such as those encountered in the microcirculation, human red blood cells are known to form aggregate structures (`rouleaux'). These aggregates may range in size from a simple chain containing only a few cells to complex three-dimensional structures containing tens of cells. Previous studies have attempted to characterize the aggregate size by examining the spatial distribution of transmitted light intensity resulting from transillumination of the blood flow. For experiments performed in vitro and in vivo, spectral analysis of the transmitted light intensities has shown that the presence of aggregates in the flow can linked with an increase in the spectral power at small wavenumbers. The magnitudes of the affected wavenumbers correspond to structures considerably larger than individual cells. A precise numerical correlation, however, is difficult to establish. In this work, computer simulations of aggregating blood flow are used along with statistical considerations in an attempt to better correlate the observed spectral trends with actual aggregate size.

  1. 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…

  2. 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…

  3. The Non-Cognitive Returns to Class Size

    ERIC Educational Resources Information Center

    Dee, Thomas S.; West, Martin R.

    2011-01-01

    The authors use nationally representative survey data and a research design that relies on contemporaneous within-student and within-teacher comparisons across two academic subjects to estimate how class size affects certain non-cognitive skills in middle school. Their results indicate that smaller eighth-grade classes are associated with…

  4. 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…

  5. EFFECT OF SOIL AGGREGATE SIZE DISTRIBUTION ON WATER RETENTION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quantitative information on soil water retention is in demand in hydrology, agrometeorology, agronomy, contaminant transport, and other soil-related disciplines of earth and environmental sciences. Soil aggregate composition is an important characteristic of soil structure and, as such, has been exp...

  6. 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…

  7. Size effects in models for mechanically-stressed protein crystals and aggregates

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1992-01-01

    As protein aggregates increase in size, they become easier to disrupt mechanically. Using the scaling properties of models proposed to govern protein aggregation, the effect of thermal vibrations and gravity are investigated as deforming forces. For typical protein assemblies made of 30 A proteins, the assembled diameter must remain less than 100-10,000 times the molecular radius to survive in finite thermal and gravity fields. The analysis predicts the following experimental outcomes: (1) reductions in gravitational strain should favor larger protein aggregates; (2) in comparing the aggregate stability of different proteins, the addition of peptide chains should stabilize against thermal strain, but should not affect gravitational strain; (3) critical aggregate sizes should show significant (exponential) sensitivity to cluster geometry, solution preparation and growth conditions. The analysis is extended to consider qualitative size effects in crystal damage during X-ray exposure.

  8. 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.

  9. Effect of water on deposition, aggregate size, and viscosity of asphaltenes.

    PubMed

    Aslan, Seyma; Firoozabadi, Abbas

    2014-04-01

    The aggregation and structure of polar molecules in nonpolar media may have a profound effect on bulk phase properties and transport. In this study, we investigate the aggregation and deposition of water and asphaltenes, the most polar fraction in petroleum fluids. In flow-line experiments, we vary the concentration of water from 500 up to 175,000 ppm and provide the evidence for clear changes in asphaltene deposition. Differential interference contrast (DIC) microscopy and dynamic light scattering (DLS) are used to measure the size of the aggregates. Rheological measurements are performed to get fixed ideas on the structural changes that water induces at different concentrations. This study demonstrates the significant effect of water on asphaltene aggregation and deposition and explores the molecular basis of water-asphaltene interaction. Our aggregate size measurements show that while asphaltene molecules increase the solubilization of water, there is no increase in the aggregate size. Our aggregation size measurements are different from the reports in the literature. PMID:24650340

  10. 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…

  11. 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…

  12. The Effects of Class Size: An Examination of Rival Hypotheses.

    ERIC Educational Resources Information Center

    Hedges, Larry V.; Stock, William

    1983-01-01

    The results of reanalyses of statistical procedures used in the class-size meta-analyses by Glass and Smith are reported. The analyses suggest that the use of suboptimal statistical methods did not greatly affect the results of the meta-analyses by Glass and Smith. (Author/PN)

  13. Class Size: An Amendment Reflecting Further Research on State Policies.

    ERIC Educational Resources Information Center

    Mitchell, Douglas E.; Mitchell, Ross E.

    This report, by reviewing the contents of specific state statutes and regulations, extends the discussion of actions by state legislatures and education agencies to reduce class size. Data are drawn from primary sources and from email or telephone interviews with state department of education officials. Following the design used in the original…

  14. 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…

  15. 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.

  16. 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.

  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. Impact of aggregate size and structure on the photocatalytic properties of TiO2 and ZnO nanoparticles.

    PubMed

    Jassby, David; Farner Budarz, Jeffrey; Wiesner, Mark

    2012-07-01

    Aggregation of photocatalytic semiconductors was determined to reduce the generation of free hydroxyl radicals in aqueous suspensions in a fashion dependent on aggregate size and structure. Static light scattering measurements were used to follow temporal changes in the fractal dimension of aggregating TiO(2) and ZnO nanoparticles. At length scales comparable to nanoparticle size, the structure of aggregated TiO(2) nanoparticles was independent of particle stability and the associated aggregation rate, consistent with the fused nature of TiO(2) primary particles in the initial suspension. In contrast, ZnO aggregates were characterized by smaller fractal dimensions when ionic strength, and the resulting aggregation rate, were increased. The photocatalytic activity of ZnO and TiO(2) in generating free hydroxyl radicals varied with aggregate structure and size, consistent with theory that predicts reduced reactivity as aggregates become larger and more dense. PMID:22225505

  1. Shape and Size of Microfine Aggregates: X-ray Microcomputed Tomgraphy vs. Laser Diffraction

    SciTech Connect

    Erdogan,S.; Garboczi, E.; Fowler, D.

    2007-01-01

    Microfine rock aggregates, formed naturally or in a crushing process, pass a No. 200 ASTM sieve, so have at least two orthogonal principal dimensions less than 75 {mu}m, the sieve opening size. In this paper, for the first time, we capture true 3-D shape and size data of several different types of microfine aggregates, using X-ray microcomputed tomography ({mu}CT) with a voxel size of 2 {mu}m. This information is used to generate shape analyses of various kinds. Particle size distributions are also generated from the {mu}CT data and quantitatively compared to the results of laser diffraction, which is the leading method for measuring particle size distributions of sub-millimeter size particles. By taking into account the actual particle shape, the differences between {mu}CT and laser diffraction can be qualitatively explained.

  2. 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…

  3. 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.…

  4. 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…

  5. 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…

  6. 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.

  7. 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

  8. 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.

  9. Size-dependent enrichment of waste slag aggregate fragments abraded from asphalt concrete.

    PubMed

    Takahashi, Fumitake; Shimaoka, Takayuki; Gardner, Kevin; Kida, Akiko

    2011-10-30

    Authors consider the environmental prospects of using melted waste slag as the aggregate for asphalt pavement. In particular, the enrichment of slag-derived fragments in fine abrasion dust particles originated from slag asphalt concrete and its size dependency were concerned. A series of surface abrasion tests for asphalt concrete specimens, containing only natural aggregates as reference or 30 wt% of substituted slag aggregates, were performed. Although two of three slag-asphalt concretes generated 1.5-3.0 times larger amount of abrasion dust than the reference asphalt concrete did, it could not be explained only by abrasion resistance of slag. The enrichment of slag-derived fragments in abrasion dust, estimated on the basis of the peak intensity of quartz and heavy metal concentrations, had size dependency for all slag-asphalt concretes. Slag-derived fragments were enriched in abrasion dust particles with diameters of 150-1000 μm. Enrichment factors were 1.4-2.1. In contrast, there was no enrichment in abrasion dust particles with diameter less than 75 μm. This suggests that prior airborne-size fragmentation of substituted slag aggregates does not need to be considered for tested slag aggregates when environmental risks of abrasion dust of slag-asphalt pavement are assessed. PMID:21868161

  10. 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.

  11. Significance of microhabitat heterogeneity in the spatial pattern and size-class structure of Anastatica hierochuntica L.

    NASA Astrophysics Data System (ADS)

    Hegazy, Ahmad K.; Kabiel, Hanan F.

    2007-05-01

    Anastatica hierochuntica L. (Brassicaceae) is a desert monocarpic annual species characterized by a topochory/ombrohydrochory type of seed dispersal. The hygrochastic nature of the dry skeletons (dead individuals) permits controlling seed dispersal by rain events. The amount of dispersed seeds is proportional to the intensity of rainfall. When light showers occur, seeds are released and remain in the site. Seeds dispersed in the vicinity of the mother or source plant (primary type of seed dispersal) resulted in clumped pattern and complicated interrelationships among size-classes of the population. Following heavy rainfall, most seeds are released and transported into small patches and shallow depressions which collect runoff water. The dead A. hierochuntica skeletons demonstrate site-dependent size-class structure, spatial pattern and spatial interrelationships in different microhabitats. Four microhabitat types have been sampled: runnels, patches and simple and compound depressions in two sites (gravel and sand). Ripley's K-function was used to analyze the spatial pattern in populations of A. hierochuntica skeletons in the study microhabitats. Clumped patterns were observed in nearly all of the study microhabitats. Populations of A. hierochuntica in the sand site were more productive than in the gravel site and usually had more individuals in the larger size-classes. In the compound-depression microhabitat, the degree of clumping decreased from the core zone to the intermediate zone then shifted into overdispersed pattern in the outer zone. At the within size-class level, the clumped pattern dominated in small size classes but shifted into random and overdispersed patterns in the larger size classes. Aggregation between small and large size-classes was not well-defined but large individuals were found closer to the smaller individuals than to those of their own class. In relation to the phytomass and the size-class structure, the outer zone of the simple

  12. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  14. Optimal Context Size in Elementary Schools: Disentangling the Effects of Class Size and School Size

    ERIC Educational Resources Information Center

    Ready, Douglas D.; Lee, Valerie E.

    2007-01-01

    Young children's learning--and how their learning is distributed by social background--may be influenced by the structural and organizational properties of their school. This study focuses on one important structural dimension of these educational contexts: "size." This study differs from extant studies linking size to student outcomes in four…

  15. 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

  16. Class Size Effects on the Number and Types of Student-Teacher Interactions in Primary Classrooms

    ERIC Educational Resources Information Center

    Folmer-Annevelink, Elvira; Doolaard, Simone; Mascareno, Mayra; Bosker, Roel J.

    2010-01-01

    This paper addresses the relationship between class size and student-teacher interactions as an explanation for effects of class size on achievement. Observations were conducted in kindergarten and Grade 1 classes from 46 Dutch primary schools in order to address the effect of class size on the amount and type of student-teacher interactions. The…

  17. Aggregate size and architecture determine microbial activity balance for one-stage partial nitritation and anammox.

    PubMed

    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

    2010-02-01

    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

  18. 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.

  19. Effects of size polydispersity on the extinction spectra of colloidal nanoparticle aggregates

    NASA Astrophysics Data System (ADS)

    Ershov, Alexander E.; Isaev, Ivan L.; Semina, Polina N.; Markel, Vadim A.; Karpov, Sergei V.

    2012-01-01

    We investigate the effect of particle polydispersity on the optical extinction spectra of colloidal aggregates of spherical metallic (silver) nanoparticles, taking into account the realistic interparticle gaps caused by layers of stabilizing polymer adsorbed on the metal surface (adlayers). The spectra of computer-generated aggregates are computed using two different methods. The coupled-multipole method is used in the quasistatic approximation and the coupled-dipole method beyond the quasistatics. The latter approach is applicable if the interparticle gaps are sufficiently wide relative to the particle radii. Simulations are performed for two different particle size distribution functions (bimodal and Gaussian), varying the number of particles per aggregate, and different distribution functions of the interparticle gap width. The strong influence of the latter factor on the spectra is demonstrated and investigated in detail.

  20. 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.

  1. 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

  2. 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.

  3. Bacterial Community Composition of Size-Fractioned Aggregates within the Phycosphere of Cyanobacterial Blooms in a Eutrophic Freshwater Lake

    PubMed Central

    Cai, Haiyuan; Jiang, Helong; Krumholz, Lee R.; Yang, Zhen

    2014-01-01

    Bacterial community composition of different sized aggregates within the Microcystis cyanobacterial phycosphere were determined during summer and fall in Lake Taihu, a eutrophic lake in eastern China. Bloom samples taken in August and September represent healthy bloom biomass, whereas samples from October represent decomposing bloom biomass. To improve our understanding of the complex interior structure in the phycosphere, bloom samples were separated into large (>100 µm), medium (10–100 µm) and small (0.2–10 µm) size aggregates. Species richness and library coverage indicated that pyrosequencing recovered a large bacterial diversity. The community of each size aggregate was highly organized, indicating highly specific conditions within the Microcystis phycosphere. While the communities of medium and small-size aggregates clustered together in August and September samples, large- and medium-size aggregate communities in the October sample were grouped together and distinct from small-size aggregate community. Pronounced changes in the absolute and relative percentages of the dominant genus from the two most important phyla Proteobacteria and Bacteroidetes were observed among the various size aggregates. Bacterial species on large and small-size aggregates likely have the ability to degrade high and low molecular weight compounds, respectively. Thus, there exists a spatial differentiation of bacterial taxa within the phycosphere, possibly operating in sequence and synergy to catalyze the turnover of complex organic matters. PMID:25144467

  4. A uniform measurement expression for cross method comparison of nanoparticle aggregate size distributions.

    PubMed

    Dudkiewicz, Agnieszka; Wagner, Stephan; Lehner, Angela; Chaudhry, Qasim; Pietravalle, Stéphane; Tiede, Karen; Boxall, Alistair B A; Allmaier, Guenter; Tiede, Dirk; Grombe, Ringo; von der Kammer, Frank; Hofmann, Thilo; Mølhave, Kristian

    2015-08-01

    Available measurement methods for nanomaterials are based on very different measurement principles and hence produce different values when used on aggregated nanoparticle dispersions. This paper provides a solution for relating measurements of nanomaterials comprised of nanoparticle aggregates determined by different techniques using a uniform expression of a mass equivalent diameter (MED). The obtained solution is used to transform into MED the size distributions of the same sample of synthetic amorphous silica (nanomaterial comprising aggregated nanoparticles) measured by six different techniques: scanning electron microscopy in both high vacuum (SEM) and liquid cell setup (Wet-SEM); gas-phase electrophoretic mobility molecular analyzer (GEMMA); centrifugal liquid sedimentation (CLS); nanoparticle tracking analysis (NTA); and asymmetric flow field flow fractionation with inductively coupled plasma mass spectrometry detection (AF4-ICP-MS). Transformed size distributions are then compared between the methods and conclusions drawn on methods' measurement accuracy, limits of detection and quantification related to the synthetic amorphous silca's size. Two out of the six tested methods (GEMMA and AF4-ICP-MS) cross validate the MED distributions between each other, providing a true measurement. The measurement accuracy of other four techniques is shown to be compromised either by the high limit of detection and quantification (CLS, NTA, Wet-SEM) or the sample preparation that is biased by increased retention of smaller nanomaterials (SEM). This study thereby presents a successful and conclusive cross-method comparison of size distribution measurements of aggregated nanomaterials. The authors recommend the uniform MED size expression for application in nanomaterial risk assessment studies and clarifications in current regulations and definitions concerning nanomaterials. PMID:26081166

  5. Single-shot measurement of soot aggregate sizes by wide-angle light scattering (WALS)

    NASA Astrophysics Data System (ADS)

    Oltmann, H.; Reimann, J.; Will, S.

    2012-01-01

    The wide-angle light scattering (WALS) approach has been utilized for the measurement of soot aggregate sizes (radii of gyration) in flames on a single-shot basis. Key elements are a pulsed laser and an ellipsoidal mirror, which images the light scattered within a plane onto an intensified CCD camera, thus allowing for an instantaneous acquisition of a full scattering diagram with high resolution. Results for a laminar premixed flame exhibit good agreement with averaged data and demonstrate the feasibility of the method. The applicability of the technique to unsteady combustion processes is demonstrated by measuring aggregate sizes in a weakly turbulent jet-diffusion flame. In both cases light scattering results are verified by data obtained from electron microscopy analysis of sampled soot.

  6. 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

  7. Size distribution of particles in Saturn's rings from aggregation and fragmentation.

    PubMed

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

    2015-08-01

    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

  8. 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…

  9. Making Sense of Continuing and Renewed Class-Size Findings and Interest.

    ERIC Educational Resources Information Center

    Achilles, C. M.; Finn, J. D.

    In this paper, the authors examine several factors related to class size. The purpose of the presentation is to: (1) trace the evolution of class-size research; (2) briefly describe the Student Achievement Ratio (STAR) class-size experiment; (3) summarize the early and the later student outcomes of STAR participants; (4) outline the…

  10. The Effects of Class Size on Student Achievement in Higher Education: Applying an Earnings Function.

    ERIC Educational Resources Information Center

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

    This paper uses an earnings function to model how class size affects the grade students earn. It tests the model using an ordinal logit with and without fixed effects on 363,023 undergraduate observations. It finds that class size negatively affects grades. Average grade point average declines as class size increases, precipitously up to class…

  11. 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…

  12. 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…

  13. Class Size: What Does Research Tell Us? Spotlight on Student Success.

    ERIC Educational Resources Information Center

    Finn, Jeremy D.

    This report summarizes the findings of some recent pivotal studies of class size, especially as they relate to students at risk. Of particular note is a large-scale study of class size, which was designed to test the conclusions of G. Glass and M. Smith (1978) and G. Robinson (1990) about the advantages of small class size. This study, Project…

  14. 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…

  15. Does Class Size Make a Difference? Recent Findings from State and District Initiatives.

    ERIC Educational Resources Information Center

    Egelson, Paula; And Others

    Research has indicated that educators view class size as a factor in improving student learning. This publication summarizes findings about some recently implemented class-size initiatives. It highlights results from Tennessee's reduced class-size experiment of the 1980s; summarizes the efforts and results from other recent state-level initiatives…

  16. 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.

  17. 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.

  18. 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…

  19. 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

  20. Effects of Aggregate Morphology and Size on SP2 Measurements of Black Carbon

    NASA Astrophysics Data System (ADS)

    Bambha, R.; Michelsen, H. A.

    2015-12-01

    We have used a Single-Particle Soot Photometer (SP2) to measure time-resolved laser-induced incandescence (LII) and laser scatter from combustion-generated mature soot with a fractal dimension of 1.88 extracted from a burner. We have also made measurements on restructured mature-soot particles with a fractal dimension of 2.4. The soot samples were size selected using a differential mobility analyzer and characterized with a scanning mobility particle sizer and centrifugal particle mass analyzer. We reproduced the LII and scattering temporal profiles with an energy- and mass-balance model, which accounted for heating of particles passed through a CW-laser beam over laser-particle interaction times of ~10 microseconds. The results demonstrate a strong influence of aggregate size and morphology on LII and scattering signals. Conductive cooling competes with absorptive heating on these time scales; the effects are reduced with increasing aggregate size and fractal dimension. These effects can lead to a significant delay in the onset of the LII signal, which could be mistaken for a coating effect. These effects may also explain an apparent low bias in the SP2 measurements for small particle sizes, particularly for fresh, mature soot. The results additionally reveal significant perturbations to the measured scattering signal from LII interference and suggest swelling or popping of the aggregates during sublimation. We are characterizing black carbon measurement techniques prior to deployment of instrumentation in Barrow, Alaska for a project focused on measurements and modeling of black carbon in the Arctic.

  1. 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

  2. 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

  3. 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

  4. 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. PMID:26418563

  5. CLASS SIZE AND ACHIEVEMENT GAINS IN SEVENTH- AND EIGHTH-GRADE ENGLISH AND MATHEMATICS.

    ERIC Educational Resources Information Center

    JOHNSON, MAURITZ; SCRIVEN, ELDON

    USING DATA OBTAINED BY THE QUALITY MEASUREMENT PROJECT ON SOME 70,000 PUPILS, THIS STUDY ATTEMPTED TO PRODUCE EVIDENCE REGARDING THE INFLUENCE OF CLASS SIZE AND CLASS HOMOGENEITY ON ACHIEVEMENT GAINS IN GRADES 7 AND 8. A TOTAL OF 130 ENGLISH AND 135 MATHEMATICS CLASSES CLASSIFIED ACCORDING TO SIZE AND HOMOGENEITY WERE EXAMINED. THE READING…

  6. 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…

  7. "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…

  8. Adenosine diphosphate-induced aggregation of human platelets in flow through tubes. I. Measurement of concentration and size of single platelets and aggregates.

