Publications

"superclusters" of metal-line systems (thought to be associated with galaxies) at large redshift, analogous to the absorbers found in the field surrounding the southern pair Tol 1037/1038. The unique ability of QSO absorption lines to reveal modest columns of gas at high redshift allows a pencil-beam survey of interesting fields. By concentrating on QSOs with known, rich, metal-line absorption systems and searching catalogs for nearby QSOs lying behind the proposed clusters, we have identified a number of promising fields. Initial results from QSOs surrounding Q1303+308 support the BAL hypothesis for the absorption in this object. We show that further observations will be of substantial use in delineating the extent and overdensity of superclustering at redshifts z ~ 1-2.

Recent theoretical studies inspired by experiments on the Kitaev magnet α-RuCl3 highlight the nontrivial impact of phonons on the thermal Hall conductivity of chiral topological phases. Here, we introduce mixed mesoscopic-macroscopic devices that allow refined thermal-transport probes of non-Abelian spin liquids with Ising topological order. These devices feature a quantum-coherent region with quantized or negligible phonon conductance, flanked by macroscopic lobes that facilitate efficient thermalization between chiral Majorana edge modes and bulk phonons. We show that our devices enable (i) accurate determination of the quantized thermal Hall conductivity, (ii) identification of non-Abelian Ising anyons via the temperature dependence of the thermal conductance, and, most interestingly, (iii) single-anyon detection through heat-based anyon interferometry. Analogous results apply broadly to phonon-coupled chiral topological orders.

A novel surface reaction for the reduction of MgCl2 by AlEt3 in the presence of Au is reported. MgCl2 submonolayer and multilayer films are prepared by gas-phase deposition over polycrystalline gold in UHV. When submonolayer MgCl2 films are exposed to liquid AlEt3, the halide is reduced, with the formation of Mg clusters or islands, covered with hydrocarbon fragments. The reduction of the halide at the Au surface is faster, and more complete, when MgCl2 and AlEt3 molecular beams are simultaneously directed at the metal surface. The reduced Mg surface reacts promptly with gas-phase TiCl4, and a TiCl2/TiCl4 film is thus deposited. This experiment demonstrates the feasibility of producing a MgCl2 support with a large fraction of its surface capable of TiCl4 chemisorption. The possibility of synthesizing Ziegler−Natta catalysts with a large density of active sites is discussed.

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

In this letter, we study the use of adaptive controllers to maintain the synchronization of two Chua's oscillators when the channel and circuit parameters are time-varying. We present both computer simulation results and physical experimental results to verify the operation of the designs.

We discuss a series of spectra of the Type Ic (helium-poor Ib) supernova (SN) 1987M in the Sc galaxy NGC 2715, obtained over a 6 month interval following its discovery. Two spectra of SNe Ia, SN 1987L in NGC 2336 and SN 1987N in NGC 7606, are also illustrated for comparison. Near maximum brightness, SN 1987M showed all the spectroscopic characteristics of the "helium-poor" variety of SNe Ib identified in 1987 by Wheeler and collaborators, but it may have been subluminous by only 0.6 mag (B) instead of the average value of 1.5 mag. The possible presence of very weak H<SUB>alpha</SUB> must be verified through spectral synthesis. Strong P Cygni profiles of O I λ 7774 and Ca II are visible at early times in the near-infrared spectrum, as previously predicted. The Type IIb SN 1987K, by contrast, exhibits prominent H<SUB>alpha</SUB>_ but no O I λ 7774, although the two objects appear quite similar at blue and visual wavelengths. Strong Co II and Fe II absorption may be present at near-ultraviolet wavelengths in SN 1987M, as in SNe Ia. The data clearly reveal, for the first time, the remarkable transition to the "supernebular phase" of SNe Ib and Ic. Unambiguous [O I] and [Ca II] lines begin to appear less than two months past maximum. The ejected mass is estimated to be small, M&lt;~1 M_sun_, although this number is highly uncertain. Multicolor light curves of SN 1987M, derived from CCD images and spectra, show a rapid decline from maximum brightness, perhaps even steeper than that of typical SNe I. This also suggests a relatively low ejected mass. Furthermore, unlike many SNe Ib, SN 1987M was not superposed on a luminous H II region. It is possible that SNe Ic, such as SN 1987M, have different progenitors or explosion mechanisms than SNe Ib. Specifically, we postulate that SNe Ic result from explosions of white dwarfs, while core collapse in massive, hydrogen- deficient stars produces SNe Ib.

An algorithm is described for planning the motions of several mobile robots which share the same workspace. Each robot is capable of independent translational motion in two dimensions, and the workspace contains polygonal obstacles. The algorithm computes a path for each robot which avoids all obstacles in the workspace as well as the other robots. It is guaranteed to find a solution if one exists. The algorithm takes a cell decomposition approach, where the decomposition used is based on the idea of a product operation defined on the cells in a decomposition of a two-dimensional free space. This algorithm is being implemented for the case of two robots as part of ongoing research into useful algorithms for task-level programming of the RobotWorld system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>