3,885 research outputs found
Effect of Samarium doping on the nucleation of fcc-Aluminum in undercooled liquids
The effect of Sm doping on the fcc-Al nucleation was investigated in Al-Sm
liquids with low Sm concentrations (xSm) with molecular dynamics simulations.
The nucleation in the moderately undercooled liquid is achieved by the recently
developed persistent-embryo method. Systematically computing the nucleation
rate with different xSm (xSm=0%, 1%, 2%, 3%, 5%) at 700 K, we found Sm dopant
reduces the nucleation rate by up to 25 orders of magnitudes with only 5%
doping concentration. This effect is mostly associated with the increase in the
free energy barrier with a minor contribution from suppression of the
attachment to the nucleus caused by Sm doping.Comment: 4 figure
Phase delaying the human circadian clock with a single light pulse and moderate delay of the sleep/dark episode: no influence of iris color
<p>Abstract</p> <p>Background</p> <p>Light exposure in the late evening and nighttime and a delay of the sleep/dark episode can phase delay the circadian clock. This study assessed the size of the phase delay produced by a single light pulse combined with a moderate delay of the sleep/dark episode for one day. Because iris color or race has been reported to influence light-induced melatonin suppression, and we have recently reported racial differences in free-running circadian period and circadian phase shifting in response to light pulses, we also tested for differences in the magnitude of the phase delay in subjects with blue and brown irises.</p> <p>Methods</p> <p>Subjects (blue-eyed n = 7; brown eyed n = 6) maintained a regular sleep schedule for 1 week before coming to the laboratory for a baseline phase assessment, during which saliva was collected every 30 minutes to determine the time of the dim light melatonin onset (DLMO). Immediately following the baseline phase assessment, which ended 2 hours after baseline bedtime, subjects received a 2-hour bright light pulse (~4,000 lux). An 8-hour sleep episode followed the light pulse (i.e. was delayed 4 hours from baseline). A final phase assessment was conducted the subsequent night to determine the phase shift of the DLMO from the baseline to final phase assessment.</p> <p>Phase delays of the DLMO were compared in subjects with blue and brown irises. Iris color was also quantified from photographs using the three dimensions of red-green-blue color axes, as well as a lightness scale. These variables were correlated with phase shift of the DLMO, with the hypothesis that subjects with lighter irises would have larger phase delays.</p> <p>Results</p> <p>The average phase delay of the DLMO was -1.3 ± 0.6 h, with a maximum delay of ~2 hours, and was similar for subjects with blue and brown irises. There were no significant correlations between any of the iris color variables and the magnitude of the phase delay.</p> <p>Conclusion</p> <p>A single 2-hour bright light pulse combined with a moderate delay of the sleep/dark episode delayed the circadian clock an average of ~1.5 hours. There was no evidence that iris color influenced the magnitude of the phase shift. Future studies are needed to replicate our findings that iris color does not impact the magnitude of light-induced circadian phase shifts, and that the previously reported differences may be due to race.</p
A Study of the Effect of Anger on Immoral Judgment of Internet Privacy Invasion
With the emergence of Web 2.0, people are able to share their thoughts and photos with their friends and strangers. Yet, they also risk invasion of their privacy. Information privacy has therefore become an important issue in the information age. In this research, we focus on the influence of anger on immoral judgment of privacy invasion in cyberspace. Specifically, two scenarios, nonviolent and violent-depiction, are designed to investigate the influence of anger on immoral decision making. Our results revealed that the level of anger will increase immoral judgment in nonviolent and violent depiction scenarios, respectively. And the level of anger in violent-depiction scenario is higher than in nonviolent-depiction scenario. The research findings show that college students easily make an immoral judgment in violent situations. In violent depiction scenario, however, high moral obligation group can enhance the effect of ethical self-efficacy for moral judgment
Temperature dependence of the solid-liquid interface free energy of Ni and Al from molecular dynamics simulation of nucleation
The temperature dependence of the solid-liquid interfacial free energy,
{\gamma}, is investigated for Al and Ni at the undercooled temperature regime
based on a recently developed persistent-embryo method. The atomistic
description of the nucleus shape is obtained from molecular dynamics
simulations. The computed {\gamma} shows a linear dependence on the
temperature. The values of {\gamma} extrapolated to the melting temperature
agree well with previous data obtained by the capillary fluctuation method.
