BIMA N2H+ 1-0 mapping observations of L183 -- fragmentation and spin-up in a collapsing, magnetized, rotating, pre-stellar core

We have used the Berkeley-Illinois-Maryland Array (BIMA) to make deep N2H+ 1-0 maps of the pre-stellar core L183, in order to study the spatial and kinematic substructure within the densest part of the core. Three spatially and kinematically distinct clumps are detected, which we label L183-N1, L183-N2 and L183-N3. L183-N2 is approximately coincident with the submillimetre dust peak and lies at the systemic velocity of L183. Thus we conclude that L183-N2 is the central dense core of L183. L183-N1 and 3 are newly-discovered fragments of L183, which are marked by velocity gradients that are parallel to, but far stronger than, the velocity gradient of L183 as a whole, as detected in previous single-dish data. Furthermore, the ratio of the large-scale and small-scale velocity gradients, and the ratio of their respective size-scales, are consistent with the conservation of angular momentum for a rotating, collapsing core undergoing spin-up. The inferred axis of rotation is parallel to the magnetic field direction, which is offset from its long axis, as we have seen in other pre-stellar cores. Therefore, we propose that we have detected a fragmenting, collapsing, filamentary, pre-stellar core, rotating about its B-field, which is spinning up as it collapses. It will presumably go on to form a multiple protostellar system.Comment: 7 figures, 1 table, 21 pages, accepted for publication in Ap

Diethynylrhodacyclopentadienes: a new class of luminescent organometallics

A series of mer,cis-[tris(trimethylphosphine)-X-2,5-bis(4-R-phenylethynyl)-3,4- bis(4-R-phenyl)rhodacyclopenta-2,4-diene] compounds have been synthesised by the regiospecific reductive coupling of 1,4-bis(4-R-phenyl)buta-1,3-diynes with КҺ(РМe(_3))(_4)Х (where X = -C≡С –TMS, -С≡С(_6)Н(_4)-4-ММe(_2), -С≡С-С≡С-С(_6)Н(_4)-4-МРһ(_2), and R = H, Me, ОМе, SMe, СF(_3), CN, СО(_2)Ме, NMe(_2), NO(_2), C≡C-TMS). The compounds absorb strongly in the range 453-544 nm, and are photoluminescent, in solution at room temperature, emitting in the range 496-631 nm with singlet lifetimes and quantum yields of 3-18 %. The photophysical properties are strongly influenced by the nature of R, but appear to be almost independent of the acetylide used; the latter is related to unfavourable steric interactions. Acceptor R groups red-shift both absorption and emission much more significantly than donor groups. A number of the structures have been solved by single crystal X-ray diffraction and the structures are compared and contrasted. Analogous compounds with X = Me and СІ have also been prepared. The absorbance properties are similar to the acetylide-substituted derivatives, although absorption maxima are slightly shifted to lower energy. Also correlated with this are the values of J(_Rh-P) for the sets of compounds which surprisingly suggest better donating ability of both Me and СІ over the acetylides. The СІ compound is luminescent, its emission maximum again shifted to lower energy from that of the acetylide examples. In stark contrast to the acetylide and СІ rhodacycle derivatives, the Me compounds are not emissive at room temperature in solution. The rhodacycles react slowly, with additional diyne only under forcing conditions, to form highly substituted benzenes. It is shown that the rhodacycles can catalyse the regiospecific cyclotrimerisation of 1,4-bis(4-R-phenyl)buta-1,3-diynes to give l,2,4-tris(4- R-phenylethynyl)-2,5,6-tri(4-R-phenyl)benzenes exclusively. The activity of the rhodacycles as catalysts for trimerisation are low, but due to the 2,5- selectivity of the rhodacycle formation, the reaction is regiospecific. The cyclotrimers are luminescent and the photophysical properties have been studied. The single-crystal X-ray structure for the parent cyclotrimer, l,2,4-tris(phenylethynyl)-2,5,6-tri(phenyl)benzene, has been obtained and is discussed. The mechanism for rhodacycle formation has been probed. A number of Rh-diyne π-complexes, in which one of the diyne C≡C bonds is coordinated to Rh, which were observed as intermediates during rhodacycle syntheses, have been isolated and characterised. 1H, (^19) F{(^1)H} and (^31) P{(^1)H} NMR spectroscopy has been used to propose a general structure, and several related Rh- π -complexes of symmetrical and unsymmetrical tolans have been prepared to support this, some of which have been characterised by X-ray diffraction and are discussed. The crystal structures of two solvates of the unusual centrosymmetric bimetallic complex, [Rh(PMe(_3))(_3)(Cl)](μ-( 1 ,2-ƞ(^2)):(3,4- ƞ(^2))-4-F (_3)C-C(_6)H(_4)-C≡C-C≡C-C(_6)H(_4)-4-CF(_3)) have also been obtained

