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

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 $\exp(-E/kT)$ in the switching rate, not by lowering the barrier $E$, but by raising the effective spin temperature $T$. 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

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

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

Attosecond spectroscopy reveals alignment dependent core-hole dynamics in the ICl molecule.

The removal of electrons located in the core shells of molecules creates transient states that live between a few femtoseconds to attoseconds. Owing to these short lifetimes, time-resolved studies of these states are challenging and complex molecular dynamics driven solely by electronic correlation are difficult to observe. Here, we obtain few-femtosecond core-excited state lifetimes of iodine monochloride by using attosecond transient absorption on iodine 4d-16p transitions around 55 eV. Core-level ligand field splitting allows direct access of excited states aligned along and perpendicular to the ICl molecular axis. Lifetimes of 3.5 ± 0.4 fs and 4.3 ± 0.4 fs are obtained for core-hole states parallel to the bond and 6.5 ± 0.6 fs and 6.9 ± 0.6 fs for perpendicular states, while nuclear motion is essentially frozen on this timescale. Theory shows that the dramatic decrease of lifetime for core-vacancies parallel to the covalent bond is a manifestation of non-local interactions with the neighboring Cl atom of ICl

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