13,680 research outputs found
Segregation in a fluidized binary granular mixture: Competition between buoyancy and geometric forces
Starting from the hydrodynamic equations of binary granular mixtures, we
derive an evolution equation for the relative velocity of the intruders, which
is shown to be coupled to the inertia of the smaller particles. The onset of
Brazil-nut segregation is explained as a competition between the buoyancy and
geometric forces: the Archimedean buoyancy force, a buoyancy force due to the
difference between the energies of two granular species, and two geometric
forces, one compressive and the other-one tensile in nature, due to the
size-difference. We show that inelastic dissipation strongly affects the phase
diagram of the Brazil nut phenomenon and our model is able to explain the
experimental results of Breu et al. (PRL, 2003, vol. 90, p. 01402).Comment: 5 pages, 2 figure
SET based experiments for HTSC materials: II
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations
[i.e. quasiparticle or collective], spin-charge separation, stripes [static
and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn,
Ni] and any other phenomenon in these materials must be consistently
understood. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
Clear Experimental Signature of Charge-Orbital density wave in NdCaMnO
Single Crystals of NdCaMnO have been prepared by the
travelling floating-zone method, and possible evidence of a charge -orbital
density wave in this material presented earlier [PRB68,092405 (2003)] using
High Resolution Electron Microscopy [HRTEM] and Electron Diffraction [ED]. In
the current note we present direct evidence of charge-orbital ordering in this
material using heat capacity measurements. Our heat capacity measurements
indicate a clear transition consistent with prior observation. We find two main
transitions, one at temperature K, and other at
K. In addition, we may also conclude that there is a strong electron-phonon
coupling in this material.Comment: 7 pages, 8 figure
Experimental determination of the state-dependent enhancement of the electron-positron momentum density in solids
The state-dependence of the enhancement of the electron-positron momentum
density is investigated for some transition and simple metals (Cr, V, Ag and
Al). Quantitative comparison with linearized muffin-tin orbital calculations of
the corresponding quantity in the first Brillouin zone is shown to yield a
measurement of the enhancement of the s, p and d states, independent of any
parameterizations in terms of the electron density local to the positron. An
empirical correction that can be applied to a first-principles state-dependent
model is proposed that reproduces the measured state-dependence very well,
yielding a general, predictive model for the enhancement of the momentum
distribution of positron annihilation measurements, including those of angular
correlation and coincidence Doppler broadening techniques
Enskog Theory for Polydisperse Granular Mixtures II. Sonine Polynomial Approximation
The linear integral equations defining the Navier-Stokes (NS) transport
coefficients for polydisperse granular mixtures of smooth inelastic hard disks
or spheres are solved by using the leading terms in a Sonine polynomial
expansion. Explicit expressions for all the NS transport coefficients are given
in terms of the sizes, masses, compositions, density and restitution
coefficients. In addition, the cooling rate is also evaluated to first order in
the gradients. The results hold for arbitrary degree of inelasticity and are
not limited to specific values of the parameters of the mixture. Finally, a
detailed comparison between the derivation of the current theory and previous
theories for mixtures is made, with attention paid to the implication of the
various treatments employed to date.Comment: 26 pages, to be published in Phys. Rev.
Structural, elastic, and electronic properties of newly discovered Li2PtSi3 superconductor: Effect of transition metals
First-principles calculations within the density functional theory (DFT) with
GGA-PBE exchange-correlation scheme have been employed to predict the
structural, the elastic and the electronic properties of newly discovered
lithium silicide superconductor, Li2PtSi3, for the first time. All the
theoretical results are compared with those calculated recently for
isostructural Li2IrSi3. The present study sheds light on the effect of
replacement of transition metal element Ir with Pt on different mechanical,
electronic, and superconducting properties. The effect of spin-orbit coupling
on electronic band structure was found to be insignificant for Li2PtSi3. The
difference in superconducting transition temperatures of Li2PtSi3 and Li2IrSi3
arises primarily due to the difference in electronic energy density of states
at the Fermi level. Somewhat reduced Debye temperature in Li2PtSi3 plays a
minor role. We have discussed the implications of the theoretical results in
details in this study.Comment: Submitted for publicatio
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