17,923 research outputs found
Geometrical interpretation and graphical solution to minimum energy discrete-data control Scientific report no. 9
Linear PAM regulator minimum energy design by geometric interpretation and graphical solutio
Covalency and the metal-insulator transition in titanate and vanadate perovskites
A combination of density functional and dynamical mean-field theory is
applied to the perovskites SrVO, LaTiO and LaVO. We show that
DFT+DMFT in conjunction with the standard fully localized-limit (FLL)
double-counting predicts that LaTiO and LaVO are metals even though
experimentally they are correlation-driven ("Mott") insulators. In addition,
the FLL double counting implies a splitting between oxygen and transition
metal levels which differs from experiment. Introducing into the theory an
\textit{ad hoc} double counting correction which reproduces the experimentally
measured insulating gap leads also to a - splitting consistent with
experiment if the on-site interaction is chosen in a relatively narrow
range ( eV). The results indicate that these early transition
metal oxides will serve as critical test for the formulation of a general
\textit{ab initio} theory of correlated electron metals.Comment: 5 pages, 3 figure
Quantum Spin Dynamics with Pairwise-Tunable, Long-Range Interactions
We present a platform for the simulation of quantum magnetism with full
control of interactions between pairs of spins at arbitrary distances in one-
and two-dimensional lattices. In our scheme, two internal atomic states
represent a pseudo-spin for atoms trapped within a photonic crystal waveguide
(PCW). With the atomic transition frequency aligned inside a band gap of the
PCW, virtual photons mediate coherent spin-spin interactions between lattice
sites. To obtain full control of interaction coefficients at arbitrary
atom-atom separations, ground-state energy shifts are introduced as a function
of distance across the PCW. In conjunction with auxiliary pump fields,
spin-exchange versus atom-atom separation can be engineered with arbitrary
magnitude and phase, and arranged to introduce non-trivial Berry phases in the
spin lattice, thus opening new avenues for realizing novel topological spin
models. We illustrate the broad applicability of our scheme by explicit
construction for several well known spin models.Comment: 18 pages, 10 figure
High-risk Sexual Behavior is Associated with Post-Exposure Prophylaxis Non-adherence among Men who have Sex with Men Enrolled in a Combination Prevention Intervention.
Methamphetamine use among men who have sex with men (MSM) is associated with increased HIV prevalence, due to increased engagement in high-risk sexual behavior. Fifty-three HIV-negative, methamphetamine-using MSM were enrolled in a biobehavioral combination prevention intervention in Los Angeles, CA, to assess the feasibility of administering postexposure prophylaxis (PEP) in combination with contingency management (CM) to prevent HIV seroconversion. The study combined a CM behavioral intervention targeting reductions in methamphetamine use with a PEP biomedical intervention for HIV prevention. Those who reported recent exposure to HIV were initiated on tenofovir/emtricitabine- (Truvada)-based PEP (n=35). This secondary analysis sought to determine whether recent and/or lifetime sexual risk taking was associated with PEP adherence. Regression analyses controlling for participant sociodemographics demonstrated that, at baseline, increased number of lifetime sexually transmitted diseases (STDs; Coef.=-0.07; 95% CI=(-0.12) - (-0.01)) and recent episodes of unprotected anal intercourse (UAI; Coef.=-0.01; 95% CI= (-.01) - (-0.002)) were each associated with reductions in medication adherence. Given these associations between baseline sexual risk and PEP adherence, providers working with high-risk MSM may look to target reductions in sexual risk taking; this will reduce direct risk of HIV infection and may work to optimize medication adherence in the case of PEP initiation. Clinicaltrials.gov identifier: NCT00856323
Superradiance for atoms trapped along a photonic crystal waveguide
We report observations of superradiance for atoms trapped in the near field
of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge
near the D transition of atomic cesium, strong interaction is achieved
between trapped atoms and guided-mode photons. Following short-pulse
excitation, we record the decay of guided-mode emission and find a superradiant
emission rate scaling as for average atom number atoms, where
is the peak single-atom radiative decay
rate into the PCW guided mode and is the Einstein- coefficient
for free space. These advances provide new tools for investigations of
photon-mediated atom-atom interactions in the many-body regime.Comment: 11 pages, 10 figure
Rare K decays in a model of quark and lepton masses
An extension of a model of neutrino masses to the quark sector provides an
interesting link between these two sectors. A parameter which is important to
describe neutrino oscillations and masses is found to be a crucial one
appearing in various ``penguin'' operators, in particular the so-called Z
penguin. This parameter is severely constrained by the rare decay process
. This in turn has interesting implications on the
decay rates of other rare processes such as , etc..., as well
as on the masses of the neutrinos and the masses of the vector-like quarks and
leptons which appear in our model.Comment: 34 pages, 10 figures, corrected some typos in the introductio
On 1-loop diagrams in AdS space and the random disorder problem
We study the complex scalar loop corrections to the boundary-boundary gauge
two point function in pure AdS space in Poincare coordinates, in the presence
of a boundary quadratic perturbation to the scalar. These perturbations
correspond to double trace perturbations in the dual CFT and modify the
boundary conditions of the bulk scalars in AdS. We find that, in addition to
the usual UV divergences, the 1-loop calculation suffers from a divergence
originating in the limit as the loop vertices approach the AdS horizon. We show
that this type of divergence is independent of the boundary coupling, and
making use of which we extract the finite relative variation of the imaginary
part of the loop via Cutkosky rules as the boundary perturbation varies.
Applying our methods to compute the effects of a time-dependent impurity to the
conductivities using the replica trick in AdS/CFT, we find that generally an
IR-relevant disorder reduces the conductivity and that in the extreme low
frequency limit the correction due to the impurities overwhelms the planar CFT
result even though it is supposedly suppressed. Comments on the effect
of time-independent impurity in such a system are presented.Comment: 22 pages, 3 figures, Boundary conditions clarified, some typos fixed,
presentations improved and references adde
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