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Sample records for aggregate concentration cac

  1. Stoichiometry and Physical Chemistry of Promiscuous Aggregate-Based Inhibitors

    PubMed Central

    Coan, Kristin E. D.

    2009-01-01

    Many false positives in early drug discovery owe to nonspecific inhibition by colloid-like aggregates of organic molecules. Despite their prevalence, little is known about aggregate concentration, structure, or dynamic equilibrium; the binding mechanism, stoichiometry with, and affinity for enzymes remain uncertain. To investigate the elementary question of concentration, we counted aggregate particles using flow cytometry. For seven aggregate-forming molecules, aggregates were not observed until the concentration of monomer crossed a threshold, indicating a “critical aggregation concentration” (CAC). Above the CAC, aggregate count increased linearly with added organic material, while the particles dispersed when diluted below the CAC. The concentration of monomeric organic molecule is constant above the CAC, as is the size of the aggregate particles. For two compounds that form large aggregates, nicardipine and miconazole, we measured particle numbers directly by flow cytometry, determining that the aggregate concentration just above the CAC ranged from 5 to 30 fM. By correlating inhibition of an enzyme with aggregate count for these two drugs, we determined that the stoichiometry of binding is about 10 000 enzyme molecules per aggregate particle. Using measured volumes for nicardipine and miconazole aggregate particles (2.1 × 1011 and 4.7 × 1010 Å3, respectively), computed monomer volumes, and the observation that past the CAC all additional monomer forms aggregate particles, we find that aggregates are densely packed particles. Finally, given their size and enzyme stoichiometry, all sequestered enzyme can be comfortably accommodated on the surface of the aggregate. PMID:18588298

  2. Self-Assembly and Critical Aggregation Concentration Measurements of ABA Triblock Copolymers with Varying B Block Types: Model Development, Prediction, and Validation.

    PubMed

    Aydin, Fikret; Chu, Xiaolei; Uppaladadium, Geetartha; Devore, David; Goyal, Ritu; Murthy, N Sanjeeva; Zhang, Zheng; Kohn, Joachim; Dutt, Meenakshi

    2016-04-21

    The dissipative particle dynamics (DPD) simulation technique is a coarse-grained (CG) molecular dynamics-based approach that can effectively capture the hydrodynamics of complex systems while retaining essential information about the structural properties of the molecular species. An advantageous feature of DPD is that it utilizes soft repulsive interactions between the beads, which are CG representation of groups of atoms or molecules. In this study, we used the DPD simulation technique to study the aggregation characteristics of ABA triblock copolymers in aqueous medium. Pluronic polymers (PEG-PPO-PEG) were modeled as two segments of hydrophilic beads and one segment of hydrophobic beads. Tyrosine-derived PEG5K-b-oligo(desaminotyrosyl tyrosine octyl ester-suberate)-b-PEG5K (PEG5K-oligo(DTO-SA)-PEG5K) block copolymers possess alternate rigid and flexible components along the hydrophobic oligo(DTO-SA) chain, and were modeled as two segments of hydrophilic beads and one segment of hydrophobic, alternate soft and hard beads. The formation, structure, and morphology of the initial aggregation of the polymer molecules in aqueous medium were investigated by following the aggregation dynamics. The dimensions of the aggregates predicted by the computational approach were in good agreement with corresponding results from experiments, for the Pluronic and PEG5K-oligo(DTO-SA)-PEG5K block copolymers. In addition, DPD simulations were utilized to determine the critical aggregation concentration (CAC), which was compared with corresponding results from an experimental approach. For Pluronic polymers F68, F88, F108, and F127, the computational results agreed well with experimental measurements of the CAC measurements. For PEG5K-b-oligo(DTO-SA)-b-PEG5K block polymers, the complexity in polymer structure made it difficult to directly determine their CAC values via the CG scheme. Therefore, we determined CAC values of a series of triblock copolymers with 3-8 DTO-SA units using DPD

  3. 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 %).

  4. Metal concentrations in aggregate interiors, exteriors, whole aggregates, and bulk of Costa Rican soils

    SciTech Connect

    Wilcke, W.; Kretzschmar, S.; Bundt, M.; Zech, W.

    1999-10-01

    In many temperate soils the preferential weathering and leaching of aggregate surfaces and the nonaggregated material between aggregates depletes geogenic metals. It also shifts metals from strongly to more weakly bound metal forms. Deposited metals are sorbed preferentially on aggregate surfaces and between aggregates. The authors examined whether preferential desilication under tropical climate causes an enrichment in the aggregate exteriors in oxidic forms of metals. They also studied where deposited metals are bound in these soils. Aggregates (2--20 mm) were selected manually from the A horizons of eight Oxisols, six Andisols, two Mollisols, and two Inceptisols in Costa Rica. All samples were fractionated into interior and exterior portions and treated with a seven-step sequence to extract Al, Cd, Cu, Fe, Mn, Pb, and Zn. Total concentrations of all metals except Zn were higher in the aggregate exteriors than in the interiors. The average Cd and Pb concentrations in easily extractable fractions were significantly higher in the aggregate exteriors. There were no significant differences in metal partitioning between interiors and exteriors except for Pb, which had higher proportions in extractable forms with NH{sub 2}OH {center{underscore}dot} HCl {gt} NH{sub 4} - acetate, pH 6.0 {gt} EDTA in the exteriors. There were few significant differences in metal concentrations and partitioning between bulk soil and whole aggregates. The results may be explained by (i) preferential desilication of the aggregate exteriors and (ii) preferential sorption of deposited heavy metals mainly in easily extractable forms.

  5. Aggregation of Phosphoinositides at Phisiological Calcium Concentrations

    NASA Astrophysics Data System (ADS)

    Kazadi Badiambile, Adolphe; Forstner, Martin B.

    2012-02-01

    Phosphoinositides play a crucial role in many cellular functions such as calcium signaling, endocytosis, exocytosis and the targeting of proteins to specific membrane sites. To maintain functional specificity, it has been suggested that phosphoinositides are spatially organized in ``pools'' in the cellular plasma membrane. A possible mechanism that could induce and regulate such organization of phosphoinositides is their interaction with Ca2+ ions. Understanding the physicochemical mechanism that can regulate membrane structure is a crucial step in the development of adaptive biomimetic membrane systems. Using Langmuir monolayers, we investigated the effect of bivalent calcium and magnesium cations on the surface pressure-area/lipid isotherm of monolayers of phosphatidylinositol (PI), phosphatidylinositol bisphosphate (PIP2) and dioleoylphosphatidylglycerol (DOPG) and dipalmitoylphosphatidylcholine (DPPC). It is found that the decrease of area per lipid, i.e. the increase in aggregation, is dependent on both the lipid's head group charge, the bivalent cation and temperature. However, electrostatics are not sufficient to account for all experimental observations. Thus additional interactions between ions and phosphoinositides need to be considered.

  6. Aggregation-fragmentation model of robust concentration gradient formation

    NASA Astrophysics Data System (ADS)

    Saunders, Timothy E.

    2015-02-01

    Concentration gradients of signaling molecules are essential for patterning during development and they have been observed in both unicellular and multicellular systems. In subcellular systems, clustering of the signaling molecule has been observed. We develop a theoretical model of cluster-mediated concentration gradient formation based on the Becker-Döring equations of aggregation-fragmentation processes. We show that such a mechanism produces robust concentration gradients on realistic time and spatial scales so long as the process of clustering does not significantly stabilize the signaling molecule. Finally, we demonstrate that such a model is applicable to the pom1p subcellular gradient in fission yeast.

  7. Concentration-controlled formation of myoglobin/gold nanosphere aggregates.

    PubMed

    Sevilla, Paz; Sánchez-Cortés, Santiago; García-Ramos, José V; Feis, Alessandro

    2014-05-15

    Gold nanoparticles are being increasingly proposed as biotechnological tools for medical diagnosis and therapy purposes. Their safety for human beings and the environment is therefore becoming an emerging issue, which calls for basic research on the interactions between nanostructured gold particles and biological materials, including physicochemical studies of model systems. In this Article, we focus on the "reaction products" of a widely known nanoparticle type, citrate-capped 30 nm gold nanospheres, with a model protein, horse myoglobin. Protein adsorption and partial denaturation were accompanied by the formation of nanoparticle aggregates with strongly distinct optical spectroscopy properties and shapes, as observed by transmission electron microscopy. We singled out the concentration of myoglobin as the determinant of these differences, and verified on this basis that surface-enhanced Raman scattering (SERS) spectra can only be obtained by aggregates with strong interparticle optical coupling, which are obtained at low protein concentration. The results can be useful both in improving the spectroscopy of biomolecules and in understanding the formation of the protein corona in biomedical applications.

  8. Pressure-induced structural transformation of CaC2.

    PubMed

    Wang, Lu; Huang, Xiaoli; Li, Da; Huang, Yanping; Bao, Kuo; Li, Fangfei; Wu, Gang; Liu, Bingbing; Cui, Tian

    2016-05-21

    The high pressure structural changes of calcium carbide CaC2 have been investigated with Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques in a diamond anvil cell at room temperature. At ambient conditions, two forms of CaC2 co-exist. Above 4.9 GPa, monoclinic CaC2-ii diminished indicating the structural phase transition from CaC2-ii to CaC2-i. At about 7.0 GPa, both XRD patterns and Raman spectra confirmed that CaC2-i transforms into a metallic Cmcm structure which contains polymeric carbon chains. Along with the phase transition, the isolated C2 dumbbells are polymerized into zigzag chains resulting in a large volume collapse with 22.4%. Above 30.0 GPa, the XRD patterns of CaC2 become featureless and remain featureless upon decompression, suggesting an irreversible amorphization of CaC2.

  9. Pressure-induced structural transformation of CaC2

    NASA Astrophysics Data System (ADS)

    Wang, Lu; Huang, Xiaoli; Li, Da; Huang, Yanping; Bao, Kuo; Li, Fangfei; Wu, Gang; Liu, Bingbing; Cui, Tian

    2016-05-01

    The high pressure structural changes of calcium carbide CaC2 have been investigated with Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques in a diamond anvil cell at room temperature. At ambient conditions, two forms of CaC2 co-exist. Above 4.9 GPa, monoclinic CaC2-ii diminished indicating the structural phase transition from CaC2-ii to CaC2-i. At about 7.0 GPa, both XRD patterns and Raman spectra confirmed that CaC2-i transforms into a metallic Cmcm structure which contains polymeric carbon chains. Along with the phase transition, the isolated C2 dumbbells are polymerized into zigzag chains resulting in a large volume collapse with 22.4%. Above 30.0 GPa, the XRD patterns of CaC2 become featureless and remain featureless upon decompression, suggesting an irreversible amorphization of CaC2.

  10. CAC - NUCLEAR THERMAL ROCKET CORE ANALYSIS CODE

    NASA Technical Reports Server (NTRS)

    Clark, J. S.

    1994-01-01

    One of the most important factors in the development of nuclear rocket engine designs is to be able to accurately predict temperatures and pressures throughout a fission nuclear reactor core with axial hydrogen flow through circular coolant passages. CAC is an analytical prediction program to study the heat transfer and fluid flow characteristics of a circular coolant passage. CAC predicts as a function of time axial and radial fluid conditions, passage wall temperatures, flow rates in each coolant passage, and approximate maximum material temperatures. CAC incorporates the hydrogen properties model STATE to provide fluid-state relations, thermodynamic properties, and transport properties of molecular hydrogen in any fixed ortho-para combination. The program requires the general core geometry, the core material properties as a function of temperature, the core power profile, and the core inlet conditions as function of time. Although CAC was originally developed in FORTRAN IV for use on an IBM 7094, this version is written in ANSI standard FORTRAN 77 and is designed to be machine independent. It has been successfully compiled on IBM PC series and compatible computers running MS-DOS with Lahey F77L, a Sun4 series computer running SunOS 4.1.1, and a VAX series computer running VMS 5.4-3. CAC requires 300K of RAM under MS-DOS, 422K of RAM under SunOS, and 220K of RAM under VMS. No sample executable is provided on the distribution medium. Sample input and output data are included. The standard distribution medium for this program is a 5.25 inch 360K MS-DOS format diskette. CAC was developed in 1966, and this machine independent version was released in 1992. IBM-PC and IBM are registered trademarks of International Business Machines. Lahey F77L is a registered trademark of Lahey Computer Systems, Inc. SunOS is a trademark of Sun Microsystems, Inc. VMS is a trademark of Digital Equipment Corporation. MS-DOS is a registered trademark of Microsoft Corporation.

  11. The effect of surfactant and solid phase concentration on drug aggregates in model aerosol propellent suspensions.

    PubMed

    Bower, C; Washington, C; Purewal, T S

    1996-04-01

    The effect of increasing solid phase concentration on the morphology and flocculation rate of model aerosol suspensions has been investigated. Suspensions of micronized salbutamol sulphate and lactose in trichlorotrifluoroethane (P113) were studied under conditions of increasing shear stress. By use of image analysis techniques, measurement of aggregate size, fractal dimension and rate of aggregation was performed. The effect of the surfactant sorbitan monooleate on morphology and flocculation rate was also studied. Increased solid phase concentration caused an increase in the rate of aggregation and average aggregate size at a given value of shear stress. Surfactant addition retarded the aggregation rate, and caused a shift from a diffusion-limited cluster aggregation to a reaction-limited cluster aggregation mechanism. The aggregate profiles showed a corresponding change from rugged and crenellated without surfactant, to increasingly smooth and Euclidian with increasing surfactant concentration. The morphological changes were characterized by a decrease in the average boundary fractal dimension which also correlated well with the corresponding reduction in aggregation rate.

  12. Promotion or Inhibition of Islet Amyloid Polypeptide Aggregation by Zinc Coordination Depends on Its Relative Concentration.

    PubMed

    Nedumpully-Govindan, Praveen; Yang, Ye; Andorfer, Rachel; Cao, Weiguo; Ding, Feng

    2015-12-22

    Zinc is reported to play a complex role in islet amyloid polypeptide (IAPP) aggregation, which is associated with β-cell death in type II diabetes (T2D). Depending on their relative concentrations in vitro, zinc could either promote or inhibit IAPP aggregation. Interestingly, genomewide association studies suggested both positive and negative correlations between T2D risks and activities of a β-cell-specific zinc transporter upon mutations, which determines zinc concentration in vivo. To decipher the effect of zinc coordination on IAPP aggregation, we performed atomistic discrete molecular dynamics simulations to systemically study aggregation propensities of zinc-coordinated IAPP oligomers with different molecular weights (MWs), whose populations are determined by zinc concentration. We find that at low zinc:IAPP stoichiometry, zinc coordination promotes aggregation by forming high-MW oligomers. The aggregation is inhibited when the stoichiometry increases and zinc binds individual peptides. Our computationally derived predictions are validated by the complementary thioflavin-T fluorescence assay measuring the dependence of IAPP aggregation on a wide range of zinc concentrations. Our combined computational and experimental study offers detailed mechanistic insight into the complex role of zinc on IAPP aggregation and T2D development.

  13. Studying the concentration dependence of the aggregation number of a micellar model system by SANS.

    PubMed

    Amann, Matthias; Willner, Lutz; Stellbrink, Jörg; Radulescu, Aurel; Richter, Dieter

    2015-06-01

    We present a small-angle neutron scattering (SANS) structural characterization of n-alkyl-PEO polymer micelles in aqueous solution with special focus on the dependence of the micellar aggregation number on increasing concentration. The single micellar properties in the dilute region up to the overlap concentration ϕ* are determined by exploiting the well characterized unimer exchange kinetics of the model system in a freezing and diluting experiment. The micellar solutions are brought to thermodynamic equilibrium at high temperatures, where unimer exchange is fast, and are then cooled to low temperatures and diluted to concentrations in the limit of infinite dilution. At low temperatures the kinetics, and therefore the key mechanism for micellar rearrangement, is frozen on the experimental time scale, thus preserving the micellar structure in the dilution process. Information about the single micellar structure in the semidilute and concentrated region are extracted from structure factor analysis at high concentrations where the micelles order into fcc and bcc close packed lattices and the aggregation number can be calculated by geometrical arguments. This approach enables us to investigate the aggregation behavior in a wide concentration regime from dilute to 6·ϕ*, showing a constant aggregation number with concentration over a large concentration regime up to a critical concentration about three times ϕ*. When exceeding this critical concentration, the aggregation number was found to increase with increasing concentration. This behavior is compared to scaling theories for star-like polymer micelles. PMID:25892401

  14. Studying the concentration dependence of the aggregation number of a micellar model system by SANS.

    PubMed

    Amann, Matthias; Willner, Lutz; Stellbrink, Jörg; Radulescu, Aurel; Richter, Dieter

    2015-06-01

    We present a small-angle neutron scattering (SANS) structural characterization of n-alkyl-PEO polymer micelles in aqueous solution with special focus on the dependence of the micellar aggregation number on increasing concentration. The single micellar properties in the dilute region up to the overlap concentration ϕ* are determined by exploiting the well characterized unimer exchange kinetics of the model system in a freezing and diluting experiment. The micellar solutions are brought to thermodynamic equilibrium at high temperatures, where unimer exchange is fast, and are then cooled to low temperatures and diluted to concentrations in the limit of infinite dilution. At low temperatures the kinetics, and therefore the key mechanism for micellar rearrangement, is frozen on the experimental time scale, thus preserving the micellar structure in the dilution process. Information about the single micellar structure in the semidilute and concentrated region are extracted from structure factor analysis at high concentrations where the micelles order into fcc and bcc close packed lattices and the aggregation number can be calculated by geometrical arguments. This approach enables us to investigate the aggregation behavior in a wide concentration regime from dilute to 6·ϕ*, showing a constant aggregation number with concentration over a large concentration regime up to a critical concentration about three times ϕ*. When exceeding this critical concentration, the aggregation number was found to increase with increasing concentration. This behavior is compared to scaling theories for star-like polymer micelles.

  15. Dependence of aggregation behavior on concentration in triblock copolymer solutions: The effect of chain architecture

    SciTech Connect

    Han, Xiang-Gang Zhang, Xue-Feng

    2015-12-07

    Using the self-consistent field lattice technique, the effects of concentration and hydrophobic middle block length (where the chain length remains constant) on aggregation behavior are studied in amphiphilic symmetric triblock copolymer solutions. The heat capacity peak for the unimer-micelle transition and the distribution peaks for the different degrees of aggregation for micelles and small aggregates (submicelles) are calculated. Analysis of the conducted computer simulations shows that the transition broadness dependence on concentration is determined by the hydrophobic middle block length, and this dependence is distinctly different when the length of the hydrophobic middle block changes. Different size for small aggregates simultaneously appear in the transition region. As temperature decreases, the number of different size small aggregates for the large hydrophobic middle block length first ascends and then descends in aggregation degree order. These results indicate that any transition broadness change with concentration is related to the mechanism of fragmentation and fusion. These results are helpful for interpreting the aggregation process of amphiphilic copolymers at equilibrium.

  16. Aggregation ability of erythrocytes of patients with coronary heart disease depending on different glucose concentration

    NASA Astrophysics Data System (ADS)

    Malinova, Lidia I.; Simonenko, Georgy V.; Kirichuk, Vyacheslav F.; Denisova, Tatyana P.; Tuchin, Valery V.

    2002-07-01

    The aggregation ability of erythrocytes of patients with coronary heart disease comparing to practically healthy persons and patients with coronary heart disease combined with non insulin dependent diabetes mellitus depending on different glucose concentration in unguentums of blood incubates with the help of computer microphotometer - visual analyzer was studied. Two-phase behavior of erythrocytes size changing of practically healthy persons depending on glucose concentration in an incubation medium and instability erythrocyte systems of a whole blood to the influence of high glucose concentration were revealed. Influence of high glucose concentration on aggregation ability of erythrocytes of patients with coronary heart disease and its combination with non insulin dependent diabetes mellitus was revealed.

  17. Predictive model for diffusion-limited aggregation kinetics of nanocolloids under high concentration.

    PubMed

    Lattuada, Marco

    2012-01-12

    Smoluchowski's equation for the rate of aggregation of colloidal particles under diffusion-limited conditions has set the basis for the interpretation of kinetics of aggregation phenomena. Nevertheless, its use is limited to sufficiently dilute conditions. In this work we propose a correction to Smoluchowski's equation by using a result derived by Richards ( J. Phys. Chem. 1986 , 85 , 3520 ) within the framework of trapping theory. This corrected aggregation kernel, which accounts for concentration dependence effects, has been implemented in a population-balance equations scheme and used to model the aggregation kinetics of colloidal particles undergoing diffusion-limited aggregation under concentrated conditions (up to a particle volume fraction of 30%). The predictions of population balance calculations have been validated by means of Brownian dynamic simulations. It was found that the corrected kernel can very well reproduce the results from Brownian dynamic simulations for all concentration values investigated, and is also able to accurately predict the time required by a suspension to reach the gel point. On the other hand, classical Smoluchowski's theory substantially underpredicts the rate of aggregation as well as the onset of gelation, with deviations becoming progressively more severe as the particle volume fraction increases. PMID:22148884

  18. Molecular Dynamics Simulations to Clarify the Concentration Dependency of Protein Aggregation

    NASA Astrophysics Data System (ADS)

    Nishikawa, Naohiro; Sakae, Yoshitake; Okamoto, Yuko

    We examined the concentration dependency of amyloid protein aggregation by using several molecular dynamics simulations, which were performed with different concentrations for each system. For these simulations, we used a fragment of amyloid-β, which is believed to be the cause of Alzheimer's disease, as our simulation system. We found that high concentration of amyloid peptides promotes the formation of β-structures which is the origin of amyloid fibrils.

  19. The many phases of CaC2

    NASA Astrophysics Data System (ADS)

    Konar, Sumit; Nylén, Johanna; Svensson, Gunnar; Bernin, Diana; Edén, Mattias; Ruschewitz, Uwe; Häussermann, Ulrich

    2016-07-01

    Polymorphic CaC2 was prepared by reacting mixtures of CaH2 and graphite with molar ratios between 1:1.8 and 1:2.2 at temperatures between 700 and 1400 °C under dynamic vacuum. These conditions provided a well controlled, homogeneous, chemical environment and afforded products with high purity. The products, which were characterized by powder X-ray diffraction, solid state NMR and Raman spectroscopy, represented mixtures of the three known polymorphs, tetragonal CaC2-I and monoclinic CaC2-II and -III. Their proportion is dependent on the nominal C/CaH2 ratio of the reaction mixture and temperature. Reactions with excess carbon produced a mixture virtually free from CaC2-I, whereas high temperatures (above 1100 °C) and C-deficiency favored the formation of CaC2-I. From first principles calculations it is shown that CaC2-I is dynamically unstable within the harmonic approximation. This indicates that existing CaC2-I is structurally/dynamically disordered and may possibly even occur as slightly carbon-deficient phase CaC2-δ. It is proposed that monoclinic II is the ground state of CaC2 and polymorph III is stable at temperatures above 200 °C. Tetragonal I represents a metastable, heterogeneous, phase of CaC2. It is argued that a complete understanding of the occurrence of three room temperature modifications of CaC2 will require a detailed characterization of compositional and structural heterogeneities within the high temperature form CaC2-IV, which is stable above 450 °C. The effect of high pressure on the stability of the monoclinic forms of CaC2 was studied in a diamond anvil cell using Raman spectroscopy. CaC2-II and -III transform into tetragonal CaC2-I at about 4 and 1GPa, respectively.

  20. Challenges of CAC in Heterogeneous Wireless Cognitive Networks

    NASA Astrophysics Data System (ADS)

    Wang, Jiazheng; Fu, Xiuhua

    Call admission control (CAC) is known as an effective functionality in ensuring the QoS of wireless networks. The vision of next generation wireless networks has led to the development of new call admission control (CAC) algorithms specifically designed for heterogeneous wireless Cognitive networks. However, there will be a number of challenges created by dynamic spectrum access and scheduling techniques associated with the cognitive systems. In this paper for the first time, we recommend that the CAC policies should be distinguished between primary users and secondary users. The classification of different methods of cac policies in cognitive networks contexts is proposed. Although there have been some researches within the umbrella of Joint CAC and cross-layer optimization for wireless networks, the advent of the cognitive networks adds some additional problems. We present the conceptual models for joint CAC and cross-layer optimization respectively. Also, the benefit of Cognition can only be realized fully if application requirements and traffic flow contexts are determined or inferred in order to know what modes of operation and spectrum bands to use at each point in time. The process model of Cognition involved per-flow-based CAC is presented. Because there may be a number of parameters on different levels affecting a CAC decision and the conditions for accepting or rejecting a call must be computed quickly and frequently, simplicity and practicability are particularly important for designing a feasible CAC algorithm. In a word, a more thorough understanding of CAC in heterogeneous wireless cognitive networks may help one to design better CAC algorithms.

  1. Aggregation in concentrated protein solutions: Insights from rheology, neutron scattering and molecular simulations

    NASA Astrophysics Data System (ADS)

    Castellanos, Maria Monica

    Aggregation of therapeutic proteins is currently one of the major challenges in the bio-pharmaceutical industry, because aggregates could induce immunogenic responses and compromise the quality of the product. Current scientific efforts, both in industry and academia, are focused on developing rational approaches to screen different drug candidates and predict their stability under different conditions. Moreover, aggregation is promoted in highly concentrated protein solutions, which are typically required for subcutaneous injection. In order to gain further understanding about the mechanisms that lead to aggregation, an approach that combined rheology, neutron scattering, and molecular simulations was undertaken. Two model systems were studied in this work: Bovine Serum Albumin in surfactant-free Phosphate Buffered Saline at pH = 7.4 at concentrations from 11 mg/mL up to ˜519 mg/mL, and a monoclonal antibody in 20 mM Histidine/Histidine Hydrochloride at pH = 6.0 with 60 mg/mL trehalose and 0.2 mg/mL polysorbate-80 at concentrations from 53 mg/mL up to ˜220 mg/mL. The antibody used here has three mutations in the CH2 domain, which result in lower stability upon incubation at 40 °C with respect to the wild-type protein, based on size-exclusion chromatography assays. This temperature is below 49 °C, where unfolding of the least stable, CH2 domain occurs, according to differential scanning calorimetry. This dissertation focuses on identifying the role of aggregation on the viscosity of protein solutions. The protein solutions of this work show an increase in the low shear viscosity in the absence of surfactants, because proteins adsorb at the air/water interface forming a viscoelastic film that affects the measured rheology. Stable surfactant-laden protein solutions behave as simple Newtonian fluids. However, the surfactant-laden antibody solution also shows an increase in the low shear viscosity from bulk aggregation, after prolonged incubation at 40 °C. Small

  2. alpha-Synuclein fission yeast model: concentration-dependent aggregation without plasma membrane localization or toxicity.

    PubMed

    Brandis, Katrina A; Holmes, Isaac F; England, Samantha J; Sharma, Nijee; Kukreja, Lokesh; DebBurman, Shubhik K

    2006-01-01

    Despite fission yeast's history of modeling salient cellular processes, it has not yet been used to model human neurodegeneration-linked protein misfolding. Because alpha-synuclein misfolding and aggregation are linked to Parkinson's disease (PD), here, we report a fission yeast (Schizosaccharomyces pombe) model that evaluates alpha-synuclein misfolding, aggregation, and toxicity and compare these properties with those recently characterized in budding yeast (Saccharomyces cerevisiae). Wild-type alpha-synuclein and three mutants (A30P, A53T, and A30P/A53T) were expressed with thiamine-repressible promoters (using vectors of increasing promoter strength: pNMT81, pNMT41, and pNMT1) to test directly in living cells the nucleation polymerization hypothesis for alpha-synuclein misfolding and aggregation. In support of the hypothesis, wild-type and A53T alpha-synuclein formed prominent intracellular cytoplasmic inclusions within fission yeast cells in a concentration- and time-dependent manner, whereas A30P and A30P/A53T remained diffuse throughout the cytoplasm. A53T alpha-synuclein formed aggregates faster than wild-type alpha-synuclein and at a lower alpha-synuclein concentration. Unexpectedly, unlike in budding yeast, wild-type and A53T alpha-synuclein did not target to the plasma membrane in fission yeast, not even at low alpha-synuclein concentrations or as a precursor step to forming aggregates. Despite alpha-synuclein's extensive aggregation, it was surprisingly nontoxic to fission yeast. Future genetic dissection might yield molecular insight into this protection against toxicity. We speculate that alpha-synuclein toxicity might be linked to its membrane binding capacity. To conclude, S. pombe and S. cerevisiae model similar yet distinct aspects of alpha-synuclein biology, and both organisms shed insight into alpha-synuclein's role in PD pathogenesis.

  3. Nitric oxide inhibited the melanophore aggregation induced by extracellular calcium concentration in snakehead fish, Channa punctatus.

    PubMed

    Biswas, Saikat P; Palande, Nikhil V; Jadhao, Arun G

    2011-12-01

    We studied the role of nitric oxide (NO) and extra-cellular Ca(2+) on the melanophores in Indian snakehead teleost, Channa punctatus. Increase of Ca(2+) level in the external medium causes pigment aggregation in melanophores. This pigment-aggregating effect was found to be inhibited when the external medium contained spontaneous NO donor, sodium nitro prusside (SNP) at all the levels of concentration tested. Furthermore, it has been observed that SNP keeps the pigment in dispersed state even after increasing the amount of Ca(2+). In order to test whether NO donor SNP causes dispersion of pigments or not is checked by adding the inhibitor of nitric oxide synthase, N-omega-Nitro-L-arginine (L-NNA) in the medium. It has been noted that the inhibitor L-NNA blocked the effect of NO donor SNP causing aggregation of pigments. In that way NO is inhibiting the effect of extracellular Ca(2+), keeping the pigment dispersed.

  4. Viscosity scaling in concentrated dispersions and its impact on colloidal aggregation.

    PubMed

    Nicoud, Lucrèce; Lattuada, Marco; Lazzari, Stefano; Morbidelli, Massimo

    2015-10-01

    Gaining fundamental knowledge about diffusion in crowded environments is of great relevance in a variety of research fields, including reaction engineering, biology, pharmacy and colloid science. In this work, we determine the effective viscosity experienced by a spherical tracer particle immersed in a concentrated colloidal dispersion by means of Brownian dynamics simulations. We characterize how the effective viscosity increases from the solvent viscosity for small tracer particles to the macroscopic viscosity of the dispersion when large tracer particles are employed. Our results show that the crossover between these two regimes occurs at a tracer particle size comparable to the host particle size. In addition, it is found that data points obtained in various host dispersions collapse on one master curve when the normalized effective viscosity is plotted as a function of the ratio between the tracer particle size and the mean host particle size. In particular, this master curve was obtained by varying the volume fraction, the average size and the polydispersity of the host particle distribution. Finally, we extend these results to determine the size dependent effective viscosity experienced by a fractal cluster in a concentrated colloidal system undergoing aggregation. We include this scaling of the effective viscosity in classical aggregation kernels, and we quantify its impact on the kinetics of aggregate growth as well as on the shape of the aggregate distribution by means of population balance equation calculations.

  5. Microwave losses of bulk CaC 6

    NASA Astrophysics Data System (ADS)

    Cifariello, G.; Di Gennaro, E.; Lamura, G.; Andreone, A.; Emery, N.; Hérold, C.; Marêché, J. F.; Lagrange, P.

    2007-09-01

    We report a study of the temperature dependence of the surface resistance RS in the graphite intercalated compound (GIC) CaC6, where superconductivity at 11.5 K was recently discovered. Experiments are carried out using a copper dielectrically loaded cavity operating at 7 GHz in a "hot finger" configuration. Bulk CaC6 samples have been synthesized from highly oriented pyrolytic graphite. Microwave data allow to extract unique information on the quasiparticle density and on the nature of pairing in superconductors. The analysis of RS(T) confirms our recent experimental findings that CaC6 behaves as a weakly-coupled, fully gapped, superconductor.

  6. Predictive response surface model for heat-induced rheological changes and aggregation of whey protein concentrate.

    PubMed

    Alvarez, Pedro A; Emond, Charles; Gomaa, Ahmed; Remondetto, Gabriel E; Subirade, Muriel

    2015-02-01

    Whey proteins are now far more than a by-product of cheese processing. In the last 2 decades, food manufacturers have developed them as ingredients, with the dairy industry remaining as a major user. For many applications, whey proteins are modified (denatured) to alter their structure and functional properties. The objective of this research was to study the influence of 85 to 100 °C, with protein concentration of 8% to 12%, and treatment times of 5 to 30 min, while measuring rheological properties (storage modulus, loss modulus, and complex viscosity) and aggregation (intermolecular beta-sheet formation) in dispersions of whey protein concentrate (WPC). A Box-Behnken Response Surface Methodology modeled the heat denaturation of liquid sweet WPC at 3 variables and 3 levels. The model revealed a very significant fit for viscoelastic properties, and a lesser fit for protein aggregation, at temperatures not previously studied. An exponential increase of rheological parameters was governed by protein concentration and temperature, while a modest linear relationship of aggregation was governed by temperature. Models such as these can serve as valuable guides to the ingredient and dairy industries to develop target products, as whey is a major ingredient in many functional foods.

  7. Natural organic matter concentration and hydrochemistry influence aggregation kinetics of functionalized engineered nanoparticles.

    PubMed

    Liu, Junfeng; Legros, Samuel; von der Kammer, Frank; Hofmann, Thilo

    2013-05-01

    Understanding the colloidal stability of functionalized engineered nanoparticles (FENPs) in aquatic environments is of paramount importance in order to assess the risk related to FENPs. In this study, gold nanoparticles (GNPs) of 68 and 43 nm diameter, coated with citrate and 11-mercaptoundecanoic acid (MUA) respectively, were used as models of FENPs. Time-resolved dynamic light scattering was employed to investigate the aggregation kinetics of two types of GNPs. The results show that without Suwannee river natural organic matter (SRNOM), MUA coating resulted in greater stability than citrate coating for GNPs. Cations have a destabilizing effect on both GNPs following the order Ca(2+) ≈ Mg(2+) > Na(+); different anions (Cl(-) and SO4(2-)) showed no difference in effects. In the fast aggregation regime, adding SRNOM enhanced the stability of MUA-coated GNPs in both Ca(2+) and Mg(2+) solutions. However citrate-coated GNPs were only stabilized in Mg(2+) solution but enhanced aggregation occurred in high Ca(2+) concentration due to interparticle bridging. For the investigated GNPs and in the presence of SRNOM, Ca(2+) does not always act as a strong coagulant. This indicates that for the new materials emerging from the application of nanotechnology the well-described aggregation mechanisms of colloids in the environment require a detailed re-examination.

  8. A Dust Aggregation and Concentration System (DACS) for the Microgravity Space Environment

    NASA Technical Reports Server (NTRS)

    Giovane, F. J.; Blum, J.

    1999-01-01

    The Dust Aggregation and Concentration System, DACS, Project is an international effort intended to complete the preliminary definition of a system for suspending and concentrating dust particles in a microgravity environment for extended periods of time. The DACS design concept is based on extensive ground, drop tower, and parabolic flight tests. During the present proposed work, the DACS design will be completed, and a Science Requirements Document generated. At the end of the proposed 2 year project, DACS will be positioned to enter the advanced definition phase.

  9. Effects of supplemental feeding and aggregation on fecal glucocorticoid metabolite concentrations in elk

    USGS Publications Warehouse

    Forristal, Victoria E.; Creel, Scott; Taper, Mark L.; Scurlock, Brandon M.; Cross, Paul C.

    2012-01-01

    Habitat modifications and supplemental feeding artificially aggregate some wildlife populations, with potential impacts upon contact and parasite transmission rates. Less well recognized, however, is how increased aggregation may affect wildlife physiology. Crowding has been shown to induce stress responses, and increased glucocorticoid (GC) concentrations can reduce immune function and increase disease susceptibility. We investigated the effects of supplemental feeding and the aggregation that it induces on behavior and fecal glucocorticoid metabolite concentrations (fGCM) in elk (Cervus elaphus) using observational and experimental approaches. We first compared fGCM levels of elk on supplemental feedgrounds to neighboring elk populations wintering in native habitats using data from 2003 to 2008. We then experimentally manipulated the distribution of supplemental food on feedgrounds to investigate whether more widely distributed food would result in lower rates of aggression and stress hormone levels. Contrary to some expectations that fed elk may be less stressed than unfed elk during the winter, we found that elk on feedgrounds had fecal GC levels at least 31% higher than non-feedground populations. Within feedgrounds, fGCM levels were strongly correlated with local measures of elk density (r2 = 0.81). Dispersing feed more broadly, however, did not have a detectable effect on fGCM levels or aggression rates. Our results suggest that increases in aggregation associated with winter feedgrounds affects elk physiology, and the resulting increases in fGCM levels are not likely to be mitigated by management efforts that distribute the feed more widely. Additional research is needed to assess whether these increases in fGCMs directly alter parasite transmission and disease dynamics.

  10. Concentric Archimedean polyhedra: Mn(III)12Mn(II)9 aggregates linked into a cubic network.

    PubMed

    Nayak, Sanjit; Lan, Yanhua; Clérac, Rodolphe; Anson, Christopher E; Powell, Annie K

    2008-11-30

    A Mn(III)(12)Mn(II)(9) aggregate has a structure built up of concentric polyhedra with these units linked into a cubic network to give a remarkably pleasing structure isotypic with iron pyrites. PMID:19009052

  11. “Clicked” Sugar–Curcumin Conjugate: Modulator of Amyloid-β and Tau Peptide Aggregation at Ultralow Concentrations

    PubMed Central

    2011-01-01

    The synthesis of a water/plasma soluble, noncytotoxic, “clicked” sugar-derivative of curcumin with amplified bioefficacy in modulating amyloid-β and tau peptide aggregation is presented. Curcumin inhibits amyloid-β and tau peptide aggregation at micromolar concentrations; the sugar–curcumin conjugate inhibits Aβ and tau peptide aggregation at concentrations as low as 8 nM and 0.1 nM, respectively. In comparison to curcumin, this conveniently synthesized Alzheimer’s drug candidate is a more powerful antioxidant. PMID:22860163

  12. "Clicked" sugar-curcumin conjugate: modulator of amyloid-β and tau peptide aggregation at ultralow concentrations.

    PubMed

    Dolai, Sukanta; Shi, Wei; Corbo, Christopher; Sun, Chong; Averick, Saadyah; Obeysekera, Dinali; Farid, Mina; Alonso, Alejandra; Banerjee, Probal; Raja, Krishnaswami

    2011-12-21

    The synthesis of a water/plasma soluble, noncytotoxic, "clicked" sugar-derivative of curcumin with amplified bioefficacy in modulating amyloid-β and tau peptide aggregation is presented. Curcumin inhibits amyloid-β and tau peptide aggregation at micromolar concentrations; the sugar-curcumin conjugate inhibits Aβ and tau peptide aggregation at concentrations as low as 8 nM and 0.1 nM, respectively. In comparison to curcumin, this conveniently synthesized Alzheimer's drug candidate is a more powerful antioxidant. PMID:22860163

  13. Concentrating Aggregation-Induced Fluorescence in Planar Waveguides: A Proof-of-Principle

    NASA Astrophysics Data System (ADS)

    Banal, James L.; White, Jonathan M.; Ghiggino, Kenneth P.; Wong, Wallace W. H.

    2014-04-01

    The photophysical properties of fluorescent dyes are key determinants in the performance of luminescent solar concentrators (LSCs). First-generation dyes - coumarin, perylenes, and rhodamines - used in LSCs suffer from both concentration quenching in the solid-state and small Stokes shifts which limit the current LSC efficiencies to below theoretical limits. Here we show that fluorophores that exhibit aggregation-induced emission (AIE) are promising materials for LSC applications. Experiments and Monte Carlo simulations show that the optical quantum efficiencies of LSCs with AIE fluorophores are at least comparable to those of LSCs with first-generation dyes as the active materials even without the use of any optical accessories to enhance the trapping efficiency of the LSCs. Our results demonstrate that AIE fluorophores can potentially solve some key limiting properties of first-generation LSC dyes.

  14. 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.

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

    PubMed

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

    2012-07-01

    The application of reverse osmosis for the treatment of landfill leachate is becoming widespread in Turkey as well as in Europe. A major drawback of this process is the production of concentrate, which could be as much as 30% of the feed stream, and high concentrations of salts and contaminants. The reverse osmosis concentrate is disposed of by using several methods including re-infiltration, drying, incineration and solidification/stabilization. In this study, solidification/stabilization (S/S) technology was studied for the treatment of reverse osmosis concentrate produced from landfill leachate. In order to benefit from its capability to absorb heavy metals, ammonia and some other pollutants, zeolite and different aggregate materials were used in solidification experiments. Main pollutants in the leachate concentrate, TOC, DOC, TDS and ammonia were successfully solidified and approximately 1% of TOC, DOC, TDS and ammonia remained in the eluate water. The results indicated that the landfill disposal limits could be attained by solidification/stabilization process. PMID:22498574

  16. The influence of nickel slag aggregate concentration to compressive and flexural strength on fly ash-based geopolymer composite

    NASA Astrophysics Data System (ADS)

    Sujiono, E. H.; Setiawan, A.; Husain, H.; Irhamsyah, A.; Samnur, S.; Subaer, S.

    2016-04-01

    Fly ash-based geopolymer with nickel slag aggregate has been successfully produced. Fly ash and nickel slag were obtained from Bosowa Jeneponto Power Plant and PT. Vale Indonesia, respectively. This research aims to investigate the influence of nickel slag concentration to compressive strength, flexural strength, and microstructure of geopolymer composite. The increment of nickel slag aggregate on fly ash was relative to the weight of samples. Geopolymer composite were synthesized by using alkali activated method, cured at temperature of 70 °C for 1 hour. The resulting composites were left at room temperature for 14 days, before compressive and flexural strength were performed. The results showed that the addition of nickel slag aggregate was found to increase the compressive strength of the material. The optimum compressive strength was 14.81 MPa with the addition of 10% aggregate. The optimum flexural strength was 2.63 MPa with the addition of 15% aggregate.

  17. Heterogeneity in (2-butoxyethanol + water) mixtures: Hydrophobicity-induced aggregation or criticality-driven concentration fluctuations?

    NASA Astrophysics Data System (ADS)

    Indra, Sandipa; Biswas, Ranjit

    2015-05-01

    Micro-heterogeneity in aqueous solutions of 2-butoxyethanol (BE), a system with closed loop miscibility gap, has been explored via absorption and time-resolved fluorescence measurements of a dissolved dipolar solute, coumarin 153 (C153), in the water-rich region at various BE mole fractions (0 ≤ XBE ≤ 0.25) in the temperature range, 278 ≤ T/K ≤ 320. Evidences for both alcohol-induced H-bond strengthening and subsequent structural transition of H-bond network have been observed. Analyses of steady state and time-resolved spectroscopic data for these aqueous mixtures and comparisons with the results for aqueous solutions of ethanol and tertiary butanol indicate that alcohol aggregation in BE/water mixtures is driven by hydrophobic interaction with no or insignificant role for criticality-driven concentration fluctuations preceding phase separation. Excitation energy dependence of fluorescence emission of C153 confirms formation of aggregated structures at very low BE mole fractions. No asymptotic critical power law dependence for relaxation rates of the type, k ∝ (|T - Tc|/Tc)γ, with γ denoting universal critical constant, has been observed for both solute's rotational relaxation and population relaxation rates in these mixtures upon either approaching to critical concentration or critical temperature. Estimated activation energies for rotational relaxation rate of C153 and solution viscosity have been found to follow each other with no abrupt changes in either of them at any mixture composition. In addition, measured C153 rotation times at various compositions and temperatures reflect near-hydrodynamic viscosity coupling through the dependence, <τr> ∝ (η/T)p, with p = 0.8-1.0, suggesting solute's orientational relaxation dynamics being, on an average, temporally homogeneous.

  18. Photocatalytic degradation of an azo dye Sunset Yellow under UV-A light using TiO2/CAC composite catalysts.

    PubMed

    Rajamanickam, D; Shanthi, M

    2014-07-15

    The photocatalytic activity and the promoting effect of titania (TiO2) by commercial activated carbon (CAC) for removing the pollutant in wastewater were investigated. The TiO2/CAC composite photocatalysts with various ratios of CAC to TiO2 were prepared by sol-gel method. The catalyst was characterized by X-ray diffraction (XRD), high resolution scanning electron microscope (HR-SEM), energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area measurement methods. The photocatalytic activity of TiO2/CAC was investigated for the degradation of Sunset Yellow (SY) in aqueous solution using UV-A light. The TiO2/CAC is found to be more efficient than prepared TiO2 and TiO2-P25 at pH 7 for the mineralization of SY. The synergism between TiO2 and CAC may increase the catalytic activity. The effects of operational parameters such as the amount of photocatalyst, dye concentration and initial pH on photo mineralization of SY have been analyzed. The mineralization of SY has been confirmed by COD measurements. The catalyst is found to be reusable.

  19. Photocatalytic degradation of an azo dye Sunset Yellow under UV-A light using TiO2/CAC composite catalysts

    NASA Astrophysics Data System (ADS)

    Rajamanickam, D.; Shanthi, M.

    2014-07-01

    The photocatalytic activity and the promoting effect of titania (TiO2) by commercial activated carbon (CAC) for removing the pollutant in wastewater were investigated. The TiO2/CAC composite photocatalysts with various ratios of CAC to TiO2 were prepared by sol-gel method. The catalyst was characterized by X-ray diffraction (XRD), high resolution scanning electron microscope (HR-SEM), energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area measurement methods. The photocatalytic activity of TiO2/CAC was investigated for the degradation of Sunset Yellow (SY) in aqueous solution using UV-A light. The TiO2/CAC is found to be more efficient than prepared TiO2 and TiO2-P25 at pH 7 for the mineralization of SY. The synergism between TiO2 and CAC may increase the catalytic activity. The effects of operational parameters such as the amount of photocatalyst, dye concentration and initial pH on photo mineralization of SY have been analyzed. The mineralization of SY has been confirmed by COD measurements. The catalyst is found to be reusable.

  20. [Measurement of the concentration of free cytoplasmic calcium in the process of platelet aggregation using a fluorescent method].

    PubMed

    Popov, E G; Gavrilov, I Iu; Pozin, E Ia; Gabbasov, Z A

    1989-01-01

    A multiwavelength method for measuring free cytosolic calcium concentration is proposed. It is based on the registration of the fluorescent spectrum of calcium--sensitive probe indo-1 and deconvolution of the spectrum into components corresponding to free and bound forms of the probe. Calcium concentration is calculated as a product of calcium-probe dissociation constant by calcium-bound to free form concentration ratio. The obtained values are independent of variations in light-scattering properties of the medium and total dye concentration in the optical channel. It is shown that during ADP-induced platelet aggregation calcium concentration rises without measurable delay after the addition of the inducer and significantly decreases by the time the aggregation begins.

  1. Fluorescence probe studies of the effect of concentration on the state of aggregation of surfactants in aqueous solution

    SciTech Connect

    Lianos, P.; Zana, R.

    1981-11-01

    The results obtained in this study indicate that the aggregation numbers of a zwitterionic surfactant where the charges are well separated, and of various ionic surfactants, are independent of the surfactant concentration from the critical micelle concentration to ca. 0.3 M. In the absence of added salts these n values are consistent with the quasi-spherical oil drop model for micelles. The n values obtained for a zwitterionic surfactant where the 2 charges nearly neutralize each other and for a nonionic surfactant are large, and probably indicative of rod-like micelles. In addition the aggregation number for the nonionic surfactant has been found to increase with concentration, in the concentration range investigated. The values of the 14/13 ratio confirm that pyrene is solubilized preferentially in the micelle palisade layer rather than in the hydrophobic core. 41 references.

  2. The effect of particle aggregate shape on ultrasonic anisotropy in concentrated magnetic fluids

    NASA Astrophysics Data System (ADS)

    Hornowski, T.; Józefczak, A.; Kołodziejczyk, B.; Timko, M.; Skumiel, A.; Rajnak, M.

    2015-05-01

    The effect of aggregate shape on the ultrasonic anisotropy in magnetic fluid was studied. Experimental results were compared with the theory of Ahuja and Hendee. Analysis of experimental results in terms of the theoretical model show the formation of ellipsoidal aggregates composed of several particles. The chain-like aggregates (h = b/a >> 1 a and b being minor and major axis lengths, respectively) are most conspicuous in diluted ferrofluids while dense ferrofluids are characterized by a more homogeneous drop-like (h = b/a > 1) structure. This finding is supported by some theoretical simulations.

  3. Continuous matrix assisted refolding of alpha-lactalbumin by ion exchange chromatography with recycling of aggregates combined with ultradiafiltration.

    PubMed

    Machold, Christine; Schlegl, Robert; Buchinger, Wolfgang; Jungbauer, Alois

    2005-07-01

    Continuous matrix assisted refolding (MAR) can be achieved on a solid support by using a continuous chromatographic system. Recycling the aggregate fraction, simultaneously formed during a refolding reaction, can further increase the refolding yield. Due to the nature of this reaction, aggregates are the main reason for a refolding yield below stoichiometric conversion. A preparative continuous annular chromatographic system (P-CAC) equipped with an ion exchange resin was used to continuously refold the model protein alpha-lactalbumin. For this purpose, this protein was denatured, reduced and adsorbed on the ion exchange resin. Elution was performed with or without redox reagents in the buffer system permitting fast formation of the native disulfide bonds. In the case redox reagents were present, the protein refolds then during its residence time on the matrix. However, aggregate formation is also increased and refolding yields are lower. Tightly bound aggregates were removed from the column by 2M guanidinium hydrochloride. In order to increase the system yield, this aggregate fraction was recycled after lowering the conductivity by ultradiafiltration and adjustment of the protein concentration by dilution. For on-column refolding, recycling of aggregates at a recycling rate of 0.17 increased the system yield from 25% to 30%. An algorithm was developed to show interdependencies of the single influencing parameters. The operability of the system was demonstrated but limitations due to instability of the P-CAC, especially inhomogeneous flow and peak wobbling, have to be considered.

  4. Pressure-induced superconductivity in CaC2.

    PubMed

    Li, Yan-Ling; Luo, Wei; Zeng, Zhi; Lin, Hai-Qing; Mao, Ho-kwang; Ahuja, Rajeev

    2013-06-01

    Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp(2)-, and sp(3)-hybridized bonds. sp(2)-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2-105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron-phonon coupling λ in compressed CaC2 is found, in particular for Immm phase, which has the highest λ value (0.562-0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp(2) hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline-earth metal carbides to uncover their peculiar physical properties under extreme conditions.

  5. Pressure-induced superconductivity in CaC2

    PubMed Central

    Li, Yan-Ling; Luo, Wei; Zeng, Zhi; Lin, Hai-Qing; Mao, Ho-kwang; Ahuja, Rajeev

    2013-01-01

    Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp2-, and sp3-hybridized bonds. sp2-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2–105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron–phonon coupling λ in compressed CaC2 is found, in particular for Immm phase, which has the highest λ value (0.562–0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp2 hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline–earth metal carbides to uncover their peculiar physical properties under extreme conditions. PMID:23690580

  6. Aggregation of concentrated monoclonal antibody solutions studied by rheology and neutron scattering

    NASA Astrophysics Data System (ADS)

    Castellanos, Maria Monica; Pathak, Jai; Colby, Ralph

    2013-03-01

    Protein solutions are studied using rheology and scattering techniques to investigate aggregation. Here we present a monoclonal antibody (mAb) that aggregates after incubation at 40 °C (below its unfolding temperature), with a decrease in monomer purity of 6% in 10 days. The mAb solution contains surfactant and behaves as a Newtonian fluid when reconstituted into solution from the lyophilized form (before incubation at 40 °C). In contrast, mAb solutions incubated at 40 °C for 1 month exhibit shear yielding in torsional bulk rheometers. Interfacial rheology reveals that interfacial properties are controlled by the surfactant, producing a negligible surface contribution to the bulk yield stress. These results provide evidence that protein aggregates formed in the bulk are responsible for the yield stress. Small-angle neutron scattering (SANS) measurements show an increase in intensity at low wavevectors (q < 4*10-2 nm-1) that we attribute to protein aggregation, and is not observed in solutions stored at 4 °C for 3 days before the measurement. This work suggests a correlation between the aggregated state of the protein (stability) and the yield stress from rheology. Research funded by MedImmune

  7. Computer simulation of bridging flocculation processes: The role of colloid to polymer concentration ratio on aggregation kinetics

    SciTech Connect

    Stoll, S.; Buffle, J.

    1996-06-25

    The flocculation of colloidal particles by adsorbing polymers is one of the central issues of colloid science and a very important topic in many industrial, biological, and environmental processes. The authors report a computer simulation study of a 2- and 3-dimensional model for bridging flocculation between large linear polymer chains and comparatively small colloidal particles, where the structure and growth kinetics of cluster formation are investigated. This model was developed within the framework of the cluster-cluster aggregation model using mass and fractal dimension dependent diffusion constants, where bridging flocculation is seen as a case of heterocoagulation in which, in addition, macromolecule configurations and lengths play an important role. The simulation of aggregate structure and formation kinetics obtained at different (1) relative particle concentrations, (2) polymer chain conformations, and (3) sticking probabilities are described from a qualitatively and quantitative point of view. The results suggest that the formation of large aggregates is a slow process, controlled by the reactivity of the clusters, even when the reaction between microcolloids and macrochains is very fast. Aggregation kinetics are strongly dependent on the particle/chain concentration ratio and on the configurational properties of the chains. It is shown that the scaling laws which are valid for homocoagulation processes are also applicable to the kinetics of bridging flocculation. The corresponding scaling exponents have been calculated.

  8. Superfluid density of bulk CaC 6

    NASA Astrophysics Data System (ADS)

    Lamura, G.; Aurino, M.; Cifariello, G.; Di Gennaro, E.; Andreone, A.; Emery, N.; Hérold, C.; Marêché, J.-F.; Lagrange, P.

    2007-09-01

    The recent discovery of superconductivity at 11.5 K in the graphite intercalation compound (GIC) CaC6 has opened new perspectives in the physics of graphite. One of the main open questions for superconducting GICs is related to the nature of the pairing mechanism, since the possibility of an unconventional, excitonic or plasmonic, origin of superconductivity has also been invoked as an alternative to a simple electron-phonon interaction. To better understand the origin of pairing mechanism in these compounds, a first step is to determine the symmetry of the superconducting gap function and the nature of the elementary excitations. To this aim, we have performed the first high-resolution measurement of the in-plane magnetic penetration depth, λab(T), in a c-axis oriented polycrystalline CaC6 bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of λab(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields λab(0) = (720 ± 80) Å and Δ(0) = (1.79 ± 0.08) meV. The ratio 2Δ(0)/kBTC = (3.6 ± 0.2) gives therefore indication for a conventional weakly coupled superconductor. By using these results as fixed parameters, a BCS calculation on the superfluid density in the overall temperature range shows that the sample under test lies in the local dirty limit.

  9. [Palm oil derivatives with different concentration of palmitic acid and antioxidants. Effects upon plasmatic lipids and platelet aggregation].

    PubMed

    Scorza, T; Martucci, A; Torrealba de Ron, A T

    1999-03-01

    It was evaluated the effect of diet rich with cholesterol (0.1%) and different concentration of palmitic acid (16:0) and antioxidants (vitamin C, alpha tocopherol and retinol) upon plasmatic lipids and platelet aggregability in rabbits. The animals were distributed in three groups: I. Standard chow meal (Rp Conejarina) + cholesterol (chol) 0.1%; II. Standard chow meal + chol 0.1% + semipurified palm oil 10% (16:0 = 39.8%, oleic acid 48.7%, linoleic acid 11.4%, retinol 7.3 ug/dL, alpha tocopherol 157.6 ug/dL; III. Standard chow meal + chol 0.1% + crude palm oil 10% (16:0 = 45.3%, oleic acid 46.3%, linoleic acid 7.9%, retinol 96.4 ug/dL, alpha tocopherol 322.8 ug/dL). Monthly determination of plasmatic lipids were done (Enzymatic methods) and at ten months platelet aggregability with ADP, plasmatic vitamin C, retinol and, alpha tocopherol determination were done. Total plasmatic cholesterol (TC) and LDLc increased significantly in the three groups of animals. Significant differences between groups were not found. Platelet aggregability was lower in the animals fed with palmitic acid rich diet (groups II and III) (P = 0.002 and 0.001). Retinol, alpha tocopherol plasmatic concentrations revealed no significant differences. Vitamin C in the groups I was lower than groups II and III (P < 0.05 < 0.02). In this study hypercholesterolemic rabbits fed with rich diets (crude and semipurified) had lower platelet aggregability without changes in plasmatic lipids concentrations.

  10. Linking phase behavior and reversible colloidal aggregation at low concentrations: simulations and stochastic mean field theory.

    PubMed

    Puertas, Antonio M; Odriozola, Gerardo

    2007-05-24

    We have studied the link between the kinetics of clustering and the phase behavior of dilute colloids with short range attractions of moderate strength. This was done by means of computer simulations and a theoretical kinetic model originally developed to deal with reversible colloidal aggregation. Three different regions of the phase diagram were accessed. For weak attractions, a gas phase of small clusters in equilibrium forms in the system. For intermediate attractions, the system undergoes liquid-gas separation, which is signatured by the formation of a few large droplike aggregates, a gas phase of small clusters, and an overall kinetics where a few seeds succeed in explosively growing at long times, after a lag time. Finally, for very strong attractions, fractal unbreakable clusters form and grow following DLCA-like (diffusion limited cluster aggregation) kinetics; liquid-gas separation is prevented by the strength of the bonds, which do not allow restructuration. Good qualitative and quantitative agreement is found between the dynamic simulations and the kinetic model in all the three regions.

  11. Mercury concentrations in salmonids from western U.S. National Parks and relationships with age and macrophage aggregates.

    PubMed

    Schwindt, Adam R; Fournie, John W; Landers, Dixon H; Schreck, Carl B; Kent, Michael L

    2008-02-15

    Mercury accumulation in aquatic foodwebs and its effects on aquatic biota are of growing concern both for the health of the fish and the piscivores that prey upon them. This is of particular concern for western U.S. National Parks because it is known that mountainous and Arctic areas are sinks for some contaminants. The Western Airborne Contaminants Assessment Project seeks, in part, to ascertain mercury concentrations and evaluate effects of contaminants on biota in 14 lakes from 8 National Parks or Preserves. In this paper we report that mercury has accumulated to concentrations in troutthat may negatively impact some piscivorous wildlife, indicating potential terrestrial ecosystem effects. Additionally, we show that mercury concentrations increase with age in 4 species of trout, providing evidence of bioaccumulation. Finally, we demonstrate that mercury is associated with tissue damage in the kidney and spleen, as indicated by increases in macrophage aggregates. This finding suggests that mercury, and possibly other contaminants, are Macrophage aggregates suggests that mercury, a negatively affecting the trout that inhabit these remote and protected ecosystems. Our results indicate that mercury is indeed a concern for the U.S. National Parks, from an organismic and potentially an ecosystem perspective.

  12. An aggregate analysis of personal care products in the environment: Identifying the distribution of environmentally-relevant concentrations.

    PubMed

    Hopkins, Zachary R; Blaney, Lee

    2016-01-01

    Over the past 3-4 decades, per capita consumption of personal care products (PCPs) has steadily risen, resulting in increased discharge of the active and inactive ingredients present in these products into wastewater collection systems. PCPs comprise a long list of compounds employed in toothpaste, sunscreen, lotions, soaps, body washes, and insect repellants, among others. While comprehensive toxicological studies are not yet available, an increasing body of literature has shown that PCPs of all classes can impact aquatic wildlife, bacteria, and/or mammalian cells at low concentrations. Ongoing research efforts have identified PCPs in a variety of environmental compartments, including raw wastewater, wastewater effluent, surface water, wastewater solids, sediment, groundwater, and drinking water. Here, an aggregate analysis of over 5000 reported detections was conducted to better understand the distribution of environmentally-relevant PCP concentrations in, and between, these compartments. The distributions were used to identify whether aggregated environmentally-relevant concentration ranges intersected with available toxicity data. For raw wastewater, wastewater effluent, and surface water, a clear overlap was present between the 25th-75th percentiles and identified toxicity levels. This analysis suggests that improved wastewater treatment of antimicrobials, UV filters, and polycyclic musks is required to prevent negative impacts on aquatic species. PMID:27128715

  13. Uniquely localized intra-molecular amino acid concentrations at the glycolytic enzyme catalytic/active centers of Archaea, Bacteria and Eukaryota are associated with their proposed temporal appearances on earth.

    PubMed

    Pollack, J Dennis; Gerard, David; Pearl, Dennis K

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈ 16 % of all the most-conserved sites within a volume of ≈ 7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈ 25-30 % of all amino acids within an irregular volume bounded by ≈ 24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  14. Uniquely Localized Intra-Molecular Amino Acid Concentrations at the Glycolytic Enzyme Catalytic/Active Centers of Archaea, Bacteria and Eukaryota are Associated with Their Proposed Temporal Appearances on Earth

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Gerard, David; Pearl, Dennis K.

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈16 % of all the most-conserved sites within a volume of ≈7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈25-30 % of all amino acids within an irregular volume bounded by ≈24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  15. Effect of Temperature, Solvent and Precursor Concentration on Anti-Aggregation of ZnO Nanoparticles Prepared by Polyol Method.