    PubMed Central

    Bell, D N; Spain, S; Goldsmith, H L

    1989-01-01

    A double infusion flow system and particle sizing technique were developed to study the effect of time and shear rate on adenosine diphosphate-induced platelet aggregation in Poiseuille flow. Citrated platelet-rich plasma, PRP, and 2 microM ADP were simultaneously infused into a 40-microliters cylindrical mixing chamber at a fixed flow ratio, PRP/ADP = 9:1. After rapid mixing by a rotating magnetic stirbar, the platelet suspension flowed through 1.19 or 0.76 mm i.d. polyethylene tubing for mean transit times, t, from 0.1 to 86 s, over a range of mean tube shear rate, G, from 41.9 to 1,000 s-1. Known volumes of suspension were collected into 0.5% buffered glutaraldehyde, and all particles in the volume range 1-10(5) microns 3 were counted and sized using a model ZM particle counter (Coulter Electronics Inc., Hialeah, FL) and a logarithmic amplifier. The decrease in the single platelet concentration served as an overall index of aggregation. The decrease in the total particle concentration was used to calculate the collision capture efficiency during the early stages of aggregation, and aggregate growth was followed by changes in the volume fraction of particles of successively increasing size. Preliminary results demonstrate that both collision efficiency and particle volume fraction reveal important aspects of the aggregation process not indicated by changes in the single platelet concentration alone. PMID:2605298

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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…

  14. 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

  15. 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

  16. 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

  17. 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

  18. Lifespan and Aggregate Size Variables in Specifications of Mortality or Survivorship

    PubMed Central

    Epelbaum, Michael

    2014-01-01

    A specification of mortality or survivorship provides respective explicit details about mortality's or survivorship's relationships with one or more other variables (e.g., age, sex, etc.). Previous studies have discovered and analyzed diverse specifications of mortality or survivorship; these discoveries and analyses suggest that additional specifications of mortality or survivorship have yet to be discovered and analyzed. In consistency with previous research, multivariable limited powered polynomials regression analyses of mortality and survivorship of selected humans (Swedes, 1760–2008) and selected insects (caged medflies) show age-specific, historical-time-specific, environmental-context-specific, and sex-specific mortality and survivorship. These analyses also present discoveries of hitherto unknown lifespan-specific, contemporary-aggregate-size-specific, and lifespan-aggregate-size-specific mortality and survivorship. The results of this investigation and results of previous research help identify variables for inclusion in regression models of mortality or survivorship. Moreover, these results and results of previous research strengthen the suggestion that additional specifications of mortality or survivorship have yet to be discovered and analyzed, and they also suggest that specifications of mortality and survivorship indicate corresponding specifications of frailty and vitality. Furthermore, the present analyses reveal the usefulness of a multivariable limited powered polynomials regression model-building approach. This article shows that much has yet to be learned about specifications of mortality or survivorship of diverse kinds of individuals in diverse times and places. PMID:24454719

  19. 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. PMID:26706749

  20. Bioaccessibility of environmentally aged 14C-atrazine residues in an agriculturally used soil and its particle-size aggregates.

    PubMed

    Jablonowski, Nicolai D; Modler, Janette; Schaeffer, Andreas; Burauel, Peter

    2008-08-15

    After 22 years of aging under natural conditions in an outdoor lysimeter the bioaccessibility of 14C-labeled atrazine soil residues to bacteria was tested. Entire soil samples as well as sand-sized, silt-sized, and clay-sized aggregates (>20, 20-2, and <2microm aggregate size, respectively) were investigated under slurried conditions. The mineralization of residual radioactivity in the outdoor lysimeter soil reached up to 4.5% of the total 14C-activity after 16 days, inoculated with Pseudomonas sp. strain ADP. The control samples without inoculated bacteria showed a mineralization maximum of only about 1% after 44 days of incubation. Mineralization increased in the clay-sized aggregates up to 6.2% of the total residual 14C-activity within 23 days. With decreasing soil aggregate sizes, residual 14C-activity increased per unit of weight, but only minor differences of the mineralization in the soil and soil size aggregates using mineral-media for incubation was observed. Using additional Na-citrate in the incubation, the extent of mineralization increased to 6.7% in soil after 23 days following incubation with Pseudomonas sp. strain ADP. These results show that long-term aged 14C-atrazine residues are still partly accessible to the atrazine degrading microorganism Pseudomonas sp. strain ADP. PMID:18767643

  1. 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.

  2. 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

  3. Let's Put Kids First, Finally: Getting Class Size Right.

    ERIC Educational Resources Information Center

    Achilles, Charles M.

    This book contains vignettes and observations provided by teachers who conduct small classes in primary grades. Designed for school leaders, teachers, administrators, students, and others who care about the future of education, the text presents findings from the Student Teacher Achievement Ratio (STAR), the DuPont Study, and the Lasting Benefits…

  4. Evaluation and Comparison of Intermaxillary Tooth Size Discrepancy among Class I, Class II Division 1, and Class III Subjects Using Bolton’s Analysis: An in vitro Study

    PubMed Central

    Prasanna, A Lakshmi; Venkatramana, V; Aryasri, A Srikanth; Katta, Anil Kumar; Santhanakrishnan, K; Maheshwari, Uma

    2015-01-01

    Aim: The aim of the present study was to evaluation and comparison of intermaxillary tooth size discrepancy among Class I, Class II division 1, and Class III subjects using Bolton’s analysis. Materials and Methods: The pre-treatment casts were selected from the records of patients attending the Department of Orthodontics of Meenakshi Ammal Dental College, Chennai. The sample consists of 180 pre-treatment casts with both sexes evenly distributed with 60 casts in each type of malocclusion, i.e., Class I, Class II div 1, and Class III malocclusion. The sample was selected according to angles classification. All patients were Indian nationals, between the age group of 12 to 20 years and Bolton’s analysis done on all the casts. Results: Statistically no significant difference in all types of malocclusion except anterior Bolton’s discrepancy in Class III. Conclusion: Mean Bolton’s anterior ratio for angles Class III subjects was significantly greater than for Class I and Class II subjects. When Bolton’s overall ratio was compared there was no statistically significant difference among Class I, Class II div 1, and Class III malocclusions. PMID:26435619

  5. 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

  6. An Investigation of Teachers' Perceptions of the Effects of Class Size on Teaching

    ERIC Educational Resources Information Center

    Almulla, Mohammed Abdullatif

    2015-01-01

    This study investigates the perceptions of Saudi Arabian primary school teachers in Years 4, 5 and 6 and discusses the effects of class size on teaching. The data comes from 30 teachers who teach small classes in two private schools, and 37 who teach large classes in two state schools in Alhafouf, Saudi Arabia. The study discusses whether…

  7. 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…

  8. Density, aggregation, and body size of northern pikeminnow preying on juvenile salmonids in a large river

    USGS Publications Warehouse

    Petersen, J.H.

    2001-01-01

    Predation by northern pikeminnow Ptychocheilus oregonensis on juvenile salmonids Oncorhynchus spp. occurred probably during brief feeding bouts since diets were either dominated by salmonids (>80% by weight), or contained other prey types and few salmonids (<5%). In samples where salmonids had been consumed, large rather than small predators were more likely to have captured salmonids. Transects with higher catch-per-unit of effort of predators also had higher incidences of salmonids in predator guts. Predators in two of three reservoir areas were distributed more contagiously if they had preyed recently on salmonids. Spatial and temporal patchiness of salmonid prey may be generating differences in local density, aggregation, and body size of their predators in this large river.

  9. Nanoporous Ge electrode as a template for nano-sized ( <5 nm) Au aggregates.

    PubMed

    Impellizzeri, Giuliana; Romano, Lucia; Fraboni, Beatrice; Scavetta, Erika; Ruffino, Francesco; Bongiorno, Corrado; Privitera, Vittorio; Grimaldi, Maria Grazia

    2012-10-01

    In this paper we present the extremely peculiar electrical properties of nanoporous Ge. A full and accurate electrical characterization showed an unexpected and extremely high concentration of positive carriers. Electrochemical analyses showed that nanoporous Ge has improved charge transfer properties with respect to bulk Ge. The electrode behavior, together with the large surface-to-volume ratio, make nanoporous Ge an efficient nanostructured template for the realization of other porous materials by electrodeposition. The pores were efficiently decorated by Au nanoparticles of diameter as low as 1-5 nm, prepared by electrochemical deposition. These new results demonstrate the potential and efficient use of nanoporous Ge as a nanostructured template for nano-sized Au aggregates, opening the way for the realization of innovative sensor devices. PMID:22972303

  10. 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

  11. Teacher Aides, Class Size and Academic Achievement: A Preliminary Evaluation of Indiana's Prime Time.

    ERIC Educational Resources Information Center

    Lapsley, Daniel K.; Daytner, Katrina M.; Kelly, Ken; Maxwell, Scott E.

    This large-scale evaluation of Indiana's Prime Time, a funding mechanism designed to reduce class size or pupil-teacher ratio (PTR) in grades K-3 examined the academic performance of nearly 11,000 randomly selected third graders on the state mandated standardized achievement test as a function of class size, PTR, and presence of an instructional…

  12. 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…

  13. Effects of Class Size and Adaptive Teaching Competency on Classroom Processes and Academic Outcome

    ERIC Educational Resources Information Center

    Bruhwiler, Christian; Blatchford, Peter

    2011-01-01

    In many studies of class size effects, teacher characteristics are missing, even though many argue it is not class size that is important but teacher quality. In the present study teachers' effectiveness on the learning progress was assessed while teaching a unit with predefined learning objectives. To measure adaptive teaching competency a…

  14. 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…

  15. Class Size and Language Learning in Hong Kong: The Students' Perspective

    ERIC Educational Resources Information Center

    Harfitt, Gary James

    2012-01-01

    Background: There is currently ongoing debate in Hong Kong between the teachers' union and the Government on the reduction of large class size (typically more than 40 students) in secondary schools and whether smaller class sizes might facilitate improvements in teaching and learning. In fact, many Hong Kong secondary schools have already started…

  16. 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…

  17. 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,…

  18. 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…

  19. 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…

  20. 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…

  1. 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…

  2. Estimating the Cost of National Class Size Reductions under Different Policy Alternatives.

    ERIC Educational Resources Information Center

    Brewer, Dominic J.; Krop, Cathy; Gill, Brian P.; Reichardt, Robert

    1999-01-01

    Estimates the operational costs of nationwide class-size-reduction programs under various policy alternatives, including the specified class size, flexibility in implementation, and whether the policy is targeted toward at-risk students. Depending on the options, estimated costs range from about $2 billion per year to over $11 billion per year.…

  3. 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…

  4. 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…

  5. Class Size and Sorting in Market Equilibrium: Theory and Evidence. NBER Working Paper No. 13303

    ERIC Educational Resources Information Center

    Urquiola, Miguel; Verhoogen, Eric

    2007-01-01

    This paper examines how schools choose class size and how households sort in response to those choices. Focusing on the highly liberalized Chilean education market, we develop a model in which schools are heterogeneous in an underlying productivity parameter, class size is a component of school quality, households are heterogeneous in income and…

  6. 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…

  7. 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…

  8. Attempting To Understand the Class Size and Pupil-Teacher Ratio (PTR) Confusion: A Pilot Study.

    ERIC Educational Resources Information Center

    Achilles, C. M.; Sharp, Mark; Nye, B. A.

    Confusion over the concepts of class size and pupil-teacher ratio (PTR) creates a conundrum for researchers, policy makers, and practitioners. An examination of how these two concepts are different is presented in this paper. A review of the literature suggests that class-size reduction makes a positive overall difference in student achievement,…

  9. 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

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

    NASA Astrophysics Data System (ADS)

    Ozen, Murat; Guler, Murat

    2014-02-01

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

  11. 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

  12. Sex differences in the latent class structure of alcohol use disorder: Does (dis)aggregation of indicators matter?

    PubMed

    Shireman, Emilie M; Steinley, Douglas; Sher, Kenneth

    2015-08-01

    Many researchers have argued for a differential presentation of alcohol use disorder (AUD) between men and women. Latent class analysis is the most commonly used analytic technique for modeling AUD subcategories, and latent class analyses have supported a variety of class structures of AUD. This article examines whether these differential results are, in part, an artifact of whether researchers have (a) analyzed men and women in the same analysis and (b) aggregated item-level symptoms into AUD diagnostic criteria prior to analysis. These related methodological issues are examined using Wave 2 data from the National Epidemiologic Survey of Alcohol and Related Conditions (N = 22,177). Direct comparison of results when the sexes are modeled separately or together shows that women are classified differently depending on whether men are included in the analysis. A comparison of disaggregated item-level symptoms and aggregated AUD criteria suggests that aggregating data remove a subgroup, individuals who exhibit tolerance but are normative on all other AUD symptoms, which is of theoretical and clinical interest. Consequently, basic methodological issues that are rarely systematically studied appear to be important determinants of studies seeking to determine whether male and female alcoholism are structurally isomorphic. PMID:26237327

  13. 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

  14. 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.

  15. Chemical Composition of Soil Horizons and Aggregate Size Fractions Under the Hawaiian Fern Dicranopteris and Angiosperm Cheirodendrom

    NASA Astrophysics Data System (ADS)

    Stewart, C. E.; Amatangelo, K.; Neff, J.

    2007-12-01

    Soil organic matter (SOM) inherits much of its chemical nature from the dominant vegetation, including phenolic (lignin-derived), aromatic, and aliphatic (cutin and wax-derived) compounds. However, relatively stable recalcitrant compounds may also be formed as a result of condensation and complexation reactions through decomposition and protected with association with mineral particles. The Hawaiian fern species Dicranopteris decomposes more slowly than the angiosperm, Cheirodendrom due to high concentrations of recalcitrant C compounds. These aliphatic fern leaf waxes are well-preserved and may comprise a large portion of the recalcitrant organic matter in these soils. Our objective was to determine the chemical composition of the SOM under the O- (litter-dominated) and the A- (mineral) horizons formed under fern and angiosperm vegetation. To determine the effect of mineral-association, we fractioned the soil into four size classes; 850-590 μm, 590-180 μm, 180-53 μm and <53 μm and characterized the SOM via pyrolysis-gas chromatography-mass spectrometry (py-GC/MS). As the soils developed from the O- to the A-horizon, there was a decrease of lignin-derived phenolic compounds and an increase in more recalcitrant, aromatic and aliphatic C. Soils under ferns had greater relative concentrations of phenolic compounds, while the angiosperms had greater concentrations of fatty-acid methyl esters and furans (some polysaccharide-derived). Differences between size fractions were most evident in the O-horizon of both species. Recalcitrant fern-derived cutin and leaf waxes (alkene and alkanes structures) occurred in the 180-53 μm fraction, which has been shown to be the most stable of the aggregate-size fractions. Soils developed under fern versus angiosperm vegetation have distinct chemical signatures, which likely determine the recalcitrance of the SOM.

  16. Characterisation of Stress-Induced Aggregate Size Distributions and Morphological Changes of a Bi-Specific Antibody Using Orthogonal Techniques.

    PubMed

    Hamrang, Zahra; Hussain, Maryam; Tingey, Katie; Tracka, Malgorzata; Casas-Finet, José R; Uddin, Shahid; van der Walle, Christopher F; Pluen, Alain

    2015-08-01

    A critical step in monoclonal antibody (mAb) screening and formulation selection is the ability of the mAb to resist aggregation following exposure to environmental stresses. Regulatory authorities welcome not only information on the presence of micron-sized particles, but often any information on sub-visible particles in the size range obtained by orthogonal sizing techniques. The present study demonstrates the power of combining established techniques such as dynamic light scattering (DLS) and micro-flow imaging (MFI), with novel analyses such as raster image correlation spectroscopy (RICS) that offer to bridge existent particle sizing gaps in this area. The influence of thermal and freeze-thaw stress treatments on particle size and morphology was assessed for a bi-specific antibody (mAb2). Aggregation of mAb2 was confirmed to be concentration- and treatment-dependent following thermal stress and freeze-thaw cycling. Particle size and count data show concentration- and treatment-dependent behaviour of aggregate counts, morphological descriptors and particle size distributions. Complementarity in particle size output was observed between all approaches utilised, where RICS bridged the analytical size gap (∼0.5-5 μm) between DLS and MFI. Overall, this study highlights the potential of orthogonal image analyses such as RICS (analytical size gap) and MFI (particle morphology) for formulation screening. PMID:26053418

  17. 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

  18. 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…

  19. 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,…

  20. Clarifying the Class Size Question. Evaluation and Synthesis of Studies Related to the Effects of Class Size, Pupil-Adult, and Pupil-Teacher Ratios.

    ERIC Educational Resources Information Center

    Ryan, Doris W.; Greenfield, T. Barr

    This publication presents the proceedings of a seminar on class size research that was held in May 1975 at the Ontario Institute for Studies in Education. Most of the publication consists of papers presented at the seminar and reactions to those papers by other conference participants. Also included is a summary of remarks made during the panel…

  1. 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

  2. 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.

  3. 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)

  4. 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.

  5. 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…

  6. Class Sizes for Kindergarten and Primary Grades: A Review of the Research.

    ERIC Educational Resources Information Center

    Helmich, Edith; Wasem, Leighton

    Most teachers and the public believe that children in kindergarten and the primary grades benefit from small classes because of children's need for individualized instruction and teacher attention. This report, part of a comprehensive policy study of early childhood education, presents a review of the research on the effect of class size on…

  7. Two Roads to Reform: Comparing the Research on Vouchers and Class-Size Reduction.

    ERIC Educational Resources Information Center

    Neas, Ralph G.

    Both educational vouchers and class size reduction are high-profile proposals for improving education. While the body of research on vouchers is small and unconvincing, the research on smaller classes is abundant and compelling. Researchers have been able to compare the impact of both of these policy alternatives on student performance. Their…

  8. Relationships between Class Size and Teaching: A Multimethod Analysis of English Infant Schools.

    ERIC Educational Resources Information Center

    Blatchford, Peter; Moriarty, Viv; Edmonds, Suzanne; Martin, Clare

    2002-01-01

    Studied connections between class size and teaching interactions using a multimethod approach and data from a longitudinal study of more than 10,000 children and their teachers over 3 years. Results show, overall, that in smaller classes, there is more individualized teacher support for learning. Interprets results in the context of teacher time…

  9. 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…

  10. 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…

  11. 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…

  12. 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)

  13. 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…

  14. 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…

  15. 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…

  16. 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.

  17. 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

  18. Modulus enhancement of natural rubber through the dispersion size reduction of protein/fiber aggregates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Improved mechanical properties of natural rubber are required for various rubber applications. Aggregates of protein and fiber that constitute soy protein concentrate were shear-reduced and used to enhance the tensile modulus of natural rubber. The aqueous dispersion of the shear-reduced aggregates ...

  19. 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. PMID:23872123

  20. 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

  1. 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

  2. Influence of calcium carbonate and charcoal application on aggregation processes and organic matter retention at the silt-size scale

    NASA Astrophysics Data System (ADS)

    Asefaw Berhe, Asmeret; Kaiser, Michael; Ghezzehei, Teamrat; Myrold, David; Kleber, Markus

    2013-04-01

    The effectiveness of charcoal and calcium carbonate applications to improve soil conditions has been well documented. However, their influence on the formation of silt-sized aggregates and the amount and protection of associated organic matter (OM) against microbial decomposition is still largely unknown. For sustainable management of agricultural soils, silt-sized aggregates (2-53 µm) are of particularly large importance because they store up to 60% of soil organic carbon with mean residence times between 70 and 400 years. The objectives are i) to analyze the ability of CaCO3 and/or charcoal application to increase the amount of silt-sized aggregates and associated OM, ii) vary soil mineral conditions to establish relevant boundary conditions for amendment-induced aggregation processes, iii) to determine how amendment-induced changes in formation of silt-sized aggregates relate to microbial decomposition of OM. We set up artificial high reactive (HR, clay: 40%, sand: 57%, OM: 3%) and low reactive soils (LR, clay: 10%, sand: 89%, OM: 1%) and mixed them with charcoal (CC, 1%) and/or calcium carbonate (Ca, 0.2%). The samples were adjusted to a water potential of 0.3 bar and sub samples were incubated with microbial inoculum (MO). After a 16-weeks aggregation experiment, size fractions were separated by wet-sieving and sedimentation. Since we did not use mineral compounds in the artificial mixtures within the size range of 2 to 53 µm, we consider material recovered in this fraction as silt-sized aggregates, which was confirmed by SEM analyses. For the LR mixtures, we detected increasing N concentrations within the 2-53 µm fractions of the charcoal amended samples (CC, CC+Ca, and CC+Ca+MO) as compared to the Control sample with the strongest effect for the CC+Ca+MO sample. This indicates an association of N-containing microbial derived OM with silt-sized aggregates. For the charcoal amended LR and HR mixtures, the C concentrations of the 2-53 µm fractions are

  3. 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

  4. 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

  5. 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

  6. H-aggregates of oligophenyleneethynylene (OPE)-BODIPY systems in water: guest size-dependent encapsulation mechanism and co-aggregate morphology.

