19,082 research outputs found
Investigations into the burning-out of organic substances in the ceramic body
Pressed compacts were made of spray dried alumina containing water soluble polyvinyl alcohol or cellulose derivative binder. The burning out of organic binder on gradual heating was investigated by visual and microscopic observations of the cross section and by thermogravimetry. Burning out proceeds inward from the peripheries, gradually reducing the size of the black core, which first consists of a dark boundary layer and later turns uniformly black with a sharp boundary. A detailed mechanism of the burning out process between and within the spray dried granules is observed under the microscope. Oxygen atmosphere accelerates the burning out process
Current reversal and exclusion processes with history-dependent random walks
A class of exclusion processes in which particles perform history-dependent
random walks is introduced, stimulated by dynamic phenomena in some biological
and artificial systems. The particles locally interact with the underlying
substrate by breaking and reforming lattice bonds. We determine the
steady-state current on a ring, and find current-reversal as a function of
particle density. This phenomenon is attributed to the non-local interaction
between the walkers through their trails, which originates from strong
correlations between the dynamics of the particles and the lattice. We
rationalize our findings within an effective description in terms of
quasi-particles which we call front barriers. Our analytical results are
complemented by stochastic simulations.Comment: 5 pages, 6 figure
On the metal-insulator transition in the two-chain model of correlated fermions
The doping-induced metal-insulator transition in two-chain systems of
correlated fermions is studied using a solvable limit of the t-J model and the
fact that various strong- and weak-coupling limits of the two-chain model are
in the same phase, i.e. have the same low-energy properties. It is shown that
the Luttinger-liquid parameter K_\rho takes the universal value unity as the
insulating state (half-filling) is approached, implying dominant d-type
superconducting fluctuations, independently of the interaction strength. The
crossover to insulating behavior of correlations as the transition is
approached is discussed.Comment: 7 pages, 1 figur
Phase diagram of the one dimensional Hubbard-Holstein Model at 1/2 and 1/4 filling
The Hubbard-Holstein model is one of the simplest to incorporate both
electron-electron and electron-phonon interactions. In one dimension at half
filling the Holstein electron-phonon coupling promotes onsite pairs of
electrons and a Peierls charge density wave while the Hubbard onsite Coulomb
repulsion U promotes antiferromagnetic correlations and a Mott insulating
state. Recent numerical studies have found a possible third intermediate phase
between Peierls and Mott states. From direct calculations of charge and spin
susceptibilities, we show that (i) As the electron-phonon coupling is
increased, first a spin gap opens, followed by the Peierls transition. Between
these two transitions the metallic intermediate phase has a spin gap, no charge
gap, and properties similar to the negative-U Hubbard model. (ii) The
transitions between Mott/intermediate and intermediate/Peierls states are of
the Kosterlitz-Thouless form. (iii) For larger U the two transitions merge at a
tritical point into a single first order Mott/Peierls transition. In addition
we show that an intermediate phase also occurs in the quarter-filled model.Comment: 10 pages, 10 eps figure
Mott-Superfluid transition in bosonic ladders
We show that in a commensurate bosonic ladder, a quantum phase transition
occurs between a Mott insulator and a superfluid when interchain hopping
increases. We analyse the properties of such a transition as well as the
physical properties of the two phases. We discuss the physical consequences for
experimental systems such as Josephson Junction arrays.Comment: 4 pages, 2 figures, revtex
Quantum many particle systems in ring-shaped optical lattices
In the present work we demonstrate how to realize 1d-optical closed lattice
experimentally, including a {\it tunable} boundary phase-twist. The latter may
induce ``persistent currents'', visible by studing the atoms' momentum
distribution. We show how important phenomena in 1d-physics can be studied by
physical realization of systems of trapped atoms in ring-shaped optical
lattices. A mixture of bosonic and/or fermionic atoms can be loaded into the
lattice, realizing a generic quantum system of many interacting particles.Comment: 10 pages, 5 figures. To be published in PR
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