12,612 research outputs found
Well-localized edge states in two-dimensional topological insulators: ultrathin Bi films
We theoretically study the generic behavior of the penetration depth of the
edge states in two-dimensional quantum spin Hall systems. We found that the
momentum-space width of the edge-state dispersion scales with the inverse of
the penetration depth. As an example of well-localized edge states, we take the
Bi(111) ultrathin film. Its edge states are found to extend almost over the
whole Brillouin zone. Correspondingly, the bismuth (111) 1-bilayer system is
proposed to have well-localized edge states in contrast to the HgTe quantum
well.Comment: 4 pages, 4 figure
Decoherence in Phase Space
Much of the discussion of decoherence has been in terms of a particle moving
in one dimension that is placed in an initial superposition state (a
Schr\"{o}dinger "cat" state) corresponding to two widely separated wave
packets. Decoherence refers to the destruction of the interference term in the
quantum probability function. Here, we stress that a quantitative measure of
decoherence depends not only on the specific system being studied but also on
whether one is considering coordinate, momentum or phase space. We show that
this is best illustrated by considering Wigner phase space where the measure is
again different. Analytic results for the time development of the Wigner
distribution function for a two-Gaussian Schrodinger "cat" state have been
obtained in the high-temperature limit (where decoherence can occur even for
negligible dissipation) which facilitates a simple demonstration of our
remarks.Comment: in press in Laser Phys.13(2003
Comparative Morphology of the Penis and Clitoris in Four Species of Moles (Talpidae).
The penile and clitoral anatomy of four species of Talpid moles (broad-footed, star-nosed, hairy-tailed, and Japanese shrew moles) were investigated to define penile and clitoral anatomy and to examine the relationship of the clitoral anatomy with the presence or absence of ovotestes. The ovotestis contains ovarian tissue and glandular tissue resembling fetal testicular tissue and can produce androgens. The ovotestis is present in star-nosed and hairy-tailed moles, but not in broad-footed and Japanese shrew moles. Using histology, three-dimensional reconstruction, and morphometric analysis, sexual dimorphism was examined with regard to a nine feature masculine trait score that included perineal appendage length (prepuce), anogenital distance, and presence/absence of bone. The presence/absence of ovotestes was discordant in all four mole species for sex differentiation features. For many sex differentiation features, discordance with ovotestes was observed in at least one mole species. The degree of concordance with ovotestes was highest for hairy-tailed moles and lowest for broad-footed moles. In relationship to phylogenetic clade, sex differentiation features also did not correlate with the similarity/divergence of the features and presence/absence of ovotestes. Hairy-tailed and Japanese shrew moles reside in separated clades, but they exhibit a high degree of congruence. Broad-footed and hairy-tailed moles reside within the same clade but had one of the lowest correlations in features and presence/absence of ovotestes. Thus, phylogenetic affinity and the presence/absence of ovotestes are poor predictors for most sex differentiation features within mole external genitalia
Distribution of Microscopic Energy Flux in Equilibrium State
The distribution function P(j) of the microscopic energy flux, j, in
equilibrium state is studied. It is observed that P(j) has a broad peak in
small j regime and a stretched-exponential decay for large j. The peak
structure originates in a potential advection term and energy transfer term
between the particles. The stretched exponential tail comes from the momentum
energy advection term.Comment: 5 pages, 2 figure
ASCA observations of the galactic bulge hard x-ray source GRS 1758--258
GRS 1758-258 is one of the few persistent hard X-ray emitters (E>100 keV) in
the Galaxy. Using the ASCA satellite, we have obtained the first detailed data
on GRS 1758-258 in the 1-10 keV range, where previous observations were
affected by confusion problems caused by the nearby strong source GX5-1. The
spectrum is well described by a power law with photon index 1.7 without strong
Fe emission lines. A prominent soft excess, as observed with ROSAT when the
hard X-ray flux was in a lower intensity state, was not detected. However, the
presence of a soft spectral component, accounting for at most 5% of the 0.1-300
keV flux, cannot be excluded. The accurate measurement of interstellar
absorption (N_H=(1.5+-0.1) x 10^22 cm -2) corresponds to an optical extinction
