744 research outputs found
An Adaptive, Kink-Based Approach to Path Integral Calculations
A kink-based expression for the canonical partition function is developed
using Feynman's path integral formulation of quantum mechanics and a discrete
basis set. The approach is exact for a complete set of states. The method is
tested on the 3x3 Hubbard model and overcomes the sign problem seen in
traditional path integral studies of fermion systems. Kinks correspond to
transitions between different N-electron states, much in the same manner as
occurs in configuration interaction calculations in standard ab initio methods.
The different N-electron states are updated, based on which states occur
frequently during a Monte Carlo simulation, giving better estimates of the true
eigenstates of the Hamiltonian.Comment: 24 pages, to be published in J. Chem. Phy
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Depression and cardiovascular disease: Selected findings, controversies, and clinical implications from 2009
We systematically searched published empirical research on depression and cardiovascular disease (CVD) and found 494 unique articles published in 2009. Several particularly notable and provocative findings and controversies emerged from this survey of the 2009 literature. First, multiple large observational studies found that antidepressant use was associated with increased risk of incident stroke, CVD, or sudden cardiac death. Second, four randomized controlled trials on depression interventions in CVD patients reported important efficacy results that should guide future trials. Finally, the vigorous debate on whether patients with CVD should be routinely screened (and subsequently treated) for depression continued in 2009 even as some observed that routine screening for CVD in depressed patients is more evidence-based and appropriate. This article reviews these selected provocative findings and controversies from our search and explores their clinical implications
Coherent transport of neutral atoms in spin-dependent optical lattice potentials
We demonstrate the controlled coherent transport and splitting of atomic wave
packets in spin-dependent optical lattice potentials. Such experiments open
intriguing possibilities for quantum state engineering of many body states.
After first preparing localized atomic wave functions in an optical lattice
through a Mott insulating phase, we place each atom in a superposition of two
internal spin states. Then state selective optical potentials are used to split
the wave function of a single atom and transport the corresponding wave packets
in two opposite directions. Coherence between the wave packets of an atom
delocalized over up to 7 lattice sites is demonstrated.Comment: 4 pages, 6 figure
NASA space station automation: AI-based technology review
Research and Development projects in automation for the Space Station are discussed. Artificial Intelligence (AI) based automation technologies are planned to enhance crew safety through reduced need for EVA, increase crew productivity through the reduction of routine operations, increase space station autonomy, and augment space station capability through the use of teleoperation and robotics. AI technology will also be developed for the servicing of satellites at the Space Station, system monitoring and diagnosis, space manufacturing, and the assembly of large space structures
Symmetry breaking perturbations and strange attractors
The asymmetrically forced, damped Duffing oscillator is introduced as a
prototype model for analyzing the homoclinic tangle of symmetric dissipative
systems with \textit{symmetry breaking} disturbances. Even a slight fixed
asymmetry in the perturbation may cause a substantial change in the asymptotic
behavior of the system, e.g. transitions from two sided to one sided strange
attractors as the other parameters are varied. Moreover, slight asymmetries may
cause substantial asymmetries in the relative size of the basins of attraction
of the unforced nearly symmetric attracting regions. These changes seems to be
associated with homoclinic bifurcations. Numerical evidence indicates that
\textit{strange attractors} appear near curves corresponding to specific
secondary homoclinic bifurcations. These curves are found using analytical
perturbational tools
NASA space station automation: AI-based technology review. Executive summary
Research and Development projects in automation technology for the Space Station are described. Artificial Intelligence (AI) based technologies are planned to enhance crew safety through reduced need for EVA, increase crew productivity through the reduction of routine operations, increase space station autonomy, and augment space station capability through the use of teleoperation and robotics
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