2,621 research outputs found
Phase Splitting for Periodic Lie Systems
In the context of the Floquet theory, using a variation of parameter
argument, we show that the logarithm of the monodromy of a real periodic Lie
system with appropriate properties admits a splitting into two parts, called
dynamic and geometric phases. The dynamic phase is intrinsic and linked to the
Hamiltonian of a periodic linear Euler system on the co-algebra. The geometric
phase is represented as a surface integral of the symplectic form of a
co-adjoint orbit.Comment: (v1) 15 pages. (v2) 16 pages. Some typos corrected. References and
further comments added. Final version to appear in J. Phys. A
Diffraction of complex molecules by structures made of light
We demonstrate that structures made of light can be used to coherently
control the motion of complex molecules. In particular, we show diffraction of
the fullerenes C60 and C70 at a thin grating based on a standing light wave. We
prove experimentally that the principles of this effect, well known from atom
optics, can be successfully extended to massive and large molecules which are
internally in a thermodynamic mixed state and which do not exhibit narrow
optical resonances. Our results will be important for the observation of
quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure
A Web-Based, Positive Emotion Skills Intervention for Enhancing Posttreatment Psychological Well-Being in Young Adult Cancer Survivors (EMPOWER): Protocol for a Single-Arm Feasibility Trial
BACKGROUND: Adolescent and young adult cancer survivors (AYAs) experience clinically significant distress and have limited access to supportive care services. Interventions to enhance psychological well-being have improved positive affect and reduced depression in clinical and healthy populations but have not been routinely tested in AYAs.
OBJECTIVE: The aim of this protocol is to (1) test the feasibility and acceptability of a Web-based positive emotion skills intervention for posttreatment AYAs called Enhancing Management of Psychological Outcomes With Emotion Regulation (EMPOWER) and (2) examine proof of concept for reducing psychological distress and enhancing psychological well-being.
METHODS: The intervention development and testing are taking place in 3 phases. In phase 1, we adapted the content of an existing, Web-based positive emotion intervention so that it would be suitable for AYAs. EMPOWER targets 8 skills (noticing positive events, capitalizing, gratitude, mindfulness, positive reappraisal, goal setting, personal strengths, and acts of kindness) and is delivered remotely as a 5-week, Web-based intervention. Phase 2 consisted of a pilot test of EMPOWER in a single-arm trial to evaluate feasibility, acceptability, retention, and adherence and to collect data on psychosocial outcomes for proof of concept. In phase 3, we are refining study procedures and conducting a second pilot test.
RESULTS: The project was part of a career development award. Pilot work began in June 2015, and data collection was completed in March 2019. The analysis is ongoing, and results will be submitted for publication by May 2020.
CONCLUSIONS: If this intervention proves feasible and acceptable, EMPOWER will be primed for a subsequent large, multisite randomized controlled trial. As a scalable intervention, it will be ideally suited for AYA survivors who would otherwise not have access to supportive care interventions to help manage posttreatment distress and enhance well-being.
TRIAL REGISTRATION: ClinicalTrials.gov NCT02832154, https://clinicaltrials.gov/ct2/show/NCT02832154.
INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/1707
Genetic basis of octanoic acid resistance in Drosophila sechellia: functional analysis of a fine‐mapped region
Drosophila sechellia is a species of fruit fly endemic to the Seychelles islands. Unlike its generalist sister species, D. sechellia has evolved to be a specialist on the host plant Morinda citrifolia. This specialization is interesting because the plant’s fruit contains secondary defence compounds, primarily octanoic acid (OA), that are lethal to most other Drosophilids. Although ecological and behavioural adaptations to this toxic fruit are known, the genetic basis for evolutionary changes in OA resistance is not. Prior work showed that a genomic region on chromosome 3R containing 18 genes has the greatest contribution to differences in OA resistance between D. sechellia and D. simulans. To determine which gene(s) in this region might be involved in the evolutionary change in OA resistance, we knocked down expression of each gene in this region in D. melanogaster with RNA interference (RNAi) (i) ubiquitously throughout development, (ii) during only the adult stage and (iii) within specific tissues. We identified three neighbouring genes in the Osiris family, Osiris 6 (Osi6), Osi7 and Osi8, that led to decreased OA resistance when ubiquitously knocked down. Tissue‐specific RNAi, however, showed that decreasing expression of Osi6 and Osi7 specifically in the fat body and/or salivary glands increased OA resistance. Gene expression analyses of Osi6 and Osi7 revealed that while standing levels of expression are higher in D. sechellia, Osi6 expression is significantly downregulated in salivary glands in response to OA exposure, suggesting that evolved tissue‐specific environmental plasticity of Osi6 expression may be responsible for OA resistance in D. sechellia.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136293/1/mec14001_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136293/2/mec14001.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136293/3/mec14001-sup-0001-SupInfo.pd
Coherently Controlled Nanoscale Molecular Deposition
Quantum interference effects are shown to provide a means of controlling and
enhancing the focusing a collimated neutral molecular beam onto a surface. The
nature of the aperiodic pattern formed can be altered by varying laser field
characteristics and the system geometry.Comment: 13 pages (inculding 4 figures), LaTeX (Phys. Rev. Lett., 2000, in
Press
Talbot Oscillations and Periodic Focusing in a One-Dimensional Condensate
An exact theory for the density of a one-dimensional Bose-Einstein condensate
with hard core particle interactions is developed in second quantization and
applied to the scattering of the condensate by a spatially periodic impulse
potential. The boson problem is mapped onto a system of free fermions obeying
the Pauli exclusion principle to facilitate the calculation. The density
exhibits a spatial focusing of the probability density as well as a periodic
self-imaging in time, or Talbot effect. Furthermore, the transition from single
particle to many body effects can be measured by observing the decay of the
modulated condensate density pattern in time. The connection of these results
to classical and atom optical phase gratings is made explicit
Short time evolved wave functions for solving quantum many-body problems
The exact ground state of a strongly interacting quantum many-body system can
be obtained by evolving a trial state with finite overlap with the ground state
to infinite imaginary time. In this work, we use a newly discovered fourth
order positive factorization scheme which requires knowing both the potential
and its gradients. We show that the resultaing fourth order wave function
alone, without further iterations, gives an excellent description of strongly
interacting quantum systems such as liquid 4He, comparable to the best
variational results in the literature.Comment: 5 pages, 3 figures, 1 tabl
A Constrained Path Monte Carlo Method for Fermion Ground States
We describe and discuss a recently proposed quantum Monte Carlo algorithm to
compute the ground-state properties of various systems of interacting fermions.
In this method, the ground state is projected from an initial wave function by
a branching random walk in an over-complete basis of Slater determinants. By
constraining the determinants according to a trial wave function
, we remove the exponential decay of signal-to-noise ratio
characteristic of the sign problem. The method is variational and is exact if
is exact. We illustrate the method by describing in detail its
implementation for the two-dimensional one-band Hubbard model. We show results
for lattice sizes up to and for various electron fillings and
interaction strengths. Besides highly accurate estimates of the ground-state
energy, we find that the method also yields reliable estimates of other
ground-state observables, such as superconducting pairing correlation
functions. We conclude by discussing possible extensions of the algorithm.Comment: 29 pages, RevTex, 3 figures included; submitted to Phys. Rev.
Issues and Observations on Applications of the Constrained-Path Monte Carlo Method to Many-Fermion Systems
We report several important observations that underscore the distinctions
between the constrained-path Monte Carlo method and the continuum and lattice
versions of the fixed-node method. The main distinctions stem from the
differences in the state space in which the random walk occurs and in the
manner in which the random walkers are constrained. One consequence is that in
the constrained-path method the so-called mixed estimator for the energy is not
an upper bound to the exact energy, as previously claimed. Several ways of
producing an energy upper bound are given, and relevant methodological aspects
are illustrated with simple examples.Comment: 28 pages, REVTEX, 5 ps figure
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