    PubMed

    Shanmugaml, Sathish; Muthu, Kesavan; Subramanian, Balakumar

    2016-01-01

    We have investigated the formation mechanism of ZnO microspheres in polyol medium. The synthesis conditions have been varied with respect to temperature, medium and Zn-precursor concentration. The X-ray diffraction (XRD) and Raman spectroscopy result shows that the prepared ZnO nanoparticles are hexagonal wurtzite crystal structure and quite crystalline in nature. High resolution transmission electron microscopy (HRTEM) image indicates that the microsphere consists of aggregated nanoparticles in the range of 6 nm to 15 nm. The samples prepared in ethylene glycol medium shows a characteristic ether bond vibration mode in FTIR and it is additionally confirmed by NMR analysis. Initially, the nanoparticles are self-assembled into loosely packed microsphere and then the particles are densely packed by ether bonds formed between the glycol molecules adsorbed on adjacent particles which then grow as perfect microspheres. The sample prepared in EG medium at 150 °C did not show much aggregation. This study proposes the possible mechanism for the formation of ZnO microsphere. PMID:27398470

  16. Laboratory Detection and Pure Rotational Spectrum of the CaC Radical (X3Σ-)

    NASA Astrophysics Data System (ADS)

    Halfen, D. T.; Apponi, A. J.; Ziurys, L. M.

    2002-09-01

    The calcium carbide radical, CaC, has been observed in the laboratory for the first time using millimeter/submillimeter direct absorption spectroscopy. The species was created in the gas phase by the reaction of calcium vapor and methane under extreme DC discharge conditions. Eleven rotational transitions of CaC in its X3Σ- ground state were recorded in the frequency range 247-536 GHz. Each transition of CaC was found to consist of triplets due to fine-structure interactions that indicate that the ground state is 3Σ-, as opposed to 5Σ-, both of which have been suggested by theory. The data were analyzed in a Hund's case (b) basis, and rotational, spin-spin, and spin-rotation constants have been accurately determined. CaC may be detectable in circumstellar envelopes of asymptotic giant branch stars, in particular those that are carbon-rich.

  17. Mercury concentrations in salmonids from western U.S. National Parks and relationships with age and macrophage aggregates

    USGS Publications Warehouse

    Schwindt, A.R.; Fournie, J.W.; Landers, D.H.; Schreck, C.B.; Kent, M.L.

    2008-01-01

    Mercury accumulation in aquatic foodwebs and its effects on aquatic biota are of growing concern both for the health of the fish and the piscivores that prey upon them. This is of particular concern for western U.S. National Parks because it is known that mountainous and Arctic areas are sinks for some contaminants. The Western Airborne Contaminants Assessment Project seeks, in part, to ascertain mercury concentrations and evaluate effects of contaminants on biota in 14 lakes from 8 National Parks or Preserves. In this paper we report that mercury has accumulated to concentrations in trout that may negatively impact some piscivorous wildlife, indicating potential terrestrial ecosystem effects. Additionally, we show that mercury concentrations increase with age in 4 species of trout, providing evidence of bioaccumulation. Finally, we demonstrate that mercury is associated with tissue damage in the kidney and spleen, as indicated by increases in macrophage aggregates. This finding suggests that mercury, and possibly other contaminants, are negatively affecting the trout that inhabit these remote and protected ecosystems. Our results indicate that mercury is indeed a concern for the U.S. National Parks, from an organismic and potentially an ecosystem perspective. ?? 2008 American Chemical Society.

  18. Behavioral Responses of Plum Curculio (Coleoptera: Curculionidae) to Different Enantiomer Concentrations and Blends of the Synthetic Aggregation Pheromone Grandisoic Acid.

    PubMed

    Hock, Virginia; Chouinard, Gérald; Lucas, Éric; Cormier, Daniel; Leskey, Tracy C; Wright, Starker E; Zhang, Aijun; Pichette, André

    2015-04-01

    The plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important pest of fruit in North America. Males produce an aggregation pheromone (grandisoic acid) that attracts both sexes of the northern univoltine and the southern multivoltine strains. Grandisoic acid ((1R,2S)-1-methyl-2-(1-methylethenyl)-cyclobutaneacetic acid) is a chiral molecule containing one chiral center. A synthetic racemic mixture will contain two optical isomers that are mirror images of each other with equal amounts of (+)- and (-)-enantiomeric isomers. Male plum curculio only produce the (+) enantiomer. Some enantiomers can have antagonistic effects on the attraction of weevils to pheromones. An understanding of the effect of both enantiomers on the behaviour of plum curculio is needed to develop more efficient trap baits. Behavioural bioassays were conducted in a dual-choice still-air vertical olfactometer using a quantity of 1.5 ml of both (+) and (-) synthetic enantiomers and the racemic mixture of grandisoic acid with live female responders to determine which concentration and enantiomeric purity is the most attractive and if there is an antagonistic effect of the unnatural (-) enantiomer. Results indicated that plum curculio were attracted to low concentrations of the (+) enantiomer at 72% enantiomeric excess, but that strains were attracted to different concentrations of the (+) enantiomer (2×10(-7) mg/ml for univoltine, 2×10(-9) mg/ml for multivoltine).

  19. Behavioral Responses of Plum Curculio (Coleoptera: Curculionidae) to Different Enantiomer Concentrations and Blends of the Synthetic Aggregation Pheromone Grandisoic Acid.

    PubMed

    Hock, Virginia; Chouinard, Gérald; Lucas, Éric; Cormier, Daniel; Leskey, Tracy C; Wright, Starker E; Zhang, Aijun; Pichette, André

    2015-04-01

    The plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important pest of fruit in North America. Males produce an aggregation pheromone (grandisoic acid) that attracts both sexes of the northern univoltine and the southern multivoltine strains. Grandisoic acid ((1R,2S)-1-methyl-2-(1-methylethenyl)-cyclobutaneacetic acid) is a chiral molecule containing one chiral center. A synthetic racemic mixture will contain two optical isomers that are mirror images of each other with equal amounts of (+)- and (-)-enantiomeric isomers. Male plum curculio only produce the (+) enantiomer. Some enantiomers can have antagonistic effects on the attraction of weevils to pheromones. An understanding of the effect of both enantiomers on the behaviour of plum curculio is needed to develop more efficient trap baits. Behavioural bioassays were conducted in a dual-choice still-air vertical olfactometer using a quantity of 1.5 ml of both (+) and (-) synthetic enantiomers and the racemic mixture of grandisoic acid with live female responders to determine which concentration and enantiomeric purity is the most attractive and if there is an antagonistic effect of the unnatural (-) enantiomer. Results indicated that plum curculio were attracted to low concentrations of the (+) enantiomer at 72% enantiomeric excess, but that strains were attracted to different concentrations of the (+) enantiomer (2×10(-7) mg/ml for univoltine, 2×10(-9) mg/ml for multivoltine). PMID:26470165

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    sampling locations were selected based on the quantities of SOC from previous analysis (on samples collected at sites across the entire region). We chose the samples to encompass a wide range of SOC concentrations (1.2-7%) within each of six strongly contrasting soil parent material (PM) groups (sandstone, mudstone, clay, chalk, limestone and marine alluvium). The DR values (calculated using re-scaled size distributions for particle diameters < 500 µm) ranged from 17 to 151 µm. The co-efficient of variation for DR analyses using fourteen aliquots of the RM was reasonably small (21 %). The PM groups accounted for a larger proportion of the variation in DR than SOC concentrations; together they accounted for around 50% of the variation in DR values. There was no evidence to include an interaction term between PM and SOC concentration. The proportion of clay-sized particles in the material after sonication was not a statistically significant predictor of DR. Pre-wetting the aggregates typically resulted in substantially smaller values of DR by comparison to using air-dried aggregates in our test. We suggest that the effects of differential clay swelling as a disruptive force during the wetting stage are greater than those associated with slaking (fragmentation due to trapped air). We believe this rapid (duration after the wetting procedure is 10 minutes), reproducible test could could be an effective means to monitor changes in this important soil property and improve predictions of soil erosion. Reference: Rawlins, B. G., Wragg, J. & Lark, R. M. 2012. Application of a novel method for soil aggregate stability measurement by laser granulometry with sonication. European Journal of Soil Science, 64, 92-103.

  1. TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability.

    PubMed

    Loosli, Frédéric; Le Coustumer, Philippe; Stoll, Serge

    2013-10-15

    The behavior of manufactured TiO2 nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO2 nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO2 nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO2 nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO2 nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO2 nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO2 nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO2 nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO2 nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO2 nanoparticles.

  2. Anamorelin hydrochloride for the treatment of cancer-anorexia-cachexia (CACS) in nonsmall cell lung cancer

    PubMed Central

    Zhang, Hongjie; Garcia, Jose M

    2015-01-01

    Introduction Cancer anorexia-cachexia syndrome (CACS) is associated with increased morbidity and mortality. Anamorelin is a novel, orally active ghrelin receptor agonist in clinical development for the treatment of CACS in non-small cell lung cancer (NSCLC). The aim of this review is to summarize preclinical and clinical studies evaluating anamorelin as a potential promising treatment for CACS in NSCLC. Area covered Pharmacodynamics, pharmacokinetics and metabolism, clinical efficacy, safety, and tolerability of anamorelin for the treatment of CACS in NSCLC were reviewed. Anamorelin administration may lead to increases in food intake, body weight and lean body mass, and a stimulatory effect on GH secretion in NSCLC patients. Anamorelin is well tolerated with no dose-limiting toxicities identified to date. Expert opinion Targeting ghrelin receptors presents the advantage of potentially addressing multiple mechanisms of CACS simultaneously including appetite, muscle protein balance, adipose tissue metabolism, energy expenditure and inflammation. Clinical data suggest that anamorelin is well tolerated and it effectively increases appetite, body weight and lean mass in patients with advanced NSCLC. Long-term safety remains unknown at this time. The potential synergistic effects of anamorelin with nutritional support or exercise as well as its efficacy/safety in other tumor types are also unknown. PMID:25945893

  3. Linear and nonlinear electrodynamic responses of bulk CaC6 in the microwave regime

    NASA Astrophysics Data System (ADS)

    Andreone, A.; Cifariello, G.; Di Gennaro, E.; Lamura, G.; Emery, N.; Hérold, C.; Marêché, J. F.; Lagrange, P.

    2007-08-01

    The linear and nonlinear responses to a microwave electromagnetic field of two c-axis oriented polycrystalline samples of the recently discovered superconductor CaC6 (TC≈11.5K ) is studied in the superconducting state down to 2K. The surface resistance RS and the third order intermodulation distortion, arising from a two-tone excitation, have been measured as a function of temperature and microwave circulating power. Experiments are carried out using a dielectrically loaded copper cavity operating at 7GHz in a "hot finger" configuration. The results confirm recent experimental findings that CaC6 behaves as a weakly coupled, fully gapped, superconductor.

  4. Viral Lysis of Cells Influences The Concentration and Compostion of Dissolved Organic Matter and The Formation of Organic Aggregates (marine Snow)

    NASA Astrophysics Data System (ADS)

    Weinbauer, M. G.; Peduzzi, P.

    The effect of moderately (ca. 2.5 fold) increasing the concentration of the virus-size fraction (VSF) of seawater on the chemical composition of the dissolved organic mat- ter (DOM) pool during the formation of organic aggregates (marine snow) was tested experimentally with seawater samples collected in the Northern Adriatic Sea. The VSF enrichment did not significantly change the concentration of selected DOM com- pounds, whereas viral abundance was ca. 2-fold higher. During long-term experiments (40 - 200 hrs), bacterial abundance was on average 25% lower in the VSF amended than in the control incubations, and the frequency of visibly infected cells was stimu- lated by ca. 50%. VSF delayed the development of phytoplankton blooms (diatoms), but in the end of the experiments, Chl a concentrations in the VSF amended incuba- tions exceeded those in the control incubations. The VSF enrichment caused an enrich- ment of Serine and Threonine in the dissolved hydrolysable amino acid (AA) fraction indicative of viral lysis of diatoms. Bulk dissolved free AA acid and monomeric car- bohydrate (CHO) concentrations were repressed, whereas bulk dissolved hydrolysable AA and CHO concentrations were stimulated in the VSF enriched incubations. Viral lysis was likely the major reason for the stimulation of hydrolysable DOM. The for- mation of organic aggregates was repressed by the VSF enrichment, but the aggregates were larger and more persistent in the VSF amended than in the control incubations. Stimulation of hydrolysable DOM and sticky viral lysis products might be the reason for the larger and more persistent aggregates. This demonstrates that bioactive mate- rial in the VSF of seawater can have major implications for primary production and the cycling of organic carbon in the ocean.

  5. Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6.

    PubMed

    Li, Yan-Ling; Luo, Wei; Chen, Xiao-Jia; Zeng, Zhi; Lin, Hai-Qing; Ahuja, Rajeev

    2013-11-26

    Pressure can tune material's electronic properties and control its quantum state, making some systems present disconnected superconducting region as observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6 superconductor (Tc of 11.5 K), applying pressure first Tc increases and then suppresses and the superconductivity of this compound is eventually disappeared at about 18 GPa. Here, we report a theoretical finding of the re-emergence of superconductivity in heavily compressed CaC6. The predicted phase III (space group Pmmn) with formation of carbon nanofoam is found to be stable at wide pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has bad metallic behavior, indicating again departure from superconductivity. Re-emerged superconductivity in compressed CaC6 paves a new way to design new-type superconductor by inserting metal into nanoporous host lattice.

  6. Practical Issues in Estimating Classification Accuracy and Consistency with R Package cacIRT

    ERIC Educational Resources Information Center

    Lathrop, Quinn N.

    2015-01-01

    There are two main lines of research in estimating classification accuracy (CA) and classification consistency (CC) under Item Response Theory (IRT). The R package cacIRT provides computer implementations of both approaches in an accessible and unified framework. Even with available implementations, there remains decisions a researcher faces when…

  7. Behavioral responses of plum curculio (Coleoptera: Curculionidae) to different enantiomer concentrations and blends of the synthetic aggregation pheromone grandisoic acid

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Host plant odors are important for insect location of food and mates. Synergy between host plant odors and aggregation pheromones occurs in many Curculionidae species. The plum curculio Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) is a major pest of pome and stone fruit. Males produce t...

  8. Interlayer-state-driven superconductivity in CaC6 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kyung, Wonshik; Kim, Yeongkwan; Han, Garam; Leem, Choonshik; Kim, Chul; Koh, Yoonyoung; Kim, Beomyoung; Kim, Youngwook; Kim, Jun Sung; Kim, Keun Su; Rotenberg, Eli; Denlinger, Jonathan D.; Kim, Changyoung

    2015-12-01

    We performed angle-resolved photoemission experiments on CaC6 and measured kz-dependent electronic structures to investigate the interlayer states. The results reveal a spherical interlayer Fermi surface centered at the Γ point. We also find that the graphene-driven band possesses a weak kz dispersion. The overall electronic structure shows a peculiar single-graphene-layer periodicity in the kz direction although the CaC6 unit cell is supposed to contain three graphene layers. This suggests that the c -axis ordering of Ca has little effect on the electronic structure of CaC6. In addition to CaC6, we also studied the a low-temperature superconductor BaC6. For BaC6, the graphene-band Dirac-point energy is smaller than that of CaC6. Based on data from CaC6 and BaC6, we rule out the Cx y phonon mode as the origin of the superconductivity in CaC6, which strongly suggests interlayer-state-driven superconductivity.

  9. Corrosion of aluminium metal in OPC- and CAC-based cement matrices

    SciTech Connect

    Kinoshita, Hajime; Swift, Paul; Utton, Claire; Carro-Mateo, Beatriz; Collier, Nick; Milestone, Neil

    2013-08-15

    Corrosion of aluminium metal in ordinary Portland cement (OPC) based pastes produces hydrogen gas and expansive reaction products causing problems for the encapsulation of aluminium containing nuclear wastes. Although corrosion of aluminium in cements has been long known, the extent of aluminium corrosion in the cement matrices and effects of such reaction on the cement phases are not well established. The present study investigates the corrosion reaction of aluminium in OPC, OPC-blast furnace slag (BFS) and calcium aluminate cement (CAC) based systems. The total amount of aluminium able to corrode in an OPC and 4:1 BFS:OPC system was determined, and the correlation between the amount of calcium hydroxide in the system and the reaction of aluminium obtained. It was also shown that a CAC-based system could offer a potential matrix to incorporate aluminium metal with a further reduction of pH by introduction of phosphate, producing a calcium phosphate cement.

  10. Impact of The Protective Renin-Angiotensin System (RAS) on The Vasoreparative Function of CD34+ CACs in Diabetic Retinopathy

    NASA Technical Reports Server (NTRS)

    Duan, Yaqian; Moldovan, Leni; Miller, Rehae C.; Beli, Eleni; Salazar, Tatiana; Hazra, Sugata; Al-Sabah, Jude; Chalam, KV; Raghunandan, Sneha; Vyas, Ruchi; Parsons-Wingerter, Patricia; Oudit, Gavin Y.; Grant, Maria B.

    2016-01-01

    Purpose: In diabetes, the impaired vasoreparative function of Circulating Angiogenic Cells (CACs) is believed to contribute to the progression of diabetic retinopathy (DR). Accumulating evidence suggests that the protective arm of renin-angiotensin system (RAS) ACE2 Angiotensin-(1-7) Mas plays an important role in restoring the function of diabetic CACs. We examined the protective RAS in CACs in diabetic individuals with different stages of retinopathy. Methods: Study subjects (n43) were recruited as controls or diabetics with either no DR, mild non-proliferative DR (NPDR), moderate NPDR, severe NPDR or proliferative DR (PDR). Fundus photography and fluorescein angiograms were analyzed using Vessel Generation Analysis (VESGEN) software in a cohort of subjects. CD34+ CACs were isolated from peripheral blood of diabetics and control subjects. RAS gene expressions in CACs were measured by qPCR. The vasoreparative function of CACs was assessed by migration ability toward CXCL12 using the QCM 5M 96-well chemotaxis cell migration assay. Results: ACE2 gene is a key enzyme converting the deleterious Angiotensin II to the beneficial Angiotensin-(1-7). ACE2 expression in CACs from diabetic subjects without DR was increased compared to controls, suggestive of compensation (p0.0437). The expression of Mas (Angiotensin-(1-7) receptor) in CACs was also increased in diabetics without DR, while was reduced in NPDR compared to controls (p0.0002), indicating a possible loss of compensation of the protective RAS at this stage of DR. The presence of even mild NPDR was associated with CD34+ CAC migratory dysfunction. When pretreating CACs of DR subjects with Angiotensin-(1-7), migratory ability to a chemoattractant CXCL12 was restored (p0.0008). By VESGEN analysis, an increase in small vessel density was observed in NPDR subjects when compared with the controls. Conclusions: These data suggest the protective RAS axis within diabetic CACs may help maintain their vasoreparative potential

  11. Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure

    NASA Astrophysics Data System (ADS)

    Nylén, Johanna; Konar, Sumit; Lazor, Peter; Benson, Daryn; Häussermann, Ulrich

    2012-12-01

    The effects of high pressure (up to 30 GPa) on the structural properties of lithium and calcium carbide, Li2C2 and CaC2, were studied at room temperature by Raman spectroscopy in a diamond anvil cell. Both carbides consist of C2 dumbbells which are coordinated by metal atoms. At standard pressure and temperature two forms of CaC2 co-exist. Monoclinic CaC2-II is not stable at pressures above 2 GPa and tetragonal CaC2-I possibly undergoes a minor structural change between 10 and 12 GPa. Orthorhombic Li2C2 transforms to a new structure type at around 15 GPa. At pressures above 18 GPa (CaC2) and 25 GPa (Li2C2) Raman spectra become featureless, and remain featureless upon decompression which suggests an irreversible amorphization of the acetylide carbides. First principles calculations were used to analyze the pressure dependence of Raman mode frequencies and structural stability of Li2C2 and CaC2. A structure model for the high pressure phase of Li2C2 was searched by applying an evolutionary algorithm.

  12. Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure.

    PubMed

    Nylén, Johanna; Konar, Sumit; Lazor, Peter; Benson, Daryn; Häussermann, Ulrich

    2012-12-14

    The effects of high pressure (up to 30 GPa) on the structural properties of lithium and calcium carbide, Li(2)C(2) and CaC(2), were studied at room temperature by Raman spectroscopy in a diamond anvil cell. Both carbides consist of C(2) dumbbells which are coordinated by metal atoms. At standard pressure and temperature two forms of CaC(2) co-exist. Monoclinic CaC(2)-II is not stable at pressures above 2 GPa and tetragonal CaC(2)-I possibly undergoes a minor structural change between 10 and 12 GPa. Orthorhombic Li(2)C(2) transforms to a new structure type at around 15 GPa. At pressures above 18 GPa (CaC(2)) and 25 GPa (Li(2)C(2)) Raman spectra become featureless, and remain featureless upon decompression which suggests an irreversible amorphization of the acetylide carbides. First principles calculations were used to analyze the pressure dependence of Raman mode frequencies and structural stability of Li(2)C(2) and CaC(2). A structure model for the high pressure phase of Li(2)C(2) was searched by applying an evolutionary algorithm.

  13. Cryptococcus neoformans senses CO2 through the carbonic anhydrase Can2 and the adenylyl cyclase Cac1.

    PubMed

    Mogensen, Estelle Geweiss; Janbon, Guilhem; Chaloupka, James; Steegborn, Clemens; Fu, Man Shun; Moyrand, Frédérique; Klengel, Torsten; Pearson, David S; Geeves, Michael A; Buck, Jochen; Levin, Lonny R; Mühlschlegel, Fritz A

    2006-01-01

    Cryptococcus neoformans, a fungal pathogen of humans, causes fatal meningitis in immunocompromised patients. Its virulence is mainly determined by the elaboration of a polysaccharide capsule surrounding its cell wall. During its life, C. neoformans is confronted with and responds to dramatic variations in CO2 concentrations; one important morphological change triggered by the shift from its natural habitat (0.033% CO2) to infected hosts (5% CO2) is the induction of capsule biosynthesis. In cells, CO2 is hydrated to bicarbonate in a spontaneous reaction that is accelerated by carbonic anhydrases. Here we show that C. neoformans contains two beta-class carbonic anhydrases, Can1 and Can2. We further demonstrate that CAN2, but not CAN1, is abundantly expressed and essential for the growth of C. neoformans in its natural environment, where CO2 concentrations are limiting. Structural studies reveal that Can2 forms a homodimer in solution. Our data reveal Can2 to be the main carbonic anhydrase and suggest a physiological role for bicarbonate during C. neoformans growth. Bicarbonate directly activates the C. neoformans Cac1 adenylyl cyclase required for capsule synthesis. We show that this specific activation is optimal at physiological pH. PMID:16400172

  14. The Association Between Serum Magnesium Concentrations and Coronary Artery Calcification Scores in Astronauts

    NASA Technical Reports Server (NTRS)

    Betcher, Jenna; Zwart, Sara; Smith, Scott M.

    2016-01-01

    Magnesium is a natural calcium antagonist, and is inversely associated with coronary heart disease, cardiovascular mortality rates, and vascular calcification. Coronary artery calcification score is a tool used to evaluate the prognosis of coronary artery disease in individuals. Higher magnesium intake is associated with lower coronary artery calcification scores (CACS), and recent studies have found a significant inverse relationship between serum magnesium concentrations and CACS in Korean and Mexican-mestizo populations. The correlation between serum magnesium concentrations and CACS is not well researched, so our aim was to examine this relationship in astronauts. We found that a higher serum magnesium concentration is significantly related to a higher coronary artery calcification score (p=.0217), and that there is a significant difference in magnesium concentrations of subjects who have a CACS greater than 100 and a CACS less than 100.

  15. Impact of short range hydrophobic interactions and long range electrostatic forces on the aggregation kinetics of a monoclonal antibody and a dual-variable domain immunoglobulin at low and high concentrations.

    PubMed

    Kumar, Vineet; Dixit, Nitin; Zhou, Liqiang Lisa; Fraunhofer, Wolfgang

    2011-12-12

    The purpose of this work was to determine the nature of long and short-range forces governing protein aggregation kinetics at low and high concentrations for a monoclonal antibody (IgG1) and a dual-variable-domain immunoglobulin (DVD-Ig). Protein-protein interactions (PPI) were studied under dilute conditions by utilizing the methods of static (B(22)) and dynamic light scattering (k(D)). PPI in solutions containing minimal ionic strengths were characterized to get detailed insights into the impact of ionic strength on aggregation. Microcalorimetry and susceptibility to denature at air-liquid interface were used to assess the tertiary structure and quiescent stability studies were conducted to study aggregation characteristics. Results for IgG1 showed that electrostatic interactions governed protein aggregation kinetics both under dilute and concentrated conditions (i.e., 5 mg/mL and 150 mg/mL). For DVD-Ig molecules, on the other hand, although electrostatic interactions governed protein aggregation under dilute conditions, hydrophobic forces clearly determined the kinetics at high concentrations. This manuscript shows for the first time that short-range hydrophobic interactions can outweigh electrostatic forces and play an important role in determining protein aggregation at high concentrations. Additionally, results show that although higher-order virial coefficients become significant under low ionic strength conditions, removal of added charges may be used to enhance the aggregation stability of dilute protein formulations.

  16. Experimental Evidence of s-Wave Superconductivity in Bulk CaC6

    NASA Astrophysics Data System (ADS)

    Lamura, G.; Aurino, M.; Cifariello, G.; di Gennaro, E.; Andreone, A.; Emery, N.; Hérold, C.; Marêché, J.-F.; Lagrange, P.

    2006-03-01

    The temperature dependence of the in-plane magnetic penetration depth, λab(T), has been measured in a c-axis oriented polycrystalline CaC6 bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of λab(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields λab(0)=(720±80)Å and Δ(0)=(1.79±0.08)meV. The ratio 2Δ(0)/kBTc=(3.6±0.2) gives indication for a weakly coupled superconductor.

  17. Partial least squares regression for linking aggregate pore characteristics to the detachment of undisturbed soil by simulating concentrated flow in Ultisols (subtropical China)

    NASA Astrophysics Data System (ADS)

    Ma, Renming; Cai, Chongfa; Wang, Junguang; Wang, Tianwei; Li, Zhaoxia; Xiao, Tiqiao; Peng, Guanyun

    2015-05-01

    Soil pores are known as an effective medium for water, air, and chemical movement. However, quantifying pore structures and their relationship to the detachment of undisturbed soil by concentrated flow is not fully understood. The objectives of this study were to quantify 3D aggregate microstructures using synchrotron-based high-resolution X-ray micro-computed tomography (SR-μCT) under wetting and drying cycles and to investigate the effects of pore characteristics on the detachment of undisturbed soil by simulating concentrated flow. The detachment rates (Dr) of undisturbed topsoil samples, which were subjected to a pretreatment of zero to eleven wetting and drying cycles, were measured in a 3.8-m-long, 0.2-m-wide hydraulic flume under unitary flow shear stresses (τ = 14.49 Pa); 3-5 mm aggregates were collected from the pretreatment soils, which were subjected to zero, five, and eleven wetting and drying cycles and were scanned at a 3.7 μm voxel-resolution for reconstructing three-dimensional microtomography images. The relationships among pore characteristics and Dr were analyzed using partial least squares regression (PLSR). The results indicated that Dr and the aggregate microstructure changed significantly after the wetting and drying cycles. Dr was closely associated with the pore characteristics. The pore characteristics, such as a >100 μm porosity, total porosity, fraction of regular pores, 30-75 μm porosity, fraction of elongated pores, and fraction of irregular pores, were identified as the primary parameters that control the Dr. The pore characteristics and clay content could account for as much as 68.2% of the variation in Dr. Dr was significantly and positively related to a >100 μm porosity, total porosity, and fraction of elongated pores. Thus, soil fragmentation depended on microcracks that formed during the wetting and drying cycles and on the geometrical characteristics of the pores or cracks. The results from this study provide a

  18. Constraints on compaction rate and equilibrium in the pressure solution creep of quartz aggregates and fractures: Controls of aqueous concentration

    NASA Astrophysics Data System (ADS)

    Taron, Joshua; Elsworth, Derek

    2010-07-01

    A relationship is developed to examine dissolution precipitation creep in crustal rocks with implicit coupling of the dissolution-diffusion-precipitation system and without requiring the iterative solution of a linear equation system. Implicit control is maintained over aqueous silica concentrations within hydrated solid contacts and in open pore space. For arbitrary conditions of temperature, pressure, and mechanical stress, the simple equation system conforms to a polynomial solution for aqueous concentrations set within a small iterative compaction scheme. Equilibrium (long-term) pressure solution compaction, previously ill constrained, is explored with two alternate methods: (1) a modified form of critical stress and (2) rate-controlled growth of diffusion limiting cement at the periphery of solid contacts. Predictions are compared to previous experimental results that allow compaction equilibrium to be achieved. Only the modified critical stress is capable of reproducing these results. In this case the agreement is strong across a range of conditions (400°C-500°C, 20-150 MPa, and 3-120 μm mean particle diameter). Compaction rates are overestimated in very early times in a manner suggesting the importance of plastic flow during this period. Predictions are also compared to concentration independent simplifications at general conditions of 350°C and 50 MPa. Compared to the implicit coupling, these methods represent the mean behavior, slightly underestimating rates in dissolution control and slightly overestimating in diffusion control. Aqueous concentration is influential in either regime. The solution is applicable to open and closed systems, is extended to systems with boundary influx, and may be applied to granular media or fractures, differing only in the method defining evolving contact geometry.

  19. Targeted deletion of Kif18a protects from colitis-associated colorectal (CAC) tumors in mice through impairing Akt phosphorylation

    SciTech Connect

    Zhu, Houbao; Xu, Wangyang; Zhang, Hongxin; Liu, Jianbing; Xu, Haimin; Lu, Shunyuan; Dang, Suying; Kuang, Ying; Jin, Xiaolong; Wang, Zhugang

    2013-08-16

    Highlights: •Kif18A is up-regulated in CAC of mouse model. •Kif18a{sup −/−} mice are protected from CAC. •Tumor cells from Kif18a{sup −/−} mice undergo more apoptosis. •Kif18A deficiency induces poor Atk phosphorylation. -- Abstract: Kinesins are a superfamily of molecular motors involved in cell division or intracellular transport. They are becoming important targets for chemotherapeutic intervention of cancer due to their crucial role in mitosis. Here, we demonstrate that the kinesin-8 Kif18a is overexpressed in murine CAC and is a crucial promoter during early CAC carcinogenesis. Kif18a-deficient mice are evidently protected from AOM–DSS-induced colon carcinogenesis. Kif18A is responsible for proliferation of colonic tumor cells, while Kif18a ablation in mice promotes cell apoptosis. Mechanistically, Kif18a is responsible for induction of Akt phosphorylation, which is known to be associated with cell survival regulation. In conclusion, Kif18a is critical for colorectal carcinogenesis in the setting of inflammation by mechanisms of increased PI3K-AKT signaling. Inhibition of Kif18A activity may be useful in the prevention or chemotherapeutic intervention of CAC.

  20. Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

    NASA Astrophysics Data System (ADS)

    Ali, Anwar; Tasneem, Shadma; Bidhuri, Priyanka; Bhushan, Vidiksha; Malik, Nisar Ahmad

    2012-12-01

    Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (β) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (Δ G {m/°}, Δ H {m/°}, and Δ S {m/°}) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, ( V ϕ), apparent molar volumes at infinite dilution, ( V {ϕ/°}), apparent molar compressibilities, ( K ϕ), of HTAB in the pre- and post-micellar regions, and volume change on micellization (Δ V {ϕ/ m }) were also estimated. Large positive values of TΔ S {m/°} and small negative values of Δ H {m/°} suggest that micellization process is driven primarily by entropy increase. The increase in Δ V {ϕ/ m } and K ϕ with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.

  1. CDC28 phosphorylates Cac1p and regulates the association of chromatin assembly factor I with chromatin.

    PubMed

    Jeffery, Daniel C B; Kakusho, Naoko; You, Zhiying; Gharib, Marlene; Wyse, Brandon; Drury, Erin; Weinreich, Michael; Thibault, Pierre; Verreault, Alain; Masai, Hisao; Yankulov, Krassimir

    2015-01-01

    Chromatin Assembly Factor I (CAF-I) plays a key role in the replication-coupled assembly of nucleosomes. It is expected that its function is linked to the regulation of the cell cycle, but little detail is available. Current models suggest that CAF-I is recruited to replication forks and to chromatin via an interaction between its Cac1p subunit and the replication sliding clamp, PCNA, and that this interaction is stimulated by the kinase CDC7. Here we show that another kinase, CDC28, phosphorylates Cac1p on serines 94 and 515 in early S phase and regulates its association with chromatin, but not its association with PCNA. Mutations in the Cac1p-phosphorylation sites of CDC28 but not of CDC7 substantially reduce the in vivo phosphorylation of Cac1p. However, mutations in the putative CDC7 target sites on Cac1p reduce its stability. The association of CAF-I with chromatin is impaired in a cdc28-1 mutant and to a lesser extent in a cdc7-1 mutant. In addition, mutations in the Cac1p-phosphorylation sites by both CDC28 and CDC7 reduce gene silencing at the telomeres. We propose that this phosphorylation represents a regulatory step in the recruitment of CAF-I to chromatin in early S phase that is distinct from the association of CAF-I with PCNA. Hence, we implicate CDC28 in the regulation of chromatin reassembly during DNA replication. These findings provide novel mechanistic insights on the links between cell-cycle regulation, DNA replication and chromatin reassembly.

  2. CDC28 phosphorylates Cac1p and regulates the association of chromatin assembly factor i with chromatin

    PubMed Central

    Jeffery, Daniel CB; Kakusho, Naoko; You, Zhiying; Gharib, Marlene; Wyse, Brandon; Drury, Erin; Weinreich, Michael; Thibault, Pierre; Verreault, Alain; Masai, Hisao; Yankulov, Krassimir

    2015-01-01

    Chromatin Assembly Factor I (CAF-I) plays a key role in the replication-coupled assembly of nucleosomes. It is expected that its function is linked to the regulation of the cell cycle, but little detail is available. Current models suggest that CAF-I is recruited to replication forks and to chromatin via an interaction between its Cac1p subunit and the replication sliding clamp, PCNA, and that this interaction is stimulated by the kinase CDC7. Here we show that another kinase, CDC28, phosphorylates Cac1p on serines 94 and 515 in early S phase and regulates its association with chromatin, but not its association with PCNA. Mutations in the Cac1p-phosphorylation sites of CDC28 but not of CDC7 substantially reduce the in vivo phosphorylation of Cac1p. However, mutations in the putative CDC7 target sites on Cac1p reduce its stability. The association of CAF-I with chromatin is impaired in a cdc28–1 mutant and to a lesser extent in a cdc7–1 mutant. In addition, mutations in the Cac1p-phosphorylation sites by both CDC28 and CDC7 reduce gene silencing at the telomeres. We propose that this phosphorylation represents a regulatory step in the recruitment of CAF-I to chromatin in early S phase that is distinct from the association of CAF-I with PCNA. Hence, we implicate CDC28 in the regulation of chromatin reassembly during DNA replication. These findings provide novel mechanistic insights on the links between cell-cycle regulation, DNA replication and chromatin reassembly. PMID:25602519

  3. Shotcrete -- Understanding of the hydration process of mixes containing CAC and Portland cement and proposal for a simple rheological characterization

    SciTech Connect

    Bayoux, J.P.; Testud, M.; Guinot, D.; Willocq, J.; Capmas, A.

    1995-12-31

    In order to better understand the performances of CAC-slag cement and CAC--PC cement the hydration study of these mixes was undertaken. The hydrates which are responsible for the early stiffening/strengthening are identical in both mixes; it is only the time of appearance and amount which varies. Ettringite always forms first followed by the precipitation of C{sub 4}AH{sub 13}. They will both form faster then the temperature rises. As a complement, a simple laboratory equipment is proposed to characterize the stiffening behavior of the mixes straight after gauging.

  4. Charge density waves in the graphene sheets of the superconductor CaC(6).

    PubMed

    Rahnejat, K C; Howard, C A; Shuttleworth, N E; Schofield, S R; Iwaya, K; Hirjibehedin, C F; Renner, Ch; Aeppli, G; Ellerby, M

    2011-01-01

    Graphitic systems have an electronic structure that can be readily manipulated through electrostatic or chemical doping, resulting in a rich variety of electronic ground states. Here we report the first observation and characterization of electronic stripes in the highly electron-doped graphitic superconductor, CaC(6), by scanning tunnelling microscopy and spectroscopy. The stripes correspond to a charge density wave with a period three times that of the Ca superlattice. Although the positions of the Ca intercalants are modulated, no displacements of the carbon lattice are detected, indicating that the graphene sheets host the ideal charge density wave. This provides an exceptionally simple material-graphene-as a starting point for understanding the relation between stripes and superconductivity. Furthermore, our experiments suggest a strategy to search for superconductivity in graphene, namely in the vicinity of striped 'Wigner crystal' phases, where some of the electrons crystallize to form a superlattice. PMID:22127054

  5. Theoretical estimation of the critical packing parameter of amphiphilic self-assembled aggregates

    NASA Astrophysics Data System (ADS)

    Khalil, Rabah A.; Zarari, Al-hakam A.

    2014-11-01

    The estimating of critical packing parameter (p) of amphiphilic compounds is considered as a hypothetical rather than an empirical. Consequently, an attempt has been made for determining such a dimensionless parameter for homologous series of sodium p-n-alkyl benzoates (n = 0-8) hydrotropes using quantum mechanical calculations that depend on density functional theory (DFT). The calculations were based on the following well-defined model, p = v/a0lc, where v is the volume of the hydrotrope tail, a0 is the effective head group area and lc is the length of the extended hydrotrope tail. It was found that the magnitude of both v and lc parameters can be estimated directly from quantum mechanical calculations. While the investigations found that the a0 parameter is parallel to the Connolly solvent accessible surface area (Csa) which could also be determined through theoretical computations. The obtained results were in good agreement with published data using small angle neutron scattering (SANS) technique. Hence, the theoretical model for predicting p of amphiphilic at critical micelle- or aggregation-concentration (cmc or cac) is p = v/Csalc. An apparent success was observed through applying this simple model to some randomly selected surfactants. It has been concluded that the theoretical calculations that based on quantum mechanical (DFT) method can be considered as a powerful tool for estimating the critical packing parameter of amphiphilic molecules. Finally, the results strongly suggest the employment of the presented model for estimating p of amphiphilic molecules at cmc or cac by computational chemistry software.

  6. The Cac1 subunit of histone chaperone CAF-1 organizes CAF-1-H3/H4 architecture and tetramerizes histones

    PubMed Central

    Liu, Wallace H; Roemer, Sarah C; Zhou, Yeyun; Shen, Zih-Jie; Dennehey, Briana K; Balsbaugh, Jeremy L; Liddle, Jennifer C; Nemkov, Travis; Ahn, Natalie G; Hansen, Kirk C; Tyler, Jessica K; Churchill, Mair EA

    2016-01-01

    The histone chaperone Chromatin Assembly Factor 1 (CAF-1) deposits tetrameric (H3/H4)2 histones onto newly-synthesized DNA during DNA replication. To understand the mechanism of the tri-subunit CAF-1 complex in this process, we investigated the protein-protein interactions within the CAF-1-H3/H4 architecture using biophysical and biochemical approaches. Hydrogen/deuterium exchange and chemical cross-linking coupled to mass spectrometry reveal interactions that are essential for CAF-1 function in budding yeast, and importantly indicate that the Cac1 subunit functions as a scaffold within the CAF-1-H3/H4 complex. Cac1 alone not only binds H3/H4 with high affinity, but also promotes histone tetramerization independent of the other subunits. Moreover, we identify a minimal region in the C-terminus of Cac1, including the structured winged helix domain and glutamate/aspartate-rich domain, which is sufficient to induce (H3/H4)2 tetramerization. These findings reveal a key role of Cac1 in histone tetramerization, providing a new model for CAF-1-H3/H4 architecture and function during eukaryotic replication. DOI: http://dx.doi.org/10.7554/eLife.18023.001 PMID:27690308

  7. 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.

  8. Superconducting graphene sheets in CaC6 enabled by phonon-mediated interband interactions

    PubMed Central

    Yang, S.-L.; Sobota, J. A.; Howard, C. A.; Pickard, C. J.; Hashimoto, M.; Lu, D. H.; Mo, S.-K.; Kirchmann, P. S.; Shen, Z.-X.

    2014-01-01

    There is a great deal of fundamental and practical interest in the possibility of inducing superconductivity in a monolayer of graphene. But while bulk graphite can be made to superconduct when certain metal atoms are intercalated between its graphene sheets, the same has not been achieved in a single layer. Moreover, there is a considerable debate about the precise mechanism of superconductivity in intercalated graphite. Here we report angle-resolved photoelectron spectroscopy measurements of the superconducting graphite intercalation compound CaC6 that distinctly resolve both its intercalant-derived interlayer band and its graphene-derived π* band. Our results indicate the opening of a superconducting gap in the π* band and reveal a substantial contribution to the total electron–phonon-coupling strength from the π*-interlayer interband interaction. Combined with theoretical predictions, these results provide a complete account for the superconducting mechanism in graphite intercalation compounds and lend support to the idea of realizing superconducting graphene by creating an adatom superlattice. PMID:24651261

  9. CACUL1/CAC1 Regulates the Antioxidant Response by Stabilizing Nrf2

    PubMed Central

    Kigoshi, Yu; Fukuda, Tomomi; Endo, Tomoyuki; Hayasaka, Nami; Iemura, Shun-ichiro; Natsume, Toru; Tsuruta, Fuminori; Chiba, Tomoki

    2015-01-01

    Nrf2 is the pre-dominant transcription activator responsible for coordinated up-regulation of ARE-driven antioxidant and detoxification genes. The activity of Nrf2 is tightly regulated at basal levels through its ubiquitination by Cul3-Keap1 and consequential degradation. Upon exposure to stress, the Cul3-Keap1 ligase is inhibited, leading to Nrf2 stabilization and activation. Here we describe CACUL1/CAC1 as a positive regulator of the Nrf2 pathway. We found that CACUL1 is up-regulated by Nrf2-activating oxidative stresses in cells and in mice. The association of CACUL1 with the Cul3-Keap1 complex led to a decrease in Nrf2 ubiquitination levels at non-stressed as well as stressed conditions, and sensitized cells for higher Nrf2 activation. Furthermore, CACUL1 knock-down led to a decrease in Nrf2 activity and cell viability under stress. Our results show that CACUL1 is a regulator of Nrf2 ubiquitination, adding another regulatory layer to the Nrf2 antioxidant stress response. PMID:26238671

  10. 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%.

  11. 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.

  12. Structural basis underlying CAC RNA recognition by the RRM domain of dimeric RNA-binding protein RBPMS

    PubMed Central

    Teplova, Marianna; Farazi, Thalia A.; Tuschl, Thomas; Patel, Dinshaw J.

    2015-01-01

    RNA-binding protein with multiple splicing (designated RBPMS) is a higher vertebrate mRNA-binding protein containing a single RNA recognition motif (RRM). RBPMS has been shown to be involved in mRNA transport, localization and stability, with key roles in axon guidance, smooth muscle plasticity, as well as regulation of cancer cell proliferation and migration. We report on structure-function studies of the RRM domain of RBPMS bound to a CAC-containing single-stranded RNA. These results provide insights into potential topologies of complexes formed by the RBPMS RRM domain and the tandem CAC repeat binding sites as detected by photoactivatable-ribonucleoside-enhanced crosslinking and immunoprecipitation. These studies establish that the RRM domain of RBPMS forms a symmetrical dimer in the free state, with each monomer binding sequence-specifically to all three nucleotides of a CAC segment in the RNA bound state. Structure-guided mutations within the dimerization and RNA-binding interfaces of RBPMS RRM on RNA complex formation resulted in both disruption of dimerization and a decrease in RNA-binding affinity as observed by size exclusion chromatography and isothermal titration calorimetry. As anticipated from biochemical binding studies, over-expression of dimerization or RNA-binding mutants of Flag-HA-tagged RBPMS were no longer able to track with stress granules in HEK293 cells, thereby documenting the deleterious effects of such mutations in vivo. PMID:26347403

  13. Nebular history of amoeboid olivine aggregates

    NASA Astrophysics Data System (ADS)

    Sugiura, N.; Petaev, M. I.; Kimura, M.; Miyazaki, A.; Hiyagon, H.

    2009-05-01

    Minor element (Ca, Cr, and Mn) concentrations in amoeboid olivine aggregates (AOAs) from primitive chondrites were measured and compared with those predicted by equilibrium condensation in the solar nebula. CaO concentrations in forsterite are low, particularly in porous aggregates. A plausible explanation appears that an equilibrium Ca activity was not maintained during the olivine condensation. CaO and MnO in forsterite are negatively correlated, with CaO being higher in compact aggregates. This suggests that the compact aggregates formed either by a prolonged reheating of the porous aggregates or by condensation and aggregation of forsterite during a very slow cooling in the nebula.

  14. Menaquinone-7 Supplementation to Reduce Vascular Calcification in Patients with Coronary Artery Disease: Rationale and Study Protocol (VitaK-CAC Trial).

    PubMed

    Vossen, Liv M; Schurgers, Leon J; van Varik, Bernard J; Kietselaer, Bas L J H; Vermeer, Cees; Meeder, Johannes G; Rahel, Braim M; van Cauteren, Yvonne J M; Hoffland, Ge A; Rennenberg, Roger J M W; Reesink, Koen D; de Leeuw, Peter W; Kroon, Abraham A

    2015-10-28

    Coronary artery calcification (CAC) develops early in the pathogenesis of atherosclerosis and is a strong and independent predictor of cardiovascular disease (CVD). Arterial calcification is caused by an imbalance in calcification regulatory mechanisms. An important inhibitor of calcification is vitamin K-dependent matrix Gla protein (MGP). Both preclinical and clinical studies have shown that inhibition of the vitamin K-cycle by vitamin K antagonists (VKA) results in elevated uncarboxylated MGP (ucMGP) and subsequently in extensive arterial calcification. This led us to hypothesize that vitamin K supplementation may slow down the progression of calcification. To test this, we designed the VitaK-CAC trial which analyses effects of menaquinone-7 (MK-7) supplementation on progression of CAC. The trial is a double-blind, randomized, placebo-controlled trial including patients with coronary artery disease (CAD). Patients with a baseline Agatston CAC-score between 50 and 400 will be randomized to an intervention-group (360 microgram MK-7) or a placebo group. Treatment duration will be 24 months. The primary endpoint is the difference in CAC-score progression between both groups. Secondary endpoints include changes in arterial structure and function, and associations with biomarkers. We hypothesize that treatment with MK-7 will slow down or arrest the progression of CAC and that this trial may lead to a treatment option for vascular calcification and subsequent CVD.

  15. Menaquinone-7 Supplementation to Reduce Vascular Calcification in Patients with Coronary Artery Disease: Rationale and Study Protocol (VitaK-CAC Trial)

    PubMed Central

    Vossen, Liv M.; Schurgers, Leon J.; van Varik, Bernard J.; Kietselaer, Bas L. J. H.; Vermeer, Cees; Meeder, Johannes G.; Rahel, Braim M.; van Cauteren, Yvonne J. M.; Hoffland, Ge A.; Rennenberg, Roger J. M. W.; Reesink, Koen D.; de Leeuw, Peter W.; Kroon, Abraham A.

    2015-01-01

    Coronary artery calcification (CAC) develops early in the pathogenesis of atherosclerosis and is a strong and independent predictor of cardiovascular disease (CVD). Arterial calcification is caused by an imbalance in calcification regulatory mechanisms. An important inhibitor of calcification is vitamin K-dependent matrix Gla protein (MGP). Both preclinical and clinical studies have shown that inhibition of the vitamin K-cycle by vitamin K antagonists (VKA) results in elevated uncarboxylated MGP (ucMGP) and subsequently in extensive arterial calcification. This led us to hypothesize that vitamin K supplementation may slow down the progression of calcification. To test this, we designed the VitaK-CAC trial which analyses effects of menaquinone-7 (MK-7) supplementation on progression of CAC. The trial is a double-blind, randomized, placebo-controlled trial including patients with coronary artery disease (CAD). Patients with a baseline Agatston CAC-score between 50 and 400 will be randomized to an intervention-group (360 microgram MK-7) or a placebo group. Treatment duration will be 24 months. The primary endpoint is the difference in CAC-score progression between both groups. Secondary endpoints include changes in arterial structure and function, and associations with biomarkers. We hypothesize that treatment with MK-7 will slow down or arrest the progression of CAC and that this trial may lead to a treatment option for vascular calcification and subsequent CVD. PMID:26516910

  16. Concentration-Induced J-Aggregate Formation Causes a Biphasic Change in the Release of trans-Combretastatin A4 Disodium Phosphate from Archaeosomes and the Subsequent Cytotoxicity on Mammary Cancer Cells.

    PubMed

    Daswani, Varsha P; Ayesa, Umme; Venegas, Berenice; Chong, Parkson Lee-Gau

    2015-10-01

    Combretastatin A4 disodium phosphate (CA4P) is a fluorescent, water-soluble prodrug able to induce vascular shutdown within tumors at doses less than one-tenth of the maximum tolerated dose. As a continued effort to develop efficient liposomal CA4P to treat solid tumor, we herein investigate the physical and spectroscopic properties of CA4P in aqueous solution and the mechanism of CA4P release from archaeal tetraether liposomes (archaeosomes). We found that cis-CA4P can be photoisomerized to trans-CA4P. This photoisomerization results in an increase in fluorescence intensity. Both cis- and trans-CA4P undergo fluorescence intensity self-quenching after they reach a critical concentration Cq (∼0.15-0.25 mM). Moreover, both cis- and trans-CA4P in buffer exhibit a red shift in their excitation spectrum and an increase in excitation spectrum band sharpness with increasing concentration, which can be attributed to the formation of J-aggregates. The onset of the dramatic change in excitation maximum occurs at concentrations close to Cq, suggesting that the self-quenching arises from extensive J-aggregate formation and that, when CA4P concentration exceeds Cq, J-aggregate formation begins to increase sharply. Our data also suggest that the extent of J-aggregate formation plays a critical role in CA4P release from tetraether archaeosomes and in the subsequent cytotoxicity on cultured human breast cancer MCF-7 cells. The drug leakage and cytotoxicity rate constants vary with the initial CA4P concentration entrapped inside archaeosomes in a biphasic manner, reaching a local maximum at 0.25-0.50 mM. A mechanism based on the concept of J-aggregate formation has been proposed to explain the biphasic changes in drug release and cytotoxicity with increasing drug concentration. Tetraether archaeosomes are extraordinarily stable and relatively nontoxic to animals; thus, they are promising nano drug carriers. The results obtained from this study pave the way for future development

  17. The concentration of intracellular nickel in Haemophilus influenzae is linked to its surface properties and cell-cell aggregation and biofilm formation.

    PubMed

    Ng, Jiaqi; Kidd, Stephen P

    2013-04-01

    Of the known proteins which use nickel as a co-factor, Haemophilus influenzae contains only urease and glyoxalase I (gloA). We have recently reported that this pathogen harbours a unique nickel uptake system (nikKLMQO-nimR). Unusually, the disruption of the nickel uptake system (nikQ or nimR mutants) resulted in cells that aggregated and formed an increased biofilm compared to the wild type cells. Using a gloA mutant strain and urease-specific inhibitor we showed that this phenotype is not due to the loss-of-function of these enzymes. By generating H. influenzae "resting cells" which are enzymatically inactive but maintain their structural integrity we have shown that the cell aggregation in the nikQ/nimR mutants is not due to the loss of enzymatic function. The nikQ mutant was unable to accumulate nickel but the addition of excess nickel did restore intracellular nickel levels and this resulted in the nikQ mutant returning to the wild type "free-living" phenotype; cells with no aggregation and no biofilm formation. We used a range of techniques which showed that the nikQ mutant possesses changes to its cell surface properties. The mutant was more negatively charged than wild type cells as well as being more hydrophobic. Analysis of the outer membrane constituents showed that there were molecular differences. Although the nikQ mutant appears to grow the same as its wild type cell we have shown that there is a change in the "lifestyle" of these nickel limited cells and this induces changes to the surface of the cell to promote cell-cell aggregation and biofilm formation. PMID:23499478

  18. 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.

  19. 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.

  20. 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.

  1. An Aggregation Advisor for Ligand Discovery.

    PubMed

    Irwin, John J; Duan, Da; Torosyan, Hayarpi; Doak, Allison K; Ziebart, Kristin T; Sterling, Teague; Tumanian, Gurgen; Shoichet, Brian K

    2015-09-10

    Colloidal aggregation of organic molecules is the dominant mechanism for artifactual inhibition of proteins, and controls against it are widely deployed. Notwithstanding an increasingly detailed understanding of this phenomenon, a method to reliably predict aggregation has remained elusive. Correspondingly, active molecules that act via aggregation continue to be found in early discovery campaigns and remain common in the literature. Over the past decade, over 12 thousand aggregating organic molecules have been identified, potentially enabling a precedent-based approach to match known aggregators with new molecules that may be expected to aggregate and lead to artifacts. We investigate an approach that uses lipophilicity, affinity, and similarity to known aggregators to advise on the likelihood that a candidate compound is an aggregator. In prospective experimental testing, five of seven new molecules with Tanimoto coefficients (Tc's) between 0.95 and 0.99 to known aggregators aggregated at relevant concentrations. Ten of 19 with Tc's between 0.94 and 0.90 and three of seven with Tc's between 0.89 and 0.85 also aggregated. Another three of the predicted compounds aggregated at higher concentrations. This method finds that 61 827 or 5.1% of the ligands acting in the 0.1 to 10 μM range in the medicinal chemistry literature are at least 85% similar to a known aggregator with these physical properties and may aggregate at relevant concentrations. Intriguingly, only 0.73% of all drug-like commercially available compounds resemble the known aggregators, suggesting that colloidal aggregators are enriched in the literature. As a percentage of the literature, aggregator-like compounds have increased 9-fold since 1995, partly reflecting the advent of high-throughput and virtual screens against molecular targets. Emerging from this study is an aggregator advisor database and tool ( http://advisor.bkslab.org ), free to the community, that may help distinguish between

  2. Pressure induced polymerization of acetylide anions in CaC2 and 107 fold enhancement of electrical conductivity

    DOE PAGES

    Zheng, Haiyan; Wang, Lijuan; Li, Kuo; Yang, Youyou; Wang, Yajie; Wu, Jiajia; Dong, Xiao; Wang, Chun -Hai; Tulk, Christopher A.; Molaison, Jamie J.; et al

    2016-08-17

    Transformation between different types of carbon–carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC2) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C66– are identified with gas chromatography-mass spectrometry and several other techniques,more » which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 107 fold enhancement of the electrical conductivity. As a result, the polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.« less

  3. Detection and aggregation of the antitumoral drug parietin in ethanol/water mixture and on plasmonic metal nanoparticles studied by surface-enhanced optical spectroscopy: Effect of pH and ethanol concentration

    NASA Astrophysics Data System (ADS)

    Lopez-Tobar, Eduardo; Verebova, Valeria; Blascakova, Ludmila; Jancura, Daniel; Fabriciova, Gabriela; Sanchez-Cortes, Santiago

    2016-04-01

    In the present paper, we have investigated the effect of ethanol in aqueous media, the pH and the presence of Ag nanoparticles (NPs) on the aggregation processes of the antitumoral anthraquinone parietin in aqueous media and on the metal surface. UV-visible absorption, fluorescence and Raman spectra of parietin were used for such purpose. The present study provides information about the deprotonation and molecular aggregation processes occurring in parietin under different environments: ethanol/water mixture and when adsorbed onto Ag nanoparticles. The effect of ethanol on the optical properties of parietin in alcohol-water mixtures was also investigated at different ethanol concentrations with the time. For the case of the adsorption and organization of parietin molecules on the surface of Ag NPs, special attention was paid to the use of surface-enhanced optical techniques, SEF (surface-enhanced fluorescence) and SERS (surface-enhanced Raman scattering), for the characterization of the parietin aggregates and the ionization of the molecule on the surface. In particular, we have studied the variation of the SEF signal with the pH, which depends on the molecular organization of the molecule on the surface. Furthermore, a detailed analysis of the SERS spectra at different pH was accomplished and the main Raman bands of the protonated, mono-deprotonated and di-deprotonated parietin were identified. Finally, the second ionization pK of parietin on metal NPs was deduced from the SERS spectra.

  4. Detection and aggregation of the antitumoral drug parietin in ethanol/water mixture and on plasmonic metal nanoparticles studied by surface-enhanced optical spectroscopy: Effect of pH and ethanol concentration.

    PubMed

    Lopez-Tobar, Eduardo; Verebova, Valeria; Blascakova, Ludmila; Jancura, Daniel; Fabriciova, Gabriela; Sanchez-Cortes, Santiago

    2016-04-15

    In the present paper, we have investigated the effect of ethanol in aqueous media, the pH and the presence of Ag nanoparticles (NPs) on the aggregation processes of the antitumoral anthraquinone parietin in aqueous media and on the metal surface. UV-visible absorption, fluorescence and Raman spectra of parietin were used for such purpose. The present study provides information about the deprotonation and molecular aggregation processes occurring in parietin under different environments: ethanol/water mixture and when adsorbed onto Ag nanoparticles. The effect of ethanol on the optical properties of parietin in alcohol-water mixtures was also investigated at different ethanol concentrations with the time. For the case of the adsorption and organization of parietin molecules on the surface of Ag NPs, special attention was paid to the use of surface-enhanced optical techniques, SEF (surface-enhanced fluorescence) and SERS (surface-enhanced Raman scattering), for the characterization of the parietin aggregates and the ionization of the molecule on the surface. In particular, we have studied the variation of the SEF signal with the pH, which depends on the molecular organization of the molecule on the surface. Furthermore, a detailed analysis of the SERS spectra at different pH was accomplished and the main Raman bands of the protonated, mono-deprotonated and di-deprotonated parietin were identified. Finally, the second ionization pK of parietin on metal NPs was deduced from the SERS spectra.

  5. 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).

  6. Stable activity of a deubiquitylating enzyme (Usp2-cc) in the presence of high concentrations of urea and its application to purify aggregation-prone peptides

    SciTech Connect

    Shahnawaz, Mohammad; Thapa, Arjun; Park, Il-Seon . E-mail: parkis@chosun.ac.kr

    2007-08-03

    Chemical synthesis of long or aggregation-prone peptide has been problematic. Its biological production has an advantage in that point, but it often forms inclusion body which creates difficulties in recovery of targets. As a deubiquitylating enzyme (Usp2-cc) was shown in this study to maintain its activity even in the presence of up to 4 M urea, target peptide was purified by a single step of chromatography after overexpression as inclusion body, solubilization in urea and cleavage by the enzyme from the fusion protein consisting of GroES (used for high expression and easy to handle), ubiquitin (as a cleavage site) and target peptide. This system is a convenient tool for production of peptides that are difficult to be chemically synthesized and biologically purified.

  7. Stable activity of a deubiquitylating enzyme (Usp2-cc) in the presence of high concentrations of urea and its application to purify aggregation-prone peptides.

    PubMed

    Shahnawaz, Mohammad; Thapa, Arjun; Park, Il-Seon

    2007-08-01

    Chemical synthesis of long or aggregation-prone peptide has been problematic. Its biological production has an advantage in that point, but it often forms inclusion body which creates difficulties in recovery of targets. As a deubiquitylating enzyme (Usp2-cc) was shown in this study to maintain its activity even in the presence of up to 4M urea, target peptide was purified by a single step of chromatography after overexpression as inclusion body, solubilization in urea and cleavage by the enzyme from the fusion protein consisting of GroES (used for high expression and easy to handle), ubiquitin (as a cleavage site) and target peptide. This system is a convenient tool for production of peptides that are difficult to be chemically synthesized and biologically purified. PMID:17560941

  8. An indoxyl compound 5-bromo-4-chloro-3-indolyl 1,3-diacetate, CAC-0982, suppresses activation of Fyn kinase in mast cells and IgE-mediated allergic responses in mice

    SciTech Connect

    Lee, Jun Ho; Kim, Tae Hyung; Kim, Hyuk Soon; Kim, A-Ram; Kim, Do-Kyun; Nam, Seung Taek; Kim, Hyun Woo; Park, Young Hwan; Her, Erk; Park, Yeong Min; Kim, Hyung Sik; Kim, Young Mi; Choi, Wahn Soo

    2015-06-15

    Mast cells, constituents of virtually all organs and tissues, are critical cells in IgE-mediated allergic responses. The aim of this study was to investigate the effect and mechanism of an indoxyl chromogenic compound, 5-bromo-4-chloro-3-indolyl 1,3-diacetate, CAC-0982, on IgE-mediated mast cell activation and allergic responses in mice. CAC-0982 reversibly suppressed antigen-stimulated degranulation in murine mast cells (IC{sub 50}, ~ 3.8 μM) and human mast cells (IC{sub 50}, ~ 3.0 μM). CAC-0982 also inhibited the expression and secretion of IL-4 and TNF-α in mast cells. Furthermore, CAC-0982 suppressed the mast cell-mediated allergic responses in mice in a dose-dependent manner (ED{sub 50} 27.9 mg/kg). As for the mechanism, CAC-0982 largely suppressed the phosphorylation of Syk and its downstream signaling molecules, including LAT, Akt, Erk1/2, p38, and JNK. Notably, the tyrosine kinase assay of antigen-stimulated mast cells showed that CAC-0982 inhibited Fyn kinase, one of the upstream tyrosine kinases for Syk activation in mast cells. Taken together, these results suggest that CAC-0982 may be used as a new treatment for regulating IgE-mediated allergic diseases through the inhibition of the Fyn/Syk pathway in mast cells. - Highlights: • The anti-allergic effect of 5-bromo-4-chloro-3-indolyl 1,3-diacetate, CAC-0982, was measured. • CAC-0982 reversibly suppressed the activation of mast cells by IgE and antigen. • CAC-0982 inhibited passive cutaneous anaphylaxis in mice. • CAC-0982 suppresses mast cells through inhibition of Fyn activation in mast cells.

  9. The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations.

    PubMed

    Gormley-Gallagher, Aine Marie; Douglas, Richard William; Rippey, Brian

    2015-01-01

    Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 μg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water.