    PubMed

    Allampally, Naveen Kumar; Florian, Alexander; Mayoral, María José; Rest, Christina; Stepanenko, Vladimir; Fernández, Gustavo

    2014-08-18

    The synthesis of a new oligophenyleneethynylene (OPE)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bolaamphiphile 1 and its aqueous self-assembly are reported. Compound 1 forms H-type aggregates in aqueous and polar media, as demonstrated by UV/Vis and fluorescence experiments. Concentration-dependent (1)H NMR studies in CD3CN reveal that the BODIPY units are arranged on top of each other into π-stacks with H-type excitonic coupling, as supported by ROESY NMR and theoretical calculations and visualized by Cryo-SEM studies. A detailed analysis of the spectral changes observed in temperature-dependent UV/Vis studies reveals that 1 self-assembles in a non-cooperative (isodesmic) fashion in water. The hydrophobic interior of these self-assembled structures can be exploited to encapsulate hydrophobic dyes, such as tetracene and anthracene. Both dyes absorb in a complementary region of the UV/Vis spectrum and are small enough to interact with the hydrophobic segments of 1. Temperature-dependent UV/Vis studies reveal that the spectral changes associated to the encapsulation mechanism of tetracene can be fitted to a Boltzmann function, and the initially flexible fibres of 1 rigidify upon guest addition. In contrast, the co-assembly of 1 and anthracene is a highly cooperative process, which suggests that a different class of (more-ordered) aggregates is formed. TEM and Cryo SEM imaging show the formation of uniform spherical nanoparticles, indicating that a subtle change in the guest molecular structure induces a significant change in the encapsulation mechanism and, consequently, the aggregate morphology. PMID:25042858

  7. Transport and Aggregation of Nanoparticles in Packed Beds: Effects of Pore Velocity and Initially-Fed Particle Size on Transient Particle Size Distributions

    NASA Astrophysics Data System (ADS)

    Pham, Ngoc; Papavassiliou, Dimitrios

    2015-11-01

    Aggregation of colloidal particles in flow through porous media has received careful consideration, as it reduces particle breakthrough due to pore clogging and sedimentation. Additionally, in unstable colloidal systems, deposition of colloidal aggregates on the pore surfaces can create sub-surfaces for further colloidal attachment. This phenomenon is known as ripening effect. In this study, transient particle size distributions of nano-particle systems, propagating in a bed packed with spheres are numerically investigated. In our simulation, only pair interactions are considered, and the aggregation rate is varied with the relative position of two particles in a pair. The packed bed consists of spheres of known size, randomly packed in a simulation box. To generate the velocity field of water inside the porous medium, the lattice Boltzmann method (LBM) is used. In conjunction with that, the trajectories of thousands of massless particles moving with the flow under convection and diffusion are recorded employing a Lagrangian framework. While pore clogging is neglected, we draw attention to the change of the distribution of particle size under different pore velocities and different initially-fed particle sizes.

  8. 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.

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

    PubMed

    Baran, Anthony J

    2003-05-20

    The scalar optical properties (extinction coefficient, mass extinction coefficient, single-scattering albedo, and asymmetry parameter) of a distribution of randomly oriented ice aggregates are simulated generally to well within 4% accuracy by use of a size-shape distribution of randomly oriented circular ice cylinders at wavelengths in the terrestrial window region. The single-scattering properties of the ice aggregates are calculated over the whole size distribution function by the finite-difference time-domain and improved geometric optics methods. The single-scattering properties of the size-shape distribution of circular ice cylinders are calculated by the T-matrix method supplemented by scattering solutions obtained from complex-angular-momentum theory. Moreover, radiative-transfer studies demonstrate that the maximum error in brightness temperature space when the size-shape distribution of circular ice cylinders is used to represent scattering from ice aggregates is only approximately 0.4 K The methodology presented should find wide applicability in remote sensing of ice cloud and parameterization of cirrus cloud scalar optical properties in climate models. PMID:12777019

  10. 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.

  11. Differences in in vivo fluorescence yield between three phytoplankton size classes

    USGS Publications Warehouse

    Alpine, Andrea E.; Cloern, James E.

    1985-01-01

    The size-dependent relationship between in vivo fluorescence (IVF) and chlorophyll a was determined for monthly phytoplankton samples from the San Francisco Bay estuary. Chlorophyll a and IVF were both measured on netplankton (>22 μm), nanoplankton (5–22 μm), and ultraplankton (<5 μm) samples that were separated with screens. IVF and chlorophyll a were linearly related for each size class, but the IVF per unit chlorophyll a (R) was significantly different between these three size classes. The ultraplankton R was twice that of the nanoplankton which was in turn twice the netplankton R. Hence, accurate size fractionation of phytoplankton biomass from measures of IVF requires correction for size-dependent variations in R.

  12. School Size and Class Size in Texas Public Schools. Policy Research Report Number 12.

    ERIC Educational Resources Information Center

    Texas Education Agency, Austin. Div. of Policy Planning and Evaluation.

    In response to an enrollment increase of 666,961 students over the past 10 years, Texas public schools have increased in both number and size. The number of Texas high schools with over 2,000 students increased by 35 percent from 1987-88 to 1997-98, and these very large schools now make up 14 percent of all regular instructional high schools.…

  13. 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})

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. Aggregating Student Achievement Trends across States with Different Tests: Using Standardized Slopes as Effect Sizes

    ERIC Educational Resources Information Center

    Yin, Robert K.; Schmidt, R. James; Besag, Frank

    2006-01-01

    The study of federal education initiatives that takes place over multiple years in multiple settings often calls for aggregating and comparing data-in particular, student achievement data-across a broad set of schools, districts, and states. The need to track the trends over time is complicated by the fact that the data from the different schools,…

  20. 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

  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. 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.

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

    PubMed

    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

  4. 4-Methyl-3-(arylsulfonyl)furoxans: a new class of potent inhibitors of platelet aggregation.

    PubMed

    Calvino, R; Fruttero, R; Ghigo, D; Bosia, A; Pescarmona, G P; Gasco, A

    1992-08-21

    A series of 4-methyl-3-(arylthio)furoxans were synthesized by oxidation of 1-(arylthio)-2-methylglyoxymes with dinitrogen tetroxide. Reduction with trimethyl phosphite of the furoxan derivatives afforded the corresponding furazans, while oxidation with an equimolar amount of 30% hydrogen peroxide in acetic acid or with an excess of 81% hydrogen peroxide in trifluoroacetic acid afforded the corresponding arylsulfinyl and arylsulfonyl analogues, respectively. All the furoxan and furazan derivatives showed activity as inhibitors of platelet aggregation. 4-Methyl-3-(arylsulfonyl)furoxans were the most potent derivatives of the series. 4-Methyl-3-(phenylsulfonyl)furoxan (10a), one of the most active derivatives, inhibits the AA-induced increase of cytosolic free Ca2+ and production of malondialdehyde. A primary action of the compound on cyclooxygenase is excluded, as a stable epoxymethano analogue of prostaglandin H2 does not reverse the inhibitory effect of 10a. This compound produces a significant increase in cGMP which is likely to cause inhibition at an early stage of the platelet activation pathway. PMID:1324320

  5. Effects of class I heparin binding growth factor and fibronectin on platelet adhesion and aggregation

    SciTech Connect

    Greisler, H.P.; Klosak, J.J.; Steinam, S.J.; Lam, T.M.; Burgess, W.H.; Kim, D.U. )

    1990-05-01

    Fibronectin and heparin binding growth factor-type 1 have been affixed to vascular graft surfaces to enhance the attachment and the proliferation of transplanted endothelial cells, respectively. The current study examines the effect of fibronectin and heparin binding growth factor-type 1 on platelet adhesion and activation in vivo and on platelet aggregation in vitro. Expanded polytetrafluoroethylene prostheses (5 cm x 4 mm internal diameter) were treated either with fibronectin (n = 9), fibronectin/heparin/heparin binding growth factor-type 1/heparin (n = 12), or neither (n = 13) and were interposed into canine aortoiliac systems bilaterally. Autogenous radiolabeled (Indium 111 oxine, 650 microCi) platelets were injected intravenously before reestablishment of circulation. Perfusion was maintained for 30 minutes, and prostheses were removed with segments of native aorta and distal iliac arteries bilaterally. Specimens were examined for thrombus-free surface area, by gamma well counting for adherent radiolabeled platelets, and by light microscopy and transmission and scanning electron microscopic techniques. Results showed that both the fibronectin and fibronectin/heparin/heparin binding growth factor-type 1/heparin pretreated prostheses contained significantly greater numbers of platelets and adherent radioactivity than did control graft segments when normalized to their ipsilateral iliac arteries. Fibronectin/heparin/heparin binding growth factor-type 1/heparin pretreated prostheses contained 27 +/- 16 times more radioactivity per square millimeter than ipsilateral iliac arteries, fibronectin pretreated prostheses had 13 +/- 8 times more radioactivity per square millimeter than ipsilateral iliac arteries, and untreated expanded polytetrafluoroethylene had 4 +/- 3 times more radioactivity per square millimeter than ipsilateral iliac arteries.

  6. The Political Economy of Education Policy: The Case of Class Size Reduction.

    ERIC Educational Resources Information Center

    Mitchell, Douglas E.; Mitchell, Ross E.

    2003-01-01

    Develops a political economy framework for mapping and interpreting the competing purposes of schooling by examining five paradoxes in national policy debates addressing class size in public elementary schools. The framework highlights answers to the question: What kind of an economic good is education? (education as a service industry, producer…

  7. 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.…

  8. An Examination of the Relationship between Online Class Size and Instructor Performance

    ERIC Educational Resources Information Center

    Sorensen, Chris

    2015-01-01

    With no physical walls, the online classroom has the potential to house a large number of students. A concern by some is what happens to the quality of instruction in courses with high enrollments. The purpose of this research was to examine online class size and its relationship to, and potential influence on, an instructor's performance.…

  9. 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…

  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. Project STAR Research Synopsis: The Effect of Reduced Class Size on Kindergarten Reading Readiness.

    ERIC Educational Resources Information Center

    Bain, Helen Pate; Jacobs, Roseanne

    Effects of teacher-pupil ratio on kindergartners' mastery of reading readiness objectives were studied. The study was part of Tennessee's Project STAR, a 4-year study of class size. About 2,850 students in 38 elementary schools that served 4 types of communities: innercity, suburban, urban, and rural, in 26 Tennessee school systems participated.…

  12. Factors in the Determination of Cost Effective Class Sizes. Report No. 009-79.

    ERIC Educational Resources Information Center

    Woods, Nancy A.

    A system to determine cost effectiveness of class size should be based on both budgeted and actual expenditures and credit hours at the individual course section level. These two factors, in combination, are often expressed as cost per credit hour, and this statistic forms the primary means of evaluating planned "inputs" against actual "outputs."…

  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. 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…

  15. 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…

  16. 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…

  17. 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…

  18. Class Size and Educational Achievement: A Review of Methodology with Particular Reference to Study Design.

    ERIC Educational Resources Information Center

    Goldstein, Harvey; Blatchford, Peter

    1998-01-01

    Reviews research into class size effects from a methodological viewpoint, concentrating on various strengths and weaknesses of randomized controlled trials (RCT) and observational studies. Discusses population definitions, causation, and generally sets out criteria for valid inferences from such studies. Illustrates with new findings from data in…

  19. 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…

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

    PubMed

    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

  1. Characterizing Single-Scattering Properties of Snow Aggregate Particles Integrated over Size Distributions in the Microwave Spectrum

    NASA Astrophysics Data System (ADS)

    Kuo, K.; Van Aartsen, B.; Haddad, Z. S.; Tanelli, S.; Skofronick Jackson, G.; Olson, W. S.

    2012-12-01

    Approximately 7000 snow aggregate particles have been synthesized, using a heuristic aggregation algorithm, from 9 realistic snowflake habits simulated using the now famous Snowfake ice crystal growth model. These particles exhibit mass-dimension relations consistent with those derived from observations. In addition, ranging from 0.1 to 3.5 mm in liquid-equivalent diameter, the sizes of these particle cover ranges wide enough for assemblies of realistic particle size distributions. The single-scattering properties, such as scattering/absorption/extinction/backscatter cross sections, single-scattering albedo, asymmetry factor, as well as the scattering matrix, are obtained for each aggregate particle using the discrete-dipole approximation (DDA) code DDSCAT at 13 microwave frequencies, ranging from 10 to 190 GHz. Preliminary radiative transfer calculations show that the single-scattering properties so obtained yield much more reasonable brightness temperatures than those derived from "fluffy sphere" Mie approximations. However, in order to achieve better retrievals involving these complex particles, we need to be able to characterize their single-scattering with only a few parameters. In this study, we present such an attempt using a pair of generalized effective radii, expressed as ratios of particle volume to particle surface area and to orientation-averaged particle cross section, in addition to mass content. It is shown that these effective radii are indeed effective in characterizing the PSD-integrated single-scattering properties of these complex particles. Pristine ice crystals simulated using the "Snowfake" ice crystal growth mode (3rd row from top) and example aggregates generated using the corresponding pristine particles (bottom 3 rows, i.e. 4th to 6th rows from top).

  2. 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

  3. PicoMolar level detection of protein biomarkers based on electronic sizing of bead aggregates: theoretical and experimental considerations.

    PubMed

    Lin, Z; Cao, X; Xie, P; Liu, M; Javanmard, Mehdi

    2015-12-01

    We demonstrate a novel method for electronically detecting and quantifying protein biomarkers using microfluidic impedance cytometry. Our biosensor, which consists of gold electrodes micro-fabricated in a microchannel, detects the differences between bead aggregates of varying sizes in a micro-pore sandwiched between two micro channels. We perform a sandwich immunoassay, where the complementary antibody pairs are immobilized on two different bead types, and the presence of antigen results in bead aggregation, the amount of which depends on antigen quantity. When single beads or bead aggregates pass through the impedance sensor, differences in impedance change are detected. In this manuscript, we perform a comprehensive theoretical study on the limits imposed on sensitivity of this technique due to electronic noise and also mass transfer and reaction limits. We also experimentally characterize the performance of this technique by validating the technique on an IgG detection assay. A detection limit at the picoMolar level is demonstrated, thus comparable in sensitivity to a sandwich ELISA. PMID:26589228

  4. Granular activated carbon as nucleating agent for aerobic sludge granulation: Effect of GAC size on velocity field differences (GAC versus flocs) and aggregation behavior.

    PubMed

    Zhou, Jia-Heng; Zhao, Hang; Hu, Miao; Yu, Hai-Tian; Xu, Xiang-Yang; Vidonish, Julia; Alvarez, Pedro J J; Zhu, Liang

    2015-12-01

    Initial cell aggregation plays an important role in the formation of aerobic granules. In this study, three parallel aerobic granular sludge reactors treating low-strength wastewater were established using granular activated carbon (GAC) of different sizes as the nucleating agent. A novel visual quantitative evaluation method was used to discern how GAC size affects velocity field differences (GAC versus flocs) and aggregation behavior during sludge granulation. Results showed that sludge granulation was significantly enhanced by addition of 0.2mm GAC. However, there was no obvious improvement in granulation in reactor amended with 0.6mm GAC. Hydraulic analysis revealed that increase of GAC size enhanced the velocity field difference between flocs and GAC, which decreased the lifecycle and fraction of flocs-GAC aggregates. Overall, based on analysis of aggregation behavior, GAC of suitable sizes (0.2mm) can serve as the nucleating agent to accelerate flocs-GAC coaggregation and formation of aerobic granules. PMID:26409105

  5. 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

  6. Aggregation of grains in a turbulent pre-solar disk. [meteoritic inclusion and chondrule subcentimeter maximum size argument

    NASA Technical Reports Server (NTRS)

    Wieneke, B.; Clayton, D. D.

    1983-01-01

    The growth and evolution of grains in the protostellar nebula are investigated within the context of turbulent low-mass disk models developed by previous investigators. Because of grain collisions promoted by the turbulent velocities, particles aggregate to millimeter size in times of the order of 1000 yrs. During the growth the particles acquire a large inward radial velocity due to gas drag (Weidenschilling, 1977) and spiral into the sun. The calculations indicate that the final size of the particles does not exceed a few centimeters. This result is not very sensitive to the specific nebula parameters. For all conditions investigated it seems impossible to grow meter- or kilometer-sized bodies that could decouple from the gas motion. An additional argument is given that shows that only particles smaller than centimeter size can survive drift into the growing sun by being transported radially outward by turbulent mixing. This agrees well with the maximum size of inclusions and chondrules. Since sedimentation of grains and subsequent dust disk instability is effectively inhibited by turbulent stirring, the formation of planetesimals and planets cannot be explained in the above scenario without further assumptions.

  7. 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

  8. 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…

  9. Dynamic testing of concrete under high confined pressure. Influence of saturation ratio and aggregate size

    NASA Astrophysics Data System (ADS)

    Forquin, P.; Piotrowska, E.; Gary, G.

    2015-09-01

    Concrete structures can be exposed to intense pressure loadings such as projectile-impact or detonation near a concrete structural element. To investigate the mechanical behaviour of concrete under high confining pressure, dynamic quasi-oedometric compression tests have been performed with a large diameter (80 mm) Split Hopkinson Pressure Bar apparatus. The concrete sample is placed within a steel confining ring and compressed along its axial direction. Hydrostatic pressures as high as 800 MPa and axial strain of about - 10% are reached during the tests. In the present work, experiments have been conducted on two types of concrete: MB50 microconcrete with a maximum grain size of 2 mm and R30A7 ordinary concrete of maximum grain size about 8 mm. Both concretes are tested in dry or saturated conditions. According to these dynamic experiments it is noted that grain size has a small influence whereas water content has a strong effect on the confined behaviour of concrete.

  10. Flow strengths of quartz aggregates: grain size and pressure effects due to hydrolytic weakening

    SciTech Connect

    Kronenberg, A.K.; Tullis, J.

    1984-06-10

    Novaculites and quartzite ranging in grain size from 1.2--211 ..mu..m have been experimentally deformed at confining pressures of 350--1620 MPa under conditions of constant displacement rate and constant deviatoric stress in order to determine the effect of both grain size and pressure on the rheology of quartizite. The amount of water available to the samples was varied so that flow strengths for the entire suite of samples could be compared at several, nominally equal water concentrations; samples were vacuum dried at 800 /sup 0/C for 12 hours, left as is, or sealed in Pt jackets with 0.03--0.4 wt % water added. Novaculties deformed at 800 /sup 0/C for 12 hours, left as is, or sealed in Pt jackets with 0.03--0.4 wt% water added. Novaculities deformed at 800 /sup 0/C and 10/sup 0 -6//s/sup -1/ in the presence of 0.4 wt % water show a continuous decrease in flow strength with increasing confining pressure over the range 350--1590 MPa. At high confining pressures 950--1600 MPa, constant displacement rate experiments show three distinct grain size effects, corresponding to the three levels of water concentrations: (1) ''grain boundary hardening'' for vacuum-dried samples, (2) grain size independent strength for as is samples, and (3) ''grain boundaries weakening'' for samples deformed in the presence of water. Although grain boundary-dislocation interactions may lead to grain boundary hardening and grain boundary sliding to weakening the details of the mechanical data, in combination with microstructural observations, are inconsistent with existing models of intrinsic grain boundary effects.

  11. Stimulation of r- vs. K- selected microorganisms by elevated atmospheric CO2 depends on soil aggregate size

    NASA Astrophysics Data System (ADS)

    Dorodnikov, M.; Blagodatskaya, E.; Blagodatsky, S.; Fangmeier, A.; Kuzyakov, Y.

    2009-04-01

    Increased root exudation under elevated atmospheric CO2 and the contrasting environments in soil macro- and microaggregates could affect microbial growth strategy. We investigated the effect of elevated CO2 on the contribution of fast- (r-strategists) and slow-growing microorganisms (K-strategists) in soil macro- and microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO2 treatments of FACE-Hohenheim (Stuttgart) into large macro- (>2 mm), small macro- (0.25-2.00 mm), and microaggregates (<0.25 mm) using an "optimal moist" sieving. Microbial biomass (Cmic), the maximal specific growth rate (μ), growing microbial biomass (GMB) and lag-period (tlag) were estimated by the kinetics of CO2 emission from bulk soil and aggregates amended with glucose and nutrients. Although Corg and Cmic were unaffected by elevated CO2, μ values were significantly higher under elevated than ambient CO2 for bulk soil, small macroaggregates, and microaggregates. The substrate induced respiratory response increased with the decreasing of aggregates size under both CO2 treatments. Based on changes in μ, GMB, and lag-period, we conclude that elevated atmospheric CO2 stimulated the r-selected microorganisms, especially in soil microaggregates. Such an increase in r-selected microorganisms could increase C turnover in terrestrial ecosystems in a future elevated atmospheric CO2 environment.

