26 research outputs found
Spin relaxation time, spin dephasing time and ensemble spin dephasing time in -type GaAs quantum wells
We investigate the spin relaxation and spin dephasing of -type GaAs
quantum wells. We obtain the spin relaxation time , the spin dephasing
time and the ensemble spin dephasing time by solving the
full microscopic kinetic spin Bloch equations, and we show that, analogous to
the common sense in an isotropic system for conduction electrons, ,
and are identical due to the short correlation time. The
inhomogeneous broadening induced by the D'yakonov-Perel term is suppressed by
the scattering, especially the Coulomb scattering, in this system.Comment: 4 pages, 2 figures, to be published in Phys. Lett.
Increased numbers of oligodendrocyte lineage cells in the optic nerves of cerebroside sulfotransferase knockout mice
Sulfatide is a myelin glycolipid that functions in the formation of paranodal axo-glial junctions in vivo and in the regulation of oligodendrocyte differentiation in vitro. Cerebroside sulfotransferase (CST) catalyzes the production of two sulfated glycolipids, sulfatide and proligodendroblast antigen, in oligodendrocyte lineage cells. Recent studies have demonstrated significant increases in oligodendrocytes from the myelination stage through adulthood in brain and spinal cord under CST-deficient conditions. However, whether these result from excess migration or in situ proliferation during development is undetermined. In the present study, CST-deficient optic nerves were used to examine migration and proliferation of oligodendrocyte precursor cells (OPCs) under sulfated glycolipid-deficient conditions. In adults, more NG2-positive OPCs and fully differentiated cells were observed. In developing optic nerves, the number of cells at the leading edge of migration was similar in CST-deficient and wild-type mice. However, BrdU+ proliferating OPCs were more abundant in CST-deficient mice. These results suggest that sulfated glycolipids may be involved in proliferation of OPCs in vivo
Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star
A search of the time-series photometry from NASA's Kepler spacecraft reveals
a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626
with a period of 290 days. The characteristics of the host star are well
constrained by high-resolution spectroscopy combined with an asteroseismic
analysis of the Kepler photometry, leading to an estimated mass and radius of
0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for
the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the
planet. The system passes a battery of tests for false positives, including
reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A
full BLENDER analysis provides further validation of the planet interpretation
by showing that contamination of the target by an eclipsing system would rarely
mimic the observed shape of the transits. The final validation of the planet is
provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year
span. Although the velocities do not lead to a reliable orbit and mass
determination, they are able to constrain the mass to a 3{\sigma} upper limit
of 124 MEarth, safely in the regime of planetary masses, thus earning the
designation Kepler-22b. The radiative equilibrium temperature is 262K for a
planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is
a rocky planet, it is the first confirmed planet with a measured radius to
orbit in the Habitable Zone of any star other than the Sun.Comment: Accepted to Ap
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes
A chromosphere is a universal attribute of stars of spectral type later than
~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae
binaries) show extended and highly turbulent chromospheres, which develop into
slow massive winds. The associated continuous mass loss has a significant
impact on stellar evolution, and thence on the chemical evolution of galaxies.
Yet despite the fundamental importance of those winds in astrophysics, the
question of their origin(s) remains unsolved. What sources heat a chromosphere?
What is the role of the chromosphere in the formation of stellar winds? This
chapter provides a review of the observational requirements and theoretical
approaches for modeling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including physical
models that have recently been proposed. It describes the successes that have
been achieved so far by invoking acoustic and MHD waves to provide a physical
description of plasma heating and wind acceleration, and discusses the
challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript;
accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake
(Berlin: Springer
Collisional and Radiative Processes in Optically Thin Plasmas
Most of our knowledge of the physical processes in distant plasmas is obtained
through measurement of the radiation they produce. Here we provide an overview of the
main collisional and radiative processes and examples of diagnostics relevant to the microphysical
processes in the plasma. Many analyses assume a time-steady plasma with ion
populations in equilibrium with the local temperature and Maxwellian distributions of particle
velocities, but these assumptions are easily violated in many cases. We consider these
departures from equilibrium and possible diagnostics in detail
Simvastatin treatment reduces the cholesterol content of membrane/lipid rafts, implicating the N -methyl-D-aspartate receptor in anxiety: a literature review
UDP-Uronic acid transporters are important providing galacturonic acid and arabinose, but not xylose, into the cell wall
International audienc
Darwin’s progress and the problem of slavery
Legendary as a ‘genius’ out of time, Charles Darwin is said to have revolutionized our understanding of life on earth by explaining nature-history as the purposeless product of directionless variation naturally selected through a chancy struggle for existence. Yet, whatever may be deduced from his theory of natural selection as understood today, Darwin himself was not bound by any such conclusions. His vision of nature-history, for all its haphazardness, was directional, meliorative and hopeful. In the 1830s he went out of his way to develop privately a subversive theory of human evolution, and he pursued the subject with tenacity for three decades before publishing The descent of man in 1871. Underpinning his research was a belief in racial brotherhood rooted in the greatest moral movement of the age, for the abolition of slavery. Darwin extended the abolitionists’ common-descent image to the rest of life, making not just the races, but all races, kin. Human slavery, however, did not evolve into or out of existence. To Darwin it was a ‘sin’ to ‘expiate’ by moral action, and the Origin of species was written with a view towards undermining slavery’s creationist ideologues, most notably the Harvard professor Louis Agassiz. Intractable slavery collided with Darwin’s post-Christian progressivism in the US Civil War, clouding his hopes for humanity, but the Northern victory in 1865 enabled him to carry ‘the grand idea of God hating sin and loving righteousness’ into The descent of man, where the driving of formerly enslaved races out of existence is naturalized as a byproduct of historical progress in which ‘virtue will be triumphant’ at last