  10. The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations

    PubMed Central

    Gormley-Gallagher, Aine Marie; Douglas, Richard William; Rippey, Brian

    2015-01-01

    Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 μg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water. PMID:26200885

  11. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    PubMed

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  12. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    PubMed

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501967

  13. Surface fractals in liposome aggregation.

    PubMed

    Roldán-Vargas, Sándalo; Barnadas-Rodríguez, Ramon; Quesada-Pérez, Manuel; Estelrich, Joan; Callejas-Fernández, José

    2009-01-01

    In this work, the aggregation of charged liposomes induced by magnesium is investigated. Static and dynamic light scattering, Fourier-transform infrared spectroscopy, and cryotransmission electron microscopy are used as experimental techniques. In particular, multiple intracluster scattering is reduced to a negligible amount using a cross-correlation light scattering scheme. The analysis of the cluster structure, probed by means of static light scattering, reveals an evolution from surface fractals to mass fractals with increasing magnesium concentration. Cryotransmission electron microscopy micrographs of the aggregates are consistent with this interpretation. In addition, a comparative analysis of these results with those previously reported in the presence of calcium suggests that the different hydration energy between lipid vesicles when these divalent cations are present plays a fundamental role in the cluster morphology. This suggestion is also supported by infrared spectroscopy data. The kinetics of the aggregation processes is also analyzed through the time evolution of the mean diffusion coefficient of the aggregates. PMID:19257067

  14. Surface fractals in liposome aggregation.

    PubMed

    Roldán-Vargas, Sándalo; Barnadas-Rodríguez, Ramon; Quesada-Pérez, Manuel; Estelrich, Joan; Callejas-Fernández, José

    2009-01-01

    In this work, the aggregation of charged liposomes induced by magnesium is investigated. Static and dynamic light scattering, Fourier-transform infrared spectroscopy, and cryotransmission electron microscopy are used as experimental techniques. In particular, multiple intracluster scattering is reduced to a negligible amount using a cross-correlation light scattering scheme. The analysis of the cluster structure, probed by means of static light scattering, reveals an evolution from surface fractals to mass fractals with increasing magnesium concentration. Cryotransmission electron microscopy micrographs of the aggregates are consistent with this interpretation. In addition, a comparative analysis of these results with those previously reported in the presence of calcium suggests that the different hydration energy between lipid vesicles when these divalent cations are present plays a fundamental role in the cluster morphology. This suggestion is also supported by infrared spectroscopy data. The kinetics of the aggregation processes is also analyzed through the time evolution of the mean diffusion coefficient of the aggregates.

  15. 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.

  16. Concentration of Specific Amino Acids at the Catalytic/Active Centers of Highly-Conserved ``Housekeeping'' Enzymes of Central Metabolism in Archaea, Bacteria and Eukaryota: Is There a Widely Conserved Chemical Signal of Prebiotic Assembly?

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Pan, Xueliang; Pearl, Dennis K.

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within ˜15 Å of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the “movement” of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 Å moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model’s peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  17. Concentration of specific amino acids at the catalytic/active centers of highly-conserved "housekeeping" enzymes of central metabolism in archaea, bacteria and Eukaryota: is there a widely conserved chemical signal of prebiotic assembly?

    PubMed

    Pollack, J Dennis; Pan, Xueliang; Pearl, Dennis K

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within approximately 15 A of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the "movement" of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 A moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model's peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  18. Time resolved study of three ruthenium(II) complexes at micellar surfaces: A new long excited state lifetime probe for determining critical micelle concentration of surfactant nano-aggregates.

    PubMed

    Patra, Digambara; Chaaban, Ahmad H; Darwish, Shaza; Saad, Huda A; Nehme, Ali S; Ghaddar, Tarek H

    2016-02-01

    Three different ruthenium complexes have been synthesized and their luminescence properties in different solvent environments are reported. Luminescence intensities and excited state lifetimes of Ru-I, Ru-II and Ru-III vary with solvent viscosity. The excited state lifetime of Ru-I linearly increases in the viscosity range 1.76-12,100cP. Ru-II shows two linear increases: one in the low and another in the high viscosity ranges, whereas Ru-III illustrates a linear enhancement only in the low viscosity range. Interestingly, luminescence intensities and excited state lifetimes of Ru-I, Ru-II and Ru-III are found to be sensitive to nano-aggregation. However, the surfactant head charge and that of the ruthenium center as well as the hydrophobic tail of the ancillary ligand of the complexes have a great role in deciding the nature of the interaction and on the excited state properties at micellar surfaces. It is proposed that the long lifetime of Ru-III in water could be due to the coiling of the carbon chain of the ancillary ligand around the ruthenium center. At micelle surface, this coiling of the carbon chain is lost due to the parallel alignment with surfactants and thus quenching of the excited state lifetime is seen. Furthermore, it is shown that the variation of the excited state lifetime with respect to the change in surfactant concentration is a result of the formation of micelles from the surfactant monomer, thus, a novel technique for the determination of the critical micelle concentration (cmc) based on the long excited state lifetime of Ru-III located at the micellar nano-aggregates is reported.

  19. Changes in fractal dimension during aggregation.

    PubMed

    Chakraborti, Rajat K; Gardner, Kevin H; Atkinson, Joseph F; Van Benschoten, John E

    2003-02-01

    Experiments were performed to evaluate temporal changes in the fractal dimension of aggregates formed during flocculation of an initially monodisperse suspension of latex microspheres. Particle size distributions and aggregate geometrical information at different mixing times were obtained using a non-intrusive optical sampling and digital image analysis technique, under variable conditions of mixing speed, coagulant (alum) dose and particle concentration. Pixel resolution required to determine aggregate size and geometric measures including the fractal dimension is discussed and a quantitative measure of accuracy is developed. The two-dimensional fractal dimension was found to range from 1.94 to 1.48, corresponding to aggregates that are either relatively compact or loosely structured, respectively. Changes in fractal dimension are explained using a conceptual model, which describes changes in fractal dimension associated with aggregate growth and changes in aggregate structure. For aggregation of an initially monodisperse suspension, the fractal dimension was found to decrease over time in the initial stages of floc formation.

  20. 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.

  1. Cyclosporine A enhances platelet aggregation.

    PubMed

    Grace, A A; Barradas, M A; Mikhailidis, D P; Jeremy, J Y; Moorhead, J F; Sweny, P; Dandona, P

    1987-12-01

    In view of the reported increase in thromboembolic episodes following cyclosporine A (CyA) therapy, the effect of this drug on platelet aggregation and thromboxane A2 release was investigated. The addition of CyA, at therapeutic concentrations to platelet rich plasma from normal subjects in vitro was found to increase aggregation in response to adrenaline, collagen and ADP. Ingestion of CyA by healthy volunteers was also associated with enhanced platelet aggregation. The CyA-mediated enhancement of aggregation was further enhanced by the addition in vitro of therapeutic concentrations of heparin. Platelets from renal allograft recipients treated with CyA also showed hyperaggregability and increased thromboxane A2 release, which were most marked at "peak" plasma CyA concentration and less so at "trough" concentrations. Platelet hyperaggregability in renal allograft patients on long-term CyA therapy tended to revert towards normal following the replacement of CyA with azathioprine. Hypertensive patients with renal allografts on nifedipine therapy had normal platelet function and thromboxane release in spite of CyA therapy. These observations suggest that CyA-mediated platelet activation may contribute to the pathogenesis of the thromboembolic phenomena associated with the use of this drug. The increased release of thromboxane A2 (a vasoconstrictor) may also play a role in mediating CyA-related nephrotoxicity.

  2. Streaming instability of aggregating slime mold amoebae

    NASA Astrophysics Data System (ADS)

    Levine, Herbert; Reynolds, William

    1991-05-01

    We propose a new model of aggregation in the cellular slime mold D. Discoideum. Our approach couples the excitable signaling system to amoeba chemotaxis; the resultant system of equations is tractable to analytical and numerical approaches. Using our model, we derive the existence of a streaming instability for the concentric target aggregation pattern.

  3. Microbial aggregates in anaerobic wastewater treatment.

    PubMed

    Kosaric, N; Blaszczyk, R

    1990-01-01

    The phenomenon aggregation of anaerobic bacteria gives an opportunity to speed up the digestion rate during methanogenesis. The aggregates are mainly composed of methanogenic bacteria which convert acetate and H2/CO2 into methane. Other bacteria are also included in the aggregates but their concentration is rather small. The aggregates may also be formed during acetogenesis or even hydrolysis but such aggregates are not stable and disrupt quickly when not fed. A two stage process seems to be suitable when high concentrated solid waste must be treated. Special conditions are necessary to promote aggregate formation from methanogenic bacteria but aggregates once formed are stable without feeding even for a few years. The structure, texture and activity of bacterial aggregates depend on several parameters: (1)--temperature and pH, (2)--wastewater composition and (3)--hydrodynamic conditions within the reactor. The common influence of all these parameters is still rather unknown but some recommendations may be given. Temperature and pH should be maintained in the range which is optimal for methanogenic bacteria e.g. a temperature between 32 and 50 degrees C and a value pH between 6.5 and 7.5. Wastewaters should contain soluble wastes and the specific loading rate should be around one kgCOD(kgVSS)-1 d-1. The concentration of the elements influences aggregate composition and probably structure and texture. At high calcium concentration a change in the colour of the granules has been observed. Research is necessary to investigate the influence of other elements and organic toxicants on maintenance of the aggregates. Hydrodynamic conditions seem to influence the stability of the granules over long time periods. At low liquid stream rates, aggregates may starve and lysis within the aggregates is possible which results in hollowing of aggregates and their floating. At high liquid stream rates the aggregates may be disrupted and washed out of the reactor as a flocculent

  4. Cellular strategies for regulating functional and nonfunctional protein aggregation.

    PubMed

    Gsponer, Jörg; Babu, M Madan

    2012-11-29

    Growing evidence suggests that aggregation-prone proteins are both harmful and functional for a cell. How do cellular systems balance the detrimental and beneficial effect of protein aggregation? We reveal that aggregation-prone proteins are subject to differential transcriptional, translational, and degradation control compared to nonaggregation-prone proteins, which leads to their decreased synthesis, low abundance, and high turnover. Genetic modulators that enhance the aggregation phenotype are enriched in genes that influence expression homeostasis. Moreover, genes encoding aggregation-prone proteins are more likely to be harmful when overexpressed. The trends are evolutionarily conserved and suggest a strategy whereby cellular mechanisms specifically modulate the availability of aggregation-prone proteins to (1) keep concentrations below the critical ones required for aggregation and (2) shift the equilibrium between the monomeric and oligomeric/aggregate form, as explained by Le Chatelier's principle. This strategy may prevent formation of undesirable aggregates and keep functional assemblies/aggregates under control. PMID:23168257

  5. First-principles and Monte Carlo studies on the magnetic stability of half-metallic zinc-blende CaC and similar compounds

    NASA Astrophysics Data System (ADS)

    Dong, Shengjie; Ding, Hang-Chen; Zhou, Baozeng; Duan, Chun-Gang; Wu, Ping; Zhao, Hui

    2015-03-01

    Using the first-principles calculation based on density functional theory and Monte Carlo simulation within the Heisenberg Hamiltonian, we have investigated the magnetic stability at finite pressure and temperature of CaC and some other selected hypothetical IIA-IVA compounds with the zinc-blende crystal structure. The results from simulated external pressure and temperature test indicate that the magnetic stability is dependent on the variation in atomic number of anion or cation element. Additionally, the origin of sp magnetism is mentioned briefly in this work and the dependence of Curie temperature on the volume is also discussed. First-principles computational charge-injection test show that the magnetization of these sp compounds originates in the spin polarization of the p shell of anions. For CaC, the exchange parameter J1 of the Heisenberg Hamiltonian depends strongly on the lattice constant, while the J2 and J3 are weakly dependent on the lattice constant. Moreover, discussion of volume-conserving deformations for CaC further demonstrates the stability of ferromagnetism and half metallicity for the compounds.

  6. Waves and aggregation patterns in myxobacteria

    NASA Astrophysics Data System (ADS)

    Igoshin, Oleg A.; Welch, Roy; Kaiser, Dale; Oster, George

    2004-03-01

    Under starvation conditions, a population of myxobacteria aggregates to build a fruiting body whose shape is species-specific and within which the cells sporulate. Early in this process, cells often pass through a "ripple phase" characterized by traveling linear, concentric, and spiral waves. These waves are different from the waves observed during slime mold aggregation that depend on diffusible morphogens, because myxobacteria communicate by direct contact. The difference is most dramatic when waves collide: rather than annihilating one another, myxobacterial waves appear to pass through one another unchanged. Under certain conditions, the spacing and location of the nascent fruiting bodies is determined by the wavelength and pattern of the waves. Later in fruiting body development, waves are replaced by streams of cells that circulate around small initial aggregates enlarging and rounding them. Still later, pairs of motile aggregates coalesce to form larger aggregates that develop into fruiting bodies. Here we present a mathematical model that quantitatively explains these wave and aggregation phenomena.

  7. 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.

  8. 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.

  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. Acetal phosphatidic acids: novel platelet aggregating agents.

    PubMed

    Brammer, J P; Maguire, M H; Walaszek, E J; Wiley, R A

    1983-05-01

    1 Palmitaldehyde, olealdehyde and linolealdehyde acetal phosphatidic acids induced rapid shape change and dose-dependent biphasic aggregation of human platelets in platelet-rich plasma; aggregation was reversible at low doses and irreversible at high doses of the acetal phosphatidic acids. The palmitaldehyde congener elicited monophasic dose-dependent aggregation of sheep platelets in platelet-rich plasma.2 The threshold concentration for palmitaldehyde acetal phosphatidic acid (PGAP)-induced platelet aggregation was 2.5-5 muM for human platelets and 0.25-0.5 muM for sheep platelets. PGAP was 4-5 times as potent versus human platelets as the olealdehyde and linolealdehyde acetal phosphatidic acids, which were equipotent.3 PGAP-induced irreversible aggregation of [(14)C]-5-hydroxytryptamine ([(14)C]-5-HT)-labelled human platelets in platelet-rich plasma was accompanied by release of 44.0+/-2.4% (s.e.) of the platelet [(14)C]-5-HT; reversible aggregation was not associated with release. In contrast, PGAP-induced release of [(14)C]-5-HT-labelled sheep platelets was dose-dependent.4 The adenosine diphosphate (ADP) antagonist, 2-methylthio-AMP, and the cyclo-oxygenase inhibitor, aspirin, abolished PGAP-induced second phase aggregation and release in human platelets but did not affect the first, reversible, phase of aggregation. Both the first and second phases of PGAP-induced aggregation were abolished by chlorpromazine, by the phospholipase A(2) inhibitor, mepacrine, and by nmolar concentrations of prostaglandin E(1) (PGE(1)); these agents abolished the second, but not the first phase of ADP-induced aggregation.5 The related phospholipids, lecithin, lysolecithin and phosphatidic acid, at <100 muM, neither induced aggregation of human platelets in platelet-rich plasma, nor modified PGAP-induced aggregation; 1-palmityl lysophosphatidic acid elicited aggregation of human platelets at a threshold concentration of 100 muM.6 It is concluded that the acetal phosphatidic acids

  11. Aggregation Dynamics Using Phase Wave Signals and Branching Patterns

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Kusagaki, Takuma

    2016-09-01

    The aggregation dynamics of slime mold is studied using coupled equations of phase ϕ and cell concentration n. Phase waves work as tactic signals for aggregation. Branching structures appear during the aggregation. A stationary branching pattern appears like a river network, if cells are uniformly supplied into the system.

  12. Natural aggregates of the conterminous United States

    USGS Publications Warehouse

    Langer, William H.

    1988-01-01

    Crushed stone and sand and gravel are the two main sources of natural aggregates. These materials are commonly used construction materials and frequently can be interchanged with one another. They are widely used throughout the United States, with every State except two producing crushed stone. Together they amount to about half the mining volume in the United States. Approximately 96 percent of sand and gravel and 77 percent of the crushed stone produced in the United States are used in the construction industry. Natural aggregates are widely distributed throughout the United States in a variety of geologic environments. Sand and gravel deposits commonly are the results of the weathering of bedrock and subsequent transportation and deposition of the material by water or ice (glaciers). As such, they commonly occur as river or stream deposits or in glaciated areas as glaciofluvial and other deposits. Crushed stone aggregates are derived from a wide variety of parent bedrock materials. Limestone and other carbonates account for approximately three quarters of the rocks used for crushed stone, with granite and other igneous rocks making up the bulk of the remainder. Limestone deposits are widespread throughout the Central and Eastern United States and are scattered in the West. Granites are widely distributed in the Eastern and Western United States, with few exposures in the Midwest. Igneous rocks (excluding granites) are largely concentrated in the Western United States and in a few isolated localities in the East. Even though natural aggregates are widely distributed throughout the United States, they are not universally available for consumptive use. Some areas are devoid of sand and gravel, and potential sources of crushed stone may be covered with sufficient unconsolidated material to make surface mining impractical. In some areas many aggregates do not meet the physical property requirements for certain uses, or they may contain mineral constituents that react

  13. Competitive aggregation dynamics using phase wave signals.

    PubMed

    Sakaguchi, Hidetsugu; Maeyama, Satomi

    2014-10-21

    Coupled equations of the phase equation and the equation of cell concentration n are proposed for competitive aggregation dynamics of slime mold in two dimensions. Phase waves are used as tactic signals of aggregation in this model. Several aggregation clusters are formed initially, and target patterns appear around the localized aggregation clusters. Owing to the competition among target patterns, the number of the localized aggregation clusters decreases, and finally one dominant localized pattern survives. If the phase equation is replaced with the complex Ginzburg-Landau equation, several spiral patterns appear, and n is localized near the center of the spiral patterns. After the competition among spiral patterns, one dominant spiral survives. PMID:24956327

  14. Application of Fisher fusion techniques to improve the individual performance of sonar computer-aided detection/computer-aided classification (CAD/CAC) algorithms

    NASA Astrophysics Data System (ADS)

    Ciany, Charles M.; Zurawski, William C.

    2009-05-01

    Raytheon has extensively processed high-resolution sidescan sonar images with its CAD/CAC algorithms to provide classification of targets in a variety of shallow underwater environments. The Raytheon CAD/CAC algorithm is based on non-linear image segmentation into highlight, shadow, and background regions, followed by extraction, association, and scoring of features from candidate highlight and shadow regions of interest (ROIs). The targets are classified by thresholding an overall classification score, which is formed by summing the individual feature scores. The algorithm performance is measured in terms of probability of correct classification as a function of false alarm rate, and is determined by both the choice of classification features and the manner in which the classifier rates and combines these features to form its overall score. In general, the algorithm performs very reliably against targets that exhibit "strong" highlight and shadow regions in the sonar image- i.e., both the highlight echo and its associated shadow region from the target are distinct relative to the ambient background. However, many real-world undersea environments can produce sonar images in which a significant percentage of the targets exhibit either "weak" highlight or shadow regions in the sonar image. The challenge of achieving robust performance in these environments has traditionally been addressed by modifying the individual feature scoring algorithms to optimize the separation between the corresponding highlight or shadow feature scores of targets and non-targets. This study examines an alternate approach that employs principles of Fisher fusion to determine a set of optimal weighting coefficients that are applied to the individual feature scores before summing to form the overall classification score. The results demonstrate improved performance of the CAD/CAC algorithm on at-sea data sets.

  15. A comparative study on the aggregating effects of guanidine thiocyanate, guanidine hydrochloride and urea on lysozyme aggregation

    SciTech Connect

    Emadi, Saeed Behzadi, Maliheh

    2014-08-08

    Highlights: • Lysozyme aggregated in guanidine thiocyanate (1.0 and 2.0 M). • Lysozyme aggregated in guanidine hydrochloride (4 and 5 M). • Lysozyme did not aggregated at any concentration (0.5–5 M) of urea. • Unfolding pathway is more important than unfolding per se in aggregation. - Abstract: Protein aggregation and its subsequent deposition in different tissues culminate in a diverse range of diseases collectively known as amyloidoses. Aggregation of hen or human lysozyme depends on certain conditions, namely acidic pH or the presence of additives. In the present study, the effects on the aggregation of hen egg-white lysozyme via incubation in concentrated solutions of three different chaotropic agents namely guanidine thiocyanate, guanidine hydrochloride and urea were investigated. Here we used three different methods for the detection of the aggregates, thioflavin T fluorescence, circular dichroism spectroscopy and atomic force microscopy. Our results showed that upon incubation with different concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 5.0 M) of the chemical denaturants, lysozyme was aggregated at low concentrations of guanidine thiocyanate (1.0 and 2.0 M) and at high concentrations of guanidine hydrochloride (4 and 5 M), although no fibril formation was detected. In the case of urea, no aggregation was observed at any concentration.

  16. Blood viscosity: influence of erythrocyte aggregation.

    PubMed

    Chien, S; Usami, S; Dellenback, R J; Gregersen, M I; Nanninga, L B; Guest, M M

    1967-08-18

    The addition of purified canine or bovine fibrinogen to suspensions of canine erythocytes in Ringer solution caused an increase in viscosity and the formation of aggregates of erythocytes. Both of these effects became increasingly pronounced as the fibrinogen concentration was raised, and they approached plateaus with 1 gram of fibrinogen per 100 milliliters. An increase in shear rate (or shear stress) reduced both the effect on viscosity and the aggregate size. The data suggest that fibrinogen causes an increase in blood viscosity and a departure from Newtonian behavior by interacting with erythrocytes to form cell aggregates which can be dispersed by shear stress. PMID:17842794

  17. Aggregation kinetics and shear rheology of aqueous silica suspensions

    NASA Astrophysics Data System (ADS)

    Metin, Cigdem O.; Bonnecaze, Roger T.; Lake, Larry W.; Miranda, Caetano R.; Nguyen, Quoc P.

    2012-12-01

    The kinetics of aggregation of silica nanoparticle solutions as a function of NaCl and silica concentrations is studied experimentally and theoretically. Silica nanoparticles form fractal aggregates due to the collapse of the electrical double layer at high salt concentrations and resulting reduction in stabilizing repulsive force. We propose a convenient model to describe the aggregation of silica nanoparticles and the growth of their aggregate size that depends on particle size and concentration and salt concentration. The model agrees well with experimental data. The aggregation of silica nanoparticles also affects the rheology of the suspension. We propose an equilibrium approach for sediment volume fraction to determine the maximum effective packing fraction. The results for the relative viscosity of silica aggregates agree well with the proposed viscosity model, which also collapses onto a single master curve.

  18. Association of serum calcium concentrations with fibrinogen and homocysteine in nondiabetic Korean subjects

    PubMed Central

    Cho, Hyun Sun; Lee, Sung Won; Shin, Juyoung; Moon, Sung Dae; Han, Je Ho; Cha, Bong Yun; Kim, Eun Sook

    2016-01-01

    Abstract Considerable evidence shows that increased serum calcium levels are associated with metabolic disorders, cardiovascular disease, and increased mortality. This study investigated whether serum calcium, within a normal range, is significantly associated with serum fibrinogen and homocysteine, markers of increased cardiovascular disease risk in nondiabetic Korean subjects. A cross-sectional analysis was performed on 1096 subjects (mean age, 55.1 ± 11.1 years; 36.1% women) undergoing a general health checkup. Serum biochemistry was analyzed including serum albumin-corrected calcium (Cac), insulin resistance (IR, using homeostasis model assessment [HOMA]), fibrinogen, and homocysteine. Compared with patients within the lowest Cac quartile, those with higher Cac levels had increased fibrinogen and homocysteine levels as well as an increased proportion of smoking, dyslipidemia, and HOMA-IR. Correlation analyses revealed linear relationships for Cac with fibrinogen and homocysteine in both genders. After adjustment for confounding factors, serum Cac was significantly associated with high fibrinogen (odds ratio [OR] for the highest vs the lowest quartile = 1.76, 95% confidence interval [CI] = 1.09–2.83, P = 0.02) and homocysteine (OR = 1.83, 95% CI = 1.07–3.11, P = 0.027). Multivariate regression models showed that Cac was linearly associated with fibrinogen (standardized β = 0.14, P < 0.001) and homocysteine (standardized β = 0.07, P = 0.009). High normal calcium concentrations were independently associated with increased levels of fibrinogen and homocysteine. Further investigation is needed to validate whether slightly increased calcium levels within the normal range indicate a higher risk of cardiovascular disease. PMID:27310988

  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. Protein aggregation in salt solutions

    PubMed Central

    Kastelic, Miha; Kalyuzhnyi, Yurij V.; Hribar-Lee, Barbara; Dill, Ken A.; Vlachy, Vojko

    2015-01-01

    Protein aggregation is broadly important in diseases and in formulations of biological drugs. Here, we develop a theoretical model for reversible protein–protein aggregation in salt solutions. We treat proteins as hard spheres having square-well-energy binding sites, using Wertheim’s thermodynamic perturbation theory. The necessary condition required for such modeling to be realistic is that proteins in solution during the experiment remain in their compact form. Within this limitation our model gives accurate liquid–liquid coexistence curves for lysozyme and γ IIIa-crystallin solutions in respective buffers. It provides good fits to the cloud-point curves of lysozyme in buffer–salt mixtures as a function of the type and concentration of salt. It than predicts full coexistence curves, osmotic compressibilities, and second virial coefficients under such conditions. This treatment may also be relevant to protein crystallization. PMID:25964322

  1. Protein aggregation in salt solutions.

    PubMed

    Kastelic, Miha; Kalyuzhnyi, Yurij V; Hribar-Lee, Barbara; Dill, Ken A; Vlachy, Vojko

    2015-05-26

    Protein aggregation is broadly important in diseases and in formulations of biological drugs. Here, we develop a theoretical model for reversible protein-protein aggregation in salt solutions. We treat proteins as hard spheres having square-well-energy binding sites, using Wertheim's thermodynamic perturbation theory. The necessary condition required for such modeling to be realistic is that proteins in solution during the experiment remain in their compact form. Within this limitation our model gives accurate liquid-liquid coexistence curves for lysozyme and γ IIIa-crystallin solutions in respective buffers. It provides good fits to the cloud-point curves of lysozyme in buffer-salt mixtures as a function of the type and concentration of salt. It than predicts full coexistence curves, osmotic compressibilities, and second virial coefficients under such conditions. This treatment may also be relevant to protein crystallization.

  2. 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

  3. Impact of Particle Aggregation on Nanoparticle Reactivity

    NASA Astrophysics Data System (ADS)

    Jassby, David

    2011-12-01

    nanoparticle that photoluminesces after exposure to UV; TiO2 and ZnO nanoparticles---photocatalytic nanoparticles that generate reactive oxygen species upon UV irradition; and, fullerene nanoparticles used in the filtration experiments, selected for their potential use, small size, and surface chemistry. Our primary methods used to characterize particle and aggregate characteristics include dynamic light scattering used to describe particle size, static light scattering used to characterize aggregate structure (fractal dimension), transmission electron microscopy used to verify primary particle sizes, and electrophoretic mobility measurements to evaluate suspension stability. The reactive property of ZnS that was measured as a function of aggregation was photoluminescence, which was measured using a spectrofluorometer. The reactive property of TiO2 and ZnO that was studied was their ability to generate hydroxyl radicals; these were measured by employing a fluorescent probe that becomes luminescent upon interaction with the hydroxyl radical. To detect the presence of fullerene nanoparticles and calculate removal efficiencies, we used total organic carbon measurements. Additionally, we used UV-vis spectroscopy to approximate the impact of particle shadowing in TiO2 and ZnO aggregates, and Fourier transformed infrared spectroscopy to determine how different electrolytes interact with fullerene surface groups. Our findings indicate that the impact of aggregation on nanoparticle reactivity is material specific. ZnS nanoparticles exhibit a 2-fold increase in band-edge photoluminescence alongside a significant decrease in defect-site photoluminescence. This is attributed to aggregate size-dependent surface tension. Additionally, we used photoluminescence measurements to develop a new method for calculating the critical coagulation concentration of a nanoparticle suspension. The ability of both TiO2 and ZnO to generate hydroxyl radicals was significantly hampered by aggregation. The

  4. Aggregation behaviour of biohybrid microgels from elastin-like recombinamers.

    PubMed

    Singh, Smriti; Demco, Dan Eugen; Rahimi, Khosrow; Fechete, Radu; Rodriguez-Cabello, José Carlos; Möller, Martin

    2016-07-20

    Investigation of the aggregation behavior of biohybrid microgels, which can potentially be used as drug carriers, is an important topic, because aggregation not only causes loss of activity, but also toxicity and immunogenicity. To study this effect we synthesized microgels from elastin-like recombinamers (ELRs) using the miniemulsion technique. The existence of aggregation for such biohybrid microgels at different concentrations and temperatures was studied by different methods which include dynamic light scattering (DLS), (1)H high-resolution magic angle sample spinning (HRMAS) NMR spectroscopy, relaxometry and diffusometry. A hysteresis effect was detected in the process of aggregation by DLS as a function of temperature that strongly depends on ELR microgel concentration. The aggregation process was further quantitatively analyzed by the concentration dependence of the (1)H amino-acid residue chemical shifts and microgel diffusivity measured by NMR methods using the population balance kinetic aggregation model. PMID:27378252

  5. Spectroscopic characterization of phenazinium dye aggregates in water and acetonitrile media: effect of methyl substitution on the aggregation phenomenon.

    PubMed

    Sarkar, Deboleena; Das, Paramita; Girigoswami, Agnishwar; Chattopadhyay, Nitin

    2008-10-01

    Absorption, fluorescence, and fluorescence excitation spectral studies of two planar, cationic phenazinium dyes, namely, phenosafranin (PSF) and safranin-T (ST), have been performed in protic and aprotic polar solvents. The studies reveal the formation of both J- and H-aggregates in concentrated solutions. The planarity of the phenazinium skeleton and the presence of a positive charge are attributed to be the driving force for this aggregation behavior. The aggregates are established to be dimers only. The positive inductive effect of the methyl substituents in safranin-T augments the aggregation process. The experiments reveal that for both dyes, the polar protic solvent favors the aggregation process more than the aprotic solvent.

  6. 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.

  7. Improvements in computer-aided detection/computer-aided classification (CAD/CAC) of bottom mines through post analysis of a diverse set of very shallow water (VSW) environmental test data

    NASA Astrophysics Data System (ADS)

    Ciany, Charles M.; Zurawski, William C.

    2004-09-01

    In 1999 Raytheon adapted its shallow-water Side-Looking Sonar (SLS) Computer Aided Detection/Computer Aided Classification (CAD/CAC) algorithm to process side-scan sonar data obtained with the Woods Hole Oceanographic Institute's Remote Environmental Monitoring Units (REMUS) autonomous underwater vehicle (AUV). To date, Raytheon has demonstrated the ability to effectively execute mine-hunting missions with the REMUS vehicle through the fusion of its CAD/CAC algorithm with several other CAD/CAC algorithms to achieve low false alarm rates while maintaining a high probability of correct detection/classification. Mine-hunting in the very shallow water (VSW) environment poses a host of difficulties including such issues as: a higher incidence of man made clutter, significant interference due to biological sources (such as kelp or silt), the scouring of mines into the bottom, interference from surface/bottom bounce, and image distortion due to vehicle motion during image generation. These issues coupled with highly variable bottom conditions and small bottom targets make reliable hunting in the VSW environment very difficult. In order to be operationally viable, the individual CAD/CAC algorithms must demonstrate robustness over these very different mine-hunting environments. A higher normalized false alarm rate per algorithm is considered acceptable based on the false alarm reduction achieved through multi-algorithm fusion. Raytheon's recent CAD/CAC algorithm enhancements demonstrate a significant improvement in overall CAD/CAC performance across a diverse set of environments, from the relatively benign Gulf of Mexico environment to the more challenging areas off the coast of southern California containing significant biological and bottom clutter. The improvements are attributed to incorporating an image normalizer into the algorithm's pre-processing stage in conjunction with several other modifications. The algorithm enhancements resulted in an 11% increase in overall

  8. 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.

  9. 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.

  10. Evaluation of the Hydrodynamic Focusing Bioreactor (HDFB) and the Centrifugal Absorption Cartridge System (CACS) Performance Under Micro G

    NASA Technical Reports Server (NTRS)

    Gonda, Steve; Lee, Wenshan; Flechsig, Steve

    1999-01-01

    The Hydrodynamic Focusing Bioreactor (HDFB) technology is designed to provide a flow field with nearly uniform shear force throughout the vessel, which can provide the desired low shear force spatial environment to suspend three-dimensional cell aggregates while providing optimum mass transfer. The reactor vessel consists of a dome-shaped cell culture vessel, a viscous spinner, an access port, and a rotating base. The domed vessel face has a radius of R(o). and rotates at 0mega(o) rpm, while the internal viscous spinner has a radius of R(i) and rotates at 0mega(i) rpm. The culture vessel is completely filled with cell culture medium into which three-dimensional cellular structures are introduced. The HDFB domed vessel and spinner were driven by two independent step motors,

  11. Cell aggregation and sedimentation.

    PubMed

    Davis, R H

    1995-01-01

    The aggregation of cells into clumps or flocs has been exploited for decades in such applications as biological wastewater treatment, beer brewing, antibiotic fermentation, and enhanced sedimentation to aid in cell recovery or retention. More recent research has included the use of cell aggregation and sedimentation to selectively separate subpopulations of cells. Potential biotechnological applications include overcoming contamination, maintaining plasmid-bearing cells in continuous fermentors, and selectively removing nonviable hybridoma cells from perfusion cultures.

  12. 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

  13. Thermodynamics of Micellization of Surfactants of Low Aggregation Number: The Aggregation of Propranolol Hydrochloride.

    PubMed

    Mosquera; Ruso; Attwood; Jones; Prieto; Sarmiento

    1999-02-01

    The self-association of propranolol hydrochloride in aqueous solution has been studied as a function of temperature. The critical concentration (C*) and the degree of ionization (alpha) were determined by conductivity measurements at temperatures over the range 298.15 to 313.15 K. The enthalpy change on aggregation in water was measured by microcalorimetry. To calculate changes in the thermodynamic properties of aggregation the mass action model for high and low aggregation numbers was applied, the latter model giving better agreement between experimental and theoretical enthalpy changes. Copyright 1999 Academic Press.

  14. Fibronectin Aggregation and Assembly

    PubMed Central

    Ohashi, Tomoo; Erickson, Harold P.

    2011-01-01

    The mechanism of fibronectin (FN) assembly and the self-association sites are still unclear and contradictory, although the N-terminal 70-kDa region (I1–9) is commonly accepted as one of the assembly sites. We previously found that I1–9 binds to superfibronectin, which is an artificial FN aggregate induced by anastellin. In the present study, we found that I1–9 bound to the aggregate formed by anastellin and a small FN fragment, III1–2. An engineered disulfide bond in III2, which stabilizes folding, inhibited aggregation, but a disulfide bond in III1 did not. A gelatin precipitation assay showed that I1–9 did not interact with anastellin, III1, III2, III1–2, or several III1–2 mutants including III1–2KADA. (In contrast to previous studies, we found that the III1–2KADA mutant was identical in conformation to wild-type III1–2.) Because I1–9 only bound to the aggregate and the unfolding of III2 played a role in aggregation, we generated a III2 domain that was destabilized by deletion of the G strand. This mutant bound I1–9 as shown by the gelatin precipitation assay and fluorescence resonance energy transfer analysis, and it inhibited FN matrix assembly when added to cell culture. Next, we introduced disulfide mutations into full-length FN. Three disulfide locks in III2, III3, and III11 were required to dramatically reduce anastellin-induced aggregation. When we tested the disulfide mutants in cell culture, only the disulfide bond in III2 reduced the FN matrix. These results suggest that the unfolding of III2 is one of the key factors for FN aggregation and assembly. PMID:21949131

  15. H- and J-aggregation of fluorene-based chromophores.

    PubMed

    Deng, Yonghong; Yuan, Wen; Jia, Zhe; Liu, Gao

    2014-12-11

    Understanding of H- and J-aggregation behaviors in fluorene-based polymers is significant both for determining the origin of various red-shifted emissions occurring in blue-emitting polyfluorenes and for developing polyfluorene-based device performance. In this contribution, we demonstrate a new theory of the H- and J-aggregation of polyfluorenes and oligofluorenes, and understand the influence of chromosphere aggregation on their photoluminescent properties. H- and J-aggregates are induced by a continuous increasing concentration of the oligofluorene or polyfluorene solution. A relaxed molecular configuration is simulated to illustrate the spatial arrangement of the bonding of fluorenes. It is indicated that the relaxed state adopts a 21 helical backbone conformation with a torsion angle of 18° between two connected repeat units. This configuration makes the formation of H- and J-aggregates through the strong π-π interaction between the backbone rings. A critical aggregation concentration is observed to form H- and J-aggregates for both polyfluorenes and oligofluorenes. These aggregates show large spectral shifts and distinct shape changes in photoluminescent excitation (PLE) and emission (PL) spectroscopy. Compared with "isolated" chromophores, H-aggregates induce absorption spectral blue-shift and fluorescence spectral red-shift but largely reduce fluorescence efficiency. "Isolated" chromophores not only refer to "isolated molecules" but also include those associated molecules if their conjugated backbones are not compact enough to exhibit perturbed absorption and emission. J-aggregates induce absorption spectral red-shift and fluorescence spectral red-shift but largely enhance fluorescence efficiency. The PLE and PL spectra also show that J-aggregates dominate in concentrated solutions. Different from the excimers, the H- and J-aggregate formation changes the ground-state absorption of fluorene-based chromophores. H- and J-aggregates show changeable

  16. H- and J-aggregation of fluorene-based chromophores.

    PubMed

    Deng, Yonghong; Yuan, Wen; Jia, Zhe; Liu, Gao

    2014-12-11

    Understanding of H- and J-aggregation behaviors in fluorene-based polymers is significant both for determining the origin of various red-shifted emissions occurring in blue-emitting polyfluorenes and for developing polyfluorene-based device performance. In this contribution, we demonstrate a new theory of the H- and J-aggregation of polyfluorenes and oligofluorenes, and understand the influence of chromosphere aggregation on their photoluminescent properties. H- and J-aggregates are induced by a continuous increasing concentration of the oligofluorene or polyfluorene solution. A relaxed molecular configuration is simulated to illustrate the spatial arrangement of the bonding of fluorenes. It is indicated that the relaxed state adopts a 21 helical backbone conformation with a torsion angle of 18° between two connected repeat units. This configuration makes the formation of H- and J-aggregates through the strong π-π interaction between the backbone rings. A critical aggregation concentration is observed to form H- and J-aggregates for both polyfluorenes and oligofluorenes. These aggregates show large spectral shifts and distinct shape changes in photoluminescent excitation (PLE) and emission (PL) spectroscopy. Compared with "isolated" chromophores, H-aggregates induce absorption spectral blue-shift and fluorescence spectral red-shift but largely reduce fluorescence efficiency. "Isolated" chromophores not only refer to "isolated molecules" but also include those associated molecules if their conjugated backbones are not compact enough to exhibit perturbed absorption and emission. J-aggregates induce absorption spectral red-shift and fluorescence spectral red-shift but largely enhance fluorescence efficiency. The PLE and PL spectra also show that J-aggregates dominate in concentrated solutions. Different from the excimers, the H- and J-aggregate formation changes the ground-state absorption of fluorene-based chromophores. H- and J-aggregates show changeable

  17. 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.

  18. 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.

  19. Influence of Phenylalanine on Carotenoid Aggregation

    NASA Astrophysics Data System (ADS)

    Lu, L.; Ni, X.; Luo, X.

    2015-01-01

    The carotenoids lutein and β-carotene form, in 1:1 ethanol-water mixtures H-aggregates, of different strengths. The effects of phenylalanine on these aggregates were recorded by UV-Vis absorption, steady-state fluorescence, and Raman spectra. The H-aggregate of lutein was characterized by a large 78 nm blue shift in the absorption spectra, confirming the strong coupling between hydroxyl groups of adjacent molecules. The 15 nm blue shift in the β-carotene mixture also indicates that it was assembled by weak coupling between polyenes. After adding phenylalanine, the reducing absorption strength of the aggregates of lutein and reappearance of vibrational substructure indicate that the hydroxyl and amino groups of phenylalanine may coordinate to lutein and disaggregate the H-aggregates. However, phenylalanine had no effect on aggregates of β-carotene. The Raman spectra show three bands of carotenoids whose intensities decreased with increasing phenylalanine concentration. The frequency of ν1 corresponding to the length of the conjugated region was more sensitive to the solution of lutein. This coordination of phenylalanine to lutein could increase the length of the conjugated region. In addition, phenylalanine significantly affected the excited electronic states of carotenoids, which were crucial in the energy transfer from carotenoids to chlorophyll a in vivo.

  20. Proline inhibits aggregation during protein refolding.

    PubMed Central

    Samuel, D.; Kumar, T. K.; Ganesh, G.; Jayaraman, G.; Yang, P. W.; Chang, M. M.; Trivedi, V. D.; Wang, S. L.; Hwang, K. C.; Chang, D. K.; Yu, C.

    2000-01-01

    The in vitro refolding of hen egg-white lysozyme is studied in the presence of various osmolytes. Proline is found to prevent aggregation during protein refolding. However, other osmolytes used in this study fail to exhibit a similar property. Experimental evidence suggests that proline inhibits protein aggregation by binding to folding intermediate(s) and trapping the folding intermediate(s) into enzymatically inactive, "aggregation-insensitive" state(s). However, elimination of proline from the refolded protein mixture results in significant recovery of the bacteriolytic activity. At higher concentrations (>1.5 M), proline is shown to form loose, higher-order molecular aggregate(s). The supramolecular assembly of proline is found to possess an amphipathic character. Formation of higher-order aggregates is believed to be crucial for proline to function as a protein folding aid. In addition to its role in osmoregulation under water stress conditions, the results of this study hint at the possibility of proline behaving as a protein folding chaperone. PMID:10716186

  1. 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

    (about 10 mm in size) selected per treatment (mulched or conventional tillage) and crop (apricot, citrus and wheat). In this case, every set of aggregates was randomly divided in three groups (n = 30) for assessing stability to slaking, WR and OC, respectively. OC 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 OC content in aggregates with different size varied among soils under different crops, generally increasing with decreasing size. At the intra-aggregate level, OC concentrated preferably in the exterior layer of differently sized aggregates and of aggregate coatings and interior 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 differently sized aggregates under different crops in the 0-10 cm layer, 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 OC in different layers of aggregate from conventionally tilled soils, great or significant differences in the distribution of water repellency at the intra-aggregate level were not found. In case of mulched soils such differences were not significant. Finally, the intensity of water repellency was much more important than the concentration of OC in the stability to slaking of aggregates.

  2. 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

  3. 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.

  4. Aggregation kinetics of nanosilver in different water conditions

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Feng; Zhang, Hongyin

    2012-09-01

    In this study the effect of different water conditions on the aggregation kinetics of nanosilver (nAg) is evaluated. The obtained results show that the aggregation rate of nAg increases with increasing electrolyte concentration. Divalent cation (Ca2+) can more effectively induce aggregation than monovalent cation (Na+). Critical coagulation concentration of nAg in NaCl solution is about 40 times higher than that in CaCl2 solution. This study also indicates that aggregation rate of nAg in water condition containing high Ca2+ concentration in presence of humic acid is higher than that without humic acid due to the bridging effect of humic acid-Ca2+ complex. Finally, aggregation rate of nAg in seawater is higher than that in lake water.

  5. Macromolecular cell surface engineering for accelerated and reversible cellular aggregation.

    PubMed

    Amaral, Adérito J R; Pasparakis, George

    2015-12-25

    We report the synthesis of two simple copolymers that induce rapid cell aggregation within minutes in a fully reversible manner. The polymers can act as self-supporting "cellular glues" or as "drivers" of 3D cell spheroids/aggregates formation at minute concentrations.

  6. Aggregates, broccoli and cauliflower

    NASA Astrophysics Data System (ADS)

    Grey, Francois; Kjems, Jørgen K.

    1989-09-01

    Naturally grown structures with fractal characters like broccoli and cauliflower are discussed and compared with DLA-type aggregates. It is suggested that the branching density can be used to characterize the growth process and an experimental method to determine this parameter is proposed.

  7. Optical Properties and Aggregation of Graphene Nanoplatelets.

    PubMed

    Melezhyk, A V; Kotov, V A; Tkachev, A G

    2016-01-01

    In the present paper, the optical density of dispersions of randomly oriented multilayer graphene nanoplatelets (GNPs) was estimated. Calculated and experimental data were compared for aqueous GNP dispersions stabilized with various surfactants. It was shown that the sonication of an expanded graphite compound (EGC) in aqueous surfactant solutions leads to the transformation of EGC worm-like particles into weak GNP aggregates which are able to pass into solution upon dilution and agitation of the system. They may be filtered and washed out of surfactants. The concentrated GNP dispersions containing these weak aggregates can be used to synthesize different graphene-based nanostructures and obtain novel composite materials. PMID:27398570

  8. Production of prone-to-aggregate proteins.

    PubMed

    Lebendiker, Mario; Danieli, Tsafi

    2014-01-21

    Expression of recombinant proteins in Escherichia coli (E. coli) remains the most popular and cost-effective method for producing proteins in basic research and for pharmaceutical applications. Despite accumulating experience and methodologies developed over the years, production of recombinant proteins prone to aggregate in E. coli-based systems poses a major challenge in most research applications. The challenge of manufacturing these proteins for pharmaceutical applications is even greater. This review will discuss effective methods to reduce and even prevent the formation of aggregates in the course of recombinant protein production. We will focus on important steps along the production path, which include cloning, expression, purification, concentration, and storage. PMID:24211444

  9. Intraspecific Signals Inducing Aggregation in Periplaneta americana (Insecta: Dictyoptera).

    PubMed

    Imen, Saïd; Christian, Malosse; Virginie, Durier; Colette, Rivault

    2015-06-01

    Chemical communication is necessary to induce aggregation and to maintain the cohesion of aggregates in Periplaneta americana (L.) cockroaches. We aimed to identify the chemical message inducing aggregation in this species. Two types of bioassays were used-binary choice tests in Petri dishes and tests in Y-olfactometer. Papers conditioned by direct contact of conspecifics induce aggregation when proposed in binary choice tests and were attractive in a Y-olfactometer. The identification of the molecules present on these conditioned papers indicated that dichloromethane extracts contained mainly cuticular hydrocarbons whereas methanol extracts contained more volatile molecules. Only a mixture of extracts in both solvents induced aggregation. High concentrations of cuticular hydrocarbons are necessary to induce aggregation when presented alone. When presented with volatile molecules present in methanol extracts, low concentrations of cuticular hydrocarbons are sufficient to induce aggregation if they are presented in contact. Among volatile molecules collected on filter paper, a mixture of three compounds-hexadecanoic acid, pentadecanoic acid, and pentaethylene glycol-induced aggregation. Our results provide evidence that aggregation processes in P. americana relies on a dual mechanism: attraction over long distances by three volatile molecules and maintenance on site by contact with cuticular hydrocarbons. PMID:26313978

  10. Effect of Phosphoric Acid Concentration on the Characteristics of Sugarcane Bagasse Activated Carbon

    NASA Astrophysics Data System (ADS)

    Adib, M. R. M.; Suraya, W. M. S. W.; Rafidah, H.; Amirza, A. R. M.; Attahirah, M. H. M. N.; Hani, M. S. N. Q.; Adnan, M. S.

    2016-07-01

    Impregnation method is one of the crucial steps involved in producing activated carbon using chemical activation process. Chemicals employed in this step is effective at decomposing the structure of material and forming micropores that helps in adsorption of contaminants. This paper explains thorough procedures that have been involved in producing sugarcane bagasse activated carbon (SBAC) by using 5%, 10%, 20%, 30% phosphoric acid (H3PO4) during the impregnation step. Concentration of H3PO4 used in the process of producing SBAC was optimized through several tests including bulk density, ash content, iodine adsorption and pore size diameter and the charactesristic of optimum SBAC produced has been compared with commercial activated carbon (CAC). Batch study has been carried out by using the SBAC produced from optimum condition to investigate the performance of SBAC in removal of turbidity and chemical oxygen demand (COD) from textile wastewater. From characteristic study, SBAC with 30% H3PO4 has shown the optimum value of bulk density, ash content, iodine adsorption and pore size diameter of 0.3023 g cm-3, 4.35%, 974.96 mg/g and 0.21-0.41 µm, respectively. These values are comparable to the characteristics of CAC. Experimental result from the batch study has been concluded that the SBAC has a promising potential in removing turbidity and COD of 75.5% and 66.3%, respectively which was a slightly lower than CAC which were able to remove 82.8% of turbidity and 70% of COD. As a conclusion, the SBAC is comparable with CAC in terms of their characteristics and the capability of removing contaminants from textile wastewater. Therefore, it has a commercial value to be used as an alternative of low-cost material in producing CAC.

  11. Detergent-mediated protein aggregation.

    PubMed

    Neale, Chris; Ghanei, Hamed; Holyoake, John; Bishop, Russell E; Privé, Gilbert G; Pomès, Régis

    2013-04-01

    Because detergents are commonly used to solvate membrane proteins for structural evaluation, much attention has been devoted to assessing the conformational bias imparted by detergent micelles in comparison to the native environment of the lipid bilayer. Here, we conduct six 500-ns simulations of a system with >600,000 atoms to investigate the spontaneous self assembly of dodecylphosphocholine detergent around multiple molecules of the integral membrane protein PagP. This detergent formed equatorial micelles in which acyl chains surround the protein's hydrophobic belt, confirming existing models of the detergent solvation of membrane proteins. In addition, unexpectedly, the extracellular and periplasmic apical surfaces of PagP interacted with the headgroups of detergents in other micelles 85 and 60% of the time, respectively, forming complexes that were stable for hundreds of nanoseconds. In some cases, an apical surface of one molecule of PagP interacted with an equatorial micelle surrounding another molecule of PagP. In other cases, the apical surfaces of two molecules of PagP simultaneously bound a neat detergent micelle. In these ways, detergents mediated the non-specific aggregation of folded PagP. These simulation results are consistent with dynamic light scattering experiments, which show that, at detergent concentrations ≥600 mM, PagP induces the formation of large scattering species that are likely to contain many copies of the PagP protein. Together, these simulation and experimental results point to a potentially generic mechanism of detergent-mediated protein aggregation.

  12. 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

  13. Cellular Strategies for Regulating Functional and Nonfunctional Protein Aggregation

    PubMed Central

    Gsponer, Jörg; Babu, M. Madan

    2012-01-01

    Summary Growing evidence suggests that aggregation-prone proteins are both harmful and functional for a cell. How do cellular systems balance the detrimental and beneficial effect of protein aggregation? We reveal that aggregation-prone proteins are subject to differential transcriptional, translational, and degradation control compared to nonaggregation-prone proteins, which leads to their decreased synthesis, low abundance, and high turnover. Genetic modulators that enhance the aggregation phenotype are enriched in genes that influence expression homeostasis. Moreover, genes encoding aggregation-prone proteins are more likely to be harmful when overexpressed. The trends are evolutionarily conserved and suggest a strategy whereby cellular mechanisms specifically modulate the availability of aggregation-prone proteins to (1) keep concentrations below the critical ones required for aggregation and (2) shift the equilibrium between the monomeric and oligomeric/aggregate form, as explained by Le Chatelier’s principle. This strategy may prevent formation of undesirable aggregates and keep functional assemblies/aggregates under control. PMID:23168257

  14. Aggregation of organic matter by pelagic tunicates

    SciTech Connect

    Pomeroy, L.R.; Deibel, D.

    1980-07-01

    Three genera of pelagic tunicates were fed concentrates of natural seston and an axenic diatom culture. Fresh and up to 4-day-old feces resemble flocculent organic aggregates containing populations of microorganisms, as described from highly productive parts of the ocean, and older feces resemble the nearly sterile flocculent aggregates which are ubiquitous in surface waters. Fresh feces consist of partially digested phytoplankton and other inclusions in an amorphous gelatinous matrix. After 18 to 36 h, a population of large bacteria develops in the matrix and in some of the remains of phytoplankton contained in the feces. From 48 to 96 h, protozoan populations arise which consume the bacteria and sometimes the remains of the phytoplankton in the feces. Thereafter only a sparse population of microorganisms remains, and the particles begin to fragment. Water samples taken in or below dense populations of salps and doliolids contained greater numbers of flocculent aggregates than did samples from adjacent stations.

  15. Contrasting effects of nanoparticle-protein attraction on amyloid aggregation

    PubMed Central

    Radic, Slaven; Davis, Thomas P; Ke, Pu Chun; Ding, Feng

    2015-01-01

    Nanoparticles (NPs) have been experimentally found to either promote or inhibit amyloid aggregation of proteins, but the molecular mechanisms for such complex behaviors remain unknown. Using coarse-grained molecular dynamics simulations, we investigated the effects of varying the strength of nonspecific NP-protein attraction on amyloid aggregation of a model protein, the amyloid-beta peptide implicated in Alzheimer's disease. Specifically, with increasing NP-peptide attraction, amyloid aggregation on the NP surface was initially promoted due to increased local protein concentration on the surface and destabilization of the folded state. However, further increase of NP-peptide attraction decreased the stability of amyloid fibrils and reduced their lateral diffusion on the NP surface necessary for peptide conformational changes and self-association, thus prohibiting amyloid aggregation. Moreover, we found that the relative concentration between protein and NPs also played an important role in amyloid aggregation. With a high NP/protein ratio, NPs that intrinsically promote protein aggregation may display an inhibitive effect by depleting the proteins in solution while having a low concentration of the proteins on each NP's surface. Our coarse-grained molecular dynamics simulation study offers a molecular mechanism for delineating the contrasting and seemingly conflicting effects of NP-protein attraction on amyloid aggregation and highlights the potential of tailoring anti-aggregation nanomedicine against amyloid diseases. PMID:26989481

  16. Characterization and modeling of thermal diffusion and aggregation in nanofluids.

    SciTech Connect

    Gharagozloo, Patricia E.; Goodson, Kenneth E.

    2010-05-01

    Fluids with higher thermal conductivities are sought for fluidic cooling systems in applications including microprocessors and high-power lasers. By adding high thermal conductivity nanoscale metal and metal oxide particles to a fluid the thermal conductivity of the fluid is enhanced. While particle aggregates play a central role in recent models for the thermal conductivity of nanofluids, the effect of particle diffusion in a temperature field on the aggregation and transport has yet to be studied in depth. The present work separates the effects of particle aggregation and diffusion using parallel plate experiments, infrared microscopy, light scattering, Monte Carlo simulations, and rate equations for particle and heat transport in a well dispersed nanofluid. Experimental data show non-uniform temporal increases in thermal conductivity above effective medium theory and can be well described through simulation of the combination of particle aggregation and diffusion. The simulation shows large concentration distributions due to thermal diffusion causing variations in aggregation, thermal conductivity and viscosity. Static light scattering shows aggregates form more quickly at higher concentrations and temperatures, which explains the increased enhancement with temperature reported by other research groups. The permanent aggregates in the nanofluid are found to have a fractal dimension of 2.4 and the aggregate formations that grow over time are found to have a fractal dimension of 1.8, which is consistent with diffusion limited aggregation. Calculations show as aggregates grow the viscosity increases at a faster rate than thermal conductivity making the highly aggregated nanofluids unfavorable, especially at the low fractal dimension of 1.8. An optimum nanoparticle diameter for these particular fluid properties is calculated to be 130 nm to optimize the fluid stability by reducing settling, thermal diffusion and aggregation.

  17. Solute effects on the irreversible aggregation of serum albumin.

    PubMed

    Bagger, Heidi L; Øgendal, Lars H; Westh, Peter

    2007-10-01

    Thermal stress on bovine serum albumin (BSA) promotes protein aggregation through the formation of intermolecular beta-sheets. We have used light scattering and chromatography to study effects of (<1 M) Na(2)SO(4), NaSCN, sucrose, sorbitol and urea on the rate of the thermal aggregation. Both salts were strong inhibitors of BSA aggregation and they reduced both the size and number (concentration) of aggregate particles compared to non-ionic solutes (or pure buffer). Hence, the salts appear to suppress both nucleation- and growth rate. The non-electrolyte additives reduced the initial aggregation rate (compared to pure buffer), but did not significantly limit the extent of aggregation in samples quenched after 27 min. heat exposure (40-50% aggregation in all samples). The non-electrolytes did, however, modify the aggregation process as they consistently brought about smaller but more concentrated aggregates than pure buffer. The results are discussed along the lines of linkage- and transition state theories. In this framework, the rate of the aggregation process is governed by the equilibrium between a thermally denatured state (D) and the transition state D( not equal). Thus, the effect of a solute relies on its preferential interactions with respectively D and D( not equal). The current results do not show any correlation between the solutes' preferential interactions with native BSA and their effect on the rate of aggregation. This suggests that non-specific, "Hofmeister-type" interactions, which scale with the solvent accessible surface area, are of minor importance. Rather, salt induced suppression of aggregation is suggested to depend on the modulation of specific electrostatic forces in the D( not equal) state.

  18. Stress distributions in flowing aggregated colloidal suspensions

    SciTech Connect

    Silbert, L.E.; Farr, R.S.; Melrose, J.R.; Ball, R.C.

    1999-09-01

    Simulations of the flow of concentrated aggregated colloidal systems, at the particulate level, are used to investigate the distribution of stresses in the shear-thinning regime. It is found that the distribution of shear stress carried by interparticle bonds decays approximately exponentially at large stresses, but with a double-exponential distribution for values of positive stress. The microstructural mechanisms associated with large stresses are manifested in clusters which dominate the positive contribution to the stress in the system. Towards the end of shear thinning the highest forces occur along bonds defining rods of particles aligned approximately along the flow-compression direction. We propose that the rheology of such systems is determined by a rupture{endash}reformation process of these clusters of stress concentration during the flow. The aggregation forces play the role of enhancing such stress concentration by stabilizing clusters against buckling. {copyright} {ital 1999 American Institute of Physics.}

  19. Interactions and Aggregation of Charged Nanoparticles in Uncharged Polymer Solutions.

    PubMed

    Pandav, Gunja; Pryamitsyn, Victor; Ganesan, Venkat

    2015-11-17

    We employ an extension of the single chain in mean field simulation method to study mixtures of charged particles and uncharged polymers. We examine the effect of particle charge, polymer concentration, and particle volume fraction on the resulting particle aggregates. The structures of aggregates were characterized using particle-particle radial distribution functions and cluster size distributions. We observe that the level of aggregation between particles increases with increasing particle volume fraction and polymer concentration and decreasing particle charge. At intermediate regimes of particle volume fraction and polymer concentrations, we observe the formation of equilibrium clusters with a preferred size. We also examined the influence of manybody effects on the structure of a charged particle-polymer system. Our results indicate that the effective two-body approximation overpredicts the aggregation between particles even at dilute particle concentrations. Such effects are thought to be a consequence of the interplay between the respective manybody effects on the depletion and electrostatic interactions.

  20. Strong enhancement of spin ordering by A -site magnetic ions in the ferrimagnet CaC u3F e2O s2O12

    NASA Astrophysics Data System (ADS)

    Deng, Hongshan; Liu, Min; Dai, Jianhong; Hu, Zhiwei; Kuo, Changyang; Yin, Yunyu; Yang, Junye; Wang, Xiao; Zhao, Qing; Xu, Yuanji; Fu, Zhaoming; Cai, Jianwang; Guo, Haizhong; Jin, Kuijuan; Pi, Tunwen; Soo, Yunliang; Zhou, Guanghui; Cheng, Jinguang; Chen, Kai; Ohresser, Philippe; Yang, Yi-feng; Jin, Changqing; Tjeng, Liu-Hao; Long, Youwen

    2016-07-01

    A B O3 perovskite is a kind of very important functional material with versatile physical properties. Although B -site chemical substitution with various magnetic ions has been widely investigated, the A -site doping with magnetic transition metal is little known. Here we report A A3'B2B2'O12 -type A - and B -site ordered ferrimagnet CaC u3F e2O s2O12 with magnetic transition metals occupying three different atomic sites (A', B , and B' sites). This compound is synthesized by a special high-pressure annealing process. It possesses a much higher Curie temperature TC of 580 K compared with that of the B -site-only ordered C a2FeOs O6 (TC=320 K ) without magnetic ion at the A site. First-principles numerical calculations reveal that this enhancement primarily originates from the additional spin interaction between the A'-site C u2 + and the B'-site O s5 + , generating a strong C u2 +(↑) F e3 +(↑) O s5 +(↓) ferrimagnetic spin coupling. This work opens up an alternative way for enhancing the spin ordering temperature by introducing A -site magnetic ions.

  1. Measuring and modeling hemoglobin aggregation below the freezing temperature.

    PubMed

    Rosa, Mónica; Lopes, Carlos; Melo, Eduardo P; Singh, Satish K; Geraldes, Vitor; Rodrigues, Miguel A

    2013-08-01

    Freezing of protein solutions is required for many applications such as storage, transport, or lyophilization; however, freezing has inherent risks for protein integrity. It is difficult to study protein stability below the freezing temperature because phase separation constrains solute concentration in solution. In this work, we developed an isochoric method to study protein aggregation in solutions at -5, -10, -15, and -20 °C. Lowering the temperature below the freezing point in a fixed volume prevents the aqueous solution from freezing, as pressure rises until equilibrium (P,T) is reached. Aggregation rates of bovine hemoglobin (BHb) increased at lower temperature (-20 °C) and higher BHb concentration. However, the addition of sucrose substantially decreased the aggregation rate and prevented aggregation when the concentration reached 300 g/L. The unfolding thermodynamics of BHb was studied using fluorescence, and the fraction of unfolded protein as a function of temperature was determined. A mathematical model was applied to describe BHb aggregation below the freezing temperature. This model was able to predict the aggregation curves for various storage temperatures and initial concentrations of BHb. The aggregation mechanism was revealed to be mediated by an unfolded state, followed by a fast growth of aggregates that readily precipitate. The aggregation kinetics increased for lower temperature because of the higher fraction of unfolded BHb closer to the cold denaturation temperature. Overall, the results obtained herein suggest that the isochoric method could provide a relatively simple approach to obtain fundamental thermodynamic information about the protein and the aggregation mechanism, thus providing a new approach to developing accelerated formulation studies below the freezing temperature.