  12. 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.

  13. Magnetic cross-linked laccase aggregates--bioremediation tool for decolorization of distinct classes of recalcitrant dyes.

    PubMed

    Kumar, Vaidyanathan Vinoth; Sivanesan, Subramanian; Cabana, Hubert

    2014-07-15

    The increasing use of laccase in waste water industries is useful to explore the high benefit/cost ratio of insolubilization technologies like cross linked enzyme aggregates (CLEAs) for the decolorization and detoxification of distinctive classes of recalcitrant dyes. Amino-functionalized magnetic nanoparticles bonded to CLEAs increased the potential of laccase-based CLEAs and are applicable for commercial implementation of this technology in environmental applications. The activity recovery obtained from the stable rigid structure of magnetic CLEAs was around 32%. High volumetric activity, increased in thermal and operational stability of laccase and its resistance to extreme conditions were the properties provided by these magnetic CLEAs. Kinetic studies show that the catalytic efficiency of the enzyme, based on the kcat/km value, changed significantly upon CLEAs and magnetic CLEA formations. When 0.2U/mL of magnetic CLEAs was used, the biocatalyst rapidly decolorized 61-96% of remazol brilliant blue R, malachite green and reactive black 5 initially at 50mgL(-1) at 20°C and pH7.0. Investigation of dye degradation using both active and heat denatured CLEAs revealed a slight adsorption of dyes on inactivated biocatalysts. A laboratory scale perfusion basket reactor (BR) was used to study the continuous decolorization of dyes. The efficient decolorization (>90%) of remazol brilliant blue R and slight decrease in CLEA activity were measured over a 10h period of continuous operation, which illustrates the potential of CLEAs for the wastewater treatment. The present findings will advance the understanding of dye decolorization mechanism by CLEA laccase, which could provide useful references for developing industrial wastewater treatment. PMID:24785303

  14. Combination of microwell structures and direct oxygenation enables efficient and size-regulated aggregate formation of an insulin-secreting pancreatic β-cell line.

    PubMed

    Shinohara, Marie; Kimura, Hiroshi; Montagne, Kevin; Komori, Kikuo; Fujii, Teruo; Sakai, Yasuyuki

    2014-01-01

    Spherical three-dimensional (3D) cellular aggregates are valuable for various applications such as regenerative medicine or cell-based assays due to their stable and high functionality. However, previous methods to form aggregates have shown drawbacks, being labor-intensive, showing low productivity per unit area or volume and difficulty to form homogeneous aggregates. We proposed a novel strategy based on oxygen-permeable polydimethylsiloxane (PDMS) honeycomb microwell sheets, which can theoretically supply about 80 times as much oxygen as conventional polystyrene culture dishes, to produce recoverable aggregates in controllable sizes using mouse insulinoma cells (MIN6-m9). In 48 hours of culture, the PDMS sheets produced aggregates whose diameters were strictly controlled (≃32, 60, 90, 150 and 280 mm) even at an inoculum density eight times higher (8.0×105 cells/cm(2) ) than that of normal confluent monolayers (1.0×105 cells/cm(2) ). Measurement of the oxygen tension near the cell layer and glucose/lactate analysis clearly showed that cells exhibit aerobic respiration on the PDMS-based culture system. Glucose-responsive insulin secretion of the recovered aggregates showed that the aggregates around 90 mm in diameter secreted the largest amounts of insulin. This confirmed the advantages of 3D cellular organization and the existence of a suitable aggregate size, above which excess organization leads to a decreased metabolic response. These results demonstrated that this microwell-based PDMS culture system provides a promising method to form size-regulated and better functioning 3D cellular aggregates of various kinds of cells with a high yield per surface area. PMID:24265060

  15. 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.

  16. 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

  17. 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…

  18. 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…

  19. The Relationship between Teaching Practices and Student Achievement in First Year Classes: A Comparative Study of Small Size and Standard Size Classes

    ERIC Educational Resources Information Center

    Clanet, Joel

    2010-01-01

    This study investigated the links between the teaching practices of primary school teachers (n = 200) who were observed while presenting a new text to their first year classes, and the student achievement levels in those classes. The teaching practices are specifically concerned with the way the teachers supported and encouraged students'…

  20. 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

  1. In Vivo Venous Assessment of Red Blood Cell Aggregate Sizes in Diabetic Patients with a Quantitative Cellular Ultrasound Imaging Method: Proof of Concept

    PubMed Central

    Tripette, Julien; Nguyen, Linh-Chi; Allard, Louise; Robillard, Pierre; Soulez, Gilles; Cloutier, Guy

    2015-01-01

    Background Diabetic patients present higher level of red blood cell (RBC) aggregation contributing to the development of vascular complications. While it has been suggested that this hematology/rheology parameter could bring additional prognostic information for the management of those patients, RBC aggregation screening is not included as a clinical practice. Most medical centers are not equipped to measure properly this parameter, although sedimentation tests can bring some indication. Here, we aimed at evaluating the feasibility of using ultrasound to assess in-vivo hyper-aggregation in type 2 diabetic patients. Research design and methods Seventeen diabetic patients and 15 control subjects underwent ultrasound measurements of RBC aggregation in both cephalic and great saphenous veins. Non-invasive in-vivo ultrasound measurements were performed using a newly developed cellular imaging technique, the structure factor size and attenuation estimator (SFSAE). Comparisons with an ex-vivo gold standard rheometry technique were done, along with measurements of pro-aggregating plasma molecule concentrations. Results In-vivo RBC aggregation was significantly higher in diabetic patients compared with controls for cephalic vein measurements, while a trend (p = 0.055) was noticed in the great saphenous vein. SFSAE measurements were correlated with gold standard in-vitro measures, fibrinogen and C-reactive protein plasma concentrations. Conclusion RBC aggregation can be measured in-vivo in diabetic patients using ultrasound. Prospective studies are needed to determine whether the SFSAE method could help clinicians in the early management of vascular complications in this patient population. PMID:25906140

  2. 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. PMID:25899089

  3. A Test of the Association of Class Size to Students' Attitudes Toward Science. Research Paper No. 9.

    ERIC Educational Resources Information Center

    Ward, William H.

    Analysis of data, collected by the Minnesota Research and Evaluation Project during 1972, on high school biology, chemistry, and physics classes from 12 states in 3 regions of the United States showed no association between class size and student attitude toward science. Potential effects of teachers' attitudes toward science and students'…

  4. 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…

  5. Brokering Dialogue between Secondary Students and Teachers to Co-Construct Appropriate Pedagogy in Reduced-Size Classes

    ERIC Educational Resources Information Center

    Harfitt, Gary James

    2014-01-01

    This study focuses on how two teachers working in reduced-size secondary classes of the same grade adapted their pedagogy as a result of a brokered dialogue between myself as researcher and 43 grade 10 students from the teachers' classes. Research was carried out over the course of one academic year. First, students' perspectives on…

  6. Effects of Class Size and Length of Day on Kindergartners' Academic Achievement: Findings from Early Childhood Longitudinal Study

    ERIC Educational Resources Information Center

    Yan, Wenfan; Lin, Qiuyun

    2005-01-01

    The study explored the effects of two kindergarten program organization factors--length of school day and class size--on kindergartners' reading, math and general knowledge achievement at the end of the kindergarten year. Two waves of data were drawn from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K) with an…

  7. 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

  8. 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

  9. 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. PMID:27107247

  10. Complex aggregation patterns in drying nanocolloidal suspensions: size matters when it comes to the thermomechanical stability of nanoparticle-based structures.

    PubMed

    Darwich, Samer; Mougin, Karine; Haidara, Hamidou

    2010-11-16

    We report the results of a model study on the interrelation among the occurrence of complex aggregation patterns in drying nanofluids, the size of the constitutive nanoparticles (NPs), and the drying temperature, which is a critical issue in the genesis of complex drying patterns that was never systematically reported before. We show that one can achieve fine control over the occurrence and topological features of these drying-mediated complex structures through the combination of the particle size, the drying temperature, and the substrate surface energy. Most importantly, we show that a transition in the occurrence of the patterns appears with the temperature and the particle size, which accounts for the size dependence of the thermomechanical stability of the aggregates in the nanoscale range. Using simple phenomenological and scaling considerations, we showed that the thermomechanical stability of the aggregates was underpinned by physical quantities that scale with the size of the NPs (R) either as R(-2) or R(-3). These insights into the size-dependent dissipation mechanisms in nanoclusters should help in designing NPs-based structures with tailored thermomechanical and environmental stability and hence with an optimized morphological stability that guarantees their long-term functional properties. PMID:20883008

  11. Health Science students’ evaluation of courses and Instructors: the effect of response rate and class size interaction

    PubMed Central

    Kuwaiti, Ahmed Al

    2015-01-01

    Objective This study aims at investigating the effect of response rate and class size interaction on students’ evaluation of instructors and the courses offered at heath science colleges in Saudi Arabia. Methodology A retrospective study design was adapted to ascertain Course Evaluation Surveys (CES) conducted at the health science colleges of the University of Dammam [UOD] in the academic year 2013–2014. Accordingly, the CES data which was downloaded from an exclusive online application ‘UDQUEST’ which includes 337 different courses and 15,264 surveys were utilized in this study. Two-way analysis of variance was utilized to test whether there is any significant interaction between the class size and the response rate on the students’ evaluation of courses and instructors. Results The study showed that high response rate is required for student evaluation of instructors at Health Science colleges when the class size is small whereas a medium response rate is required for students’ evaluation of courses. On the other hand, when the class size is medium, a medium or high response rate is needed for students’ evaluation of both instructors and courses. Conclusions The results of this study recommend that the administrators of the health science colleges to be aware of the interpretation of students’ evaluations of courses and instructors. The study also suggests that the interaction between response rate and class size is a very important factor that needs to be taken into consideration while interpreting the findings of the students’ evaluation of instructors and courses. PMID:25901133

  12. 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

  13. Major Histocompatibility Complex Class II Inhibits Fas Antigen-Mediated Gastric Mucosal Cell Apoptosis through Actin-Dependent Inhibition of Receptor Aggregation

    PubMed Central

    Stoicov, Calin; Cai, Xun; Li, Hanchen; Klucevsek, Kristine; Carlson, Jane; Saffari, Reza; Houghton, JeanMarie

    2005-01-01

    Escape from normal apoptotic controls is thought to be essential for the development of cancer. During Helicobacter pylori infection, the leading cause of gastric cancer, activation of the Fas antigen (Fas Ag) apoptotic pathway is responsible for early atrophy and tissue loss. As disease progresses, metaplastic and dysplastic glands arise which express Fas Ag but are resistant to apoptosis and are believed to be the precursor cells for adenocarcinoma. In this report, we show that one mechanism of acquired Fas resistance is inhibition of receptor aggregation via a major histocompatibility complex class II (MHCII)-mediated, actin-dependent mechanism. For these studies we used the well-described C57BL/6 mouse model of Helicobacter pylori and Helicobacter felis infection. Under normal conditions, Fas Ag is expressed at low levels, and MHCII expression on gastric mucosal cells is negligible. With infection and inflammation, both receptors are upregulated, and 6.1% of gastric mucosal cells express MHCII in combination with Fas Ag. Using the rat gastric mucosal cell line RGM-1 transfected with murine Fas Ag and MHCIIαβ chains, we demonstrate that MHCII prevents Fas receptor aggregation and inhibits Fas-mediated signaling through its effects on the actin cytoskeleton. Depolymerization of actin with cytochalasin D allows receptors to aggregate and restores Fas sensitivity. These findings offer one mechanism by which gastric mucosal cells acquire Fas resistance. PMID:16177302

  14. 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

  15. 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

  16. Effects of orthovanadate-based nanoparticles of various sizes on the aggregation behavior of polymethine dyes in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Grygorova, Ganna; Klochkov, Vladimir; Yefimova, Svetlana; Malyukin, Yuri

    2015-02-01

    Optical absorption spectroscopy and dynamic light scattering have been used to study the aggregation behavior of 1,1-diethyl-2,2-carbocyanine (PIN) and 3,3-dimethyl-9-(2-thienyl)-thiacarbocyanine (L-21) dyes in aqueous solutions containing orthovanadate-based ReEuVO4 (Re = Gd, Y, La) nanoparticles (NPs) of various form-factor. It has been shown that the interaction of cationic dye molecules with the negatively charged surface of NPs leads to the dye aggregation and formation of large dye aggregates/NPs complexes. The coagulation process is found to be governed by the NPs surface area, rather than its form factor. The dye aggregate structure is analyzed within the Kasha and McRae exciton model framework.

  17. 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…

  18. Size-selective concentration and label-free characterization of protein aggregates using a Raman active nanofluidic device.

    PubMed

    Choi, Inhee; Huh, Yun Suk; Erickson, David

    2011-02-21

    Trace detection and physicochemical characterization of protein aggregates have a large impact in understanding and diagnosing many diseases, such as ageing-related neurodegeneration and systemic amyloidosis, for which the formation of protein aggregates is one of the pathological hallmarks. Here we demonstrate an innovative label-free method for detecting and characterizing small amounts of early stage protein aggregates using a Raman active nanofluidic device. Sub-micrometre channels formed by a novel elastomeric collapse technique enable the separation and concentration of matured protein aggregates from small protein molecules. The Raman enhancement by gold nanoparticle clusters fixed below a micro/nanofluidic junction allows characterization of intrinsic properties of protein aggregates at concentration levels (∼fM) much lower than can be done with traditional analytical tools. With our device we show for the first time the concentration dependence of protein aggregation over these low concentration ranges. We expect that our method could facilitate definitive diagnosis and possible therapeutics of diseases at early stages. PMID:21120240

  19. Observations of grain size sensitive power law creep of olivine aggregates over a large range of lattice-preferred orientation strength

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob A.; Hansen, Lars N.; Tasaka, Miki; Meyers, Cameron; Zimmerman, Mark E.; Kohlstedt, David L.

    2016-02-01

    Grain size sensitive (GSS) power law creep of San Carlos olivine aggregates was investigated by comparing strain rates measured in laboratory deformation experiments to strain rates determined from a micromechanical model of intragranular dislocation processes. The plastic flow behavior of olivine aggregates due solely to intragranular slip was determined using flow laws for olivine single crystals in combination with grain orientations measured by electron backscatter diffraction. Measured strain rates were compared to results from the micromechanical model for samples deformed in compression to an axial strain of <0.2 and in torsion to a shear strain of up to 7.4. Olivine aggregates deform up to a factor of 4.6 times faster than the maximum possible rates determined from the micromechanical model of intragranular slip. Comparison of our data to published flow laws indicates that diffusion creep cannot account for this difference. The ratio of experimentally determined strain rates to those from the micromechanical model is strongly dependent upon grain size but is independent of stress and strength of lattice-preferred orientation. These observations indicate that GSS power law creep, consistent with dislocation-accommodated grain boundary sliding, occurs in both weakly and strongly textured olivine aggregates at the studied conditions.

  20. Changes in carbon stability and microbial activity in size fractions of micro-aggregates in a rice soil chronosequence under long term rice cultivation

    NASA Astrophysics Data System (ADS)

    Pan, Genxing; Liu, Yalong; Wang, Ping; Li, Lianqinfg; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Bian, Rongjun; Ding, Yuanjun; Ma, Chong

    2016-04-01

    Recent studies have shown soil carbon sequestration through physical protection of relative labile carbon intra micro-aggregates with formation of large sized macro-aggregates under good management of soil and agricultural systems. While carbon stabilization had been increasingly concerned as ecosystem properties, the mechanisms underspin bioactivity of soil carbon with increased carbon stability has been still poorly understood. In this study, topsoil samples were collected from rice soils derived from salt marsh under different length of rice cultivation up to 700 years from eastern China. Particle size fractions (PSF) of soil aggregates were separated using a low energy dispersion protocol. Carbon fractions in the PSFs were analyzed either with FTIR spectroscopy. Soil microbial community of bacterial, fungal and archaeal were analyzed with molecular fingerprinting using specific gene primers. Soil respiration and carbon gain from amended maize as well as enzyme activities were measured using lab incubation protocols. While the PSFs were dominated by the fine sand (200-20μm) and silt fraction (20-2μm), the mass proportion both of sand (2000-200μm) and clay (<2μm) fraction increased with prolonged rice cultivation, giving rise to an increasing trend of mean weight diameter of soil aggregates (also referred to aggregate stability). Soil organic carbon was found most enriched in coarse sand fraction (40-60g/kg), followed by the clay fraction (20-24.5g/kg), but depleted in the silt fraction (~10g/kg). Phenolic and aromatic carbon as recalcitrant pool were high (33-40% of total SOC) in both coarse sand and clay fractions than in both fine sand and silt fractions (20-29% of total SOC). However, the ratio of LOC/total SOC showed a weak decreasing trend with decreasing size of the aggregate fractions. Total gene content in the size fractions followed a similar trend to that of SOC. Bacterial and archaeal gene abundance was concentrated in both sand and clay fractions

  1. An Examination of Teachers' Perceptions and Practice when Teaching Large and Reduced-Size Classes: Do Teachers Really Teach Them in the Same Way?

    ERIC Educational Resources Information Center

    Harfitt, Gary James

    2012-01-01

    Class size research suggests that teachers do not vary their teaching strategies when moving from large to smaller classes. This study draws on interviews and classroom observations of three experienced English language teachers working with large and reduced-size classes in Hong Kong secondary schools. Findings from the study point to subtle…

  2. 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.

  3. 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

  4. 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. (USGS)

  5. 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.

  6. 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…

  7. 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…

  8. 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…

  9. 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…

  10. 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…

  11. 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...

  12. 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...

  13. 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...

  14. 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...

  15. 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...

  16. 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.…

  17. 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…

  18. 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…

  19. 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…

  20. 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

  1. Rapid changes in microbial biomass and aggregate size distribution in response to changes in organic matter management in grass pasture

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Adding high quantities of organic matter can increase carbon (C) inputs to soil and help maintain soil structure. This study investigated short-term effects of application of different levels of composted dairy manure (CDM) versus interseeding a legume into grass pasture on aggregate stability and s...

  2. Purine twisted-intercalating nucleic acids: a new class of anti-gene molecules resistant to potassium-induced aggregation.

    PubMed

    Paramasivam, Manikandan; Cogoi, Susanna; Filichev, Vyacheslav V; Bomholt, Niels; Pedersen, Erik B; Xodo, Luigi E

    2008-06-01

    Sequence-specific targeting of genomic DNA by triplex-forming oligonucleotides (TFOs) is a promising strategy to modulate in vivo gene expression. Triplex formation involving G-rich oligonucleotides as third strand is, however, strongly inhibited by potassium-induced TFO self-association into G-quartet structures. We report here that G-rich TFOs with bulge insertions of (R)-1-O-[4-(1-pyrenylethynyl)-phenylmethyl] glycerol (called twisted intercalating nucleic acids, TINA) show a much lower tendency to aggregate in potassium than wild-type analogues do. We designed purine-motif TINA-TFOs for binding to a regulatory polypurine-polypyrimidine (pur/pyr) motif present in the promoter of the KRAS proto-oncogene. The binding of TINA-TFOs to the KRAS target has been analysed by electrophoresis mobility shift assays and DNase I footprinting experiments. We discovered that in the presence of potassium the wild-type TFOs did not bind to the KRAS target, differently from the TINA analogues, whose binding was observed up to 140 mM KCl. The designed TINA-TFOs were found to abrogate the formation of a DNA-protein complex at the pur/pyr site and to down-regulate the transcription of CAT driven by the murine KRAS promoter. Molecular modelling of the DNA/TINA-TFO triplexes are also reported. This study provides a new and promising approach to create TFOs to target in vivo the genome. PMID:18456705

  3. Complex polyion-surfactant ion salts in equilibrium with water: changing aggregate shape and size by adding oil.

    PubMed

    Bernardes, Juliana S; Norrman, Jens; Piculell, Lennart; Loh, Watson

    2006-11-23

    The phase behavior of ternary mixtures containing an alkyltrimethylammonium polyacrylate complex salt, water, and a nonpolar "oil" (n-decanol, p-xylene or cyclohexane) is investigated. The complex salts were prepared with short or long polyacrylates (30 or 6000 repeating units) and with hexadecyltrimethylammonium or dodecyltrimethylammonium surfactant ions. Phase diagrams and structures were determined by visual inspection and small-angle X-ray scattering analyses. Systems containing decanol display a predominance of lamellar phases, while hexagonal phases prevail in systems containing p-xylene or cyclohexane. The difference is interpreted as a result of the different locations of the oils within the surfactant aggregates. Decanol is incorporated at the aggregate interface, leading to a decrease in its curvature, which favors the appearance of lamellar structures. p-Xylene and cyclohexane, on the other hand, are mostly incorporated in the interior of the cylindrical aggregate, as reflected by its swelling as the oil content increases. The comparison of these results with those reported for similar systems with monovalent (bromide) counterions indicates a much more limited swelling of the lamellar phases with polymeric counterions by water. This limited swelling behavior is predominantly ascribed to bridging due to the polyions. PMID:17107195

  4. 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.

