Antarctic meteorite descriptions, 1980

Specimens found in the Alan Hills area include 361 ordinary chondrites, 4 carbonaceous chondrites, 6 achondrites, and 2 irons. Thirteen specimens measured over 11 cm in diameter and 69 between 5 to 10 cm in diameter are reported. The remainder of the finds were small, and many were paired. One of the irons was estimated to weigh about 20 kilograms

Stability of librational motion in the spatial circular restricted three-body problem for high inclinations and mass ratios

In the spatial circular restricted three-body problem librational motion around the Lagrangian points L_4 and L_5 exists up to high inclinations of the massless object. We report the results of numerical investigations on the stability of this librational motion for systematic variations in the inclination of the Trojan and the mass-ratio μ of the two massive bodies. We show that stable motion prevails for inclinations below 60 degrees and mass-ratios μ 6 revolution periods. At even higher mass-ratios - beyond the critical mass-ratio for the planar case - stable orbits were found to exist for up to 107 periods at moderate inclinations. We extracted the librational frequencies on a grid in the parameter space from the Fourier spectra and traced their variation. Several resonances between the short and long period librational frequency as well as the vertical frequency lie inside the investigated region. The application of the Lyapunov characteristic indicator and spectral number methods also reveals the chaotic regions. This simple model is equally applicable in the Solar system for low mass ratios for Trojans of the planets, as well as to Trojan-type exoplanets in binary star systems at high mass-ratios

Stability and secondary resonances in the spatial restricted three-body problem for small mass ratios

This paper is devoted to the study of secondary resonances and the stability of the Lagrangian point L-4 in the spatial restricted three-body problem for moderate mass ratios mu, meaning that mu <= 0.0045. However, we concentrated our investigations on small mass ratios mu <= 0.001, which represent the mass ratios for stable configurations of tadpole orbits in the Solar system. The stability is investigated by numerical methods, computing stability maps in different parameter planes. We started investigating the mass of the secondary: from Earth-mass bodies up to Jupiter-mass bodies. In addition, we changed the orbital elements (eccentricity and inclination) of the secondary and Trojan body. For this parameter space, we found high-order secondary resonances, which are present for various inclinations. To determine secondary resonances we used Rabe's equation and the frequency analysis. In addition, we investigated the stability in and around these secondary resonances

On the Capacity Degradation in Broadband MIMO Satellite Downlinks with Atmospheric Impairments

Abstract—We investigate the impact of atmospheric impairments on the theoretical bandwidth efficiency of Multiple-Input Multiple-Output (MIMO) geostationary satellite links which are shaped to optimize the channel bandwidth efficiency. We analyze the impairments caused by precipitation, since this is the most severe atmospheric effect causing capacity degradations. By theory, the MIMO channel capacity is strongly affected by signal attenuation as well as signal phase shifts that might reduce the number and strength of spatial subchannels (eigenmodes). We will show, however, that the characteristics of the phase disturbances prevent a loss of capacity. Regarding the additional attenuation, which the signals may encounter passing through the troposphere, we will quantify outage values for several levels of link capacity degradation. Although a loss of capacity cannot be avoided in total, it still turns out that MIMO systems outperform conventional Single-Input Single-Output (SISO) designs in terms of reliability. Even in the presence of atmospheric perturbations, MIMO systems still provide enormous capacity gains and vast reliability improvements. Thus, the MIMO satellite systems presented are perfectly suited to establish the backbone network of future broadband wireless standards (e.g. DVB-SH), supporting high data rates for a variety of worldwide services. I

Self-dual Yang-Mills fields in pseudoeuclidean spaces

The self-duality Yang-Mills equations in pseudoeuclidean spaces of dimensions $d\leq 8$ are investigated. New classes of solutions of the equations are found. Extended solutions to the D=10, N=1 supergravity and super Yang-Mills equations are constructed from these solutions.Comment: 9 pages, LaTeX, no figure

Correlation between the exchange bias effect and antisite disorders in Sr2−x_{2-x}Lax_xCoNbO6_6

