Gamma-ray bursts: optical afterglows in the deep Newtonian phase

Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase.     

Keck observations of near-Earth asteroids in the thermal infrared

We present the results of thermal-infrared observations of 20 near-Earth asteroids (NEAs) obtained in the period March 2000-February 2002 with the 10-m Keck-I telescope on Mauna Kea, Hawaii. The measured fluxes have been fitted with thermal-model emission continua to determine sizes and albedos. This work increases the number of NEAs having measured albedos by 35%. The spread of albedos derived is very large (p_v=0.02−0.55); the mean value is 0.25, which is much higher than that of observed main-belt asteroids. In most cases the albedos are in the ranges expected for the spectral types, although some exceptions are evident. Our results are consistent with a trend of increasing albedo with decreasing size for S-type asteroids with diameters below 20 km. A number of objects are found to have unexpectedly low apparent color temperatures, which may reflect unusual thermal properties. However, the results from our limited sample suggest that high thermal-inertia, regolith-free objects may be uncommon, even amongst NEAs with diameters of less than 1 km. We discuss the significance of our results in the light of information on these NEAs taken from the literature and the uncertainties inherent in applying thermal models to near-Earth asteroids.     

Short-lived asteroids in the 7/3 Kirkwood gap and their relationship to the Koronis and Eos families

A population of 23 asteroids is currently observed in a very unstable region of the main belt, the 7/3 Kirkwood gap. The small size of these bodies—with the notable exception of (677) Aaltje (∼30 km)—as well as the computation of their dynamical lifetimes (3<T_D<172 Myr) shows that they cannot be on their primordial orbits, but were recently injected in the resonance. The distribution of inclinations appears to be bimodal, the two peaks being close to 2° and 10°. We argue that the resonant population is constantly being replenished by the slow leakage of asteroids from both the Koronis (I∼2°) and Eos (I∼10°) families, due to the drift of their semi-major axes, caused by the Yarkovsky effect. Assuming previously reported values for the Yarkovsky mean drift rate, we calculate the flux of family members needed to sustain the currently observed population in steady state. The number densities with respect to semi-major axis of the observed members of both families are in very good agreement with our calculations. The fact that (677) Aaltje is currently observed in the resonance is most likely an exceptional event. This asteroid should not be genetically related to any of the above families. Its size and the eccentricity of its orbit suggest that the Yarkovsky effect should have been less efficient in transporting this body to the resonance than close encounters with Ceres.     

EMERGY ANALYSIS OF GRAIN PRODUCTION SYSTEM IN JIANGSU AND SHAANXI PROVINCES

Efficiency and sustainability of grain production are now important in China. In this study, the grain production systems of Jiangsu and Shaanxi Provinces were compared, to analyze their efficiency and sustainability in terms of utilization of natural resources, inputs of purchased energy and materials, and outputs. Flows of energy and materials between environment and human society were identified, and the natural and human work involved in generating inputs as materials or energy were valued in terms of equivalent amount of solar energy required for their production using emergy method. The results showed environmental resources were continually playing a less important role in the systems, when inorganic subsidiary emergy inputs increased drastically while organic ones decreased or increased little. Deterioration of input emergy structure affected the systems‘ efficiency and sustainability, resulting in emergy investment ratios and environmental loading ratios increasing while yield ratios and sustainability indices decreasing. In general, efficiency and sustainability of grain production in Jiangsu are worse than those in Shaanxi. This analysis also suggested that inorganic subsidiary emergy should be introduced properly, and peasants in Jiangsu should utilize natural conditions wisely while those in Shaanxi pay enough attention to soil and surface water conservation.     

Binaries in the universe. possible dynamical mechanisms of formation,evolution and disruption of different kinds of constituents of the universe

We study the dynamics of extended shells of relatively low-mass particles around and inside the orbit of two heavy centres of gravity (a binary) by computer simulations. The binary components are surrounded byN = 16 000 small mass particles in uniform random distribution on few spherical envelopes with different radii expanding with respective velocities. Some shells are inside the orbit of binary.We apply this model to binary galaxy systems with baryonic dark matter, e.g., massive black holes. In principle, we can apply this model to different kinds of objects (from binary star systems until superclusters of galaxies).It is shown that the shell expands homologously with a decreasing velocity and then, falls back into the binary system forming zones of compressed matter. At some moment of time there could be a collapse of these particles on to the heavier component of the binary. Further in time, some part of particles which were outside the binary orbit escape from the system. Other particles which were initially inside of the orbit are captured by binary components.We consider a number of different models with different initial parameters. For models with smaller radii of shells, about one-half of the particles escape from systems; whereas for larger values the shell disrupts as a whole. Escaping particles form collimated flows in planes of orbits of binaries. Positions of flows and directions of motion depend on positions of heavier components of binaries at the moment of a closest approach of particles and on ratios of masses of binary components.We show that during evolution of our models different kinds of structures of systems often are very similar to the observed structures of galaxies: spiral and elliptical galaxies, interacting galaxies, different kinds of flows and jets. Totally systems are expanding - after 40 periods of rotation of the binary the system expands by 300 times.     

Light curve and O−C diagram analysis of RZ Cassiopeiae

The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed.     

Results from several persistent train spectra intercompared

Some results following from two contemporary photographical programs (Slovakia and Japan) for persistent meteor train spectra are compared. It shows that even though both programs are not too different according to their lenses and films used, the spectral interval detected is very different. In this respect prism as a dispersion element is more favourable than the grating with blaze wavelength near 610 nm. However, some results previously assumed as typicai for presented persistent trains-e.g. the forbidden Herzberg O₂ emission, the NO₂ continuum and OH red emissions-seem to be substanciated especially due to higher and linear dispersion of those grating spectra.     

Oil, water, ice and light

The boehaviour and ultimate effect and fate of oil in the marine environment in the polar region depend on a large number of factors. From a chemical point of view the most important ones to consider are the intrinsic chemical properties of the oil, the consequences of oil/water interactions, the influence of ice on physical and chemical processes, and the interactions between oil and light when the influx of solar energy shows great seasonal changes. This paper reviews the main aspects of these issues.