  5. 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

  6. 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.

  7. 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…

  8. 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…

  9. 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. PMID:26641528

  10. 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…

  11. 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…

  12. 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…

  13. 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 ...

  14. 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.

  15. Effects of viewing geometry, aggregation state, and particle size on reflectance spectra of the Murchison CM2 chondrite deconvolved to Dawn FC band passes

    NASA Astrophysics Data System (ADS)

    Izawa, Matthew R. M.; Schäfer, Tanja; Pietrasz, Valerie B.; Cloutis, Edward A.; Mann, Paul; Nathues, Andreas; Mengel, Kurt; Schäfer, Michael; Thangjam, Guneshwar; Hoffmann, Martin; Tait, Kimberly T.; Applin, Daniel M.

    2016-03-01

    Several current and soon-to-launch missions will investigate 'dark' asteroids, whose spectra have few weak or no distinct spectral features. Some carbonaceous chondrites, particularly the CI and CM groups, are reasonable material analogues for many dark asteroid surfaces. In addition to compositional variations, many non-compositional effects, including viewing geometry, surface particle size and particle sorting, can influence reflectance spectra, potentially complicating mineralogical interpretation of such data from remote surfaces. We have carried out an investigation of the effects of phase angle, particle size, aggregation state, and intra-sample heterogeneity on the reflectance spectra (0.4-1.0 μm) of the Murchison CM2 carbonaceous chondrite, deconvolved to Dawn Framing Camera (FC) band passes. This study was motivated by the desire to derive information about the surface of Ceres from Dawn FC data. Key spectral parameters derived from the FC multispectral data include various two-band reflectance ratios as well as three-band ratios that have been derived for mineralogical analysis. Phase angle effects include increased visible slope with increasing phase angle, a trend that may reverse at very high phase angles. Fine-grained particles exert a strong influence on spectral properties relative to their volumetric proportion. Grain size variation effects include a decrease in spectral contrast and increased visible spectral slope with decreasing grain size. Intra-sample heterogeneity, while spectrally detectable, is of relatively limited magnitude.

  16. 40Gbit/s-class-λ-tunable WDM/TDM-PON using λ-selectable B-Tx and 4 x M cyclic AWG router for flexible photonic aggregation networks.

    PubMed

    Nakamura, Hirotaka; Taguchi, Katsuhisa; Tamaki, Shinya; Mizuno, Takayuki; Hashizume, Yasuaki; Yamada, Takashi; Ito, Mikitaka; Takahashi, Hiroshi; Kimura, Shunji; Yoshimoto, Naoto

    2013-01-14

    This paper proposes a 40Gbit/s-class-λ-tunable WDM/TDM-PON for flexible photonic aggregation networks that achieves the aggregation of a large number of users using the DWBA algorithm without an L2-SW. It also clarifies the scalability of the proposed system in terms of the transmission distance and the number of users. A λ-switching transmission experiment was conducted using a newly developed 10Gbit/s x 4λ selectable B-Tx and 4 x 4 cyclic AWG router. PMID:23388940

  17. 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...

  18. 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.

  19. Long-term tillage and cropping sequence influence on dryland soil aggregate-carbon dynam

    NASA Astrophysics Data System (ADS)

    Sainju, U.; Tonthat, T.-C.; Jabro, J. D.

    2009-04-01

    Sequestration and transformation of soil C as a result of long-term management practices occur mainly in aggregates. This study evaluated the 21-yr effect of tillage and cropping sequence combinations on dryland soil C sequestration and transformation into various C fractions in aggregates at the 0-20 cm depth in eastern Montana, USA. Tillage and cropping sequences were no-tilled continuous spring wheat (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat-barley (1984-1999) followed by spring wheat-pea (2000-2004) (FSTW-B/P), and spring-tilled spring wheat-fallow (STW-F). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Total amount of crop biomass (stems + leaves) residue returned to soil from 1984 to 2004 was lower in STW-F than in other treatments. Aggregate proportion was greater in NTCW than in FSTCW in 4.75-2.00 mm aggregate-size class at 0-5 cm but was greater in STW-F than in STCW in 2.00-0.25 mm size class at 5-20 cm. The SOC and POC were greater in NTCW and STCW than in STW-F in all aggregate-size classes at 0-5 cm and greater in NTCW than in STW-F in 4.75-2.00 mm and <0.25 mm size classes at 5-20 cm. The PCM was greater in STCW and FSTCW than in STW-F in all aggregate-size classes at 0-5 cm and greater in STCW than in NTCW, FSTCW, and STW-F in 4.75-2.00 mm size class at 5-20 cm. Similarly, MBC was greater in NTCW and STCW than in STW-F in <2.00 mm size class at 0-5 cm and greater in STCW and FSTCW than in STW-F in 4.75-0.25 mm class size at 5-20 cm. No-till increased aggregate proportion and POC but reduced PCM and MBC compared with tilled practices in the continuous spring wheat system in 4.75-2.00 mm size class. Aggregate proportion was greater in 2.00-0.25 mm size class than in other aggregate-size classes. The SOC, POC, and PCM were greater in 4.75-2.00 mm than in <0

  20. Effect of ionic strength and pH on the size and dynamic aggregation of TiO2 nanoparticle dispersions

    NASA Astrophysics Data System (ADS)

    Ibrahim, Hesham; Al-Turki, Ali; Al-Farraj, Abdullah

    2016-04-01

    The widespread use of TiO2 nanoparticles in many products has led to increased concern over their fate in the environment. The stability of TiO2 nanoparticles in aqueous dispersions plays a key role in the aggregation process and subsequently affect the retention and transport of nanoparticles in aquatic systems. We investigated the effect of ionic strength (0.0001-1 M NaCl), and pH (3-11) on the hydrodynamic size and zeta potential of 50 mg L‑1 TiO2dispersions. Dynamic aggregation of the TiO2 nanoparticles was monitored via time-resolved optical absorbance at a wavelength of 300 nm. Results showed that the hydrodynamic size of the TiO2 nanoparticles increased by increasing the ionic strength at all pH values. The average hydrodynamic size of the TiO2 nanoparticle dispersions with ionic strength of 1-0.1M reached 1522 nm. At lower ionic strength (0.01-0.0001M), the hydrodynamic size varied considerably by variation in pH values. Smaller hydrodynamic size was observed at both lower (3-5) and highest (11) pH values, and the hydrodynamic size reached 292 and 255 nm, respectively. For TiO2 dispersions with pH values 7 to 9, the hydrodynamic size reached 1595 nm because of the lower surface charge as the pH of the dispersion approaches the point of zero charge of the TiO2 nanoparticles. Zeta potential of the TiO2 nanoparticles were found to be positive for pH ≤ 5 and reached an average of 9.2 and 30.9 mV for TiO2 dispersions with 1-0.1M and 0.01-0.0001M, respectively. For pH ≥ 7, zeta potential was negative and showed the largest value of -42.6 mV at lower ionic strength and pH values above 9. Increasing the ionic strength caused the relative concentration (C/Co) of the TiO2 nanoparticles to decline indicating lower TiO2 nanoparticles stability. The average relative concentration of the TiO2 nanoparticles reached 0.14, 0.17, and 0.23 for the 1, 0.1, and < 0.01M, respectively. The maximum TiO2 nanoparticles stability reached an average of 0.79, and was observed at

  1. Photophoretic force on aggregate grains

    NASA Astrophysics Data System (ADS)

    Matthews, Lorin S.; Kimery, Jesse B.; Wurm, Gerhard; de Beule, Caroline; Kuepper, Markus; Hyde, Truell W.

    2016-01-01

    The photophoretic force may impact planetary formation by selectively moving solid particles based on their composition and structure. This generates collision velocities between grains of different sizes and sorts the dust in protoplanetary discs by composition. This numerical simulation studied the photophoretic force acting on fractal dust aggregates of μm-scale radii. Results show that aggregates tend to have greater photophoretic drift velocities than spheres of similar mass or radii, though with a greater spread in the velocity. While the drift velocities of compact aggregates continue to increase as the aggregates grow larger in size, fluffy aggregates have drift velocities which are relatively constant with size. Aggregates formed from an initially polydisperse size distribution of dust grains behave differently from aggregates formed from a monodisperse population, having smaller drift velocities with directions which deviate substantially from the direction of illumination. Results agree with microgravity experiments which show the difference of photophoretic forces with aggregation state.

  2. 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…

  3. Unequilibrated, equilibrated, and reduced aggregates in anhydrous interplanetary dust particles

    NASA Astrophysics Data System (ADS)

    Bradley, J. P.

    1993-03-01

    Track-rich anhydrous IDP's are probably the most primitive IDP's because they have escaped significant post-accretional alteration; they exhibit evidence of (nebular) gas phase reactions; their mineralogy is similar to comet Halley's dust; and some of them exhibit comet-like IR spectral characteristics. However, basic questions about the mineralogy and petrography of anhydrous IDP's remain unanswered, because they contain aggregated components that can be heterogeneous on a scale of nanometers. In some IDP's, aggregates account for greater than 75 percent of the volume of the particle. The aggregates have been systematically examined using an analytical electron microscope (AEM), which provides probe-forming optics and (x-ray and electron) spectrometers necessary to analyze individual nanometer-sized grains. The AEM results reveal at least three mineralogically distinct classes of aggregates in an hydrous IDP's, with mineralogies reflecting significantly different formation/aggregation environments.

  4. 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

  5. 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.

  6. 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. PMID:12261445

  7. 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

  8. IfkA, a presumptive eIF2α kinase of Dictyostelium, is required for proper timing of aggregation and regulation of mound size

    PubMed Central

    Fang, Rui; Xiong, Yanhua; Singleton, Charles K

    2003-01-01

    Background The transition from growth to development in Dictyostelium is initiated by amino acid starvation of growing amobae. In other eukaryotes, a key sensor of amino acid starvation and mediator of the resulting physiological responses is the GCN2 protein, an eIF2α kinase. GCN2 downregulates the initiation of translation of bulk mRNA and enhances translation of specific mRNAs by phosphorylating the translation initiation factor eIF2α. Two eIF2α kinases were identified in Dictyostelium and studied herein. Results Neither of the eIF2α kinases appeared to be involved in sensing amino acid starvation to initiate development. However, one of the kinases, IfkA, was shown to phosphorylate eIF2α from 1 to 7 hours after the onset of development, resulting in a shift from polysomes to free ribosomes for bulk mRNA. In the absence of the eIF2α phosphorylation, ifkA null cells aggregated earlier than normal and formed mounds and ultimately fruiting bodies that were larger than normal. The early aggregation phenotype in ifkA null cells reflected an apparent, earlier than normal establishment of the cAMP pulsing system. The large mound phenotype resulted from a reduced extracellular level of Countin, a component of the counting factor that regulates mound size. In wild type cells, phosphorylation of eIF2α by IfkA resulted in a specific stabilization and enhanced translational efficiency of countin mRNA even though reduced translation resulted for bulk mRNA. Conclusions IfkA is an eIF2α kinase of Dictyostelium that normally phosphorylates eIF2α from 1 to 7 hours after the onset of development, or during the preaggregation phase. This results in an overall reduction in the initiation of protein synthesis during this time frame and a concomitant reduction in the number of ribosomes associated with most mRNAs. For some mRNAs, however, initiation of protein synthesis is enhanced or stabilized under the conditions of increased eIF2α phosphorylation. This includes countin

  9. Patterns of stomatal conductance among blue oak (Quercus douglasii) size classes and populations: implications for seedling establishment.

    PubMed

    Matzner, Steven L; Rice, Kevin J; Richards, James H

    2003-08-01

    Quercus douglasii Hook. & Arn. (blue oak) is a deciduous white oak that is currently failing to regenerate throughout much of its range in California, USA. Patterns of water use were observed in adult trees, saplings and seedlings to determine if ontogenetic changes in water use occur, which might be important in the establishment of this long-lived perennial species in a Mediterranean-type system. Seasonal and diurnal stomatal conductance (g(s)), late-season predawn xylem water potentials (Psi(pre)), carbon isotopic ratio (delta(13)C) and soil water status were compared among the three size classes at three sites differing in mean precipitation and soil water characteristics. Comparisons were also made between microsites with and without regeneration (defined by the presence or absence of saplings). Overall patterns of water use were consistent among the three sites, except that, at the site with the highest rainfall, Q. douglasii plants had higher g(s) and more positive Psi(pre) values. Although no differences in water use patterns were found between regeneration and non-regeneration microsites, the observed ontogenetic differences in water use may have important implications for Q. douglasii establishment. Compared with adult trees and saplings, seedlings had higher gas exchange rates during periods of high soil water content (early in the season and in the morning). Seedling g(s) was correlated with percent extractable soil water (ESW) throughout the season; adult tree and sapling g(s) was correlated with ESW between June and September. Despite experiencing greater water stress (indicated by more negative Psi(pre) values) than older trees, seedlings had more negative delta(13)C values, implying lower water-use efficiencies. PMID:12839731

  10. 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.

  11. Does Small Really Make a Difference? A Review of the Literature on the Effects of Class Size on Teaching Practice and Pupils' Behaviour and Attainment. SCRE Research Report.

    ERIC Educational Resources Information Center

    Wilson, Valerie

    This literature review focuses on the effects of class size on styles of teaching practice, and on pupil behavior and attainment. Most of the literature is from the United States. Evidence from previous reviews, correlational studies, meta-analyses, and experimental interventions are presented in this document. Much of the existing evidence is at…

  12. GED Acquisition Rates From An At-Risk Youth Program's Curriculum as Influenced by Three Criteria: Multiple Intelligence Usage, Class Size, and Its Mentorship Program

    ERIC Educational Resources Information Center

    Fleming, Angela Rene

    2005-01-01

    The purpose of this study was to determine whether a combination of three factors: (1) a reduced student teacher ratio (class size education); (2) a mentorship program and (3) a varied curriculum, via use of the multiple intelligences would successfully improve secondary at risk youths' high school graduation rates. The graduation rate and GED…

  13. 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…

  14. Effects of Class Size on Reading Achievement in Grades 1-3 in the Madison Metropolitan School District (1974-1976).

    ERIC Educational Resources Information Center

    Madison Public Schools, WI.

    A study was conducted to determine the effects of class size on the reading achievement of 517 representative Madison (Wisconsin) students in a three year longitudinal sample. Data included reading achievement, IQ, attitudes toward reading, parents' and teachers' ratings of student interest in reading, sex, age, socioeconomic status, and average…

  15. 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…

  16. Towards an operational implementation of particle aggregation in ash dispersion models (Invited)

    NASA Astrophysics Data System (ADS)

    Mastin, L. G.; Van Eaton, A. R.; Durant, A. J.; Schwaiger, H. F.; Denlinger, R. P.

    2013-12-01

    During volcanic unrest, ash transport models are used by volcano observatories and civil protection authorities to forecast areas at risk from tephra deposition. These models can effectively forecast areas affected due to their reliance on modern numerical wind fields. But they cannot yet accurately forecast the mass distribution in deposits, due largely to one process--particle aggregation--that is not considered in most models. Aggregation rates vary with particle concentration, size distribution, and the amount and phases of water present. Relationships between these variables are not yet well quantified. Although modeling studies have reproduced the observed distribution of tephra deposits from several key eruptions, most have done so only a posteriori, through ad-hoc adjustments in grain-size distribution or settling velocity. Here, we report early attempts to incorporate aggregation into the transport and deposition model Ash3d in a simplified form that can be implemented operationally. This project includes three steps: (1) characterizing aggregate size and abundance starting from deposit measurements at Mount St. Helens, Redoubt, and Spurr volcanoes; (2) developing a scheme to characterize aggregation using 2 or 3 parameters whose values can be ascertained for atmospheric and source conditions; and (3) incorporating the scheme into the model so that parameter values can be assigned prior to each simulation. For example, the May 18, 1980 Mount St. Helens deposit can be simulated using two aggregation parameters A (=2.8) and B (=1.9), both in phi units, where A represents the largest size class incorporated into aggregates and B represents the dominant size of aggregates (with assumed density 600 kg m-3). The mass fraction Fφ of each size class φ incorporated into aggregates is assumed to follow Fφ=1-exp(-max(0,φ-A)). We will report the success of this scheme to model several other well-characterized deposits.

  17. Polymorphism of the SOD1-DNA aggregation species can be modulated by DNA.

    PubMed

    Jiang, Wei; Zhang, Bo; Yin, Jun; Liu, Liang; Wang, Li; Liu, Changlin

    2008-12-01

    Proteinaceous aggregates rich in copper, zinc superoxide dismutase (SOD1) have been found in both in vivo and in vitro models. We have shown that double-stranded DNA that acts as a template accelerates the in vitro formation of wild-type SOD1 aggregates. Here, we examined the polymorphism of templated-SOD1 aggregates generated in vitro upon association with DNA under different conditions. Electron microscopy imaging indicates that this polymorphism is capable of being manipulated by the shapes, structures, and doses of the DNAs tested. The nanometer- and micrometer-scale aggregates formed under acidic conditions and under neutral conditions containing ascorbate fall into three classes: aggregate monomers, oligomeric aggregates, and macroaggregates. The aggregate monomers observed at given DNA doses exhibit a polymorphism that is markedly corresponded to the coiled shapes of linear DNA and structures of plasmid DNA. On the other hand, the regularly branched structures observed under both atomic force microscopy and optical microscope indicate that the DNAs tested are simultaneously condensed into a nanoparticle with a specific morphology during SOD1 aggregation, revealing that SOD1 aggregation and DNA condensation are two concurrent phenomena. The results might provide the basis of therapeutic approaches to suppress the formation of toxic protein oligomers or aggregates by screening the toxicity of the protein aggregates with various sizes and morphologies. PMID:18690666

  18. 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.

  19. Weighted aggregation

    NASA Technical Reports Server (NTRS)

    Feiveson, A. H. (Principal Investigator)

    1979-01-01

    The use of a weighted aggregation technique to improve the precision of the overall LACIE estimate is considered. The manner in which a weighted aggregation technique is implemented given a set of weights is described. The problem of variance estimation is discussed and the question of how to obtain the weights in an operational environment is addressed.

  20. A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class aves.

    PubMed

    Gregory, T Ryan

    2002-01-01

    For half a century, variation in genome size (C-value) has been an unresolved puzzle in evolutionary biology. While the initial "C-value paradox" was solved with the discovery of noncoding DNA, a much more complex "C-value enigma" remains. The present study focuses on one aspect of this puzzle, namely the small genome sizes of birds. Significant negative correlations are reported between resting metabolic rate and both C-value and erythrocyte size. Cell size is positively correlated with both nucleus size and C-value in birds, as in other vertebrates. These findings shed light on the constraints acting on genome size in birds and illustrate the importance of interactions among various levels of the biological hierarchy, ranging from the subchromosomal to the ecological. Following from a discussion of the mechanistic bases of the correlations reported and the processes by which birds achieved and/or maintain small genomes, a pluralistic approach to the C-value enigma is recommended. PMID:11913657

  1. 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.

  2. 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

  3. 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

  4. 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%.

  5. 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.

  6. 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

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

    PubMed

    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. PMID:27015111

  8. 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

  9. 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.

  10. Spatial data aggregation for spatio-temporal individual-level models of infectious disease transmission.

    PubMed

    Deeth, Lorna E; Deardon, Rob

    2016-05-01

    A class of complex statistical models, known as individual-level models, have been effectively used to model the spread of infectious diseases. These models are often fitted within a Bayesian Markov chain Monte Carlo framework, which can have a sig nificant computational expense due to the complex nature of the likelihood function associated with this class of models. Increases in population size or duration of the modeled epidemic can contribute to this computational burden. Here, we explore the effect of reducing this computational expense by aggregating the data into spatial clusters, and therefore reducing the overall population size. Individual-level models, reparameterized to account for this aggregation effect, may then be fitted to the spatially aggregated data. The ability of two reparameterized individual-level models, when fitted to this reduced data set, to identify a covariate effect is investigated through a simulation study. PMID:27246276

  11. 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.

