5,990 research outputs found
Compliance with legal minimum wages and overtime pay regulations in China
A matched firm-employee data set is used to examine the extent of compliance with minimum wage and overtime pay regulations in Chinese formal sector firms. Evidence shows that there is broad compliance with legal minimum wages in
China; fewer than 3.5% of full-time workers earn less than the legal monthly minimum wage. On the other hand, there is substantial non-compliance with overtime pay regulations; almost 29% of the employees who work overtime are not paid any additional wage for overtime hours, and 70% are paid less than the legally-required 1.5 times the regular wage
Correlated electron emission in laser-induced nonsequence double ionization of Helium
In this paper, we have investigated the correlated electron emission of the
nonsequence double ionization (NSDI) in an intense linearly polarized field.
The theoretical model we employed is the semiclassical rescattering model, the
model atom we used is the helium. We find a significant correlation between
magnitude and direction of the momentum of two emission electrons, and give a
good explanation for this striking phenomenon by observing the classical
collisional trajectories. We argue that this correlation phenomenon is
universal in NSDI process, as revealed by the recent experiment on the argon.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.
Boundary of two mixed Bose-Einstein condensates
The boundary of two mixed Bose-Einstein condensates interacting repulsively
was considered in the case of spatial separation at zero temperature.
Analytical expressions for density distribution of condensates were obtained by
solving two coupled nonlinear Gross-Pitaevskii equations in cases corresponding
weak and strong separation. These expressions allow to consider excitation
spectrum of a particle confined in the vicinity of the boundary as well as
surface waves associated with surface tension.Comment: 6 pages, 3 figures, submitted to Phys.Rev.
Claudins in intestines
Intestines are organs that not only digest food and absorb nutrients, but also provide a defense barrier against pathogens and noxious agents ingested. Tight junctions (TJs) are the most apical component of the junctional complex, providing one form of cell-cell adhesion in enterocytes and playing a critical role in regulating paracellular barrier permeability. Alteration of TJs leads to a number of pathophysiological diseases causing malabsorption of nutrition and intestinal structure disruption, which may even contribute to systemic organ failure. Claudins are the major structural and functional components of TJs with at least 24 members in mammals. Claudins have distinct charge-selectivity, either by tightening the paracellular pathway or functioning as paracellular channels, regulating ions and small molecules passing through the paracellular pathway. In this review, we have discussed the functions of claudin family members, their distribution and localization in the intestinal tract of mammals, their alterations in intestine-related diseases and chemicals/agents that regulate the expression and localization of claudins as well as the intestinal permeability, which provide a therapeutic view for treating intestinal diseases
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Turbulence and Steady Flows in 3D Global Stratified MHD Simulations of Accretion Disks
We present full 2 Pi global 3-D stratified MHD simulations of accretion
disks. We interpret our results in the context of proto-planetary disks. We
investigate the turbulence driven by the magneto-rotational instability (MRI)
using the PLUTO Godunov code in spherical coordinates with the accurate and
robust HLLD Riemann solver. We follow the turbulence for more than 1500 orbits
at the innermost radius of the domain to measure the overall strength of
turbulent motions and the detailed accretion flow pattern. We find that regions
within two scale heights of the midplane have a turbulent Mach number of about
0.1 and a magnetic pressure two to three orders of magnitude less than the gas
pressure, while outside three scale heights the magnetic pressure equals or
exceeds the gas pressure and the turbulence is transonic, leading to large
density fluctuations. The strongest large-scale density disturbances are spiral
density waves, and the strongest of these waves has m=5. No clear meridional
circulation appears in the calculations because fluctuating radial pressure
gradients lead to changes in the orbital frequency, comparable in importance to
the stress gradients that drive the meridional flows in viscous models. The net
mass flow rate is well-reproduced by a viscous model using the mean stress
distribution taken from the MHD calculation. The strength of the mean turbulent
magnetic field is inversely proportional to the radius, so the fields are
approximately force-free on the largest scales. Consequently the accretion
stress falls off as the inverse square of the radius.Comment: Accepted for publication in Ap
On the magnetic stability at the surface in strongly correlated electron systems
The stability of ferromagnetism at the surface at finite temperatures is
investigated within the strongly correlated Hubbard model on a semi-infinite
