432 research outputs found
Kinetic arrest of the first order ferromagnetic to antiferromagnetic transition in Ce(FeRu) : formation of a magnetic-glass
We present results of dc magnetization and magnetic relaxation study showing
the kinetic arrest of a first order ferromagnetic to antiferromagnetic
transition in Ce(FeRu). This leads to the formation of a
non-ergodic glass-like magnetic state. The onset of the magnetic-glass
transformation is tracked through the slowing down of the magnetization
dynamics. This glassy state is formed with the assistance of an external
magnetic field and this is distinctly different from the well known
'spin-glass' state.Comment: 10 pages of text and 4 figure
Studies on Magnetic-field induced first-order transitions
We shall discuss magnetization and transport measurements in materials
exhibiting a broad first-order transition. The phase transitions would be
caused by varying magnetic field as well as by varying temperature, and we
concentrate on ferromagnetic to antiferromagnetic transitions in magnetic
materials. We distinguish between metastable supercooled phases and metastable
glassy phase.Comment: 50th Golden Jubilee Solid State Physics Symposium during Dec.5-9
(2005) in Mumbai - manuscript of Invited tal
Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems
This series of papers is devoted to identifying and explaining the properties
of strongly correlating liquids, i.e., liquids with more than 90% correlation
between their virial W and potential energy U fluctuations in the NVT ensemble.
Paper IV [N. Gnan et al., J. Chem. Phys. v131, 234504 (2009)] showed that
strongly correlating liquids have "isomorphs", which are curves in the phase
diagram along which structure, dynamics, and some thermodynamic properties are
invariant in reduced units. In the present paper, using the fact that
reduced-unit radial distribution functions are isomorph invariant, we derive an
expression for the shapes of isomorphs in the WU phase diagram of generalized
Lennard-Jones systems of one or more types of particles. The isomorph shape
depends only on the Lennard-Jones exponents; thus all isomorphs of standard
Lennard-Jones systems (with exponents 12 and 6) can be scaled onto to a single
curve. Two applications are given. One is testing the prediction that the
solid-liquid coexistence curve follows an isomorph by comparing to recent
simulations by Ahmed and Sadus [J. Chem. Phys. v131, 174504 (2009)]. Excellent
agreement is found on the liquid side of the coexistence, whereas the agreement
is worse on the solid side. A second application is the derivation of an
approximate equation of state for generalized Lennard-Jones systems by
combining the isomorph theory with the Rosenfeld-Tarazona expression for the
temperature dependence of potential energy on isochores. It is shown that the
new equation of state agrees well with simulations.Comment: 12 pages, 14 figures, Section on solid-liquid coexistence expande
A model for the generic alpha relaxation of viscous liquids
Dielectric measurements on molecular liquids just above the glass transition
indicate that alpha relaxation is characterized by a generic high-frequency
loss varying as , whereas deviations from this come from one or
more low-lying beta processes [Olsen et al, Phys. Rev. Lett. {\bf 86} (2001)
1271]. Assuming that long-wavelength fluctuations dominate the dynamics, a
model for the dielectric alpha relaxation based on the simplest coupling
between the density and dipole density fields is proposed here. The model,
which is solved in second order perturbation theory in the Gaussian
approximation, reproduces the generic features of alpha relaxation
Strong pressure-energy correlations in van der Waals liquids
Strong correlations between equilibrium fluctuations of the configurational
parts of pressure and energy are found in the Lennard-Jones liquid and other
simple liquids, but not in hydrogen-bonding liquids like methanol and water.
The correlations, that are present also in the crystal and glass phases,
reflect an effective inverse power-law repulsive potential dominating
fluctuations, even at zero and slightly negative pressure. In experimental data
for supercritical Argon, the correlations are found to be approximately 96%.
Consequences for viscous liquid dynamics are discussed.Comment: Phys. Rev. Lett., in pres
Feasibility of single-order parameter description of equilibrium viscous liquid dynamics
Molecular dynamics results for the dynamic Prigogine-Defay ratio are
presented for two glass-forming liquids, thus evaluating the experimentally
relevant quantity for testing whether metastable-equilibrium liquid dynamics to
a good approximation are described by a single parameter. For the Kob-Andersen
binary Lennard-Jones mixture as well as for an asymmetric dumbbell model liquid
a single-parameter description works quite well. This is confirmed by
time-domain results where it is found that energy and pressure fluctuations are
strongly correlated on the alpha-time scale in the NVT ensemble; in the NpT
ensemble energy and volume fluctuations similarly correlate strongly.Comment: Phys. Rev. E, in pres
Programmable models of growth and mutation of cancer-cell populations
In this paper we propose a systematic approach to construct mathematical
models describing populations of cancer-cells at different stages of disease
development. The methodology we propose is based on stochastic Concurrent
Constraint Programming, a flexible stochastic modelling language. The
methodology is tested on (and partially motivated by) the study of prostate
cancer. In particular, we prove how our method is suitable to systematically
reconstruct different mathematical models of prostate cancer growth - together
with interactions with different kinds of hormone therapy - at different levels
of refinement.Comment: In Proceedings CompMod 2011, arXiv:1109.104
Solidity of Viscous Liquids
Recent NMR experiments on supercooled toluene and glycerol by Hinze and
Bohmer show that small rotation angles dominate with only few large molecular
rotations. These results are here interpreted by assuming that viscous liquids
are solid-like on short length scales. A characteristic length, the "solidity
length", separates solid-like behavior from liquid-like behavior.Comment: Plain RevTex file, no figure
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