  2. 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.

  3. Impact of aggregate formation on the viscosity of protein solutions.

    PubMed

    Nicoud, Lucrèce; Lattuada, Marco; Yates, Andrew; Morbidelli, Massimo

    2015-07-21

    Gaining knowledge on the stability and viscosity of concentrated therapeutic protein solutions is of great relevance to the pharmaceutical industry. In this work, we borrow key concepts from colloid science to rationalize the impact of aggregate formation on the changes in viscosity of a concentrated monoclonal antibody solution. In particular, we monitor the kinetics of aggregate growth under thermal stress by static and dynamic light scattering, and we follow the rise in solution viscosity by measuring the diffusion coefficient of tracer nanoparticles with dynamic light scattering. Moreover, we characterize aggregate morphology in the frame of the fractal geometry. We show that the curves of the increase in viscosity with time monitored at three different protein concentrations collapse on one single master curve when the reaction profiles are normalized based on an effective volume fraction occupied by the aggregates, which depends on the aggregate size, concentration and morphology. Importantly, we find that the viscosity of an aggregate sample is lower than the viscosity of a monomeric sample of a similar occupied volume fraction due to the polydispersity of the aggregate distribution.

  4. 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.

  5. Hydrophobically modified polyelectrolytes: Characterization, aggregation and adsorption

    NASA Astrophysics Data System (ADS)

    Islam, Mohammad Ferdous

    The focus of our work was to experimentally study the aggregation and adsorption behavior of model HM polyelectrolytes. Hydrophobically modified alkali soluble emulsions (HASE), the model HM polyelectrolytes, were chosen because they had complex architecture yet possessed key variables for systematic study. The HASE polymers have methacrylic acid (MAA) and ethyl acrylate (EA) in the backbone with pendent hydrophobic groups. Characterization of a single molecule is an important first step in understanding the aggregation and adsorption of these polymers. However, characterizations of the HASE polymers using conventional techniques such as gel permeation chromatography or static light scattering were difficult because of the hydrophobic association. In this study, two different approaches have been taken to prevent the hydrophobic association in aqueous solution: (1) hydrolyze the polymer to cleave the hydrophobic constituents, and (2) use methyl beta-cyclodextrin that has a hydrophobic cavity and a hydrophilic outer shell, to shield the hydrophobes from associating. By taking these two approaches and using gel permeation chromatography (GPC), dynamic (DLS) and static (SLS) light scattering techniques, the molecular weight, hydrodynamic radius and radius of gyration of a single molecule were determined. Except for one chemical site, we were able to determine that branching or grafting did not occur in the polymer chain during synthesis. Our aggregation studies showed that, in aqueous solutions, the HASE polymers formed small aggregates (presumably single micelles of single or a few chains) and large aggregates (presumably formed by bridging between micelles). The radii and masses of the larger aggregates, measured using DLS and SLS, were found to increase with an increase in the polymer concentration, indicating an open association process for the HASE polymers. Our SLS results also showed that, at high salt concentration, the aggregates of the HASE polymer with

  6. 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

  7. 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

  8. Asphaltene Aggregation and Fouling Behavior

    NASA Astrophysics Data System (ADS)

    Derakhshesh, Marzie

    . Analysis of the spectra of the whole asphaltene samples in toluene indicates that the absorbance of visible light with wavelengths > 600 nm follows a lambda--4 dependence. This functional dependence is consistent with Rayleigh scattering. Rayleigh scattering provides strong evidence that the apparent absorption of visible light by asphaltenes from 600-800 nm is not a molecular absorption phenomenon but rather a scattering mechanism. Rayleigh scattering equations were combined with experimental visible spectra to estimate the average nanoaggregate sizes, which were in a very good agreement with the sizes reported in the literature. The occlusion of two polynuclear aromatic hydrocarbons (PAHs) (pyrene and phenanthrene) in asphaltene precipitates was tested by adding PAHs to the asphaltene in toluene solutions, precipitating by n-pentane and determining the amount of PAHs in precipitates using simulated distillation instrument. Pyrene and phenanthrene, which are normally soluble in the toluene-n-pentane solutions, were detected in the asphaltene precipitates at up to 6 wt% concentration. Trapping of PAHs outside of the nanoaggregates during precipitation gave 7-14 times less of the PAHs in the solid precipitate. This study shows that asphaltene aggregates can interact significantly with PAHs. The results are consistent with the presence open porous asphaltene nanoaggregates in solutions such as toluene.

  9. Kinetics of protein aggregation

    NASA Astrophysics Data System (ADS)

    Knowles, Tuomas

    2015-03-01

    Aggregation into linear nanostructures, notably amyloid and amyloid-like fibrils, is a common form of behaviour exhibited by a range of peptides and proteins. This process was initially discovered in the context of the aetiology of a range of neurodegenerative diseases, but has recently been recognised to of general significance and has been found at the origin of a number of beneficial functional roles in nature, including as catalytic scaffolds and functional components in biofilms. This talk discusses our ongoing efforts to study the kinetics of linear protein self-assembly by using master equation approaches combined with global analysis of experimental data.

  10. 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.

  11. 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

  12. Cholesteric liquid crystal devices with nanoparticle aggregation.

    PubMed

    Jeng, Shie-Chang; Hwang, Shug-June; Hung, Yu-Hsiang; Chen, Sheng-Chieh

    2010-10-11

    A broadband cholesteric liquid crystal (CLC) device with a multi-domain structure is demonstrated by using an aggregation of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in the CLC layer. The aggregation pattern of the self-assembled POSS nanoparticles depends on the concentration of POSS doped in the mixture of POSS/CLC and the cooling rate of the mixture from a temperature higher than the clear point. POSS-induced changes in the bulk and surface properties of the cholesteric cells, such as a promotion of homeotropic alignment, help to form a cholesteric structure with a broadband reflection of light; the latter can be used for improvement of bistable CLC devices. A higher POSS concentration and a higher cooling rate both improve the appearance of the black-white CLC device. PMID:20941154

  13. Detergent-mediated protein aggregation

    PubMed Central

    Neale, Chris; Ghanei, Hamed; Holyoake, John; Bishop, Russell E.; Privé, Gilbert G.; Pomès, Régis

    2016-01-01

    Because detergents are commonly used to solvate membrane proteins for structural evaluation, much attention has been devoted to assessing the conformational bias imparted by detergent micelles in comparison to the native environment of the lipid bilayer. Here, we conduct six 500-ns simulations of a system with >600,000 atoms to investigate the spontaneous self assembly of dodecylphosphocholine detergent around multiple molecules of the integral membrane protein PagP. This detergent formed equatorial micelles in which acyl chains surround the protein’s hydrophobic belt, confirming existing models of the detergent solvation of membrane proteins. In addition, unexpectedly, the extracellular and periplasmic apical surfaces of PagP interacted with the headgroups of detergents in other micelles 85 and 60% of the time, respectively, forming complexes that were stable for hundreds of nanoseconds. In some cases, an apical surface of one molecule of PagP interacted with an equatorial micelle surrounding another molecule of PagP. In other cases, the apical surfaces of two molecules of PagP simultaneously bound a neat detergent micelle. In these ways, detergents mediated the non-specific aggregation of folded PagP. These simulation results are consistent with dynamic light scattering experiments, which show that, at detergent concentrations ≥600 mM, PagP induces the formation of large scattering species that are likely to contain many copies of the PagP protein. Together, these simulation and experimental results point to a potentially generic mechanism of detergent-mediated protein aggregation. PMID:23466535

  14. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences.

  15. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences. PMID:27588427

  16. Control of binder viscosity and hygroscopicity on particle aggregation efficiency

    NASA Astrophysics Data System (ADS)

    Mueller, Sebastian B.; Kueppers, Ulrich; Ayris, Paul M.; Jacob, Michael; Delmelle, Pierre; Dingwell, Donald B.

    2016-04-01

    In the course of explosive volcanic eruptions, large amounts of ash are released into the atmosphere and may subsequently pose a threat to infrastructure, such as aviation industry. Ash plume forecasting is therefore a crucial tool for volcanic hazard mitigation but may be significantly affected by aggregation, altering the aerodynamic properties of particles. Models struggle with the implementation of aggregation since external conditions promoting aggregation have not been completely understood; in a previous study we have shown the rapid generation of ash aggregates through liquid bonding via the use of fluidization bed technology and further defined humidity and temperature ranges necessary to trigger aggregation. Salt (NaCl) was required for the recovery of stable aggregates, acting as a cementation agent and granting aggregate cohesion. A numerical model was used to explain the physics behind particle aggregation mechanisms and further predicted a dependency of aggregation efficiency on liquid binder viscosity. In this study we proof the effect of viscosity on particle aggregation. HCl and H2SO4 solutions were diluted to various concentrations resulting in viscosities between 1 and 2 mPas. Phonolitic and rhyolitic ash samples as well as soda-lime glass beads (serving as analogue material) were fluidized in the ProCell Lab® of Glatt Ingenieurtechnik GmbH and treated with the acids via a bottom-spray technique. Chemically driven interaction between acid liquids and surfaces of the three used materials led to crystal precipitation. Salt crystals (e.g. NaCl) have been confirmed through scanning electron microscopy (SEM) and leachate analysis. Both volcanic ash samples as well as the glass beads showed a clear dependency of aggregation efficiency on viscosity of the sprayed HCl solution. Spraying H2SO4 provoked a collapse of the fluidized bed and no aggregation has been observed. This is accounted by the high hygroscopicity of H2SO4. Dissolving CaCl2 (known to be

  17. [Influence of various anions and biological macromolecules on bacterial aggregation in vitro].

    PubMed

    Belcourt, A

    1975-09-01

    The effects of various anions on experimental bacterial aggregation has been studied with Streptococcus mutans OMZ 175 and Actinomyces viscosus X1, using an experimental system, based on the measurement of optical density in an aqueous polyethyleneglycol medium. Monovolent anions (acétate, chloride and fluoride) and sulphate had no effects on bacterial aggregation in salivary concentrations. However carbonate, mono and dihydrogenophosphates gave an important aggregation in relatively small saline concentrations. The study of the aggregation of Strep. mutans OMZ 175, grown in presence of sucrose for 12 to 96 hours, showed an increased aggregation of the micro-organims up to 24 hours. For longer incubation times, aggregation decreased. Finally a calcium precipitable salivary glycoprotein, at small concentrations, gave a bacterial aggregation of about 25% and may be important in dental plaque formation.

  18. STAND: Surface Tension for Aggregation Number Determination.

    PubMed

    Garrido, Pablo F; Brocos, Pilar; Amigo, Alfredo; García-Río, Luis; Gracia-Fadrique, Jesús; Piñeiro, Ángel

    2016-04-26

    Taking advantage of the extremely high dependence of surface tension on the concentration of amphiphilic molecules in aqueous solution, a new model based on the double equilibrium between free and aggregated molecules in the liquid phase and between free molecules in the liquid phase and those adsorbed at the air/liquid interface is presented and validated using literature data and fluorescence measurements. A key point of the model is the use of both the Langmuir isotherm and the Gibbs adsorption equation in terms of free molecules instead of the nominal concentration of the solute. The application of the model should be limited to non ionic compounds since it does not consider the presence of counterions. It requires several coupled nonlinear fittings for which we developed a software that is publicly available in our server as a web application. Using this tool, it is straightforward to get the average aggregation number of an amphiphile, the micellization free energy, the adsorption constant, the maximum surface excess (and so the minimum area per molecule), the distribution of solute in the liquid phase between free and aggregate species, and the surface coverage in only a couple of seconds, just by uploading a text file with surface tension vs concentration data and the corresponding uncertainties. PMID:27048988

  19. [A new highly sensitive method of analysis of thrombocyte aggregation].

    PubMed

    Gabbasov, Z A; Popov, E G; Gavrilov, I Iu; Pozin, E Ia; Markosian, R A

    1989-01-01

    The new method for studies of the platelet aggregation kinetics is based on the creation of a platelet stream through the optic canal and on an analysis of fluctuations in the intensity of the luminous flux that has passed through the sample. The relative dispersion of fluctuations in the intensity of the light passed through the sample is suggested as a parameter for the estimation of the platelet aggregation and for analysis of their aggregation kinetics. The method permits recording the platelet aggregation in citrate plasma, enriched for platelets, after exposure to the inductor in very low concentrations (0.05-0.15 microM ADP). Scanning electron microscopy has shown that aggregates are indeed formed in such cases, and they can be recorded from the increase of the relative dispersion in the fluctuations in the passed light intensity but cannot be recorded by Born's optic method.

  20. 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.

  1. Aggregation Properties of the Chromonic Liquid Crystal Benzopurpurin 4B

    NASA Astrophysics Data System (ADS)

    McKitterick, Christopher; Collings, Peter

    2009-03-01

    Benzopurpurin 4B (BPP) is a textile dye very similar to the common indicator Congo Red. As is true for all chromonics, the absorption spectrum is concentration dependent at low concentrations. If this dependence is used to estimate a free energy change for aggregation, it is higher than has been determined for other systems. Unlike other recently investigated chromonic liquid crystals, BPP forms a liquid crystal phase at extremely low concentrations, about 0.5 wt%. Also unlike these other chromonic liquid crystals, the aggregation kinetics are exceedingly slow. X-ray diffraction and light scattering measurements indicate that the aggregates of BPP are much larger than for chromonic systems that form liquid crystals at higher concentrations. BPP aggregates can be imaged using confocal microscopy, revealing a length distribution centered at 3 μm for a solution forced through a 0.2 μm filter. Over days the aggregates lengthen to well over 10 μm. The diameter of the aggregate images is slightly greater than the diffraction limit of the microscope, placing an upper limit on the diameter of 0.14 μm. These dimensions are consistent with the light scattering results.

  2. 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

  3. Aggregation of human polymorphonuclear leucocytes during phagocytosis of bacteria.

    PubMed Central

    Henricks, P A; van der Tol, M E; Verhoef, J

    1984-01-01

    The process of aggregation of human polymorphonuclear leucocytes (PMN) during the uptake of bacteria was studied. Radiolabelled S. aureus were opsonized in different sera, washed, resuspended in buffer and added to the PMN. Uptake of the bacteria and aggregation of the PMN were measured simultaneously. Maximal aggregation occurred within 6 min, when 5 X 10(6) PMN had phagocytosed 2.5 X 10(8) S. aureus. Also the effects of serum concentrations and different sera for opsonization of the bacteria on PMN aggregation were studied. Despite normal uptake, aggregation of PMN was low when bacteria were opsonized in complement-deficient sera. Furthermore when PMN were treated with pronase to inactivate complement receptors on the cell surface of the PMN, and bacteria preopsonized in immune serum were added, no change in uptake occurred, although the degree of aggregation halved compared to control PMN. So, interaction between the bacteria and the complement receptor of the PMN cell membrane is needed for triggering the process of aggregation. By using dansylcadaverin and diphenylamine to modulate lysosomal enzyme release, azide or PMN from a chronic granulomatous disease patient to study the effect of the formation of oxygen species, and theophylline, DB-cAMP or 8 Br-cAMP to increase cAMP levels, it was concluded that aggregation of PMN during phagocytosis was not dependent on oxygen metabolism, degranulation or cAMP levels of PMN. PMID:6086503

  4. [Physico-chemical methods for studing β-amyloid aggregation].

    PubMed

    Radko, S P; Khmeleva, S A; Suprun, E V; Kozin, S A; Bodoev, N V; Makarov, A A; Archakov, A I; Shumyantseva, V V

    2015-01-01

    Alzheimer's disease is the most prevalent neurodegenerative pathology. According to the amyloid cascade hypothesis, a key event of the Alzheimer's disease pathogenesis is a transition of the β-amyloid peptide (Аβ) from the monomeric form to the aggregated state. The mechanism of Аβ aggregation is intensively studied in vitro, by means of synthetic peptides and various physico-chemical methods allowing evaluation of size, molecular structure, and morphology of the formed aggregates. The paper reviews both the well-known and recently introduced physico-chemical methods for analysis of Аβ aggregation, including microscopу, optical and fluorescent methods, method of electron paramagnetic resonance, electrochemical and electrophoretic methods, gel-filtration, and mass spectrometric methods. Merits and drawbacks of the methods are discussed. The unique possibility to simultaneously observe Аβ monomers as well oligomers and large aggregates by means of atomic force microscopy or fluorescence correlation spectroscopy is emphasized. The high detection sensitivity of the latter method, monitoring the aggregation process in Аβ solutions at low peptide concentrations is underlined. Among mass spectrometric methods, the ion mobility mass spectrometry is marked out as a method enabling to obtain information about both the spectrum of Аβ oligomers and their structure. It is pointed out that the use of several methods giving the complementary data about Аβ aggregates is the best experimental approach to studying the process of b-amyloid peptide aggregation in vitro.

  5. Beyond diffusion-limited aggregation kinetics in microparticle suspensions.

    PubMed

    Erb, Randall M; Krebs, Melissa D; Alsberg, Eben; Samanta, Bappaditya; Rotello, Vincent M; Yellen, Benjamin B

    2009-11-01

    Aggregation in nondiffusion limited colloidal particle suspensions follows a temporal power-law dependence that is consistent with classical diffusion limited cluster aggregation models; however, the dynamic scaling exponents observed in these systems are not adequately described by diffusion limited cluster aggregation models, which expect these scaling exponents to be constant over all experimental conditions. We show here that the dynamic scaling exponents for 10 microm particles increase with the particle concentration and the particle-particle free energy of interaction. We provide a semiquantitative explanation for the scaling behavior in terms of the long-ranged particle-particle interaction potential. PMID:20364980

  6. Aggregation kinetics and dissolution of coated silver nanoparticles.

    PubMed

    Li, Xuan; Lenhart, John J; Walker, Harold W

    2012-01-17

    Determining the fate of manufactured nanomaterials in the environment is contingent upon understanding how stabilizing agents influence the stability of nanoparticles in aqueous systems. In this study, the aggregation and dissolution tendencies of uncoated silver nanoparticles and the same particles coated with three common coating agents, trisodium citrate, sodium dodecyl sulfate (SDS), and Tween 80 (Tween), were evaluated. Early stage aggregation kinetics of the uncoated and coated silver nanoparticles were assessed by dynamic light scattering over a range of electrolyte types (NaCl, NaNO(3), and CaCl(2)) and concentrations that span those observed in natural waters. Although particle dissolution was observed, aggregation of all particle types was still consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The aggregation of citrate-coated particles and SDS-coated particles were very similar to that for the uncoated particles, as the critical coagulation concentrations (CCC) of the particles in different electrolytes were all approximately the same (40 mM NaCl, 30 mM NaNO(3), and 2 mM CaCl(2)). The Tween-stabilized particles were significantly more stable than the other particles, however, and in NaNO(3) aggregation was not observed up to an electrolyte concentration of 1 M. Differences in the rate of aggregation under diffusion-limited aggregation conditions at high electrolyte concentrations for the SDS and Tween-coated particles, in combination with the moderation of their electrophoretic mobilities, suggest SDS and Tween imparted steric interactions to the particles. The dissolution of the silver nanoparticles was inhibited by the SDS and Tween coatings, but not by the citrate coating, and in chloride-containing electrolytes a secondary precipitate of AgCl was observed bridging the individual particles. These results indicate that coating agents could significant influence the fate of silver nanoparticles in aquatic systems, and in some

  7. Peptide aggregation in neurodegenerative disease.

    PubMed

    Murphy, Regina M

    2002-01-01

    In the not-so-distant past, insoluble aggregated protein was considered as uninteresting and bothersome as yesterday's trash. More recently, protein aggregates have enjoyed considerable scientific interest, as it has become clear that these aggregates play key roles in many diseases. In this review, we focus attention on three polypeptides: beta-amyloid, prion, and huntingtin, which are linked to three feared neurodegenerative diseases: Alzheimer's, "mad cow," and Huntington's disease, respectively. These proteins lack any significant primary sequence homology, yet their aggregates possess very similar features, specifically, high beta-sheet content, fibrillar morphology, relative insolubility, and protease resistance. Because the aggregates are noncrystalline, secrets of their structure at nanometer resolution are only slowly yielding to X-ray diffraction, solid-state NMR, and other techniques. Besides structure, the aggregates may possess similar pathways of assembly. Two alternative assembly pathways have been proposed: the nucleation-elongation and the template-assisted mode. These two modes may be complementary, not mutually exclusive. Strategies for interfering with aggregation, which may provide novel therapeutic approaches, are under development. The structural similarities between protein aggregates of dissimilar origin suggest that therapeutic strategies successful against one disease may have broad utility in others. PMID:12117755

  8. Topics in Probabilistic Judgment Aggregation

    ERIC Educational Resources Information Center

    Wang, Guanchun

    2011-01-01

    This dissertation is a compilation of several studies that are united by their relevance to probabilistic judgment aggregation. In the face of complex and uncertain events, panels of judges are frequently consulted to provide probabilistic forecasts, and aggregation of such estimates in groups often yield better results than could have been made…

  9. Mineral of the month: aggregates

    USGS Publications Warehouse

    Tepordei, Valentin V.

    2005-01-01

    Natural aggregates, consisting of crushed stone, and sand and gravel, are a major contributor to economic health, and have an amazing variety of uses. Aggregates are among the most abundant mineral resources and are major basic raw materials used by construction, agriculture and other industries that employ complex chemical and metallurgical processes.

  10. Theory for the aggregation of proteins and copolymers

    SciTech Connect

    Fields, G.B.; Alonso, D.O.V.; Stigter, D.; Dill, K.A.

    1992-05-14

    We develop mean-field lattice statistical mechanics theory for the equilibrium between denatured and aggregated states of proteins and other random copolymers of hydrophobic and polar monomers in aqueous solution. We suppose that the aggregated state is a mixture of amorphous polymer plus solvent and that the driving forces are the hydrophobic interaction, which favors aggregation, and conformational and translational entropies, which favor disaggregation. The theory predicts that the phase diagram for thermal aggregation is an asymmetric closed loop, and for denaturants (guanidinium hydrochloride of urea) it is asymmetric with an upper consolute point. The theory predicts that a copolymer in a poor solvent will expand with increasing polymer concentration because of {open_quotes}screening{close_quotes} of the solvent interactions by the other chains; the chain ultimately reaches a theta-like state in the absence of solvent. The screening concentration depends strongly on the copolymer composition. We find two striking features of these copolymer phase diagrams. First, they are extraordinarily sensitive to the copolymer composition; a change of one amino acid can substantially change the aggregation behavior. Second, relative to homopolymers, copolymers should be stable against aggregation at concentrations that are higher by many orders of magnitude. 43 refs., 13 figs.

  11. Aggregation by depletion attraction in cultures of bacteria producing exopolysaccharide

    PubMed Central

    Dorken, Gary; Ferguson, Gail P.; French, Chris E.; Poon, Wilson C. K.

    2012-01-01

    In bacteria, the production of exopolysaccharides—polysaccharides secreted by the cells into their growth medium—is integral to the formation of aggregates and biofilms. These exopolysaccharides often form part of a matrix that holds the cells together. Investigating the bacterium Sinorhizobium meliloti, we found that a mutant that overproduces the exopolysaccharide succinoglycan showed enhanced aggregation, resulting in phase separation of the cultures. However, the aggregates did not appear to be covered in polysaccharides. Succinoglycan purified from cultures was applied to different concentrations of cells, and observation of the phase behaviour showed that the limiting polymer concentration for aggregation and phase separation to occur decreased with increasing cell concentration, suggesting a ‘crowding mechanism’ was occurring. We suggest that, as found in colloidal dispersions, the presence of a non-adsorbing polymer in the form of the exopolysaccharide succinoglycan drives aggregation of S. meliloti by depletion attraction. This force leads to self-organization of the bacteria into small clusters of laterally aligned cells, and, furthermore, leads to aggregates clustering into biofilm-like structures on a surface. PMID:22896568

  12. Sans study of asphaltene aggregation

    SciTech Connect

    Overfield, R.E.; Sheu, E.Y.; Sinha, S.K.; Liang, K.S. )

    1988-06-01

    The colloidal properties of asphaltenes have long been recognized from peculiarities in their solubility and colligative properties. A layered micellar model or asphaltenes was proposed by others in which a highly condensed alkyl aromatic formed the central part, and molecules of decreasingly aromatic character (resins) clustered around them. Numerous studies, based on a variety of techniques such as ultracentrifugation and electron microscopy indicated a particulate nature for asphaltenes with size 20-40 A diameter. Others have proposed a refined model based on x-ray diffraction and small angle scattering. In this model, interactions between flat sheets of condensed aromatic rings form the central ''crystallite'' part of a spherical particle with the outer part being comprised of the aliphatic positions of the same molecules. These particles are bunched together with some degree of entanglement into ''micelles''. Concentration and solvent dependent radii of gyration, ranging from 30-50 A were reported. The aggregation creates a good deal of uncertainty as to the true molecular size or weight of asphaltenes. Neutron scattering offers novel contrast relative to light scattering (refractive index) and x-ray scattering (electron density). This is because the scattering length of proton is negative, whereas that from deuterium and other nuclei such as C, S, O, and N are positive. Thus by replacing hydrogen with deuterium in either the solvent or the scatterer the contrast can be varied, and different parts of the molecule can be highlighted.

  13. Aggregated models for integrated distillation systems

    SciTech Connect

    Caballero, J.A.; Grossmann, I.E.

    1999-06-01

    In this work the authors present an aggregated representation for distillation columns that can be used in the synthesis of separation sequences with heat integration. A new aggregated model is first presented for the stripping and rectifying sections of individual distillation columns. This model is based on mass balances and equilibrium feasibility, expressed in terms of flows, inlet concentrations, and recoveries. The energy balance can then be decoupled from the mass balance, and the utilities can be calculated for each separation task. The proposed model is applied to three different superstructures: state task network, state equipment network, and an intermediate representation. The proposed model yields a lower bound to the vapor flow or to the total cost of the utilities. Performance of the different superstructure representations in terms of robustness and computational time is illustrated with several examples.

  14. 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.

  15. Molecular aggregation of humic substances

    USGS Publications Warehouse

    Wershaw, R. L.

    1999-01-01

    Humic substances (HS) form molecular aggregates in solution and on mineral surfaces. Elucidation of the mechanism of formation of these aggregates is important for an understanding of the interactions of HS in soils arid natural waters. The HS are formed mainly by enzymatic depolymerization and oxidation of plant biopolymers. These reactions transform the aromatic and lipid plant components into amphiphilic molecules, that is, molecules that consist of separate hydrophobic (nonpolar) and hydrophilic (polar) parts. The nonpolar parts of the molecules are composed of relatively unaltered segments of plant polymers and the polar parts of carboxylic acid groups. These amphiphiles form membrane-like aggregates on mineral surfaces and micelle-like aggregates in solution. The exterior surfaces of these aggregates are hydrophilic, and the interiors constitute separate hydrophobic liquid-like phases.

  16. Nanoparticle aggregation: principles and modeling.

    PubMed

    Zhang, Wen

    2014-01-01

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

  17. Immunogenicity of Therapeutic Protein Aggregates.

    PubMed

    Moussa, Ehab M; Panchal, Jainik P; Moorthy, Balakrishnan S; Blum, Janice S; Joubert, Marisa K; Narhi, Linda O; Topp, Elizabeth M

    2016-02-01

    Therapeutic proteins have a propensity for aggregation during manufacturing, shipping, and storage. The presence of aggregates in protein drug products can induce adverse immune responses in patients that may affect safety and efficacy, and so it is of concern to both manufacturers and regulatory agencies. In this vein, there is a lack of understanding of the physicochemical determinants of immunological responses and a lack of standardized analytical methods to survey the molecular properties of aggregates associated with immune activation. In this review, we provide an overview of the basic immune mechanisms in the context of interactions with protein aggregates. We then critically examine the literature with emphasis on the underlying immune mechanisms as they relate to aggregate properties. Finally, we highlight the gaps in our current understanding of this issue and offer recommendations for future research. PMID:26869409

  18. Mechanics of fire ant aggregations

    NASA Astrophysics Data System (ADS)

    Tennenbaum, Michael; Liu, Zhongyang; Hu, David; Fernandez-Nieves, Alberto

    2016-01-01

    Fire ants link their bodies to form aggregations; these can adopt a variety of structures, they can drip and spread, or withstand applied loads. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks.

  19. Mechanics of fire ant aggregations.

    PubMed

    Tennenbaum, Michael; Liu, Zhongyang; Hu, David; Fernandez-Nieves, Alberto

    2016-01-01

    Fire ants link their bodies to form aggregations; these can adopt a variety of structures, they can drip and spread, or withstand applied loads. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks. PMID:26501413

  20. Adsorption-induced colloidal aggregation

    NASA Astrophysics Data System (ADS)

    Law, B. M.; Petit, J.-M.; Beysens, D.

    1998-03-01

    Reversible colloidal aggregation in binary liquid mixtures has been studied for a number of years. As the phase separation temperature of the liquid mixture is approached the thickness of an adsorption layer around the colloidal particles increases. Beysens and coworkers have demonstrated experimentally that this adsorption layer is intimately connected with the aggregation of the colloidal particles, however, no definitive theory has been available which can explain all of the experimental observations. In this contribution we describe an extension of the Derjaguin, Landau, Verwey, and Overbeek theory of colloidal aggregation which takes into account the presence of the adsorption layer and which more realistically models the attractive dispersion interactions. This modified theory can quantitatively account for many of the observed experimental features such as the characteristics of the aggregated state, the general shape of the aggregation line, and the temperature dependence of the second virial coefficient for a lutidine-water mixture containing a small volume fraction of silica colloidal particles.

  1. Aggregate-based sub-CMC Solubilization of Hexadecane by Surfactants

    PubMed Central

    Zhong, Hua; Yang, Lei; Zeng, Guangming; Brusseau, Mark L.; Wang, Yake; Li, Yang; Liu, Zhifeng; Yuan, Xingzhong; Tan, Fei

    2015-01-01

    Solubilization of hexadecane by two surfactants, SDBS and Triton X-100, at concentrations near the critical micelle concentration (CMC) and the related aggregation behavior was investigated in this study. Solubilization was observed at surfactant concentrations lower than CMC, and the apparent solubility of hexadecane increased linearly with surfactant concentration for both surfactants. The capacity of SDBS to solubilize hexadecane is stronger at concentrations below CMC than above CMC. In contrast, Triton X-100 shows no difference. The results of dynamic light scattering (DLS) and cryogenic TEM analysis show aggregate formation at surfactant concentrations lower than CMC. DLS-based size of the aggregates (d) decreases with increasing surfactant concentration. Zeta potential of the SDBS aggregates decreases with increasing SDBS concentration, whereas it increases for Triton X-100. The surface excess (Γ) of SDBS calculated based on hexadecane solubility and aggregate size data increases rapidly with increasing bulk concentration, and then asymptotically approaches the maximum surface excess (Γmax). Conversely, there is only a minor increase in Γ for Triton X-100. Comparison of Γ and d indicates that excess of surfactant molecules at aggregate surface has great impact on surface curvature. The results of this study demonstrate formation of aggregates at surfactant concentrations below CMC for hexadecane solubilization, and indicate the potential of employing low-concentration strategy for surfactant application such as remediation of HOC contaminated sites. PMID:26925230

  2. 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.

  3. Study of colloidal particle Brownian aggregation by low-coherence fiber optic dynamic light scattering.

    PubMed

    Xia, Hui; Pang, Ru Yi; Zhang, Rui; Miao, Cai Xia; Wu, Xiao Yun; Hou, Xue Shun; Zhong, Cheng

    2012-06-15

    The aggregation kinetics of particles in dense polystyrene latex suspensions is studied by low-coherence fiber optic dynamic light scattering. Low-coherence fiber optic dynamic light scattering is used to measure the hydrodynamic radius of the aggregates. The aggregation kinetics data obtained can be fitted into a single exponential function, which is the characteristic of slow aggregation. It is found that the aggregation rate of particles increased with higher electrolyte levels and with larger particle concentrations. The experimental results can be explained by use of the Derjaruin-Landau-Verwey-Overbeer (DLVO) theory. PMID:22446146

  4. 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

  5. Early (pre-DLVO) studies of particle aggregation.

    PubMed

    Vincent, Brian

    2012-01-15

    The history of colloid science, from its modern foundations in the mid-nineteenth century, has been strongly concerned with studies of the aggregation of colloidal particles. It was Thomas Graham (1861) who defined the word "colloid" (from the Greek word for glue) for those materials which could not pass through membranes, unlike smaller, truly-dissolved materials. Subsequently, Graham (1864), following earlier studies, principally by Selmi and Faraday, described "the power possessed by salts for destroying colloidal solutions". Although numerous, quantitative studies of particle aggregation were made in the years that followed, in particular, the determination of minimum electrolyte concentrations for the onset of particle aggregation and aggregation rates, no general theoretical framework emerged to account for these quantitative findings until the middle of the twentieth century. It was during and immediately following the Second World War that two sets of authors, Derjaguin and Landau, in Russia, and Verwey and Overbeek, in the Netherlands, independently came up with the theory that is now universally referred to as the DLVO theory of particle interactions and aggregation. All modern developments of the theory of particle aggregation use the DLVO theory as the keystone. However, the DLVO theory itself was based on a large body of experimental data in regard to particle aggregation obtained over the previous hundred years or so. This article is an attempt to review that body of experimental data and to show how this guided the DLVO authors in their thinking.

  6. Purified human plasma kallikrein aggregates human blood neutrophils.

    PubMed Central

    Schapira, M; Despland, E; Scott, C F; Boxer, L A; Colman, R W

    1982-01-01

    Exposure of human blood polymorphonuclear leukocytes (PMN) to purified active plasma kallikrein resulted in PMN aggregation when kallikrein was present at concentrations ranging from 0.4 to 0.6 U/ml (0.18-0.27 microM). Kallikrein-induced PMN aggregation was not mediated through C5-derived peptides, because identical responses were observed whether or not kallikrein had been preincubated with an antibody to C5. Moreover, kallikrein was specific for aggregating PMN, because no aggregation was observed with Factor XII active fragments (23 nM), Factor XIa (0.6 U/ml or 15nM), thrombin (1.6 microM), plasmin (2 microM), porcine pancreatic elastase (2 microM), bovine pancreatic chymotrypsin (2 microM), or bradykinin (1 microM). Bovine pancreatic trypsin (2 microM) aggregated PMN, but to a lesser extent than kallikrein (0.18 microM). Kallikrein was a potent aggregant agent for PMN because similar responses were observed with kallikrein (0.5 U/ml or 0.23 microM) and an optimal dose (0.2 microM) of N-formyl-methionyl-leucyl-phenylalanine. In addition, PMN incubation with kallikrein resulted in stimulation of their oxidative metabolism as assessed by an increased oxygen uptake. Neutropenia and leukostasis observed in diseases associated with activation of the contact phase system may be the result of PMN aggregation by plasma kallikrein. PMID:6917855

  7. Fractal aggregates in Titan's atmosphere

    NASA Astrophysics Data System (ADS)

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

    1993-04-01

    The cluster structure of Titan's atmosphere was modeled by using an Eulerian microphysical model with the specific formulation of microphysical laws applying to fractal particles. The growth of aggregates in the settling phase was treated by introducing the fractal dimension as a parameter of the model. The model was used to obtain a vertical distribution of size and number density of the aggregates for different production altitudes. Results confirm previous estimates of the formation altitude of photochemical aerosols. The vertical profile of the effective radius of aggregates was calculated as a function of the visible optical depth.

  8. Monodisperse magnetite nanofluids: Synthesis, aggregation, and thermal conductivity

    NASA Astrophysics Data System (ADS)

    Jiang, Wei; Wang, Liqiu

    2010-12-01

    Magnetic nanofluids possess some unique properties that can significantly affect their thermal conductivity. We synthesize monodispersed magnetite (Fe3O4) nanofluids in toluene with the particle size from 4 to 12 nm and obtain aqueous nanofluids by a simple "one-step" phase transfer. Even without the effect of external field, the magnetic-interaction-induced self-assembled aggregation can still be significant in magnetite nanofluids. Investigation of the microstructures of self-assembled aggregation is carried out by the dynamic light scattering, which unveils the variation of aggregated configurations with particle concentration and time. Based on the calculation from the existing models, the aggregates decrease the thermal conductivity of both themselves and the entire system, mainly due to the less solid contents and weaker mobility compared with the single particles as well as the increase in interfacial thermal resistance. As the manifestation of the aggregation-structure variation, the measured thermal conductivity is of a wavelike shape as a function of particle concentration. The particle coating layers are also of importance in cluster formation so that nanofluid thermal conductivity can be manipulated for some nanofluids by changing the stabilizer used and thus controlling the particle aggregated structures. Due to the effects of temperature, viscosity and coating layers, the thermal conductivity for aqueous system varies in a different way as that for the toluene system.

  9. Lysozyme Aggregation and Fibrillation Monitored by Dynamic Light Scattering

    NASA Astrophysics Data System (ADS)

    Nemzer, Louis; Flanders, Bret; Schmit, Jeremy; Sorensen, Christopher

    2012-02-01

    The aggregation of amyloidogenic proteins provides a rich phase space with significant biomedical implications, including a link with several age-related diseases. We employed dynamic light scattering to monitor the aggregation of lysozyme, a model protein, from a monomeric state until the formation of micron-sized fibrils. For an aqueous lysozyme solution buffered at pH 2, the auto-correlation function of the scattered light intensity was found to be well-fit by a single exponential function with decay time τ = 1/(2Dq^2) = 0.25 ms, which corresponds to a mean hydrodynamic radius (RH) of 2.2 nm, very likely generated by monomers. Ethanol (4% v/v final concentration) induced a partial unfolding, to RH = 4.6 nm. The subsequent addition of 70 mM KCl was found to shrink the size back to RH = 2.5 nm, as expected when a denatured protein refolds due to partial screening of the intramolecular repulsion. However, further aggregation was not observed. At pH 4, using a low-salt acetate buffer, more ethanol (10% v/v) was required to initiate unfolding, but once it occurred, larger aggregates formed. These results are consistent with the model that partial unfolding, which exposes beta-motif secondary structure, is a prerequisite for aggregation and fibrillation, but the aggregation fate depends on the protein charge state (pH) and screening (salt concentration).

  10. Paradoxical Acceleration of Dithiothreitol-Induced Aggregation of Insulin in the Presence of a Chaperone

    PubMed Central

    Bumagina, Zoya; Gurvits, Bella; Artemova, Natalya; Muranov, Konstantin; Kurganov, Boris

    2010-01-01

    The kinetics of dithiothreitol (DTT)-induced aggregation of human recombinant insulin and the effect of α-crystallin, a representative of the family of small heat shock proteins, on the aggregation process have been studied using dynamic light scattering technique. Analysis of the distribution of the particles by size measured in the course of aggregation showed that the initial stage of the aggregation process was the stage of formation of the start aggregates with a hydrodynamic radius (Rh) of about 90 nm. When studying the effect of α-crystallin on the rate of DTT-induced aggregation of insulin, it was demonstrated that low concentrations of α-crystallin dramatically accelerated the aggregation process, whereas high concentrations of α-crystallin suppressed insulin aggregation. In the present study, at the molar stoichiometric ratio (insulin:α-crystallin) less than 1:0.5, a pronounced accelerating effect of α-crystallin was observed; whereas a ratio exceeding the value of 1:0.6 caused suppression of insulin aggregation. The mechanisms underlying the dual effect of α-crystallin have been proposed. It is assumed that heterogeneous nucleation occurring on the surface of the α-crystallin particle plays the key role in the paradoxical acceleration of insulin aggregation by α-crystallin that may provide an alternative biologically significant pathway of the aggregation process. PMID:21151456

  11. Perturbing Streaming in Dictyostelium discoidium Aggregation

    NASA Astrophysics Data System (ADS)

    Rericha, Erin; Garcia, Gene; Parent, Carole; Losert, Wolfgang

    2009-03-01

    The ability of cells to move towards environmental cues is a critical process allowing the destruction of intruders by the immune system, the formation of the vascular system and the whole scale remodeling of tissues during embryo development. We examine the initial transition from single cell to group migration in the social amoeba Dictyostelium discoidium. Upon starvation, D. discoidium cells enter into a developmental program that triggers solitary cells to aggregate into a multicellular structure. The aggregation is mediated by the small molecule, cyclic-AMP, that cells sense, synthesize, secrete and migrate towards often in a head-to-tail fashion called a stream. Using experiment and numerical simulation, we study the sensitivity of streams to perturbations in the cyclic-AMP concentration field. We find the stability of the streams requires cells to shape the cyclic-AMP field through localized secretion and degradation. In addition, we find the streaming phenotype is sensitive to changes in the substrate properties, with slicker surfaces leading to longer more branched streams that yield large initial aggregates.

  12. Platelet aggregation associated with ethanol intoxication

    SciTech Connect

    Volk, S.; Walenga, J.; Fareed, J.; Schumacher, H. )

    1989-02-09

    Alcohol is known to produce profound effects on blood; during chronic intoxication, prolongation of bleeding time has been reported. Utilizing human platelet rich plasma, we have studied the effect of alcohol on epinephrine, arachidonic acid and ADP induced aggregation. Control responses were obtained with saline from which the relative inhibition by alcohol was calculated. These studies were carried out at a concentration of 1.25-5.0 mg/ml which represents 0.125-0.5% alcohol blood levels. From 25 normal male and female volunteers, without prior hemostatic defects or drug ingestion, a dose-dependent inhibition by alcohol of all three agonist induced aggregations was noted. Alcohol itself did not produce any aggregation response. These studies demonstrate that alcohol at levels which are reached during intoxication is capable of impairing platelet function. The implication of this finding on the bleeding complications in healthy intoxicated patients may be significant during traumatic events, and individuals taking antiplatelet drugs may present a more serious hemostatic deficit during alcohol intoxication.

  13. Diffusion-limited aggregates grown on nonuniform substrates

    NASA Astrophysics Data System (ADS)

    Cornette, V.; Centres, P. M.; Ramirez-Pastor, A. J.; Nieto, F.

    2013-12-01

    In the present paper, patterns of diffusion-limited aggregation (DLA) grown on nonuniform substrates are investigated by means of Monte Carlo simulations. We consider a nonuniform substrate as the largest percolation cluster of dropped particles with different structures and forms that occupy more than a single site on the lattice. The aggregates are grown on such clusters, in the range the concentration, p, from the percolation threshold, pc up to the jamming coverage, pj. At the percolation threshold, the aggregates are asymmetrical and the branches are relatively few. However, for larger values of p, the patterns change gradually to a pure DLA. Tiny qualitative differences in this behavior are observed for different k sizes. Correspondingly, the fractal dimension of the aggregates increases as p raises in the same range pc≤p≤pj. This behavior is analyzed and discussed in the framework of the existing theoretical approaches.

  14. Lubrication properties of protein aggregate dispersions in a soft contact.

    PubMed

    Chojnicka, Agnieszka; de Jong, Saskia; de Kruif, Cornelus G; Visschers, Ronald W

    2008-02-27

    The lubrication, rheological, and molecular properties of two different protein aggregate dispersions were compared: globular aggregates of whey protein isolate (WPI) and fibrillar aggregates of ovalbumin from egg white. These dispersions are models for the lubricating fluid that is present between the tongue and the palate when consuming liquid or gelled products. To simulate oral conditions, a commercial tribometer was modified so that soft rubber surfaces could be used. This allowed us to measure friction at low contact pressures similar to those present between the tongue and palate. Clear correlations were observed between the measured friction coefficients and specific properties of the lubricating fluid such as protein concentration and aggregate size and shape. Furthermore, surface properties like elasticity, surface-surface interactions, and surface roughness had a significant effect on the friction under conditions that are relevant for texture perception. We conclude that in vitro measurements at low contact pressure provide valuable information for understanding and controlling food properties that modulate oral friction.

  15. Thiazine dyes: Evaluation of monomeric and aggregate forms

    NASA Astrophysics Data System (ADS)

    Vara, Jimena; Ortiz, Cristina S.

    2016-09-01

    The aggregation phenomenon of Azure B, monobrominated Azure B, Thionine and Methylene Blue was studied by UV-Visible spectrophotometry in different media as a function of dye concentration and temperature variations. The tests carried out in organic solvents allowed the identification of monomeric species of these compounds, which have not been reported in literature and have been wrongly assigned for years. The results obtained in water allowed demonstrating that different kinds of aggregates are present in this medium. In addition, the aggregation tendency of these dyes in organic solvent and aqueous media was established. Several parameters such as lipophilicity, effect of bulky substituents and interactions with media were considered to interpret the aggregation behavior of thiazine dyes.

  16. Fluorescent aggregates Cyan 40 and Thiazole Orange dyes in solution

    NASA Astrophysics Data System (ADS)

    Nizomov, Negmat; Kurtaliev, Eldar N.; Rahimov, Sherzod I.

    2012-12-01

    Absorption and fluorescence electronic spectra of cyanine dyes Cyan 40 and Thiazole Orange (TO) in water and in binary mixtures: water + ethanol, water + DMF, water + dioxane and chloroform + hexane were studied. It was revealed, that increase of concentration of Cyan 40 and TO dyes in water and chloroform + hexane binary mixture promotes the formation of fluorescent H-aggregates. Meanwhile, in contrary to the well-known fluorescent aggregates, electronic absorption band of aggregated molecules is shifted to the shorter wavelengths and fluorescence band is shifted to the longer wavelengths relative to the bands of the monomer molecules. Observed spectral changes are explained on the basis of Davidov's theory of molecular excitons as splitting of the electron-excited states due to the aggregation of dye molecules.

  17. Preparation of controlled gold nanoparticle aggregates using a dendronization strategy.

    PubMed

    Paez, Julieta I; Coronado, Eduardo A; Strumia, Miriam C

    2012-10-15

    In this work, a dendronization strategy was used to control interparticle spacing and the optical properties of gold nanoparticle (NP) aggregates in aqueous media. To achieve this goal, two dendritic disulfides bearing different functionalities on their periphery were synthesized and used as ligands to dendronize gold NPs. The dendronized NPs then undergo aggregation; this process was followed by UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electronic microscopy (TEM) measurements and correlated with Generalized Mie Theory electrodynamics calculations. For comparison, NP functionalization was also studied using a nondendritic ligand. It was found that the use of dendritic disulfides allows for the preparation of controlled NP aggregates. This study demonstrates how different dendronization parameters, such as disulfide concentration, temperature, time and nature of the ligand (dendritic vs nondendritic), determine the control exerted over the size and stability of the NP aggregates.

  18. Reversible NaCl-induced aggregation of a monoclonal antibody at low pH: Characterization of aggregates and factors affecting aggregation.

    PubMed

    Bickel, Fabian; Herold, Eva Maria; Signes, Alba; Romeijn, Stefan; Jiskoot, Wim; Kiefer, Hans

    2016-10-01

    We investigated the influence of pH and sodium chloride concentration on aggregation kinetics of a monoclonal antibody. Aggregation was induced by sodium chloride addition at low pH. Protein conformation before and after salt addition was determined as well as the reversibility of aggregation. Aggregation was monitored at pH values between 2 and 7 with NaCl up to 1.5M by turbidity measurement and size-exclusion chromatography. Particle size distribution was assessed by using size-exclusion chromatography as well as nanoparticle tracking analysis and flow imaging microscopy. Structural changes were monitored by circular dichroism, Fourier transform infrared and fluorescence spectroscopy. Thermal stability was measured by differential scanning fluorimetry. Aggregation propensity was maximal at low pH and high ionic strength. While thermal stability decreased with pH, the secondary structure remained unchanged down to pH 3.5 and up to 1.5M NaCl. Precipitated protein could be largely reverted to monomers by dilution into salt-free buffer. The re-solubilized antibody was indistinguishable in structure, solubility and monodispersity from the unstressed protein. Also, binding to Protein A was steady. Aggregation could be reduced in the presence of trehalose. The results suggest a reversible aggregation mechanism characterized by a limited change in tertiary structure at low pH and a subsequent loss of colloidal stability resulting from electrostatic repulsion once salt is added to the sample. The experimental setup is robust and allows high-throughput quantification of the effect of additives on aggregation kinetics. PMID:27449627

  19. Reversible NaCl-induced aggregation of a monoclonal antibody at low pH: Characterization of aggregates and factors affecting aggregation.

    PubMed

    Bickel, Fabian; Herold, Eva Maria; Signes, Alba; Romeijn, Stefan; Jiskoot, Wim; Kiefer, Hans

    2016-10-01

    We investigated the influence of pH and sodium chloride concentration on aggregation kinetics of a monoclonal antibody. Aggregation was induced by sodium chloride addition at low pH. Protein conformation before and after salt addition was determined as well as the reversibility of aggregation. Aggregation was monitored at pH values between 2 and 7 with NaCl up to 1.5M by turbidity measurement and size-exclusion chromatography. Particle size distribution was assessed by using size-exclusion chromatography as well as nanoparticle tracking analysis and flow imaging microscopy. Structural changes were monitored by circular dichroism, Fourier transform infrared and fluorescence spectroscopy. Thermal stability was measured by differential scanning fluorimetry. Aggregation propensity was maximal at low pH and high ionic strength. While thermal stability decreased with pH, the secondary structure remained unchanged down to pH 3.5 and up to 1.5M NaCl. Precipitated protein could be largely reverted to monomers by dilution into salt-free buffer. The re-solubilized antibody was indistinguishable in structure, solubility and monodispersity from the unstressed protein. Also, binding to Protein A was steady. Aggregation could be reduced in the presence of trehalose. The results suggest a reversible aggregation mechanism characterized by a limited change in tertiary structure at low pH and a subsequent loss of colloidal stability resulting from electrostatic repulsion once salt is added to the sample. The experimental setup is robust and allows high-throughput quantification of the effect of additives on aggregation kinetics.

  20. Formation of large micellar aggregates before equilibrium in diluted solutions

    NASA Astrophysics Data System (ADS)

    de Moraes, J. N. B.; Figueiredo, W.

    2013-06-01

    We study the formation of premicelles for different values of the concentration of amphiphile molecules in water. Our model consists of a square lattice with water molecules occupying one cell of the lattice while the amphiphilic molecules, represented by chains of five interconnected sites, occupy five cells of the lattice. We perform Monte Carlo simulations in the NVT ensemble, for a fixed temperature and different concentration of amphiphiles, ranging from below to above the critical micelle concentration. We start our simulations from a monomeric state and follow in time all the aggregates sizes until the equilibrium state is reached. We pay particular attention to two aggregate sizes, one related to the minimum and the other to the maximum of the aggregate-size distribution curve obtained at equilibrium. We show that these aggregates evolve in time exhibiting a maximum concentration well before the equilibrium state, revealing the formation of premicelles. The times to reach these maximum concentrations decrease exponentially with the total concentration of the system.

  1. Aggregation of Adenovirus 2 in Source Water and Impacts on Disinfection by Chlorine

    PubMed Central

    Cromeans, Theresa L.; Metcalfe, Maureen G.; Humphrey, Charles D.; Hill, Vincent R.

    2016-01-01

    It is generally accepted that viral particles in source water are likely to be found as aggregates attached to other particles. For this reason, it is important to investigate the disinfection efficacy of chlorine on aggregated viruses. A method to produce adenovirus particle aggregation was developed for this study. Negative stain electron microscopy was used to measure aggregation before and after addition of virus particles to surface water at different pH and specific conductance levels. The impact of aggregation on the efficacy of chlorine disinfection was also examined. Disinfection experiments with human adenovirus 2 (HAdV2) in source water were conducted using 0.2 mg/L free chlorine at 5 °C. Aggregation of HAdV2 in source water (≥3 aggregated particles) remained higher at higher specific conductance and pH levels. However, aggregation was highly variable, with the percentage of particles present in aggregates ranging from 43 to 71 %. Upon addition into source water, the aggregation percentage dropped dramatically. On average, chlorination CT values (chlorine concentration in mg/L × time in min) for 3-log10 inactivation of aggregated HAdV2 were up to three times higher than those for dispersed HAdV2, indicating that aggregation reduced the disinfection rate. This information can be used by water utilities and regulators to guide decision making regarding disinfection of viruses in water. PMID:26910058

  2. Electromagnetic charges in aggregation phenomena.

    NASA Astrophysics Data System (ADS)

    Rioux, Claude; Slobodrian, R. J.

    Introduction The mechanism of fine particles aggregation is of great importance in many areas of research, in particular environment sciences where the state of aggregation defines the removal speed of dust from the atmosphere. The study of this mechanism is also important to understand the first stage of planet formation from the solar nebula. The aggregates formed are generally fractals and, as mentioned in the literature [1], the fractal dimensions and the site growth probability measures of the resulting fractal structures strongly depend on the properties of the forces that cause the aggregation. Theory and experimental apparatus We began this study by the aggregation between two charged particles and we are now consid-ering the aggregation between two magnetized particles. The aggregations are produced in a gas at a pressure between 10 and 1000 mbar and by using the applicable simplifications; we find that the distance (r) between the particles as a function of time (t) is given by the following equations: r=Ce(tf -t)1/3 for the electrical attraction r=Cm(tf -t)1/5 for the magnetic dipoles aligned in an external magnetic field. The apparatus built for these measurements consists of an experimental cell from which two perpendicular views are combined via an optical system in one image recorded by a video camera. From the video, we can then measure the distance between the particles as a function of time and reconstruct the trajectories in 3-D. The horizontal and vertical resolutions are respectively 0.86 and 0.92 microns per pixel. With a depth of field of 250 microns, the usable volume for 3-D observation in then 250 microns x 250 microns x 443 microns. Results and discussion A first version of the apparatus was tested on an electrical force aggregation and the results [2] show that the corresponding equation is a good representation of the phenomenon. Preliminary results, from an experiment using iron particles, show that the magnetic force can be seen in

  3. 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

  4. Aggregated Indexing of Biomedical Time Series Data

    PubMed Central

    Woodbridge, Jonathan; Mortazavi, Bobak; Sarrafzadeh, Majid; Bui, Alex A.T.

    2016-01-01

    Remote and wearable medical sensing has the potential to create very large and high dimensional datasets. Medical time series databases must be able to efficiently store, index, and mine these datasets to enable medical professionals to effectively analyze data collected from their patients. Conventional high dimensional indexing methods are a two stage process. First, a superset of the true matches is efficiently extracted from the database. Second, supersets are pruned by comparing each of their objects to the query object and rejecting any objects falling outside a predetermined radius. This pruning stage heavily dominates the computational complexity of most conventional search algorithms. Therefore, indexing algorithms can be significantly improved by reducing the amount of pruning. This paper presents an online algorithm to aggregate biomedical times series data to significantly reduce the search space (index size) without compromising the quality of search results. This algorithm is built on the observation that biomedical time series signals are composed of cyclical and often similar patterns. This algorithm takes in a stream of segments and groups them to highly concentrated collections. Locality Sensitive Hashing (LSH) is used to reduce the overall complexity of the algorithm, allowing it to run online. The output of this aggregation is used to populate an index. The proposed algorithm yields logarithmic growth of the index (with respect to the total number of objects) while keeping sensitivity and specificity simultaneously above 98%. Both memory and runtime complexities of time series search are improved when using aggregated indexes. In addition, data mining tasks, such as clustering, exhibit runtimes that are orders of magnitudes faster when run on aggregated indexes.

  5. 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.

  6. Glycation precedes lens crystallin aggregation

    SciTech Connect

    Swamy, M.S.; Perry, R.E.; Abraham, E.C.

    1987-05-01

    Non-enzymatic glycosylation (glycation) seems to have the potential to alter the structure of crystallins and make them susceptible to thiol oxidation leading to disulfide-linked high molecular weight (HMW) aggregate formation. They used streptozotocin diabetic rats during precataract and cataract stages and long-term cell-free glycation of bovine lens crystallins to study the relationship between glycation and lens crystallin aggregation. HMW aggregates and other protein components of the water-soluble (WS) and urea-soluble (US) fractions were separated by molecular sieve high performance liquid chromatography. Glycation was estimated by both (/sup 3/H)NaBH/sub 4/ reduction and phenylboronate agarose affinity chromatography. Levels of total glycated protein (GP) in the US fractions were about 2-fold higher than in the WS fractions and there was a linear increase in GP in both WS and US fractions. This increase was parallelled by a corresponding increase in HMW aggregates. Total GP extracted by the affinity method from the US fraction showed a predominance of HMW aggregates and vice versa. Cell-free glycation studies with bovine crystallins confirmed the results of the animals studies. Increasing glycation caused a corresponding increase in protein insolubilization and the insoluble fraction thus formed also contained more glycated protein. It appears that lens protein glycation, HMW aggregate formation, and protein insolubilization are interrelated.

  7. Structure-activity relationship of cyanine tau aggregation inhibitors

    PubMed Central

    Chang, Edward; Congdon, Erin E.; Honson, Nicolette S.; Duff, Karen E.; Kuret, Jeff

    2009-01-01

    A structure-activity relationship for symmetrical cyanine inhibitors of human tau aggregation was elaborated using a filter trap assay. Antagonist activity depended on cyanine heterocycle, polymethine bridge length, and the nature of meso- and N-substituents. One potent member of the series, 3,3’-diethyl-9-methylthiacarbocyanine iodide (compound 11), retained submicromolar potency and had calculated physical properties consistent with blood-brain barrier and cell membrane penetration. Exposure of organotypic slices prepared from JNPL3 transgenic mice (which express human tau harboring the aggregation prone P301L tauopathy mutation) to compound 11 for one week revealed a biphasic dose response relationship. Low nanomolar concentrations decreased insoluble tau aggregates to half those observed in slices treated with vehicle alone. In contrast, high concentrations (≥300 nM) augmented tau aggregation and produced abnormalities in tissue tubulin levels. These data suggest that certain symmetrical carbocyanine dyes can modulate tau aggregation in the slice biological model at concentrations well below those associated with toxicity. PMID:19432420

  8. Crystal aggregation in kidney stones; a polymer aggregation problem?

    NASA Astrophysics Data System (ADS)

    Wesson, J.; Beshensky, A.; Viswanathan, P.; Zachowicz, W.; Kleinman, J.

    2008-03-01

    Kidney stones most frequently form as aggregates of calcium oxalate monohydrate (COM) crystals with organic layers between them, and the organic layers contain principally proteins. The pathway leading to the formation of these crystal aggregates in affected people has not been identified, but stone forming patients are thought to have a defect in the structure or distribution of urinary proteins, which normally protect against stone formation. We have developed two polyelectrolyte models that will induce COM crystal aggregation in vitro, and both are consistent with possible urinary protein compositions. The first model was based on mixing polyanionic and polycationic proteins, in portions such that the combined protein charge is near zero. The second model was based on reducing the charge density on partially charged polyanionic proteins, specifically Tamm-Horsfall protein, the second most abundant protein in urine. Both models demonstrated polymer phase separation at solution conditions where COM crystal aggregation was observed. Correlation with data from other bulk crystallization measurements suggest that the anionic side chains form critical binding interactions with COM surfaces that are necessary along with the phase separation process to induce COM crystal aggregation.

  9. Light scattering / SEC study of iota-carageenan aggregation

    NASA Astrophysics Data System (ADS)

    Sharp, Erica; Thomson, Robert; Norwood, David

    2003-11-01

    Carrageenans are believed to change conformation from random coil to helix when varying temperature and/or salt concentration. It is a point of contention as to whether this helix is formed from one coil or two. We present a study of this conformation change using viscometry and multi-angle laser light scattering (MALLS) with size-exclusion chromatography (SEC). Light scattering results show a clear increase in molecular weight and radius of gyration within 30 minutes of adding NaCl to high concentrations of iota-carrageenan, which may be interpreted as the conformation change described. However, estimates of persistence length ( ˜ R_G^2 / M_W) show no strong variation when increasing added salt. This suggests that the molecular weight increase reflects an aggregation of polymer molecules instead of a change in conformation. The iota-carrageenan molecules continue to aggregate slowly (hours to days depending on NaCl concentration). The final molecular weight of the aggregates depends on salt concentration, but the aggregation time seems to depend only on polymer concentration. If samples mixed in pure water are injected while the SEC system flows a NaCl mobile phase, we see effects typical of salting a linear polyelectrolyte.

  10. On the dynamics of the TPPS4 aggregation in aqueous solutions: successive formation of H and J aggregates.

    PubMed

    Aggarwal, Lucimara P F; Borissevitch, Iouri E

    2006-01-01

    The dynamics of aggregation of meso-tetrakis (p-sulfonatofenyl) porphyrin (TPPS4) in function of its concentration, pH and ionic strength was studied by optical absorption, fluorescence and resonance light scattering (RLS) techniques. In the region of pH, where TPPS4 exists in biprotonated form, the addition of NaCl induces the TPPS4 aggregation due to the formation of the "cloud" of counter ions around the TPPS4 molecule thus reducing electrostatic repulsion between the porphyrin molecules. The formation of this "cloud" shifts the pKa value to acid region (from 5.0 in the absence of salt to 4.5 at [NaCl] = 0.4 M), reduces the TPPS4 absorption in all spectral range and quantum yield and lifetime of fluorescence (from 0.27 to 0.17 and from 4.00+/-0.04 to 3.00+/-0.03 ns in the absence of salt and in the presence of NaCl, respectively). The aggregation process involves two successive stages: initially H aggregates are formed, which in time are transformed in J ones. The existence of these two stages was confirmed by the fluorescence and RLS data. The kinetics of the formation of J aggregates is characterized by the induction time t1 and the average growth time t2, which depend on both TPPS4 and salt concentrations. The induction period t1 appears as a result of initial formation of H aggregates and their successive transformation in J ones. At very high TPPS4 concentrations, the J aggregates are united in more complex structures such as hollow cylinders or helixes.

