132 research outputs found
Why do gallium clusters have a higher melting point than the bulk?
Density functional molecular dynamical simulations have been performed on
Ga and Ga clusters to understand the recently observed
higher-than-bulk melting temperatures in small gallium clusters [Breaux {\em et
al.}, Phys. Rev. Lett. {\bf 91}, 215508 (2003)]. The specific-heat curve,
calculated with the multiple-histogram technique, shows the melting temperature
to be well above the bulk melting point of 303 K, viz. around 650 K and 1400 K
for Ga and Ga, respectively. The higher-than-bulk melting
temperatures are attributed mainly to the covalent bonding in these clusters,
in contrast with the covalent-metallic bonding in the bulk.Comment: 4 pages, including 6 figures. accepted for publication in Phys. Rev.
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Melting Point and Lattice Parameter Shifts in Supported Metal Nanoclusters
The dependencies of the melting point and the lattice parameter of supported
metal nanoclusters as functions of clusters height are theoretically
investigated in the framework of the uniform approach. The vacancy mechanism
describing the melting point and the lattice parameter shifts in nanoclusters
with decrease of their size is proposed. It is shown that under the high vacuum
conditions (p<10^-7 torr) the essential role in clusters melting point and
lattice parameter shifts is played by the van der Waals forces of
cluster-substrate interation. The proposed model satisfactorily accounts for
the experimental data.Comment: 6 pages, 3 figures, 1 tabl
Size--sensitive melting characteristics of gallium clusters: Comparison of Experiment and Theory for Ga and Ga
Experiments and simulations have been performed to examine the
finite-temperature behavior of Ga and Ga clusters.
Specific heats and average collision cross sections have been measured as a
function of temperature, and the results compared to simulations performed
using first principles Density--Functional Molecular--Dynamics. The
experimental results show that while Ga apparently undergoes a
solid--liquid transition without a significant peak in the specific--heat,
Ga melts with a relatively sharp peak. Our analysis of the
computational results indicate a strong correlation between the ground--state
geometry and the finite--temperature behavior of the cluster. If the
ground--state geometry is symmetric and "ordered" the cluster is found to have
a distinct peak in the specific--heat. However, if the ground--state geometry
is amorphous or "disordered" the cluster melts without a peak in the
specific--heat.Comment: 6 figure
Impurity effects on the melting of Ni clusters
We demonstrate that the addition of a single carbon impurity leads to
significant changes in the thermodynamic properties of Ni clusters consisting
of more than a hundred atoms. The magnitude of the change induced is dependent
upon the parameters of the Ni-C interaction. Hence, thermodynamic properties of
Ni clusters can be effectively tuned by the addition of an impurity of a
particular type. We also show that the presence of a carbon impurity
considerably changes the mobility and diffusion of atoms in the Ni cluster at
temperatures close to its melting point. The calculated diffusion coefficients
of the carbon impurity in the Ni cluster can be used for a reliable estimate of
the growth rate of carbon nanotubes.Comment: 27 pages, 13 figure
A soy-based phosphatidylserine/ phosphatidic acid complex (PAS) normalizes the stress reactivity of hypothalamus-pituitary-adrenal-axis in chronically stressed male subjects: a randomized, placebo-controlled study
Metal Matrix–Metal Nanoparticle Composites with Tunable Melting Temperature and High Thermal Conductivity for Phase-Change Thermal Storage
Evidence-based Kernels: Fundamental Units of Behavioral Influence
This paper describes evidence-based kernels, fundamental units of behavioral influence that appear to underlie effective prevention and treatment for children, adults, and families. A kernel is a behavior–influence procedure shown through experimental analysis to affect a specific behavior and that is indivisible in the sense that removing any of its components would render it inert. Existing evidence shows that a variety of kernels can influence behavior in context, and some evidence suggests that frequent use or sufficient use of some kernels may produce longer lasting behavioral shifts. The analysis of kernels could contribute to an empirically based theory of behavioral influence, augment existing prevention or treatment efforts, facilitate the dissemination of effective prevention and treatment practices, clarify the active ingredients in existing interventions, and contribute to efficiently developing interventions that are more effective. Kernels involve one or more of the following mechanisms of behavior influence: reinforcement, altering antecedents, changing verbal relational responding, or changing physiological states directly. The paper describes 52 of these kernels, and details practical, theoretical, and research implications, including calling for a national database of kernels that influence human behavior
Melting, Premelting, and Structural Transitions in Size-Selected Aluminum Clusters with around 55 Atoms
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