622 research outputs found
Reduced density matrix hybrid approach: Application to electronic energy transfer
Electronic energy transfer in the condensed phase, such as that occurring in
photosynthetic complexes, frequently occurs in regimes where the energy scales
of the system and environment are similar. This situation provides a challenge
to theoretical investigation since most approaches are accurate only when a
certain energetic parameter is small compared to others in the problem. Here we
show that in these difficult regimes, the Ehrenfest approach provides a good
starting point for a dynamical description of the energy transfer process due
to its ability to accurately treat coupling to slow environmental modes. To
further improve on the accuracy of the Ehrenfest approach, we use our reduced
density matrix hybrid framework to treat the faster environmental modes quantum
mechanically, at the level of a perturbative master equation. This combined
approach is shown to provide an efficient and quantitative description of
electronic energy transfer in a model dimer and the Fenna-Matthews-Olson
complex and is used to investigate the effect of environmental preparation on
the resulting dynamics.Comment: 11 pages, 8 figure
Predicting Muscularity-Related Behavior, Emotions, and Cognitions in Men: The Role of Psychological Need Thwarting, Drive for Muscularity, and Mesomorphic Internalization
We examine the relationships that internalization, need thwarting (NT), and drive for muscularity (DFM), along with their interactions, had with weightlifting, muscle dissatisfaction (MD), and muscle-related-worry (MRW). A sample of 552 men (MAGE = 20.5 years, SD = 3.1) completed the Psychological Need Thwarting Scale, the Internalization subscale of the male version of the Sociocultural Attitudes Towards Appearance Questionnaire, the Drive for Muscularity Scale-Attitudes subscale, the Male Body Attitudes Scale-Muscularity subscale, the Body Change Inventory-Worry subscale, and an inventory assessing weightlifting behavior. DFM significantly predicted weightlifting, MRW, and MD. Internalization significantly predicted weightlifting and MRW. NT significantly predicted weightlifting and MD, and its relationship with MRW approached significance. The interaction terms did not predict weightlifting or MRW. The NT/DFM and NT/Internalization interaction terms predicted MD. These results highlight the role of NT in predicting appearance variables in men
The Ursinus Weekly, May 19, 1958
Haag prexy of men\u27s student government • Annual banquet held by Varsity Club Tues., May 13 • Seniors feted at annual banquet • Special editorial: Customs • Dr. Cooke speaks on mental difficulties of our children • Election results for officers are announced • Ottenberg speaks on the problems of skid rowers • Editorial: Leadership and service • Inner peace • Letters to the editor • To the hilt • Against me • Cindermen whip Washington squad; Lose to Dickinson • Tennis team picks up first two wins; Loses close tilt • Bears nine win two; Beaten by Wilkes, 3-2 • Drexel defeated by lacrosse team • West Chester wallops JV varsity softball teams • Tennis team routs strongest rival • Dr. Hugh Borton to speak at foreign traders dinner • Library accessionshttps://digitalcommons.ursinus.edu/weekly/1408/thumbnail.jp
Efficient multiple time scale molecular dynamics: using colored noise thermostats to stabilize resonances
Multiple time scale molecular dynamics enhances computational efficiency by
updating slow motions less frequently than fast motions. However, in practice
the largest outer time step possible is limited not by the physical forces but
by resonances between the fast and slow modes. In this paper we show that this
problem can be alleviated by using a simple colored noise thermostatting scheme
which selectively targets the high frequency modes in the system. For two
sample problems, flexible water and solvated alanine dipeptide, we demonstrate
that this allows the use of large outer time steps while still obtaining
accurate sampling and minimizing the perturbation of the dynamics. Furthermore,
this approach is shown to be comparable to constraining fast motions, thus
providing an alternative to molecular dynamics with constraints.Comment: accepted for publication by the Journal of Chemical Physic
The Ursinus Weekly, May 19, 1958
Haag prexy of men\u27s student government • Annual banquet held by Varsity Club Tues., May 13 • Seniors feted at annual banquet • Special editorial: Customs • Dr. Cooke speaks on mental difficulties of our children • Election results for officers are announced • Ottenberg speaks on the problems of skid rowers • Editorial: Leadership and service • Inner peace • Letters to the editor • To the hilt • Against me • Cindermen whip Washington squad; Lose to Dickinson • Tennis team picks up first two wins; Loses close tilt • Bears nine win two; Beaten by Wilkes, 3-2 • Drexel defeated by lacrosse team • West Chester wallops JV varsity softball teams • Tennis team routs strongest rival • Dr. Hugh Borton to speak at foreign traders dinner • Library accessionshttps://digitalcommons.ursinus.edu/weekly/1408/thumbnail.jp
Efficient stochastic thermostatting of path integral molecular dynamics
The path integral molecular dynamics (PIMD) method provides a convenient way
to compute the quantum mechanical structural and thermodynamic properties of
condensed phase systems at the expense of introducing an additional set of
high-frequency normal modes on top of the physical vibrations of the system.