  11. Sensitive detection of aggregated prion protein via proximity ligation.

    PubMed

    Hammond, Maria; Wik, Lotta; Deslys, Jean-Philippe; Comoy, Emmanuel; Linné, Tommy; Landegren, Ulf; Kamali-Moghaddam, Masood

    2014-01-01

    The DNA assisted solid-phase proximity ligation assay (SP-PLA) provides a unique opportunity to specifically detect prion protein (PrP) aggregates by investigating the collocation of 3 or more copies of the specific protein. We have developed an SP-PLA that can detect PrP aggregates in brain homogenates from infected hamsters even after a 10(7)-fold dilution. In contrast, brain homogenate from uninfected animals did not generate a detectable signal at 100-fold higher concentration. Using either of the 2 monoclonal anti-PrP antibodies, 3F4 and 6H4, we successfully detected low concentrations of aggregated PrP. The presented results provide a proof of concept that this method might be an interesting tool in the development of diagnostic approaches of prion diseases.

  12. Evaluation of Nanoparticle Tracking for Characterization of Fibrillar Protein Aggregates

    PubMed Central

    Yang, Dennis T.; Lu, Xiaomeng; Fan, Yamin; Murphy, Regina M.

    2015-01-01

    Amyloidogenesis is the process of formation of protein aggregates with fibrillar morphology. Because amyloidogenesis is linked to neurodegenerative disease, there is interest in understanding the mechanism of fibril growth. Kinetic models of amyloidogenesis require data on the number concentration and size distribution of aggregates, but this information is difficult to obtain using conventional methods. Nanoparticle tracking analysis (NTA) is a relatively new technique that may be uniquely suited for obtaining these data. In NTA, the two-dimensional (2-D) trajectory of individual particles is tracked, from which the diffusion coefficient, and, hence, hydrodynamic radius is obtained. Here we examine the validity of NTA in tracking number concentration and size of DNA, as a model of a fibrillar macromolecule. We use NTA to examine three amyloidogenic materials: beta-amyloid, transthyretin, and polyglutamine-containing peptides. Our results are instructive in demonstrating the advantages and some limitations of single-particle diffusion measurements for investigating aggregation in protein systems. PMID:25843955

  13. Different aggregation dynamics of benzene-water mixtures.

    PubMed

    Fu, Cen-Feng; Tian, Shan Xi

    2014-10-28

    All-atom molecular dynamics simulations for benzene-water mixtures are performed, aiming to explore the relationship between the microscopic structures and the thermodynamic properties, in particular, the transformation dynamics from the mutually soluble state to the phase-separated state. We find that the molecular aggregation of benzene in the water-rich mixture is distinctly different from that of water in the benzene-rich mixture. This aggregation difference is attributed to the different intermolecular interactions: the clustering of benzene molecules in the water-rich mixture is primarily driven by weak short-distance π-π interactions; while the formation of water clusters in the benzene-rich solution is triggered by long-range dipole-dipole electrostatic interactions. Moreover, the molecular aggregations show double-scaled features: firstly assembling in a quasi-plane at a low concentration, then bulking in three dimensions with an increase in concentration.

  14. Fractal Aggregates in Tennis Ball Systems

    ERIC Educational Resources Information Center

    Sabin, J.; Bandin, M.; Prieto, G.; Sarmiento, F.

    2009-01-01

    We present a new practical exercise to explain the mechanisms of aggregation of some colloids which are otherwise not easy to understand. We have used tennis balls to simulate, in a visual way, the aggregation of colloids under reaction-limited colloid aggregation (RLCA) and diffusion-limited colloid aggregation (DLCA) regimes. We have used the…

  15. Aggregated Recommendation through Random Forests

    PubMed Central

    2014-01-01

    Aggregated recommendation refers to the process of suggesting one kind of items to a group of users. Compared to user-oriented or item-oriented approaches, it is more general and, therefore, more appropriate for cold-start recommendation. In this paper, we propose a random forest approach to create aggregated recommender systems. The approach is used to predict the rating of a group of users to a kind of items. In the preprocessing stage, we merge user, item, and rating information to construct an aggregated decision table, where rating information serves as the decision attribute. We also model the data conversion process corresponding to the new user, new item, and both new problems. In the training stage, a forest is built for the aggregated training set, where each leaf is assigned a distribution of discrete rating. In the testing stage, we present four predicting approaches to compute evaluation values based on the distribution of each tree. Experiments results on the well-known MovieLens dataset show that the aggregated approach maintains an acceptable level of accuracy. PMID:25180204

  16. Novel insights into amylin aggregation

    PubMed Central

    Pillay, Karen; Govender, Patrick

    2014-01-01

    Amylin is a peptide that aggregates into species that are toxic to pancreatic beta cells, leading to type II diabetes. This study has for the first time quantified amylin association and dissociation kinetics (association constant (ka) = 28.7 ± 5.1 L mol−1 s−1 and dissociation constant (kd) = 2.8 ± 0.6 ×10−4 s−1) using surface plasmon resonance (SPR). Thus far, techniques used for the sizing of amylin aggregates do not cater for the real-time monitoring of unconstrained amylin in solution. In this regard we evaluated recently innovated nanoparticle tracking analysis (NTA). In addition, both SPR and NTA were used to study the effect of previously synthesized amylin derivatives on amylin aggregation and to evaluate their potential as a cell-free system for screening potential inhibitors of amylin-mediated cytotoxicity. Results obtained from NTA highlighted a predominance of 100–300 nm amylin aggregates and correlation to previously published cytotoxicity results suggests the toxic species of amylin to be 200–300 nm in size. The results seem to indicate that NTA has potential as a new technique to monitor the aggregation potential of amyloid peptides in solution and also to screen potential inhibitors of amylin-mediated cytotoxicity. PMID:26019498

  17. Triethylenetetramine prevents insulin aggregation and fragmentation during copper catalyzed oxidation.

    PubMed

    Torosantucci, Riccardo; Weinbuch, Daniel; Klem, Robin; Jiskoot, Wim

    2013-08-01

    Metal catalyzed oxidation via the oxidative system Cu(2+)/ascorbate is known to induce aggregation of therapeutic proteins, resulting in enhanced immunogenicity. Hence, inclusion of antioxidants in protein formulations is of great interest. In this study, using recombinant human insulin (insulin) as a model, we investigated the ability of several excipients, in particular triethylenetetramine (TETA), reduced glutathione(GSH) and ethylenediamine tetraacetic acid (EDTA), for their ability to prevent protein oxidation, aggregation, and fragmentation. Insulin (1mg/ml) was oxidized with 40 μM Cu(2+) and 4mM ascorbic acid in absence or presence of excipients. Among the excipients studied, 1mM of TETA, EDTA, or GSH prevented insulin aggregation upon metal catalyzed oxidation (MCO) for 3h at room temperature, based on size exclusion chromatography (SEC). At lower concentration (100 μM), for 72 h at +4 °C, TETA was the only one to inhibit almost completely oxidation-induced insulin aggregation, fragmentation, and structural changes, as indicated by SEC, nanoparticle tracking analysis, light obscuration particle counting, intrinsic/extrinsic fluorescence, circular dichroism, and chemical derivatization. In contrast, GSH had a slight pro-oxidant effect, as demonstrated by the higher percentage of aggregates and a more severe structural damage, whereas EDTA offered substantially less protection. TETA also protected a monoclonal IgG1 against MCO-induced aggregation, suggesting its general applicability. In conclusion, TETA is a potential candidate excipient for inclusion in formulations of oxidation-sensitive proteins.

  18. Kinetic Model for 1D aggregation of yeast ``prions''

    NASA Astrophysics Data System (ADS)

    Kunes, Kay; Cox, Daniel; Singh, Rajiv

    2004-03-01

    Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeast have proteins which can undergo similar reconformation and aggregation processes to PrP; yeast forms are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein(1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics(2). The model assumes reconformation only upon aggregation, and includes aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates. We will compare to a more realistic stochastic kinetics model and present prelimary attempts to describe recent experiments on SUP35 strains. *-Supported by U.S. Army Congressionally Mandated Research Fund. 1) P. Chien and J.S. Weissman, Nature 410, 223 (2001); http://online.kitp.ucsb.edu/online/bionet03/collins/. 2) J. Masel, V.A.> Jansen, M.A. Nowak, Biophys. Chem. 77, 139 (1999).

  19. Cell aggregation on agar as an indicator for cell-matrix adhesion: effects of opioids.

    PubMed

    Debruyne, Delphine; Mareel, Marc; Vanhoecke, Barbara; Bracke, Marc

    2009-09-01

    The slow aggregation assay is generally used to study the functionality of cell-cell adhesion complexes. Single cells are seeded on a semisolid agar substrate in a 96-well plate and the cells spontaneously aggregate. We used HEK FLAG-MOP cells that stably overexpress the mu opioid receptor and the mu-opioid-receptor-selective agonists DAMGO and morphine to study whether other factors than functionality of cell-cell adhesions complexes can contribute to changes in the pattern of slow aggregation on agar. HEK FLAG-MOP cells formed small compact aggregates. In the presence of DAMGO and morphine, larger and fewer aggregates were formed in comparison to the vehicle control. These aggregates were localized in the center of the agar surface, whereas in the vehicle control they were dispersed over the substrate. However, in suspension culture on a Gyrotory shaker, no stimulation of aggregation was observed by DAMGO and morphine, showing that opioids do not affect affinity. A dissociation experiment revealed that HEK FLAG-MOP aggregates formed in the absence or presence of opioids are resistant to de-adhesion. We demonstrated that the larger aggregates are neither the result of cell growth stimulation by DAMGO and morphine. Since manipulations of the substrate such as increasing the agar concentration or mixing agar with agarose induced the same changes in the pattern of slow aggregation as treatment with opioids, we suggest that cell-substrate adhesion may be involved in opioid-stimulated aggregation.

  20. Serum Phosphorus Concentration and Coronary Artery Calcification in Subjects without Renal Dysfunction

    PubMed Central

    Park, Kyung Sun; Park, Jongha; Choi, Seong Hoon; Ann, Seo Hee; Singh, Gillian Balbir; Shin, Eun-Seok; Lee, Jong Soo; Chung, Hyun Chul

    2016-01-01

    Serum phosphorus (P) concentration is associated with coronary artery calcification (CAC) as well as cardiovascular events in patients with chronic kidney disease. It has been suggested that this relationship is extended to subjects without renal dysfunction, but further explorations in diverse races and regions are still needed. We performed a cross-sectional study of 2,509 Korean subjects (Far Eastern Asian) with an estimated glomerular filtration rate of ≥60 ml/min/1.73m2 and who underwent coronary computerized tomography. Serum P concentration was divided into pre-determined 4 categories: ≤3.2, 3.2< to ≤3.6, 3.6< to ≤4.0 and >4.0 mg/dL. Agatston score (AS), an index of CAC, was divided into 3 categories: 0, 0< to ≤100, and >100. A multinomial logit model (baseline outcome: AS = 0) was applied to estimate the odds ratio (OR) for each serum P category (reference: ≤3.2mg/dL). Mean age of subjects was 53.5±9.1 years and 36.9% were female. In the adjusted model, serum P concentration of 3.6< to ≤4.0 mg/dL and >4.0 mg/dL showed high ORs for AS of >100 [OR: 1.58, 95% confidence interval (CI): 1.04–2.40 and OR: 2.11, 95% CI: 1.34–3.32, respectively]. A unit (mg/dL) increase in serum P concentration was associated with 50% increase in risk of AS >100 (OR: 1.50, 95% CI: 1.16–1.94). A higher serum P concentration, even within a normal range, may be associated with a higher CAC in subjects with normal renal function. PMID:26992166

  1. Do chemical gradients within soil aggregates reflect plant/soil interactions?

    NASA Astrophysics Data System (ADS)

    Krüger, Jaane; Hallas, Till; Kinsch, Lena; Stahr, Simon; Prietzel, Jörg; Lang, Friederike

    2016-04-01

    As roots and hyphae often accumulate at the surface of soil aggregates, their formation and turnover might be related to the bioavailability especially of immobile nutrients like phosphorus. Several methods have been developed to obtain specific samples from aggregate surfaces and aggregate cores and thus to investigate differences between aggregate shell and core. However, these methods are often complex and time-consuming; therefore most common methods of soil analysis neglect the distribution of nutrients within aggregates and yield bulk soil concentrations. We developed a new sequential aggregate peeling method to analyze the distribution of different nutrients within soil aggregates (4-20 mm) from four forest sites (Germany) differing in concentrations of easily available mineral P. Aggregates from three soil depths (Ah, BwAh, Bw) were isolated, air-dried, and peeled with a sieving machine performing four sieving levels with increasing sieving intensity. This procedure was repeated in quadruplicate, and fractions of the same sample and sieving level were pooled. Carbon and N concentration, citric acid-extractable PO4 and P, as well as total element concentrations (P, K, Mg, Ca, Al, Fe) were analyzed. Additionally, synchrotron-based P K-edge XANES spectroscopy was applied on selected samples to detect P speciation changes within the aggregates. The results reveal for most samples a significantly higher C and N concentration at the surface compared to the interior of the aggregates. Carbon and N gradients get more pronounced with increasing soil depth and decreasing P status of study sites. This might be explained by lower aggregate turnover rates of subsoil horizons and intense bioturbation on P-rich sites. This assumption is also confirmed by concentrations of citric acid-extractable PO4 and P: gradients within aggregates are getting more pronounced with increasing soil depth and decreasing P status. However, the direction of these gradients is site

  2. In vitro effects of ethanol on the pathways of platelet aggregation

    SciTech Connect

    Rand, M.L.; Kinlough-Rathbone, R.L.; Packham, M.A.; Mustard, J.F.

    1986-03-01

    Ethanol is reported to inhibit platelet aggregation in vivo and in vitro, but the mechanisms of its action on stimulus-response coupling in platelets is unknown. Platelet aggregation to thrombin occurs through at least three pathways: released ADP; thromboxane A/sub 2/ (TXA/sub 2/); and a third pathway(s). Aggregation of rabbit platelets in citrated platelet-rich plasma (PRP) or washed suspensions to ADP (0.5-10 ..mu..M) was not affected by ethanol, at concentrations up to 5 mg/ml (lethal). Primary ADP-induced (5 ..mu..M) aggregation of human platelets in PRP was also unaffected by ethanol, but secondary aggregation and release of /sup 14/C-serotonin, due to TXA/sub 2/ formation, was inhibited by ethanol (2 and 4 mg/ml). Since arachidonate (AA)-induced (25-250 ..mu..M) aggregation and release by washed rabbit platelets was unaltered by ethanol, it may inhibit mobilization of AA from platelet membrane phospholipids. Ethanol (2-4 mg/ml) inhibited rabbit platelet aggregation and release to low concentrations of thrombin (< 10 mU/ml) or collagen, and also inhibited aggregation and release of aspirin-treated (500 ..mu.. M) rabbit platelets (that cannot form TXA/sub 2/) to low concentrations of thrombin (< 10 mU/ml). Thus, ethanol does not inhibit the mobilization of AA, and partially inhibits the third pathway(s) of platelet aggregation.

  3. Equilibrium structure of ferrofluid aggregates

    SciTech Connect

    Yoon, Mina; Tomanek, David

    2010-01-01

    We study the equilibrium structure of large but finite aggregates of magnetic dipoles, representing a colloidal suspension of magnetite particles in a ferrofluid. With increasing system size, the structural motif evolves from chains and rings to multi-chain and multi-ring assemblies. Very large systems form single- and multi-wall coils, tubes and scrolls. These structural changes result from a competition between various energy terms, which can be approximated analytically within a continuum model. We also study the effect of external parameters such as magnetic field on the relative stability of these structures. Our results may give insight into experimental data obtained during solidification of ferrofluid aggregates at temperatures where thermal fluctuations become negligible in comparison to inter-particle interactions. These data may also help to experimentally control the aggregation of magnetic particles.

  4. Customer Aggregation: An Opportunity for Green Power?

    SciTech Connect

    Holt, E.; Bird, L.

    2001-02-26

    We undertook research into the experience of aggregation groups to determine whether customer aggregation offers an opportunity to bring green power choices to more customers. The objectives of this report, therefore, are to (1) identify the different types of aggregation that are occurring today, (2) learn whether aggregation offers an opportunity to advance sales of green power, and (3) share these concepts and approaches with potential aggregators and green power advocates.

  5. Fractal aggregates in tennis ball systems

    NASA Astrophysics Data System (ADS)

    Sabin, J.; Bandín, M.; Prieto, G.; Sarmiento, F.

    2009-09-01

    We present a new practical exercise to explain the mechanisms of aggregation of some colloids which are otherwise not easy to understand. We have used tennis balls to simulate, in a visual way, the aggregation of colloids under reaction-limited colloid aggregation (RLCA) and diffusion-limited colloid aggregation (DLCA) regimes. We have used the images of the cluster of balls, following Forrest and Witten's pioneering studies on the aggregation of smoke particles, to estimate their fractal dimension.

  6. Assembly of naphthalenediimide conjugated peptides: aggregation induced changes in fluorescence.

    PubMed

    Basak, Shibaji; Nanda, Jayanta; Banerjee, Arindam

    2013-08-01

    Naphthalenediimide appended peptide based self-assembly was studied. Interestingly, an aggregation induced drastic change in the fluorescence property and gel formation were observed depending on the solvent composition (chloroform : methylcyclohexane) at a fixed concentration of 1.6 mM at room temperature. PMID:23799544

  7. Aggregation and deposition behavior of boron nanoparticles in porous media.

    PubMed

    Liu, Xuyang; Wazne, Mahmoud; Christodoulatos, Christos; Jasinkiewicz, Kristin L

    2009-02-01

    New kinds of solid fuels and propellants comprised of nanomaterials are making their way into civilian and military applications yet the impact of their release on the environment remains largely unknown. One such material is nano boron, a promising solid fuel and propellant. The fate and transport of nano boron under various aquatic systems was investigated in aggregation and deposition experiments. Column experiments were performed to examine the effects of electrolyte concentration and flow velocity on the transport of boron nanoparticles under saturated conditions, whereas aggregation tests were conducted to assess the effects of electrolytes on the aggregation of the boron nanoparticles. Aggregation tests indicated the presence of different reaction-controlled and diffusion-controlled regimes and yielded critical coagulation concentrations (CCC) of 200 mM, 0.7 mM and 1.5 mM for NaCl, CaCl(2), and MgCl(2), respectively. Aggregation and deposition experimental data corresponded with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) model and the constant attachment efficiency filtration model, respectively. Theoretical calculations indicated that both the primary and secondary energy minima play important roles in the deposition of nano boron in sand columns.

  8. Recovering industrial sludge-derived slag as fine aggregate.

    PubMed

    Huang, Yi-Chin; Li, Kung-Cheh; Chiang, Hui-Hsien

    2005-01-01

    This study presents the result of using melting to recover both industrial sludge slag (the main constituent of which is calcium fluoride) and water works sludge slag as fine aggregate in cement. The main characteristics of both slag and cement mortars were measured to evaluate the feasibility of using slag as aggregate. In this study, the slag replacement ratios were 0, 10, 20, 30, 40, and 50% (w/w), and the curing periods were 7, 28, and 90 days. Slag quality was determined according to the standards of fine aggregates in the ASTM specifications, and cement mortars with various slag replacement ratios were evaluated based on their compressive strength, and Toxicity Characteristic Leaching Procedure (TCLP). The crushed slag produced in this study met the ASTM standards for fine aggregate, including gravity, unit weight, absorption, and grading, and the TCLP leached concentrations are far below existing limits, establishing the safety and suitability of slag as fine aggregate. The TCLP leached concentrations of slag and cement mortar were not significantly related to the replacement ratio, and declined with increasing curing period, revealing that the hydration strongly influenced metal leaching. The compressive strength test results of the cement mortars demonstrated that the optimal replacement ratio for maximizing compressive strength was 40%. This study also discussed the effects of replacement ratio and curing periods on cement mortars.

  9. Environmentalism and natural aggregate mining

    USGS Publications Warehouse

    Drew, L.J.; Langer, W.H.; Sachs, J.S.

    2002-01-01

    Sustaining a developed economy and expanding a developing one require the use of large volumes of natural aggregate. Almost all human activity (commercial, recreational, or leisure) is transacted in or on facilities constructed from natural aggregate. In our urban and suburban worlds, we are almost totally dependent on supplies of water collected behind dams and transported through aqueducts made from concrete. Natural aggregate is essential to the facilities that produce energy-hydroelectric dams and coal-fired powerplants. Ironically, the utility created for mankind by the use of natural aggregate is rarely compared favorably with the environmental impacts of mining it. Instead, the empty quarries and pits are seen as large negative environmental consequences. At the root of this disassociation is the philosophy of environmentalism, which flavors our perceptions of the excavation, processing, and distribution of natural aggregate. The two end-member ideas in this philosophy are ecocentrism and anthropocentrism. Ecocentrism takes the position that the natural world is a organism whose arteries are the rivers-their flow must not be altered. The soil is another vital organ and must not be covered with concrete and asphalt. The motto of the ecocentrist is "man must live more lightly on the land." The anthropocentrist wants clean water and air and an uncluttered landscape for human use. Mining is allowed and even encouraged, but dust and noise from quarry and pit operations must be minimized. The large volume of truck traffic is viewed as a real menace to human life and should be regulated and isolated. The environmental problems that the producers of natural aggregate (crushed stone and sand and gravel) face today are mostly difficult social and political concerns associated with the large holes dug in the ground and the large volume of heavy truck traffic associated with quarry and pit operations. These concerns have increased in recent years as society's demand for

  10. Particle Formation and Aggregation of a Therapeutic Protein in Nanobubble Suspensions.

    PubMed

    Snell, Jared R; Zhou, Chen; Carpenter, John F; Randolph, Theodore W

    2016-10-01

    The generation of nanobubbles following reconstitution of lyophilized trehalose formulations has recently been reported. Here, we characterize particle formation and aggregation of recombinant human interleukin-1 receptor antagonist (rhIL-1ra) in reconstituted formulations of lyophilized trehalose. Particle characterization methods including resonant mass measurement and nanoparticle tracking analysis were used to count and size particles generated upon reconstitution of lyophilized trehalose formulations. In addition, accelerated degradation studies were conducted to monitor rhIL-1ra aggregation in solutions containing various concentrations of suspended nanobubbles. Reconstitution of lyophilized trehalose formulations with solutions containing rhIL-1ra reduced nanobubble concentrations and generated negatively buoyant particles attributed to aggregated rhIL-1ra. Furthermore, levels of rhIL-1ra aggregation following incubation in aqueous solution correlated with concentrations of suspended nanobubbles. The results of this study suggest that nanobubbles may be a contributor to protein aggregation and particle formation in reconstituted, lyophilized therapeutic protein formulations.

  11. [Effect of troxerutin and cerebroproptein hydrolysate injection on platelet aggregation and thrombosis].

    PubMed

    Chen, Qiu-Chen; Yu, Zhao-Jin; Sun, Hai-Gang; Yu, Jian-Kun; Wei, Min-Jie

    2011-02-01

    This study was purposed to explore the effect of troxerotin and cerebroproptein hydrolysate injection (TCHI) on platelet aggregation in vitro and thrombosis in vivo. The inhibitory rate of TCHI at different concentrations on platelet aggregation was determined by platelet aggregometer. The relationship between dose and effect was established. The effect of troxerutin and cerebroproptein hydrolysate injection on thrombosis was determined by the carotid thrombosis model of rats. The results showed that the TCHI could inhibit thrombosis and platelet aggregation in a concentration-dependent way. When the concentration of TCHI total nitrogen was 5 µg/ml, the inhibition rate of platelet aggregation reached to the highest value of 28.61 ± 22.07%, which is 2.5 times as much as that with 100 µg/ml aspirin. It is concluded that the TCHI has antiaggregative and antithrombotic activity effects against platelet aggregation and thrombosis.

  12. Kinetics of insulin aggregation in aqueous solutions upon agitation in the presence of hydrophobic surfaces.

    PubMed Central

    Sluzky, V; Tamada, J A; Klibanov, A M; Langer, R

    1991-01-01

    The stability of protein-based pharmaceuticals (e.g., insulin) is important for their production, storage, and delivery. To gain an understanding of insulin's aggregation mechanism in aqueous solutions, the effects of agitation rate, interfacial interactions, and insulin concentration on the overall aggregation rate were examined. Ultraviolet absorption spectroscopy, high-performance liquid chromatography, and quasielastic light scattering analyses were used to monitor the aggregation reaction and identify intermediate species. The reaction proceeded in two stages; insulin stability was enhanced at higher concentration. Mathematical modeling of proposed kinetic schemes was employed to identify possible reaction pathways and to explain greater stability at higher insulin concentration. Images PMID:1946348

  13. Aggregation-based detection of M. smegmatis using D-arabinose-functionalized fluorescent silica nanoparticles.

    PubMed

    Jayawardana, Kalana W; Wijesundera, Samurdhi A; Yan, Mingdi

    2015-11-14

    Fluorescein-doped silica nanoparticles (FSNPs) functionalized with D-arabinose (Ara) showed strong interactions with Mycobacterium smegmatis (M. smegmatis) and caused the bacteria to aggregate. This aggregate formation was used as a means to detect M. smegmatis at the concentration of 10(4) CFU per mL. PMID:26379182

  14. Kinetics, aggregation behavior and optimization of the fractionation of whey protein isolate with hydrochloric acid

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Concentrated WPI solutions (10% (w/w)) containing approximately 30% alpha-lactalbumin (alpha-LA) and 60% beta-lactoglobulin (beta-LG) were fractionated with HCl at acidic pH and moderate temperatures to denature alpha-LA and recover the alpha-LA aggregates via centrifugation. Aggregation behavior an...

  15. Aggregation-based detection of M. smegmatis using D-arabinose-functionalized fluorescent silica nanoparticles.

    PubMed

    Jayawardana, Kalana W; Wijesundera, Samurdhi A; Yan, Mingdi

    2015-11-14

    Fluorescein-doped silica nanoparticles (FSNPs) functionalized with D-arabinose (Ara) showed strong interactions with Mycobacterium smegmatis (M. smegmatis) and caused the bacteria to aggregate. This aggregate formation was used as a means to detect M. smegmatis at the concentration of 10(4) CFU per mL.

  16. Studies on recycled aggregates-based concrete.

    PubMed

    Rakshvir, Major; Barai, Sudhirkumar V

    2006-06-01

    Reduced extraction of raw materials, reduced transportation cost, improved profits, reduced environmental impact and fast-depleting reserves of conventional natural aggregates has necessitated the use of recycling, in order to be able to conserve conventional natural aggregate. In this study various physical and mechanical properties of recycled concrete aggregates were examined. Recycled concrete aggregates are different from natural aggregates and concrete made from them has specific properties. The percentages of recycled concrete aggregates were varied and it was observed that properties such as compressive strength showed a decrease of up to 10% as the percentage of recycled concrete aggregates increased. Water absorption of recycled aggregates was found to be greater than natural aggregates, and this needs to be compensated during mix design.

  17. RAGG - R EPISODIC AGGREGATION PACKAGE

    EPA Science Inventory

    The RAGG package is an R implementation of the CMAQ episodic model aggregation method developed by Constella Group and the Environmental Protection Agency. RAGG is a tool to provide climatological seasonal and annual deposition of sulphur and nitrogen for multimedia management. ...

  18. Analysis of aggregation of platelets in thrombosis

    NASA Astrophysics Data System (ADS)

    Ahuja, Suresh

    Platelets are key players in thrombus formation by first rolling over collagen bound von Willebrand factor followed by formation of a stable interaction with collagen. The first adhered platelets bind additional platelets until the whole injury is sealed off by a platelet aggregate. The coagulation system stabilizes the formed platelet plug by creating a tight fibrin network, and then wound contraction takes place because of morphological changes in platelets. Coagulation takes place by platelet activation and aggregation mainly through fibrinogen polymerization into fibrin fibers. The process includes multiple factors, such as thrombin, plasmin, and local shear-rate which regulate and control the process. Coagulation can be divided into two pathways: the intrinsic pathway and the extrinsic pathway. The intrinsic pathway is initiated by the exposure of a negatively charged. It is able to activate factor XII, using a complex reaction that includes prekallikrein and high-molecular-weight kininogen as cofactors.. Thrombin is the final enzyme that is needed to convert fibrinogen into fibrin. The extrinsic pathway starts with the exposure of tissue factor to the circulating blood, which is the major initiator of coagulation. There are several feedback loops that reinforce the coagulation cascade, resulting in large amounts of thrombin. It is dependent on the presence of pro-coagulant surfaces of cells expressing negatively charged phospholipids--which include phosphatidylserine (PS)--on their outer membrane. PS-bearing surfaces are able to increase the efficiency of the reactions by concentrating and co-localizing coagulation factors.. Aggregation of platelets are analyzed and compared to adhesion of platelet to erythrocyte and to endothelial cells. This abstract is replacing MAR16-2015-020003.

  19. Sequence-dependent Internalization of Aggregating Peptides*

    PubMed Central

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

    2015-01-01

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

  20. Determination of aggregation thresholds of UV absorbing anionic surfactants by frontal analysis continuous capillary electrophoresis.

    PubMed

    Le Saux, Thomas; Varenne, Anne; Gareil, Pierre

    2004-06-01

    Aggregation of anionic surfactants was investigated by frontal analysis continuous capillary electrophoresis (FACCE), a method involving the continuous electrokinetic introduction of the surfactant sample into the separation capillary. This process results in a partial separation of the monomeric and aggregated forms without perturbing the monomer-aggregate equilibrium. The critical micelle concentration (CMC) can then be easily derived from the height of the firstly detected migration front, corresponding to the monomeric form. This approach is exemplified with octyl and dodecylbenzenesulfonates and compared with conductimetry and surface tension measurements. FACCE turns out to be an effective method for the determination of CMC and intermediate aggregation phenomena with very small sample and short time requirements.

  1. Colloidal aggregation in microgravity by critical Casimir forces

    NASA Astrophysics Data System (ADS)

    Veen, Sandra; Schall, Peter; Antoniuk, Oleg; Potenza, Marco; Alaimo, Matteo; Mazzoni, Stefano; Wegdam, Gerard

    2012-02-01

    We study aggregation and crystal growth of spherical Teflon colloids in binary liquid mixtures in microgravity by the critical Casimir effect. The critical Casimir effect induces interactions between colloids due to the confinement of bulk fluctuations (density or concentration) near the critical point of liquids. The strength and range of the interaction depends on the length scale of these fluctuations which increase as one approaches the critical point. The interaction potential can thus be tuned with temperature. We follow the growth of structures in real time with Near Field Scattering. Measurements are performed in microgravity in order to study pure diffusion limited aggregation, without disturbance by sedimentation or flow.

  2. Orientational Alignment of Amyloidogenic Proteins in Pre-Aggregated Solutions

    NASA Astrophysics Data System (ADS)

    Schröder, C.; Steinhauser, O.; Sasisanker, P.; Weingärtner, H.

    2015-03-01

    In the present study we combine dielectric relaxation spectroscopy with generalized Born simulations to explore the role of orientational order for protein aggregation in solutions of bovine pancreatic insulin at various p H conditions. Under aggregation-prone conditions at low p H , insulin monomers prefer antiparallel dipole alignments, which are consistent with the orientation of the monomeric subunits in the dimer structure. This alignment is also true for two dimers, suggesting that already at moderate protein concentrations the species assemble in equilibrium clusters, in which the molecules adopt preferred orientations also found for the protomers of the corresponding oligomers.

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

    SciTech Connect

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

    2015-09-28

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

  4. Ion aggregation in high salt solutions. V. Graph entropy analyses of ion aggregate structure and water hydrogen bonding network.

    PubMed

    Choi, Jun-Ho; Cho, Minhaeng

    2016-05-28

    Dissolved ions in water tend to form polydisperse ion aggregates such as ion pairs, relatively compact ion clusters, and even spatially extended ion networks with increasing salt concentration. Combining molecular dynamics simulation and graph theoretical analysis methods, we recently studied morphological structures of ion aggregates with distinctively different characteristics. They can be distinguished from each other by calculating various spectral graph theoretical properties such as eigenvalues and eigenvectors of adjacency matrices of ion aggregates and water hydrogen-bonding networks, minimum path lengths, clustering coefficients, and degree distributions. Here, we focus on percolation and graph entropic properties of ion aggregates and water hydrogen-bonding networks in high salt solutions. Ion network-forming K(+) and SCN(-) ions at high concentrations show a percolating behavior in their aqueous solutions, but ion cluster-forming ions in NaCl solutions do not show such a transition from isolated ion aggregates to percolating ion-water mixture morphology. Despite that the ion aggregate structures are strikingly different for either cluster- or network-forming ions in high salt solutions, it is interesting that the water structures remain insensitive to the electrostatic properties, such as charge densities and polydentate properties, of dissolved ions, and morphological structures of water H-bonding networks appear to be highly robust regardless of the nature and concentration of salt. We anticipate that the present graph entropy analysis results would be of use in understanding a variety of anomalous behaviors of interfacial water around biomolecules as well as electric conductivities of high electrolyte solutions.

  5. Ion aggregation in high salt solutions. V. Graph entropy analyses of ion aggregate structure and water hydrogen bonding network

    NASA Astrophysics Data System (ADS)

    Choi, Jun-Ho; Cho, Minhaeng

    2016-05-01

    Dissolved ions in water tend to form polydisperse ion aggregates such as ion pairs, relatively compact ion clusters, and even spatially extended ion networks with increasing salt concentration. Combining molecular dynamics simulation and graph theoretical analysis methods, we recently studied morphological structures of ion aggregates with distinctively different characteristics. They can be distinguished from each other by calculating various spectral graph theoretical properties such as eigenvalues and eigenvectors of adjacency matrices of ion aggregates and water hydrogen-bonding networks, minimum path lengths, clustering coefficients, and degree distributions. Here, we focus on percolation and graph entropic properties of ion aggregates and water hydrogen-bonding networks in high salt solutions. Ion network-forming K+ and SCN- ions at high concentrations show a percolating behavior in their aqueous solutions, but ion cluster-forming ions in NaCl solutions do not show such a transition from isolated ion aggregates to percolating ion-water mixture morphology. Despite that the ion aggregate structures are strikingly different for either cluster- or network-forming ions in high salt solutions, it is interesting that the water structures remain insensitive to the electrostatic properties, such as charge densities and polydentate properties, of dissolved ions, and morphological structures of water H-bonding networks appear to be highly robust regardless of the nature and concentration of salt. We anticipate that the present graph entropy analysis results would be of use in understanding a variety of anomalous behaviors of interfacial water around biomolecules as well as electric conductivities of high electrolyte solutions.

  6. Cation-induced aggregation of membrane vesicles isolated from vascular smooth muscle

    SciTech Connect

    Kwan, C.Y.

    1986-12-01

    Cations stimulated aortic muscle membrane aggregation with increasing potency according to their effective charge, e.g., K+ less than Mg2+ less than La3+, and the stimulation is reciprocally related to the apparent affinity for these cations. Divalent metal ion-induced membrane aggregation showed a dependence on the ionic radius, being optimal for Cd2+. Polyvalent cation-induced membrane aggregation was reversibly suppressed by high ionic strength as well as by metal ion chelators, irreversibly inhibited by the cross-linking agent glutaraldehyde, and enhanced by increasing concentrations of ethanol and increased temperature of the medium. When the pH is lowered below 6.0, membrane aggregation progressively increased with a concomitant decrease in cation-induced aggregation. The patterns of aggregation of microsomal membranes and further purified plasma membranes were almost identical whereas the aggregation of the heterogeneous mitochondrial membrane-enriched fraction was distinctly different in the initial rate of aggregation, its pH dependence, and metal ion concentration dependence. Our results indicate that cation-induced membrane aggregation can also be used to isolate a plasma membrane-enriched fraction from vascular smooth muscle.

  7. Electric Dipole Aggregates in Very Dilute Polar Liquids:. Theory and Experimental Evidence

    NASA Astrophysics Data System (ADS)

    Yinnon, Tamar A.; Yinnon, Carmi A.

    We show that rotational excited aggregates with an electric dipole moment may be created in polar liquids. Under proper storage conditions, the life times of the aggregates are very long, e.g., days and even years. In solutions, the aggregates are composed of solvent molecules only or a combination of these and solute particles. The process steps leading to the formation of the aggregates are: (1) vigorous succussing the liquid or its solution; (2) adding nonsuccussed liquid; (3) repetition of step (1) and (2). In solutions, formation of the aggregates requires that these steps are repeated until the concentration is reduced below a solvent and solute specific molarity, which under room temperature and pressure conditions, typically, is of the order of 10-4 M or below. The characteristics of liquids containing aggregates with an electric dipole, theoretically derived in this paper, conform to the experimentally observed ones, reported in the literature.

  8. Single-Molecule Imaging of Individual Amyloid Protein Aggregates in Human Biofluids

    PubMed Central

    2016-01-01

    The misfolding and aggregation of proteins into amyloid fibrils characterizes many neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases. We report here a method, termed SAVE (single aggregate visualization by enhancement) imaging, for the ultrasensitive detection of individual amyloid fibrils and oligomers using single-molecule fluorescence microscopy. We demonstrate that this method is able to detect the presence of amyloid aggregates of α-synuclein, tau, and amyloid-β. In addition, we show that aggregates can also be identified in human cerebrospinal fluid (CSF). Significantly, we see a twofold increase in the average aggregate concentration in CSF from Parkinson’s disease patients compared to age-matched controls. Taken together, we conclude that this method provides an opportunity to characterize the structural nature of amyloid aggregates in a key biofluid, and therefore has the potential to study disease progression in both animal models and humans to enhance our understanding of neurodegenerative disorders. PMID:26800462

  9. Determination of monomer concentrations in crystallizing lysozyme solutions

    NASA Technical Reports Server (NTRS)

    Wilson, L. J.; Pusey, Marc L.

    1992-01-01

    We have developed a non-optical technique for the study of aggregation in lysozyme and other protein solutions. By monitoring the rate at which lysozyme traverses a semipermeable membrane it was possible to quantitate the degree of aggregation in supersaturated solutions. Using this technique, we have measured the concentration of monomers and larger aggregates in under- and oversaturated lysozyme solutions, and in the presence of crystals, at pH 4.0 and 3 percent NaCl (0.1M NaAc). Comparison of these concentration profiles with (110) face growth rate data supports the theory that tetragonal lysozyme crystals grow by addition of preformed aggregates and not by monomer addition. The data suggest that a considerable population of aggregates larger than dimers are present at lysozyme concentrations above 22 mg/ml. Determination of dimer concentrations, and equilibrium constants for subsequent aggregation levels, are currently underway.

  10. Experimentally constraining the boundary conditions for volcanic ash aggregation

    NASA Astrophysics Data System (ADS)

    Kueppers, U.; Auer, B.; Cimarelli, C.; Scolamacchia, T.; Guenthel, M.; Dingwell, D. B.

    2011-12-01

    Volcanic ash is the primary product of various volcanic processes. Due to its size, ash can remain in the atmosphere for a prolonged period of time. Aggregation processes are a first-order influence on the residence time of ash in the atmosphere and its dispersion from the vent. Due to their internal structure, ash aggregates have been classified as ash pellets or accretionary lapilli. Although several concomitant factors may play a role during aggregation, there is a broad consensus that both 1) particle collision and 2) humidity are required for particles to aggregate. However, direct observation of settling aggregates and record of the boundary conditions favourable to their formation are rare, therefore limiting our understanding of the key processes that determine ash aggregates formation. Here, we present the first results from experiments aimed at reproducing ash aggregation by constraining the required boundary conditions. We used a ProCell Lab System of Glatt Ingenieurtechnik GmbH that is conventionally used for food and chemical applications. We varied the following parameters: 1) air flow speed [40-120 m3/h], 2) air temperature [30-60°C], 3) relative humidity [20-50 %], and 4) liquid droplets composition [water and 25% water glass, Na2SiO3]. The starting material (125-90 μm) is obtained by milling natural basaltic lapilli (Etna, Italy). We found that the experimental duration and the chosen conditions were not favourable for the production of stable aggregates when using water as spraying liquid. Using a 25% water-glass solution as binder we could successfully generate and investigate aggregates of up to 2 mm size. Many aggregates are spherical and resemble ash pellets. In nature, ash pellets and accretionary lapilli are the product of complex processes taking place at very different conditions (temperature, humidity, ash concentration, degree of turbulence). These experiments shed some first light on the ash agglomeration process for which direct

  11. Fractal model of consolidation of weakly aggregated colloidal dispersions

    NASA Astrophysics Data System (ADS)

    Potanin, A. A.; Russel, W. B.

    1996-04-01

    A microrheological model for the consolidation of aggregated colloidal dispersion is presented. Interparticle forces are responsible for the formation of the fractal-like network of particles chains. Aggregation is supposed to be weak in that the chains are gradually created and annihilated. In the framework of this model a constitutive equation is proposed which includes linear dependence of the normal stress upon consolidation rate at low stresses and yieldlike behavior as the stress reaches critical value. Our constitutive equation thus generalizes earlier models based on the compressive yield stress concept by taking into account the deformation in the low-compression limit (analog to the Newtonian flow in the low-shear limit). The constitutive equation is employed to calculate numerically concentration profiles of consolidating samples in better agreement with the experimental data for weakly aggregated alumina dispersions.

  12. An improved collision efficiency model for particle aggregation

    NASA Astrophysics Data System (ADS)

    Olsen, Aaron; Franks, George; Biggs, Simon; Jameson, Graeme J.

    2006-11-01

    A generalized geometric model is presented which describes the collision efficiency factor of aggregation (the probability of a binary particle or aggregate collision resulting in adhesion) for systems comprised of two oppositely charged species. Application of the general model to specific systems requires calculation of the area of each species available for collision with a second species. This is in contrast to previous models developed for polymer-particle flocculation that are based on the fractional surface coverage of adsorbed polymer. The difference between these approaches is suggested as an explanation for previously observed discrepancies between theory and observation. In the current work the specific case of oppositely charged nondeformable spherical particles (heteroaggregation) is quantitatively addressed. The optimum concentration of oppositely charged particles for rapid aggregation (maximum collision efficiency) as a function of relative particle size is calculated and an excellent correlation is found with data taken from literature.

  13. An improved collision efficiency model for particle aggregation.

    PubMed

    Olsen, Aaron; Franks, George; Biggs, Simon; Jameson, Graeme J

    2006-11-14

    A generalized geometric model is presented which describes the collision efficiency factor of aggregation (the probability of a binary particle or aggregate collision resulting in adhesion) for systems comprised of two oppositely charged species. Application of the general model to specific systems requires calculation of the area of each species available for collision with a second species. This is in contrast to previous models developed for polymer-particle flocculation that are based on the fractional surface coverage of adsorbed polymer. The difference between these approaches is suggested as an explanation for previously observed discrepancies between theory and observation. In the current work the specific case of oppositely charged nondeformable spherical particles (heteroaggregation) is quantitatively addressed. The optimum concentration of oppositely charged particles for rapid aggregation (maximum collision efficiency) as a function of relative particle size is calculated and an excellent correlation is found with data taken from literature. PMID:17115794

  14. PRODUCTION OF CONSTRUCTION AGGREGATES FROM FLUE GAS DESULFURIZATION SLUDGE

    SciTech Connect

    M.M. Wu; D.C. McCoy; R.O. Scandrol; M.L. Fenger; J.A. Withum; R.M. Statnick

    2000-05-01

    The three main conclusions of this report are: (1) The pilot plant successfully demonstrated the continuous, fully-integrated, long-term process operation, including the mixing, pelletizing, and curing steps for aggregate production. The curing vessel, which was designed for the pilot plant test, was operated in a mass flow mode and performed well during pilot plant operation. (2) The pilot plant test demonstrated process flexibility. The same equipment was used to produce lightweight, medium-weight, and road aggregates. The only change was the mix formulation. Aggregates were produced from a variety of mix designs and from FGD sludge with solids concentrations between 45.0% and 56.7% and moisture contents between 55.0% and 43.3%. (3) The pilot plant provided operating data and experience to design and cost a commercial plant, which was not part of the cooperative agreement.

  15. Role of streams in myxobacteria aggregate formation

    NASA Astrophysics Data System (ADS)

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

    2004-10-01

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

  16. Mesoscale aggregation properties of C60 in toluene and chlorobenzene.

    PubMed

    Guo, Rong-Hao; Hua, Chi-Chung; Lin, Po-Chang; Wang, Ting-Yu; Chen, Show-An

    2016-07-20

    The mesoscale aggregation properties of C60 in two distinct aromatic solvents (toluene and chlorobenzene) and a practical range of concentrations (c = 1-2 and c = 1-5 mg mL(-1), respectively) were systematically explored by static/dynamic light scattering (SLS/DLS), small angle X-ray scattering (SAXS), depolarized dynamic light scattering (DDLS), and cryogenic transmission electron microscopy (cryo-TEM) analyses. The central observations were as follows: (1) aggregate species of sizes in the range of several hundred nanometers have been independently revealed by SLS, DLS, and DDLS analyses for both solvent systems. (2) DDLS and cryo-TEM measurements further revealed that while C60 clusters are notably anisotropic (rod-like) in chlorobenzene, they are basically isotropic (spherical) in toluene. (3) Detailed analyses of combined SLS and SAXS profiles suggested that varied, yet self-similar, solvent-induced aggregate units were responsible for the distinct (mesoscale) aggregation features noted above. (4) From a dynamic perspective, specially commissioned DLS measurements ubiquitously displayed two relaxation modes (fast and slow mode), with the second (slow) mode being q (wave vector) independent. While the fast mode in both solvent systems was basically diffusive by nature and leads to geometrical features in good agreement with the above static analyses, the slow mode was analyzed and tentatively suggested to reflect the effect of mutual confinement. (5) Micron-scale aggregate morphology of drop-cast thin films displays similar contrasting features for the two solvent media used. Overall, this study suggests that solvent-induced, nanoscale, aggregate units may be a promising factor to control a hierarchy of microscopic aggregation properties of C60 solutions and thin films.

  17. Epicuticular lipids induce aggregation in Chagas disease vectors

    PubMed Central

    Figueiras, Alicia N Lorenzo; Girotti, Juan R; Mijailovsky, Sergio J; Juárez, M Patricia

    2009-01-01

    Background The triatomine bugs are vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. Aggregation behavior plays an important role in their survival by facilitating the location of refuges and cohesion of aggregates, helping to keep them safely assembled into shelters during daylight time, when they are vulnerable to predators. There are evidences that aggregation is mediated by thigmotaxis, by volatile cues from their faeces, and by hexane-extractable contact chemoreceptive signals from their cuticle surface. The epicuticular lipids of Triatoma infestans include a complex mixture of hydrocarbons, free and esterified fatty acids, alcohols, and sterols. Results We analyzed the response of T. infestans fifth instar nymphs after exposure to different amounts either of total epicuticular lipid extracts or individual lipid fractions. Assays were performed in a circular arena, employing a binary choice test with filter papers acting as aggregation attractive sites; papers were either impregnated with a hexane-extract of the total lipids, or lipid fraction; or with the solvent. Insects were significantly aggregated around papers impregnated with the epicuticular lipid extracts. Among the lipid fractions separately tested, only the free fatty acid fraction promoted significant bug aggregation. We also investigated the response to different amounts of selected fatty acid components of this fraction; receptiveness varied with the fatty acid chain length. No response was elicited by hexadecanoic acid (C16:0), the major fatty acid component. Octadecanoic acid (C18:0) showed a significant assembling effect in the concentration range tested (0.1 to 2 insect equivalents). The very long chain hexacosanoic acid (C26:0) was significantly attractant at low doses (≤ 1 equivalent), although a repellent effect was observed at higher doses. Conclusion The detection of contact aggregation pheromones has practical application in Chagas disease

  18. Mesoscale aggregation properties of C60 in toluene and chlorobenzene.

    PubMed

    Guo, Rong-Hao; Hua, Chi-Chung; Lin, Po-Chang; Wang, Ting-Yu; Chen, Show-An

    2016-07-20

    The mesoscale aggregation properties of C60 in two distinct aromatic solvents (toluene and chlorobenzene) and a practical range of concentrations (c = 1-2 and c = 1-5 mg mL(-1), respectively) were systematically explored by static/dynamic light scattering (SLS/DLS), small angle X-ray scattering (SAXS), depolarized dynamic light scattering (DDLS), and cryogenic transmission electron microscopy (cryo-TEM) analyses. The central observations were as follows: (1) aggregate species of sizes in the range of several hundred nanometers have been independently revealed by SLS, DLS, and DDLS analyses for both solvent systems. (2) DDLS and cryo-TEM measurements further revealed that while C60 clusters are notably anisotropic (rod-like) in chlorobenzene, they are basically isotropic (spherical) in toluene. (3) Detailed analyses of combined SLS and SAXS profiles suggested that varied, yet self-similar, solvent-induced aggregate units were responsible for the distinct (mesoscale) aggregation features noted above. (4) From a dynamic perspective, specially commissioned DLS measurements ubiquitously displayed two relaxation modes (fast and slow mode), with the second (slow) mode being q (wave vector) independent. While the fast mode in both solvent systems was basically diffusive by nature and leads to geometrical features in good agreement with the above static analyses, the slow mode was analyzed and tentatively suggested to reflect the effect of mutual confinement. (5) Micron-scale aggregate morphology of drop-cast thin films displays similar contrasting features for the two solvent media used. Overall, this study suggests that solvent-induced, nanoscale, aggregate units may be a promising factor to control a hierarchy of microscopic aggregation properties of C60 solutions and thin films. PMID:27376417

  19. 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

  20. Hail formation triggers rapid ash aggregation in volcanic plumes.

    PubMed

    Van Eaton, Alexa R; Mastin, Larry G; Herzog, Michael; Schwaiger, Hans F; Schneider, David J; Wallace, Kristi L; Clarke, Amanda B

    2015-01-01

    During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized 'wet' eruption. The 2009 eruption of Redoubt Volcano, Alaska, incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits and numerical modelling demonstrate that hail-forming processes in the eruption plume triggered aggregation of ∼95% of the fine ash and stripped much of the erupted mass out of the atmosphere within 30 min. Based on these findings, we propose a mechanism of hail-like ash aggregation that contributes to the anomalously rapid fallout of fine ash and occurrence of concentrically layered aggregates in volcanic deposits. PMID:26235052

  1. Inhibition of rat platelet aggregation by Urtica dioica leaves extracts.

    PubMed

    El Haouari, Mohammed; Bnouham, Mohamed; Bendahou, Mourad; Aziz, Mohammed; Ziyyat, Abderrahim; Legssyer, Abdelkhaleq; Mekhfi, Hassane

    2006-07-01

    Platelet hyperactivity plays an important role in arterial thrombosis and atherosclerosis. The present study was undertaken to investigate the effects of different extracts of Urtica dioica leaves on platelet aggregation. Rat platelets were prepared and incubated in vitro with different concentrations of the tested extracts and aggregation was induced by different agonists including thrombin (0.5 U/mL), ADP (10 microm), epinephrine (100 microm) and collagen (5 mg/mL). The crude aqueous extract inhibited thrombin-induced platelet aggregation in a dose-dependent manner. At 1 mg/mL, the percent inhibition was 17.1 +/- 4.2%. Soxhlet extraction of the plant leaves with different successive solvents showed that the ethyl acetate extract exhibited the most antiaggregant effect with an inhibition of 76.8 +/- 6.1% at 1 mg/mL. Flavonoids isolated from the plant leaves, produced a strong inhibitory effect on thrombin-induced platelet aggregation with an IC(50) of 0.25 +/- 0.05 and 0.40 +/- 0.04 mg/mL for genins and heterosidic flavonoids, respectively. Flavonoids also markedly inhibited platelet aggregation induced by ADP, collagen and epinephrine. It is concluded that Urtica dioica has an antiplatelet action in which flavonoids are mainly implicated. These results support the traditional use of Urtica dioica in the treatment and/or prevention of cardiovascular disease. PMID:16619332

  2. Colloidal Recycling: Reconfiguration of Random Aggregates into Patchy Particles.

    PubMed

    Meester, Vera; Verweij, Ruben W; van der Wel, Casper; Kraft, Daniela J

    2016-04-26

    The key ingredients to the successful bottom-up construction of complex materials are believed to be colloids with anisotropic shapes and directional, or patchy, interactions. We present an approach for creating such anisotropic patchy particles based on reconfiguring randomly shaped aggregates of colloidal spheres. While colloidal aggregates are often undesirable in colloidal dispersions due to their random shapes, we exploit them as a starting point to synthesize patchy particles. By a deliberate destabilization of the colloidal particles, diffusion-limited aggregation is induced which partitions the particles into randomly shaped aggregates with controlled size distribution. We achieve a reconfiguration of the aggregates into uniform structures by swelling the polymer spheres with an apolar solvent. The swelling lowers the attractive van der Waals forces, lubricates the contact area between the spheres, and drives the reorganization through minimization of the interfacial energy of the swollen polymer network. This reorganization process yields patchy particles whose patch arrangement is uniform for up to five patches. For particles with more patches, we find that the patch orientation depends on the degree of phase separation between the spheres and the monomer. This enables the synthesis of patchy particles with unprecedented patch arrangements. We demonstrate the broad applicability of this recycling strategy for making patchy particles as well as clusters of spheres by varying the swelling ratio, swelling solvent, surfactant concentration, and swelling time. PMID:27014995

  3. Colloidal Recycling: Reconfiguration of Random Aggregates into Patchy Particles.

    PubMed

    Meester, Vera; Verweij, Ruben W; van der Wel, Casper; Kraft, Daniela J

    2016-04-26

    The key ingredients to the successful bottom-up construction of complex materials are believed to be colloids with anisotropic shapes and directional, or patchy, interactions. We present an approach for creating such anisotropic patchy particles based on reconfiguring randomly shaped aggregates of colloidal spheres. While colloidal aggregates are often undesirable in colloidal dispersions due to their random shapes, we exploit them as a starting point to synthesize patchy particles. By a deliberate destabilization of the colloidal particles, diffusion-limited aggregation is induced which partitions the particles into randomly shaped aggregates with controlled size distribution. We achieve a reconfiguration of the aggregates into uniform structures by swelling the polymer spheres with an apolar solvent. The swelling lowers the attractive van der Waals forces, lubricates the contact area between the spheres, and drives the reorganization through minimization of the interfacial energy of the swollen polymer network. This reorganization process yields patchy particles whose patch arrangement is uniform for up to five patches. For particles with more patches, we find that the patch orientation depends on the degree of phase separation between the spheres and the monomer. This enables the synthesis of patchy particles with unprecedented patch arrangements. We demonstrate the broad applicability of this recycling strategy for making patchy particles as well as clusters of spheres by varying the swelling ratio, swelling solvent, surfactant concentration, and swelling time.

  4. 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

  5. Two-Dimensional Aggregation and Semidilute Ordering in Cellulose Nanocrystals.

    PubMed

    Uhlig, Martin; Fall, Andreas; Wellert, Stefan; Lehmann, Maren; Prévost, Sylvain; Wågberg, Lars; von Klitzing, Regine; Nyström, Gustav

    2016-01-19

    The structural properties and aggregation behavior of carboxymethylated cellulose nanocrystals (CNC-COOH) were analyzed with small angle neutron scattering (SANS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS) and compared to sulfuric acid hydrolyzed cellulose nanocrystals (CNC-SO3H). The CNC-COOH system, prepared from single carboxymethylated cellulose nanofibrils, was shown to laterally aggregate into 2D-stacks that were stable both in bulk solution and when adsorbed to surfaces. CNC-SO3H also showed a 2D aggregate structure with similar cross sectional dimensions (a width to height ratio of 8) as CNC-COOH, but a factor of 2 shorter length. SANS and DLS revealed a reversible ordering of the 2D aggregates under semidilute conditions, and a structure peak was observed for both systems. This indicates an early stage of liquid crystalline arrangement of the crystal aggregates, at concentrations below those assessed using birefringence or polarized optical microscopy. PMID:26684549

  6. Hail formation triggers rapid ash aggregation in volcanic plumes

    USGS Publications Warehouse

    Van Eaton, Alexa R.; Mastin, Larry G.; Herzog, M.; Schwaiger, Hans F.; Schneider, David J.; Wallace, Kristi; Clarke, Amanda B

    2015-01-01

    During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized ‘wet’ eruption. The 2009 eruption of Redoubt Volcano in Alaska incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits, and numerical modeling demonstrate that volcanic hail formed rapidly in the eruption plume, leading to mixed-phase aggregation of ~95% of the fine ash and stripping much of the cloud out of the atmosphere within 30 minutes. Based on these findings, we propose a mechanism of hail-like aggregation that contributes to the anomalously rapid fallout of fine ash and the occurrence of concentrically-layered aggregates in volcanic deposits.

  7. Hail formation triggers rapid ash aggregation in volcanic plumes

    PubMed Central

    Van Eaton, Alexa R.; Mastin, Larry G.; Herzog, Michael; Schwaiger, Hans F.; Schneider, David J.; Wallace, Kristi L.; Clarke, Amanda B.

    2015-01-01

    During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized ‘wet' eruption. The 2009 eruption of Redoubt Volcano, Alaska, incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits and numerical modelling demonstrate that hail-forming processes in the eruption plume triggered aggregation of ∼95% of the fine ash and stripped much of the erupted mass out of the atmosphere within 30 min. Based on these findings, we propose a mechanism of hail-like ash aggregation that contributes to the anomalously rapid fallout of fine ash and occurrence of concentrically layered aggregates in volcanic deposits. PMID:26235052

  8. Inhibitors of ex vivo aggregation of human platelets induced by decompression, during reduced barometric pressure.

    PubMed

    Murayama, M; Kumaroo, K K

    1986-05-15

    It has been shown experimentally ex vivo that human platelet aggregation is induced by decompression (reduced pressure) produced by various means, i.e., reduced barometric pressure, reduced hydrostatic pressure, and reduced hydrodynamic pressure due to Bernoulli's principle. We report here that the spontaneous platelet aggregation induced by reduced barometric pressure (253 torr for three hours) is inhibited by 1:10(7) diluted Japanese herbal plant oil (JHP) and also by two of its major constituents, menthone and menthol with the median inhibitory concentration (IC50) in the millimolar range. These drugs gave essentially similar results when collagen and ADP were used as aggregating agents. Inhibitor concentrations were determined by microscopic examination of platelets in wet preparations when the aggregating stimulus was reduced pressure and by optical aggregometry when collagen and ADP were the aggregating agents. Potential usefulness of these compounds in the prevention of decompression syndrome (DCS) and acute mountain sickness (AMS) are discussed.

  9. Glass/Jamming Transition in Colloidal Aggregation

    NASA Technical Reports Server (NTRS)

    Segre, Philip N.; Prasad, Vikram; Weitz, David A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    We have studied colloidal aggregation in a model colloid plus polymer system with short-range attractive interactions. By varying the colloid concentration and the strength of the attraction, we explored regions where the equilibrium phase is expected to consist of colloidal crystallites in coexistance with colloidal gas (i.e. monomers). This occurs for moderate values of the potential depth, U approximately equal to 2-5 kT. Crystallization was not always observed. Rather, over an extended sub-region two new metastable phases appear, one fluid-like and one solid-like. These were examined in detail with light scattering and microscopy techniques. Both phases consist of a near uniform distribution of small irregular shaped clusters of colloidal particles. The dynamical and structural characteristics of the ergodic-nonergodic transition between the two phases share much in common with the colloidal hard sphere glass transition.

  10. Tau Phosphorylation, Aggregation, and Cell Toxicity

    PubMed Central

    Avila, J.; Santa-María, I.; Pérez, M.; Hernández, F.; Moreno, F.

    2006-01-01

    Protein aggregation takes place in many neurodegenerative disorders. However, there is a controversy about the possible toxicity of these protein aggregates. In this review, this controversy is discussed, focussing on the tau aggregation that takes place in those disorders known as tauopathies. PMID:17047313

  11. Mineral resource of the month: aggregates

    USGS Publications Warehouse

    Willett, Jason C.

    2012-01-01

    Crushed stone and construction sand and gravel, the two major types of natural aggregates, are among the most abundant and accessible natural resources on the planet. The earliest civilizations used aggregates for various purposes, mainly construction. Today aggregates provide the basic raw materials for the foundation of modern society.

  12. Sedimentation of particles and aggregates in colloids considering both streaming and seepage

    NASA Astrophysics Data System (ADS)

    Song, Dongxing; Jin, Hui; Jin, Jingyu; Jing, Dengwei

    2016-10-01

    Sedimentation of colloids is a common phenomenon in various industrial processes. Aggregation of nanoparticles is expected to occur during the processes. However, previous studies often ignore the important features of aggregates, e.g. porosity and possible seepage, leading to a mathematical description of the sedimentation processes of low reliability. In this study, we successfully elaborated the partial differential equation of the dynamic concentration distribution of regimented colloids based on the Stokes approximation and diffusion along the negative gradient of concentration. The permeability of aggregates was obtained by the finite volume method and the ratios of the velocities of flowing around (u f) to seepage through (u s) aggregates over various primary particle sizes and aggregation structures were obtained based on the Darcy equations. After validation of the model, the effects of size and density of the particles and aggregates on the concentration profiles were investigated. Our results indicate that both an increase in size and density of particles and aggregates can accelerate the sedimentation process, and lead to more ‘thorough’ sedimentation. We mathematically explain why suspensions with high particle concentration are more unstable. What is more, replacing gravity with other volume forces, e.g. centrifugal force and magnetic forces, our model is expected to be applicable to centrifugation or magnetic sedimentation processes.