  12. 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…

  13. 21 CFR 1303.13 - Adjustments of aggregate production quotas.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... Federal Register his final order determining the aggregate production for the basic class of controlled... 21 Food and Drugs 9 2010-04-01 2010-04-01 false Adjustments of aggregate production quotas. 1303... Aggregate Production and Procurement Quotas § 1303.13 Adjustments of aggregate production quotas. (a)...

  14. Physical characterization and in vitro biological impact of highly aggregated antibodies separated into size-enriched populations by fluorescence-activated cell sorting

    PubMed Central

    Telikepalli, Srivalli; Shinogle, Heather E.; Thapa, Prem S.; Kim, Jae Hyun; Deshpande, Meghana; Jawa, Vibha; Middaugh, C. Russell; Narhi, Linda O.; Joubert, Marisa K.; Volkin, David B.

    2015-01-01

    An IgG2 monoclonal antibody (mAb) solution was subjected to stirring, generating high concentrations of nanometer and subvisible particles, which were then successfully size enriched into different size bins by low speed centrifugation or a combination of gravitational sedimentation and Fluorescence-Activated Cell Sorting (FACS). The size-fractionated mAb particles were assessed for their ability to elicit the release of cytokines from a population of donor-derived human peripheral blood mononuclear cells (PBMC) at two phases of the immune response. Fractions enriched in nanometer-sized particles showed a lower response than those enriched in micron-sized particles in this assay. Particles of 5–10 μm in size displayed elevated cytokine release profiles compared to other size ranges. Stir-stressed mAb particles had amorphous morphology, contained protein with partially altered secondary structure, elevated surface hydrophobicity (compared to controls), and trace levels of elemental fluorine. FACS size-enriched the mAb particle samples, yet did not notably alter the overall morphology or composition of particles as measured by Microflow imaging, Transmission Electron Microscopy, and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy. The utility and limitations of FACS for size separation of mAb particles and potential of in-vitro PBMC studies to rank order the immunogenic potential of various types of mAb particles is discussed. PMID:25753756

  15. 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

  16. 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

  17. Cucurbitacin IIa: a novel class of anti-cancer drug inducing non-reversible actin aggregation and inhibiting survivin independent of JAK2/STAT3 phosphorylation

    PubMed Central

    Boykin, C; Zhang, G; Chen, Y-H; Zhang, R-W; Fan, X-E; Yang, W-M; Lu, Q

    2011-01-01

    Background: Cucurbitacin (Cuc) and triterpene-derived natural products exhibit anti-cancer potential in addition to their conspicuous anti-bacterial and anti-inflammatory activity. Recently, inhibition of Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling was shown to underlie the effects of Cuc family on inducing cell death in cancer. Method: We purified Cuc IIa, the active component from the medicinal plant Hemsleya amalils Diels, which shows different structural modifications from other Cuc derivatives. We investigated the mechanisms of its inhibitory effects on cancer cells in vitro and tumour growth in vivo. Results: Cuc IIa induced the irreversible clustering of filamentous actin and arrested cell cycle by the increases in G2/M populations. Cuc IIa resulted in the reduced phospho-Histone H3 and markedly increased cleavage of poly-(ADP-ribose) polymerase or PARP, immediate upstream of DNA breakdown as the result of caspase activation, consistent with mitotic blockage-induced cell death. However, unlike other Cuc members, Cuc IIa did not suppress JAK2/STAT3 phosphorylation or alter phosphorylation of mitogen-activated protein kinases. Instead, the expression of the cell cycle-regulated Inhibitor of Apoptosis Protein (IAP) survivin was reduced. Introducing oncoprotein δ-catenin, which increased survivin expression and suppressed small GTPase RhoA, reduced efficacy of Cuc IIa to induce cell death. Supporting the effects of Cuc IIa on actin cytoskeletal signaling, RhoA phosphorylation was reduced suggesting its increased activity. Conclusion: Cuc IIa is a novel class of anti-cancer drug in suppression of cancer cell expansion by disrupting the actin cytoskeleton and directing the cell to undergo PARP-mediated apoptosis through the inhibition of survivin downstream of JAK2/STAT3. PMID:21304528

  18. 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

  19. 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

  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. 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

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

    PubMed

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

    2016-05-01

    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

  3. 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.

  4. 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.

  5. Laser-induced breakdown detection of temperature-ramp generated aggregates of therapeutic monoclonal antibody.

    PubMed

    Menzen, Tim; Friess, Wolfgang; Niessner, Reinhard; Haisch, Christoph

    2015-08-01

    The detection and characterization of protein aggregation is essential during development and quality control of therapeutic proteins, as aggregates are typically inactive and may trigger anti-drug-antibody formation in patients. Especially large multi-domain molecules, such as the important class of therapeutic monoclonal antibodies (mAbs), can form various aggregates that differ in size and morphology. Although particle analysis advanced over the recent years, new techniques and orthogonal methods are highly valued. To our knowledge, the physical principle of laser-induced breakdown detection (LIBD) was not yet applied to sense aggregates in therapeutic protein formulations. We established a LIBD setup to monitor the temperature-induced aggregation of a mAb. The obtained temperature of aggregation was in good agreement with the results from previously published temperature-ramped turbidity and dynamic light scattering measurements. This study demonstrates the promising applicability of LIBD to investigate aggregates from therapeutic proteins. The technique is also adaptive to online detection and size determination, and offers interesting opportunities for morphologic characterization of protein particles and impurities, which will be part of future studies. PMID:26158409

  6. Imbibition kinetics of spherical aggregates

    NASA Astrophysics Data System (ADS)

    Hébraud, Pascal; Lootens, Didier; Debacker, Alban

    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 : in the first one, the imbibition proceeds by compressing the air inside the aggregate. Then, the solvent stops when the pressure of the compressed air is equal to the Laplace pressure at the meniscus of the wetting solvent in the porous aggregate. The interface is pinned and the aggregate slowly degases, up to a point where the pressure of the entrapped air stops decreasing and is controlled by the Laplace pressure of small bubbles. Depending on the curvature of the bubble, the system may then be in an unstable state. The imbibition then starts again, but with an inner pressure in equilibrium with these bubbles. This last stage leads to the complete infiltration of the aggregate.

  7. 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

  8. 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

  9. 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

  10. Dual switchable CRET-induced luminescence of CdSe/ZnS quantum dots (QDs) by the hemin/G-quadruplex-bridged aggregation and deaggregation of two-sized QDs.

    PubMed

    Hu, Lianzhe; Liu, Xiaoqing; Cecconello, Alessandro; Willner, Itamar

    2014-10-01

    The hemin/G-quadruplex-catalyzed generation of chemiluminescence through the oxidation of luminol by H2O2 stimulates the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs), resulting in the luminescence of the QDs. By the cyclic K(+)-ion-induced formation of the hemin/G-quadruplex linked to the QDs, and the separation of the G-quadruplex in the presence of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence of the QDs is demonstrated. QDs were modified with nucleic acids consisting of the G-quadruplex subunits sequences and of programmed domains that can be cross-linked through hybridization, using an auxiliary scaffold. In the presence of K(+)-ions, the QDs aggregate through the cooperative stabilization of K(+)-ion-stabilized G-quadruplex bridges and duplex domains between the auxiliary scaffold and the nucleic acids associated with the QDs. In the presence of 18-crown-6-ether, the K(+)-ions are eliminated from the G-quadruplex units, leading to the separation of the aggregated QDs. By the cyclic treatment of the QDs with K(+)-ions/18-crown-6-ether, the reversible aggregation/deaggregation of the QDs is demonstrated. The incorporation of hemin into the K(+)-ion-stabilized G-quadruplex leads to the ON-OFF switchable CRET-stimulated luminescence of the QDs. By the mixing of appropriately modified two-sized QDs, emitting at 540 and 610 nm, the dual ON-OFF activation of the luminescence of the QDs is demonstrated. PMID:25216118

  11. 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.

  12. 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).

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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→∞.

  18. Amblyomma americanum tick saliva serine protease inhibitor 6 is a cross-class inhibitor of serine proteases and papain-like cysteine proteases that delays plasma clotting and inhibits platelet aggregation

    PubMed Central

    Mulenga, A.; Kim, T.; Ibelli, A. M. G.

    2013-01-01

    We previously demonstrated that Amblyomma americanum tick serine protease inhibitor 6 (AamS6) was secreted into the host during tick feeding and that both its mRNA and protein were ubiquitously and highly expressed during the first 3 days of tick feeding. This study demonstrates that AamS6 is a cross-class inhibitor of both serine- and papain-like cysteine proteases that has apparent antihaemostatic functions. Consistent with the typical inhibitory serpin characteristics, enzyme kinetics analyses revealed that Pichia pastoris-expressed recombinant (r) AamS6 reduced initial velocities of substrate hydrolysis (V0) and/or maximum enzyme velocity (Vmax) of trypsin, chymotrypsin, elastase, chymase, and papain in a dose–response manner. We speculate that rAamS6 inhibited plasmin in a temporary fashion in that while rAamS6 reduced V0 of plasmin by up to ~53%, it had no effect on Vmax. Our data also suggest that rAmS6 has minimal or no apparent effect on V0 or Vmax of thrombin, factor Xa, and kallikrein. We speculate that AamS6 is apparently involved in facilitating blood meal feeding in that various amounts of rAamS6 reduced platelet aggregation by up to ~47% and delayed plasma clotting time in the recalcification time assay by up to ~210 s. AamS6 is most likely not involved with the tick’s evasion of the host’s complement defense mechanism, in that rAamS6 did not interfere with the complement activation pathway. Findings in this study are discussed in the context of expanding our understanding of tick proteins that control bloodmeal feeding and hence tick-borne disease transmission by ticks. PMID:23521000

  19. Ammonia concentrations in different size classes of ovarian follicles of sheep (Ovis aries): Possible mechanisms of accumulation and its effect on oocyte and granulosa cell growth in vitro.

    PubMed

    Nandi, S; Gupta, P S P; Mondal, S

    2016-03-01

    The present study investigated the concentrations and the mechanisms of accumulation of ammonia in different sizes of ovarian follicles and the effect of ammonia on oocyte and granulosa cell growth and functions in vitro with sheep (Ovis aries) as an animal model. The effects of cyclicity, seasonality, phases of the estrous cycle, and seasons (environmental) on ammonia concentrations in follicular fluid were also investigated. The effect of ammonia on in vitro development of oocytes (maturation rate, viability rate, cleavage rate, morulae/blastocysts yield) recovered from different sizes of follicles was examined at the levels of 0, 50, 100, 150, 250, 300, and 500 μM. Same concentrations of ammonia were examined on growth parameters (metabolic activity, viability, cell number increment, monolayer formation, apoptosis rate) and hormone (progesterone, estrogen) secretion activity of granulosa cells in vitro. Results suggested as the follicle size increased, ammonia concentrations decreased. The ammonia concentrations in ovine follicular fluid were found to be 261.5 ± 32.4, 157.7 ± 19.2, and 42.9 ± 8.3 μM, respectively, for small, medium, and large follicles. The corresponding ranges were 290 to 238 μM, 184 to 142 μM, and 70 to 22 μM. The differences were due to more accumulation of fluid, less metabolic activity of granulosa cells, and elevation of protein, potassium, and chloride as the follicle size increased. The seasonality and phases of the estrous cycle did not have any effect on ammonia level in ovarian follicles. Ammonia concentrations in all size classes of follicles examined were significantly reduced in ewes during hot seasons compared to cold seasons and in acyclic animals compared to cyclic ones. Ammonia impaired oocyte development at 300 μM when the oocytes were isolated from small follicles and at 250 μM when the oocytes were isolated from medium and large follicles. In contrast, ammonia caused the negative impact on granulosa cells growth

  20. Aggregation dynamics and magnetic properties of magnetic micrometer-sized particles dispersed in a fluid under the action of rotating magnetic fields

    NASA Astrophysics Data System (ADS)

    Llera, María; Codnia, Jorge; Jorge, Guillermo A.

    2015-06-01

    We present a dynamic study of soft magnetic, commercial Fe and Ni micrometer-sized particles dispersed in oleic acid and subjected to a variable (rotating) magnetic field in the horizontal plane. A very complex structure is formed after the particles decant towards the bottom liquid-solid interface and the magnetic field is applied for several minutes. The dynamics of structure formation was studied by means of the registration and analysis of microscopic video images, through a Matlab image analysis script. Several parameters, such as the number of clusters, the perimeter-based fractal dimension and circularity, were calculated as a function of time. The time evolution of the number of clusters was found to follow a power-law behavior, with an exponent consistent with that found in other studies for magnetic systems, whereas the typical formation time depends on the particle diameter and field configuration. Complementarily, the magnetic properties of the formed structure were studied, reproducing the experiment with liquid paraffin as the containing fluid, and then letting it solidify. The sample obtained was studied by vibrating sample magnetometry. The magnetization curves show that the material obtained is a planar magnetically anisotropic material, which could eventually be used as an anisotropic magnetic sensor or actuator.

  1. 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

  2. Weighted Random Mixing and Exact Finite Lattice Descriptions of Molecular Aggregation Equilibria

    NASA Astrophysics Data System (ADS)

    Ben-Amotz, Dor

    2014-03-01

    Entropic and energetic contributions to a broad class of molecular aggregation and self-assembly processes are described by performing a mean field Boltzmann average over aggregate size distributions pertaining to an idealized random mixture. Predictions obtained using the resulting weighted random mixing (WRM) model are compared with exact finite lattice and fluid molecular dynamics simulation results for systems in which each aggregate resembles a central molecule with multiple ligand binding sites. Good agreement between the exact and WRM results is found for systems with interaction energies of various magnitudes (and signs), both in the large and small cohesive interaction energy regimes (or at low and high temperature, respectively). The latter two regimes are separated by a critical point on either side of which qualitatively different aggregation behavior is predicted and observed. More specifically, both the WRM model and exact finite lattice aggregation results reveal that when half the ligand binding sites are filled, the corresponding aggregate size distributions are bimodal below and unimodal above the corresponding critical temperature, whose value depends on the ligand-ligand interaction energy, but is independent of the binding energy of each ligand to the central molecule. This work was carried out in collaboration with Blake M. Rankin and B. Widom (at Cornell University), and was supported by NSF Grant Number CHE-1213338.

  3. 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. PMID:27253725

  4. 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.

  5. 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.

  6. 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.

  7. Kinetic model for erythrocyte aggregation.

    PubMed

    Bertoluzzo, S M; Bollini, A; Rasia, M; Raynal, A

    1999-01-01

    It is well known that light transmission through blood is the most widely utilized method for the study of erythrocyte aggregation. The curves obtained had been considered empirically as exponential functions. In consequence, the process becomes characterized by an only parameter that varies with all the process factors without discrimination. In the present paper a mathematical model for RBC aggregation process is deduced in accordance with von Smoluchowski's theory about the kinetics of colloidal particles agglomeration. The equation fitted the experimental pattern of the RBC suspension optical transmittance closely and contained two parameters that estimate the most important characteristics of the aggregation process separately, i.e., (1) average size of rouleaux at equilibrium and (2) aggregation rate. The evaluation of the method was assessed by some factors affecting erythrocyte aggregation, such as temperature, plasma dilutions, Dextran 500, Dextran 70 and PVP 360, at different media concentrations, cellular membrane alteration by the alkylating agent TCEA, and decrease of medium osmolarity. Results were interpreted considering the process characteristics estimated by the parameters, and there were also compared with similar studies carried out by other authors with other methods. This analysis allowed us to conclude that the equation proposed is reliable and useful to study erythrocyte aggregation. PMID:10660481

  8. Deterministic aggregation kinetics of superparamagnetic colloidal particles

    NASA Astrophysics Data System (ADS)

    Reynolds, Colin P.; Klop, Kira E.; Lavergne, François A.; Morrow, Sarah M.; Aarts, Dirk G. A. L.; Dullens, Roel P. A.

    2015-12-01

    We study the irreversible aggregation kinetics of superparamagnetic colloidal particles in two dimensions in the presence of an in-plane magnetic field at low packing fractions. Optical microscopy and image analysis techniques are used to follow the aggregation process and in particular study the packing fraction and field dependence of the mean cluster size. We compare these to the theoretically predicted scalings for diffusion limited and deterministic aggregation. It is shown that the aggregation kinetics for our experimental system is consistent with a deterministic mechanism, which thus shows that the contribution of diffusion is negligible.

  9. 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.

  10. 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…

  11. The Impacts of Budget Reductions on Indiana's Public Schools: The Impact of Budget Changes on Student Achievement, Personnel, and Class Size for Public School Corporations in the State of Indiana

    ERIC Educational Resources Information Center

    Jarman, Del W.; Boyland, Lori G.

    2011-01-01

    In recent years, economic downturn and changes to Indiana's school funding have resulted in significant financial reductions in General Fund allocations for many of Indiana's public school corporations. The main purpose of this statewide study is to examine the possible impacts of these budget reductions on class size and student achievement. This…

  12. 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.

  13. Simultaneous Measurement of Amyloid Fibril Formation by Dynamic Light Scattering and Fluorescence Reveals Complex Aggregation Kinetics

    PubMed Central

    Streets, Aaron M.; Sourigues, Yannick; Kopito, Ron R.; Melki, Ronald; Quake, Stephen R.

    2013-01-01

    An apparatus that combines dynamic light scattering and Thioflavin T fluorescence detection is used to simultaneously probe fibril formation in polyglutamine peptides, the aggregating subunit associated with Huntington's disease, in vitro. Huntington's disease is a neurodegenerative disorder in a class of human pathologies that includes Alzheimer's and Parkinson's disease. These pathologies are all related by the propensity of their associated protein or polypeptide to form insoluble, β-sheet rich, amyloid fibrils. Despite the wide range of amino acid sequence in the aggregation prone polypeptides associated with these diseases, the resulting amyloids display strikingly similar physical structure, an observation which suggests a physical basis for amyloid fibril formation. Thioflavin T fluorescence reports β-sheet fibril content while dynamic light scattering measures particle size distributions. The combined techniques allow elucidation of complex aggregation kinetics and are used to reveal multiple stages of amyloid fibril formation. PMID:23349924

  14. Implications of Aggregation and Mass Fractal Nature of Aggregates on the Properties of Organic Pigments and Polymer Composites

    NASA Astrophysics Data System (ADS)

    Agashe, Nikhil; Beaucage, Gregory; Skillas, George; Jemian, Peter; Long, Gabrielle; Ilavsky, Jan; Clapp, Lisa; Schwartz, Russell

    2002-03-01

    Aggregation of organic pigments was studied by small and ultra-small angle x-ray scattering. The aggregation of organic pigments and the implications for optical properties has not been previously reported in the literature, although extensive literature of this type exists for inorganic pigments such as titanium oxide. The pigments were also inspected for primary particle-size by electron microscopy and aggregate size by light scattering. All the pigments exhibited mass-fractal behavior when mixed into various polymers. Some pigments exhibited mass-fractal behavior even in powder form. The scattering patterns reflected differences in mass fractal dimension and particle size. The mass fractal dimension and the size of the aggregates in the polymer depend on the chemical nature of the pigment, the size and strength of the primary particle, the surface characteristics of the pigment, the interaction between the pigment and the polymer and the type of polymer used. A relation between the aggregate size and optimal optical properties is proposed. Aggregates having size around 0.5 microns show best optical properties and hence the pigment aggregate growth needs to be controlled during processing. The processes of aggregation were examined for these pigments. Some of the pigments formed aggregates by a reaction limited aggregation process while others exhibited diffusion limited aggregation.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. Aggregation Kinetics for IgG1-Based Monoclonal Antibody Therapeutics.

    PubMed

    Singla, A; Bansal, R; Joshi, Varsha; Rathore, Anurag S

    2016-05-01

    Monoclonal antibodies (mAbs) as a class of therapeutic molecules are finding an increasing demand in the biotechnology industry for the treatment of diseases like cancer and multiple sclerosis. A key challenge associated to successful commercialization of mAbs is that from the various physical and chemical instabilities that are inherent to these molecules. Out of all probable instabilities, aggregation of mAbs has been a major problem that has been associated with a change in the protein structure and is a hurdle in various upstream and downstream processes. It can stimulate immune response causing protein misfolding having deleterious and harmful effects inside a cell. Also, the extra cost incurred to remove aggregated mAbs from the rest of the batch is huge. Size exclusion chromatography (SEC) is a major technique for characterizing aggregation in mAbs where change in the aggregates' size over time is estimated. The current project is an attempt to understand the rate and mechanism of formation of higher order oligomers when subjected to different environmental conditions such as buffer type, temperature, pH, and salt concentration. The results will be useful in avoiding the product exposure to conditions that can induce aggregation during upstream, downstream, and storage process. Extended Lumry-Eyring model (ELE), Lumry-Eyring Native Polymerization model (LENP), and Finke-Watzky model (F-W) have been employed in this work to fit the aggregation experimental data and results are compared to find the best fit model for mAb aggregation to connect the theoretical dots with the reality. PMID:26902302

  1. Platelet aggregation test

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/003669.htm Platelet aggregation test To use the sharing features on this page, please enable JavaScript. The platelet aggregation blood test checks how well platelets , a ...

