3,253 research outputs found
Anomalous structural and mechanical properties of solids confined in quasi one dimensional strips
We show using computer simulations and mean field theory that a system of
particles in two dimensions, when confined laterally by a pair of parallel hard
walls within a quasi one dimensional channel, possesses several anomalous
structural and mechanical properties not observed in the bulk. Depending on the
density and the distance between the walls , the system shows
structural characteristics analogous to a weakly modulated liquid, a strongly
modulated smectic, a triangular solid or a buckled phase. At fixed , a
change in leads to many reentrant discontinuous transitions involving
changes in the number of layers parallel to the confining walls depending
crucially on the commensurability of inter-layer spacing with . The solid
shows resistance to elongation but not to shear. When strained beyond the
elastic limit it fails undergoing plastic deformation but surprisingly, as the
strain is reversed, the material recovers completely and returns to its
original undeformed state. We obtain the phase diagram from mean field theory
and finite size simulations and discuss the effect of fluctuations.Comment: 14 pages, 13 figures; revised version, accepted in J. Chem. Phy
Effect of strain on the transport properties of the manganite systems
The effect of strain on the resistivity and thermopower of ferromagnetic
manganites has been examined based on the model that incorporates the
electron-lattice interaction through the Jahn-Teller effect and an effective
hopping determined by nearest neighbour spin-spin correlation of t2g electrons.
The metal insulator transition temperature associated with resistivity
decreases with increase in strain. In the presence of large strain the system
remains in the semiconducting state. Thermopower (S) is positive and increasing
function of strain and it exhibits a maximum with temperature. The temperature
where maximum of S appears, shifts towards higher (lower) value with in the
presence of magnetic field (strain). A large magneto-thermopower that depends
on strain is obtained around metal-insulator transition.Comment: 11pages, 4 figure
Relaxation dynamics in a transient network fluid with competing gel and glass phases
We use computer simulations to study the relaxation dynamics of a model for
oil-in-water microemulsion droplets linked with telechelic polymers. This
system exhibits both gel and glass phases and we show that the competition
between these two arrest mechanisms can result in a complex, three-step decay
of the time correlation functions, controlled by two different localization
lengthscales. For certain combinations of the parameters, this competition
gives rise to an anomalous logarithmic decay of the correlation functions and a
subdiffusive particle motion, which can be understood as a simple crossover
effect between the two relaxation processes. We establish a simple criterion
for this logarithmic decay to be observed. We also find a further
logarithmically slow relaxation related to the relaxation of floppy clusters of
particles in a crowded environment, in agreement with recent findings in other
models for dense chemical gels. Finally, we characterize how the competition of
gel and glass arrest mechanisms affects the dynamical heterogeneities and show
that for certain combination of parameters these heterogeneities can be
unusually large. By measuring the four-point dynamical susceptibility, we probe
the cooperativity of the motion and find that with increasing coupling this
cooperativity shows a maximum before it decreases again, indicating the change
in the nature of the relaxation dynamics. Our results suggest that compressing
gels to large densities produces novel arrested phases that have a new and
complex dynamics.Comment: 16 pages, 15 figure
Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates
A new type of quasi-two-dimensional complex plasma system was observed which
consisted of monodisperse microspheres and their binary agglomerations
(dimers). The particles and their dimers levitated in a plasma sheath at
slightly different heights and formed two distinct sublayers. The sys- tem did
not crystallize and may be characterized as disordered solid. The dimers were
identified based on their characteristic appearance in defocused images, i.e.,
rotating interference fringe pat- terns. The in-plane and inter-plane particle
separations exhibit nonmonotonic dependence on the discharge pressure which
agrees well with theoretical predictions
When gel and glass meet: A mechanism for multistep relaxation
We use computer simulations to study the dynamics of a physical gel at high
densities where gelation and the glass transition interfere. We report and
provide detailed physical understanding of complex relaxation patterns for time
correlation functions which generically decay in a three-step process. For
certain combinations of parameters we find logarithmic decays of the
correlators and subdiffusive particle motion.Comment: 4 pages, 5 figure
A semidefinite relaxation procedure for fault-tolerant observer design
A fault-tolerant observer design methodology is proposed. The aim is to guarantee a minimum level of closed-loop performance under all possible sensor fault combinations while optimizing performance under the nominal, fault-free condition. A novel approach is proposed to tackle the combinatorial nature of the problem, which is computationally intractable even for a moderate number of sensors, by recasting the problem as a robust performance problem, where the uncertainty set is composed of all combinations of a set of binary variables. A procedure based on an elimination lemma and an extension of a semidefinite relaxation procedure for binary variables is then used to derive sufficient conditions (necessary and sufficient in the case of one binary variable) for the solution of the problem which significantly reduces the number of matrix inequalities needed to solve the problem. The procedure is illustrated by considering a fault-tolerant observer switching scheme in which the observer outputs track the actual sensor fault condition. A numerical example from an electric power application is presented to illustrate the effectiveness of the design
Ray optics in flux avalanche propagation in superconducting films
Experimental evidence of wave properties of dendritic flux avalanches in
superconducting films is reported. Using magneto-optical imaging the
propagation of dendrites across boundaries between a bare NbN film and areas
coated by a Cu-layer was visualized, and it was found that the propagation is
refracted in full quantitative agreement with Snell's law. For the studied film
of 170 nm thickness and a 0.9 mkm thick metal layer, the refractive index was
close to n=1.4. The origin of the refraction is believed to be caused by the
dendrites propagating as an electromagnetic shock wave, similar to damped modes
considered previously for normal metals. The analogy is justified by the large
dissipation during the avalanches raising the local temperature significantly.
Additional time-resolved measurements of voltage pulses generated by segments
of the dendrites traversing an electrode confirm the consistency of the adapted
physical picture.Comment: 4 pages, 4 figure
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