554 research outputs found
Equilibrium glassy phase in a polydisperse hard sphere system
The phase diagram of a polydisperse hard sphere system is examined by
numerical minimization of a discretized form of the Ramakrishnan-Yussouff free
energy functional. Crystalline and glassy local minima of the free energy are
located and the phase diagram in the density-polydispersity plane is mapped out
by comparing the free energies of different local minima. The crystalline phase
disappears and the glass becomes the equilibrium phase beyond a "terminal"
value of the polydispersity. A crystal to glass transition is also observed as
the density is increased at high polydispersity. The phase diagram obtained in
our study is qualitatively similar to that of hard spheres in a quenched random
potential.Comment: 4 pages, 4 figure
Laser induced reentrant freezing in two-dimensional attractive colloidal systems
The effects of an externally applied one-dimensional periodic potential on
the freezing/melting behaviour of two-dimensional systems of colloidal
particles with a short-range attractive interaction are studied using Monte
Carlo simulations. In such systems, incommensuration results when the
periodicity of the external potential does not match the length-scale at which
the minimum of the attractive potential occurs. To study the effects of this
incommensuration, we consider two different models for the system. Our
simulations for both these models show the phenomenon of reentrant freezing as
the strength of the periodic potential is varied. Our simulations also show
that different exotic phases can form when the strength of the periodic
potential is high, depending on the length-scale at which the minimum of the
attractive pair-potential occurs.Comment: 24 pages (including figures) in preprint forma
Characterization of the Dynamics of Glass-forming Liquids from the Properties of the Potential Energy Landscape
We develop a framework for understanding the difference between strong and
fragile behavior in the dynamics of glass-forming liquids from the properties
of the potential energy landscape. Our approach is based on a master equation
description of the activated jump dynamics among the local minima of the
potential energy (the so-called inherent structures) that characterize the
potential energy landscape of the system. We study the dynamics of a small
atomic cluster using this description as well as molecular dynamics simulations
and demonstrate the usefulness of our approach for this system. Many of the
remarkable features of the complex dynamics of glassy systems emerge from the
activated dynamics in the potential energy landscape of the atomic cluster. The
dynamics of the system exhibits typical characteristics of a strong supercooled
liquid when the system is allowed to explore the full configuration space. This
behavior arises because the dynamics is dominated by a few lowest-lying minima
of the potential energy and the potential energy barriers between these minima.
When the system is constrained to explore only a limited region of the
potential energy landscape that excludes the basins of attraction of a few
lowest-lying minima, the dynamics is found to exhibit the characteristics of a
fragile liquid.Comment: 13 pages, 6 figure
Anthelmintic activity of extracts of coriandrum sativum linn. In indian earthworm
Coriandrum sativum Linn. (CSL) is popularly known as coriander in India belongs to family Apiaceae. The objective of the present work was to evaluate the in-vitro anthelmintic potency of the ethanolic extract and carbon tetrachloride extract of Coriandrum sativum Linn. plant using Indian earthworms (Pheretima posthumad). The various concentrations (50, 100, and 150 mg/ml) of the ethanolic extract and carbon tetrachloride extract were tested in-vitro for anthelmintic potency by determination of time of paralysis and time of death of worm. Piperazine citrate (15mg/ml) used as standard. The result of present study indicates that the Coriandrum sativum Linn. potentiate to paralyze earthworm and also caused its death after some time. The shortest time of paralysis was observed at higher dose (150 mg/ml) of both ethanolic extract and carbon tetrachloride were found to 28 min and 45 min respectively. The results of the study are comparable to standard Piperazine citrate. The result showed that ethanolic extract of Coriandrum sativum Linn. took less time to cause paralysis of the earthworm than that of carbon tetrachloride extract Coriandrum sativum Linn.. Thus the present study demonstrate that the Coriandrum sativum Linn. as an anthelmintic has been confirm as the ethanolic and carbon tetrachloride extracts of whole plant displayed activity against the earthworm used in study. Key word: CSL, Paralysis, death of earthworm
Entropic Origin of the Growth of Relaxation Times in Simple Glassy Liquids
Transitions between ``glassy'' local minima of a model free-energy functional
for a dense hard-sphere system are studied numerically using a
``microcanonical'' Monte Carlo method that enables us to obtain the transition