  2. 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.

  3. Platelet aggregation test

    MedlinePlus

    The platelet aggregation blood test checks how well platelets , a part of blood, clump together and cause blood to clot. ... Decreased platelet aggregation may be due to: Autoimmune ... Fibrin degradation products Inherited platelet function defects ...

  4. A competitive aggregation model for flash nanoprecipitation.

    PubMed

    Cheng, Janine Chungyin; Vigil, R D; Fox, R O

    2010-11-15

    Flash NanoPrecipitation (FNP) is a novel approach for producing functional nanoparticles stabilized by amphiphilic block copolymers. FNP involves the rapid mixing of a hydrophobic active (organic) and an amphiphilic di-block copolymer with a non-solvent (water) and subsequent co-precipitation of nanoparticles composed of both the organic and copolymer. During this process, the particle size distribution (PSD) is frozen and stabilized by the hydrophilic portion of the amphiphilic di-block copolymer residing on the particle surface. That is, the particle growth is kinetically arrested and thus a narrow PSD can be attained. To model the co-precipitation process, a bivariate population balance equation (PBE) has been formulated to account for the competitive aggregation of the organic and copolymer versus pure organic-organic or copolymer-copolymer aggregation. Aggregation rate kernels have been derived to account for the major aggregation events: free coupling, unimer insertion, and aggregate fusion. The resulting PBE is solved both by direct integration and by using the conditional quadrature method of moments (CQMOM). By solving the competitive aggregation model under well-mixed conditions, it is demonstrated that the PSD is controlled primarily by the copolymer-copolymer aggregation process and that the energy barrier to aggregate fusion plays a key role in determining the PSD. It is also shown that the characteristic aggregation times are smaller than the turbulent mixing time so that the FNP process is always mixing limited. PMID:20800847

  5. 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.

  6. 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 %). PMID:26284891

  7. 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

  8. Aggregation of sodium alkylbenzenesulfonates in aqueous solution

    SciTech Connect

    Magid, L.J.; Shaver, R.J.; Gulari, E.; Bedwell, B.; Alkhafaji, S.

    1981-01-01

    The surfactant 6 phenyl C/sub 12/SNa forms small spherical micelles in aqueous solution, having an aggregation number of 20 to 30 and a fractional charge of 0.45. These micelles are hydrated to the extent of approximately 18 moles H/sub 2/O per moles of surfactant. A second larger aggregate is also present in 6 phenyl C/sub 12/SNa solutions; its importance increases with solution age. Addition of NaCl causes both aggregates to apparently increase modestly in size. The surfactant 8 phenyl C/sub 16/SNa also contains both aggregates in its solutions; the larger one is relatively more important here. The larger aggregate does not correspond to dispersed bits of a liquid crystalline mesophase.

  9. 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

  10. 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,…

  11. Linking Microbial Community Structure to β-Glucosidic Function in Soil Aggregates

    SciTech Connect

    Bailey, Vanessa L.; Fansler, Sarah J.; Stegen, James C.; McCue, Lee Ann

    2013-10-01

    To link microbial community 16S structure to a measured function in a natural soil we have scaled both DNA and β-glucosidase assays down to a volume of soil that may approach a unique microbial community. β-glucosidase activity was assayed in 450 individual aggregates which were then sorted into classes of high or low activities, from which groups of 10 or 11 aggregates were identified and grouped for DNA extraction and pyrosequencing. Tandem assays of ATP were conducted for each aggregate in order to normalize these small groups of aggregates for biomass size. In spite of there being no significant differences in the richness or diversity of the microbial communities associated with high β-glucosidase activities compared with the communities associated with low β-glucosidase communities, several analyses of variance clearly show that the communities of these two groups differ. The separation of these groups is partially driven by the differential abundances of members of the Chitinophagaceae family. It may be that observed functional differences in otherwise similar soil aggregates can be largely attributed to differences in resource availability, rather than to presence or absence of particular taxonomic groups.

  12. 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

  13. 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

  14. 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.

  15. "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…

  16. Long-term effect of conservation tillage on structural properties and organic carbon in aggregates of a Mediterranean loamy soil

    NASA Astrophysics Data System (ADS)

    Blanco-Moure, Nuria; López, M. Victoria; Angurel, Luis A.; Ángeles Limón, M.; Gracia, Ricardo

    2010-05-01

    The architectural arrangement of the soil matrix determines the functions required for plant growth and the sustainability of the ecosystem. In agricultural lands inadequate tillage management leads to a decline in soil structure and, consequently, soil degradation, but little is known about the impact of the tillage practices on the individual aggregate properties. The understanding of mechanical properties of aggregates is crucial to explain the macroscale functions of the soil system because the properties of aggregates may differ from those of the whole soil due the dynamics of aggregate formation. In semiarid Aragon (NE Spain), particular soil and climate characteristics make this region prone to land degradation by wind and water erosion. Conservation tillage has been proposed as a management alternative to preserve soil and water resources in this area. The objective of this work was the evaluation of the long-term effect of conservation tillage after (20 years) on structural properties of soil aggregates and the role that SOC plays in these properties. Soil surface samples (0-5 cm) were taken from four adjacent fields. Three of them were cultivated sites under different tillage systems: conventional tillage (CT, mouldboard ploughing), reduced tillage (RT, chisel ploughing) and no-till (NT).The fourth was a nearby uncultivated land (NAT). The soil samples were dry sieved in order to obtain aggregates of four different sizes (16-8, 8-4, 4-2 and 2-1 mm). Tensile strength (TS) and organic carbon (OC) content of soil aggregates were determined for all sizes while water aggregate stability (WAS) was assessed only in 2-1 mm class. The TS was significantly lower in soil aggregates from NAT and NT fields than those from CT and RT for all aggregate sizes. The highest TS values corresponded to the smallest aggregate size, indicating an important effect of the aggregate size in this property. In fact, aggregate size and organic carbon explained a 90% of the TS

  17. 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

  18. [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

  19. 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)

  20. 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.

  1. Modeling the Microwave Single-scattering Properties of Aggregate Snowflakes

    NASA Astrophysics Data System (ADS)

    Nowell, H.; Honeyager, R. E.; Liu, G.

    2014-12-01

    A new snowflake aggregation model is developed to study single-scattering properties of aggregate snowflakes. Snowflakes are generated by random aggregation of 6-bullet rosette crystals and constrained by size-density relationships derived from previous field observations. Due to random generation, aggregates may have the same size or mass, yet differing morphology allowing for a study into how shape influences their scattering properties. Furthermore, three different aggregate shapes are created: randomly generated, oblate and prolate flakes. The single-scattering properties of the aggregates are investigated using the discrete dipole approximation (DDA) at 10 frequencies. Results are compared to those of Mie theory for solid and soft spheres (density 10% that of solid ice) and to T-matrix results for solid and soft spheroidal cases with aspect ratios of 0.8 (randomly generated) and 0.6 (oblate and prolate). Above size parameter 0.75, neither the solid nor the soft sphere and spheroidal approximations accurately represent the DDA results for the randomly generated or oblate aggregates. Asymmetry and the normalized scattering and backscattering cross-sections of the randomly generated and oblate aggregates fall between the soft and solid spherical and spheroidal approximations. This implies that evaluating snow scattering properties using realistic shapes, such as the aggregates created in this study instead of a simplified crystal shape, is of paramount importance. The dependence of the single-scattering properties on each aggregate's detailed structure seems of secondary importance. Oblate and prolate preliminary results indicate that backscattering for prolate and oblate flakes is lower than that of the randomly generated flakes. Detailed analyses are conducted to answer: (a) why aggregates of similar size yet dissimilar shape backscatter differently and (b) why prolate and oblate aggregates backscatter differently than randomly generated aggregates.

  2. Phosphorus recovery from wastewater by struvite crystallization: property of aggregates.

    PubMed

    Ye, Zhilong; Shen, Yin; Ye, Xin; Zhang, Zhaoji; Chen, Shaohua; Shi, Jianwen

    2014-05-01

    Struvite crystallization is a promising method to remove and recover phosphorus from wastewater to ease both the scarcity of phosphorus rock resources and water eutrophication worldwide. To date, although various kinds of reactor systems have been developed, supporting methods are required to control the struvite fines flushing out of the reactors. As an intrinsic property, aggregation is normally disregarded in the struvite crystallization process, although it is the key factor in final particle size and therefore guarantees phosphorus recovery efficiency. The present study developed a method to analyze the characteristics of struvite aggregates using fractal geometry, and the influence of operational parameters on struvite aggregation was evaluated. Due to its typical orthorhombic molecular structure, struvite particles are prone to crystallize into needle or rod shapes, and aggregate at the corners or edges of crystals. The determined fractal dimension (Dpf) of struvite aggregates was 1.52-1.31, with the corresponding range of equivalent diameter (d0.5) at 295.9-85.4 μm. Aggregates formed in relatively low phosphorus concentrations (3.0-5.0 mmol/L) and mildly alkaline conditions (pH 9.0-9.5) displayed relatively compact structures, large aggregate sizes and high aggregation strength. Increasing pH values led to continuous decrease of aggregate sizes, while the variation of Dpf was insignificant. As to the aggregate evolution, fast growth in a short time followed by a long steady stage was observed. PMID:25079629

  3. Particle aggregation mechanisms in ionic liquids.

    PubMed

    Szilagyi, Istvan; Szabo, Tamas; Desert, Anthony; Trefalt, Gregor; Oncsik, Tamas; Borkovec, Michal

    2014-05-28

    Aggregation of sub-micron and nano-sized polystyrene latex particles was studied in room temperature ionic liquids (ILs) and in their water mixtures by time-resolved light scattering. The aggregation rates were found to vary with the IL-to-water molar ratio in a systematic way. At the water side, the aggregation rate is initially small, but increases rapidly with increasing IL content, and reaches a plateau value. This behaviour resembles simple salts, and can be rationalized by the competition of double-layer and van der Waals forces as surmised by the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). At the IL side, aggregation slows down again. Two generic mechanisms could be identified to be responsible for the stabilization in ILs, namely viscous stabilization and solvation stabilization. Viscous stabilization is important in highly viscous ILs, as it originates from the slowdown of the diffusion controlled aggregation due to the hindrance of the diffusion in a viscous liquid. The solvation stabilization mechanism is system specific, but can lead to a dramatic slowdown of the aggregation rate in ILs. This mechanism is related to repulsive solvation forces that are operational in ILs due to the layering of the ILs close to the surfaces. These two stabilization mechanisms are suspected to be generic, as they both occur in different ILs, and for particles differing in surface functionalities and size. PMID:24727976

  4. Aggregation of commercial heparin samples in storage.

    PubMed

    Racey, T J; Rochon, P; Awang, D V; Neville, G A

    1987-04-01

    The size distribution of heparin aggregates in commercial heparin preparations was examined with the technique of quasi-elastic light scattering. The size distributions were initially examined to determine if any relationship existed between the physical state of the heparin preparation, its age, and its biological activity. It was found that commercial heparin samples change their aggregation state in storage. The amount of aggregation appears to be related to the amount of time in storage and to the storage history. Storage of the samples under conditions of refrigeration and handling represents the storage history that most noticeably increases the aggregation state of the heparin preparations. These aggregates, once formed, appear to be stable. The biological activity of the heparin samples (as measured by the official test) was found to still fall within the accepted limits, independent of the aggregation state of the samples. It is not known what effect, if any, a change in the physical state of the commercial preparation should have on its biological activity. PMID:3598891

  5. 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.

  6. 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.

  7. 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...

  8. 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

  9. Charged Dust Aggregate Interactions

    NASA Astrophysics Data System (ADS)

    Matthews, Lorin; Hyde, Truell

    2015-11-01

    A proper understanding of the behavior of dust particle aggregates immersed in a complex plasma first requires a knowledge of the basic properties of the system. Among the most important of these are the net electrostatic charge and higher multipole moments on the dust aggregate as well as the manner in which the aggregate interacts with the local electrostatic fields. The formation of elongated, fractal-like aggregates levitating in the sheath electric field of a weakly ionized RF generated plasma discharge has recently been observed experimentally. The resulting data has shown that as aggregates approach one another, they can both accelerate and rotate. At equilibrium, aggregates are observed to levitate with regular spacing, rotating about their long axis aligned parallel to the sheath electric field. Since gas drag tends to slow any such rotation, energy must be constantly fed into the system in order to sustain it. A numerical model designed to analyze this motion provides both the electrostatic charge and higher multipole moments of the aggregate while including the forces due to thermophoresis, neutral gas drag, and the ion wakefield. This model will be used to investigate the ambient conditions leading to the observed interactions. This research is funded by NSF Grant 1414523.

  10. Restructuring of Dust Aggregates in the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Dominik, C.; Tielens, A. G. G. M.

    1996-01-01

    We discuss the results of a recent effort to analyze the mechanical stability of dust aggregates with a detailed model of the physical properties of a contact between grains. This model contains both elastic repulsion forces and attractive van der Waals/dipole/metallic forces along with a description of the energy dissipation due to rolling, sliding, and breaking of contacts. We find that (1) aggregates formed from single sized grains via Particle-Cluster-Aggregation remain fluffy, (2) collisions with other aggregates and with large grains may lead to compaction (3) the velocities of small grains and aggregates in the early solar nebula are too small to produce marked compaction as long as the aggregates are small, and (4) internal restructuring of aggregates is a potentially large sink of energy which could enable the sticking of large bodies even at collision velocities of the order of several hundred cm/s.

  11. 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.

  12. 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. PMID:10379027

  13. 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

  14. 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.

  15. Aggregates: Waste and recycled materials; new rapid evaluation technology. Soils, geology, and foundations; materials and construction. Transportation research record

    SciTech Connect

    Not Available

    1994-01-01

    ;Contents: Engineering Properties of Shredded Tires in Lightweight Fill Applications; Using Recovered Glass as Construction Aggregate Feedstock; Utilization of Phosphogypsum-Based Slag Aggregate in Portland Cement Concrete Mixtures; Waste Foundry Sand in Asphalt Concrete; Toward Automating Size-Gradation Analysis of Mineral Aggregate; Evaluation of Fine Aggregate Angularity Using National Aggregate Association Flow Test; Siliceous Content Determination of Sands Using Automatic Image Analysis; and Methodology for Improvement of Oxide Residue Models for Estimation of Aggregate Performance Using Stoichiometric Analysis.

  16. 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.

  17. 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.

  18. 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…

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. Wheat roots and residue effects on soil aggregation and carbon

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Crop residues have been identified for a number of off-field uses. Poor understanding of the role of crop residues in key soil processes limits our ability to predict sustainable crop residue removal rates. A study was conducted to compare aggregate size distribution, aggregate stability, and soil ...

  5. A population balance equation model of aggregation dynamics in Taxus suspension cell cultures

    PubMed Central

    Kolewe, Martin E.; Roberts, Susan C.; Henson, Michael A.

    2011-01-01

    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 data sets 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. PMID:21910121

  6. 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. PMID:21910121

  7. 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

  8. Aggregation and species coexistence of ectoparasites of marine fishes.

    PubMed

    Morand, S; Poulin, R; Rohde, K; Hayward, C

    1999-05-01

    Interspecific interaction may lead to species exclusion but there are several ways in which species can coexist. One way is by reducing the overall intensity of competition via aggregated utilisation of fragmented resources. Known as the 'aggregation model of coexistence', this system assumes saturation and an equilibrium number of species per community. In this study we tested the effects of interspecific aggregation on the level of intraspecific aggregation among ectoparasites of marine fishes (36 communities of gill and head ectoparasite species). If parasite species are distributed in a way that interspecific aggregation is reduced relative to intraspecific aggregation then species coexistence is facilitated. We found a positive relationship between parasite species richness and fish body size, controlling for host phylogeny. A positive relationship between infracommunity species richness and total parasite species richness was also found, providing no evidence for saturation. This result supports the view that infracommunities of parasites are not saturated by local parasite residents. The observed lack of saturation implies that we are far from a full exploitation of the fish resource by parasites. Ectoparasites were aggregated at both population and species levels. However, only half of the ectoparasite communities were dominated by negative interspecific aggregation. We found that infracommunity parasite species richness was positively correlated with the level of intraspecific aggregation versus interspecific aggregation. This means that intraspecific aggregation increases compared with interspecific aggregation when total parasite species richness increases, controlling fish size and phylogeny. This supports one assumption of the 'aggregation model of coexistence', which predicts that interspecific interactions are reduced relative to intraspecific interactions, facilitating species coexistence. PMID:10404260

  9. Photoacoustic assessment of oxygen saturation: effect of red blood cell aggregation

    NASA Astrophysics Data System (ADS)

    Hysi, Eno; Saha, Ratan K.; Kolios, Michael C.

    2013-03-01

    The simultaneous photoacoustic assessment of oxygen saturation and red blood cell aggregation is presented. Aggregation was induced on porcine red blood cells using Dextran-70 at multiple hematocrit levels. Samples were exposed to 750 nm and 1064 nm for each hematocrit and aggregate size in order to compute the oxygen saturation. As the size of the aggregate increased, the photoacoustic signal amplitude increased monotonically. The same trend was observed for increasing hematocrit at each aggregation level. The oxygen saturation of aggregated samples was 30% higher than non-aggregated samples at each hematocrit level. This suggests that the presence of red blood cell aggregates impairs the release of oxygen to the surrounding environment. Such a result has important implications for detecting red blood cell aggregation non-invasively and making clinical decisions based on the simulatenous assessment of oxygen saturation.

  10. 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,…

  11. 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…

  12. Cluster Growth Mechanism in Sputtering Gas-Aggregation Nanocluster Source

    NASA Astrophysics Data System (ADS)

    Tarsem Singh, M.; Han, H.; Sundararajan, J. A.; Qiang, Y.

    2010-03-01

    We have studied the influence of some parameters for cluster growth of core shell iron- iron oxide magnetic nanoparticles (MNPs). The nanocluster source which combines a magnetron sputtering gun with a gas aggregation chamber is used to produce MNPs. Nanoclusters of various mean sizes ranging from 1-100 nm can be synthesized by varying the aggregation distance, Ar to He gas ratio, pressure in the aggregation tube, sputter power, and temperature of the aggregation tube. Physical properties -- magnetic measurements by VSM and SQUID and size distribution by SEM and TEM were studied for different MNPs. The significance of this research is to understand the growth mechanism and physical properties as the size of particles grow from few nanometer to hundred of nanometer. Growth of the particles is theoretically explained by the homogenous and heterogeneous growth process. Based on this study, different size of MNPs fits into different category of applications from data storage to biomedical field.

  13. Asphaltene aggregation and impact of alkylphenols.

    PubMed

    Goual, Lamia; Sedghi, Mohammad; Wang, Xiaoxiao; Zhu, Ziming

    2014-05-20

    The main objective of this study was to provide novel insights into the mechanism of asphaltene aggregation in toluene/heptane (Heptol) solutions and the effect of alkylphenols on asphaltene dispersion through the integration of advanced experimental and modeling methods. High-resolution transmission electron microscope (HRTEM) images revealed that the onset of asphaltene flocculation occurs near a toluene/heptane volume ratio of 70:30 and that flocculates are well below 1 μm in size. To assess the impact of alkylphenols on asphaltene aggregation, octylphenol (OP) and dodecylphenol (DP) were evaluated by impedance analysis based on their ability to delay the precipitation onset and to reduce the size of nonflocculated asphaltene aggregates in 80:20 toluene/heptane solutions. Although a longer dispersant chain length did not affect the precipitation onset, it reduced the size of the aggregates. Molecular dynamics simulations were then performed to understand the mechanism of interaction between a model asphaltene and OP in heptane. OP molecules saturated the H-bonding sites of asphaltenes and prevented them from interacting laterally between themselves. This explained why OP favored the formation of flocculates with filamentary rather than globular structures, which were clearly observed by HRTEM. Although OP proved to be an effective dispersant, its effectiveness was hindered by its self-association and the fact that it interacted at the periphery of asphaltenes, leaving their aromatic cores uncovered. PMID:24784502

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. H- and J-aggregate behavior in polymeric semiconductors.