The Meeting of Two Cultures: Public Broadcasting on the Threshold of the Digital Age

Provides a summary of discussions held in November 2007 on "Public Broadcasting: The Digital Challenge" among representatives of foundations, public broadcasting corporations and academia. Includes essays on visions for the future of public media

Distributed computing system with dual independent communications paths between computers and employing split tokens

This is a distributed computing system providing flexible fault tolerance; ease of software design and concurrency specification; and dynamic balance of the loads. The system comprises a plurality of computers each having a first input/output interface and a second input/output interface for interfacing to communications networks each second input/output interface including a bypass for bypassing the associated computer. A global communications network interconnects the first input/output interfaces for providing each computer the ability to broadcast messages simultaneously to the remainder of the computers. A meshwork communications network interconnects the second input/output interfaces providing each computer with the ability to establish a communications link with another of the computers bypassing the remainder of computers. Each computer is controlled by a resident copy of a common operating system. Communications between respective ones of computers is by means of split tokens each having a moving first portion which is sent from computer to computer and a resident second portion which is disposed in the memory of at least one of computer and wherein the location of the second portion is part of the first portion. The split tokens represent both functions to be executed by the computers and data to be employed in the execution of the functions. The first input/output interfaces each include logic for detecting a collision between messages and for terminating the broadcasting of a message whereby collisions between messages are detected and avoided

Design rules for dislocation filters

The efficacy of strained layer threading dislocation filter structures in single crystal epitaxial layers is evaluated using numerical modeling for (001) face-centred cubic materials, such as GaAs or Si(1-x)Ge(x), and (0001) hexagonal materials such as GaN. We find that threading dislocation densities decay exponentially as a function of the strain relieved, irrespective of the fraction of threading dislocations that are mobile. Reactions between threading dislocations tend to produce a population that is a balanced mixture of mobile and sessile in (001) cubic materials. In contrast, mobile threading dislocations tend to be lost very rapidly in (0001) GaN, often with little or no reduction in the immobile dislocation density. The capture radius for threading dislocation interactions is estimated to be approx. 40nm using cross section transmission electron microscopy of dislocation filtering structures in GaAs monolithically grown on Si. We find that the minimum threading dislocation density that can be obtained in any given structure is likely to be limited by kinetic effects to approx. 1.0e+04 to 1.0e+05 per square cm.Comment: 18 pages, 9 figure

Thioxoethenylidene (CCS) as a bridging ligand

The reaction of [Mo(≡CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with [Fe2(μ-SLi)2(CO)6] affords, inter alia, the unsymmetrical binuclear thioxoethenylidene complex [Mo2(μ,σ(C):η2(C′S)-CCS)(CO)4(Tp*)2], which may be more directly obtained from [Mo(≡CBr)(CO)2(Tp*)] and Li2S. The reaction presumably proceeds via the intermediacy of the bis(alkylidynyl)thioether complex S{C≡Mo(CO)2(Tp*)}2, which was, however, not directly observed but explored computationally and found to lie 78.6 kJ mol–1 higher in energy than the final thioxoethenylidene product. Computational interrogation of the molecules [M2(μ-C2S)(CO)2(Tp*)2] (M = Mo, W, Re, Os) reveals three plausible coordination modes for a thioxoethenylidene bridge which involve a progressive strengthening of the C–C bond and weakening of the M–C and M–S bonds, as might be expected from simple effective atomic number considerations.This work was supported by the Australian Research Council (DP130102598 and DP110101611)

