Electron petrography of silica polymorphs associated with pseudotachylite, Vredefort structure, South Africa

High-pressure silica polymorphs (coesite and stishovite) were described from the Vredefort structure in association with pseudotachylite veinlets. In addition to the fundamental significance of the polymorphs to genetic interpretations of the structure, it was additionally argued that the type of pseudotachylite with which they occur forms during the compressional phase of the shock process, while the larger, classic pseudotachylite occurrences are barren of polymorphs and formed during passage of the rarefaction wave. This identification of temporal relationships among transient shock features at a regional scale is similar to observations from the Manicouagan structure, Quebec, where texturally distinct diaplectic plagioclase glasses formed during both compressional and decompressional phases of the shock process. The clarification of such relationships impinges directly on interpretations of natural shock processes and the identification of high probability targets for polymorph searches. Detailed analytical scanning (SEM) and transmission electron microscopy (TEM) were utilized to further establish the nature of both the pseudotachylite and the silica polymorph occurrences in the Vredefort rocks. The results of this investigation are discussed

Phase noise in distributed oscillators

The phase noise of a distributed oscillator is evaluated very simply by identifying an effective capacitance equal to the total capacitance distributed along the transmission lines. The contributions of the various passive and active noise sources to the total phase noise are calculated revealing several guidelines for improved distributed oscillator designs

Synchronization and oscillatory dynamics in heterogeneous mutually inhibited neurons

We study some mechanisms responsible for synchronous oscillations and loss of synchrony at physiologically relevant frequencies (10-200 Hz) in a network of heterogeneous inhibitory neurons. We focus on the factors that determine the level of synchrony and frequency of the network response, as well as the effects of mild heterogeneity on network dynamics. With mild heterogeneity, synchrony is never perfect and is relatively fragile. In addition, the effects of inhibition are more complex in mildly heterogeneous networks than in homogeneous ones. In the former, synchrony is broken in two distinct ways, depending on the ratio of the synaptic decay time to the period of repetitive action potentials ($\tau_s/T$), where $T$ can be determined either from the network or from a single, self-inhibiting neuron. With $\tau_s/T > 2$, corresponding to large applied current, small synaptic strength or large synaptic decay time, the effects of inhibition are largely tonic and heterogeneous neurons spike relatively independently. With $\tau_s/T < 1$, synchrony breaks when faster cells begin to suppress their less excitable neighbors; cells that fire remain nearly synchronous. We show numerically that the behavior of mildly heterogeneous networks can be related to the behavior of single, self-inhibiting cells, which can be studied analytically.Comment: 17 pages, 6 figures, Kluwer.sty. Journal of Compuational Neuroscience (in press). Originally submitted to the neuro-sys archive which was never publicly announced (was 9802001

Roles, service knowledge and priorities in the provision of palliative care: a postal survey of London GPs

Objectives: To explore general practitioners' (GPs) current involvement in and attitudes towards the provision of palliative care in primary care. Methods: Postal survey of 356 London-based GPs, assessing attitudes towards palliative care provision, district nursing and specialist palliative care services, and priorities for future service development. Results: Currently, 65% of GPs were providing palliative care to patients on their list; 72% agreed or strongly agreed palliative care was a central part of their role; and 27% wanted to hand care over to specialists. Most GPs (66%) disagreed with the statement that 'palliative care is mainly district nursing (DN) work'. Many were unaware of out-of-hours DN and specialist palliative care services. Multi-variable analysis found four GP characteristics - larger practice size, more years experience as a GP, receipt of palliative care education, and current provision of palliative care - were associated with agreement that palliative care was central to a GP's role. Conclusion: A minority of NHS GPs in London would rather have no involvement in palliative care in primary care. Knowledge of current services for palliative care is generally poor among GPs. These findings highlight potential gaps in services, particularly in small practices. Specialists will need to consider these factors in working with GPs to develop primary palliative care and to enable greater access to specialist palliative care