    PubMed

    Spano, Frank C; Silva, Carlos

    2014-01-01

    Aggregates of conjugated polymers exhibit two classes of fundamental electronic interactions: those occurring within a given chain and those occurring between chains. The impact of such excitonic interactions on the photophysics of polymer films can be understood using concepts of J- and H-aggregation originally developed by Kasha and coworkers to treat aggregates of small molecules. In polymer assemblies, intrachain through-bond interactions lead to J-aggregate behavior, whereas interchain Coulombic interactions lead to H-aggregate behavior. The photophysics of common emissive conjugated polymer films are determined by a competition between intrachain, J-favoring interactions and interchain, H-favoring interactions. We review formalisms describing absorption and photoluminescence lineshapes, based on intra- and intermolecular excitonic coupling, electron-vibrational coupling, and correlated energetic disorder. Examples include regioregular polythiophenes, pheneylene-vinylenes, and polydiacetylene. PMID:24423378

  1. Digital image processing of nanometer-size metal particles on amorphous substrates

    NASA Astrophysics Data System (ADS)

    Soria, F.; Artal, P.; Bescos, J.; Heinemann, K.

    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.

  2. 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.

  3. 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.

  4. Seasonal variability of cohesive sediment aggregation in the Bach Dang-Cam Estuary, Haiphong (Vietnam)

    NASA Astrophysics Data System (ADS)

    Lefebvre, Jean-Pierre; Ouillon, Sylvain; Vinh, Vu Duy; Arfi, Robert; Panché, Jean-Yves; Mari, Xavier; Van Thuoc, Chu; Torréton, Jean-Pascal

    2012-04-01

    In the Bach Dang-Cam Estuary, northern Vietnam, mechanisms governing cohesive sediment aggregation were investigated in situ in 2008-2009. As part of the Red River delta, this estuary exhibits a marked contrast in hydrological conditions between the monsoon and dry seasons. The impact on flocculation processes was assessed by means of surveys of water discharge, suspended particulate matter concentration and floc size distributions (FSDs) conducted during a tidal cycle at three selected sites along the estuary. A method was developed for calculating the relative volume concentration for the modes of various size classes from FSDs provided by the LISST 100X (Sequoia Scientific Inc.). It was found that all FSDs comprised four modes identified as particles/flocculi, fine and coarse microflocs, and macroflocs. Under the influence of the instantaneous turbulent kinetic energy, their proportions varied but without significant modification of their median diameters. In particular, when the turbulence level corresponded to a Kolmogorov microscale of less than ˜235 μm, a major breakup of flocs resulted in the formation of particles/flocculi and fine microflocs. Fluctuations in turbulence level were governed by seasonal variations in freshwater discharge and by the tidal cycle. During the wet season, strong freshwater input induced a high turbulent energy level that tended to generate sediment transfer from the coarser size classes (macroflocs, coarse microflocs) to finer ones (particles/flocculi and fine microflocs), and to promote a transport of sediment seawards. During the dry season, the influence of tides predominated. The turbulent energy level was then only episodically sufficiently high to generate transfer of sediment between floc size classes. At low turbulent energy, modifications in the proportions of floc size classes were due to differential settling. Tidal pumping produced a net upstream transport of sediment. Associated with the settling of sediment

  5. 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

  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. Aggregation kinetics and structure of cryoimmunoglobulins clusters

    NASA Astrophysics Data System (ADS)

    Spirito, M. De; Chiappini, R.; Bassi, F. Andreasi; Stasio, E. Di; Giardina, B.; Arcovito, G.

    2002-02-01

    Cryoimmunoglobulins are pathological antibodies characterized by a temperature-dependent reversible insolubility. Rheumatoid factors (RF) are immunoglobulins possessing anti-immunoglobulin activity and usually consist of an IgM antibody that recognizes IgG as antigen. These proteins are present in sera of patients affected by a large variety of different pathologies, such as HCV infection, neoplastic and autoimmune diseases. Aggregation and precipitation of cryoimmunoglobulins, leading to vasculiti, are physical phenomena behind such pathologies. A deep knowledge of the physico-chemical mechanisms regulating such phenomena plays a fundamental role in biological and clinical applications. In this work, a preliminary investigation of the aggregation kinetics and of the final macromolecular structure of the aggregates is presented. Through static light scattering techniques, the gyration radius Rg and the fractal dimension Dm of the growing clusters have been determined. However, while the initial aggregation mechanism could be described using the universal reaction-limited cluster-cluster aggregation (RLCCA) theory, at longest times from the beginning of the process, the RLCCA theory fails and a restructuring of clusters is observed together with an increase of the cluster fractal dimension Dm up to a value Dm∼3. The time tn, at which the restructuring takes place, and the final cluster size can be modulated by varying the quenching temperature.

  8. Mechanisms and Rates of Bacterial Colonization of Sinking Aggregates

    PubMed Central

    Kiørboe, Thomas; Grossart, Hans-Peter; Ploug, Helle; Tang, Kam

    2002-01-01

    Quantifying the rate at which bacteria colonize aggregates is a key to understanding microbial turnover of aggregates. We used encounter models based on random walk and advection-diffusion considerations to predict colonization rates from the bacteria's motility patterns (swimming speed, tumbling frequency, and turn angles) and the hydrodynamic environment (stationary versus sinking aggregates). We then experimentally tested the models with 10 strains of bacteria isolated from marine particles: two strains were nonmotile; the rest were swimming at 20 to 60 μm s−1 with different tumbling frequency (0 to 2 s−1). The rates at which these bacteria colonized artificial aggregates (stationary and sinking) largely agreed with model predictions. We report several findings. (i) Motile bacteria rapidly colonize aggregates, whereas nonmotile bacteria do not. (ii) Flow enhances colonization rates. (iii) Tumbling strains colonize aggregates enriched with organic substrates faster than unenriched aggregates, while a nontumbling strain did not. (iv) Once on the aggregates, the bacteria may detach and typical residence time is about 3 h. Thus, there is a rapid exchange between attached and free bacteria. (v) With the motility patterns observed, freely swimming bacteria will encounter an aggregate in <1 day at typical upper-ocean aggregate concentrations. This is faster than even starving bacteria burn up their reserves, and bacteria may therefore rely solely on aggregates for food. (vi) The net result of colonization and detachment leads to a predicted equilibrium abundance of attached bacteria as a function of aggregate size, which is markedly different from field observations. This discrepancy suggests that inter- and intraspecific interactions among bacteria and between bacteria and their predators may be more important than colonization in governing the population dynamics of bacteria on natural aggregates. PMID:12147501

  9. From static micrographs to particle aggregation dynamics in three dimensions.

    PubMed

    Häbel, H; Särkkä, A; Rudemo, M; Hamngren Blomqvist, C; Olsson, E; Abrahamsson, C; Nordin, M

    2016-04-01

    Studies on colloidal aggregation have brought forth theories on stability of colloidal gels and models for aggregation dynamics. Still, a complete link between developed frameworks and obtained laboratory observations has to be found. In this work, aggregates of silica nanoparticles (20 nm) are studied using diffusion limited cluster aggregation (DLCA) and reaction limited cluster aggregation (RLCA) models. These processes are driven by the probability of particles to aggregate upon collision. This probability of aggregation is one in the DLCA and close to zero in the RLCA process. We show how to study the probability of aggregation from static micrographs on the example of a silica nanoparticle gel at 9 wt%. The analysis includes common summary functions from spatial statistics, namely the empty space function and Ripley's K-function, as well as two newly developed summary functions for cluster analysis based on graph theory. One of the new cluster analysis functions is related to the clustering coefficient in communication networks and the other to the size of a cluster. All four topological summary statistics are used to quantitatively compare in plots and in a least-square approach experimental data to cluster aggregation simulations with decreasing probabilities of aggregation. We study scanning transmission electron micrographs and utilize the intensity - mass thickness relation present in such images to create comparable micrographs from three-dimensional simulations. Finally, a characterization of colloidal silica aggregates and simulated structures is obtained, which allows for an evaluation of the cluster aggregation process for different aggregation scenarios. As a result, we find that the RLCA process fits the experimental data better than the DLCA process. PMID:26584453

  10. In Situ Observation of Hematite Nanoparticle Aggregates Using Liquid Cell Transmission Electron Microscopy.

    PubMed

    Liu, Juan; Wang, Zhiwei; Sheng, Anxu; Liu, Feng; Qin, Fuyu; Wang, Zhong Lin

    2016-06-01

    Aggregation of nanoparticles impacts their reactivity, stability, transport, and fate in aqueous environments, but limited methods are available to characterize structural features and movement of aggregates in liquid. Here, liquid cell transmission electron microscopy (LCTEM) was utilized to directly observe the size, morphology, and motion of aggregates that were composed of 9 and 36 nm hematite nanoparticles, respectively, in water or NaCl solution. When mass concentrations were same, the aggregates of 9 nm nanoparticles were statistically more compact and slightly larger than those of 36 nm nanoparticles. Aggregates in both samples were typically nonspherical. Increasing ionic strength resulted in larger aggregates, and also enhanced the stability of aggregates under electron-beam irradiation. In water, small aggregates moved randomly and approached repeatedly to large aggregates before final attachment. In NaCl solution, small aggregates moved directly toward large aggregates and attached to the latter quickly. This observation provided a direct confirmation of the DLVO theory that the energy barrier to aggregation is higher in water than in salt solutions. This study not only presented the influences of particle size and ionic strength on aggregation state, but also demonstrated that LCTEM is a promising method to link aggregation state to dynamic processes of nanoparticles. PMID:27127831

  11. Fecal Coliform Interaction with Soil Aggregates: Effect of Water Content and Bovine Manure Application

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aims: To test the hypothesis that fecal coliform (FC) interaction with soil aggregates is affected by aggregate size, water content and bovine manure application. Methods and Results: Tyler loam soil aggregates were separated into fractions of 3.35-4.75 mm, 4.75-7.93 mm and 7.93-9.5 mm. Air-dry an...

  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. 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…

  14. Regulation and aggregation of intrinsically disordered peptides

    PubMed Central

    Levine, Zachary A.; Larini, Luca; LaPointe, Nichole E.; Feinstein, Stuart C.; Shea, Joan-Emma

    2015-01-01

    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. PMID:25691742

  15. 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. PMID:25691742

  16. Optical properties of light absorbing carbon aggregates mixed with sulfate: assessment of different model geometries for climate forcing calculations.

    PubMed

    Kahnert, Michael; Nousiainen, Timo; Lindqvist, Hannakaisa; Ebert, Martin

    2012-04-23

    Light scattering by light absorbing carbon (LAC) aggregates encapsulated into sulfate shells is computed by use of the discrete dipole method. Computations are performed for a UV, visible, and IR wavelength, different particle sizes, and volume fractions. Reference computations are compared to three classes of simplified model particles that have been proposed for climate modeling purposes. Neither model matches the reference results sufficiently well. Remarkably, more realistic core-shell geometries fall behind homogeneous mixture models. An extended model based on a core-shell-shell geometry is proposed and tested. Good agreement is found for total optical cross sections and the asymmetry parameter. PMID:22535095

  17. 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

  18. 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

  19. 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

  20. 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

  1. 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.

  2. Cu nanoclusters with aggregation induced emission enhancement.

    PubMed

    Jia, Xiaofang; Li, Jing; Wang, Erkang

    2013-11-25

    A facile and versatile method for preparing water-soluble, stable, luminescent Cu nanoclusters (NCs) via the process of size-focusing etching from nonluminescent nanocrystals is presented. Using glutathione as a model ligand, the smallest cluster, Cu2 , is selectively synthesized to form a nearly monodisperse product, eliminating the need for tedious size fractionation. Evolution of photoluminescence and absorption spectra reveal that the formation of stable cluster species occurs through surface etching. Intriguingly, the as-prepared CuNCs exhibit an aggregation-induced emission enhancement effect. The CuNCs emit a faint light when dispersed in aqueous solution, but generate a striking fluorescence intensity enhancement upon aggregation. Armed with these attractive properties, the emissive CuNCs are expected to open new opportunities for the construction of light-emitting diodes, chemosensors, and bioimaging systems. PMID:23670847

  3. Orbital Aggregation and Space Infrastructure Systems (OASIS)

    NASA Technical Reports Server (NTRS)

    Troutman, Patrick A.; Mazanek, Daniel D.; Stillwagen, Frederic H.; Antol, Jeffrey; Sarver-Verhey, Timothy R.; Chato, David J.; Saucillo, Rudolf J.; Blue, Douglas R.; Carey, David; Krizan, Shawn A.

    2002-01-01

    This paper summarizes the results of a NASA lead study performed to identify synergistic opportunities and concepts between human exploration initiatives and commercialization of space. The goal of this initiative, called Orbital Aggregation & Space Infrastructure Systems (OASIS), is to develop an in-space architecture and associated concepts that provide common infrastructure for enabling a large class of space missions. The concepts include communications, navigation and power systems, propellant modules, tank farms, habitats, and in-space transportation systems using several propulsion technologies. OASIS features in-space aggregation of systems and resources in support of mission objectives. The concepts feature a high level of reusability and are supported by inexpensive launch of propellant and logistics payloads from the Earth/moon system. Industry, NASA and other users could share infrastructure costs. The anticipated benefits of synergistic utilization of space infrastructure are reduced mission costs and increased mission flexibility for future space exploration and commercialization initiatives.

  4. Are Teacher Effects Larger in Small Classes?

    ERIC Educational Resources Information Center

    Konstantopoulos, Spyros; Sun, Min

    2014-01-01

    Teachers spend most of their time in school in classrooms, and their instruction and teaching practices may be affected by classroom context such as class size. We examine whether teacher effects interact with classroom context such as class size. Specifically, we seek to determine whether teacher effects are more pronounced in small classes than…

  5. 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

  6. 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.

  7. 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.

  8. Surface properties of heat-induced soluble soy protein aggregates of different molecular masses.

    PubMed

    Guo, Fengxian; Xiong, Youling L; Qin, Fang; Jian, Huajun; Huang, Xiaolin; Chen, Jie

    2015-02-01

    Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large-size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium-size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications. PMID:25586667

  9. Preliminary morphometrics of spleen and kidney macrophage aggregates in clinically normal blue gourami Trichogaster trichopterus and freshwater angelfish Pterophyllum scalare.

    PubMed

    Russo, Riccardo; Yanong, Roy P E; Terrell, Scorr P

    2007-03-01

    Macrophage aggregate (MA) morphometry and pigment composition are believed to be dependent on the species, age, and health status of the fish. The aim of this study was to characterize a "normal" morphometry baseline of spleen and kidney MAs in blue gourami Trichogaster trichopterus and freshwater angelfish Pterophyllum scalare. Three size-classes of clinically normal fish were analyzed. Blue gourami and freshwater angelfish were obtained from three local ornamental fish farms; for each size-class, 10 fish from each farm were analyzed. Hematoxylin- and eosin-stained tissue sections were analyzed by light microscopy at 100x magnification and an image analysis program. The percentage of tissue occupied by MAs, MA size, and MA number were calculated on three arbitrarily selected fields of view from each spleen and kidney. In clinically normal blue gourami, increases in the percentage of tissue occupied by MAs and in MA size were associated with an increase in fish size, but in clinically normal angelfish no correlation was observed. Furthermore, in angelfish, a high variability in MA morphometry was observed, even among fish from the same sample group. In both species, a significant difference in the value of the morphometric parameters was observed among farms. Because iridoviruses inhibit macrophage activity and (possibly) proliferation, MAs in 25 clinical cases of iridovirus-infected blue gourami were analyzed. Preliminary data indicate that in iridovirus-infected blue gourami, there is a decrease in MA size and MA number compared with those of healthy fish. PMID:18236633

  10. Making Graphene Resist Aggregation

    NASA Astrophysics Data System (ADS)

    Luo, Jiayan

    Graphene-based sheets have stimulated great interest in many scientific disciplines and shown promise for wide potential applications. Among various ways of creating single atomic layer carbon sheets, a promising route for bulk production is to first chemically exfoliate graphite powders to graphene oxide (GO) sheets, followed by reduction to form chemically modified graphene (CMG). Due to the strong van der Waals attraction between graphene sheets, CMG tends to aggregate. The restacking of sheets is largely uncontrollable and irreversible, thus it reduces their processability and compromises properties such as accessible surface area. Strategies based on colloidal chemistry have been applied to keep CMG dispersed in solvents by introducing electrostatic repulsion to overcome the van der Waals attraction or adding spacers to increase the inter-sheet spacing. In this dissertation, two very different ideas that can prevent CMG aggregation without extensively modifying the material or introducing foreign spacer materials are introduced. The van der Waals potential decreases with reduced overlapping area between sheets. For CMG, reducing the lateral dimension from micrometer to nanometer scale should greatly enhance their colloidal stability with additional advantages of increased charge density and decreased probability to interact. The enhanced colloidal stability of GO and CMG nanocolloids makes them especially promising for spectroscopy based bio-sensing applications. For potential applications in a compact bulk solid form, the sheets were converted into paper-ball like structure using capillary compression in evaporating aerosol droplets. The crumpled graphene balls are stabilized by locally folded pi-pi stacked ridges, and do not unfold or collapse during common processing steps. They can tightly pack without greatly reducing the surface area. This form of graphene leads to scalable performance in energy storage. For example, planer sheets tend to aggregate and

  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. 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.

  13. 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

  14. 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.

  15. 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…

  16. Experimental investigation and population balance equation modeling of solid lipid nanoparticle aggregation dynamics.

    PubMed

    Yang, Yihui; Corona, Alessandro; Henson, Michael A

    2012-05-15

    Solid lipid nanoparticles (SLNs) have applications in drug delivery and the encapsulation of bioactive, lipophilic compounds. However, SLNs tend to aggregate when stored due to the lipid crystals undergoing a polymorphic transformation from the unstable α form to the stable β form. We developed a population balance equation (PBE) model for prediction of average polymorph content and aggregate size distribution to better understand this undesirable behavior. Experiments with SLNs stored at room temperature showed that polymorphic transformation was the rate determining step for our system, SLNs with smaller initial size distributions aggregated more rapidly, and aggregates contained particles with both α and β crystals. Using parameter values estimated from our data, the PBE model was able to capture the bimodal nature of aggregate size distributions, the α-to-β polymorph ratio, and the faster aggregation dynamics of SLNs with smaller initial size distributions. However, the model was unable to adequately capture the fast disappearance rate of primary particles, the broad size distributions of formed aggregates, and the significant α content of aggregating particles. These discrepancies suggest that a PBE model which accounts for polymorph content as an internal variable along with aggregate size may be required to better reproduce experimental observations. PMID:22405582

  17. 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

  18. On the use of photoacoustics to detect red blood cell aggregation

    PubMed Central

    Hysi, Eno; Saha, Ratan K.; Kolios, Michael C.

    2012-01-01

    The feasibility of detecting red blood cell (RBC) aggregation with photoacoustics (PAs) was investigated theoretically and experimentally using human and porcine RBCs. The theoretical PA signals and spectra generated from such samples were examined for several hematocrit levels and aggregates sizes. The effect of a finite transducer bandwidth on the received PA signal was also examined. The simulation results suggest that the dominant frequency of the PA signals from non-aggregated RBCs decreases towards clinical frequency ranges as the aggregate size increases. The experimentally measured mean spectral power increased by ~6 dB for the largest aggregate compared to the non-aggregated samples. Such results confirm the theoretical predictions and illustrate the potential of using PA imaging for detecting RBC aggregation. PMID:23024924

  19. Interplay between the hydrophobic effect and dipole interactions in peptide aggregation at interfaces.

    PubMed

    Ganesan, Sai J; Matysiak, Silvina

    2016-01-28

    Protein misfolding is an intrinsic property of polypeptides, and misfolded conformations have a propensity to aggregate. In the past decade, the development of various coarse-grained models for proteins has provided key insights into the driving forces in folding and aggregation. We recently developed a low resolution Water Explicit Polarizable PROtein coarse-grained Model (WEPPROM) by adding oppositely charged dummy particles inside protein backbone beads. With this model, we were able to achieve significant α/β secondary structure content, without any added bias. We now extend the model to study peptide aggregation at hydrophobic-hydrophilic interfaces and draw comparisons to aggregation in explicit water solvent. Elastin-like octapeptides (GV)4 are used as a model system for this study. A condensation-ordering mechanism of aggregation is observed in water. Our results suggest that backbone interpeptide dipolar interactions, not hydrophobicity, plays a more significant role in fibril-like peptide aggregation. We observe a cooperative effect in hydrogen bonding or dipolar interactions, with an increase in aggregate size in water and at interfaces. Based on this cooperative effect, we provide a potential explanation for the observed nucleus size in peptide aggregation pathways. The presence of a hydrophobic-hydrophilic interface increases both (a) order of aggregates formed, and (b) rate of the aggregation process. Without dipolar particles, peptide aggregation is not observed at the hydrophilic-hydrophobic interface. Thus, the presence of dipoles, not hydrophobicity, plays a key role in aggregation observed at hydrophobic interfaces. PMID:26698374

  20. 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.