Electron-drift driven ion-acoustic mode in a dusty plasma with collisional effects

Instabilities of ion-acoustic waves in a dusty plasma with electron-drift, collisional, and dust charge fluctuations effects, have been investigated. The regimes are clearly marked out where the theory is applicable. The critical electron-drift velocity required to drive the instability is predicted. It is also shown that electron thermal conductivity and charged grains concentration enhance the growth of the ion-acoustic mode whereas ion-viscosity, ion-thermal conductivity, and dust charge fluctuations have a stabilizing effect.Comment: 7 pages, 3 PS-LaTeX figures (to be published in Physics of Plasmas

A characterization of the central shell-focusing singularity in spherical gravitational collapse

We give a characterization of the central shell-focusing curvature singularity that can form in the spherical gravitational collapse of a bounded matter distribution obeying the dominant energy condition. This characterization is based on the limiting behaviour of the mass function in the neighbourhood of the singularity. Depending on the rate of growth of the mass as a function of the area radius R, the singularity may be either covered or naked. The singularity is naked if this growth rate is slower than R, covered if it is faster than R, and either naked or covered if the growth rate is same as R.Comment: 12 pages, Latex, significantly revised version, including change of title. Revised version to appear in Classical and Quantum Gravit

The walking robot project

A walking robot was designed, analyzed, and tested as an intelligent, mobile, and a terrain adaptive system. The robot's design was an application of existing technologies. The design of the six legs modified and combines well understood mechanisms and was optimized for performance, flexibility, and simplicity. The body design incorporated two tripods for walking stability and ease of turning. The electrical hardware design used modularity and distributed processing to drive the motors. The software design used feedback to coordinate the system and simple keystrokes to give commands. The walking machine can be easily adapted to hostile environments such as high radiation zones and alien terrain. The primary goal of the leg design was to create a leg capable of supporting a robot's body and electrical hardware while walking or performing desired tasks, namely those required for planetary exploration. The leg designers intent was to study the maximum amount of flexibility and maneuverability achievable by the simplest and lightest leg design. The main constraints for the leg design were leg kinematics, ease of assembly, degrees of freedom, number of motors, overall size, and weight

Collective Oscillations of Strongly Correlated One-Dimensional Bosons on a Lattice

We study the dipole oscillations of strongly correlated 1D bosons, in the hard-core limit, on a lattice, by an exact numerical approach. We show that far from the regime where a Mott insulator appears in the system, damping is always present and increases for larger initial displacements of the trap, causing dramatic changes in the momentum distribution, $n_k$. When a Mott insulator sets in the middle of the trap, the center of mass barely moves after an initial displacement, and $n_k$ remains very similar to the one in the ground state. We also study changes introduced by the damping in the natural orbital occupations, and the revival of the center of mass oscillations after long times.Comment: 4 pages, 5 figures, published versio

Изучение структуры сбережений и инвестиций на примере выборочных фермерских хозяйств

The saving and investment pattern of different forms sample group was studied during 2014-16 and it was observed that large farm holders were able to save higher income than small farmers while lowest income group had negative savings. In respect of investment on different fixed assets, irrigation was on first priority, followed by purchase of milch animals, farms buildings and investment in land and its improvement. Investment on working capital amongst different cash inputs, hired human labourer accounted highest share (29.44 per cent), followed by manure & fertilizers (22.33 per cent), hired power tractor (16.96 per cent), irrigation (13.61 per cent) and seeds (13.50 per cent) to total cash inputs. Marginal farmers could not invest for nonfarm physical capital because of no savings with them. Small and large farmers groups invested in all the items in which it was highest in working capital (61.28 to 61.84 per cent), followed by investment in fixed capital (14.41 to 16.84 per cent), financial capital (12-14 per cent) and non-farm capital (7-12 per cent). The highest investment was made on working capital (69.02 per cent) by sample farmers. Current income was found to be the main source of finance in all income groups which accounted for 49.70 to 94.79 per cent share of the total investment followed by savings which shared for 40.10 to 49.12 per cent in total investment.Структура сбережений и инвестиций в различных группах выборки изучали в течение 2014-2016 годов. Было замечено, что крупные фермерские хозяйства смогли сэкономить более высокий доход, чем мелкие фермеры, в то время как группа с самым низким доходом имела отрицательные сбережения. Что касается инвестиций в различные основные фонды, первоочередной задачей было орошение, за которым последовали покупка дойного скота, хозяйственных построек и инвестиции в землю и ее улучшение. Инвестиции в оборотный капитал среди различных денежных затрат, наемный рабочий составлял наибольшую долю (29,44%), за ним следовали навоз и удобрения (22,33 процента), наемный трактор (16,96%), ирригация (13,61%) и семена (13,50%) к общему количеству денежных вложений. Маржинальные фермеры не могли вкладывать средства в физический капитал, не связанный с сельским хозяйством, из-за отсутствия у них сбережений. Группы мелких и крупных фермеров инвестировали во все статьи, по которым они были самыми высокими, в оборотный капитал (от 61,28 до 61,84%), за которыми следовали инвестиции в основной капитал (от 14,41 до 16,84%), финансовый капитал (12-14%) и несельскохозяйственный капитал (7-12%). Наибольшие инвестиции в оборотный капитал (69,02%) были вложены фермерами из выборки. Текущий доход оказался основным источником финансирования во всех доходных группах, на долю которых приходилось от 49,70 до 94,79% от общего объема инвестиций, за которыми следовали сбережения, на которые приходилось от 40,10 до 49,12% от общего объема инвестиций

Orbital order, stacking defects and spin-fluctuations in the pp-electron molecular solid RbO2_2

We examine magnon and orbiton behavior in localized O$_2$ anti-bonding molecular $\pi^*$ orbitals using an effective Kugel-Khomskii Hamiltonian derived from a two band Hubbard model with hopping parameters taken from {\em ab initio} density functional calculations. The considerable difference between intraband and interband hoppings leads to a strong coupling between the spin wave dispersion and the orbital ground state, providing a straightforward way of experimentally determining the orbital ground state from the measured magnon dispersion. The near degeneracy of different orbital ordered states leads to stacking defects which further modulate spin-fluctuation spectra. Proliferation of orbital domains disrupts long-range magnetic order, thus causing a significant reduction in the observed N\'eel temperature.Comment: 5 pages, 2 figure

X-ray spectrum of the high polarization quasar PKS 1510-089

We present results on the X-ray spectra of the radio-loud, high-polarization quasar, PKS 1510-089, based on new data obtained using ASCA, and from archival ROSAT data. The X-ray spectrum obtained by ASCA is unusually hard, with the photon index=1.30+-0.06, while the (non-simultaneous) ROSAT data indicate a steeper spectrum (1.9+-0.3). The X-ray flux at 1 keV is within 10% during both observations. A break in the underlying continuum at about 0.7 keV is suggested. Flat X-ray spectra seem to be the characteristic of high polarization quasars, and their spectra also appear to be harder than that of the other radio-loud but low-polarization quasars. The multiwavelength spectrum of PKS 1510-089 is similar to many other gamma-ray blazars, suggesting the emission is dominated by that from a relativistic jet. A big blue-bump is also seen in its multiwavelength spectrum, suggesting the presence of a strong thermal component as well.Comment: 19 pages (Latex + 5 ps figures), Accpeted for publication in the Astrophysical Journal, December 20, 199