which definitely excludes the presence of a massive companion.Comment: 7 pages, AAS latex [11pt,aaspptwo,flushrt,tighten], + 1.ps figure
Accepted for pubblication in ApJ, 09 02 96 Also available at
http://fy.chalmers.se/~haardt/personal/curr.html Figures 1 and 2 available
upon request at [email protected]
Spin Transport Properties in Heisenberg Antiferromagnetic Spin Chains: Spin Current induced by Twisted Boundary Magnetic Fields
Spin transport properties of the one-dimensional Heisenberg antiferromagnetic
spin systems for both and S=1 are studied by applying twisted boundary
magnetic field. The spin current displays significantly different behavior of
the spin transport properties between and S=1 cases. For the spin-half
case, a London equation for the current and the detection of an alternating
electric field are proposed for the linear response regime. The correlation
functions reveal the spiral nature of spin configuration for both ground state
and the spinon excitations. For the spin-one chain otherwise, a kink is
generated in the ground state for the size is larger than the correlation
length, leading to an exponential dependence of spin current with respect to
the chains length. The midgap state emerges from the degenerate ground state
even for small boundary fields.Comment: 4 pages, 5 figure
Generating high-order optical and spin harmonics from ferromagnetic monolayers
High-order harmonic generation (HHG) in solids has entered a new phase of
intensive research, with envisioned band-structure mapping on an ultrashort
time scale. This partly benefits from a flurry of new HHG materials discovered,
but so far has missed an important group. HHG in magnetic materials should have
profound impact on future magnetic storage technology advances. Here we
introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG
carries spin information and sensitively depends on the relativistic spin-orbit
coupling; and if they are dispersed into the crystal momentum space,
harmonics originating from real transitions can be -resolved and carry
the band structure information. Geometrically, the HHG signal is sensitive to
spatial orientations of monolayers. Different from the optical counterpart, the
spin HHG, though probably weak, only appears at even orders, a consequence of
SU(2) symmetry. Our findings open an unexplored frontier -- magneto-high-order
harmonic generation.Comment: 19 pages, 4 figure
Fracture mechanics approach to design analysis of notches, steps and internal cut-outs in planar components
A new approach to the assessment and optimization of geometric stress-concentrating features is proposed on the basis of the correspondence between sharp crack or corner stressfield intensity factors and conventional elastic stress concentration factors (SCFs) for radiused transitions. This approach complements the application of finite element analysis (FEA) and the use of standard SCF data from the literature. The method makes it possible to develop closed-form solutions for SCFs in cases where corresponding solutions for the sharp crack geometries exist. This is helpful in the context of design optimization. The analytical basis of the correspondence is shown, together with the limits on applicability where stress-free boundaries near the stress concentrating feature are present or adjacent features interact. Examples are given which compare parametric results derived from FEA with closed-form solutions based on the proposed method. New information is given on the stress state at a 90° corner or width step, where the magnitude of the stress field intensity is related to that of the corresponding crack geometry. This correspondence enables the user to extend further the application of crack-tip stress-field intensity information to square-cornered steps, external U-grooves, and internal cut-outs
Preparing and selecting actions with neural populations: toward cortical circuit mechanisms
How the brain selects one action among multiple alternatives is a central question of neuroscience. An influential model is that action preparation and selection arise from subthreshold activation of the very neurons encoding the action. Recent work, however, shows a much greater diversity of decision-related and action-related signals coexisting with other signals in populations of motor and parietal cortical neurons. We discuss how such distributed signals might be decoded by biologically plausible mechanisms. We also discuss how neurons within cortical circuits might interact with each other during action selection and preparation and how recurrent network models can help to reveal dynamical principles underlying cortical computation.info:eu-repo/semantics/publishedVersio
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