5,770 research outputs found
Temperature Dependent Empirical Pseudopotential Theory For Self-Assembled Quantum Dots
We develop a temperature dependent empirical pseudopotential theory to study
the electronic and optical properties of self-assembled quantum dots (QDs) at
finite temperature. The theory takes the effects of both lattice expansion and
lattice vibration into account. We apply the theory to the InAs/GaAs QDs. For
the unstrained InAs/GaAs heterostructure, the conduction band offset increases
whereas the valence band offset decreases with increasing of the temperature,
and there is a type-I to type-II transition at approximately 135 K. Yet, for
InAs/GaAs QDs, the holes are still localized in the QDs even at room
temperature, because the large lattice mismatch between InAs and GaAs greatly
enhances the valence band offset. The single particle energy levels in the QDs
show strong temperature dependence due to the change of confinement potentials.
Because of the changes of the band offsets, the electron wave functions
confined in QDs increase by about 1 - 5%, whereas the hole wave functions
decrease by about 30 - 40% when the temperature increases from 0 to 300 K. The
calculated recombination energies of exciton, biexciton and charged excitons
show red shifts with increasing of the temperature, which are in excellent
agreement with available experimental data
Destruction of density-wave states by a pseudo-gap in high magnetic fields: application to (TMTSF)ClO
A model is presented for the destruction of density-wave states in
quasi-one-dimensional crystals by high magnetic fields. The model is consistent
with previously unexplained properties of the organic conductors
(TMTSF)ClO and (BEDT-TTF)MHg(SCN) (M=K,Rb,Tl). As the magnetic
field increases quasi-one-dimensional density-wave fluctuations increase,
producing a pseudo-gap in the electronic density of states near the transition
temperature. When the pseudo-gap becomes larger than the mean-field transition
temperature formation of a density-wave state is not possible.Comment: 4 pages, RevTeX, 2 figures in uuencoded compressed tar file. Small
changes to text and Figure 1. Final version to appear in Physical Review
Letter
Scaling picture of magnetism formation in the anomalous f-systems: interplay of the Kondo effect and spin dynamics
Formation of magnetically ordered state in the Kondo lattices is treated
within the degenerate exchange and Coqblin-Schrieffer models. The Kondo
renormalizations of the effective coupling parameter, magnetic moment and spin
excitation frequencies are calculated within perturbation theory. The results
of one-loop scaling consideration of the magnetic state in Kondo lattices are
analyzed. The dependence of the critical values of the bare model parameters on
the type of the magnetic phase and space dimensionality is investigated.
Renormalization of the effective Kondo temperature by the interatomic exchange
interactions is calculated. An important role of the character of spin dynamics
(existence of well-defined magnon excitations, presence of magnetic anisotropy
etc.) is demonstrated. The regime of strongly suppressed magnetic moments,
which corresponds to magnetic heavy-fermion system, may occur in a rather
narrow parameter region only. At the same time, in the magnetically ordered
phases the renormalized Kondo temperature depends weakly on the bare coupling
parameter in some interval. The critical behavior, corresponding to the
magnetic transition with changing the bare coupling parameter, is
investigated. In the vicinity of the strong coupling regime, the spectrum of
the Bose excitations becomes softened. Thus on the borderline of magnetic
instability the Fermi-liquid picture is violated in some temerature interval
due to scattering of electrons by these bosons. This may explain the fact that
a non-Fermi-liquid behavior often takes place in the heavy-fermion systems near
the onset of magnetic ordering.Comment: 20 pages, RevTeX, 13 figure
Magnetothemopower study of quasi two-dimensional organic conductor -(BEDT-TTF)KHg(SCN)
We have used a low-frequency magneto-thermopower (MTEP) method to probe the
high magnetic field ground state behavior of
-(BEDT-TTF)KHg(SCN) along all three principal crystallographic
axes at low temperatures. The thermopower tensor coefficients (
and ) have been measured to 30 T, beyond the anomalous low temperature,
field-induced transition at 22.5 T. We find a significant anisotropy in the
MTEP signal, and also observe large quantum oscillations associated with the de