  13. Aggregation of liposomes in presence of La3+: a study of the fractal dimension.

    PubMed

    Sabín, Juan; Prieto, Gerardo; Ruso, Juan M; Messina, Paula; Sarmiento, Félix

    2007-07-01

    A study of the fractal dimension of the aggregation of three different types of large unilamellar vesicles, formed by egg yolk phosphatidylcholine (EYPC), dimyristoyl-phosphocholine (DMPC), and dipalmitoyl-phosphocholine (DPPC), in the presence of La3+, is presented. Aggregate liposome fractal dimensions were calculated by two methods, aggregation kinetics, using the approaches diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) and angle-scattering light dispersion. Electrophoretic measurements show a similar variation of the zeta potential (zeta potential) for EYPC and DPPC, with a small increase of initial positive values. However, the zeta potential of DMPC changes from a initial negative value to near zero with increasing La3+ concentration. The evolution of the aggregate sizes was followed by light scattering. DPPC and DMPC show a RLCA regimen growth at low La3+ concentrations and a DLCA regimen at higher concentrations. In the case of EYPC, the final size of aggregation strongly depends on La3+ concentration. The calculated fractal dimension is in the range 1.8 to 2.1.

  14. A study of the behaviour of ampicillin in aqueous solution and thermodynamic characterization of its aggregation

    NASA Astrophysics Data System (ADS)

    Besada, Lina; Martinez-Landeira, Pablo; Seoane, Laura; Prieto, Gerardo; Sarmiento, Felix; Ruso, Juan M.

    The aggregation of ampicillin in water has been examined by conductivity measurements over the temperature range 288.15-313.15 K and light scattering. These measurements indicate the formation of two critical concentrations over the range 0-0.35 mol kg -1 . Aggregation number and effective aggregate charge were calculated from the static light scattering data according to the Anacker and Westwell treatment. Thermodynamic parameters of aggregate formation were obtained from a form of the mass action model applicable to systems of low aggregation number. This method was applied at both critical concentrations. A valence of one was used for the monomers present in the first equilibrium. The second equilibrium was between aggregates of two different sizes, in this case, the valence of the aggregates being the effective charge calculated from the Anacker and Westwell treatment. Experimental results show that free energies of micellization for ampicillin are higher for the first critical concentration and in the same range, but lower than for other penicillins. The enthalpies of micellization become negative when the temperature is increased, but the variation is three times greater for the first critical concentration than for the second.

  15. Development of a method to quantify platelet adhesion and aggregation under static conditions

    PubMed Central

    Baker-Groberg, Sandra M.; Cianchetti, Flor A.; Phillips, Kevin G.; McCarty, Owen J.T.

    2014-01-01

    Platelets are important players in hemostasis and thrombosis. Thus, accurate assessment of platelet function is crucial for identifying platelet function disorders and measuring the efficacy of antiplatelet therapies. We have developed a novel platelet aggregation technique that utilizes the physical parameter of platelet concentration in conjunction with volume and mass measurements to evaluate platelet adhesion and aggregation. Platelet aggregates were formed by incubating purified platelets on fibrinogen- or fibrillar collagen-coated surfaces at platelet concentrations ranging from 20,000 to 500,000 platelets/ L. Platelets formed aggregates under static conditions in a platelet concentration-dependent manner, with significantly greater mean volume and mass at higher platelet concentrations ( 400,000 platelets/ L). We show that a platelet glycoprotein IIb/IIIa inhibitor abrogated platelet-platelet aggregation, which significantly reduced the volume and mass of the platelets on the collagen surface. This static platelet aggregation technique is amenable to standardization and represents a useful tool to investigate the mechanism of platelet activation and aggregation under static conditions. PMID:24883127

  16. Surfactant-induced aggregation patterns of thiazole orange: a photophysical study.

    PubMed

    Choudhury, Sharmistha Dutta; Bhasikuttan, Achikanath C; Pal, Haridas; Mohanty, Jyotirmayee

    2011-10-18

    The aggregation behavior of the DNA marker dye thiazole orange (TO), has been investigated in two types of surfactant assemblies, namely, premicelles/micelles of sodium dodecyl sulfate (SDS) and pre reverse micelles/reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT). In the case of an SDS/water system, absorption spectral changes of TO signify the formation of H-aggregates and H-dimers of the dye at premicellar concentrations, which subsequently convert to the monomeric form beyond the critical micellar concentration (cmc). Interestingly, the observed changes in the absorption and emission characteristics due to the surfactant-induced formation of H-aggregates/dimers of TO are found to be useful to estimate the surfactant concentration parameters for premicellar aggregation of SDS. In the case of an AOT/n-heptane system, similarly, H-aggregates/dimers are observed at low AOT concentrations, below the cmc. However, in this case, the H-dimers persist even beyond the cmc. This is attributed to the strong tendency of TO for self-aggregation and its favorable electrostatic interactions with the AOT head groups. With increasing water content in the AOT reverse micelles, the hydration of the dye leads to the conversion of H-dimers to the monomeric form. The steady-state fluorescence results are nicely corroborated with those from time-resolved fluorescence studies and demonstrate the interesting behavior of the surfactant-induced aggregation of TO dye.

  17. Floating mucus aggregates derived from benthic microorganisms on rocky intertidal reefs: Potential as food sources for benthic animals

    NASA Astrophysics Data System (ADS)

    Tamura, Y.; Tsuchiya, M.

    2011-09-01

    Mucus films, flocs or foams consisting of fine sand, algae and detritus frequently occur in the surface waters of rocky intertidal reef flats during incoming tide. These masses are referred to as mucus aggregates. We examined the developmental process of mucus aggregates and their abundance, distribution, migration and trophic composition. The trophic composition of mucus aggregates was then compared to those of sediments to evaluate their potential nutritional value for benthic animals. The organic matter content, chlorophyll a concentration, microalgal density and bacteria-derived fatty acid contents of mucus aggregates were higher than those observed in sediment, suggesting that mucus aggregates contain not only high levels of organic matter but also dense concentrations of microalgae and bacteria; therefore, mucus aggregates may serve as a qualitatively more energetic food source for benthic fauna compared to sediments. Benthic diatoms were the most abundant organisms in mucus aggregates. Large numbers of diatoms were trapped in fine mineral particles and mucilage-like strings, suggesting that a portion of the mucus is secreted by these benthic microalgae. Mucus aggregate accounted for only 0.01-3.9% of the daily feeding requirements of the dominant detritivore, Ophiocoma scolopendrina (Echinodermata: Ophiuroidea) over the entire sampling area. In contrast, for the species population on the back reef, where mucus aggregates ultimately accumulate, mucus aggregates provided from 0.4 to 113.3% of food for this species. These results suggest that mucus aggregate availability varies spatiotemporally and that they do not always provide adequate food sources for O. scolopendrina populations.

  18. Controlling the formation of cyanine dye H- and J-aggregates with cucurbituril hosts in the presence of anionic polyelectrolytes.

    PubMed

    Gadde, Suresh; Batchelor, Elizabeth K; Kaifer, Angel E

    2009-06-01

    The presence of anionic polyelectrolytes enhances the tendency of cationic cyanine dyes to form aggregates in aqueous media. In this work we investigate the interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), with polystyrenesulfonate (PSS) as the key additive to develop J- and H-aggregates. We also take advantage of the binding properties of the cucurbit[7]uril (CB7) host to control formation of these aggregates through its host-guest interactions with the dye molecules. UV/Vis absorption spectroscopic studies clearly demonstrate the PSS-enhanced formation of J-aggregates in the case of PIC and H-aggregates in the case of PIN. Electrostatic interactions between the cyanine dye molecules and the polyelectrolyte chains assist the formation of J- or H-aggregates at very low dye concentrations (ca. 10 microM). Optimum development of dye aggregates was observed at a sulfonate/dye molar ratio of about 3:1. Departures from this stoichiometric ratio seem to perturb the optimal aggregate structure. Furthermore, the presence of CB7 was found to effectively disrupt the interactions responsible for dye aggregation. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. UV/Vis and emission spectroscopic studies clearly indicate that binding of CB7 to both dye molecules removes them from the aggregate structures. Our spectroscopic data clearly indicate that regulation of the relative molar ratios of dye, CB7 host, and polyelectrolyte sulfonate groups leads to a quantitative control of dye aggregation, yielding variable amounts of PIC J- and PIN H-aggregates in these solutions. PMID:19402091

  19. Aggregation-Induced Emission Mechanism of Dimethoxy-Tetraphenylethylene in Water Solution: Molecular Dynamics and QM/MM Investigations.

    PubMed

    Sun, Guangxu; Zhao, Yi; Liang, WanZhen

    2015-05-12

    Molecular dynamics simulations and combined quantum mechanics and molecular mechanics calculations are employed to investigate dimethoxy-tetraphenylethylene (DMO-TPE) molecules in water solution for their detailed aggregation process and the mechanism of aggregation-induced emission. The molecular dynamics simulations show that the aggregates start to appear in the nanosecond time scale, and small molecular aggregates appear at low concentration; whereas the large aggregates with a chain-type structure appear at high concentration, and the intramolecular rotation is largely restricted by a molecular aggregated environment. The average radical distribution demonstrates that the waters join the aggregation process and that two types of hydrogen bonds between DMO-TPE and water molecules are built with the peaks at about 0.5 and 0.7 nm, respectively. The spectral features further reveal that the aggregates dominantly present J-type aggregation although they fluctuate between J-type and H-type at a given temperature. The statistical absorption, emission spectra, and the aggregation-induced emission enhancement with respect to the solution concentration agree well with the experimental measurements, indicating the significant effect of molecular environments on the molecular properties. PMID:26574424

  20. A modified Stokes-Einstein equation for Aβ aggregation

    PubMed Central

    2011-01-01

    Background In all amyloid diseases, protein aggregates have been implicated fully or partly, in the etiology of the disease. Due to their significance in human pathologies, there have been unprecedented efforts towards physiochemical understanding of aggregation and amyloid formation over the last two decades. An important relation from which hydrodynamic radii of the aggregate is routinely measured is the classic Stokes-Einstein equation. Here, we report a modification in the classical Stokes-Einstein equation using a mixture theory approach, in order to accommodate the changes in viscosity of the solvent due to the changes in solute size and shape, to implement a more realistic model for Aβ aggregation involved in Alzheimer’s disease. Specifically, we have focused on validating this model in protofibrill lateral association reactions along the aggregation pathway, which has been experimentally well characterized. Results The modified Stokes-Einstein equation incorporates an effective viscosity for the mixture consisting of the macromolecules and solvent where the lateral association reaction occurs. This effective viscosity is modeled as a function of the volume fractions of the different species of molecules. The novelty of our model is that in addition to the volume fractions, it incorporates previously published reports on the dimensions of the protofibrils and their aggregates to formulate a more appropriate shape rather than mere spheres. The net result is that the diffusion coefficient which is inversely proportional to the viscosity of the system is now dependent on the concentration of the different molecules as well as their proper shapes. Comparison with experiments for variations in diffusion coefficients over time reveals very similar trends. Conclusions We argue that the standard Stokes-Einstein’s equation is insufficient to understand the temporal variations in diffusion when trying to understand the aggregation behavior of Aβ42 proteins. Our

  1. Aggregate-associated carbon and nitrogen in reclaimed sandy loam soils

    SciTech Connect

    Wick, A.F.; Stahl, P.D.; Ingram, L.J.

    2009-11-15

    Minimal research has been conducted on aggregate, C, and N in coarse-textured soils used to reclaim surface coal mine lands. Furthermore, little is known about the contribution different plant communities make to the recovery of aggregation in these soils. Two chronosequences of semiarid reclaimed sites with sandy loam soils were sampled under shrub- and grass-dominated communities. Aggregation, aggregate fractions, and associated C and N were measured. No definitive trends of increasing macroaggregates between sites were observed undershrubs; however, macro- and microaggregation was greater in the 16-yr-old (0.20 and 0.23 kg aggregate kg{sup -1} soil, respectively) than in the 5-yr-old soils (0.02 and 0.08 kg aggregate kg{sup -1} soil, respectively) under grasses. Although C and N concentrations were drastically reduced (50-75%) with mining activity between the <1-yr-old and native soils, aggregate C and N concentrations tinder shrubs and grasses were similar to each other and to the native soils in the 5-yr-old site. Sods under grass in the 16-yr-old site had lower available and aggregate-occluded C and N concentrations than the 5-yr-old site, while C and N concentrations did not change between 5- and 16-yr-old soils under shrubs. Conversely, aggregate C and N pool sizes under shrubs and grasses both increased with site age to conditions similar to those observed in the native soil. Reclaimed shrub site soils had consistently higher C concentrations in the older reclaimed sites (10 and 16 yr old) than the soils under grasses, indicating greater accumulation and retention of C and N in organic material under shrub than grass communities in semiarid reclaimed sites.

  2. Cellular Models of Aggregation-dependent Template-directed Proteolysis to Characterize Tau Aggregation Inhibitors for Treatment of Alzheimer Disease*

    PubMed Central

    Harrington, Charles R.; Storey, John M. D.; Clunas, Scott; Harrington, Kathleen A.; Horsley, David; Ishaq, Ahtsham; Kemp, Steven J.; Larch, Christopher P.; Marshall, Colin; Nicoll, Sarah L.; Rickard, Janet E.; Simpson, Michael; Sinclair, James P.; Storey, Lynda J.; Wischik, Claude M.

    2015-01-01

    Alzheimer disease (AD) is a degenerative tauopathy characterized by aggregation of Tau protein through the repeat domain to form intraneuronal paired helical filaments (PHFs). We report two cell models in which we control the inherent toxicity of the core Tau fragment. These models demonstrate the properties of prion-like recruitment of full-length Tau into an aggregation pathway in which template-directed, endogenous truncation propagates aggregation through the core Tau binding domain. We use these in combination with dissolution of native PHFs to quantify the activity of Tau aggregation inhibitors (TAIs). We report the synthesis of novel stable crystalline leucomethylthioninium salts (LMTX®), which overcome the pharmacokinetic limitations of methylthioninium chloride. LMTX®, as either a dihydromesylate or a dihydrobromide salt, retains TAI activity in vitro and disrupts PHFs isolated from AD brain tissues at 0.16 μm. The Ki value for intracellular TAI activity, which we have been able to determine for the first time, is 0.12 μm. These values are close to the steady state trough brain concentration of methylthioninium ion (0.18 μm) that is required to arrest progression of AD on clinical and imaging end points and the minimum brain concentration (0.13 μm) required to reverse behavioral deficits and pathology in Tau transgenic mice. PMID:25759392

  3. Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation.

    PubMed

    Brown, Keith A; Vassiliou, Christophoros C; Issadore, David; Berezovsky, Jesse; Cima, Michael J; Westervelt, R M

    2010-10-01

    The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2CP of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2CP and details of the aggregate. We find that in the motional averaging regime T2CP scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2CP∝N-0.44 for aggregates with d = 2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2CP is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times. PMID:20689678

  4. The lantibiotic nisin induces lipid II aggregation, causing membrane instability and vesicle budding.

    PubMed

    Scherer, Katharina M; Spille, Jan-Hendrik; Sahl, Hans-Georg; Grein, Fabian; Kubitscheck, Ulrich

    2015-03-10

    The antimicrobial peptide nisin exerts its activity by a unique dual mechanism. It permeates the cell membranes of Gram-positive bacteria by binding to the cell wall precursor Lipid II and inhibits cell wall synthesis. Binding of nisin to Lipid II induces the formation of large nisin-Lipid II aggregates in the membrane of bacteria as well as in Lipid II-doped model membranes. Mechanistic details of the aggregation process and its impact on membrane permeation are still unresolved. In our experiments, we found that fluorescently labeled nisin bound very inhomogeneously to bacterial membranes as a consequence of the strong aggregation due to Lipid II binding. A correlation between cell membrane damage and nisin aggregation was observed in vivo. To further investigate the aggregation process of Lipid II and nisin, we assessed its dynamics by single-molecule microscopy of fluorescently labeled Lipid II molecules in giant unilamellar vesicles using light-sheet illumination. We observed a continuous reduction of Lipid II mobility due to a steady growth of nisin-Lipid II aggregates as a function of time and nisin concentration. From the measured diffusion constants of Lipid II, we estimated that the largest aggregates contained tens of thousands of Lipid II molecules. Furthermore, we observed that the formation of large nisin-Lipid II aggregates induced vesicle budding in giant unilamellar vesicles. Thus, we propose a membrane permeation mechanism that is dependent on the continuous growth of nisin-Lipid II aggregation and probably involves curvature effects on the membrane.

  5. The Effects of Latrepirdine on Amyloid-β Aggregation and Toxicity

    PubMed Central

    Porter, Tenielle; Bharadwaj, Prashant; Groth, David; Paxman, Adrian; Laws, Simon M.; Martins, Ralph N.; Verdile, Giuseppe

    2016-01-01

    Latrepirdine (Dimebon™) has been demonstrated to be a neuroprotective and cognition improving agent in neurodegenerative diseases that feature protein aggregation and deposition, such as Alzheimer’s disease (AD). The accumulation of amyloid-β (Aβ) protein aggregates is a key event in the neurodegenerative process in AD. This study explores if latrepirdine modulation of protein aggregation contributes to its neuroprotective mechanism of action. Assessment of neuronal cell death showed that there was a significant reduction in lactate dehydrogenase release at an equimolar ratio of Aβ:latrepirdine and with lower concentrations of latrepirdine. The ability of latrepirdine to alter the formation of Aβ42 aggregates was assessed by thioflavin-T fluorescence, western immunoblotting and atomic force microscopy (AFM). Despite showing a reduction in thioflavin-T fluorescence with latrepirdine treatment, indicating a decrease in aggregation, immunoblotting and AFM showed a modest increase in both the formation and size of Aβ aggregates. The discrepancies between thioflavin-T and the other assays are consistent with previous evidence that cyclic molecules can interfere with thioflavin-T binding of amyloid protein preparations. The ability of latrepirdine to modulate Aβ aggregation appears to be independent of its neuroprotective effects, and is unlikely to be a mechanism by which latrepirdine offers protection. This study investigates the effect of latrepirdine on Aβ aggregation, and presents evidence suggesting that caution should be applied in the use of thioflavin-T fluorescence based assays as a method for screening compounds for protein aggregation altering properties. PMID:26836170

  6. Phase diagram of aggregation of oppositely charged colloids in salty water.

    PubMed

    Zhang, R; Shklovskii, B I

    2004-02-01

    Aggregation of two oppositely charged colloids in salty water is studied. We focus on the role of Coulomb interaction in strongly asymmetric systems in which the charge and size of one colloid is much larger than the other one. In the solution, each large colloid (macroion) attracts a certain number of oppositely charged small colloids (Z-ion) to form a complex. If the concentration ratio of the two colloids is such that complexes are not strongly charged, they condense in a macroscopic aggregate. As a result, the phase diagram in a plane of concentrations of two colloids consists of an aggregation domain sandwiched between two domains of stable solutions of complexes. The aggregation domain has a central part of total aggregation and two wings corresponding to partial aggregation. A quantitative theory of the phase diagram in the presence of monovalent salt is developed. It is shown that as the Debye-Hückel screening radius r(s) decreases, the aggregation domain grows, but the relative size of the partial aggregation domains becomes much smaller. As an important application of the theory, we consider solutions of long double-helix DNA with strongly charged positive spheres (artificial chromatin). We also consider implications of our theory for in vitro experiments with the natural chromatin. Finally, the effect of different shapes of macroions on the phase diagram is discussed.

  7. Microwave extinction characteristics of nanoparticle aggregates

    NASA Astrophysics Data System (ADS)

    Wu, Y. P.; Cheng, J. X.; Liu, X. X.; Wang, H. X.; Zhao, F. T.; Wen, W. W.

    2016-07-01

    Structure of nanoparticle aggregates plays an important role in microwave extinction capacity. The diffusion-limited aggregation model (DLA) for fractal growth is utilized to explore the possible structures of nanoparticle aggregates by computer simulation. Based on the discrete dipole approximation (DDA) method, the microwave extinction performance by different nano-carborundum aggregates is numerically analyzed. The effects of the particle quantity, original diameter, fractal structure, as well as orientation on microwave extinction are investigated, and also the extinction characteristics of aggregates are compared with the spherical nanoparticle in the same volume. Numerical results give out that proper aggregation of nanoparticle is beneficial to microwave extinction capacity, and the microwave extinction cross section by aggregated granules is better than that of the spherical solid one in the same volume.

  8. What favors convective aggregation and why?

    NASA Astrophysics Data System (ADS)

    Muller, Caroline; Bony, Sandrine

    2015-07-01

    The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self-aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self-aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a "radiative aggregation." In that case, sufficient spatial variability of radiative cooling rates yields a low-level circulation, which induces the upgradient energy transport and radiative-convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak ("moisture-memory aggregation"), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self-aggregation to various parameters, including resolution or domain size.

  9. Simulation of J-aggregate microcavity photoluminescence

    NASA Astrophysics Data System (ADS)

    Michetti, Paolo; La Rocca, Giuseppe C.

    2008-05-01

    We have developed a model in order to account for the photoexcitation dynamics of J-aggregate films and strongly coupled J-aggregate microcavities. The J aggregates are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. The correspondence between the photophysics in J-aggregate films and that in J-aggregate microcavities is obtained by introducing a model polariton wave function mixing cavity photon modes and J-aggregate super-radiant excitons. With the same description of the material properties, we have calculated both absorption and luminescence spectra for the J-aggregate film and the photoluminescence of strongly coupled organic microcavities. The model is able to account for the fast relaxation dynamics in organic microcavities following nonresonant pumping and explains the temperature dependence of the ratio between the upper polariton and the lower polariton luminescence.

  10. Quantifying intra- and extracellular aggregation of iron oxide nanoparticles and its influence on specific absorption rate.

    PubMed

    Jeon, Seongho; Hurley, Katie R; Bischof, John C; Haynes, Christy L; Hogan, Christopher J

    2016-09-21

    A promising route to cancer treatment is hyperthermia, facilitated by superparamagnetic iron oxide nanoparticles (SPIONs). After exposure to an alternating external magnetic field, SPIONs generate heat, quantified by their specific absorption rate (SAR, in W g(-1) Fe). However, without surface functionalization, commercially available, high SAR SPIONs (EMG 308, Ferrotec, USA) aggregate in aqueous suspensions; this has been shown to reduce SAR. Further reduction in SAR has been observed for SPIONs in suspensions containing cells, but the origin of this further reduction has not been made clear. Here, we use image analysis methods to quantify the structures of SPION aggregates in the extra- and intracellular milieu of LNCaP cell suspensions. We couple image characterization with nanoparticle tracking analysis and SAR measurements of SPION aggregates in cell-free suspensions, to better quantify the influence of cellular uptake on SPION aggregates and ultimately its influence on SAR. We find that in both the intra- and extracellular milieu, SPION aggregates are well-described by a quasifractal model, with most aggregates having fractal dimensions in the 1.6-2.2 range. Intracellular aggregates are found to be significantly larger than extracellular aggregates and are commonly composed of more than 10(3) primary SPION particles (hence they are "superaggregates"). By using high salt concentrations to generate such superaggregates and measuring the SAR of suspensions, we confirm that it is the formation of superaggregates in the intracellular milieu that negatively impacts SAR, reducing it from above 200 W g(-1) Fe for aggregates composed of fewer than 50 primary particles to below 50 W g(-1) for superaggregates. While the underlying physical mechanism by which aggregation leads to reduction in SAR remains to be determined, the methods developed in this study provide insight into how cellular uptake influences the extent of SPION aggregation, and enable estimation of the

  11. Influence of mineral aggregates on the rheological properties of concrete mixture

    NASA Astrophysics Data System (ADS)

    Klovas, A.; Daukšys, M.

    2015-04-01

    The aim of this research was to determine how the change of concrete mixture constituents: concentration of fine and coarse aggregate as well as the amount of fine particles, not exceeding 0.25 mm, influence concrete mixture's rheological properties. Firstly, inner- concentration of fine aggregate (sand, fraction of 0/1 and 0/4) was changed. Secondly, coarse aggregate (gravel, fraction of 4/16) concentration was changed and finally, the amount of fine particles was changed. Results have shown that with the increase of sand (fraction of 0/1) quantity, the plastic viscosity also increased. On the other hand, yield stress, at the beginning decreased, but eventually - increased. The increase of coarse aggregate quantity acted differently: plastic viscosity and yield stress decreased. Finally, the increase of fine particles quantity decreased the plastic viscosity as well as yield stress of concrete mixture.

  12. Radon exhalation from sub-slab aggregate used in home construction in Canada.

    PubMed

    Bergman, Lauren; Lee, Jaeyoung; Sadi, Baki; Chen, Jing

    2015-06-01

    Exposure to elevated levels of radon in homes has been shown to result in an increased risk of developing lung cancer. The two largest contributors to indoor radon are radon in soil gas, formed from the rocks and soil surrounding the home, and building materials such as aggregate. This study measured the surface radon exhalation rates for 35 aggregate samples collected from producers across Canada. The radon exhalation rates ranged from 2.3 to 479.9 Bq m(-2) d(-1), with a mean of 80.7±112 Bq m(-2) d(-1). Using a simple, conservative analysis, the aggregate contribution to radon concentrations in an unfinished basement was determined. The maximum estimated radon concentration was 32.5±2.7 Bq m(-3), or ~16 % of the Canadian Radon Guideline. It can be concluded that under normal conditions radon exhalation from aggregate contributes very little to the total radon concentration in indoor air.

  13. Investigation of the interaction between sodium dodecyl sulfate and cationic polymers.

    PubMed

    Lee, Jungno; Moroi, Yoshikiyo

    2004-05-25

    Aggregation properties of sodium dodecyl sulfate (SDS) on a cationic hydroxyethyl cellulose, Polyquaternium-10 (PQ-10), of low charge density were studied by potentiometric and pyrene fluorescence methods and compared with those of poly(diallyldimethylammomium chloride) (PDADMAC) of high charge density. The critical aggregation concentration (cac) was measured with the potentiometric method and further confirmed with the fluorescence method. The former was found to be more accurate. The value of the cac for the SDS/PQ-10 system was measured at 100, 200, and 400 ppm polymer and at 288.2,298.2, and 308.2 K. They showed almost the same cac value, 0.04 mmol dm-3. The I1/I3 value of the pyrene fluorescence spectrum in the SDS/PQ-10 system at higher SDS concentration was smaller than that in SDS/PDADMAC solution and much larger than that of water. From the binding isotherm by the potentiometric method, the free DS- concentration (Cf) and the bound DS- concentration (Cb) could be evaluated with ease over the SDS concentration range above the cac. The aggregation number of DS- aggregates for both the above polymers was evaluated from the fluorescence quenching method using the values of Cf and Cb from the potentiometric method. Because Cf in the SDS/PQ-10 system above the cac did not maintain a constant value contrary to that in the SDS/PDADMAC system but increased quite a lot, Cb should not be regarded as [SDS] - cac above the cac. The aggregation number in the SDS/PQ-10 system increased almost linearly with increasing total concentration of SDS, while that in the SDS/PDADMAC system reached a plateau. With increasing temperature, the aggregation number of the SDS/PDADMAC system decreased more rapidly than that of the SDS/PQ-10 system. PMID:15969141

  14. [Reasons of drifting floating objects aggregating rainbow runner (Elagatis bipinnulata)].

    PubMed

    Wang, Xue-Fang; Zhou, Cheng; Zhu, Guo-Ping; Tang, Hao; Xu, Liu-Xiong

    2014-01-01

    Many pelagic species tend to aggregate under drifting floating objects. This has led to the development of drifting fish aggregation devices (FADs) to attract the tropical tunas for the tuna purse seine fishery. However, FADs can also attract other non-targeting small pelagic species such as rainbow runner Elagatis bipinnulata, although it is still unclear why those species can be attracted and aggregated under an FAD. Using the fishery biological data collected in the Western and Central Pacific Ocean by the scientific observers on board Chinese tuna purse seine fishing vessels, we evaluated the potential motivations for rainbow runner to aggregate under drifting objects. This study indicated 1) Fork length of rainbow runner ranged from 30.0 to 90.6 cm, with the dominant fork lengths of 60.0 to 80.0 cm, accounting for 76.3% of the total sampled fish, suggesting large rainbow runner dominating around the drifting objects; 2) Size (fork length) of E. bipinnulata at 50% maturity was 65.7 cm, and mature individuals were dominant under the FADs; and 3) Some commonly observed small fish species, such as Decapterus macarellus, Kyphosus cinerascens, Caranx sexfasciatus, Katsuwonus pelamis and the juveniles of Thunnus obesus and Thunnus albacares, were found in the stomach of rainbow runner, which suggested that rainbow runner under FAD preyed on other associated small pelagic species. As an oceanic predator associated with drifting objects, feeding is perhaps one of the most possible motivations for adult E. bipinnulata to aggregate under the FAD. Both the "concentration of food supply" hypothesis and the "comfortability stipulation" hypothesis can be used to explain why E. bipinnulata aggregate under drifting floating objects. PMID:24765868

  15. Experimental aggregation of volcanic ash: the role of liquid bonding

    NASA Astrophysics Data System (ADS)

    Mueller, S.; Kueppers, U.; Jacob, M.; Ayris, P. M.; Dingwell, D. B.

    2015-12-01

    Explosive volcanic eruptions may release vast quantities of ash. Because of its size, it has the greatest dispersal potential and can be distributed globally. Ash may pose severe risks for 1) air traffic, 2) human and animal health, 3) agriculture and 4) infrastructure. Such ash particles can however cluster and form ash aggregates that range in size from millimeters to centimeters. During their growth, weight and aerodynamic properties change. This leads to significantly changed transport and settling behavior. The physico-chemical processes involved in aggregation are quantitatively poorly constrained. We have performed laboratory ash aggregation experiments using the ProCell Lab System® of Glatt Ingenieurtechnik GmbH. Solid particles are set into motion in a fluidized bed over a range of well-controlled boundary conditions (e.g., air flow rate, gas temperature, humidity, liquid composition). In this manner we simulate the variable gas-particle flow conditions expected in eruption plumes and pyroclastic density currents. We have used 1) soda-lime glass beads as an analogue material and 2) natural volcanic ash from Laacher See Volcano (Germany). In order to influence form, size, stability and the production rate of aggregates, a range of experimental conditions (e.g., particle concentration, degree of turbulence, temperature and moisture in the process chamber and the composition of the liquid phase) have been employed. We have successfully reproduced several features of natural ash aggregates, including round, internally structured ash pellets up to 3 mm in diameter. These experimental results help to constrain the boundary conditions required for the generation of spherical, internally-structured ash aggregates that survive deposition and are preserved in the volcanological record. These results should also serve as input parameters for models of ash transport and ash mass distribution.

  16. Acidic-store depletion is required for human platelet aggregation.

    PubMed

    Amor, Nidhal Ben; Zbidi, Hanene; Bouaziz, Aicha; Jardin, Isaac; Isaac, Jardin; Hernández-Cruz, Juan M; Salido, Ginés M; Rosado, Juan A; Bartegi, Aghleb

    2009-10-01

    Platelet stimulation with thrombin induces an elevation in cytoplasmic free Ca(2+) concentration ([Ca(2+)]c) due to Ca(2+) release from intracellular stores and entry from the extracellular medium. Two different intracellular Ca(2+) stores have been described in human platelets: the dense tubular system and the lysosomal-like acidic stores. In the present study, we investigated the contribution of the acidic stores in thrombin-induced platelet aggregation. We have found that platelet aggregation induced by thrombin is reduced in a Ca(2+)-free medium. Discharge of the acidic Ca(2+) stores by treatment with the sarcoendoplasmic Ca(2+)-ATPase (SERCA)3 selective inhibitor 2,5-di-(tert-butyl)-1,4-hydroquinone reduced thrombin-evoked platelet aggregation. In the presence of 2,5-di-(tert-butyl)-1,4-hydroquinone, platelet aggregation induced by the protease-activated receptor (PAR)-1 and PAR-4 agonist peptides, SFLLRN and AYPGKF, respectively, was significantly reduced. In cells with depleted acidic stores, activation of GPIb-IX-V by thrombin resulted in reduced or no platelet aggregation in a medium containing 1 mmol/l Caor in a Ca(2+)-free medium, respectively. This finding suggests that Ca(2+) accumulation in the acidic Ca(2+) compartments is required for platelet aggregation induced by activation of the G-coupled PAR-1 and PAR-4 thrombin receptors and, by the occupation of the leucine-rich glycoprotein GPIb-IX-V and provide evidence supporting a functional role of the lysosomal-like acidic Ca(2+) stores in human platelets. PMID:19587585

  17. [Reasons of drifting floating objects aggregating rainbow runner (Elagatis bipinnulata)].

    PubMed

    Wang, Xue-Fang; Zhou, Cheng; Zhu, Guo-Ping; Tang, Hao; Xu, Liu-Xiong

    2014-01-01

    Many pelagic species tend to aggregate under drifting floating objects. This has led to the development of drifting fish aggregation devices (FADs) to attract the tropical tunas for the tuna purse seine fishery. However, FADs can also attract other non-targeting small pelagic species such as rainbow runner Elagatis bipinnulata, although it is still unclear why those species can be attracted and aggregated under an FAD. Using the fishery biological data collected in the Western and Central Pacific Ocean by the scientific observers on board Chinese tuna purse seine fishing vessels, we evaluated the potential motivations for rainbow runner to aggregate under drifting objects. This study indicated 1) Fork length of rainbow runner ranged from 30.0 to 90.6 cm, with the dominant fork lengths of 60.0 to 80.0 cm, accounting for 76.3% of the total sampled fish, suggesting large rainbow runner dominating around the drifting objects; 2) Size (fork length) of E. bipinnulata at 50% maturity was 65.7 cm, and mature individuals were dominant under the FADs; and 3) Some commonly observed small fish species, such as Decapterus macarellus, Kyphosus cinerascens, Caranx sexfasciatus, Katsuwonus pelamis and the juveniles of Thunnus obesus and Thunnus albacares, were found in the stomach of rainbow runner, which suggested that rainbow runner under FAD preyed on other associated small pelagic species. As an oceanic predator associated with drifting objects, feeding is perhaps one of the most possible motivations for adult E. bipinnulata to aggregate under the FAD. Both the "concentration of food supply" hypothesis and the "comfortability stipulation" hypothesis can be used to explain why E. bipinnulata aggregate under drifting floating objects.

  18. Mechanism of cellular response to nanoscale aggregates of small molecules

    NASA Astrophysics Data System (ADS)

    Kuang, Yi

    This dissertation research focused on the illustration of the molecular mechanism of cellular response to nanoscale aggregates formed by small molecules. There are five chapters in this dissertation. Chapter 1 summarizes the current research on the evaluation of cell response (i.e., biocompatibility/cytotoxicity) to small molecular hydrogelators. Chapter 2 describes an interesting phenomenon that supramolecular hydrogelators consisting of N-terminated dipeptides, which exhibit selective inhibitory effects against cancer cells. This study calls for the development of a new approach for identification of protein targets of the hydrogelators. Chapter 3 describes the evaluation of interactions between cytosol proteins of a mammalian cell line and morphologically different nanoscale molecular aggregates formed by small peptidic molecules. Chapter 4 describes the research on the mechanism of a type of molecular aggregates, which cluster short microtubules to prevent the growth of microtubule. This unprecedented mechanism of "self-assembly to interfere with self-organization " contributes to inhibiting growth of cancer cells in several mammalian cell based assays and a xenograft tumor mice model. At the end, Chapter 5 reports a novel supramolecular hydrogelator, which consists of fluorene and the pentapeptide epitope (TIGYG) of potassium ion (K+) channels, to self-assemble in water to form the tunable, hierarchical nanostructures dictated by the concentration of K+. In conclusion, this dissertation research demonstrates a new approach for investigating cellular target and molecular mechanism of self-assembled aggregates formed by small peptide derivatives based hydrogelators, which will make contribution to the development of supramolecular hydrogelators as biomaterials. Moreover, the differential cytotoxicity of molecular aggregates illustrated in this research promises a new direction for developing anti-cancer drug based on interactions between molecular aggregates and

  19. Inhomogeneous diffusion-limited aggregation

    NASA Technical Reports Server (NTRS)

    Selinger, Robin Blumberg; Nittmann, Johann; Stanley, H. E.

    1989-01-01

    It is demonstrated here that inhomogeneous diffusion-limited aggregation (DLA) model can be used to simulate viscous fingering in a medium with inhomogeneous permeability and homogeneous porosity. The medium consists of a pipe-pore square-lattice network in which all pores have equal volume and the pipes have negligible volume. It is shown that fluctuations in a DLA-based growth process may be tuned by noise reduction, and that fluctuations in the velocity of the moving interface are multiplicative in form.

  20. Familial Aggregation of Absolute Pitch

    PubMed Central

    Baharloo, Siamak; Service, Susan K.; Risch, Neil; Gitschier, Jane; Freimer, Nelson B.

    2000-01-01

    Absolute pitch (AP) is a behavioral trait that is defined as the ability to identify the pitch of tones in the absence of a reference pitch. AP is an ideal phenotype for investigation of gene and environment interactions in the development of complex human behaviors. Individuals who score exceptionally well on formalized auditory tests of pitch perception are designated as “AP-1.” As described in this report, auditory testing of siblings of AP-1 probands and of a control sample indicates that AP-1 aggregates in families. The implications of this finding for the mapping of loci for AP-1 predisposition are discussed. PMID:10924408

  1. Antibiotics promote aggregation within aquatic bacterial communities

    PubMed Central

    Corno, Gianluca; Coci, Manuela; Giardina, Marco; Plechuk, Sonia; Campanile, Floriana; Stefani, Stefania

    2014-01-01

    The release of antibiotics (AB) into the environment poses several threats for human health due to potential development of AB-resistant natural bacteria. Even though the use of low-dose antibiotics has been promoted in health care and farming, significant amounts of AB are observed in aquatic environments. Knowledge on the impact of AB on natural bacterial communities is missing both in terms of spread and evolution of resistance mechanisms, and of modifications of community composition and productivity. New approaches are required to study the response of microbial communities rather than individual resistance genes. In this study a chemostat-based experiment with 4 coexisting bacterial strains has been performed to mimicking the response of a freshwater bacterial community to the presence of antibiotics in low and high doses. Bacterial abundance rapidly decreased by 75% in the presence of AB, independently of their concentration, and remained constant until the end of the experiment. The bacterial community was mainly dominated by Aeromonas hydrophila and Brevundimonas intermedia while the other two strains, Micrococcus luteus and Rhodococcus sp. never exceed 10%. Interestingly, the bacterial strains, which were isolated at the end of the experiment, were not AB-resistant, while reassembled communities composed of the 4 strains, isolated from treatments under AB stress, significantly raised their performance (growth rate, abundance) in the presence of AB compared to the communities reassembled with strains isolated from the treatment without AB. By investigating the phenotypic adaptations of the communities subjected to the different treatments, we found that the presence of AB significantly increased co-aggregation by 5–6 fold. These results represent the first observation of co-aggregation as a successful strategy of AB resistance based on phenotype in aquatic bacterial communities, and can represent a fundamental step in the understanding of the effects of

  2. Aggregation-based growth of silver nanowires at room temperature

    NASA Astrophysics Data System (ADS)

    Sun, Lanlan; Wang, Li; Song, Yonghai; Guo, Cunlan; Sun, Yujing; Peng, Chongyang; Liu, Zhelin; Li, Zhuang

    2008-02-01

    We describe an aggregation-based growth mechanism for formation of silver nanowires at room temperature. It is found that the pH of solution and the concentration of L-cysteine capping molecules have an important effect on the formation and growth of nanowires. Characterization by atomic force microscopy (AFM) and UV-vis spectroscopy recorded as time clearly shows that the silver nanowires are grown at the expense of nanoparticles.

  3. Attracted diffusion-limited aggregation.

    PubMed

    Rahbari, S H Ebrahimnazhad; Saberi, A A

    2012-07-01

    In this paper we present results of extensive Monte Carlo simulations of diffusion-limited aggregation (DLA) with a seed placed on an attractive plane as a simple model in connection with the electrical double layers. We compute the fractal dimension of the aggregated patterns as a function of the attraction strength α. For the patterns grown in both two and three dimensions, the fractal dimension shows a significant dependence on the attraction strength for small values of α and approaches that of the ordinary two-dimensional (2D) DLA in the limit of large α. For the nonattracting case with α = 1, our results in three dimensions reproduce the patterns of 3D ordinary DLA, while in two dimensions our model leads to the formation of a compact cluster with dimension 2. For intermediate α, the 3D clusters have a quasi-2D structure with a fractal dimension very close to that of the ordinary 2D DLA. This allows one to control the morphology of a growing cluster by tuning a single external parameter α. PMID:23005417

  4. Attracted diffusion-limited aggregation

    NASA Astrophysics Data System (ADS)

    Rahbari, S. H. Ebrahimnazhad; Saberi, A. A.

    2012-07-01

    In this paper we present results of extensive Monte Carlo simulations of diffusion-limited aggregation (DLA) with a seed placed on an attractive plane as a simple model in connection with the electrical double layers. We compute the fractal dimension of the aggregated patterns as a function of the attraction strength α. For the patterns grown in both two and three dimensions, the fractal dimension shows a significant dependence on the attraction strength for small values of α and approaches that of the ordinary two-dimensional (2D) DLA in the limit of large α. For the nonattracting case with α=1, our results in three dimensions reproduce the patterns of 3D ordinary DLA, while in two dimensions our model leads to the formation of a compact cluster with dimension 2. For intermediate α, the 3D clusters have a quasi-2D structure with a fractal dimension very close to that of the ordinary 2D DLA. This allows one to control the morphology of a growing cluster by tuning a single external parameter α.

  5. Sectoral shifts and aggregate unemployment

    SciTech Connect

    Loungani, P.

    1986-01-01

    Some recent research has taken the view that sectoral or industry-specific shocks significantly affect aggregate unemployment by increasing the amount of inter-industry labor reallocation required. The empirical evidence for this view rests on the finding that during the 1950s - and again during the 1970s - there was a positive correlation between aggregate unemployment and the dispersion of employment growth rates. This thesis demonstrates that this correlation arises largely because oil price shocks affect both unemployment and the dispersion of employment growth. Once the dispersion due to oil shocks is accounted for, the residual dispersion in employment has very low explanatory power for unemployment. Since the dispersion index does not measure pure sectoral shifts, an alternate measure of dispersion is developed that serves as a better proxy for the amount of inter-industry labor reallocation required each period. Estimates using this measure suggest that, during the 1950s, temporary increases in the relative price of oil were responsible for generating the observed correlation. On the other hand, sectoral shifts were important during the 1970s; in particular, the 1973 oil price increase has had significant reallocative effects on the economy. This contention is subjected to further tests by looking at the time-series behavior of employment in durable-goods industries and also by following the inter-industry movements of workers over time through the use of panel data.

  6. Applications of aggregation theory to sustainability assessment

    SciTech Connect

    Pollesch, N.; Dale, V. H.

    2015-04-01

    In order to aid in transition towards operations that promote sustainability goals, researchers and stakeholders use sustainability assessments. Although assessments take various forms, many utilize diverse sets of indicators that can number anywhere from two to over 2000. Indices, composite indicators, or aggregate values are used to simplify high dimensional and complex data sets and to clarify assessment results. Although the choice of aggregation function is a key component in the development of the assessment, there are few examples to be found in literature to guide appropriate aggregation function selection. This paper develops a connection between the mathematical study of aggregation functions and sustainability assessment in order to aid in providing criteria for aggregation function selection. Relevant mathematical properties of aggregation functions are presented and interpreted. Lastly, we provide cases of these properties and their relation to previous sustainability assessment research. Examples show that mathematical aggregation properties can be used to address the topics of compensatory behavior and weak versus strong sustainability, aggregation of data under varying units of measurements, multiple site multiple indicator aggregation, and the determination of error bounds in aggregate output for normalized and non-normalized indicator measures.

  7. Applications of aggregation theory to sustainability assessment

    DOE PAGES

    Pollesch, N.; Dale, V. H.

    2015-04-01

    In order to aid in transition towards operations that promote sustainability goals, researchers and stakeholders use sustainability assessments. Although assessments take various forms, many utilize diverse sets of indicators that can number anywhere from two to over 2000. Indices, composite indicators, or aggregate values are used to simplify high dimensional and complex data sets and to clarify assessment results. Although the choice of aggregation function is a key component in the development of the assessment, there are few examples to be found in literature to guide appropriate aggregation function selection. This paper develops a connection between the mathematical study ofmore » aggregation functions and sustainability assessment in order to aid in providing criteria for aggregation function selection. Relevant mathematical properties of aggregation functions are presented and interpreted. Lastly, we provide cases of these properties and their relation to previous sustainability assessment research. Examples show that mathematical aggregation properties can be used to address the topics of compensatory behavior and weak versus strong sustainability, aggregation of data under varying units of measurements, multiple site multiple indicator aggregation, and the determination of error bounds in aggregate output for normalized and non-normalized indicator measures.« less

  8. Effect of alginate on the aggregation kinetics of copper oxide nanoparticles (CuO NPs): bridging interaction and hetero-aggregation induced by Ca(2.).

    PubMed

    Miao, Lingzhan; Wang, Chao; Hou, Jun; Wang, Peifang; Ao, Yanhui; Li, Yi; Lv, Bowen; Yang, Yangyang; You, Guoxiang; Xu, Yi

    2016-06-01

    The stability of CuO nanoparticles (NPs) is expected to play a key role in the environmental risk assessment of nanotoxicity in aquatic systems. In this study, the effect of alginate (model polysaccharides) on the stability of CuO NPs in various environmentally relevant ionic strength conditions was investigated by using time-resolved dynamic light scattering. Significant aggregation of CuO NPs was observed in the presence of both monovalent and divalent cations. The critical coagulation concentrations (CCC) were 54.5 and 2.9 mM for NaNO3 and Ca(NO3)2, respectively. The presence of alginate slowed nano-CuO aggregation rates over the entire NaNO3 concentration range due to the combined electrostatic and steric effect. High concentrations of Ca(2+) (>6 mM) resulted in stronger adsorption of alginate onto CuO NPs; however, enhanced aggregation of CuO NPs occurred simultaneously under the same conditions. Spectroscopic analysis revealed that the bridging interaction of alginate with Ca(2+) might be an important mechanism for the enhanced aggregation. Furthermore, significant coagulation of the alginate molecules was observed in solutions of high Ca(2+) concentrations, indicating a hetero-aggregation mechanism between the alginate-covered CuO NPs and the unabsorbed alginate. These results suggested a different aggregation mechanism of NPs might co-exist in aqueous systems enriched with natural organic matter, which should be taken into consideration in future studies. Graphical abstract Hetero-aggregation mechanism of CuO nanoparticles and alginate under high concentration of Ca(2.) PMID:26931664

  9. Aggregation of Silver Hydrosols Prepared in Air.

    PubMed

    Teiten; Burneau

    1998-10-01

    The chemistry involved in the preparation and activation of silver hydrosols was monitored by pH, potential, and surface charge measurements, by absorption spectra in the visible region, and by surface-enhanced Raman spectroscopy (SERS). The activation, displayed by a red-shift of the colloid absorption at 392 nm, corresponds to a partial aggregation of elementary silver particles as displayed by transmission electron micrographs. The participation of carbonate species in the chemistry of hydrosols handled in air was made obvious by titration with strong acids. The colloid destabilization was performed either with protons, by adding strong non-complexing acids (HNO3, HClO4), or with low concentrations of Cu2+. In contrast, HCl determined a stabilization of hydrosols related to the complexing affinity of Cl- toward silver. The successive addition of Cu(NO3)2 and HCl allowed a balance between all the chemical reactions and a very efficient activation process. Whereas the chemical reactants used are nominally inorganic, at total concentrations lower than 10(-3) M, the activated hydrosols display anomalous SER spectra which were previously assigned to organic molecules. Copyright 1998 Academic Press.

  10. Role of Multicellular Aggregates in Biofilm Formation

    PubMed Central

    Kragh, Kasper N.; Hutchison, Jaime B.; Melaugh, Gavin; Rodesney, Chris; Roberts, Aled E. L.; Irie, Yasuhiko; Jensen, Peter Ø.; Diggle, Stephen P.; Allen, Rosalind J.

    2016-01-01

    ABSTRACT In traditional models of in vitro biofilm development, individual bacterial cells seed a surface, multiply, and mature into multicellular, three-dimensional structures. Much research has been devoted to elucidating the mechanisms governing the initial attachment of single cells to surfaces. However, in natural environments and during infection, bacterial cells tend to clump as multicellular aggregates, and biofilms can also slough off aggregates as a part of the dispersal process. This makes it likely that biofilms are often seeded by aggregates and single cells, yet how these aggregates impact biofilm initiation and development is not known. Here we use a combination of experimental and computational approaches to determine the relative fitness of single cells and preformed aggregates during early development of Pseudomonas aeruginosa biofilms. We find that the relative fitness of aggregates depends markedly on the density of surrounding single cells, i.e., the level of competition for growth resources. When competition between aggregates and single cells is low, an aggregate has a growth disadvantage because the aggregate interior has poor access to growth resources. However, if competition is high, aggregates exhibit higher fitness, because extending vertically above the surface gives cells at the top of aggregates better access to growth resources. Other advantages of seeding by aggregates, such as earlier switching to a biofilm-like phenotype and enhanced resilience toward antibiotics and immune response, may add to this ecological benefit. Our findings suggest that current models of biofilm formation should be reconsidered to incorporate the role of aggregates in biofilm initiation. PMID:27006463

  11. Non-aggregated axially disubstituted silicon phthalocyanines bearing electropolymerizable ligands and their aggregation, electropolymerizaton and thermal properties.

    PubMed

    Biyiklioglu, Zekeriya; Bas, Huseyin; Alp, Hakan

    2015-08-21

    A novel series of axially disubstituted silicon(iv) phthalocyanines bearing electropolymerizable ligands were designed and synthesized for the first time. The silicon(iv) phthalocyanines were characterized by various spectroscopic techniques as well as elemental analysis. The aggregation behavior of the SiPcs were examined in different solvents and at different concentrations in chloroform. In all the studied solvents and concentrations, the SiPcs were non-aggregated. The thermal behavior of the silicon(iv) phthalocyanines was also studied. The electropolymerization properties of the silicon(iv) phthalocyanines were investigated by cyclic and square wave voltammetry. This study is the first example of the electropolymerization of axially disubstituted silicon phthalocyanines. The type of axial ligand on the phthalocyanine ring did not show any effect on the absorption and thermal properties but influenced the electropolymerization of the phthalocyanines.

  12. Sorbitol crystallization-induced aggregation in frozen mAb formulations.

    PubMed

    Piedmonte, Deirdre Murphy; Hair, Alison; Baker, Priti; Brych, Lejla; Nagapudi, Karthik; Lin, Hong; Cao, Wenjin; Hershenson, Susan; Ratnaswamy, Gayathri

    2015-02-01

    Sorbitol crystallization-induced aggregation of mAbs in the frozen state was evaluated. The effect of protein aggregation resulting from sorbitol crystallization was measured as a function of formulation variables such as protein concentration and pH. Long-term studies were performed on both IgG1 and IgG2 mAbs over the protein concentration range of 0.1-120 mg/mL. Protein aggregation was measured by size-exclusion HPLC (SE-HPLC) and further characterized by capillary-electrophoresis SDS. Sorbitol crystallization was monitored and characterized by subambient differential scanning calorimetry and X-ray diffraction. Aggregation due to sorbitol crystallization is inversely proportional to both protein concentration and formulation pH. At high protein concentrations, sorbitol crystallization was suppressed, and minimal aggregation by SE-HPLC resulted, presumably because of self-stabilization of the mAbs. The glass transition temperature (Tg ') and fragility index measurements were made to assess the influence of molecular mobility on the crystallization of sorbitol. Tg ' increased with increasing protein concentration for both mAbs. The fragility index decreased with increasing protein concentration, suggesting that it is increasingly difficult for sorbitol to crystallize at high protein concentrations.

  13. On cellulose dissolution and aggregation in aqueous tetrabutylammonium hydroxide.

    PubMed

    Gubitosi, Marta; Duarte, Hugo; Gentile, Luigi; Olsson, Ulf; Medronho, Bruno

    2016-09-12

    Aqueous tetrabutylammonium hydroxide, TBAH(aq), has been found to dissolve cellulose and to be a potential solvent for chemical processing or fiber spinning. In this paper, we have investigated the dissolution state of cellulose in 40 wt % TBAH(aq) solvent, and present an extensive study of rheology, combined with static light and small-angle X-ray scattering, to correlate cellulose aggregation with changes in the rheological parameters. Two cellulose molecular weights are compared. Microcrystalline cellulose (MCC), with a degree of polymerization of ca. 260, and a dissolving pulp with an approximately ten times higher molecular weight. Scattering data demonstrate that cellulose is molecularly dissolved at lower cellulose concentrations, while aggregates are present when the concentration exceeds a certain value. The onset of the aggregate formation is marked by a pronounced increase in the scattering intensity at low q, shear thinning behavior and violation of the empirical Cox-Merz rule. Additionally, the SAXS data suggest the presence of a solvation shell enriched in TBA(+) ions, compared to the bulk solvent. The results are consistent with the recent suggestion that while native cellulose I may still dissolve, solutions are, above a particular concentration, becoming supersaturated with respect to the more stable crystal form cellulose II. PMID:27476327

  14. Effect of sodium chloride on the binding of polyaromatic hydrocarbon guests with sodium cholate aggregates.

    PubMed

    Fuentealba, Denis; Thurber, Katie; Bovero, Enrico; Pace, Tamara C S; Bohne, Cornelia

    2011-09-01

    Sodium cholate aggregates are adaptable host systems. The effect of changing the ionic strength with the addition of NaCl on the properties for guest binding to sodium cholate aggregates was investigated by using pyrene, perylene and 1-ethylnaphthalene as guests. Fluorescence, anisotropy and laser flash photolysis studies provided information on the protection efficiency of the aggregate bound guest, and provided information on the dynamics and correlation times for the host-guest system. Different trends for the protection efficiency of the bound guests were observed when the NaCl concentration was raised depending on the charge of the aqueous solubilized quencher. The increase in ionic strength was also shown to lengthen the correlation time of the aggregate bound guest and led to faster dynamics for the host-guest complex. These results show that the properties of sodium cholate aggregates as a supramolecular host system are significantly altered with changes in the ionic strength of the medium. PMID:21472184

  15. Computational fluid dynamics of aggregating red blood cells in postcapillary venules

    PubMed Central

    Chung, Bong; Kim, Sangho; Johnson, Paul C.; Popel, Aleksander S.

    2011-01-01

    Aggregate formation of red blood cells (RBCs) in a postcapillary venular bifurcation is investigated with three-dimensional computer simulations using the Chimera grid method. Interaction energy between the RBCs is modelled by a depletion interaction theory; RBCs are modelled as rigid oblate ellipsoids. The cell–cell interactions of RBCs are strongly dependent on vessel geometry and shear rates. The experimental data on vessel geometry, pseudoshear rates, and Dextran concentration obtained in our previous in vivo RBC aggregation study in postcapillary venules of the rat spinotrapezius muscle were used to simulate RBC aggregation. The computational results were compared to the experimental results from the in vivo study. The results show that cells have a larger tendency to form an aggregate under reduced flows. Aggregate formation also depends on the angle and location of the cells before they enter the bifurcation region. Comparisons with experimental data are discussed. PMID:19675976

  16. A mechanistic model of tau amyloid aggregation based on direct observation of oligomers

    NASA Astrophysics Data System (ADS)

    Shammas, Sarah L.; Garcia, Gonzalo A.; Kumar, Satish; Kjaergaard, Magnus; Horrocks, Mathew H.; Shivji, Nadia; Mandelkow, Eva; Knowles, Tuomas P. J.; Mandelkow, Eckhard; Klenerman, David

    2015-04-01

    Protein aggregation plays a key role in neurodegenerative disease, giving rise to small oligomers that may become cytotoxic to cells. The fundamental microscopic reactions taking place during aggregation, and their rate constants, have been difficult to determine due to lack of suitable methods to identify and follow the low concentration of oligomers over time. Here we use single-molecule fluorescence to study the aggregation of the repeat domain of tau (K18), and two mutant forms linked with familial frontotemporal dementia, the deletion mutant ΔK280 and the point mutant P301L. Our kinetic analysis reveals that aggregation proceeds via monomeric assembly into small oligomers, and a subsequent slow structural conversion step before fibril formation. Using this approach, we have been able to quantitatively determine how these mutations alter the aggregation energy landscape.

  17. Low-Velocity Aggregate Collisions Simulating Planetary Ring Dynamics

    NASA Astrophysics Data System (ADS)

    Dove, A.; Colwell, J. E.; Bradley, E. T.; Vamos, C.

    2012-12-01

    Proto-planetary and planetary ring system evolution is driven by collisions between small particles and aggregates that may be composed of dust, water ice, or a combination of materials. In these collisional systems, impacts between objects can occur at very low velocities, much less than 1 m/s. Low-velocity impacts can have competing effects: at the lowest velocities, collisions may play a critical role in growth into larger aggregates; at slightly higher velocities, collisions can cause break-up and release of material. In the Saturnian ring system, for instance, particles are excited to such "higher" velocities (10's of cm/s) in regions where density waves enhance particle concentrations. These conditions are present in the A ring, and it has been hypothesized that collisions have an additional effect of modifying the spectral properties of the ring particles, which are composed of a mix of ice and dust (Nicholson et al., 2008). This modification may occur when collisions cause ejection of material with different spectral characteristics, or by breaking particles apart to reveal more pristine interiors. We have designed and built an apparatus to simulate low-velocity collisions between aggregates in a laboratory vacuum environment. In our experiment, two aggregates are launched towards each other; the resulting impact velocities are controlled by the initial spring launch velocity, the masses of the aggregates, and timing of the collisions. Initially, we use lunar regolith simulant to create the aggregates; the simulant can be packed to different densities to control the mass and porosity of the impactors. We also create aggregates that are mixtures of materials, including icy components. A high-speed digital video camera is used to record the impacts to observe the behavior of both impactors and the resulting ejecta material. We observe over a range of velocities to identify the conditions under which aggregates shed only some material from the surface, or

  18. To what extent clay mineralogy affects soil aggregation? Consequences for soil organic matter stabilization

    NASA Astrophysics Data System (ADS)

    Fernandez-Ugalde, O.; Barré, P.; Hubert, F.; Virto, I.; Chenu, C.; Ferrage, E.; Caner, L.

    2012-12-01

    Aggregation is a key process for soil functioning as it influences C storage, vulnerability to erosion and water holding capacity. While the influence of soil organic C on aggregation has been documented, much less is known about the role of soil mineralogy. Soils usually contain a mixture of clay minerals with contrasted surface properties, which should result on different abilities of clay minerals to aggregation. We took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals (illite, smectite, kaolinite, and mixed-layer illite-smectite) in aggregation. In a first step, grassland and tilled soil samples were fractionated in water in aggregate-size classes according to the hierarchical model of aggregation (Tisdall and Oades, 1982). Clay mineralogy and organic C in the aggregate-size classes were analyzed. The results showed that interstratified minerals containing swelling phases accumulated in aggregated fractions (>2 μm) compared to free clay fractions (<2 μm) in the two land-uses. The accumulation increased from large macro-aggregates (>500 μm) to micro-aggregates (50-250 μm). C concentration and C/N ratio followed the opposite trend. These results constitute a clay mineral-based evidence for the hierarchical model of aggregation, which postulates an increasing importance of the reactivity of clay minerals in the formation of micro-aggregates compared to larger aggregates. In the latter aggregates, formation relies on the physical enmeshment of particles by fungal hyphae, and root and microbial exudates. In a second step, micro-aggregates from the tilled soil samples were submitted to increasingly disaggregating treatments by sonication to evaluate the link between their water stability and clay mineralogy. Micro-aggregates with increasing stability showed an increase of interstratified minerals containing swelling phases and C concentration for low intensities of disaggregation (from 0 to 5 J mL-1

  19. Spectroscopic and microscopic investigations of phthalocyanine aggregates on Gold(111)

    NASA Astrophysics Data System (ADS)

    Nishida, Krista Rachel Akiko

    Self-assembled organic pi systems are of interest because of their potential applications in light harvesting and electron transfer. Phthalocyanines (Pc) demonstrate desirable photonic and electronic properties, thus making them excellent candidates for functional nanostructures. The specific focus of this research has been the nanoscale aggregation of a metal-free organic dye, tetrasulfonic acid phthalocyanine (TSPc) and includes the use of UV-visible Spectroscopy, Resonance Light Scattering Spectroscopy (RLS), X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and ambient and ultra-high-vacuum Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS). The UV-visible absorption studies show that TSPc aggregates upon dissolution in water and obeys Beer's Law within the concentration range of 10 -7M to 10-4M, indicating that TSPc concentration has no further effect on aggregation in aqueous solution. In addition, both ionic strength in NaCl and pH changes in the presence of NaOH, HCl or acetic acid (HAc) do affect aggregation. The RSL studies confirm these effects of pH only in the presence of HAc. The XPS studies show that the ratio of non-protonated to protonated nitrogens does not change with decreasing solution pH. STM images of TSPc deposited from pH<1 solutions reveal ordered branched web-like assemblies hundreds of nanometers in length, generally 2 nm tall and having variable widths. STM imaging shows TSPc aggregates decrease in order as pH increases. STM images of TSPc deposited from solutions with pH>10 show monolayer coverage of TSPc in salt form. High-resolution UHV-STM images of TSPc aggregates deposited from pH 0 solution on Au(111) reveal detailed coherent columnar architecture with the phthalocyanine macrocycles orientated parallel to the substrate surface. OMTS was used to identify the HOMO and LUMO of the TSPc aggregates and the results are contrasted with the same molecular states in unsubstituted metallated

  20. Acceleration of α-Synuclein Aggregation by Exosomes*

    PubMed Central

    Grey, Marie; Dunning, Christopher J.; Gaspar, Ricardo; Grey, Carl; Brundin, Patrik; Sparr, Emma; Linse, Sara

    2015-01-01

    Exosomes are small vesicles released from cells into extracellular space. We have isolated exosomes from neuroblastoma cells and investigated their influence on the aggregation of α-synuclein, a protein associated with Parkinson disease pathology. Using cryo-transmission electron microscopy of exosomes, we found spherical unilamellar vesicles with a significant protein content, and Western blot analysis revealed that they contain, as expected, the proteins Flotillin-1 and Alix. Using thioflavin T fluorescence to monitor aggregation kinetics, we found that exosomes catalyze the process in a similar manner as a low concentration of preformed α-synuclein fibrils. The exosomes reduce the lag time indicating that they provide catalytic environments for nucleation. The catalytic effects of exosomes derived from naive cells and cells that overexpress α-synuclein do not differ. Vesicles prepared from extracted exosome lipids accelerate aggregation, suggesting that the lipids in exosomes are sufficient for the catalytic effect to arise. Using mass spectrometry, we found several phospholipid classes in the exosomes, including phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, and the gangliosides GM2 and GM3. Within each class, several species with different acyl chains were identified. We then prepared vesicles from corresponding pure lipids or defined mixtures, most of which were found to retard α-synuclein aggregation. As a striking exception, vesicles containing ganglioside lipids GM1 or GM3 accelerate the process. Understanding how α-synuclein interacts with biological membranes to promote neurological disease might lead to the identification of novel therapeutic targets. PMID:25425650

  1. Disulfide cross-linked Fab-aggregates: preparation and biodistribution.

    PubMed

    Dalkara, S; Petrov, A; Trubetskoy, V S; Khaw, B A; Torchilin, V P

    1998-01-01

    The high-molecular-weight soluble aggregates of Fab fragments of murine antibodies against cardiac myosin were prepared as a potential long-circulating and low immunogenic pharmaceutical carriers by conjugation of thiolated Fab and Fab modified with succinimidyl 3-(2-pyridyldithio)propionate. The clearance time and biodistribution of 111In-radiolabeled aggregates were studied in normal and nude-mice bearing human breast tumor implant and in rabbits with experimental myocardial infarction. The aggregates had a prolonged circulation time (half clearance time ca. 3-5 h) and ability to concentrate in the tumor and in the necrotic area of infarcted myocardium. Similar tumor-to-normal and infarct-to-normal accumulation ratios (ca. 3 h in both cases) suggest that combination of long circulation with impaired filtration in necrotic tissues is responsible for this accumulation rather than a specific interaction. The aggregates prepared may serve as long-circulating drug carriers able to deliver pharmaceuticals into areas with affected and leaky vasculature.

