4,591 research outputs found
The noise spectra of a biased quantum dot
The noise spectra associated with correlations of the current through a
single level quantum dot, and with the charge fluctuations on the dot, are
calculated for a finite bias voltage. The results turn out to be sensitive to
the asymmetry of the dot's coupling to the two leads. At zero temperature, both
spectra exhibit two or four steps (as a function of the frequency), depending
on whether the resonant level lies outside or within the range between the
chemical potentials on the two leads. In addition, the low frequency shot-noise
exhibits dips in the charge noise and dips, peaks, and discontinuities in the
derivative of the current noise. In spite of some smearing, several of these
features persist at finite temperatures, where a dip can also turn into a peak
Investigation of the feasibility of sterile assembly of silver-zinc batteries
Electrical performance, bioassays, and packaging concepts evaluated in sterile assembly of silver zinc batterie
Noise spectra of an interacting quantum dot
We study the noise spectra of a many-level quantum dot coupled to two
electron reservoirs, when interactions are taken into account only on the dot
within the Hartree-Fock approximation. The dependence of the noise spectra on
the interaction strength, the coupling to the leads, and the chemical potential
is derived. For zero bias and zero temperature, we find that as a function of
the (external) frequency, the noise exhibits steps and dips at frequencies
reflecting the internal structure of the energy levels on the dot.
Modifications due to a finite bias and finite temperatures are investigated for
a non-interacting two-level dot. Possible relations to experiments are pointed
out.Comment: Added reference
B cells in the aging immune system: time to consider B-1 cells
The investigation of immune senescence has uncovered many changes in B cell development, maintenance, and function with increasing age. However, most of these studies have focused on conventional B cell subsets in the spleen. The B-1 cell subset is an essential arm of the innate immune system, which in general has been understudied in terms of immune senescence. Here, we review what is currently known about B cells during aging and go on to describe why B-1 cell biology is an important component of the aging immune system in the context of diseases that most affect the aged population
Vertical Structure of Stationary Accretion Disks with a Large-Scale Magnetic Field
In earlier works we pointed out that the disk's surface layers are
non-turbulent and thus highly conducting (or non-diffusive) because the
hydrodynamic and/or magnetorotational (MRI) instabilities are suppressed high
in the disk where the magnetic and radiation pressures are larger than the
plasma thermal pressure. Here, we calculate the vertical profiles of the {\it
stationary} accretion flows (with radial and azimuthal components), and the
profiles of the large-scale, magnetic field taking into account the turbulent
viscosity and diffusivity and the fact that the turbulence vanishes at the
surface of the disk.
Also, here we require that the radial accretion speed be zero at the disk's
surface and we assume that the ratio of the turbulent viscosity to the
turbulent magnetic diffusivity is of order unity. Thus at the disk's surface
there are three boundary conditions. As a result, for a fixed dimensionless
viscosity -value, we find that there is a definite relation between the
ratio of the accretion power going into magnetic disk winds to the
viscous power dissipation and the midplane plasma-, which is the ratio
of the plasma to magnetic pressure in the disk. For a specific disk model with
of order unity we find that the critical value required for a
stationary solution is , where the disk's
half thickness. For weaker magnetic fields, , we argue that
the poloidal field will advect outward while for it will
advect inward. Alternatively, if the disk wind is negligible (), there are stationary solutions with .Comment: 5 pages, 3 figure
Degeneration and impaired regeneration of gray matter oligodendrocytes in amyotrophic lateral sclerosis.
Oligodendrocytes associate with axons to establish myelin and provide metabolic support to neurons. In the spinal cord of amyotrophic lateral sclerosis (ALS) mice, oligodendrocytes downregulate transporters that transfer glycolytic substrates to neurons and oligodendrocyte progenitors (NG2(+) cells) exhibit enhanced proliferation and differentiation, although the cause of these changes in oligodendroglia is unknown. We found extensive degeneration of gray matter oligodendrocytes in the spinal cord of SOD1 (G93A) ALS mice prior to disease onset. Although new oligodendrocytes were formed, they failed to mature, resulting in progressive demyelination. Oligodendrocyte dysfunction was also prevalent in human ALS, as gray matter demyelination and reactive changes in NG2(+) cells were observed in motor cortex and spinal cord of ALS patients. Selective removal of mutant SOD1 from oligodendroglia substantially delayed disease onset and prolonged survival in ALS mice, suggesting that ALS-linked genes enhance the vulnerability of motor neurons and accelerate disease by directly impairing the function of oligodendrocytes
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