6,397 research outputs found
Anomalous He-Gas High-Pressure Studies on Superconducting LaO1-xFxFeAs
AC susceptibility measurements have been carried out on superconducting
LaO1-xFxFeAs for x=0.07 and 0.14 under He-gas pressures to about 0.8 GPa. Not
only do the measured values of dTc/dP differ substantially from those obtained
in previous studies using other pressure media, but the Tc(P) dependences
observed depend on the detailed pressure/temperature history of the sample. A
sizeable sensitivity of Tc(P) to shear stresses provides a possible
explanation
Precursor-mediated crystallization process in suspensions of hard spheres
We report on a large scale computer simulation study of crystal nucleation in
hard spheres. Through a combined analysis of real and reciprocal space data, a
picture of a two-step crystallization process is supported: First dense,
amorphous clusters form which then act as precursors for the nucleation of
well-ordered crystallites. This kind of crystallization process has been
previously observed in systems that interact via potentials that have an
attractive as well as a repulsive part, most prominently in protein solutions.
In this context the effect has been attributed to the presence of metastable
fluid-fluid demixing. Our simulations, however, show that a purely repulsive
system (that has no metastable fluid-fluid coexistence) crystallizes via the
same mechanism.Comment: 4 figure
Flux Tubes of Two- and Three-Quark System in Full QCD
We study the abelian color flux of two- and three-quark systems in the
maximally abelian gauge in lattice QCD with dynamical fermions. We find that
the abelian flux tube formed between quark and antiquark is very much the same
as in quenched QCD up to quark separations of 2fm. The profile of the
color electric field in three-quark system suggests ansatz, which might be
interpreted as the result of the vacuum pressure in the confined phase. In
order to clarify the flux structure, we investigate the color electric field of
the three-quark system splittting the abelian gauge field into the monopole and
photon parts.Comment: 4 pages, 4 figures, Talk given at XVI International Conference on
Particles and Nuclei (PaNic02),Osaka, Japan, Sep.30 - Oct.4, 200
Enhancement of the Critical Current Density of YBa2Cu3Ox Superconductors under Hydrostatic Pressure
The dependence of the critical current density Jc on hydrostatic pressure to
0.6 GPa is determined for a single 25-degree [001]-tilt grain boundary in a
bicrystalline ring of nearly optimally doped melt-textured YBa2Cu3Ox. Jc is
found to increase rapidly under pressure at +20 %/GPa. A new diagnostic method
is introduced (pressure-induced Jc relaxation) which reveals a sizeable
concentration of vacant oxygen sites in the grain boundary region. Completely
filling such sites with oxygen anions should lead to significant enhancements
in Jc.Comment: revised manuscript, graphic errors in figures correcte
Unquenching the Quark Model and Screened Potentials
The low-lying spectrum of the quark model is shown to be robust under the
effects of `unquenching'. In contrast, the use of screened potentials is shown
to be of limited use in models of hadrons. Applications to unquenching the
lattice Wilson loop potential and to glueball mixing in the adiabatic hybrid
spectrum are also presented.Comment: 6 pages, 3 ps figures, revtex. Version to appear in J. Phys.
The effects of disorder in dimerized quantum magnets in mean field approximations
We study theoretically the effects of disorder on Bose-Einstein condensates
(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The
condensation occurs in a strong enough magnetic field Hc, where the
concentration of bosons in the random potential is sufficient to form the
condensate. The effect of doping is partly modeled by delta - correlated
disorder potential, which (i) leads to the uniform renormalization of the
system parameters and (ii) produces disorder in the system with renormalized
parameters. These approaches can explain qualitatively the available
magnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In
addition to the magnetization, we found that the speed of the Bogoliubov mode
has a peak as a function of doping parameter, x. No evidence of the pure Bose
glass phase has been obtained in the BEC regime.Comment: Includes 19 pages, 5 figure
Mosaic Zinc Crystals
Crystals of a distinctly mosaic type (that is, a group of polycrystals with almost identical orientations) have been grown with great frequency during the last two years. Some types of these will be described and their bearing on the growth of single crystals by various methods will be discussed
3D modeling of indoor environments by a mobile robot with a laser scanner and panoramic camera
We present a method to acquire a realistic, visually convincing 3D model of indoor office environments based on a mobile robot that is equipped with a laser range scanner and a panoramic camera. The data of the 2D laser scans are used to solve the SLAM problem and to extract walls. Textures for walls and floor are built from the images of a calibrated panoramic camera. Multi-resolution blending is used to hide seams in the generated textures
One-dimensional quasi-relativistic particle in the box
Two-term Weyl-type asymptotic law for the eigenvalues of one-dimensional
quasi-relativistic Hamiltonian (-h^2 c^2 d^2/dx^2 + m^2 c^4)^(1/2) + V_well(x)
(the Klein-Gordon square-root operator with electrostatic potential) with the
infinite square well potential V_well(x) is given: the n-th eigenvalue is equal
to (n pi/2 - pi/8) h c/a + O(1/n), where 2a is the width of the potential well.
Simplicity of eigenvalues is proved. Some L^2 and L^infinity properties of
eigenfunctions are also studied. Eigenvalues represent energies of a `massive
particle in the box' quasi-relativistic model.Comment: 40 pages, 4 figures; minor correction
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