Using the temperature dependence of {\gamma}, we estimate the nucleation free
energy barrier in a wide temperature range from the classical nucleation
theory. The obtained data agree very well with the results from the brute-force
molecular dynamics simulations
Competitive B2 and B33 Nucleation during Solidification of Ni50Zr50 Alloy: Molecular Dynamics Simulation and Classical Nucleation Theory
We investigated the homogenous nucleation of the stoichiometric B2 and B33
phases in the Ni50Zr50 alloy using the persistent embryo method and the
classical nucleation theory. The two phases become very close competitors at
large supercoolings, which is consistent with the experimental observations. In
the case of the B2 phase, the linear temperature dependence of the solid-liquid
interface (SLI) free energy extrapolated to the melting temperature leads to
the same value as the one obtained from the capillarity fluctuation method
(CFM). In the case of the B33 phases, the SLI free energy is also a linear
function of temperature at large supercoolings but the extrapolation to the
melting temperature leads to a value which is considerably different from the
CFM value. This is consistent with the large anisotropy of the SLI properties
of the B33 phase nearby the melting temperature observed in the simulation of
the nominally flat interface migration
Molecular dynamics simulation of the solid-liquid interface migration in terbium
We developed a Tb embedded atom method potential which properly reproduces the liquid structure obtained from the ab initio molecular dynamics simulation, the hexagonal close packed (hcp)-body-centered cubic (bcc) phase transformation, and melting temperatures. At least three crystal phases [hcp, face-centered cubic (fcc), and bcc] described by this potential can coexist with the liquid phase. Thus, the developed potential provides an excellent test bed for studies of the completive phase nucleation and growth in a single component system. The molecular dynamics simulation showed that all crystal phases can grow from the liquid phase close to their melting temperatures. However, in the cases of the hcp and fcc growth from the liquid phase at very large supercoolings, the bcc phase forms at the solid-liquid interface in the close packed orientations in spite of the fact that both hcp and fcc phases are more stable than the bcc phase at these temperatures. This bcc phase closes the hcp and fcc phase from the liquid such that the remaining liquid solidifies into the bcc phase. The initial hcp phase then slowly continues growing in expense of the bcc phase
A self-contained algorithm for determination of solid-liquid equilibria in an alloy system
We describe a self-contained procedure to evaluate the free energy of liquid
and solid phases of an alloy system. The free energy of a single-element solid
phase is calculated with thermodynamic integration using the Einstein crystal
as the reference system. Then, free energy difference between the solid and
liquid phases is calculated by Gibbs-Duhem integration. The central part of our
method is the construction of a reversible alchemical path connecting a pure
liquid and a liquid alloy to calculate the mixing enthalpy and entropy. We have
applied the method to calculate the free energy of solid and liquid phases in
the Al-Sm system. The driving force for fcc-Al nucleation in Al-Sm liquid and
the melting curve for fcc-Al and Al3Sm are also calculated.Comment: 15 pages, 7 figures, submitting to a journa
Effects of dopants on the glass forming ability in Al-based metallic alloy
The effect of dopants on the metallic glass forming ability is usually
considered based on analysis of changes in the liquid structure or
thermodynamics. What is missing in such considerations is an analysis of how a
dopant changes the properties of the crystal phases which can form instead of
the glass. In order to illuminate this aspect we performed molecular dynamics
simulations to study the effects of Mg and Sm dopants on the crystal nucleation
in Al. The simulation data were found to be consistent with the experimental
observations that addition of Mg to Al does not lead to vitrification but
addition of only 8% Sm does. The significant effect of Sm doping was related to
the intolerance of Al to this dopant. This leads to increase in the
solid-liquid interfacial free energy, and therefore, to increase in the
nucleation barrier and to dramatic decrease in the nucleation rate. The
intolerance mechanism also significantly affects the growth kinetics
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