4,012 research outputs found
Boltzmann hierarchy for the cosmic microwave background at second order including photon polarization
Non-gaussianity and B-mode polarization are particularly interesting features
of the cosmic microwave background, as -- at least in the standard model of
cosmology -- their only sources to first order in cosmological perturbation
theory are primordial, possibly generated during inflation. If the primordial
sources are small, the question arises how large is the non-gaussianity and
B-mode background induced in second-order from the initially gaussian and
scalar perturbations. In this paper we derive the Boltzmann hierarchy for the
microwave background photon phase-space distributions at second order in
cosmological perturbation theory including the complete polarization
information, providing the basis for further numerical studies. As an aside we
note that the second-order collision term contains new sources of B-mode
polarization and that no polarization persists in the tight-coupling limit.Comment: LaTeX, 33 page
B polarization of cosmic background radiation from second-order scattering sources
B-mode polarization of the cosmic background radiation is induced from purely
scalar primordial sources at second order in perturbations of the homogeneous,
isotropic universe. We calculate the B-mode angular power spectrum C_l^{BB}
sourced by the second-order scattering term in the full second-order Boltzmann
equations for the polarized radiation phase-space density, which have recently
become available. We find that at l\approx 200 the second-order effect is
comparable to the first-order effect for a tensor-to-scalar ratio of r=10^{-6},
and to about 2\cdot 10^{-4} at l\approx 1000. It is always negligible relative
to the weak-lensing induced contribution.Comment: 32 page
IMMUNOLOGICAL TOLERANCE TO A HAPTEN : I. INDUCTION AND MAINTENANCE OF TOLERANCE TO TRINITROPHENYL WITH TRINITROBENZENE SULFONIC ACID
Treatment of mice with a nonimmunogenic preparation of free reactive hapten, trinitrobenzene sulfonic acid (TNBS), leads to the induction of a state of tolerance to the hapten, 2,4,6-trinitrophenyl (TNP). This is determined by the lack of response to the haptenic moiety in an immunogenic hapten-carrier conjugate (TNP-SRBC) as assayed both by serum antibody titrations and the hemolytic plaque assay. The tolerance produced is specific for the hapten, since the anticarrier responses are essentially unaltered compared with the control values. The unresponsiveness induced by TNBS treatment is a dose-dependent phenomenon, becoming less complete at lower doses of TNBS. The tolerance is of a definite length, both in its induction phase and in the duration of the established unresponsive state. Tolerance can be maintained and extended, and may also be reentered once escape has been initiated
Spin-torque switching: Fokker-Planck rate calculation
We describe a new approach to understanding and calculating magnetization
switching rates and noise in the recently observed phenomenon of "spin-torque
switching". In this phenomenon, which has possible applications to information
storage, a large current passing from a pinned ferromagnetic (FM) layer to a
free FM layer switches the free layer. Our main result is that the spin-torque
effect increases the Arrhenius factor in the switching rate, not
by lowering the barrier , but by raising the effective spin temperature .
To calculate this effect quantitatively, we extend Kramers' 1940 treatment of
reaction rates, deriving and solving a Fokker-Planck equation for the energy
distribution including a current-induced spin torque of the Slonczewski type.
This method can be used to calculate slow switching rates without long-time
simulations; in this Letter we calculate rates for telegraph noise that are in
good qualitative agreement with recent experiments. The method also allows the
calculation of current-induced magnetic noise in CPP (current perpendicular to
plane) spin valve read heads.Comment: 11 pages, 8 figures, 1 appendix Original version in Nature format,
replaced by Phys. Rev. Letters format. No substantive change
Virus Sharing, Genetic Sequencing, and Global Health Security
The WHO’s Pandemic Influenza Preparedness (PIP) Framework was a milestone global agreement designed to promote the international sharing of biological samples to develop vaccines, while that ensuring poorer countries would have access to those vaccines. Since the PIP Framework was negotiated, scientists have developed the capacity to use genetic sequencing data (GSD) to develop synthetic viruses rapidly for product development of life-saving technologies in a time-sensitive global emergency—threatening to unravel the Framework. Access to GSD may also have major implications for biosecurity, biosafety, and intellectual property (IP).
By rendering the physical transfer of viruses antiquated, GSD may also undermine the effectiveness of the PIP Framework itself, with disproportionate impacts on poorer countries. We examine the changes that need to be made to the PIP Framework to address the growing likelihood that GSD might be shared instead of physical virus samples. We also propose that the international community harness this opportunity to expand the scope of the PIP Framework beyond only influenza viruses with pandemic potential.
In light of non-influenza pandemic threats such as the Middle East Respiratory Syndrome (MERS) and Ebola, we call for an international agreement on the sharing of the benefits of research – such as vaccines and treatments – for other infectious diseases to ensure not only a more secure and healthy world, but also a more just world, for humanity
Correlation of patterns of anchorage-independent growth with in vivo behavior of cells from a murine fibrosarcoma.
POSTURAl CONTROL STRATEGIES IN DANCERS AND NON DANCERS
Postural stability is typically measured by assessing total excursions of either the center of pressure or whole body center of mass. One problem with measures such as these is that interpretations or postural stability are typically made without references to any stability boundaries. Further, postural control studies are typically on'y conducted on individuals with balance impairments and compared to healthy controls. Little research has been conducted on athletes with high levels of postural control. This study compares the postural dynamics of elite balancers with matched control subjects using stability measures that take into account the stability boundaries of different postures
Simulation Studies of Nanomagnet-Based Architecture
We report a simulation study on interacting ensembles of Co nanomagnets that
can perform basic logic operations and propagate logic signals, where the state
variable is the magnetization direction. Dipole field coupling between
individual nanomagnets drives the logic functionality of the ensemble and
coordinated arrangements of the nanomagnets allow for the logic signal to
propagate in a predictable way. Problems with the integrity of the logic signal
arising from instabilities in the constituent magnetizations are solved by
introducing a biaxial anisotropy term to the Gibbs magnetic free energy of each
nanomagnet. The enhanced stability allows for more complex components of a
logic architecture capable of random combinatorial logic, including horizontal
wires, vertical wires, junctions, fanout nodes, and a novel universal logic
gate. Our simulations define the focus of scaling trends in nanomagnet-based
logic and provide estimates of the energy dissipation and time per nanomagnet
reversal
A Public Health Emergency of International Concern? Response to a Proposal to Apply the International Health Regulations to Antimicrobial Resistance
Adam Kamradt-Scott critiques a proposal to apply the International Health Regulations
(IHR) to the global health threat of antimicrobial resistance
- …