High resolution CO observations of S88-B

CO J = 2-1 and 13CO J = 2-1 and 1-0 observations have been made of the H II region S88-B, using the 15-m James Clerk Maxwell telescope in Hawaii and the 20-m telescope at Onsala. The core of the cloud is resolved into a horseshoelike structure which surrounds a diffuse reflection nebula. The central core has a mass of ≥ 1000 M⊙, with 400 M⊙ in the horseshoe structure. The gas in the horse in the horseshoe appears highly fragmented, and has a kinetic temperature of ≈ 60 K, suggesting it is closely coupled to the dust temperature. A recently formed high mass star appears to be in the process of evacuating a cavity, possibly through a large molecular outflow that is found to show an accelerated component in its blue-shifted lobe. A velocity gradient across the horseshoe structure suggest ordered motion, and could represent rotation in the parental cloud

High signal/noise ¹³CO observations of the bipolar outflow in L1551

New high-signal/noise 13CO observations of the bipolar outflow in the molecular cloud L1551 are reported. Contrary to earlier observations of CO J = 1-0 and 2-1, no strong spatial dependence is found for the velocity profile of these spectra. The implications of these observations are such that the model of an empty shell for this source is less likely, and a model consisting of a shell which contains significant amounts of outflowing molecular gas inside the swept-up cavity walls is suggested

Control of Variable Watermilfoil in Bashan Lake, CT with 2,4-D: Monitoring of Lake and Well Water.

Variable watermilfoil (Myriophyllum heterophyllum Michx.) has recently become a problem in Bashan Lake, East Haddam, CT, USA. By 1998, approximately 4 ha of the 110 ha lake was covered with variable watermilfoil. In 1999, the milfoil was spot treated with Aquacide®, an 18% active ingredient of the sodium salt of 2,4-D [(2,4-dichlorophenoxy) acetic acid], applied at a rate of 114 kg/ha. Aquacide® was used because labeling regarding domestic water intakes and irrigation limitations prevented the use of Navigate® or AquaKleen®, a 19% active ingredient of the butoxyethyl ester of 2,4-D. Variable watermilfoil was partially controlled in shallow protected coves but little control occurred in deeper more exposed locations. 2,4-D levels in the treatment sites were lower than desired and offsite dilution was rapid. In 2000, the United States Environmental Protection Agency (USEPA) issued a special local need (SLN) registration to allow the use of Navigate ® or AquaKleen® in lakes with potable and irrigation water intakes. Navigate® was applied at a rate of 227 kg/ha to the same areas as treated in 1999. An additional 2 ha of variable watermilfoil was treated with Navigate® in 2001, and 0.4 ha was treated in mid-September. Dilution of the 2,4-D ester formulation to untreated areas was slower than with the salt formulation. Concentrations of 2,4-D exceeded 1000 μg/ L in several lake water samples in 2000 but not 2001. Nearly all of the treated variable watermilfoil was controlled in both years. The mid-September treatment appeared as effective as the spring and early summer treatments. Testing of homeowner wells in all 3 years found no detectable levels of 2,4-D.(PDF contains 8 pages.

Investigation of the effect of hub support parameters on two-bladed rotor oscillatory loads

The results are presented of a test program and analysis to investigate the effects of inplane hub support parameters on the oscillatory chordwise loads of a two-bladed teetering rotor. The test program was conducted in two phases. The first consisted of a shake test to define the impedance of a number of test configurations as a function of frequency. The second phase was the test of these configurations in the NASA-Langley transonic dynamics tunnel. The test showed that the one-per-rev inplane bending moments could be changed by a factor of 2.0 as a function of the pylon configuration at the same aerodynamic operating condition. The higher harmonic inplane, flapwise, and torsional bending moments, and pitch link axial loads were not affected by changes in inplane hub impedance. The maximum inplane loads occurred for the pylon configuration with the minimum spring rate and maximum inertia

Moir\'e super-lattice structures in kicked Bose-Einstein condensates

Vortex lattices in rapidly rotating Bose-Einstein condensates lead to a periodic modulation of the superfluid density with a triangular symmetry. Here we show that this symmetry can be combined with an external perturbation in order to create super-lattice structures with two or more periodicities. Considering a condensate which is kicked by an optical lattice potential, we find the appearance of transient moir\'e lattice structures, which can be identified using the kinetic energy spectrum.Comment: 7 pages, 8 figure

Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.Comment: 9 page PDF, 550 kbyte