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Search Results: 1 - 10 of 131315 matches for " Kazem V. Edmond "
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Influence of Confinement on Dynamical Heterogeneities in Dense Colloidal Samples
Kazem V. Edmond,Carolyn R. Nugent,Eric R. Weeks
Physics , 2010, DOI: 10.1103/PhysRevE.85.041401
Abstract: We study a dense colloidal suspension confined between two quasiparallel glass plates as a model system for a supercooled liquid in confined geometries. We directly observe the three-dimensional Brownian motion of the colloidal particles using laser scanning confocal microscopy. The particles form dense layers along the walls, but crystallization is avoided as we use a mixture of two particle sizes. A normally liquid-like sample, when confined, exhibits slower diffusive motion. Particle rearrangements are spatially heterogeneous, and the shapes of the rearranging regions are strongly influenced by the layering. These rearranging regions become more planar upon confinement. The wall-induced layers and changing character of the spatially heterogeneous dynamics appear strongly connected to the confinement induced glassiness.
Local influence of boundary conditions on a confined supercooled colloidal liquid
Kazem V. Edmond,Carolyn R. Nugent,Eric R. Weeks
Physics , 2010, DOI: 10.1140/epjst/e2010-01311-3
Abstract: We study confined colloidal suspensions as a model system which approximates the behavior of confined small molecule glass-formers. Dense colloidal suspensions become glassier when confined between parallel glass plates. We use confocal microscopy to study the motion of confined colloidal particles. In particular, we examine the influence particles stuck to the glass plates have on nearby free particles. Confinement appears to be the primary influence slowing free particle motion, and proximity to stuck particles causes a secondary reduction in the mobility of free particles. Overall, particle mobility is fairly constant across the width of the sample chamber, but a strong asymmetry in boundary conditions results in a slight gradient of particle mobility.
Boundary mobility controls glassiness of confined colloidal liquids
Gary L. Hunter,Kazem V. Edmond,Eric R. Weeks
Physics , 2014, DOI: 10.1103/PhysRevLett.112.218302
Abstract: We use colloidal suspensions encapsulated in emulsion droplets to model confined glass-forming liquids with tunable boundary mobility. We show dynamics in these idealized systems are governed by physical interactions with the boundary. Gradients in dynamics are present for more mobile boundaries, whereas for less mobile boundaries gradients are almost entirely suppressed. Motions in a system are not isotropic, but have a strong directional dependence with respect to the boundary. These findings bring into question the ability of conventional quantities to adequately describe confined glasses.
Tracking Rotational Diffusion of Colloidal Clusters
Gary L. Hunter,Kazem V. Edmond,Mark T. Elsesser,Eric R. Weeks
Physics , 2011, DOI: 10.1364/OE.19.017189
Abstract: We describe a novel method of tracking the rotational motion of clusters of colloidal particles. Our method utilizes rigid body transfor- mations to determine the rotations of a cluster and extends conventional proven particle tracking techniques in a simple way, thus facilitating the study of rotational dynamics in systems containing or composed of colloidal clusters. We test our method by measuring dynamical properties of simulated Brownian clusters under conditions relevant to microscopy experiments. We then use the technique to track and describe the motions of a real colloidal cluster imaged with confocal microscopy.
Slow dynamics in cylindrically confined colloidal suspensions
Nabiha Saklayen,Gary L. Hunter,Kazem V. Edmond,Eric R. Weeks
Physics , 2012, DOI: 10.1063/1.4794593
Abstract: We study bidisperse colloidal suspensions confined within glass microcapillary tubes to model the glass transition in confined cylindrical geometries. We use high speed three-dimensional confocal microscopy to observe particle motions for a wide range of volume fractions and tube radii. Holding volume fraction constant, we find that particles move slower in thinner tubes. The tube walls induce a gradient in particle mobility: particles move substantially slower near the walls. This suggests that the confinement-induced glassiness may be due to an interfacial effect.
Colloidal glass transition observed in confinement
Carolyn R. Nugent,Kazem V. Edmond,Hetal N. Patel,Eric R. Weeks
Physics , 2006, DOI: 10.1103/PhysRevLett.99.025702
Abstract: We study a colloidal suspension confined between two quasi-parallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. For higher volume fraction samples (closer to the glass transition), the onset of confinement effects occurs at larger length scales.
Brownian motion and the hydrodynamic friction tensor for colloidal particles of complex shape
Daniela J. Kraft,Raphael Wittkowski,Borge ten Hagen,Kazem V. Edmond,David J. Pine,Hartmut L?wen
Physics , 2013, DOI: 10.1103/PhysRevE.88.050301
Abstract: We synthesize colloidal particles with various anisotropic shapes and track their orientationally resolved Brownian trajectories using confocal microscopy. An analysis of appropriate short-time correlation functions provides direct access to the hydrodynamic friction tensor of the particles revealing nontrivial couplings between the translational and rotational degrees of freedom. The results are consistent with calculations of the hydrodynamic friction tensor in the low-Reynolds-number regime for the experimentally determined particle shapes.
Microwave-Assisted Oxidation of Organic Compounds with Cetyltrimethylammonium Chlorochromate  [PDF]
Mohammd Kazem Mohammadi
Open Journal of Synthesis Theory and Applications (OJSTA) , 2013, DOI: 10.4236/ojsta.2013.23011
Abstract:

An efficient and mild methodology for oxidation of organic compounds is described using Cetyltrimethylammonium Chlorochromate (CTMACC) under microwave irradiation. The reactions are performed cleanly and are controlled to stop at aldehyde stage, without over-oxidation and side products. Oxidation of organic compounds to their corresponding carbonyl compouds, are studied under microwave radiation. The easy procedure, simple workup, short reaction times, and excellent yields, are another advantages of this reagent.

On the Cozero-Divisor Graphs of Commutative Rings  [PDF]
Mojgan Afkham, Kazem Khashyarmanesh
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.47135
Abstract: Let R be a commutative ring with non-zero identity. The cozero-divisor graph of R, denoted by\"\" , is a graph with vertices in \"\", which is the set of all non-zero and non-unit elements of R, and two distinct vertices a and b in \"\" are adjacent if and only if \"\"and \"\". In this paper, we investigate some combinatorial properties of the cozero-divisor graphs \"\"and \"\"such as connectivity, diameter, girth, clique numbers and planarity. We also study the cozero-divisor graphs of the direct products of two arbitrary commutative rings.
Teachers’ Attitudes and Perceptions: Association of Teachers’ Attitudes toward Traditional and Modern Teaching Methodology According to RWCT as Well as Teachers’ Perceptions for Teaching as a Profession  [PDF]
Xhevahire Karanezi, Edmond Rapti
Creative Education (CE) , 2015, DOI: 10.4236/ce.2015.66061
Abstract: Teaching methodologies that are chosen to be used by teachers in their daily work are highly impacted by their attitudes and perceptions. According to Schoenfeld (1992) attitudes and perceptions influence teachers not only how, but what, he or she teaches. The data collection for this study was conducted using quantitative and qualitative method. There were 473 school teachers throughout Kosovo that participated in this study. Questionnaires were used to collect all quantitative data, which were compiled and adjusted in accordance with the study objectives. Focus groups discussions were conducted for the purpose of collecting the qualitative data. The data showed significant negative association between teachers’ attitudes toward traditional teaching methodologies and modern teaching methodologies according to RWCT (r = 0.446, sig = 0.000). The data also showed that there was a significant negative association between attitudes toward traditional teaching methodology and teachers’ perceptions for teaching as a profession (r = 0.092, sig = 0.046). The quantitative results were in the same line with the qualitative findings of the study.
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