Monte Carlo Studies of Water Monolayer Clusters on Substrates: Hexagonal AgI

A Monte Carlo procedure is used to study the stability and structure of small water clusters adsorbed on model basal and prism faces of hexagonal AgI. Effective pair potentials for the H2O-AgI interaction [B. N. Hale and J. Kiefer, J. Chem. Phys. 73, 923 (1980)] and the revised central force potentials for the H2O-H2O interaction [F. H. Stillinger and A. Rahman, J. Chem. Phys. 68, 666 (1978)] are used to determine average internal cluster binding energy and average cluster-substrate binding energy for water clusters containing 6, 24, and 44 water molecules at temperatures 240, 265, and 298 K. The results (using an effective substrate point charge of 0.4e) give between 5 and 6 kcal/mol per molecule for each of the above average binding energies. The iodine exposed basal AgI face organizes the H2O into five- and six-membered rings centered around the exposed I atoms. The prism face appears less effective in promoting ring structure and gives, in general, lower average internal cluster binding energies. The basal AgI face positions the water molecules (in H2O-substrate high binding sites) about 2.8 A apart while the water-water interactions orient the H2O dipole moments into configurations favorable for hydrogen bonding. The resulting six-membered ring structure is similar to that in ice Ih (crinkled) basal face layers, and appears to be qualitatively the same for all the temperatures studied

Why does the world need another rotavirus vaccine?

A “Meeting on Upstream Rotavirus Vaccines and Emerging Vaccine Producers” was held at the World Health Organization in Geneva, Switzerland on March 28–30, 2006. The purpose was to discuss, evaluate, and weigh the importance of additional rotavirus vaccine candidates following the successful international licensure of rotavirus vaccines by two major pharmaceutical companies (GlaxoSmithKline and Merck) that had been in development for many years. Both licensed vaccines are composed of live rotaviruses that are delivered orally as have been all candidate rotavirus vaccines evaluated in humans. Each is built on the experience gained with previous candidates whose development had either been discontinued or, in the case of the previously licensed rhesus rotavirus reassortant vaccine (Rotashield), was withdrawn by its manufacturer after the discovery of a rare association with intussusception. Although which alternative candidate vaccines should be supported for development and where this should be done are controversial topics, there was general agreement expressed at the Geneva meeting that further development of alternative candidates is a high priority. This development will help insure that the most safe, effective and economic vaccines are available to children in Third World nations where the vast majority of the >600,000 deaths due to rotavirus occur each year. This review is intended to provide the history and present status of rotavirus vaccines as well as a perspective on the future development of candidate vaccines as a means of promulgating plans suggested at the Geneva meeting

SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores

We have mapped linearly polarized dust emission from L183 with the JCMT SCUBA polarimeter and have analyzed these and our previously published data for the prestellar cores L183, L1544, and L43 in order to estimate magnetic field strengths in the plane of the sky, $B_{pos}$. The analysis used the Chandrasekhar-Fermi technique, which relates the dispersion in polarization position angles to $B_{pos}$. We have used these estimates of the field strengths (neglecting the unmeasured line-of-sight component) to find the mass-to-magnetic flux ratios $\lambda$ (in units of the critical ratio for magnetic support). Results are $B_{pos} \approx 80$ $\mu$G and $\lambda \approx 2.6$ for L183, $B_{pos} \approx 140$ $\mu$G and $\lambda \approx 2.3$ for L1544, and $B_{pos} \approx 160$ $\mu$G and $\lambda \approx 1.9$ for L43. Hence, without correction for geometrical biases, for all three cores the mass-to-flux ratios are supercritical by a factor of $\sim 2$, and magnetic support cannot prevent collapse. However, a statistical mean correction for geometrical bias may be up to a factor of three; this correction would reduce the individual $\lambda$'s to $\lambda_{cor} \approx 0.9$, 0.8, and 0.6, respectively; these values are approximately critical or slightly subcritical. These data are consistent with models of star formation driven by ambipolar diffusion in a weakly turbulent medium, but cannot rule out models of star formation driven by turbulence.Comment: Version 2 has minor revisions to reflect referee comments. Paper accepted for ApJ publicatio

Technology Policy: A Fixture on the National Agenda

In his commentary, Robert Kidd, president of the Maine Science and Technology Foundation, echoes the call by Rycroft, Kash and Adams in their article [this issue] for a new technology policy focused on industrial competitiveness. He defines a partnership role for states in the design and implementation of national technology priorities. James Ward, IV and Richard Hill, raise several questions in their commentary. Can we rely on the federal government to successfully direct this policy area? How would a new technology policy impact the roles and responsibilities of the private and public sectors? What can we learn from partnerships between universities and industry that have led to innovation and enhanced competitiveness and did they result from good policy or practical incentives at the local level