  2. Enhancement of Platelet Aggregation by Ursolic Acid and Oleanolic Acid

    PubMed Central

    Kim, Mikyung; Han, Chang-ho; Lee, Moo-Yeol

    2014-01-01

    The pentacyclic triterpenoid ursolic acid (UA) and its isomer oleanolic acid (OA) are ubiquitous in food and plant medicine, and thus are easily exposed to the population through natural contact or intentional use. Although they have diverse health benefits, reported cardiovascular protective activity is contentious. In this study, the effect of UA and OA on platelet aggregation was examined on the basis that alteration of platelet activity is a potential process contributing to cardiovascular events. Treatment of UA enhanced platelet aggregation induced by thrombin or ADP, which was concentration-dependent in a range of 5–50 μM. Quite comparable results were obtained with OA, in which OA-treated platelets also exhibited an exaggerated response to either thrombin or ADP. UA treatment potentiated aggregation of whole blood, while OA failed to increase aggregation by thrombin. UA and OA did not affect plasma coagulation assessed by measuring prothrombin time and activated partial thromboplastin time. These results indicate that both UA and OA are capable of making platelets susceptible to aggregatory stimuli, and platelets rather than clotting factors are the primary target of them in proaggregatory activity. These compounds need to be used with caution, especially in the population with a predisposition to cardiovascular events. PMID:25009707

  3. Hawaiian spinner dolphins aggregate midwater food resources through cooperative foraging

    NASA Astrophysics Data System (ADS)

    Benoit-Bird, Kelly; Au, Whitlow

    2003-10-01

    To test the hypothesis that spinner dolphins in Hawaii may actively aggregate their prey through cooperative foraging, a 200-kHz multi-beam sonar (Simrad MS2000) was used to observe 323 groups of spinner dolphins foraging within a midwater, micronekton sound-scattering layer off Oahu. Strong cooperation was observed in groups of 8-14 pairs of spinner dolphins. The dolphin group size was highest at midnight when the density of prey was highest and was significantly higher in Makua Beach, where the prey density was higher, than Electric Beach, where the prey density was lower. Cooperative groups of dolphins aggregated their food resources, apparently using their preys' avoidance behavior to create distinct, high-density patches in the prey. Prey aggregation was strongly stereo-typed, regardless of the distribution of the scattering layer. Dolphins swam around the edge of a 28-40 m diameter circle at least 5 times, concentrating prey within this area before pairs of dolphins on opposite sides of the circle swapped positions in the circle, swimming through the high density prey 'donut' they had formed. The hypothesis that nocturnal animals aggregate prey in midwater could not have been tested without the three-dimensional information on prey distribution and dolphin geometry provided by the multi-beam.

  4. Enrichment Ratio and Aggregate Stability Dynamics in Intensely Managed Landscapes

    NASA Astrophysics Data System (ADS)

    Wacha, K.; Papanicolaou, T.; Filley, T. R.; Hou, T.; Abban, B. K.; Wilson, C. G.; Boys, J.

    2015-12-01

    Challenges in understanding the soil carbon dynamics within intensely managed landscapes (IMLs), found throughout much the US Midwest, is highly complex due to the presence of heterogeneous landscape features and properties, as well as a mosaic of physical and biogeochemical processes occurring at different time scales. In addition, rainfall events exacerbate the effects of tillage by the impact of raindrops, which break down aggregates that encase carbon and dislodge and entrain soil particles and aggregates along the downslope. The redistribution of soil and carbon can have huge implications on biogeochemical cycling and overall carbon budgeting. In this study, we provide some rare field data on the mechanisms impacting aggregate stability, enrichment ratio values to estimate fluxes of carbon, as well as lignin chemistry to see influences on oxidation/mineralization rates. Rainfall simulation experiments were conducted within agricultural fields. Experiments were performed on the midslope (eroding) and toeslope (depositional) sections of representative hillslopes, under a variety of land managements, including row crop (conventional and conservation) and restored grasslands. Sensors were utilized to capture the evolution of soil moisture, temperature, microbial respiration pulses, and discharge rates to identify pseudo-steady state conditions. Samples collected at the weir outlet were tested for sediment concentrations and size fractions, as well as carbon and lignin fluxes. Preliminary findings show that conservation management practices have higher aggregate stability and decreased mass fluxes of carbon in the downslope than conventional tillage techniques.

  5. Increasing platelet aggregability after venepuncture is platelet, not plasma derived.

    PubMed

    Terres, W; Becker, B F; Kratzer, M A; Gerlach, E

    1986-05-15

    The time course of ADP induced aggregation of human platelets was determined in aliquots of stored platelet rich plasma 3.5, 10, 30 and 100 minutes after venepuncture. The maximal rate of aggregation was found to increase throughout this entire period, even though pH (7.4), CO2 (7 volume per cent) and temperature (35 degrees C) of the samples were kept constant. The mean acceleration (+/- SEM) between 3.5 and 100 minutes was 41.7 +/- 6.9 per cent (n = 67) at an ADP-concentration of 1 mumol/l and 18.3 +/- 6.2 per cent (n = 23) at 2 mumol/l ADP. The effect did not result from changes of any platelet regulatory factors putatively present alone in the plasma. Acceleration of aggregability was only found when the platelets themselves underwent storage, but not when freshly prepared plasma was given to prestored platelets. The change in aggregability was not diminished after inhibition of platelet cyclooxygenase by oral administration of acetylsalicylic acid. PMID:3715816

  6. Aggregation server for grid-integrated vehicles

    DOEpatents

    Kempton, Willett

    2015-05-26

    Methods, systems, and apparatus for aggregating electric power flow between an electric grid and electric vehicles are disclosed. An apparatus for aggregating power flow may include a memory and a processor coupled to the memory to receive electric vehicle equipment (EVE) attributes from a plurality of EVEs, aggregate EVE attributes, predict total available capacity based on the EVE attributes, and dispatch at least a portion of the total available capacity to the grid. Power flow may be aggregated by receiving EVE operational parameters from each EVE, aggregating the received EVE operational parameters, predicting total available capacity based on the aggregated EVE operational parameters, and dispatching at least a portion of the total available capacity to the grid.

  7. Tubular aggregates: their association with myalgia.

    PubMed Central

    Niakan, E; Harati, Y; Danon, M J

    1985-01-01

    Three thousand consecutive muscle biopsies were reviewed for the presence of tubular aggregates and their association with clinical symptomatology. Tubular aggregates were detected in 19 patients (0.6%). Twelve of these nineteen patients had severe myalgia, and the most abundant tubular aggregates were found in biopsies of patients with myalgia. Seven patients had only myalgia as their clinical symptomatology with normal physical examination. An additional five patients with tubular aggregates and myalgia had concomitant amyotrophic lateral sclerosis (2) or neuropathy (3). The high incidence of myalgia associated with tubular aggregates in our patients and the fact that tubular aggregates originate from sarcoplasmic reticulum suggest a role played by this structure in the pathogenesis of myalgia. Images PMID:2995591

  8. Multiscale simulation of red blood cell aggregation

    NASA Astrophysics Data System (ADS)

    Bagchi, P.; Popel, A. S.

    2004-11-01

    In humans and other mammals, aggregation of red blood cells (RBC) is a major determinant to blood viscosity in microcirculation under physiological and pathological conditions. Elevated levels of aggregation are often related to cardiovascular diseases, bacterial infection, diabetes, and obesity. Aggregation is a multiscale phenomenon that is governed by the molecular bond formation between adjacent cells, morphological and rheological properties of the cells, and the motion of the extra-cellular fluid in which the cells circulate. We have developed a simulation technique using front tracking methods for multiple fluids that includes the multiscale characteristics of aggregation. We will report the first-ever direct computer simulation of aggregation of deformable cells in shear flows. We will present results on the effect of shear rate, strength of the cross-bridging bonds, and the cell rheological properties on the rolling motion, deformation and subsequent breakage of an aggregate.

  9. Aggregation rate and fractal dimension of fullerene nanoparticles via simultaneous multiangle static and dynamic light scattering measurement.

    PubMed

    Meng, Zhiyong; Hashmi, Sara M; Elimelech, Menachem

    2013-02-15

    The time-evolutions of nanoparticle hydrodynamic radius and aggregate fractal dimension during the aggregation of fullerene (C(60)) nanoparticles (FNPs) were measured via simultaneous multiangle static and dynamic light scattering. The FNP aggregation behavior was determined as a function of monovalent (NaCl) and divalent (CaCl(2)) electrolyte concentration, and the impact of addition of dissolved natural organic matter (humic acid) to the solution was also investigated. In the absence of humic acid, the fractal dimension decreased over time with monovalent and divalent salts, suggesting that aggregates become slightly more open and less compact as they grow. Although the aggregates become slightly more open, the magnitude of the fractal dimension suggests intermediate aggregation between the diffusion- and reaction-limited regimes. We observed different aggregation behavior with monovalent and divalent salts upon the addition of humic acid to the solution. For NaCl-induced aggregation, the introduction of humic acid significantly suppressed the aggregation rate of FNPs at NaCl concentrations lower than 150mM. In this case, the aggregation was intermediate or reaction-limited even at NaCl concentrations as high as 500mM, giving rise to aggregates with a fractal dimension of 2.0. For CaCl(2)-induced aggregation, the introduction of humic acid enhanced the aggregation of FNPs at CaCl(2) concentrations greater than about 5mM due to calcium complexation and bridging effects. Humic acid also had an impact on the FNP aggregate structure in the presence of CaCl(2), resulting in a fractal dimension of 1.6 for the diffusion-limited aggregation regime. Our results with CaCl(2) indicate that in the presence of humic acid, FNP aggregates have a more open and loose structure than in the absence of humic acid. The aggregation results presented in this paper have important implications for the transport, chemical reactivity, and toxicity of engineered nanoparticles in aquatic

  10. Fractal aggregation of ZnO nanoparticles under different aqueous solution chemistries

    NASA Astrophysics Data System (ADS)

    Zhou, D.; Keller, A. A.

    2009-12-01

    The aggregation of ZnO nanoparticles influences not only their environmental transport but also their toxicity. In natural aquatic systems, the ubiquitous presence of natural organic matter (NOM) can lead to interactions with released ZnO nanoparticles (NPs) and influence their transport. In this study, the aggregation kinetics of ZnO with and without NOM under different ionic strength and pH were examined by both time-resolved dynamic light scattering and sedimentation experiments. ZnO aggregates faster as the pH approaches its point of zero charge. The role of ionic strength role was examined by determining the reaction-limited cluster regime (RLCR) and diffusion-limited cluster regime (DLCR). The critical coagulation concentration (CCC) was determined as 25mM using NaCl as the electrolyte at pH 8. A higher initial ZnO concentration leads to faster aggregation. DLVO calculations agreed well with the experimental data. At high NOM concentration, ZnO aggregation was significantly slowed. However, at low NOM concentration, bridging effect was observed. Finally, the fractal dimensions of ZnO aggregates under different conditions were determined by static light scattering (SLS).

  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. Platelet adhesiveness and aggregation in congenital afibrinogenemia. An investigation of three patients with post-transfusion, cross-correction studies between two of them.

    PubMed

    Girolami, A; De Marco, L; Virgolini, L; Peruffo, R; Fabris, F

    1975-02-01

    Platelet adhesiveness and aggregation were studied in three patients with congenital afibrinogenemia. The results obtained may be summarized as follows: The retention of platelets to a glass-bead filter determined with the Salzman method was significantly decreased; it was normal after fibrinogen infusion. With a modification of the Hellem test the values obtained were slightly decreased. Adrenalin-induced aggregation was absent whereas ADP-and collagen-induced aggregation was near normal or slightly decreased. Thrombofax aggregation was absent in citrated plasma. The abnormalities of platelet aggregation were corrected after fibrinogen infusion or after addition in vitro of fibrinogen, hemofilia A plasma and PPP obtained from an afibrinogenemic patient after fibrinogen infusion. The abnormalities of platelet aggregation were corrected well by ADP, collagen and Thrombofax in heparinized blood, but only a slight correction of adrenalin-induced aggregation was noted. Thrombin aggregation proved to be normal with the higher concentrations, whereas it was defective with the lower ones. Ristocetin aggregation was normal in citrated plasma at the concentration of 1.5 mg per ml but it was absent at the lower concentration (1.0 mg per ml). Ristocetin aggregation was, on the other hand absent in heparinized blood regardless of the concentration. These findings are in agreement with the presence of a prolonged bleeding time in congenital afibrinogenemia and suggest that fibrinogen plays an important role in platelet aggregation and adhesiveness.

  13. Potential for Direct Interspecies Electron Transfer in Methanogenic Wastewater Digester Aggregates

    PubMed Central

    Morita, Masahiko; Malvankar, Nikhil S.; Franks, Ashley E.; Summers, Zarath M.; Giloteaux, Ludovic; Rotaru, Amelia E.; Rotaru, Camelia; Lovley, Derek R.

    2011-01-01

    ABSTRACT Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reactor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consortia. The aggregates were electrically conductive, with conductivities 3-fold higher than the conductivities previously reported for dual-species aggregates of Geobacter species in which the two species appeared to exchange electrons via interspecies electron transfer. The temperature dependence response of the aggregate conductance was characteristic of the organic metallic-like conductance previously described for the conductive pili of Geobacter sulfurreducens and was inconsistent with electron conduction through minerals. Studies in which aggregates were incubated with high concentrations of potential electron donors demonstrated that the aggregates had no significant capacity for conversion of hydrogen to methane. The aggregates converted formate to methane but at rates too low to account for the rates at which that the aggregates syntrophically metabolized ethanol, an important component of the reactor influent. Geobacter species comprised 25% of 16S rRNA gene sequences recovered from the aggregates, suggesting that Geobacter species may have contributed to some but probably not all of the aggregate conductivity. Microorganisms most closely related to the acetate-utilizing Methanosaeta concilii accounted for more than 90% of the sequences that could be assigned to methane producers, consistent with the poor capacity for hydrogen and formate utilization. These results demonstrate for the first time that methanogenic wastewater aggregates can be electrically conductive and suggest that direct interspecies electron transfer could be an important mechanism for electron exchange in some methanogenic systems. PMID:21862629

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

    PubMed

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

    2005-12-15

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

  15. Intermolecular disulfide bond formation promotes immunoglobulin aggregation: investigation by fluorescence correlation spectroscopy.

    PubMed

    Nag, Moupriya; Bera, Kallol; Basak, Soumen

    2015-01-01

    Protein aggregation generally results from association between hydrophobic regions of individual monomers. However, additional mechanisms arising from specific interactions, such as intermolecular disulfide bond formation, may also contribute to the process. The latter is proposed to be the initiating pathway for aggregation of immunoglobulin (IgG), which is essential for triggering its immune response. To test the veracity of this hypothesis, we have employed fluorescence correlation spectroscopy to measure the kinetics of aggregation of IgG in separate experiments either allowing or inhibiting disulfide formation. Fluorescence correlation spectroscopy measurements yielded a diffusion time (τ(D)) of ∼200 µsec for Rhodamine-labeled IgG, corresponding to a hydrodynamic radius (R(H)) of 56 Å for the IgG monomer. The aggregation kinetics of the protein was followed by monitoring the time evolution of τ(D) under conditions in which its cysteine residues were either free or blocked. In both cases, the progress curves confirmed that aggregation proceeded via the nucleation-dependent polymerization pathway. However, for aggregation in the presence of free cysteines, the lag times were shorter, and the aggregate sizes bigger, than their respective counterparts for aggregation in the presence of blocked cysteines. This result clearly demonstrates that formation of intermolecular disulfide bonds represents a preferred pathway in the aggregation process of IgG. Fluorescence spectroscopy showed that aggregates formed in experiments where disulfide formation was prevented denatured at lower concentration of guanidine hydrochloride than those obtained in experiments where the disulfides were free to form, indicating that intermolecular disulfide bridging is a valid pathway for IgG aggregation. PMID:25371040

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

    PubMed

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

    2005-12-15

    The spatial and temporal distributions of different types of visible mucilaginous aggregates were investigated monthly by underwater video cameras in the northern Adriatic (NA) from June 1999 to July 2002. Small aggregates (flocs, macroflocs and stringers) were observed in all seasons with higher values in autumn and winter. Larger aggregates (ribbons, cobwebs, clouds, and false bottoms) formed only during late-spring and summer, particularly in 2000 and 2002, when the seasonal thermohaline stratification was marked. In fact, the process of mucilage formation took place mainly in the upper water column, above the main pycnocline. The spatial distribution shows that higher concentrations of small aggregates occur in the more productive coastal waters. The larger aggregates form or accumulate mainly in coastal waters in the southern part of the NA and in the central part of the Po River delta-Rovinj transect, where a gyre greatly influences the aggregates distribution. The fronts between low salinity coastal waters and high salinity waters of southern origin play an important role for accumulation and aggregation of the mucilage during spring and summer. Most of the aggregates accumulate in correspondence with strong pycnoclines with differences in density anomaly of 2 kg m(-3) or higher. False bottoms formed in correspondence with strong haloclines (DeltaS congruent with 2), while cobwebs and ribbons also occurred when the halocline was less marked (DeltaS<0.5). Meteorological conditions greatly influenced the aggregate formation. Calm weather and weak winds favour aggregation processes, while strong north-easterly winds, causing intense mixing, result in the dispersion of the mucilaginous aggregates, as occurred during the Bora event in July 2000. PMID:16289713

  17. Neuronal aggregates: formation, clearance and spreading

    PubMed Central

    Lim, Junghyun; Yue, Zhenyu

    2015-01-01

    Summary Proteostasis is maintained by multiple cellular pathways, including protein synthesis, quality control and degradation. An imbalance of neuronal proteostasis, associated with protein misfolding and aggregation, leads to proteinopathies or neurodegeneration. While genetic variations and protein modifications contribute to aggregate formation, components of the proteostasis network dictate the fate of protein aggregates. Here we provide an overview of proteostasis pathways and their interplay (particularly autophagy) with the metabolism of disease-related proteins. We review recent studies on neuronal activity-mediated regulation of proteostasis and transcellular propagation of protein aggregates in the nervous system. Targeting proteostasis pathways therapeutically remains an attractive but challenging task. PMID:25710535

  18. Immunogenicity of therapeutic proteins: influence of aggregation.

    PubMed

    Ratanji, Kirsty D; Derrick, Jeremy P; Dearman, Rebecca J; Kimber, Ian

    2014-01-01

    The elicitation of anti-drug antibodies (ADA) against biotherapeutics can have detrimental effects on drug safety, efficacy, and pharmacokinetics. The immunogenicity of biotherapeutics is, therefore, an important issue. There is evidence that protein aggregation can result in enhanced immunogenicity; however, the precise immunological and biochemical mechanisms responsible are poorly defined. In the context of biotherapeutic drug development and safety assessment, understanding the mechanisms underlying aggregate immunogenicity is of considerable interest. This review provides an overview of the phenomenon of protein aggregation, the production of unwanted aggregates during bioprocessing, and how the immune response to aggregated protein differs from that provoked by non-aggregated protein. Of particular interest is the nature of the interaction of aggregates with the immune system and how subsequent ADA responses are induced. Pathways considered here include 'classical' activation of the immune system involving antigen presenting cells and, alternatively, the breakdown of B-cell tolerance. Additionally, methods available to screen for aggregation and immunogenicity will be described. With an increased understanding of aggregation-enhanced immune responses, it may be possible to develop improved manufacturing and screening processes to avoid, or at least reduce, the problems associated with ADA.

  19. 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.

  20. Aggregate Remote Memory Copy Interface

    2006-02-23

    The purpose of the Aggregate Remote Memory Copy (ARMCI) library is to provide a general- purpose, efficient, and Widely portable remote memory access (RMA) operations (one-sided communication) optimized for Contiguous and noncontiguous (strided, scatter/gather, I/O vector) data transfers. In addition, ARMCI includes a set of atomic and mutual exclusion operations. The development ARMCI is driven by the need to support the global-addres space communication model in context of distributed regular or irregular distributed data structures,more » communication libraries, and compilers. ARMCI is a standalone system that could be used to support user-level libraries and applications that use MPI or PVM.« less

  1. Swarms: Optimum aggregations of spacecraft

    NASA Technical Reports Server (NTRS)

    Mayer, H. L.

    1980-01-01

    Swarms are aggregations of spacecraft or elements of a space system which are cooperative in function, but physically isolated or only loosely connected. For some missions the swarm configuration may be optimum compared to a group of completely independent spacecraft or a complex rigidly integrated spacecraft or space platform. General features of swarms are induced by considering an ensemble of 26 swarms, examples ranging from Earth centered swarms for commercial application to swarms for exploring minor planets. A concept for a low altitude swarm as a substitute for a space platform is proposed and a preliminary design studied. The salient design feature is the web of tethers holding the 30 km swarm in a rigid two dimensional array in the orbital plane. A mathematical discussion and tutorial in tether technology and in some aspects of the distribution of services (mass, energy, and information to swarm elements) are included.

  2. 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.

  3. Collisional Aggregation Due to Turbulence

    NASA Astrophysics Data System (ADS)

    Pumir, Alain; Wilkinson, Michael

    2016-03-01

    Collisions between particles suspended in a fluid play an important role in many physical processes. As an example, collisions of microscopic water droplets in clouds are a necessary step in the production of macroscopic raindrops. Collisions of dust grains are also conjectured to be important for planet formation in the gas surrounding young stars and to play a role in the dynamics of sand storms. In these processes, collisions are favored by fast turbulent motions. Here we review recent advances in the understanding of collisional aggregation due to turbulence. We discuss the role of fractal clustering of particles and caustic singularities of their velocities. We also discuss limitations of the Smoluchowski equation for modeling such processes. These advances lead to a semiquantitative understanding on the influence of turbulence on collision rates and point to deficiencies in the current understanding of rainfall and planet formation.

  4. Emerin expression in tubular aggregates.

    PubMed

    Manta, Panagiota; Terzis, Gerasimos; Papadimitriou, Constantinos; Kontou, Chrysanthi; Vassilopoulos, Demetris

    2004-06-01

    Emerin is an inner nuclear membrane protein that is mutated or not expressed in patients with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD/EMD). Cytoplasmic localization of emerin in cultured cells or tissues has been reported, although this remains a controversial issue. Tubular aggregates (TAs) are pathological structures seen in the sarcoplasm of human skeletal muscle fibers in various disorders. The TAs derive from the sarcoplasmic reticulum (SR) and represent, probably, an adaptive response of the SR to various insults to the muscle fibers. In the present study, we present immunohistochemical evidence of emerin expression in TAs. Muscle biopsies with tubular aggregates from four male, unrelated patients were studied. The percentage of muscle fibers containing TAs varied between 5 and 20%. Routine histochemistry revealed intense reaction of TAs with NADH-TR, AMPDA, and NSE, but not with COX, SDH, myosin ATPase (pH 9.4, 4.3, 4.6), PAS, and Oil red O staining. Immunohistochemical study revealed strong immunostaining of TAs with antibodies against emerin and 7 SERCA2-ATPase. Immunostaining of TAs was also seen with antibodies against heat shock protein and dysferlin, but not with antibodies to lamin A, dystrophin, adhalin, beta, gamma, delta sarcoglycans, and merosin. These results suggest that emerin, an inner nuclear membrane protein, is present at the TAs. The interpretation and significance of this finding is discussed in relation to experimental data suggesting that normal emerin localization at the inner nuclear membrane depends on lamin A and mutations in the N-terminal domain of emerin cause mislocalization of the protein to the sarcoplasmic membranes.

  5. Kinetic regime of dithiothreitol-induced aggregation of bovine serum albumin.

    PubMed

    Borzova, Vera A; Markossian, Kira A; Kara, Dmitriy A; Kurganov, Boris

    2015-09-01

    A search for agents, which are capable of effectively suppressing protein aggregation, and elaboration of the appropriate test systems, are among important problems of modern biochemistry and biotechnology. One such test system is based on dithiothreitol (DTT)-induced aggregation of bovine serum albumin (BSA). Study of the kinetics of DTT-induced aggregation of BSA by asymmetric flow field flow fractionation showed that a decrease in the portion of the non-aggregated protein in time followed the exponential law, the rate constant of the first order remaining unchanged at varying protein concentration (0.1M Na-phosphate buffer, pH 7.0; 45 °C). The obtained results indicate that the rate-limiting stage of the general aggregation process is that of unfolding of the protein molecule. When studying the kinetics of DTT-induced aggregation of BSA by dynamic light scattering, we proposed to use parameter K(LS) as a measure of the initial rate of aggregation. Parameter K(LS) corresponds to the initial slope of the dependence of (I-I0)(0.5) on time (I0 and I are the initial and current values of the light scattering intensity, respectively). The K(LS) value has been applied to estimate anti-aggregation activity of chemical chaperones (arginine, its derivatives and proline). PMID:26116389

  6. Extracellular polysaccharide composition of Azospirillum brasilense and its relation with cell aggregation.

    PubMed

    Burdman, S; Jurkevitch, E; Soria-Díaz, M E; Serrano, A M; Okon, Y

    2000-08-15

    The exopolysaccharide (EPS) and capsular polysaccharide (CPS) composition of four Azospirillum brasilense strains differing in their aggregation capacity was analyzed by high performance anion exchange chromatography. When growing the different strains in an aggregation inducing medium containing a high carbon:nitrogen (C:N) ratio, both EPS and CPS showed a positive correlation between aggregation and the relative amount of arabinose. Arabinose was not detected in polysaccharides from Sp72002, a pleiotrophic Tn5 mutant strain impaired in aggregation. Arabinose was also not detected in extracellular polysaccharides of bacteria grown in a low C:N ratio, non-inducing aggregation medium, with exception for a relatively small amount found in the CPS of FAJ0204, a super-aggregating mutant strain. The only monosaccharides able to significantly inhibit aggregation at low sugar concentration when tested in a bioassay were arabinose (at a higher extent) and galactose. The possibility that residues of arabinose present in the extracellular polysaccharides are involved in the aggregation of A. brasilense is discussed.

  7. Synthesis of several membrane proteins during developmental aggregation in Myxococcus xanthus.

    PubMed

    Orndorff, P E; Dworkin, M

    1982-01-01

    We have examined the pattern of synthesis of several membrane proteins during the aggregation phase of development in Myxococcus xanthus. Development was initiated by plating vegetative cells on polycarbonate filters placed on top of an agar medium that supported fruiting body formation. At various times during aggregation a filter was removed, the cells were pulse-labeled with [35S]methionine, and the membrane proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The rate of synthesis of numerous individual proteins changed during aggregation; we concentrated on six whose pattern of synthesis was greatly altered during aggregation. The rate of synthesis of five of the six proteins increased considerably during aggregation; that of the remaining protein was curtailed and appeared to be regulated by nutrient conditions. Three of the five major membrane proteins that increased during aggregation had a unique pattern of synthesis that was displayed only under conditions that are are required for development - high cell density, nutrient depletion, and a solid (agar) surface. The remaining two proteins were not unique to development; the appearance of one protein could be induced under conditions of high cell density, whereas the other could be induced by placing the cells on a solid agar surface. All of the five major proteins that appeared during development did so during the preaggregation stage, and the synthesis of four of the five proteins appeared to be curtailed late in aggregation. The synthesis of the remaining protein continued throughout aggregation. PMID:6798022

  8. Electrostatic origin of in vitro aggregation of human γ-crystallin

    PubMed Central

    Mohr, Benjamin G.; Dobson, Cassidy M.; Garman, Scott C.; Muthukumar, Murugappan

    2013-01-01

    The proteins α-, β-, and γ-crystallins are the major components of the lens in the human eye. Using dynamic light scattering method, we have performed in vitro investigations of protein-protein interactions in dilute solutions of human γ-crystallin and α-crystallin. We find that γ-crystallin spontaneously aggregates into finite-sized clusters in phosphate buffer solutions. There are two distinct populations of unaggregated and aggregated γ-crystallins in these solutions. On the other hand, α-crystallin molecules are not aggregated into large clusters in solutions of α-crystallin alone. When α-crystallin and γ-crystallin are mixed in phosphate buffer solutions, we demonstrate that the clusters of γ-crystallin are prevented. By further investigating the roles of temperature, protein concentration, pH, salt concentration, and a reducing agent, we show that the aggregation of γ-crystallin under our in vitro conditions arises from non-covalent electrostatic interactions. In addition, we show that aggregation of γ-crystallin occurs under the dilute in vitro conditions even in the absence of oxidizing agents that can induce disulfide cross-links, long considered to be responsible for human cataracts. Aggregation of γ-crystallin when maintained under reducing conditions suggests that oxidation does not contribute to the aggregation in dilute solutions. PMID:24089726

  9. Elliptical concentrators.

    PubMed

    Garcia-Botella, Angel; Fernandez-Balbuena, Antonio Alvarez; Bernabeu, Eusebio

    2006-10-10

    Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used to produce optical devices, including the use of reflective and refractive components or inverse engineering techniques. However, many of these optical components are based on translational symmetries, rotational symmetries, or free-form surfaces. We study a new family of nonimaging concentrators called elliptical concentrators. This new family of concentrators provides new capabilities and can have different configurations, either homofocal or nonhomofocal. Translational and rotational concentrators can be considered as particular cases of elliptical concentrators. PMID:17068595

  10. Aggregation and antigenicity of virus like particle in salt solution--A case study with hepatitis B surface antigen.

    PubMed

    Chen, Yi; Zhang, Yan; Quan, Can; Luo, Jian; Yang, Yanli; Yu, Mengran; Kong, Yingjun; Ma, Guanghui; Su, Zhiguo

    2015-08-20

    The phenomenon of aggregation of virus-like particles (VLPs) in salt solution and the corresponding effect upon antigenicity was reported. Asymmetrical flow field-flow fractionation (AF4) combined with multi-angle laser light scattering (MALLS) was used to characterize the size and the aggregation behavior of hepatitis B surface antigen (HBsAg). The average diameter of HBsAg VLP was 22.8±0.4 nm and it tended to aggregate in salt solution to form large particles and the antigenicity changed accordingly. In 0-4 M NaCl solution, part of HBsAg molecules aggregated rapidly into oligomeric particles (OP), whose diameter distributed from 25 to 40 nm, and the antigenicity slightly decreased about 10%. The aggregation reaction is reversible. After removing NaCl, both size and antigenicity could recover to normal level (92-96%). By contrast, the aggregation process is more complicated in (NH4)2SO4 solution. Most of HBsAg particles aggregated into OP and further aggregated into polymeric particles (PP). The diameter of the PP could reach 40 to 140 nm. The concentration of (NH4)2SO4 had remarkable influence upon the rate of aggregation. When concentration of (NH4)2SO4 was below 1 M, most of HBsAg aggregated only into OP in 1 h. While with concentration of (NH4)2SO4 above 1 M, most of particles formed PP within 1 h. The aggregation process to PP was irreversible. After removing (NH4)2SO4, the large aggregates could not recover to normal particles and the remaining antigenicity was below 30%. PMID:25862298

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  13. Flow Partitioning in Fully Saturated Soil Aggregates

    SciTech Connect

    Yang, Xiaofan; Richmond, Marshall C.; Scheibe, Timothy D.; Perkins, William A.; Resat, Haluk

    2014-03-30

    Microbes play an important role in facilitating organic matter decomposition in soils, which is a major component of the global carbon cycle. Microbial dynamics are intimately coupled to environmental transport processes, which control access to labile organic matter and other nutrients that are needed for the growth and maintenance of microorganisms. Transport of soluble nutrients in the soil system is arguably most strongly impacted by preferential flow pathways in the soil. Since the physical structure of soils can be characterized as being formed from constituent micro aggregates which contain internal porosity, one pressing question is the partitioning of the flow among the “inter-aggregate” and “intra-aggregate” pores and how this may impact overall solute transport within heterogeneous soil structures. The answer to this question is particularly important in evaluating assumptions to be used in developing upscaled simulations based on highly-resolved mechanistic models. We constructed a number of diverse multi-aggregate structures with different packing ratios by stacking micro-aggregates containing internal pores and varying the size and shape of inter-aggregate pore spacing between them. We then performed pore-scale flow simulations using computational fluid dynamics methods to determine the flow patterns in these aggregate-of-aggregates structures and computed the partitioning of the flow through intra- and inter-aggregate pores as a function of the spacing between the aggregates. The results of these numerical experiments demonstrate that soluble nutrients are largely transported via flows through inter-aggregate pores. Although this result is consistent with intuition, we have also been able to quantify the relative flow capacity of the two domains under various conditions. For example, in our simulations, the flow capacity through the aggregates (intra-aggregate flow) was less than 2% of the total flow when the spacing between the aggregates

  14. Succession of Protists on Estuarine Aggregates.

    PubMed

    Wörner; Zimmerman-Timm; Kausch

    2000-08-01

    Colonization by and succession of bacteria and bacterivorous protists on laboratory-made aggregates were determined over a period of 14 days during winter and spring in 1997. Aggregates were generated from natural water from the limnetic zone of the Elbe Estuary using a tilting tube roller system. Within 1 h after the beginning of the experiments, macroaggregates started to form. Aggregates reached a maximum size of 1 mm with a tendency toward large sizes at the end of the experiment after the 10th day. On the first day, high bacterial densities of more than 10(9) cells ml(-1) were detected within the aggregates. The abundances of flagellates and ciliates within aggregates were also two or three orders of magnitude higher than in the surrounding water. Densities of aggregate associated organisms are comparable to those occuring in sediments. The first protistan colonizers on the aggregates were small heterotrophic flagellates, such as choanoflagellates and small euglenids. Later, beginning on the 4th day, small sarcodines and ciliates became abundant. The most abundant ciliates associated with aggregates were small species of the Hypotrichia, Cyrtophorida, and Hymenostomata. After 9 days, large omnivorous and carnivorous ciliates, such as large members of the Hypotrichia and the Pleurostomatida, occurred. In spring, large heterotrophic flagellates and amebae also appeared at this time. These findings indicated the existence of a succession of protists on newly formed aggregates and a microbial food net within the aggregates based on bacterial production. Additionally, most of the species observed during this study were adapted for living on surfaces. In natural environments they are more common in benthic than in pelagic environments. For them, aggregates are havens in the water column comparable to sediment communities.

  15. Preformed Seeds Modulate Native Insulin Aggregation Kinetics.

    PubMed

    Dutta, Colina; Yang, Mu; Long, Fei; Shahbazian-Yassar, Reza; Tiwari, Ashutosh

    2015-12-10

    Insulin aggregates under storage conditions via disulfide interchange reaction. It is also known to form aggregates at the site of repeated injections in diabetes patients, leading to injection amyloidosis. This has fueled research in pharmaceutical and biotechnology industry as well as in academia to understand factors that modulate insulin stability and aggregation. The main aim of this study is to understand the factors that modulate aggregation propensity of insulin under conditions close to physiological and measure effect of "seeds" on aggregation kinetics. We explored the aggregation kinetics of insulin at pH 7.2 and 37 °C in the presence of disulfide-reducing agent dithiothreitol (DTT), using spectroscopy (UV-visible, fluorescence, and Fourier transform infrared spectroscopy) and microscopy (scanning electron microscopy, atomic force microscopy) techniques. We prepared insulin "seeds" by incubating disulfide-reduced insulin at pH 7.2 and 37 °C for varying lengths of time (10 min to 12 h). These seeds were added to the native protein and nucleation-dependent aggregation kinetics was measured. Aggregation kinetics was fastest in the presence of 10 min seeds suggesting they were nascent. Interestingly, intermediate seeds (30 min to 4 h incubation) resulted in formation of transient fibrils in 4 h that converted to amorphous aggregates upon longer incubation of 24 h. Overall, the results show that insulin under disulfide reducing conditions at pH and temperature close to physiological favors amorphous aggregate formation and seed "maturity" plays an important role in nucleation dependent aggregation kinetics.

  16. A Colloidal Description of Intermolecular Interactions Driving Fibril-Fibril Aggregation of a Model Amphiphilic Peptide.

    PubMed

    Owczarz, Marta; Motta, Anna C; Morbidelli, Massimo; Arosio, Paolo

    2015-07-14

    We apply a kinetic analysis platform to study the intermolecular interactions underlying the colloidal stability of dispersions of charged amyloid fibrils consisting of a model amphiphilic peptide (RADA 16-I). In contrast to the aggregation mechanisms observed in the large majority of proteins and peptides, where several elementary reactions involving both monomers and fibrils are present simultaneously, the system selected in this work allows the specific investigation of the fibril-fibril aggregation process. We examine the intermolecular interactions driving the aggregation reaction at pH 2.0 by changing the buffer composition in terms of salt concentration, type of ion as well as type and concentration of organic solvent. The aggregation kinetics are followed by dynamic light scattering, and the experimental data are simulated by Smoluchowski population balance equations, which allow to estimate the energy barrier between two colliding fibrils in terms of the Fuchs stability ratio (W). When normalized on a dimensionless time weighted on the Fuchs stability ratio, the aggregation profiles under a broad range of conditions collapse on a single master curve, indicating that the buffer composition modifies the aggregation kinetics without affecting the aggregation mechanism. Our results show that the aggregation process does not occur under diffusion-limited conditions. Rather, the reaction rate is limited by the presence of an activation energy barrier that is largely dominated by electrostatic repulsive interactions. Such interactions could be reduced by increasing the concentration of salt, which induces charge screening, or the concentration of organic solvent, which affects the dielectric constant. It is remarkable that the dependence of the activation energy on the ionic strength can be described quantitatively in terms of charge screening effects in the frame of the DLVO theory, although specific anion and cation effects are also observed. While anion

  17. Aggregation of quantum dots in hybrid structures based on TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kolesova, Ekaterina P.; Orlova, Anna O.; Maslov, Vladimir G.; Gun'ko, Yurii K.; Cleary, Olan; Baranov, Aleksander V.; Fedorov, Anatoly V.

    2016-04-01

    A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based on TiO2 nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir- Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of structure formation. A photodegradation of luminescence properties of the structures is associated with the formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the structure formation and the concentration of TiO2 nanoparticles. A decay of luminescence of QD aggregates in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform QD surface concentration by visible light resulted in a photopassivation of their surface, which is accompanied by significant increase of luminescence quantum yield of QDs.

  18. Depletion-mediated red blood cell aggregation in polymer solutions.

    PubMed

    Neu, Björn; Meiselman, Herbert J

    2002-11-01

    Polymer-induced red blood cell (RBC) aggregation is of current basic science and clinical interest, and a depletion-mediated model for this phenomenon has been suggested; to date, however, analytical approaches to this model are lacking. An approach is thus described for calculating the interaction energy between RBC in polymer solutions. The model combines electrostatic repulsion due to RBC surface charge with osmotic attractive forces due to polymer depletion near the RBC surface. The effects of polymer concentration and polymer physicochemical properties on depletion layer thickness and on polymer penetration into the RBC glycocalyx are considered for 40 to 500 kDa dextran and for 18 to 35 kDa poly (ethylene glycol). The calculated results are in excellent agreement with literature data for cell-cell affinities and with RBC aggregation-polymer concentration relations. These findings thus lend strong support to depletion interactions as the basis for polymer-induced RBC aggregation and suggest the usefulness of this approach for exploring interactions between macromolecules and the RBC glycocalyx. PMID:12414682

  19. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... other activities and actions. (See 40 CFR 1508.25(a)). (2) Consider reasonable alternative courses of... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification §...

  20. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... other activities and actions. (See 40 CFR 1508.25(a)). (2) Consider reasonable alternative courses of... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification §...

  1. 48 CFR 514.270 - Aggregate awards.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Aggregate awards. 514.270 Section 514.270 Federal Acquisition Regulations System GENERAL SERVICES ADMINISTRATION CONTRACTING METHODS AND CONTRACT TYPES SEALED BIDDING Solicitation of Bids 514.270 Aggregate awards....

  2. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32... the total project must be listed and described by the responsible entity in the environmental review... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false Project aggregation. 58.32...

  3. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32... the total project must be listed and described by the responsible entity in the environmental review... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Project aggregation. 58.32...

  4. Choosing Aggregation Rules for Composite Indicators

    ERIC Educational Resources Information Center

    Munda, Giuseppe

    2012-01-01

    From a formal point of view, a composite indicator is an aggregate of all dimensions, objectives, individual indicators and variables used for its construction. This implies that what defines a composite indicator is the set of properties underlying its mathematical aggregation convention. In this article, I try to revise the theoretical debate on…

  5. Teaching Aggregate Demand and Supply Models

    ERIC Educational Resources Information Center

    Wells, Graeme

    2010-01-01

    The author analyzes the inflation-targeting model that underlies recent textbook expositions of the aggregate demand-aggregate supply approach used in introductory courses in macroeconomics. He shows how numerical simulations of a model with inflation inertia can be used as a tool to help students understand adjustments in response to demand and…

  6. 7 CFR 1.6 - Aggregating requests.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 1 2010-01-01 2010-01-01 false Aggregating requests. 1.6 Section 1.6 Agriculture Office of the Secretary of Agriculture ADMINISTRATIVE REGULATIONS Official Records § 1.6 Aggregating requests. When an agency reasonably believes that a requester, or a group of requesters acting in...

  7. 42 CFR 411.106 - Aggregation rules.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 42 Public Health 2 2010-10-01 2010-10-01 false Aggregation rules. 411.106 Section 411.106 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES MEDICARE PROGRAM... Under Group Health Plans: General Provisions § 411.106 Aggregation rules. The following rules apply...

  8. 7 CFR 1.6 - Aggregating requests.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 1 2013-01-01 2013-01-01 false Aggregating requests. 1.6 Section 1.6 Agriculture Office of the Secretary of Agriculture ADMINISTRATIVE REGULATIONS Official Records § 1.6 Aggregating requests. When an agency reasonably believes that a requester, or a group of requesters acting in...

  9. Biomass round bales infield aggregation logistic scenarios

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biomass bales often need to be aggregated (collected into groups and transported) to a field-edge stack for temporary storage for feedlots or processing facilities. Aggregating the bales with the least total distance involved is a goal of producers and bale handlers. Several logistics scenarios for ...

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

    PubMed Central

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

    2015-01-01

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

  11. Fractal aggregates induced by liposome-liposome interaction in the presence of Ca2+.

    PubMed

    Sabín, J; Prieto, G; Ruso, J M; Sarmiento, F

    2007-10-01

    We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine (EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from 2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into account a repulsive force of hydration.

  12. Aggregation kinetics of multiwalled carbon nanotubes in aquatic systems: measurements and environmental implications.

    PubMed

    Saleh, Navid B; Pfefferle, Lisa D; Elimelech, Menachem

    2008-11-01

    The initial aggregation kinetics of multiwalled carbon nanotubes (MWNTs) were examined through time-resolved dynamic light scattering. Aggregation of MWNTs was evaluated by varying solution pH and the concentration of monovalent (NaCl) and divalent (CaCl2 and MgCl2) salts. Suwannee River humic acid (SRHA) was used to study the effect of background natural organic matter on MWNT aggregation kinetics, Increasing salt concentration and addition of divalent calcium and magnesium ions induced MWNT aggregation by suppressing electrostatic repulsion, similar to observations with aquatic colloidal particles. The critical coagulation concentration (CCC) values for MWNTs were estimated as 25 mM NaCI, 2.6 mM CaCl2, and 1.5 mM MgCl2. An increase in solution pH from acidic (pH 3) to basic (pH 11) conditions resulted in a substantial (over 2 orders of magnitude) decrease in MWNT aggregation kinetics, suggesting the presence of ionizable functional groups on the MWNT carbon scaffold. The presence of humic acid in solution markedly enhanced the colloidal stability of MWNTs, reducing the aggregation rate by nearly 2 orders of magnitude. The enhanced MWNT stability in the presence of humic acid is attributable to steric repulsion imparted by adsorbed humic acid macromolecules. Our results suggest that MWNTs are relatively stable at solution pH and electrolyte conditions typical of aquatic environments.

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

    PubMed

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

    2015-01-01

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

  14. Tracking Hypoxic Signaling within Encapsulated Cell Aggregates

    PubMed Central

    Skiles, Matthew L.; Sahai, Suchit; Blanchette, James O.

    2011-01-01

    nutrients, notably oxygen, is therefore reduced and limited by diffusion. This reduced oxygen availability may especially impact β-cells whose insulin secretory function is highly dependent on oxygen11-13. Capsule composition and geometry will also impact diffusion rates and lengths for oxygen. Therefore, we also describe a technique for identifying hypoxic cells within our PEG capsules. Infection of the cells with a recombinant adenovirus allows for a fluorescent signal to be produced when intracellular hypoxia-inducible factor (HIF) pathways are activated14. As HIFs are the primary regulators of the transcriptional response to hypoxia, they represent an ideal target marker for detection of hypoxic signaling15. This approach allows for easy and rapid detection of hypoxic cells. Briefly, the adenovirus has the sequence for a red fluorescent protein (Ds Red DR from Clontech) under the control of a hypoxia-responsive element (HRE) trimer. Stabilization of HIF-1 by low oxygen conditions will drive transcription of the fluorescent protein (Figure 1). Additional details on the construction of this virus have been published previously15. The virus is stored in 10% glycerol at -80° C as many 150 μL aliquots in 1.5 mL centrifuge tubes at a concentration of 3.4 x 1010 pfu/mL. Previous studies in our lab have shown that MIN6 cells encapsulated as aggregates maintain their viability throughout 4 weeks of culture in 20% oxygen. MIN6 aggregates cultured at 2 or 1% oxygen showed both signs of necrotic cells (still about 85-90% viable) by staining with ethidium bromide as well as morphological changes relative to cells in 20% oxygen. The smooth spherical shape of the aggregates displayed at 20% was lost and aggregates appeared more like disorganized groups of cells. While the low oxygen stress does not cause a pronounced drop in viability, it is clearly impacting MIN6 aggregation and function as measured by glucose-stimulated insulin secretion15. Western blot analysis of encapsulated

  15. Tracking hypoxic signaling within encapsulated cell aggregates.

    PubMed

    Skiles, Matthew L; Sahai, Suchit; Blanchette, James O

    2011-01-01

    , is therefore reduced and limited by diffusion. This reduced oxygen availability may especially impact β-cells whose insulin secretory function is highly dependent on oxygen. Capsule composition and geometry will also impact diffusion rates and lengths for oxygen. Therefore, we also describe a technique for identifying hypoxic cells within our PEG capsules. Infection of the cells with a recombinant adenovirus allows for a fluorescent signal to be produced when intracellular hypoxia-inducible factor (HIF) pathways are activated. As HIFs are the primary regulators of the transcriptional response to hypoxia, they represent an ideal target marker for detection of hypoxic signaling. This approach allows for easy and rapid detection of hypoxic cells. Briefly, the adenovirus has the sequence for a red fluorescent protein (Ds Red DR from Clontech) under the control of a hypoxia-responsive element (HRE) trimer. Stabilization of HIF-1 by low oxygen conditions will drive transcription of the fluorescent protein (Figure 1). Additional details on the construction of this virus have been published previously. The virus is stored in 10% glycerol at -80° C as many 150 μL aliquots in 1.5 mL centrifuge tubes at a concentration of 3.4 x 10(10) pfu/mL. Previous studies in our lab have shown that MIN6 cells encapsulated as aggregates maintain their viability throughout 4 weeks of culture in 20% oxygen. MIN6 aggregates cultured at 2 or 1% oxygen showed both signs of necrotic cells (still about 85-90% viable) by staining with ethidium bromide as well as morphological changes relative to cells in 20% oxygen. The smooth spherical shape of the aggregates displayed at 20% was lost and aggregates appeared more like disorganized groups of cells. While the low oxygen stress does not cause a pronounced drop in viability, it is clearly impacting MIN6 aggregation and function as measured by glucose-stimulated insulin secretion. Western blot analysis of encapsulated cells in 20% and 1% oxygen also

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

    PubMed

    Segad, M; Cabane, B; Jönsson, Bo

    2015-10-21

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

  17. Copepod Aggregations: Influences of Physics and Collective Behavior

    NASA Astrophysics Data System (ADS)

    Flierl, Glenn R.; Woods, Nicholas W.

    2015-02-01

    Dense copepod aggregations form in Massachusetts Bay and provide an important resource for right whales. We re-examine the processes which might account for the high concentrations, investigating both horizontally convergent flow, which can increase the density of depth-keeping organisms, and social behavior. We argue that the two act in concert: social behavior creates small dense patches (on the scale of a few sensing radii); physical stirring brings them together so that they merge into aggregations with larger scales; it also moves them into areas of physical convergence which retain the increasingly large patch. But the turbulence can also break this apart, suggesting that the overall high density in the convergence zone will not be uniform but will instead be composed of multiple transient patches (which are still much larger than the sensing scale).

  18. 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.

  19. Analysis of aggregated hospital infection data for accountability.

    PubMed

    Morton, A; Mengersen, K; Waterhouse, M; Steiner, S

    2010-12-01

    Analysis and reporting of among-institution aggregated hospital-acquired infection data are necessary for transparency and accountability. Different analytical methods are required for ensuring transparency and accountability for within-institution sequential analysis. In addition, unbiased summary information is needed for planning and informing the public. We believe that implementation of systems based on evidence is the key to improving institutional performance and safety. This must be accompanied by compliance, outcome audit and sequential analysis of outcome data, e.g. using statistical process control methods. Checklists can be a valuable aid for ensuring implementation of evidence-based systems. Aggregated outcome data analysis for transparency and accountability should concentrate primarily on accurately presenting the outcomes together with their precision. We describe tabulations, funnel plots and random-effects (shrinkage) analysis and avoid comparisons using league tables, star ratings and confidence intervals. PMID:20870312

  20. 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.

  1. Influences of perfluorooctanoic acid on the aggregation of multi-walled carbon nanotubes.

    PubMed

    Li, Chengliang; Schäffer, Andreas; Vereecken, Harry; Heggen, Marc; Ji, Rong; Klumpp, Erwin

    2013-03-01

    The aggregation of multi-walled carbon nanotubes (MWCNTs) in the aqueous phase not only inhibits their extensive utilization in various aspects but also dominates their environmental fate and transport. The role of surfactants at low concentration in the aggregation of MWCNTs has been studied, however the effect of perfluorinated surfactants at low concentration is uncertain. To understand this interfacial phenomenon, the influences of perfluorooctanoic acid (PFOA), and sodium dodecyl sulfate (SDS) as a control, on MWCNT aggregation in the aqueous phase were examined by the UV absorbency method. Influences of pH and cationic species on the critical coagulation concentration (CCC) value were evaluated. The CCC values were dependent on the concentration of PFOA, however a pronounced effect of SDS concentration on the CCC values was not observed. The CCC values of the MWCNTs were 51.6 mmol/L in NaCl and 0.28 mmol/L in CaCl2 solutions, which suggested pronounced differences in the effects of Na+ and Ca2+ ions on the aggregation of the MWCNTs. The presence of both PFOA and SDS significantly decreased the CCC values of the MWCNTs in NaCl solution. The aggregation of the MWCNTs took place under acidic conditions and was not notably altered under neutral and alkaline conditions due to the electrostatic repulsion of deprotonated functional groups on the surface of the MWCNTs. PMID:23923418

  2. 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

  3. Therapeutic Protein Aggregation: Mechanisms, Design, and Control

    PubMed Central

    Roberts, Christopher J.

    2014-01-01

    While it is well known that proteins are only marginally stable in their folded states, it is often less well appreciated that most proteins are inherently aggregation-prone in their unfolded or partially unfolded states, and the resulting aggregates can be extremely stable and long-lived. For therapeutic proteins, aggregates are a significant risk factor for deleterious immune responses in patients, and can form via a variety of mechanisms. Controlling aggregation using a mechanistic approach may allow improved design of therapeutic protein stability, as a complement to existing design strategies that target desired protein structures and function. Recent results highlight the importance of balancing protein environment with the inherent aggregation propensities of polypeptide chains. PMID:24908382

  4. CHARGING OF AGGREGATE GRAINS IN ASTROPHYSICAL ENVIRONMENTS

    SciTech Connect

    Ma, Qianyu; Matthews, Lorin S.; Hyde, Truell W.; Land, Victor

    2013-02-15

    The charging of dust grains in astrophysical environments has been investigated with the assumption that these grains are homogeneous spheres. However, there is evidence which suggests that many grains in astrophysical environments are irregularly shaped aggregates. Recent studies have shown that aggregates acquire higher charge-to-mass ratios due to their complex structures, which in turn may alter their subsequent dynamics and evolution. In this paper, the charging of aggregates is examined including secondary electron emission and photoemission in addition to primary plasma currents. The results show that the equilibrium charge on aggregates can differ markedly from spherical grains with the same mass, but that the charge can be estimated for a given environment based on structural characteristics of the grain. The 'small particle effect' due to secondary electron emission is also important for de terming the charge of micron-sized aggregates consisting of nano-sized particles.

  5. Formation of Tethers from Spreading Cellular Aggregates.

    PubMed

    Beaune, Grégory; Winnik, Françoise M; Brochard-Wyart, Françoise

    2015-12-01

    Membrane tubes are commonly extruded from cells and vesicles when a point-like force is applied on the membrane. We report here the unexpected formation of membrane tubes from lymph node cancer prostate (LNCaP) cell aggregates in the absence of external applied forces. The spreading of LNCaP aggregates deposited on adhesive glass substrates coated with fibronectin is very limited because cell-cell adhesion is stronger than cell-substrate adhesion. Some cells on the aggregate periphery are very motile and try to escape from the aggregate, leading to the formation of membrane tubes. Tethered networks and exchange of cargos between cells were observed as well. Growth of the tubes is followed by either tube retraction or tube rupture. Hence, even very cohesive cells are successful in escaping aggregates, which may lead to epithelial mesenchymal transition and tumor metastasis. We interpret the dynamics of formation and retraction of tubes in the framework of membrane mechanics. PMID:26509898

  6. 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

  7. Effect of Excipients on Liquid-Liquid Phase Separation and Aggregation in Dual Variable Domain Immunoglobulin Protein Solutions.

    PubMed

    Raut, Ashlesha S; Kalonia, Devendra S

    2016-03-01

    Liquid-liquid phase separation (LLPS) and aggregation can reduce the physical stability of therapeutic protein formulations. On undergoing LLPS, the protein-rich phase can promote aggregation during storage due to high concentration of the protein. Effect of different excipients on aggregation in protein solution is well documented; however data on the effect of excipients on LLPS is scarce in the literature. In this study, the effect of four excipients (PEG 400, Tween 80, sucrose, and hydroxypropyl beta-cyclodextrin (HPβCD)) on liquid-liquid phase separation and aggregation in a dual variable domain immunoglobulin protein solution was investigated. Sucrose suppressed both LLPS and aggregation, Tween 80 had no effect on either, and PEG 400 increased LLPS and aggregation. Attractive protein-protein interactions and liquid-liquid phase separation decreased with increasing concentration of HPβCD, indicating its specific binding to the protein. However, HPβCD had no effect on the formation of soluble aggregates and fragments in this study. LLPS and aggregation are highly temperature dependent; at low temperature protein exhibits LLPS, at high temperature protein exhibits aggregation, and at an intermediate temperature both phenomena occur simultaneously depending on the solution conditions.

  8. Experimental volcanic ash aggregation: Internal structuring of accretionary lapilli and the role of liquid bonding

    NASA Astrophysics Data System (ADS)

    Mueller, Sebastian B.; Kueppers, Ulrich; Ayris, Paul M.; Jacob, Michael; Dingwell, Donald B.

    2016-01-01

    Explosive volcanic eruptions can release vast quantities of pyroclastic material into Earth's atmosphere, including volcanic ash, particles with diameters less than two millimeters. Ash particles can cluster together to form aggregates, in some cases reaching up to several centimeters in size. Aggregation alters ash transport and settling behavior compared to un-aggregated particles, influencing ash distribution and deposit stratigraphy. Accretionary lapilli, the most commonly preserved type of aggregates within the geologic record, can exhibit complex internal stratigraphy. The processes involved in the formation and preservation of these aggregates remain poorly constrained quantitatively. In this study, we simulate the variable gas-particle flow conditions which may be encountered within eruption plumes and pyroclastic density currents via laboratory experiments using the ProCell Lab System® of Glatt Ingenieurtechnik GmbH. In this apparatus, solid particles are set into motion in a fluidized bed over a range of well-controlled boundary conditions (particle concentration, air flow rate, gas temperature, humidity, liquid composition). Experiments were conducted with soda-lime glass beads and natural volcanic ash particles under a range of experimental conditions. Both glass beads and volcanic ash exhibited the capacity for aggregation, but stable aggregates could only be produced when materials were coated with high but volcanically-relevant concentrations of NaCl. The growth and structure of aggregates was dependent on the initial granulometry, while the rate of aggregate formation increased exponentially with increasing relative humidity (12-45% RH), before overwetting promoted mud droplet formation. Notably, by use of a broad granulometry, we generated spherical, internally structured aggregates similar to some accretionary pellets found in volcanic deposits. Adaptation of a powder-technology model offers an explanation for the origin of natural accretionary

  9. Inhibitory effect of sulfur-containing compounds in Scorodocarpus borneensis Becc. on the aggregation of rabbit platelets.

    PubMed

    Lim, H; Kubota, K; Kobayashi, A; Seki, T; Ariga, T

    1999-02-01

    The inhibitory effects of three pure compounds isolated from wood garlic, 2,4,5-trithiahexane (I), 2,4,5,7-tetrathiaoctane (II), and 2,4,5,7-tetrathiaoctane 2,2-dioxide (III), on rabbit platelet aggregation induced by collagen, arachidonic acid, U46619, ADP (adenosine 5'-diphosphate), PAF (platelet aggregating factor), and thrombin were studied in vitro. The anti-aggregating activity of 2,4,5,7-tetrathiaoctane 4,4-dioxide (IV) was also measured with collagen and arachidonic acid. I, II, III, and IV inhibited the platelet aggregation induced by all tested agonists. I, II, and III exhibited a stronger inhibitory effect against the thrombin-induced aggregation of GFP (gel-filtered platelets) than against the aggregation induced by the other agonists. Notably, the IC50 value for III was 4 microM, which is approximately 2.5 times stronger than MATS (methyl allyl trisulfide), a major anti-platelet compound isolated from garlic. In inhibiting collagen-induced aggregation, II was as potent as MATS and aspirin, with a marked disaggregation effect on the secondary aggregation by arachidonic acid, at the rate of 47.05%/min at a concentration of 10(-4) M. I, II, and III also suppressed U46619-induced aggregation. These results suggest that sulfur-containing compounds in wood garlic not only inhibit arachidonic acid metabolism but also suppress aggregation in association with the function of the platelet plasma membrane. PMID:10192909

  10. Inhibition of precipitation and aggregation of metacinnabar (mercuric sulfide) by dissolved organic matter isolated from the Florida Everglades

    USGS Publications Warehouse

    Ravichandran, M.; Aiken, G.R.; Ryan, J.N.; Reddy, M.M.

