Variations of cosmic-ray energy in interplanetary space

A consistent theory of energy exchange between high-energy charged cosmic-ray particles and the random inhomogeneities of a magnetic field frozen in the moving solar wind plasma is developed. It is shown that the mode of the particle energy variations at a given law of plasma velocity variation in space is determined by the specific form of the particle distribution function. The equation for the density of cosmic-ray energy is obtained. Consideration is given to the generation of a charged particle energy spectrum in the course of multiple scatterings by the random inhomogeneities of the magnetic field.     

Galaxy evolution, cosmology and dark energy with the Square Kilometer Array

The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form – and astro-particle physics – inferring properties of the dark components.The Square Kilometer Array (SKA) will provide the only means of studying the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the rôles of gas accretion and galaxy merging.‘All hemisphere’ HI redshift surveys to z 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H₀ using extragalactic water masers.The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.     

Organized Subsurface Flows near Active Regions

Local helioseismic techniques, such as ring analysis and time-distance helioseismology, have already shown that large-scale flows near the surface converge towards major active regions. Ring analysis has further demonstrated that at greater depths some active regions exhibit strong outflows. A critique leveled at the ring-analysis results is that the Regularized Least Squares (RLS) inversion kernels on which they are based have negative sidelobes near the surface. Such sidelobes could result in a surface inflow being misidentified as a diverging outflow at depth. In this paper we show that the Optimally Located Averages (OLA) inversion technique, which produces kernels without significant sidelobes, generates flows markedly similar to the RLS results. Active regions are universally zones of convergence near the surface, while large complexes evince strong outflows deeper down.     

On the Saturation of Astrophysical Dynamos: Numerical Experiments with the No-Cosines Flow

In the context of astrophysical dynamos we illustrate that the no-cosines flow, with zero mean helicity, can drive fast dynamo action and we study the dynamo’s mode of operation during both the linear and non-linear saturation regimes. It turns out that in addition to a high growth rate in the linear regime, the dynamo saturates at a level significantly higher than normal turbulent dynamos, namely at exact equipartition when the magnetic Prandtl number Pr_m∼ 1. Visualization of the magnetic and velocity fields at saturation will help us to understand some of the aspects of the non-linear dynamo problem.     

On The Concept Of Periapsis In Hill’s Problem

The concept of closest approach is analyzed in Hill’s problem, resulting in a partitioning of the position space. The different behavior between the direct and retrograde motion is explained analytically, resulting in a simple estimate of the variation of Hill’s periodic and quasi-circular orbits as a function of the Jacobi constant. The local behavior of the orbits on the zero velocity surfaces and an analytical definition of local escape and capture in Hill’s problem are also given.     

The science behind the vision for U.S. space exploration: the value of a human–robotic partnership

The Vision for U.S. Space Exploration offers new opportunities for aggressively increasing the pace of scientific discoveries across the Solar System by empowering an on-site partnership between humans and robotics, enhanced by new technology-enabled capabilities. In particular, the early emphasis of this new Vision will be on development of new scientific activities on the Moon, and later on Mars. Integration of in situ traditional science activities with creative new types of applied scientific research on the Moon and Mars is a key ingredient in the US Vision. The Apollo era record of achievement involving human exploration is particularly informative, as it demonstrates the accelerated pace of scientific discovery and understanding that resulted from human “on site” activities, however briefly, on planetary surfaces. An example of how integrated human and robotic exploration can enable breakthrough science on the planet Mars is provided in order to illustrate these points. The scientific opportunities associated with the Vision for US Space Exploration are many, and with the incorporation of human-based capabilities on the Moon and Mars, an accelerated pace of discovery and understanding will be possible.     

Search for short cosmic gamma-ray bursts using data from the APEX and LILAS experiments onboard the Phobos-2 interplanetary spacecraft

A statistical analysis of the spectral and temporal parameters for 546 triggering events on the APEX gamma-ray detector onboard the Phobos-2 spacecraft has revealed a group of 28 events that are probably short cosmic gamma-ray bursts (GRBs). The distribution of the full group of 74 events of the APEX experiment in duration parameter is bimodal in shape, which is in good agreement with the bimodal shape of the BATSE GRB distribution. A search for the detected group of short events using data from the LILAS X-ray and soft gamma-ray detector onboard the same spacecraft has yielded no positive result. A comparison of the APEX and LILAS data has led us to conclude that the short GRBs have a significantly reduced soft gamma-ray flux at energies <100 keV relative to the power law dN/dE=CE^?α with the average index α=2.62.