218,084 research outputs found
Weak Ferromagnetic Exchange and Anomalous Specific Heat in ZnCu3(OH)6Cl2
Experimental evidence for a plethora of low energy spin excitations in the
spin-1/2 kagome antiferromagnet ZnCu3(OH)6Cl2 may be understandable in terms of
an extended Fermi surface of spinons coupled to a U(1) gauge field. We carry
out variational calculations to examine the possibility that such a state may
be energetically viable. A Gutzwiller-projected wavefunction reproduces the
dimerization of a kagome strip found previously by DMRG. Application to the
full kagome lattice shows that the inclusion of a small ferromagnetic
next-nearest-neighbor interaction favors a ground state with a spinon Fermi
surface.Comment: 4 pages, 3 figures, some clarifications to the tex
Melosh rotation: source of the proton's missing spin
It is shown that the observed small value of the integrated spin structure
function for protons could be naturally understood within the naive quark model
by considering the effect from Melosh rotation. The key to this problem lies in
the fact that the deep inelastic process probes the light-cone quarks rather
than the instant-form quarks, and that the spin of the proton is the sum of the
Melosh rotated light-cone spin of the individual quarks rather than simply the
sum of the light-cone spin of the quarks directly.Comment: 5 latex page
Photon-meson transition form factors of light pseudoscalar mesons
The photon-meson transition form factors of light pseudoscalar mesons , , and are systematically calculated in a
light-cone framework, which is applicable as a light-cone quark model at low
and is also physically in accordance with the light-cone pQCD approach
at large . The calculated results agree with the available experimental
data at high energy scale. We also predict the low behaviors of the
photon-meson transition form factors of , and , which are measurable in process via Primakoff
effect at JLab and DESY.Comment: 22 Latex pages, 7 figures, Version to appear in PR
A Note on Pretzelosity TMD Parton Distribution
We show that the transverse-momentum-dependent parton distribution, called as
Pretzelosity function, is zero at any order in perturbation theory of QCD for a
single massless quark state. This implies that Pretzelosity function is not
factorized with the collinear transversity parton distribution at twist-2, when
the struck quark has a large transverse momentum. Pretzelosity function is in
fact related to collinear parton distributions defined with twist-4 operators.
In reality, Pretzelosity function of a hadron as a bound state of quarks and
gluons is not zero. Through an explicit calculation of Pretzelosity function of
a quark combined with a gluon nonzero result is found.Comment: improved explanation, published version in Phys. Lett.
Ab-initio simulation and experimental validation of beta-titanium alloys
In this progress report we present a new approach to the ab-initio guided
bottom up design of beta-Ti alloys for biomedical applications using a quantum
mechanical simulation method in conjunction with experiments. Parameter-free
density functional theory calculations are used to provide theoretical guidance
in selecting and optimizing Ti-based alloys with respect to three constraints:
(i) the use of non-toxic alloy elements; (ii) the stabilization of the body
centered cubic beta phase at room temperature; (iii) the reduction of the
elastic stiffness compared to existing Ti-based alloys. Following the
theoretical predictions, the alloys of interest are cast and characterized with
respect to their crystallographic structure, microstructure, texture, and
elastic stiffness. Due to the complexity of the ab initio calculations, the
simulations have been focused on a set of binary systems of Ti with two
different high melting bcc metals, namely, Nb and Mo. Various levels of model
approximations to describe mechanical and thermodynamic properties are tested
and critically evaluated. The experiments are conducted both, on some of the
binary alloys and on two more complex engineering alloy variants, namely,
Ti-35wt.%Nb-7wt.%Zr-5wt.%Ta and a Ti-20wt.%Mo-7wt.%Zr-5wt.%Ta.Comment: 23 pages, progress report on ab initio alloy desig
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