probability as a function of the free energy and the Monte Carlo ``time''. The
growth of the height of the effective free energy barrier with density is found
to be consistent with a Vogel-Fulcher law. The dependence of the transition
probability on time indicates that this growth is primarily due to entropic
effects arising from the difficulty of finding low-free-energy saddle points
connecting glassy minima.Comment: Four pages, plus three postscript figure
Phase Diagram Of A Hard-sphere System In A Quenched Random Potential: A Numerical Study
We report numerical results for the phase diagram in the density-disorder
plane of a hard sphere system in the presence of quenched, random, pinning
disorder. Local minima of a discretized version of the Ramakrishnan-Yussouff
free energy functional are located numerically and their relative stability is
studied as a function of the density and the strength of disorder. Regions in
the phase diagram corresponding to liquid, glassy and nearly crystalline states
are mapped out, and the nature of the transitions is determined. The liquid to
glass transition changes from first to second order as the strength of the
disorder is increased. For weak disorder, the system undergoes a first order
crystallization transition as the density is increased. Beyond a critical value
of the disorder strength, this transition is replaced by a continuous glass
transition. Our numerical results are compared with those of analytical work on
the same system. Implications of our results for the field-temperature phase
diagram of type-II superconductors are discussed.Comment: 14 pages, 10 postscript figures (included), submitted to Phys. Rev.
Tetraspanin CD151 plays a key role in skin squamous cell carcinoma
Here we provide the first evidence that tetraspanin CD151 can support de novo carcinogenesis. During two-stage mouse skin chemical carcinogenesis, CD151 reduces tumor lag time and increases incidence, multiplicity, size, and progression to malignant squamous cell carcinoma (SCC), while supporting both cell survival during tumor initiation and cell proliferation during the promotion phase. In human skin SCC, CD151 expression is selectively elevated compared to other skin cancer types. CD151 support of keratinocyte survival and proliferation may depend on activation of transcription factor STAT3, a regulator of cell proliferation and apoptosis. CD151 also supports PKCα-α6β4 integrin association and PKC-dependent β4 S1424 phosphorylation, while regulating α6β4 distribution. CD151-PKCα effects on integrin β4 phosphorylation and subcellular localization are consistent with epithelial disruption to a less polarized, more invasive state. CD151 ablation, while minimally affecting normal cell and normal mouse functions, markedly sensitized mouse skin and epidermoid cells to chemicals/drugs including DMBA (mutagen) and camptothecin (topoisomerase inhibitor), as well as to agents targeting EGFR, PKC, Jak2/Tyk2, and STAT3. Hence, CD151 ‘co-targeting’ may be therapeutically beneficial. These findings not only support CD151 as a potential tumor target, but also should apply to other cancers utilizing CD151-laminin-binding integrin complexes
Free Energy Landscape Of Simple Liquids Near The Glass Transition
Properties of the free energy landscape in phase space of a dense hard sphere
system characterized by a discretized free energy functional of the
Ramakrishnan-Yussouff form are investigated numerically. A considerable number
of glassy local minima of the free energy are located and the distribution of
an appropriately defined ``overlap'' between minima is calculated. The process
of transition from the basin of attraction of a minimum to that of another one
is studied using a new ``microcanonical'' Monte Carlo procedure, leading to a
determination of the effective height of free energy barriers that separate
different glassy minima. The general appearance of the free energy landscape
resembles that of a putting green: deep minima separated by a fairly flat
structure. The growth of the effective free-energy barriers with increasing
density is consistent with the Vogel-Fulcher law, and this growth is primarily
driven by an entropic mechanism.Comment: 10 pages, 6 postscript figures, uses iopart.cls and iopart10.clo
(included). Invited talk at the ICTP Trieste Conference on "Unifying Concepts
in Glass Physics", September 1999. To be published in J. Phys. Cond. Ma
The role of social networks in students’ learning experiences
The aim of this research is to investigate the role of social networks in computer science education. The Internet shows great potential for enhancing collaboration between people and the role of social software has become increasingly relevant in recent years. This research focuses on analyzing the role that social networks play in students’ learning experiences. The construction of students’ social networks, the evolution of these networks, and their effects on the students’ learning experience in a university environment are examined
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
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