Temperature Dependence of the Cyclotron Mass in n-Type CdS

Recent cyclotron resonance experiments in n-type CdS at ultra-high magnetic fields have revealed a pronounced maximum of the electron cyclotron mass as a function of temperature. In order to interpret these data, we calculate the magneto-absorption spectra of polarons in n-CdS using the arbitrary-coupling approach. We show that in high magnetic fields the polaron effects beyond the weak-coupling approximation clearly reveal themselves in the magneto-optical absorption even at relatively small values of the Froehlich coupling constant. In particular, those effects result in a non-monotonous behaviour of the cyclotron mass as a function of temperature. We extend the theory to take into account a combined effect of several scattering mechanisms on the magneto-absorption spectra. The extended theory allows us to interpret quantitatively the experimentally observed behaviour of the cyclotron mass in CdS.Comment: 4 pages, 3 figures, E-mail addresses: [email protected], [email protected]

Discovery and Assessment of New Target Sites for Anti-HIV Therapies

Human immunodeficiency virus (HIV) infects cells by endocytosis and takes over parts of the cell’s reaction pathways in order to reproduce itself and spread the infection. One such pathway taken over by HIV becomes the inflammatory pathway which uses Nuclear Factor κB (NF-κB) as the principal transcription factor. Therefore, knocking out the NF-κB pathway would prevent HIV from reproducing itself. In this report, our goal is to produce a simple model for this pathway with which we can identify potential targets for anti-HIV therapies and test out various hypotheses. We present a very simple model with four coupled first-order ODEs and see what happens if we treat IκK concentration as a parameter that can be controlled (by some unspecified means). In Section 3, we augment this model to account for activation and deactivation of IκK, which is controlled (again, by some unspecified means) by TNF

Mediators of mechanotransduction between bone cells

Mechanical forces are known to regulate the function of tissues in the body, including bone. Bone adapts to its mechanical environment by altering its shape and increasing its size in response to increases in mechanical load associated with exercise, and by decreasing its size in response to decreases in mechanical load associated with microgravity or prolonged bed rest. Changes in bone size and shape are produced by a cooperative action of two main types of the bone cells - osteoclasts that destroy bone and osteoblasts that build bone. These cell types come from different developmental origins, and vary greatly in their characteristics, such as size, shape, and expression of receptor subtypes, which potentially may affect their responses to mechanical stimuli. The objective of this study is to compare the responses of osteoclasts and osteoblasts to mechanical stimulation. This study has allowed us to conclude the following: 1. A mediator is released from a single source cell. 2. The response to the mediator changes with distance. 3. The value of the apparent diffusion coeficient increases with distance. 4. A plausible proposed mechanism is that ATP is released and degrades to ADP. 5. Future experiments are required to confim that ATP is the mediator as suggested

Vortical, toroidal and compressible motions in 3D MHD simulations of LHD

Direct numerical simulation of fully three-dimensional, compressible and nonlinear magnetohydrodynamic equations in the Large Helical Device is carried out in combination with the passive particle simulation. In the simulation, strong vortical motions are excited by the pressure-driven instability and form the mushroom-like structures of pressure. It is shown by the passive particles analysis that the fluid volumes around the resonant magnetic surfaces experience finite compressibility and toroidal deformation, which are both excited by the strong vortical motions. The passive particles simulation helps us to investigate local structures even for low Fourier wavenumber modes

Numerical analysis and experimental study of the error of magnetic field strength measurements with single sheet testers

The error of the measurement of the magnetic field strength with a single sheet tester has been studied. Two different methods, determination by means of field sensing coils (1) and from the magnetizing current (2), have been compared. The errors of methods(1) and (2) were calculated by the finite element method (FEM), different parameters having been varied, and method (2) was additionally studied experimentally. SSTs with wound yokes and stacked yokes were considered. The results will help to decide whether the more complicated and more accurate H coil method or the easier to handle, but less accurate m.c.method is chosen.</p

The Magnetohydrodynamic Kelvin-Helmholtz Instability: A Three-Dimensional Study of Nonlinear Evolution

We investigate through high resolution 3D simulations the nonlinear evolution of compressible magnetohydrodynamic flows subject to the Kelvin-Helmholtz instability. We confirm in 3D flows the conclusion from our 2D work that even apparently weak magnetic fields embedded in Kelvin-Helmholtz unstable plasma flows can be fundamentally important to nonlinear evolution of the instability. In fact, that statement is strengthened in 3D by this work, because it shows how field line bundles can be stretched and twisted in 3D as the quasi-2D Cat's Eye vortex forms out of the hydrodynamical motions. In our simulations twisting of the field may increase the maximum field strength by more than a factor of two over the 2D effect. If, by these developments, the Alfv\'en Mach number of flows around the Cat's Eye drops to unity or less, our simulations suggest magnetic stresses will eventually destroy the Cat's Eye and cause the plasma flow to self-organize into a relatively smooth and apparently stable flow that retains memory of the original shear. For our flow configurations the regime in 3D for such reorganization is $4\lesssim M_{Ax} \lesssim 50$, expressed in terms of the Alfv\'en Mach number of the original velocity transition and the initial Alfv\'en speed projected to the flow plan. For weaker fields the instability remains essentially hydrodynamic in early stages, and the Cat's Eye is destroyed by the hydrodynamic secondary instabilities of a 3D nature. Then, the flows evolve into chaotic structures that approach decaying isotropic turbulence. In this stage, there is considerable enhancement to the magnetic energy due to stretching, twisting, and turbulent amplification, which is retained long afterwards. The magnetic energy eventually catches up to the kinetic energy, and the nature of flows become magnetohydrodynamic.Comment: 11 pages, 12 figures in degraded jpg format (2 in color), paper with original quality figures available via ftp at ftp://ftp.msi.umn.edu/pub/users/twj/mhdkh3dd.ps.gz or ftp://canopus.chungnam.ac.kr/ryu/mhdkh3dd.ps.gz, to appear in The Astrophysical Journa