We unravel the effect of La substitution and hence antisite disorders on the exchange bias (EB) mechanism in Sr$_{2-x}$La$_x$CoNbO$_6$ ($x=$ 0, 0.2) double perovskite samples using the detailed analysis of the field cooled magnetization isotherms (M--H) and training effect. The field dependence of the freezing temperature deviates from both Gabay-Toulouse (GT) and de Almeida-Thouless (AT) lines and the analysis suggests that the $x=$ 0 sample follows a different universality class with moderate anisotropy in the frozen spins. Interestingly, we find that the EB effect is significantly suppressed in the $x=$ 0.2 sample due to increase [decrease] in the size of ferromagnetic (FM) [cluster glass (CG)] domain, which reduces the effective disordered interface responsible for the EB. The changes in fraction of FM, AFM, and CG like interactions with the La substitution and applied magnetic field are found to be crucial in governing the EB effect in these samples. Further, the training effect measurements show the unequal shift in the left and right branches of the M--H loops and their different evolution with the field cycles ($n$). The analysis reveals that the rotatable spins relax approximately one order of magnitude faster than the frozen spins at the disordered interface. We find a possible correlation between the observed EB effect and the antisite disorders in these samples.Comment: submitte

1/d1/d Expansion for kk-Core Percolation

The physics of $k$-core percolation pertains to those systems whose constituents require a minimum number of $k$ connections to each other in order to participate in any clustering phenomenon. Examples of such a phenomenon range from orientational ordering in solid ortho-para ${\rm H}_2$ mixtures to the onset of rigidity in bar-joint networks to dynamical arrest in glass-forming liquids. Unlike ordinary ($k=1$) and biconnected ($k=2$) percolation, the mean field $k\ge3$-core percolation transition is both continuous and discontinuous, i.e. there is a jump in the order parameter accompanied with a diverging length scale. To determine whether or not this hybrid transition survives in finite dimensions, we present a $1/d$ expansion for $k$-core percolation on the $d$-dimensional hypercubic lattice. We show that to order $1/d^3$ the singularity in the order parameter and in the susceptibility occur at the same value of the occupation probability. This result suggests that the unusual hybrid nature of the mean field $k$-core transition survives in high dimensions.Comment: 47 pages, 26 figures, revtex

Type IIB instanton as a wave in twelve dimensions

0-brane of type IIA string theory can be interpreted as a dimensional reduction of a gravitational wave in 11 dimensions. We observe that a similar interpretation applies also to the D-instanton background of type IIB theory: it can be viewed as a reduction (along one spatial and one time-like direction) of a wave in a 12-dimensional theory. The instanton charge is thus related to a linear momentum in 12 dimensions. This suggests that the instanton should play as important role in type IIB theory as the 0-brane is supposed to play in type IIA theory.Comment: 7 pages, harvmac (minor corrections and a reference added

Long beating wavelength in the Schwarz-Hora effect

Thirty years ago, H.Schwarz has attempted to modulate an electron beam with optical frequency. When a 50-keV electron beam crossed a thin crystalline dielectric film illuminated with laser light, electrons produced the electron-diffraction pattern not only at a fluorescent target but also at a nonfluorescent target. In the latter case the pattern was of the same color as the laser light (the Schwarz-Hora effect). This effect was discussed extensively in the early 1970s. However, since 1972 no reports on the results of further attempts to repeat those experiments in other groups have appeared, while the failures of the initial such attempts have been explained by Schwarz. The analysis of the literature shows there are several unresolved up to now contradictions between the theory and the Schwarz experiments. In this work we consider the interpretation of the long-wavelength spatial beating of the Schwarz-Hora radiation. A more accurate expression for the spatial period has been obtained, taking into account the mode structure of the laser field within the dielectric film. It is shown that the discrepancy of more than 10% between the experimental and theoretical results for the spatial period cannot be reduced by using the existing quantum models that consider a collimated electron beam.Comment: 3 pages, RevTe

Uniform Circular Arrays: the Key to Optimum Channel Capacity in Mobile MIMO Satellite Links

Abstract—In this paper, we investigate the benefits of uniform circular arrays (UCAs) as an alternative antenna deployment to uniform linear arrays (ULA), which are commonly applied for multiple-input multiple-output (MIMO) systems. We consider a MIMO satellite link with focus on the Line-of-Sight (LOS) signal component of the MIMO channel between two geostationary satellites and a mobile earth terminal equipped with several antennae. The MIMO LOS channel is optimized with respect to the maximum achievable spectral efficiency. The aim of our approach is to keep this optimum spectral efficiency nearly constantly even if the terminal on earth is moving. We provide an analytical derivation for the optimum UCA arrangement and prove our results by numerical simulations. Especially for mobile applications, the UCA antenna arrangement seems to be a reasonable candidate in order to guarantee high capacity performance durably. To this end, we present a very simple triangle shaped antenna arrangement which is compact enough to allow vehicle roof top installations for S-band applications. I