6,349 research outputs found
Biaxial spin-nematic phase of two dimensional disordered rotor models and spin-one bosons in optical lattices
We show that the ground state of disordered rotor models with quadrupolar
interactions can exhibit biaxial nematic ordering in the disorder-averaged
sense. We present a mean-field analysis of the model and demonstrate that the
biaxial phase is stable against small quantum fluctuations. We point out the
possibility of experimental realization of such rotor models using ultracold
spin-one Bose atoms in a spin-dependent and disordered optical lattice in the
limit of a large number of atoms per site and also suggest an imaging
experiment to detect the biaxial nematicity in such systems.Comment: revtex file 7 pages, 2 figures, version published in PR
Twisted SUSY Invariant Formulation of Chern-Simons Gauge Theory on a Lattice
We propose a twisted SUSY invariant formulation of Chern-Simons theory on a
Euclidean three dimensional lattice. The SUSY algebra to be realized on the
lattice is the N=4 D=3 twisted algebra that was recently proposed by D'Adda et
al.. In order to keep the manifest anti-hermiticity of the action, we introduce
oppositely oriented supercharges. Accordingly, the naive continuum limit of the
action formally corresponds to the Landau gauge fixed version of Chern-Simons
theory with complex gauge group which was originally proposed by Witten. We
also show that the resulting action consists of parity even and odd parts with
different coefficients.Comment: 22 pages, 5 figures; v2,v3 added references, v4 added two paragraphs
and one figure in the summar
Physical accessible transformations on a finite number of quantum states
We consider to treat the usual probabilistic cloning, state separation,
unambiguous state discrimination, \emph{etc} in a uniform framework. All these
transformations can be regarded as special examples of generalized completely
positive trace non-increasing maps on a finite number of input states. From the
system-ancilla model we construct the corresponding unitary implementation of
pure pure, pure mixed, mixed pure, and mixed mixed
states transformations in the whole system and obtain the necessary and
sufficient conditions on the existence of the desired maps. We expect our work
will be helpful to explore what we can do on a finite set of input states.Comment: 7 page
Mixed-State Quasiparticle Spectrum for d-wave Superconductors
Controversy concerning the pairing symmetry of high- materials has
motivated an interest in those measurable properties of superconductors for
which qualitative differences exist between the s-wave and d-wave cases. We
report on a comparison between the microscopic electronic properties of d-wave
and s-wave superconductors in the mixed state. Our study is based on
self-consistent numerical solutions of the mean-field Bogoliubov-de Gennes
equations for phenomenological BCS models which have s-wave and d-wave
condensates in the absence of a magnetic field. We discuss differences between
the s-wave and the d-wave local density-of-states, both near and away from
vortex cores. Experimental implications for both scanning-tunneling-microscopy
measurements and specific heat measurements are discussed.Comment: 10 pages, REVTEX3.0, 3 figures available upon reques
Isotropic three-dimensional gap in the iron-arsenide superconductor LiFeAs from directional heat transport measurements
The thermal conductivity k of the iron-arsenide superconductor LiFeAs (Tc ~
18K) was measured in single crystals at temperatures down to T~50mK and in
magnetic fields up to H=17T, very close to the upper critical field Hc2~18T.
For both directions of the heat current, parallel and perpendicular to the
tetragonal c-axis, a negligible residual linear term k/T is found as T ->0,
revealing that there are no zero-energy quasiparticles in the superconducting
state. The increase in k with magnetic field is the same for both current
directions and it follows closely the dependence expected for an isotropic
superconducting gap. There is no evidence of multi-band character, whereby the
gap would be different on different Fermi-surface sheets. These findings show
that the superconducting gap in LiFeAs is isotropic in 3D, without nodes or
deep minima anywhere on the Fermi surface. Comparison with other iron-pnictide
superconductors suggests that a nodeless isotropic gap is a common feature at
optimal doping (maximal Tc).Comment: 4 pages, 3 figure
4-aminopyridyl-based lead compounds targeting CYP51 prevent spontaneous parasite relapse in a chronic model and improve cardiac pathology in an acute model of Trypanosoma cruzi infection.
BackgroundChagas disease, caused by the protozoan Trypanosoma cruzi, is the leading cause of heart failure in Latin America. The clinical treatment of Chagas disease is limited to two 60 year-old drugs, nifurtimox and benznidazole, that have variable efficacy against different strains of the parasite and may lead to severe side effects. CYP51 is an enzyme in the sterol biosynthesis pathway that has been exploited for the development of therapeutics for fungal and parasitic infections. In a target-based drug discovery program guided by x-ray crystallography, we identified the 4-aminopyridyl-based series of CYP51 inhibitors as being efficacious versus T.cruzi in vitro; two of the most potent leads, 9 and 12, have now been evaluated for toxicity and efficacy in mice.Methodology/principal findingsBoth acute and chronic animal models infected with wild type or transgenic T. cruzi strains were evaluated. There was no evidence of toxicity in the 28-day dosing study of uninfected animals, as judged by the monitoring of multiple serum and histological parameters. In two acute models of Chagas disease, 9 and 12 drastically reduced parasitemia, increased survival of mice, and prevented liver and heart injury. None of the compounds produced long term sterile cure. In the less severe acute model using the transgenic CL-Brenner strain of T.cruzi, parasitemia relapsed upon drug withdrawal. In the chronic model, parasitemia fell to a background level and, as evidenced by the bioluminescence detection of T. cruzi expressing the red-shifted luciferase marker, mice remained negative for 4 weeks after drug withdrawal. Two immunosuppression cycles with cyclophosphamide were required to re-activate the parasites. Although no sterile cure was achieved, the suppression of parasitemia in acutely infected mice resulted in drastically reduced inflammation in the heart.Conclusions/significanceThe positive outcomes achieved in the absence of sterile cure suggest that the target product profile in anti-Chagasic drug discovery should be revised in favor of safe re-administration of the medication during the lifespan of a Chagas disease patient. A medication that reduces parasite burden may halt or slow progression of cardiomyopathy and therefore improve both life expectancy and quality of life
Quantum Adiabatic Markovian Master Equations
We develop from first principles Markovian master equations suited for
studying the time evolution of a system evolving adiabatically while coupled
weakly to a thermal bath. We derive two sets of equations in the adiabatic
limit, one using the rotating wave (secular) approximation that results in a
master equation in Lindblad form, the other without the rotating wave
approximation but not in Lindblad form. The two equations make markedly
different predictions depending on whether or not the Lamb shift is included.
Our analysis keeps track of the various time- and energy-scales associated with
the various approximations we make, and thus allows for a systematic inclusion
of higher order corrections, in particular beyond the adiabatic limit. We use
our formalism to study the evolution of an Ising spin chain in a transverse
field and coupled to a thermal bosonic bath, for which we identify four
distinct evolution phases. While we do not expect this to be a generic feature,
in one of these phases dissipation acts to increase the fidelity of the system
state relative to the adiabatic ground state.Comment: 31 pages, 9 figures. v2: Generalized Markov approximation bound.
Included a section on thermal equilibration. v3: Added text that appears in
NJP version. Generalized Lindblad ME to include degenerate subspaces. v3.
Corrections made to Appendix E and F. We thank Kabuki Takada and Hidetoshi
Nishimori for pointing out the errors. v4: Corrected a typo in Eqt. B
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