739 research outputs found
Magnetic Silicon Fullerene
A metal-encapsulating silicon fullerene, Eu@Si20, has been predicted by
density functional theory to be by far the most stable fullerene-like silicon
structure. The Eu@Si20 structure is a dodecahedron with D2h symmetry in which
the europium atom occupies the center site. The calculated results show that
the europium atom has a large magnetic moment of nearly 7.0 Bohr magnetons. In
addition, it was found that a stable "pearl necklace" nanowire, constructed by
concatenating a series of Eu@Si20 units, with the central europium atom,
retains the high spin moment. The magnetic structure of the nanowire indicates
potential applications in the fields of spintronics and high-density magnetic
storage
Formation of a "Cluster Molecule" (C20)2 and its thermal stability
The possible formation of a "cluster molecule" (C20)2 from two single C20
fullerenes is studied by the tight-binding method. Several (C20)2 isomers in
which C20 fullerenes are bound by strong covalent forces and retain their
identity are found; actually, these C20 fullerenes play the role of "atoms" in
the "cluster molecule". The so-called open-[2+2] isomer has a minimum energy.
Its formation path and thermal stability at T = 2000 - 4000 K are analyzed in
detail. This isomer loses its molecular structure due to either the decay of
one of C20 fullerenes or the coalescence of two C20 fullerenes into a C40
cluster. The energy barriers for the metastable open-[2+2] configuration are
calculated to be U = 2 - 5 eV.Comment: 21 pages, 8 figure
First-principles study of electron transport through cages
Electron transport properties of C molecules suspended between gold
electrodes are investigated using first-principles calculations. Our study
reveals that the conductances are quite sensitive to the number of C
molecules between electrodes: the conductances of C monomers are near 1
G, while those of dimers are markedly smaller, since incident electrons
easily pass the C molecules and are predominantly scattered at the
C-C junctions. Moreover, we find both channel currents locally
circulating the outermost carbon atoms.Comment: 8 pages and 3 figure
Stability of C20 fullerene chains
The stability of (C20)N chains with N = 3 - 7 is analyzed by numerical
simulation using a tight-binding potential and molecular dynamics. Various
channels of losing the cluster-chain structure of the (C20)N complexes are
observed, including the decay of C20 clusters, their coalescence, and the
separation of one C20 fullerene from the chain.Comment: To appear in JETP Letter
Anomalous Thermal Stability of Metastable C_20 Fullerene
The results of computer simulation of the dynamics of fullerene C_20 at
different temperatures are presented. It is shown that, although it is
metastable, this isomer is very stable with respect to the transition to a
lower energy configuration and retains its chemical structure under heating to
very high temperatures, T ~ 3000 K. Its decay activation energy is found to be
E_a ~ 7 eV. Possible decay channels are studied, and the height of the minimum
potential barrier to decay is determined to be U = 5.0 eV. The results obtained
make it possible to understand the reasons for the anomalous stability of
fullerene C_20 under normal conditions.Comment: Slightly corrected version of the paper submitted to Phys. Solid
Stat
Decay and fusion as two different mechanisms of stability loss for the (C_20)_2 cluster dimer
The thermal stability of the (C_20)_2 cluster dimer consisting of two C_20
fullerenes is examined using a tight-binding approach. Molecular dynamics
simulations of the (C_20)_2 dimer at temperatures T = 2000 - 3500 K show that
the finite lifetime \tau of this metastable system is determined by two
fundamentally different processes, the decay of one of the C_20 fullerenes and
the fusion of two C_20 fullerenes into the C_40 cluster. The activation
energies for these processes Ea = 3.4 and 2.7 eV, respectively, as well as
their frequency factors, have been determined by analyzing the dependence of
\tau on T.Comment: Slightly modified version of the paper to appear in JETP Let
Structure and Stability of Two-Dimensional Complexes of C_20 Fullerenes
Two-dimensional complexes of C_20 fullerenes connected to each other by
covalent bonds have been studied. Several isomers with different types of
intercluster bonds have been revealed. The lifetimes of the (C_20)_MxM systems
with M = 2 and 3 have been directly calculated at T = 1800 - 3300 K making use
of molecular dynamics. It has been shown that these complexes lose their
periodic cluster structure due to either coalescence of two fullerenes C_20 or
decay of C_20 fullerenes. The activation energies of these processes exceed 2
eV.Comment: 17 pages, 5 figure
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An engineering model to simulate the thermal response of electronic devices during pulsed Nd:YAG laser welding
A model is developed to predict the thermal response of real electronic devices during pulsed Nd:YAG laser welding. Modeling laser-part interaction requires incorporation of weld pool hydrodynamics, and laser-metal vapor and laser-surface interactions. Although important information can be obtained from these models, they are not appropriate for use in design of actual components due to computational limitations. In lieu of solving for these detailed physics, a simple model is constructed. In this model, laser-part interactions are accounted for through an empirically determined energy transfer efficiency which is developed through the use of modeling and experiments. This engineering model is appropriate since part thermal response near the weld pool and weld pool shape is not of interest here. Reasonable agreement between predictions and experimental measurements for welding of real components are indicated
Особенности оценки профессиональных рисков в медицинской организации
Работа посвящена оценки профессионального риска для работников медицинских организаций с учетом эпидемиологической обстановки. В данной работе рассмотрено нормативно-правовое регулирование оценки профессионального риска в Российской Федерации. Проведен анализ существующих методов оценки профессионального риска. В результате исследования проведена оценка профессионального риска для работников медицинской организации и предложены мероприятия по уменьшению уровня риска.The work is devoted to the assessment of professional risk for employees of medical organizations, taking into account the epidemiological situation. This paper examines the legal regulation of professional risk assessment in the Russian Federation. The analysis of existing methods of professional risk assessment is carried out. As a result of the study, an assessment of professional risk for employees of a medical organization was carried out and measures to reduce the level of risk were proposed
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