Efficiently sampling such a wide range of frequencies provides a considerable
thermostatting challenge. Here we introduce a simple stochastic path integral
Langevin equation (PILE) thermostat which exploits an analytic knowledge of the
free path integral normal mode frequencies. We also apply a recently-developed
colored-noise thermostat based on a generalized Langevin equation (GLE), which
automatically achieves a similar, frequency-optimized sampling. The sampling
efficiencies of these thermostats are compared with that of the more
conventional Nos\'e-Hoover chain (NHC) thermostat for a number of physically
relevant properties of the liquid water and hydrogen-in-palladium systems. In
nearly every case, the new PILE thermostat is found to perform just as well as
the NHC thermostat while allowing for a computationally more efficient
implementation. The GLE thermostat also proves to be very robust delivering a
near-optimum sampling efficiency in all of the cases considered. We suspect
that these simple stochastic thermostats will therefore find useful application
in many future PIMD simulations.Comment: Accepted for publication on JC
Reduced density matrix hybrid approach: An efficient and accurate method for adiabatic and non-adiabatic quantum dynamics
We present a new approach to calculate real-time quantum dynamics in complex
systems. The formalism is based on the partitioning of a system's environment
into "core" and "reservoir" modes, with the former to be treated quantum
mechanically and the latter classically. The presented method only requires the
calculation of the system's reduced density matrix averaged over the quantum
core degrees of freedom which is then coupled to a classically evolved
reservoir to treat the remaining modes. We demonstrate our approach by applying
it to the spin-boson problem using the noninteracting blip approximation to
treat the system and core, and Ehrenfest dynamics to treat the reservoir. The
resulting hybrid methodology is accurate for both fast and slow baths, since it
naturally reduces to its composite methods in their respective regimes of
validity. In addition, our combined method is shown to yield good results in
intermediate regimes where neither approximation alone is accurate and to
perform equally well for both strong and weak system-bath coupling. Our
approach therefore provides an accurate and efficient methodology for
calculating quantum dynamics in complex systems.Comment: 10 pages, 7 figure
The Lantern Vol. 26, No. 2, Spring 1958
• The Wise Man • Of Men and Lobsters • The Painting • The Ghost of Moon Mountain • Song for the Atomic Age • Opus I • Stillnesshttps://digitalcommons.ursinus.edu/lantern/1074/thumbnail.jp
In the beginning: Role of autonomy support on the motivation, mental health and intentions of participants entering an exercise referral scheme
Self-determination theory (Deci & Ryan, 2000, Intrinsic motivation and self-determination in human behaviour. New York: Plenum Publishing) highlights the impact autonomy supportive environments can have on exercise motivation and positive health outcomes. Yet little is known about whether differential effects occur as a function of which significant other is providing this support. Further, no research has examined the relationship between motivation and the social environment with participants’ mental health and intentions to be physically active before entering an exercise intervention. Study participants were 347 British adults who were about to start an exercise referral scheme. Regression analyses revealed that the effects of autonomy support on mental health and physical activity intentions differed as a function of who provided the support (offspring, partner or physician), with the offspring having the weakest effects. A structural model was supported, indicating that autonomy support and more autonomous regulations led to more positive mental health outcomes and stronger intentions to be physically active. Knowledge of the social environmental and personal motivation of those about to commence an exercise programme can provide important insights for professionals supporting such efforts
Vibrational dynamics of confined granular material
By means of two-dimensional contact dynamics simulations, we analyze the
vibrational dynamics of a confined granular layer in response to harmonic
forcing. We use irregular polygonal grains allowing for strong variability of
solid fraction. The system involves a jammed state separating passive (loading)
and active (unloading) states. We show that an approximate expression of the
packing resistance force as a function of the displacement of the free
retaining wall from the jamming position provides a good description of the
dynamics. We study in detail the scaling of displacements and velocities with
loading parameters. In particular, we find that, for a wide range of
frequencies, the data collapse by scaling the displacements with the inverse
square of frequency, the inverse of the force amplitude and the square of
gravity. Interestingly, compaction occurs during the extension of the packing,
followed by decompaction in the contraction phase. We show that the mean
compaction rate increases linearly with frequency up to a characteristic
frequency and then it declines in inverse proportion to frequency. The
characteristic frequency is interpreted in terms of the time required for the
relaxation of the packing through collective grain rearrangements between two
equilibrium states
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