Haas - van Alphen effect. The anisotropy indicates that the ground state
properties are clearly driven by mechanisms that occur along specific
directions for the in-plane electronic structure. Both transverse and
longitudinal magnetothermopower show asymptotic behavior in field, which can be
explained in terms of magnetic breakdown of compensated closed orbits.Comment: 9 pages, 10 figure
Centralized Modularity of N-Linked Glycosylation Pathways in Mammalian Cells
Glycosylation is a highly complex process to produce a diverse repertoire of
cellular glycans that are attached to proteins and lipids. Glycans are involved
in fundamental biological processes, including protein folding and clearance,
cell proliferation and apoptosis, development, immune responses, and
pathogenesis. One of the major types of glycans, N-linked glycans, is formed by
sequential attachments of monosaccharides to proteins by a limited number of
enzymes. Many of these enzymes can accept multiple N-linked glycans as
substrates, thereby generating a large number of glycan intermediates and their
intermingled pathways. Motivated by the quantitative methods developed in
complex network research, we investigated the large-scale organization of such
N-linked glycosylation pathways in mammalian cells. The N-linked glycosylation
pathways are extremely modular, and are composed of cohesive topological
modules that directly branch from a common upstream pathway of glycan
synthesis. This unique structural property allows the glycan production between
modules to be controlled by the upstream region. Although the enzymes act on
multiple glycan substrates, indicating cross-talk between modules, the impact
of the cross-talk on the module-specific enhancement of glycan synthesis may be
confined within a moderate range by transcription-level control. The findings
of the present study provide experimentally-testable predictions for
glycosylation processes, and may be applicable to therapeutic glycoprotein
engineering
Toward Psycho-robots
We try to perform geometrization of psychology by representing mental states,
>, by points of a metric space, >. Evolution of ideas is
described by dynamical systems in metric mental space. We apply the mental
space approach for modeling of flows of unconscious and conscious information
in the human brain. In a series of models, Models 1-4, we consider cognitive
systems with increasing complexity of psychological behavior determined by
structure of flows of ideas. Since our models are in fact models of the
AI-type, one immediately recognizes that they can be used for creation of
AI-systems, which we call psycho-robots, exhibiting important elements of human
psyche. Creation of such psycho-robots may be useful improvement of domestic
robots. At the moment domestic robots are merely simple working devices (e.g.
vacuum cleaners or lawn mowers) . However, in future one can expect demand in
systems which be able not only perform simple work tasks, but would have
elements of human self-developing psyche. Such AI-psyche could play an
important role both in relations between psycho-robots and their owners as well
as between psycho-robots. Since the presence of a huge numbers of
psycho-complexes is an essential characteristic of human psychology, it would
be interesting to model them in the AI-framework
Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing
No abstract available
Nuclear dependence of the transverse single-spin asymmetry in the production of charged hadrons at forward rapidity in polarized , Al, and Au collisions at GeV
We report on the nuclear dependence of transverse single-spin asymmetries
(TSSAs) in the production of positively-charged hadrons in polarized
, Al and Au collisions at
GeV. The measurements have been performed at forward
rapidity () over the range of GeV and
. We observed a positive asymmetry for
positively-charged hadrons in \polpp collisions, and a significantly reduced
asymmetry in + collisions. These results reveal a nuclear
dependence of charged hadron in a regime where perturbative techniques
are relevant. These results provide new opportunities to use \polpA collisions
as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions
and to use TSSA as a new handle in studying small-system collisions.Comment: 303 authors from 66 institutions, 9 pages, 2 figures, 1 table. v1 is
version accepted for publication in Physical Review Letters. Plain text data
tables for the points plotted in figures for this and previous PHENIX
publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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