18,813 research outputs found
Quantum properties of two-dimensional electron gas in the inversion layer of Hg1âxCdxTe bicyrstals
The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p-type Hg1âxCdxTe bicrystals are investigated. The results clearly demonstrate the existence of a two-dimensional degenerate n-type inversion layer in the vicinity of the grain boundary. Hydrostatic pressure up to 103 MPa is used to characterize the properties of the two-dimensional electron gas in the inversion layer. At atmospheric pressure three series of quantum oscillations are revealled, indicating that tthree electric subbands are occupied. From quantum oscilations of the magnetoresistivity the characteristics parameters of the electric subbands (subband populations nsi, subband energies EFâEi, effective electron masses m*ci) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied A simple theoretical model based on the triangular-well approximation and taking into account the pressure dependence of the energy band structure of Hg1âxCdxTe is use to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters
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Identification of an interchromosomal compartment by polymerization of nuclear-targeted vimentin
A number of structural and functional subnuclear compartments have been described, including regions
exclusive of chromosomes previously hypothesized to form
a reactive nuclear space. We have now explored this
accessible nuclear space and interchromosomal
nucleoplasmic domains experimentally using Xenopus
vimentin engineered to contain a nuclear localization signal
(NLS-vimentin). In stably transfected human cells
incubated at 37°C, the NLS-vimentin formed a restricted
number of intranuclear speckles. At 28°C, the optimal
temperature for assembly of the amphibian protein, NLSvimentin
progressively extended with time out from the
speckles into strictly orientated intranuclear filamentous
arrays. This enabled us to observe the development of a
system of interconnecting channel-like areas. Quantitative
analysis based on 3-D imaging microscopy revealed that
these arrays were localized almost exclusively outside of
chromosome territories. During mitosis the filaments
disassembled and dispersed throughout the cytoplasm,
while in anaphase-telophase the vimentin was recruited
back into the nucleus and reassembled into filaments at the
chromosome surfaces, in distributions virtually identical to
those observed in the previous interphase. The filaments
also colocalized with specific nuclear RNAs, coiled bodies
and PML bodies, all situated outside of chromosome
territories, thereby interlinking these structures. This
strongly implies that these nuclear entities coexist in the
same interconnected nuclear compartment. The
assembling NLS-vimentin is restricted to and can be used
to delineate, at least in part, the formerly proposed
reticular interchromosomal domain compartment (ICD).
The properties of NLS-vimentin make it an excellent tool
for performing structural and functional studies on this
compartment
Nonlinear structural vibrations by the linear acceleration method
Numerical integration method for calculating dynamic response of nonlinear elastic structure
Cluster-Growth in Freely Cooling Granular Media
When dissipative particles are left alone, their fluctuation energy decays
due to collisional interactions, clusters build up and grow with time until the
system size is reached. When the effective dissipation is strong enough, this
may lead to the `inelastic collapse', i.e. the divergence of the collision
frequency of some particles. The cluster growth is an interesting physical
phenomenon, whereas the inelastic collapse is an intrinsic effect of the
inelastic hard sphere (IHS) model used to study the cluster growth - involving
only a negligible number of particles in the system. Here, we extend the IHS
model by introducing an elastic contact energy and the related contact duration
t_c. This avoids the inelastic collapse and allows to examine the long-time
behavior of the system. For a quantitative description of the cluster growth,
we propose a burning - like algorithm in continuous space, that readily
identifies all particles that belong to the same cluster. The criterion for
this is here chosen to be only the particle distance.
With this method we identify three regimes of behavior. First, for short
times a homogeneous cooling state (HCS) exists, where a mean-field theory works
nicely, and the clusters are tiny and grow very slowly. Second, at a certain
time which depends on the system's properties, cluster growth starts and the
clusters increase in size and mass until, in the third regime, the system size
is reached and most of the particles are collected in one huge cluster.Comment: 16 pages, 21 figures. Chaos 9(3) (in press, 1999
Broad Histogram Monte Carlo
We propose a new Monte Carlo technique in which the degeneracy of energy
states is obtained with a Markovian process analogous to that of Metropolis
used currently in canonical simulations. The obtained histograms are much
broader than those of the canonical histogram technique studied by Ferrenberg
and Swendsen. Thus we can reliably reconstruct thermodynamic functions over a
much larger temperature scale also away from the critical point. We show for
the two-dimensional Ising model how our new method reproduces exact results
more accurately and using less computer time than the conventional histogram
method. We also show data in three dimensions for the Ising ferromagnet and the
Edwards Anderson spin glass.Comment: 6 pages of a TeX file with 4 PS figures. Related papers at
http://www.if.uff.br/~tjp
Model of mobile agents for sexual interactions networks
We present a novel model to simulate real social networks of complex
interactions, based in a granular system of colliding particles (agents). The
network is build by keeping track of the collisions and evolves in time with
correlations which emerge due to the mobility of the agents. Therefore,
statistical features are a consequence only of local collisions among its
individual agents. Agent dynamics is realized by an event-driven algorithm of
collisions where energy is gained as opposed to granular systems which have
dissipation. The model reproduces empirical data from networks of sexual
interactions, not previously obtained with other approaches.Comment: 6 pages, 8 figure
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