lattice. Due to the reduced surface coordination number the effective Coulomb
correlation is enhanced at the surface compared to the bulk. Therefore, within
the well-known Stoner-picture of band ferromagnetism one would expect the
magnetic stability at the surface to be enhanced as well. However, by taking
electron correlations into account well beyond the Hartree-Fock (Stoner) level
we find the opposite behavior: As a function of temperature the magnetization
of the surface layer decreases faster than in the bulk. By varying the hopping
integral within the surface layer this behavior becomes even more pronounced. A
reduced hopping integral at the surface tends to destabilize surface
ferromagnetism whereas the magnetic stability gets enhanced by an increased
hopping integral. This behavior represents a pure correlation effect and can be
understood in terms of general arguments which are based on exact results in
the limit of strong Coulomb interaction.Comment: 6 pages, RevTeX, 4 eps figures, accepted (Phys. Rev. B), for related
work and info see http://orion.physik.hu-berlin.d
H_2 emission arises outside photodissociation regions in ultra-luminous infrared galaxies
Ultra-luminous infrared galaxies are among the most luminous objects in the
local universe and are thought to be powered by intense star formation. It has
been shown that in these objects the rotational spectral lines of molecular
hydrogen observed at mid-infrared wavelengths are not affected by dust
obscuration, leaving unresolved the source of excitation of this emission. Here
I report an analysis of archival Spitzer Space Telescope data on ultra-luminous
infrared galaxies and demonstrate that star formation regions are buried inside
optically thick clouds of gas and dust, so that dust obscuration affects
star-formation indicators but not molecular hydrogen. I thereby establish that
the emission of H_2 is not co-spatial with the buried starburst activity and
originates outside the obscured regions. This is rather surprising in light of
the standard view that H_2 emission is directly associated with star-formation
activity. Instead, I propose that H_2 emission in these objects traces shocks
in the surrounding material, which are in turn excited by interactions with
nearby galaxies, and that powerful large-scale shocks cooling by means of H_2
emission may be much more common than previously thought. In the early
universe, a boost in H_2 emission by this process may speed up the cooling of
matter as it collapsed to form the first stars and galaxies and would make
these first structures more readily observable.Comment: Main text and supplemental information, 21 pages including 6 figures,
2 table
ICTV Virus Taxonomy Profile: Pospiviroidae
[EN] Members of the family Pospiviroidae have single-stranded circular RNA genomes that adopt a rod-like or a quasi-rod-like conformation. These genomes contain a central conserved region that is involved in replication in the nucleus through an asymmetric RNA-RNA rolling-circle mechanism. Members of the family Pospiviroidae lack the hammerhead ribozymes that are typical of viroids classified in the family Avsunviroidae. The family Pospiviroidae includes the genera Apscaviroid, Cocadviroid, Coleviroid, Hostuviroid and Pospiviroid, with >25 species. This is a summary of the ICTV Report on the family Pospiviroidae, which is available at ictv.global/report/pospiviroidae.Production of this summary, the online chapter, and associated resources was funded by a grant from the Wellcome Trust (WT108418AIA).Di Serio, F.; Owens, RA.; Li, S.; Matousek, J.; Pallás Benet, V.; Randles, JW.; Sano, T.... (2021). ICTV Virus Taxonomy Profile: Pospiviroidae. Journal of General Virology. 102(2):1-2. https://doi.org/10.1099/jgv.0.00154312102
Inter- and intragrain currents in bulk melt-grown YBaCuO rings
A simple contactless method suitable to discern between the intergrain
(circular) current, which flows in the thin superconducting ring, and the
intragrain current, which does not cross the weakest link, has been proposed.
At first, we show that the intergrain current may directly be estimated from
the magnetic flux density measured by the Hall sensor positioned
in the special points above/below the ring center. The experimental
and the numerical techniques to determine the value are discussed. Being
very promising for characterization of a current flowing across the joints in
welded YBaCuO rings (its dependencies on the temperature and the external
magnetic field as well as the time dissipation), the approach has been applied
to study corresponding properties of the intra- and intergrain currents flowing
across the -twisted grain boundaries which are frequent in bulk
melt-textured YBaCuO samples. We present experimental data related to the flux
penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin
state and during the field reversal. The shielding properties and their
dependence on external magnetic fields are also studied. Besides, we consider
the flux creep effects and their influence on the current re-distribution
during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version,
corrections to perturbing effects near the weak links are introduced, one
more figure is added. lin
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