    1999-01-01

    Precipitation and aggregation of metacinnabar (black HgS) was inhibited in the presence of low concentrations (???3 mg C/L) of humic fractions of dissolved organic matter (DOM) isolated from the Florida Everglades. At low Hg concentrations (??? x 10-8 M), DOM prevented the precipitation of metacinnabar. At moderate Hg concentrations (5 x 10-5 M), DOM inhibited the aggregation of colloidal metacinnabar (Hg passed through a 0.1 ??m filter but was removed by centrifugation). At Hg concentrations greater than 5 x 10-4 M, mercury formed solid metacinnabar particles that were removed from solution by a 0.1 ??m filter. Organic matter rich in aromatic moleties was preferentially removed with the solid. Hydrophobic organic acids (humic and fulvic acids) inhibited aggregation better than hydrophilic organic acids. The presence of chloride, acetate, salicylate, EDTA, and cysteine did not inhibit the precipitation or aggregation of metacinnabar. Calcium enhanced metacinnabar aggregation even in the presence of DOM, but the magnitude of the effect was dependent on the concentrations of DOM, Hg, and Ca. Inhibition of metacinnabar precipitation appears to be a result of strong DOM-Hg binding. Prevention of aggregation of colloidal particles appears to be caused by adsorption of DOM and electrostatic repulsion.Precipitation and aggregation of metacinnabar (black HgS) was inhibited in the presence of low concentrations (???3 mg C/L) of humic fractions of dissolved organic matter (DOM) isolated from the Florida Everglades. At low Hg concentrations (???5??10-8 M), DOM prevented the precipitation of metacinnabar. At moderate Hg concentrations (5??10-5 M), DOM inhibited the aggregation of colloidal metacinnabar (Hg passed through a 0.1 ??m filter but was removed by centrifugation). At Hg concentrations greater than 5??10-4 M, mercury formed solid metacinnabar particles that were removed from solution by a 0.1 ??m filter. Organic matter rich in aromatic moieties was preferentially

  11. Reconsidering the mechanism of polyglutamine peptide aggregation.

    PubMed

    Lee, Christine C; Walters, Robert H; Murphy, Regina M

    2007-11-01

    There are at least nine neurodegenerative diseases associated with proteins that contain an unusually expanded polyglutamine domain, the best known of which is Huntington's disease. In all of these diseases, the mutant protein aggregates into neuronal inclusions; it is generally, although not universally, believed that protein aggregation is an underlying cause of the observed neuronal degeneration. In an effort to examine the role of polyglutamine in facilitating protein aggregation, investigators have used synthetic polyglutamine peptides as model systems. Analysis of kinetic data led to the conclusions that aggregation follows a simple nucleation-elongation mechanism characterized by a significant lag time, during which the peptide is monomeric, and that the nucleus is a monomer in a thermodynamically unfavorable conformation [Chen, S. M., et al. (2002) Proc. Natl. Acad. Sci. U.S.A. 99, 11884-11889]. We re-examined this hypothesis by measuring the aggregation kinetics of the polyglutamine peptide K2Q23K2, using sedimentation, static and dynamic light scattering, and size exclusion chromatography. Our data show that during the lag time in sedimentation kinetics, there is substantial organization of the peptide into soluble linear aggregates. These aggregates have no regular secondary structure as measured by circular dichroism but have particle dimensions and morphologies similar to those of mature insoluble aggregates. The soluble aggregates constitute approximately 30% of the total peptide mass, form rapidly, and continue to grow over a period of hours to days, eventually precipitating. Once insoluble aggregates form, loss of monomer from the solution phase continues. Our data support an assembly mechanism for polyglutamine peptide more complex than that previously proposed.

  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. Silica nanoparticles separation from water: aggregation by cetyltrimethylammonium bromide (CTAB).

    PubMed

    Liu, Y; Tourbin, M; Lachaize, S; Guiraud, P

    2013-07-01

    Nanoparticles will inevitably be found in industrial and domestic wastes in the near future and as a consequence soon in water resources. Due to their ultra-small size, nanoparticles may not only have new hazards for environment and human health, but also cause low separation efficiency by classical water treatments processes. Thus, it would be an important challenge to develop a specific treatment with suitable additives for recovery of nanoparticles from waters. For this propose, this paper presents aggregation of silica nanoparticles (Klebosol 30R50 (75nm) and 30R25 (30nm)) by cationic surfactant cetyltrimethylammonium bromide (CTAB). Different mechanisms such as charge neutralization, "depletion flocculation" or "volume-restriction", and "hydrophobic effect" between hydrocarbon tails of CTAB have been proposed to explicate aggregation results. One important finding is that for different volume concentrations between 0.05% and 0.51% of 30R50 suspensions, the same critical coagulation concentration was observed at CTAB=0.1mM, suggesting the optimized quantity of CTAB during the separation process for nanoparticles of about 75nm. Furthermore, very small quantities of CTAB (0.01mM) can make 30R25 nanosilica aggregated due to the "hydrophobic effect". It is then possible to minimize the sludge and allow the separation process as "greener" as possible by studying this case. It has also shown that aggregation mechanisms can be different for very small particles so that a special attention has to be paid to the treatment of nanoparticles contained in water and wastewaters.

  14. Native metastable prefibrillar oligomers are the most neurotoxic species among amyloid aggregates.

    PubMed

    Diociaiuti, Marco; Macchia, Gianfranco; Paradisi, Silvia; Frank, Claudio; Camerini, Serena; Chistolini, Pietro; Gaudiano, Maria Cristina; Petrucci, Tamara Corinna; Malchiodi-Albedi, Fiorella

    2014-09-01

    Many proteins belonging to the amyloid family share the tendency to misfold and aggregate following common steps, and display similar neurotoxicity. In the aggregation pathway different kinds of species are formed, including several types of oligomers and eventually mature fibers. It is now suggested that the pathogenic aggregates are not the mature fibrils, but the intermediate, soluble oligomers. Many kinds of aggregates have been described to exist in a metastable state and in equilibrium with monomers. Up to now it is not clear whether a specific structure is at the basis of the neurotoxicity. Here we characterized, starting from the early aggregation stages, the oligomer populations formed by an amyloid protein, salmon calcitonin (sCT), chosen due to its very slow aggregation rate. To prepare different oligomer populations and characterize them by means of photoinduced cross-linking SDS-PAGE, Energy Filtered-Transmission Electron Microscopy (EF-TEM) and Circular Dichroism (CD) spectroscopy, we used Size Exclusion Chromatography (SEC), a technique that does not influence the aggregation process leaving the protein in the native state. Taking advantage of sCT low aggregation rate, we characterized the neurotoxic potential of the SEC-separated, non-crosslinked fractions in cultured primary hippocampal neurons, analyzing intracellular Ca(2+) influx and apoptotic trend. We provide evidence that native, globular, metastable, prefibrillar oligomers (dimers, trimers and tetramers) were the toxic species and that low concentrations of these aggregates in the population was sufficient to render the sample neurotoxic. Monomers and other kind of aggregates, such as annular or linear protofibers and mature fibers, were totally biologically inactive. PMID:24932517

  15. Composition, buoyancy regulation and fate of ice algal aggregates in the Central Arctic Ocean.

    PubMed

    Fernández-Méndez, Mar; Wenzhöfer, Frank; Peeken, Ilka; Sørensen, Heidi L; Glud, Ronnie N; Boetius, Antje

    2014-01-01

    Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8-35 and 9-40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m(-2), maintaining an estimated net primary production of 0.4-40 mg C m(-2) d(-1), and accounted for 3-80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities. PMID:25208058

  16. Composition, buoyancy regulation and fate of ice algal aggregates in the Central Arctic Ocean.

    PubMed

    Fernández-Méndez, Mar; Wenzhöfer, Frank; Peeken, Ilka; Sørensen, Heidi L; Glud, Ronnie N; Boetius, Antje

    2014-01-01

    Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8-35 and 9-40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m(-2), maintaining an estimated net primary production of 0.4-40 mg C m(-2) d(-1), and accounted for 3-80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities.

  17. Composition, Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean

    PubMed Central

    Fernández-Méndez, Mar; Wenzhöfer, Frank; Peeken, Ilka; Sørensen, Heidi L.; Glud, Ronnie N.; Boetius, Antje

    2014-01-01

    Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8–35 and 9–40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m−2, maintaining an estimated net primary production of 0.4–40 mg C m−2 d−1, and accounted for 3–80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities. PMID:25208058

  18. Impact of asymmetrical flow field-flow fractionation on protein aggregates stability.

    PubMed

    Bria, Carmen R M; Williams, S Kim Ratanathanawongs

    2016-09-23

    The impact of asymmetrical flow field-flow fractionation (AF4) on protein aggregate species is investigated with the aid of multiangle light scattering (MALS) and dynamic light scattering (DLS). The experimental parameters probed in this study include aggregate stability in different carrier liquids, shear stress (related to sample injection), sample concentration (during AF4 focusing), and sample dilution (during separation). Two anti-streptavidin (anti-SA) IgG1 samples composed of low and high molar mass (M) aggregates are subjected to different AF4 conditions. Aggregates suspended and separated in phosphate buffer are observed to dissociate almost entirely to monomer. However, aggregates in citric acid buffer are partially stable with dissociation to 25% and 5% monomer for the low and high M samples, respectively. These results demonstrate that different carrier liquids change the aggregate stability and low M aggregates can behave differently than their larger counterparts. Increasing the duration of the AF4 focusing step showed no significant changes in the percent monomer, percent aggregates, or the average Ms in either sample. Syringe-induced shear related to sample injection resulted in an increase in hydrodynamic diameter (dh) as measured by batch mode DLS. Finally, calculations showed that dilution during AF4 separation is significantly lower than in size exclusion chromatography with dilution occurring mainly at the AF4 channel outlet and not during the separation. This has important ramifications when analyzing aggregates that rapidly dissociate (<∼2s) upon dilution as the size calculated by AF4 theory may be more accurate than that measured by online DLS. Experimentally, the dhs determined by online DLS generally agreed with AF4 theory except for the more well retained larger aggregates for which DLS showed smaller sizes. These results highlight the importance of using AF4 retention theory to understand the impacts of dilution on analytes. PMID

  19. Anisotropic diffusion-limited aggregation.

    PubMed

    Popescu, M N; Hentschel, H G E; Family, F

    2004-06-01

    Using stochastic conformal mappings, we study the effects of anisotropic perturbations on diffusion-limited aggregation (DLA) in two dimensions. The harmonic measure of the growth probability for DLA can be conformally mapped onto a constant measure on a unit circle. Here we map m preferred directions for growth to a distribution on the unit circle, which is a periodic function with m peaks in [-pi,pi) such that the angular width sigma of the peak defines the "strength" of anisotropy kappa= sigma(-1) along any of the m chosen directions. The two parameters (m,kappa) map out a parameter space of perturbations that allows a continuous transition from DLA (for small enough kappa ) to m needlelike fingers as kappa--> infinity. We show that at fixed m the effective fractal dimension of the clusters D(m,kappa) obtained from mass-radius scaling decreases with increasing kappa from D(DLA) approximately 1.71 to a value bounded from below by D(min) = 3 / 2. Scaling arguments suggest a specific form for the dependence of the fractal dimension D(m,kappa) on kappa for large kappa which compares favorably with numerical results. PMID:15244564

  20. Modulation of the aggregation properties of sodium deoxycholate in presence of hydrophilic imidazolium based ionic liquid: water dynamics study to probe the structural alteration of the aggregates.

    PubMed

    Kundu, Niloy; Banik, Debasis; Roy, Arpita; Kuchlyan, Jagannath; Sarkar, Nilmoni

    2015-10-14

    In this article, we have investigated the effect of a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]-BF4), on the aggregation properties of a biological surfactant, sodium deoxycholate (NaDC), in water. In solution, unlike conventional surfactants it shows stepwise aggregation and the effect of the conventional ionic liquid on the aggregation properties is rather interesting. We have observed concentration dependent dual role of the ionic liquid; at their low concentration, the aggregated structure of NaDC reorganizes itself into an elongated rod like structure. However, the aggregated network is disintegrated into small aggregates upon further addition of ionic liquid. TEM (Transmission Electron Microscopy), SEM (Scanning Electron Microscopy) and FLIM (Fluorescence Lifetime Imaging Microscopy) images also confirmed the structural alteration of NaDC upon varying the concentration of the ionic liquid. The proton NMR data indicate that hydrophobic as well as electrostatic interaction is solely responsible for such structural adaptation of NaDC in the presence of an ionic liquid. The host-guest interaction inside the aggregates is monitored using Coumarin-153 (C-153) and the location of C-153 is probed by varying the excitation wavelength from 375 nm to 440 nm and the two binding sites of the aggregates are affected in a different fashion in the presence of ionic liquid. Excitation in the blue region selects the fluorophores which preferably bind to the buried region of the aggregates, whereas 440 nm excitation corresponds to the guest molecules which are exposed to the solvent molecules. The average solvation time of C-153 is increased in the presence of 1.68 wt% [bmim]-BF4 at λexc = 440 nm i.e. the probe molecules relocate themselves to a more restricted region. However, the average solvation time became 2.6 times faster in the presence of 11.2 wt% [bmim]-BF4, which corresponds to a more polar and exposed region. The time resolved

  1. The infrared spectral transmittance of Aspergillus niger spore aggregated particle swarm

    NASA Astrophysics Data System (ADS)

    Zhao, Xinying; Hu, Yihua; Gu, Youlin; Li, Le

    2015-10-01

    Microorganism aggregated particle swarm, which is quite an important composition of complex media environment, can be developed as a new kind of infrared functional materials. Current researches mainly focus on the optical properties of single microorganism particle. As for the swarm, especially the microorganism aggregated particle swarm, a more accurate simulation model should be proposed to calculate its extinction effect. At the same time, certain parameters deserve to be discussed, which helps to better develop the microorganism aggregated particle swarm as a new kind of infrared functional materials. In this paper, take Aspergillus Niger spore as an example. On the one hand, a new calculation model is established. Firstly, the cluster-cluster aggregation (CCA) model is used to simulate the structure of Aspergillus Niger spore aggregated particle. Secondly, the single scattering extinction parameters for Aspergillus Niger spore aggregated particle are calculated by using the discrete dipole approximation (DDA) method. Thirdly, the transmittance of Aspergillus Niger spore aggregated particle swarm is simulated by using Monte Carlo method. On the other hand, based on the model proposed above, what influences can wavelength causes has been studied, including the spectral distribution of scattering intensity of Aspergillus Niger spore aggregated particle and the infrared spectral transmittance of the aggregated particle swarm within the range of 8~14μm incident infrared wavelengths. Numerical results indicate that the scattering intensity of Aspergillus Niger spore aggregated particle reduces with the increase of incident wavelengths at each scattering angle. Scattering energy mainly concentrates on the scattering angle between 0~40°, forward scattering has an obvious effect. In addition, the infrared transmittance of Aspergillus Niger spore aggregated particle swarm goes up with the increase of incident wavelengths. However, some turning points of the trend

  2. Cosolute effects on amyloid aggregation in a nondiffusion limited regime: intrinsic osmolyte properties and the volume exclusion principle.

    PubMed

    Murray, Brian; Rosenthal, Joseph; Zheng, Zhongli; Isaacson, David; Zhu, Yingxi; Belfort, Georges

    2015-04-14

    The effects of cosolutes on amyloid aggregation kinetics in vivo are critical and not fully understood. To explore the effects of cosolute additives, the in vitro behavior of destabilizing and stabilizing osmolytes with polymer cosolutes on the aggregation of a model amyloid, human insulin, is probed using experiments coupled with an amyloid aggregation reaction model. The destabilizing osmolyte, guanidine hydrochloride (GuHCl), induces biphasic behavior on the amyloid aggregation rate exhibited by an enhancement of the aggregation kinetics at low concentrations of GuHCl (<0.6 M) and a reduction in kinetics at higher GuHCl concentrations. Stabilizing osmolytes, glycerol, sorbitol and trimethylamine N-oxide, slow the rate of aggregation by reducing the rate of monomer unfolding. Polymer cosolutes, polyvinylpyrrolidone 3.5 kDa and 40 kDa, delay amyloid aggregation mainly through a decrease in the nucleation reaction. These results are in good agreement with the volume exclusion principle for polymer crowding and supports the need to include conformational rearrangement of monomers prior to nucleation. Using fluorescence correlation spectroscopy, we demonstrate that amyloid aggregation is nondiffusion limited, except during fibril accumulation in the presence of high concentrations of long chain polymers. Lastly, the neutral surface area of osmolytes correlates well with the time to initiate fibril formation, tlag, which implicates an intrinsic osmolyte property underlying preferential interactions. PMID:25803421

  3. Effects of inter- and intra-aggregate magnetic dipolar interactions on the magnetic heating efficiency of iron oxide nanoparticles.

    PubMed

    Ovejero, J G; Cabrera, D; Carrey, J; Valdivielso, T; Salas, G; Teran, F J

    2016-04-28

    Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices.

  4. Effects of inter- and intra-aggregate magnetic dipolar interactions on the magnetic heating efficiency of iron oxide nanoparticles.

    PubMed

    Ovejero, J G; Cabrera, D; Carrey, J; Valdivielso, T; Salas, G; Teran, F J

    2016-04-28

    Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices. PMID:27041536

  5. Collision simulation of sintered dust aggregates

    NASA Astrophysics Data System (ADS)

    Sirono, Sin-iti; Ueno, Haruta

    Collisional evolution of dust aggregates is the initial process of the planet formation. Sticking velocity, below which collisional sticking of an aggregate happens, is a crucial quantity in the collisional evolution. In the standard model of protoplanetary nebula, the maximum collisional velocity is around 50m/s. Therefore, if a planetesimal is formed through direct collisional sticking, the sticking velocity should be higher than 50m/s. Even if a planetesimal is formed by other mechanism such as anticyclonic vortices, substantial growth of an aggregate is required because the motion of an aggregate should be decoupled from that of gas. Collisional simulation of icy dust aggregates (Wada et al. 2009, ApJ 702, 1490) showed that the sticking velocity was larger than 50m/s and planetesimal formation by collisional sticking was possible. However, sintering of ice proceeds in a wide area of a protoplanetary nebula (Sirono 2011, ApJ 765, 50). Sintering enlarges a neck, connection between adjacent dust grains, and changes the mechanical properties of a dust aggregate. Here we performed collisional simulations between sintered dust aggregates taking account of sintering. We found that the sticking velocity was decreased substantially down to 20m/s. This result suggests that a planetesimal is not formed by direct collisional sticking and that the planetesimal formation proceeded in particular regions in a protoplanetary nebula.

  6. Efficient clustering aggregation based on data fragments.

    PubMed

    Wu, Ou; Hu, Weiming; Maybank, Stephen J; Zhu, Mingliang; Li, Bing

    2012-06-01

    Clustering aggregation, known as clustering ensembles, has emerged as a powerful technique for combining different clustering results to obtain a single better clustering. Existing clustering aggregation algorithms are applied directly to data points, in what is referred to as the point-based approach. The algorithms are inefficient if the number of data points is large. We define an efficient approach for clustering aggregation based on data fragments. In this fragment-based approach, a data fragment is any subset of the data that is not split by any of the clustering results. To establish the theoretical bases of the proposed approach, we prove that clustering aggregation can be performed directly on data fragments under two widely used goodness measures for clustering aggregation taken from the literature. Three new clustering aggregation algorithms are described. The experimental results obtained using several public data sets show that the new algorithms have lower computational complexity than three well-known existing point-based clustering aggregation algorithms (Agglomerative, Furthest, and LocalSearch); nevertheless, the new algorithms do not sacrifice the accuracy. PMID:22334025

  7. Antimicrobial preservatives induce aggregation of interferon alpha-2a: the order in which preservatives induce protein aggregation is independent of the protein.

    PubMed

    Bis, Regina L; Mallela, Krishna M G

    2014-09-10

    Antimicrobial preservatives (APs) are included in liquid multi-dose protein formulations to combat the growth of microbes and bacteria. These compounds have been shown to cause protein aggregation, which leads to serious immunogenic and toxic side-effects in patients. Our earlier work on a model protein cytochrome c (Cyt c) demonstrated that APs cause protein aggregation in a specific manner. The aim of this study is to validate the conclusions obtained from our model protein studies on a pharmaceutical protein. Interferon α-2a (IFNA2) is available as a therapeutic treatment for numerous immune-compromised disorders including leukemia and hepatitis C, and APs have been used in its multi-dose formulation. Similar to Cyt c, APs induced IFNA2 aggregation, demonstrated by the loss of soluble monomer and increase in solution turbidity. The extent of IFNA2 aggregation increased with the increase in AP concentration. IFNA2 aggregation also depended on the nature of AP, and followed the order m-cresol>phenol>benzyl alcohol>phenoxyethanol. This specific order exactly matched with that observed for the model protein Cyt c. These and previously published results on antibodies and other recombinant proteins suggest that the general mechanism by which APs induce protein aggregation may be independent of the protein.

  8. 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

  9. Seasonal variability of soil aggregate stability

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  10. Archean Earth Atmosphere Fractal Haze Aggregates: Light Scattering Calculations and the Faint Young Sun Paradox

    NASA Astrophysics Data System (ADS)

    Boness, D. A.; Terrell-Martinez, B.

    2010-12-01

    As part of an ongoing undergraduate research project of light scattering calculations involving fractal carbonaceous soot aggregates relevant to current anthropogenic and natural sources in Earth's atmosphere, we have read with interest a recent paper [E.T. Wolf and O.B Toon,Science 328, 1266 (2010)] claiming that the Faint Young Sun paradox discussed four decades ago by Carl Sagan and others can be resolved without invoking heavy CO2 concentrations as a greenhouse gas warming the early Earth enough to sustain liquid water and hence allow the origin of life. Wolf and Toon report that a Titan-like Archean Earth haze, with a fractal haze aggregate nature due to nitrogen-methane photochemistry at high altitudes, should block enough UV light to protect the warming greenhouse gas NH3 while allowing enough visible light to reach the surface of the Earth. To test this hypothesis, we have employed a rigorous T-Matrix arbitrary-particle light scattering technique, to avoid the simplifications inherent in Mie-sphere scattering, on haze fractal aggregates at UV and visible wavelenths of incident light. We generate these model aggregates using diffusion-limited cluster aggregation (DLCA) algorithms, which much more closely fit actual haze fractal aggregates than do diffusion-limited aggregation (DLA) algorithms.

  11. Aggregation of DNA by analogs of spermidine; enzymatic and structural studies.

    PubMed Central

    Srivenugopal, K S; Wemmer, D E; Morris, D R

    1987-01-01

    A homologous series of spermidine analogs, with defined abilities to replace the natural polyamine in supporting cell growth, was examined for its influence on the structure of supercoiled, aggregated DNA and on the ability of the DNA aggregates to act as substrates for various enzymes. The concentration of amine necessary to aggregate negatively supercoiled Col E1 DNA was progressively increased as the diaminobutane moiety of spermidine was extended beyond 5 methylene groups. 1H- and 31P-NMR spectroscopy suggested that less rigid DNA aggregates were formed by spermidine analogs than by spermidine itself. Spermidine and its analogs differentially modulated the activities of bacterial and mammalian type I topoisomerases and EcoRI restriction endonuclease on aggregated DNA in a manner reminiscent of the abilities of the amines to stimulate cell growth. When DNA was not aggregated, the influence of the various amines on these reactions was almost identical. These results are discussed in relation to the structures of the DNA aggregates in the presence of the various triamines. Images PMID:3031604

  12. The βγ-crystallins: native state stability and pathways to aggregation.

    PubMed

    Serebryany, Eugene; King, Jonathan A

    2014-07-01

    The βγ-crystallins are among the most stable and long-lived proteins in the human body. With increasing age, however, they transform to high molecular weight light-scattering aggregates, resulting in cataracts. This occurs despite the presence in the lens of high concentrations of the a-crystallin chaperones. Aggregation of crystallins can be induced in vitro by a variety of stresses, including acidic pH, ultraviolet light, oxidative damage, heating or freezing, and specific amino acid substitutions. Accumulating evidence points to the existence of specific biochemical pathways of protein: protein interaction and polymerization. We review the methods used for studying crystallin stability and aggregation and discuss the sometimes counterintuitive relationships between factors that favor native state stability and those that favor non-native aggregation. We discuss the behavior of βγ-crystallins in mixtures and their chaperone ability; the consequences of missense mutations and covalent damage to the side-chains; and the evolutionary strategies that have shaped these proteins. Efforts are ongoing to reveal the nature of cataractous crystallin aggregates and understand the mechanisms of aggregation in the context of key models of protein polymerization: amyloid, native-state, and domain-swapped. Such mechanistic understanding is likely to be of value for the development of therapeutic interventions and draw attention to unanswered questions about the relationship between a protein's native state stability and its transformation to an aggregated state.

  13. UV-induced self-aggregation of E. coli after low and medium pressure ultraviolet irradiation.

    PubMed

    Kollu, Kerim; Örmeci, Banu

    2015-07-01

    Presence of aggregated bacteria has been shown to decrease the efficacy of ultraviolet (UV) disinfection and there is some indication that UV irradiation may promote aggregation of bacteria among themselves. This study aims to provide an in-depth understanding of the effect of UV light on inducing self-aggregation of Escherichia coli bacteria by using microscopy and particle counter analysis techniques. The bacteria were observed and quantified before and after UV irradiation by employing size and concentration parameters. Four doses of low-pressure (LP) UV irradiation, 20, 40, 60 and 80 mJ/cm(2), and two doses of medium-pressure (MP) UV irradiation, 40 and 80 mJ/cm(2), were tested. At all LP UV doses tested, a significant increase in particle size was observed following UV exposure, indicating UV-induced self-aggregation. However, the magnitude of UV dose did not seem to have an impact. In the MP UV experiments, only a dose of 80 mJ/cm(2) had a significant impact on the formation of aggregates upon UV exposure. Changing the light intensity and exposure time to deliver the same LP UV dose resulted in different levels of aggregation. The results indicated that UV light intensity and wavelength may play a role in aggregation of bacteria. PMID:26002538

  14. Effects of oxidative modification on thermal aggregation and gel properties of soy protein by malondialdehyde.

    PubMed

    Wu, Wei; Hua, Yufei; Lin, Qinlu

    2014-03-01

    Malondialdehyde (MDA) was selected as a representative of lipid peroxidation products to investigate the effects of oxidative modification on thermal aggregation and gel properties of soy protein by lipid peroxidation products. Incubation of soy protein with increasing concentration of MDA resulted in gradual decrease of particle size and content of thermal aggregates during heat denaturation. Oxidative modification by MDA resulted in a decrease in water holding capacity, gel hardness, and gel strength of soy protein gel. An increase in coarseness and interstice of MDA modified protein gel network was accompanied by uneven distribution of interstice as MDA concentration increased. The results showed that degree of thermal aggregation of MDA-modified soy protein gradually decreased as MDA concentration increased, which contributed to a decrease in water holding capacity, gel hardness, and gel strength of MDA-modified soy protein gel. PMID:24587523

  15. Directional sensing and streaming in Dictyostelium aggregation.

    PubMed

    Almeida, Sofia; Dilão, Rui

    2016-05-01

    We merge the Kessler-Levine simple discrete model for Dictyostelium cyclic adenosine monophosphate (cAMP) production and diffusion with the Dilão-Hauser directional sensing aggregation mechanism. The resulting compound model describes all the known transient patterns that emerge during Dictyostelium aggregation, which include the spontaneous formation of cAMP self-sustained target and spiral waves and streaming. We show that the streaming patterns depend on the speed of the amoebae, on the relaxation time for the production of cAMP, on the cAMP degradation rate, and on directional sensing. Moreover, we show that different signaling centers emerge during Dictyostelium aggregation. PMID:27300919

  16. Directional sensing and streaming in Dictyostelium aggregation

    NASA Astrophysics Data System (ADS)

    Almeida, Sofia; Dilão, Rui

    2016-05-01

    We merge the Kessler-Levine simple discrete model for Dictyostelium cyclic adenosine monophosphate (cAMP) production and diffusion with the Dilão-Hauser directional sensing aggregation mechanism. The resulting compound model describes all the known transient patterns that emerge during Dictyostelium aggregation, which include the spontaneous formation of cAMP self-sustained target and spiral waves and streaming. We show that the streaming patterns depend on the speed of the amoebae, on the relaxation time for the production of cAMP, on the cAMP degradation rate, and on directional sensing. Moreover, we show that different signaling centers emerge during Dictyostelium aggregation.

  17. A look at construction aggregates production

    USGS Publications Warehouse

    Willett, Jason Christopher

    2009-01-01

    Construction aggregates are defined as the combination of crushed stone and construction sand and gravel. Aggregates are one of the most accessible natural resources on Earth and one of the fundamental building blocks of our society. They have been used from the earliest times of our civilization for a variety of applications that have increased in number and complexity with time and technological progress. Despite the relatively low but increasing unit value of its basic products, the construction aggregates industry is a major contributor to and an indicator of the economic well-being of the nation.

  18. Reusing recycled aggregates in structural concrete

    NASA Astrophysics Data System (ADS)

    Kou, Shicong

    The utilization of recycled aggregates in concrete can minimize environmental impact and reduce the consumption of natural resources in concrete applications. The aim of this thesis is to provide a scientific basis for the possible use of recycled aggregates in structure concrete by conducting a comprehensive programme of laboratory study to gain a better understanding of the mechanical, microstructure and durability properties of concrete produced with recycled aggregates. The study also explored possible techniques to of improve the properties of recycled aggregate concrete that is produced with high percentages (≧ 50%) of recycled aggregates. These techniques included: (a) using lower water-to-cement ratios in the concrete mix design; (b) using fly ash as a cement replacement or as an additional mineral admixture in the concrete mixes, and (c) precasting recycled aggregate concrete with steam curing regimes. The characteristics of the recycled aggregates produced both from laboratory and a commercially operated pilot construction and demolition (C&D) waste recycling plant were first studied. A mix proportioning procedure was then established to produce six series of concrete mixtures using different percentages of recycled coarse aggregates with and without the use of fly ash. The water-to-cement (binder) ratios of 0.55, 0.50, 0.45 and 0.40 were used. The fresh properties (including slump and bleeding) of recycled aggregate concrete (RAC) were then quantified. The effects of fly ash on the fresh and hardened properties of RAC were then studied and compared with those RAC prepared with no fly ash addition. Furthermore, the effects of steam curing on the hardened properties of RAC were investigated. For micro-structural properties, the interfacial transition zones of the aggregates and the mortar/cement paste were analyzed by SEM and EDX-mapping. Moreover, a detailed set of results on the fracture properties for RAC were obtained. Based on the experimental

  19. Exciton dynamics in perturbed vibronic molecular aggregates

    PubMed Central

    Brüning, C.; Wehner, J.; Hausner, J.; Wenzel, M.; Engel, V.

    2015-01-01

    A site specific perturbation of a photo-excited molecular aggregate can lead to a localization of excitonic energy. We investigate this localization dynamics for laser-prepared excited states. Changing the parameters of the electric field significantly influences the exciton localization which offers the possibility for a selective control of this process. This is demonstrated for aggregates possessing a single vibrational degree of freedom per monomer unit. It is shown that the effects identified for the molecular dimer can be generalized to larger aggregates with a high density of vibronic states. PMID:26798840

  20. Directional sensing and streaming in Dictyostelium aggregation.

    PubMed

    Almeida, Sofia; Dilão, Rui

    2016-05-01

    We merge the Kessler-Levine simple discrete model for Dictyostelium cyclic adenosine monophosphate (cAMP) production and diffusion with the Dilão-Hauser directional sensing aggregation mechanism. The resulting compound model describes all the known transient patterns that emerge during Dictyostelium aggregation, which include the spontaneous formation of cAMP self-sustained target and spiral waves and streaming. We show that the streaming patterns depend on the speed of the amoebae, on the relaxation time for the production of cAMP, on the cAMP degradation rate, and on directional sensing. Moreover, we show that different signaling centers emerge during Dictyostelium aggregation.

  1. Aggregation of ice crystals in cirrus

    NASA Technical Reports Server (NTRS)

    Kajikawa, Masahiro; Heymsfield, Andrew J.

    1989-01-01

    Results are given from analysis of the aggregation of thick plate, columnar, and bullet rosette ice crystals in cirrus. Data were obtained from PMS 2D-C images, oil coated slides, and aircraft meteorological measurements. Crystal size ranged from 100 to 900 microns in temperatures from -30 to -45 C. The results indicate that the ratio of the sizes of aggregating crystals and the difference of their terminal velocities are important in aggregation. The collection efficiency was calculated for the thick plate crystals from the same data.

  2. Community Advisory Committee (CAC) Leadership Training.

    ERIC Educational Resources Information Center

    Carlisle, Lynn; Lesniak, Pat

    This document presents one module in a set of training resources for trainers to use with parents and/or professionals serving children with disabilities; focus is on community advisory committee leadership training. The modules stress content and activities that build skills and offer resources to promote parent-professional collaboration. Each…

  3. Selective detection of NADPH among four pyridine-nucleotide cofactors by a fluorescent probe based on aggregation-induced emission.

    PubMed

    Noguchi, Takao; Dawn, Arnab; Yoshihara, Daisuke; Tsuchiya, Youichi; Yamamoto, Tatsuhiro; Shinkai, Seiji

    2013-05-14

    A fluorescent sensor based on guanidinium-tethered tetraphenylethene (TPE) has been investigated toward the differentiation of pyridine nucleotide cofactors (NAD(+) , NADH, NADP(+) , and NADPH). TPE selectively recognizes NADPH possessing the higher tetra-anionic net-charge, resulting in the steep "turn-on" fluorescence increase. The comparative aggregation behaviors and fluorescence response studies of TPE on the four cofactors reveal that the critical aggregate concentration of TPE against NADPH correlates directly with the concentration threshold for the fluorescence response. These results establish that TPE can selectively differentiate NADPH over the other three cofactors by the steep aggregation-induced fluorescence response accompanied by the high signal-to-background contrast.

  4. Influence of biomacromolecules and humic acid on the aggregation kinetics of single-walled carbon nanotubes.

    PubMed

    Saleh, Navid B; Pfefferle, Lisa D; Elimelech, Menachem

    2010-04-01

    The initial aggregation kinetics of single-walled carbon nanotubes (SWNTs) were studied using time-resolved dynamic light scattering. Aggregation of SWNTs was evaluated in the presence of natural organic matter [Suwannee River humic acid (SRHA)], polysaccharide (alginate), protein [bovine serum albumin (BSA)], and cell culture medium [Luria-Bertani (LB) broth] with varying solution concentrations of monovalent (NaCl) and divalent (CaCl(2)) salts. Increasing salt concentration and adding divalent calcium ions induced SWNT aggregation by screening electrostatic charge and thereby suppressing electrostatic repulsion, similar to observations with aquatic colloidal particles. The presence of biomacromolecules significantly retarded the SWNT aggregation rate. BSA protein molecules were most effective in reducing the rate of aggregation followed by SRHA, LB, and alginate. The slowing of the SWNT aggregation rate in the presence of the biomacromolecules and SRHA can be attributed to steric repulsion originating from the adsorbed macromolecular layer. The remarkably enhanced SWNT stability in the presence of BSA, compared to that with the other biomacromolecules and SRHA, is ascribed to the BSA globular molecular structure that enhances steric repulsion. The results have direct implications for the fate and behavior of SWNTs in aquatic environments and biological media.

  5. Mucin aggregation from a rod-like meso-scale model

    NASA Astrophysics Data System (ADS)

    Moreno, Nicolas; Perilla, Jairo E.; Colina, Coray M.; Lísal, Martin

    2015-05-01

    Dissipative particle dynamics, a meso-scale particle-based model, was used to study the aggregation of mucins in aqueous solutions. Concentration, strength of the mucin-water interactions, as well as the effects of size, shape, and composition of the model molecules were studied. Model proteins were represented as rod-like objects formed by coarse-grained beads. In the first model, only one type of beads formed the mucin. It was found that all the surfaces were available to form aggregates and the conformation of the aggregates was a function of the strength of the mucin-water interaction. With this model, the number of aggregates was unaffected by the initial position of the mucins in the simulation box, except for the lowest mucin concentration. In a more refined mucin model, two kinds of beads were used in the molecule in order to represent the existence of cysteine-like terminal groups in the actual molecule. With this new scheme, aggregation took place by the interaction of the terminal groups between model molecules. The kinetic analysis of the evolution of the number of aggregates with time was also studied for both mucin models.

  6. Platelet-collagen adhesion enhances platelet aggregation induced by binding of VWF to platelets

    SciTech Connect

    Laduca, F.M.; Bell, W.R.; Bettigole, R.E. State Univ. of New York, Buffalo )

    1987-11-01

    Ristocetin-induced platelet aggregation (RIPA) was evaluated in the presence of platelet-collagen adhesion. RIPA of normal donor platelet-rich plasma (PRP) demonstrated a primary wave of aggregation mediated by the binding of von Willebrand factor (VWF) to platelets and a secondary aggregation wave, due to a platelet-release reaction, initiated by VWF-platelet binding and inhibitable by acetylsalicylic acid (ASA). An enhanced RIPA was observed in PRP samples to which collagen had been previously added. These subthreshold concentrations of collagen, which by themselves were insufficient to induce aggregation, caused measurable platelet-collagen adhesion. Subthreshold collagen did not cause microplatelet aggregation, platelet release of ({sup 3}H)serotonin, or alter the dose-responsive binding of {sup 125}I-labeled VWF to platelets, which occurred with increasing ristocetin concentrations. However, ASA inhibition of the platelet release reaction prevented collagen-enhanced RIPA. These results demonstrate that platelet-collagen adhesion altered the platelet-release reaction induced by the binding of VWF to platelets causing a platelet-release reaction at a level of VWF-platelet binding not normally initiating a secondary aggregation. These findings suggest that platelet-collagen adhesion enhances platelet function mediated by VWF.

  7. [THE INFLUENCE OF HYDROGEN SULFIDE ON COLLAGEN-INDUCED AGGREGATION OF HUMAN PLATELETS].

    PubMed

    Petrova, I V; Trubacheva, O A; Mangataeva, O S; Suslova, T E; Kovalev, I V; Gusakova, S V

    2015-10-01

    Study the impact of hydrogen sulfide on collagen-induced platelet aggregation from healthy donors and patients with type 2 diabetes. In healthy individuals, in contrast to patients with type 2 diabetes, NaHS significantly inhibited platelet aggregation. Activators of cAMP signaling (forskolin and phosphodiesterase inhibitor) significantly reduced platelet aggregation in both groups of examinees. NO-synthase inhibitors increased platelet aggregation in healthy volunteers, but not in patients with type 2 diabetes. The presence of H2S donor did not alter the extent of platelet aggregation at high concentrations of cAMP or decreased production of nitric oxide. It is assumed that the antiplatelet effect of H2S is not associated with the effect on the signal system, mediated cAMP or nitric oxide. Change H2S-dependent regulation of platelet aggregation in patients with type 2 diabetes is caused by disorders have been reported with this disease: the increase of intracellular calcium ion concentration, oxidative damage to proteins, hyperhomocysteinemia, glycosylation of key proteins involved in this process.

  8. A Molecular Dynamics Study of Tributyl Phosphate and Diamyl Amyl Phosphonate Self-Aggregation in Dodecane and Octane.

    PubMed

    Servis, Michael J; Tormey, Caleb A; Wu, David T; Braley, Jenifer C

    2016-03-17

    A molecular dynamics model for tributyl phosphate (TBP) and diamyl amyl phosphonate (DAAP) is presented using the Generalized AMBER Force Field (GAFF) and the AM1-BCC method for calculated atomic charges with a modification to the phosphorus-containing dihedral parameters. The density and average molecular dipole in a neat liquid simulation, and dimerization in dodecane and octane diluents, compare favorably to experimental values. At low extractant concentration, investigation of the dimer structure reveals the offset "head-to-head" orientation as the predominant structure over a range of TBP and DAAP concentrations with a phosphoryl oxygen separation distance between dimerized extractants of 3-5.5 Å. At high extractant concentrations, a graph analysis of extractant aggregates was used to determine concentrations of each aggregate size and the average coordination number, which gives a measure of the linearity of the aggregates. For aggregates up to 7 extractant molecules, the mean free energy of association per molecule was found to be 0.55-0.59 and 0.72 kcal/mol for TBP and DAAP, respectively. In both diluents, TBP formed large aggregates more frequently than DAAP, and those aggregates were more nonlinear than their DAAP equivalents. This finding anticipates differences in aggregation chemistry between TBP and DAAP in PUREX extraction systems. PMID:26886767

  9. A Molecular Dynamics Study of Tributyl Phosphate and Diamyl Amyl Phosphonate Self-Aggregation in Dodecane and Octane.

    PubMed

    Servis, Michael J; Tormey, Caleb A; Wu, David T; Braley, Jenifer C

    2016-03-17

    A molecular dynamics model for tributyl phosphate (TBP) and diamyl amyl phosphonate (DAAP) is presented using the Generalized AMBER Force Field (GAFF) and the AM1-BCC method for calculated atomic charges with a modification to the phosphorus-containing dihedral parameters. The density and average molecular dipole in a neat liquid simulation, and dimerization in dodecane and octane diluents, compare favorably to experimental values. At low extractant concentration, investigation of the dimer structure reveals the offset "head-to-head" orientation as the predominant structure over a range of TBP and DAAP concentrations with a phosphoryl oxygen separation distance between dimerized extractants of 3-5.5 Å. At high extractant concentrations, a graph analysis of extractant aggregates was used to determine concentrations of each aggregate size and the average coordination number, which gives a measure of the linearity of the aggregates. For aggregates up to 7 extractant molecules, the mean free energy of association per molecule was found to be 0.55-0.59 and 0.72 kcal/mol for TBP and DAAP, respectively. In both diluents, TBP formed large aggregates more frequently than DAAP, and those aggregates were more nonlinear than their DAAP equivalents. This finding anticipates differences in aggregation chemistry between TBP and DAAP in PUREX extraction systems.

  10. Concentration-driven growth of model protocell membranes.

    PubMed

    Budin, Itay; Debnath, Anik; Szostak, Jack W

    2012-12-26

    The first protocell membranes may have assembled from fatty acids and related single-chain lipids available in the prebiotic environment. Prior to the evolution of complex cellular machinery, spontaneous protocell membrane growth and division had to result from the intrinsic physicochemical properties of these molecules, in the context of specific environmental conditions. Depending on the nature of the chemical and physical environment, fatty acids can partition between several different phases, including soluble monomers, micelles, and lamellar vesicles. Here we address the concentration dependence of fatty acid aggregation, which is dominated by entropic considerations. We quantitatively distinguish between fatty acid phases using a combination of physical and spectroscopic techniques, including the use of the fluorescent fatty acid analogue Laurdan, whose emission spectrum is sensitive to structural differences between micellar and lamellar aggregates. We find that the monomer-aggregate transition largely follows a characteristic pseudophase model of molecular aggregation but that the composition of the aggregate phase is also concentration dependent. At low amphiphile concentrations above the critical aggregate concentration, vesicles coexist with a significant proportion of micelles, while more concentrated solutions favor the lamellar vesicle phase. We subsequently show that the micelle-vesicle equilibrium can be used to drive the growth of pre-existing vesicles upon an increase in amphiphile concentration either through solvent evaporation or following the addition of excess lipids. We propose a simple model for a primitive environmentally driven cell cycle, in which protocell membrane growth results from evaporative concentration, followed by shear force or photochemically induced division. PMID:23198690

  11. Computational selection of inhibitors of Abeta aggregation and neuronal toxicity.

    PubMed

    Chen, Deliang; Martin, Zane S; Soto, Claudio; Schein, Catherine H

    2009-07-15

    Alzheimer's disease (AD) is characterized by the cerebral accumulation of misfolded and aggregated amyloid-beta protein (Abeta). Disease symptoms can be alleviated, in vitro and in vivo, by 'beta-sheet breaker' pentapeptides that reduce plaque load. However the peptide nature of these compounds, made them biologically unstable and unable to penetrate membranes with high efficiency. The main goal of this study was to use computational methods to identify small molecule mimetics with better drug-like properties. For this purpose, the docked conformations of the active peptides were used to identify compounds with similar activities. A series of related beta-sheet breaker peptides were docked to solid state NMR structures of a fibrillar form of Abeta. The lowest energy conformations of the active peptides were used to design three dimensional (3D)-pharmacophores, suitable for screening the NCI database with Unity. Small molecular weight compounds with physicochemical features and a conformation similar to the active peptides were selected, ranked by docking and biochemical parameters. Of 16 diverse compounds selected for experimental screening, 2 prevented and reversed Abeta aggregation at 2-3microM concentration, as measured by Thioflavin T (ThT) fluorescence and ELISA assays. They also prevented the toxic effects of aggregated Abeta on neuroblastoma cells. Their low molecular weight and aqueous solubility makes them promising lead compounds for treating AD.

  12. Aluminum induces tau aggregation in vitro but not in vivo.

    PubMed

    Mizoroki, Tatsuya; Meshitsuka, Shunsuke; Maeda, Sumihiro; Murayama, Miyuki; Sahara, Naruhiko; Takashima, Akihiko

    2007-07-01

    Etiological studies suggest that aluminum (Al) intake might increase an individual's risk of developing Alzheimer's disease (AD). Biochemical analysis data on the effects of Al, however, are inconsistent. Hence, the pathological involvement of Al in AD remains unclear. If Al is involved in AD, then it is reasonable to hypothesize that Al might be involved in the formation of either amyloid plaques or neurofibrillary tangles (NFTs). Here, we investigated whether Al might be involved in NFT formation by using an in vitro tau aggregation paradigm, a tau-overexpressing neuronal cell line (N2a), and a tau-overexpressing mouse model. Although Al induced tau aggregation in a heparin-induced tau assembly assay, these aggregates were neither thioflavin T positive nor did they resemble tau fibrils seen in human AD brains. With cell lysates from stable cell lines overexpressing tau, the accumulation of SDS-insoluble tau increased when the lysates were treated with at least 100 muM Al-maltolate. Yet Al-maltolate caused illness or death in transgenic mice overexpressing human tau and in non-transgenic littermates well before the Al concentration in the brain reached 100 muM. These results indicate that Al has no direct link to AD pathology.

  13. Tensile strength and fracture of cemented granular aggregates.

    PubMed

    Affes, R; Delenne, J-Y; Monerie, Y; Radjaï, F; Topin, V

    2012-11-01

    Cemented granular aggregates include a broad class of geomaterials such as sedimentary rocks and some biomaterials such as the wheat endosperm. We present a 3D lattice element method for the simulation of such materials, modeled as a jammed assembly of particles bound together by a matrix partially filling the interstitial space. From extensive simulation data, we analyze the mechanical properties of aggregates subjected to tensile loading as a function of matrix volume fraction and particle-matrix adhesion. We observe a linear elastic behavior followed by a brutal failure along a fracture surface. The effective stiffness before failure increases almost linearly with the matrix volume fraction. We show that the tensile strength of the aggregates increases with both the increasing tensile strength at the particle-matrix interface and decreasing stress concentration as a function of matrix volume fraction. The proportion of broken bonds in the particle phase reveals a range of values of the particle-matrix adhesion and matrix volume fraction for which the cracks bypass the particles and hence no particle damage occurs. This limit is shown to depend on the relative toughness of the particle-matrix interface with respect to the particles.

  14. Tensile strength and fracture of cemented granular aggregates.

    PubMed

    Affes, R; Delenne, J-Y; Monerie, Y; Radjaï, F; Topin, V

    2012-11-01

    Cemented granular aggregates include a broad class of geomaterials such as sedimentary rocks and some biomaterials such as the wheat endosperm. We present a 3D lattice element method for the simulation of such materials, modeled as a jammed assembly of particles bound together by a matrix partially filling the interstitial space. From extensive simulation data, we analyze the mechanical properties of aggregates subjected to tensile loading as a function of matrix volume fraction and particle-matrix adhesion. We observe a linear elastic behavior followed by a brutal failure along a fracture surface. The effective stiffness before failure increases almost linearly with the matrix volume fraction. We show that the tensile strength of the aggregates increases with both the increasing tensile strength at the particle-matrix interface and decreasing stress concentration as a function of matrix volume fraction. The proportion of broken bonds in the particle phase reveals a range of values of the particle-matrix adhesion and matrix volume fraction for which the cracks bypass the particles and hence no particle damage occurs. This limit is shown to depend on the relative toughness of the particle-matrix interface with respect to the particles. PMID:23160765

  15. Antithrombotic activity of Vitis labrusca extract on rat platelet aggregation.

    PubMed

    Kwon, Se-Uk; Lee, Hoon-Yeon; Xin, Mingjie; Ji, Su-Jeong; Cho, Hyoung-Kwon; Kim, Dae-Sung; Kim, Dae-Ki; Lee, Young-Mi

    2016-03-01

    Vitis labrusca is a grapevine that has antioxidant, neuroprotective, hepatoprotective, and anticarcinogenic activity. However, the antithrombotic effect of Vitis labrusca leaves on platelets is yet to be ascertained. We investigated the inhibitory effect of V. labrusca leaf extract (VLE) on platelet aggregation in vitro and ex vivo. The thromboxane B2 (TXB2) and serotonin concentrations were measured by ELISA. The flavonoids content was measured by ultraperformance liquid chromatography (UPLC). The antithrombotic activity of VLE was evaluated using various agonists in vitro. VLE strongly inhibited adenosine diphosphate (ADP)-induced platelet aggregation. In rats, VLE treatment (100 mg/kg) reduced ADP-stimulated platelet aggregation, without affecting tail bleeding and coagulation time. Moreover, VLE significantly suppressed TXB2 and serotonin secretion. UPLC analysis indicated that VLE contains quercetin, isorhamnetin, and rutin. Our results indicate that VLE possesses antiplatelet activity via the suppression of TXB2 and serotonin, without affecting bleeding. Further, we identified the flavonoids present in VLE. Thus, VLE may be a potential agent for the prevention of cardiovascular diseases. PMID:26340455

  16. Stable, Metastable, and Kinetically Trapped Amyloid Aggregate Phases

    PubMed Central

    2015-01-01

    Self-assembly of proteins into amyloid fibrils plays a key role in a multitude of human disorders that range from Alzheimer’s disease to type II diabetes. Compact oligomeric species, observed early during amyloid formation, are reported as the molecular entities responsible for the toxic effects of amyloid self-assembly. However, the relation between early-stage oligomeric aggregates and late-stage rigid fibrils, which are the hallmark structure of amyloid plaques, has remained unclear. We show that these different structures occupy well-defined regions in a peculiar phase diagram. Lysozyme amyloid oligomers and their curvilinear fibrils only form after they cross a salt and protein concentration-dependent threshold. We also determine a boundary for the onset of amyloid oligomer precipitation. The oligomeric aggregates are structurally distinct from rigid fibrils and are metastable against nucleation and growth of rigid fibrils. These experimentally determined boundaries match well with colloidal model predictions that account for salt-modulated charge repulsion. The model also incorporates the metastable and kinetic character of oligomer phases. Similarities and differences of amyloid oligomer assembly to metastable liquid–liquid phase separation of proteins and to surfactant aggregation are discussed. PMID:25469942

  17. Aggregation of titanium dioxide nanoparticles: role of a fulvic acid.

    PubMed

    Domingos, Rute F; Tufenkji, Nathalie; Wilkinson, Kevin I

    2009-03-01

    The increasing use of nanomaterials in consumer products has led to increased concerns abouttheir potential environmental and health impacts. To better understand the transport, fate, and behavior of nanoparticles in aquatic systems, it is essential to understand their interactions with different components of natural waters including natural organic matter over a broad range of physicochemical conditions. Fluorescence correlation spectroscopy was used to determine the diffusion coefficients of TiO2 nanoparticles having a nominal size of 5 nm. The effects of a various concentrations of the Suwannee River Fulvic Acid (SRFA) and the roles of pH and ionic strength were evaluated. Aggregation of the bare TiO2 nanoparticles increased for pH values near the zero point of charge. At any given pH, an increase in ionic strength generally resulted in increased aggregation. Furthermore, conditions which favored adsorption of the SRFA resulted in less aggregation of the TiO2 nanoparticles, presumably due to increased steric repulsion. Under the conditions studied here, nanoparticle dispersions were often stable for environmentally relevant conditions of SRFA, pH, and ionic strength, suggesting that in the natural environment, TiO2 dispersion might occur to a greater extent than expected. PMID:19350891

  18. A Statistical Aggregation Engine for Climatology and Trend Analysis

    NASA Astrophysics Data System (ADS)

    Chapman, D. R.; Simon, T. A.; Halem, M.

    2014-12-01

    Fundamental climate data records (FCDRs) from satellite instruments often span tens to hundreds of terabytes or even petabytes in scale. These large volumes make it difficult to aggregate or summarize their climatology and climate trends. It is especially cumbersome to supply the full derivation (provenance) of these aggregate calculations. We present a lightweight and resilient software platform, Gridderama that simplifies the calculation of climatology by exploiting the "Data-Cube" topology often present in earth observing satellite records. By using the large array storage (LAS) paradigm, Gridderama allows the analyst to more easily produce a series of aggregate climate data products at progressively coarser spatial and temporal resolutions. Furthermore, provenance tracking and extensive visualization capabilities allow the analyst to track down and correct for data problems such as missing data and outliers that may impact the scientific results. We have developed and applied Gridderama to calculate a trend analysis of 55 Terabytes of AIRS Level 1b infrared radiances, and show statistically significant trending in the greenhouse gas absorption bands as observed by AIRS over the 2003-2012 decade. We will extend this calculation to show regional changes in CO2 concentration from AIRS over the 2003-2012 decade by using a neural network retrieval algorithm.

  19. Opening of DNA double helix at room temperature: Application of α-cyclodextrin self-aggregates

    NASA Astrophysics Data System (ADS)

    Jaffer, Syed S.; Ghosh, Prasun; Das, Anindita; Purkayastha, Pradipta

    2010-08-01

    Self-aggregation of α-cyclodextrin (α-CD) can induce DNA opening at room temperature (25 °C) owing to the hydroxyl groups on the surface of the spherical aggregates of α-CD, which promote hydrogen bonding with the flipped-out bases in DNA duplex prohibiting them from reverting back.Self-aggregation of α-cyclodextrin (α-CD) can induce DNA opening at room temperature (25 °C) owing to the hydroxyl groups on the surface of the spherical aggregates of α-CD, which promote hydrogen bonding with the flipped-out bases in DNA duplex prohibiting them from reverting back. Electronic supplementary information (ESI) available: Experimental details; absorbance data of ds-DNA at higher concentration of α-CD. See DOI: 10.1039/c0nr00184h

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

    PubMed

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

    2006-07-01

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

  1. Self-assembled aggregates in the gravitational field: Growth and nematic order

    NASA Astrophysics Data System (ADS)

    Baulin, Vladimir A.

    2003-08-01

    The influence of the gravitational field on the reversible process of assembly and disassembly of linear aggregates is the focus of this paper. Even the earth gravitational field can affect the equilibrium properties of heavy biological aggregates such as microtubules or actin filaments. The gravity gives rise to the concentration gradient which results in the distribution of aggregates of different lengths with height. Strong enough gravitational field induces the overall growth of the aggregates. The gravitational field facilitates the isotropic to nematic phase transition reflecting in a broader transition region. Coexisting phases have notedly different length distributions and the phase transition represents the interplay between the growth in the isotropic phase and the precipitation into nematic phase. The fields in an ultracentrifuge can only reinforce the effect of gravity, so the present description can be applied to a wider range of systems.

  2. Aggregate formation of eosin-Y adsorbed on nanocrystalline TiO2 films

    NASA Astrophysics Data System (ADS)

    Yaguchi, Kaori; Furube, Akihiro; Katoh, Ryuzi

    2012-11-01

    We have studied the adsorption of eosin-Y on nanocrystalline TiO2 films with two different solvents namely acetonitrile (ACN) and ethanol (EtOH). A Langmuir-type adsorption isotherm was observed with ACN. In contrast, a Freundlich-type adsorption isotherm was observed with EtOH, suggesting that EtOH molecules co-adsorbed on TiO2 surface. Absorption spectra of the dye adsorbed films clearly show aggregate formation at high concentrations of dye in the solutions. From the analysis of the spectra, we conclude that head-to-tail type aggregates are observed with ACN, whereas various types of aggregates, including H-type and head-to-tail type aggregates, are observed with EtOH.

  3. 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.

  4. Conformational stability and aggregation of therapeutic monoclonal antibodies studied with ANS and Thioflavin T binding.

    PubMed

    Kayser, Veysel; Chennamsetty, Naresh; Voynov, Vladimir; Helk, Bernhard; Trout, Bernhardt L

    2011-01-01

    Characterization of aggregation profiles of monoclonal antibodies (mAb) is gaining importance because an increasing number of mAb-based therapeutics are entering clinical studies and gaining marketing approval. To develop a successful formulation, it is imperative to identify the critical biochemical properties of each potential mAb drug candidate. We investigated the conformational change and aggregation of a human IgG1 using external dye-binding experiments with fluorescence spectroscopy and compared the aggregation profiles obtained to the results of size-exclusion chromatography. We show that using an appropriate dye at selected mAb concentration, unfolding or aggregation can be studied. In addition, dye-binding experiments may be used as conventional assays to study therapeutic mAb stability. PMID:21540645

  5. Quantitative effects of magnesium chloride stress on aggregation of Sup35p in [psi-] yeast cells.

    PubMed

    Song, Yao; Lan, Wanjun; Wu, Xianyuan; He, Jianwei; Li, Hui; Ben, Songbin; Song, Youtao

    2010-12-01

    [PSI(+)] phenotype can be transiently induced when Magnesium chloride (MgCl(2)) was the selective pressure in SUP35 repeat-expansion mutant [psi(-)] yeast strains. We further investigated [PSI(+)] phenotype change under different MgCl(2) conditions with native Sup35p and quantified the Sup35p status changes with fluorescence recovery after photobleaching (FRAP) and semi-denaturing detergent-agarose gel electrophoresis (SDD-AGE) analysis. It was found that the [PSI(+)] phenotype presented a dose-dependent relationship with the concentrations of MgCl(2). Furthermore, Sup35p aggregated in MgCl(2) treated cells but did not form large aggregates as it does in [PSI(+)] cells, and the size of Sup35p aggregates showed a time-dependent relationship with the MgCl(2) application. The aggregation of Sup35p strictly depended on the presence of MgCl(2) stress in our strains.

  6. Surface Pressure Study of Lipid Aggregates at the Air Water Interface

    NASA Astrophysics Data System (ADS)

    Shew, Woody; Ploplis Andrews, Anna

    1996-11-01

    Qualitative and quantitative descriptions of the growth of fatty acid aggregates on a water/air interface were made by analyzing surface pressure measurements taken with a Langmuir Balance. High concentrations of palmitic acid, lauric acid, myristic acid, and also phosphatidylethanolamine in solution with chloroform were applied with a syringe to the surface of the Langmuir Balance and surface pressure was monitored as aggregates assembled spontaneously. The aggregation process for palmitic acid was determined to consist of three distinct parts. Exponential curves were fit to the individual regions of the data and growth and decay constants were determined. Surface pressure varied in very complex ways for lauric acid, myristic acid, and phosphatidylethanolamine yet kinetic measurements yield qualitative information about assembly of those aggregates. This research was supported by NSF Grant No. DMR-93-22301.

  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. Aggregation and deposition of engineered TiO2 nanoparticles in natural fresh and brackish waters

    NASA Astrophysics Data System (ADS)

    Sillanpää, Markus; Paunu, Tiina-Mari; Sainio, Pirjo

    2011-07-01

    The use and thus environmental release potential of metal-based nanoparticles have rapidly increased. Due to their size-dependent new properties, the fate and effect of nanomaterial may differ from those of the conventional form of corresponding material. The agglomeration and sedimentation were studied by spiking the TiO2-P25 particles in natural fresh and brackish water samples. The natural waters were determined for conductivity, pH, salinity, total organic carbon, turbidity, common nutrients and trace elements. The hydrodynamic diameter and concentration of TiO2-P25 particle dispersions were monitored by using a dynamic light scattering and a spectrophotometer, respectively. The experiments were performed at two particle concentrations 100 mg/l and 1 mg/l (10 mg/l for deposition studies). The aggregation rates in brackish waters were clearly higher in higher initial concentration and the sedimentation of aggregates decreased the TiO2 concentration down to 20% and 80% of initial higher and lower concentrations, respectively. One fresh water sample favoured the destabilisation of TiO2-P25 particles whereas another fresh water sample stabilised the TiO2 particle dispersion. The aggregation had a strong dependence on the particle concentration. High ionic content of brackish water probably explains the formation of aggregates, whereas organic substances and pH may account for the different agglomeration behaviour in fresh waters.

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

    SciTech Connect

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

    1984-01-01

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

  10. Nanoscale Ionic Aggregate Morphology in Zwitterionic Copolymers

    NASA Astrophysics Data System (ADS)

    Choi, Jae-Hong; Huyck, Rebecca; Salas-de La Cruz, David; Long, Timothy E.; Winey, Karen I.

    2009-03-01

    The morphology of two different zwitterionic copolymers, poly(sulfobetaine methacrylate-ran-butyl acrylate), and poly(sulfobetaine methacrylamide-ran-butyl acrylate) are investigated as a function of the mol % content of SBMA (7 and 9 mol %) and SBMAm (6, 10 and 13 mol %), respectively. In both copolymers, X-ray scattering results show a new structure in the material arising from ionic aggregates. The sizes of the ionic aggregates are obtained through the scattering model. The sizes of the ionic aggregates increase as the ion content increases. The application of scanning transmission electron microscopy to the study of ionomer morphology has enabled direct, model-independent visualization of the ionic aggregates. The correlation between X-ray scattering results and the real space imaging for morphology of these zwitterionic copolymers will be presented.

  11. 31 CFR 1023.313 - Aggregation.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... ENFORCEMENT NETWORK, DEPARTMENT OF THE TREASURY RULES FOR BROKERS OR DEALERS IN SECURITIES Reports Required To Be Made By Brokers or Dealers in Securities § 1023.313 Aggregation. Refer to § 1010.313 of this... securities....

  12. 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.

  13. 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

  14. Active matter model of Myxococcus xanthus aggregation

    NASA Astrophysics Data System (ADS)

    Patch, Adam; Bahar, Fatmagul; Liu, Guannan; Thutupalli, Shashi; Welch, Roy; Yllanes, David; Shaevitz, Joshua; Marchetti, M. Cristina

    Myxococcus