472 research outputs found
Equilibrium spherically curved 2D Lennard-Jones systems
To learn about basic aspects of nano-scale spherical molecular shells during
their formation, spherically curved two-dimensional N-particle Lennard-Jones
systems are simulated, studying curvature evolution paths at zero-temperature.
For many N-values (N<800) equilibrium configurations are traced as a function
of the curvature radius R. Sharp jumps for tiny changes in R between
trajectories with major differences in topological structure correspond to
avalanche-like transitions. For a typical case, N=25, equilibrium
configurations fall on smooth trajectories in state space which can be traced
in the E-R plane. The trajectories show-up with local energy minima, from which
growth in N at steady curvature can develop.Comment: 10 pages, 2 figures, to be published in Journal of Chemical Physic
Nuclear effects in Deep Inelastic Scattering of polarized electrons off polarized 3He and the neutron spin structure functions
It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized He are mainly
those arising from the effective proton and neutron polarizations generated by
the and waves in He. A simple and reliable equation relating the
neutron, , and He, , spin structure functions is proposed. It
is shown that the measurement of the first moment of the He structure
function can provide a significant check of the Bjorken Sum Rule.Comment: 11 pages (revTeX), DFUPG 75/93; 5 (postscript) figures available upon
request from the author
Front Propagation with Rejuvenation in Flipping Processes
We study a directed flipping process that underlies the performance of the
random edge simplex algorithm. In this stochastic process, which takes place on
a one-dimensional lattice whose sites may be either occupied or vacant,
occupied sites become vacant at a constant rate and simultaneously cause all
sites to the right to change their state. This random process exhibits rich
phenomenology. First, there is a front, defined by the position of the
left-most occupied site, that propagates at a nontrivial velocity. Second, the
front involves a depletion zone with an excess of vacant sites. The total
excess D_k increases logarithmically, D_k ~ ln k, with the distance k from the
front. Third, the front exhibits rejuvenation -- young fronts are vigorous but
old fronts are sluggish. We investigate these phenomena using a quasi-static
approximation, direct solutions of small systems, and numerical simulations.Comment: 10 pages, 9 figures, 4 table
A computational model of perception and action for cognitive robotics
Robots are increasingly expected to perform tasks in complex environments. To this end, engineers provide them with processing architectures that are based on models of human information processing. In contrast to traditional models, where information processing is typically set up in stages (i.e., from perception to cognition to action), it is increasingly acknowledged by psychologists and robot engineers that perception and action are parts of an interactive and integrated process. In this paper, we present HiTEC, a novel computational (cognitive) model that allows for direct interaction between perception and action as well as for cognitive control, demonstrated by task-related attentional influences. Simulation results show that key behavioral studies can be readily replicated. Three processing aspects of HiTEC are stressed for their importance for cognitive robotics: (1) ideomotor learning of action control, (2) the influence of task context and attention on perception, action planning, and learning, and (3) the interaction between perception and action planning. Implications for the design of cognitive robotics are discussed
Cardiorespiratory Improvements Achieved by American College of Sports Medicine's Exercise Prescription Implemented on a Mobile App
Background: Strong evidence shows that an increase in cardiorespiratory fitness (CRF) and physical activity (PA) reduces
cardiovascular disease risk.
Objective: To test whether a scientifically endorsed program to increase CRF and PA, implemented on an easy-to-use,
always-accessible mobile app would be effective in improving CRF.
Methods: Of 63 healthy volunteers participating, 18 tested the user interface of the Cardio-Fitness App (CF-App); and 45
underwent a 2-week intervention period, of whom 33 eventually concluded it. These were assigned into three groups. The
Step-based App (Step-App) group (n=8), followed 10,000 steps/day prescription, the CF-App group (n=13), and the Supervised
Cardio-Fitness (Super-CF) group (n=12), both followed a heart rate (HR)-based program according to American College of Sports
Medicine (ACSM) guidelines, but either implemented on the app, or at the gym, respectively. Participants were tested for CRF,
PA, resting systolic and diastolic blood pressures (SBP, DBP), resting, exercise, and recovery HR.
Results: CRF increased in all groups (+4.9%; P<.001). SBP decreased in all groups (-2.6 mm Hg; P=.03). DBP decrease was
higher in the Super-CF group (-3.5 mm Hg) than in the Step-App group (-2.1 mm Hg; P<.001). Posttest exercise HR decreased
in all groups (-3.4 bpm; P=.02). Posttest recovery HR was lower in the Super-CF group (-10.1 bpm) than in the other two groups
(CF-App: -4.9 bpm, Step-App: -3.3 bpm; P<.001). The CF-App group, however, achieved these improvements with more training
heart beats (P<.01).
Conclusions: A 10,000 steps/day target-based app improved CRF similar to an ACSM guideline-based program whether it was
implemented on a mobile app or in supervised gym sessions.
(JMIR Mhealth Uhealth 2016;4(2):e77) doi:10.2196/mhealth.551
Action functionals for relativistic perfect fluids
Action functionals describing relativistic perfect fluids are presented. Two
of these actions apply to fluids whose equations of state are specified by
giving the fluid energy density as a function of particle number density and
entropy per particle. Other actions apply to fluids whose equations of state
are specified in terms of other choices of dependent and independent fluid
variables. Particular cases include actions for isentropic fluids and
pressureless dust. The canonical Hamiltonian forms of these actions are
derived, symmetries and conserved charges are identified, and the boundary
value and initial value problems are discussed. As in previous works on perfect
fluid actions, the action functionals considered here depend on certain
Lagrange multipliers and Lagrangian coordinate fields. Particular attention is
paid to the interpretations of these variables and to their relationships to
the physical properties of the fluid.Comment: 40 pages, plain Te
A Closed-Form Solution of the Multi-Period Portfolio Choice Problem for a Quadratic Utility Function
In the present paper, we derive a closed-form solution of the multi-period
portfolio choice problem for a quadratic utility function with and without a
riskless asset. All results are derived under weak conditions on the asset
returns. No assumption on the correlation structure between different time
points is needed and no assumption on the distribution is imposed. All
expressions are presented in terms of the conditional mean vectors and the
conditional covariance matrices. If the multivariate process of the asset
returns is independent it is shown that in the case without a riskless asset
the solution is presented as a sequence of optimal portfolio weights obtained
by solving the single-period Markowitz optimization problem. The process
dynamics are included only in the shape parameter of the utility function. If a
riskless asset is present then the multi-period optimal portfolio weights are
proportional to the single-period solutions multiplied by time-varying
constants which are depending on the process dynamics. Remarkably, in the case
of a portfolio selection with the tangency portfolio the multi-period solution
coincides with the sequence of the simple-period solutions. Finally, we compare
the suggested strategies with existing multi-period portfolio allocation
methods for real data.Comment: 38 pages, 9 figures, 3 tables, changes: VAR(1)-CCC-GARCH(1,1) process
dynamics and the analysis of increasing horizon are included in the
simulation study, under revision in Annals of Operations Researc
Posture as Index for Approach-Avoidance Behavior
Approach and avoidance are two behavioral responses that make people tend to approach positive and avoid negative situations. This study examines whether postural behavior is influenced by the affective state of pictures. While standing on the Wii⢠Balance Board, participants viewed pleasant, neutral, and unpleasant pictures (passively viewing phase). Then they had to move their body to the left or the right (lateral movement phase) to make the next picture appear. We recorded movements in the anterior-posterior direction to examine approach and avoidant behavior. During passively viewing, people approached pleasant pictures. They avoided unpleasant ones while they made a lateral movement. These findings provide support for the idea that we tend to approach positive and avoid negative situations
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