The VLT-FLAMES survey of massive stars: stellar parameters and rotational velocities in NGC 3293, NGC 4755 and NGC 6611

An analysis is presented of VLT-FLAMES spectroscopy for three Galactic clusters, NGC3293, NGC4755 and NGC6611. Non-LTE model atmosphere calculations have been used to estimate effective temperatures (from either the helium spectrum or the silicon ionization equilibrium) and gravities (from the hydrogen spectrum). Projected rotational velocities have been deduced from the helium spectrum (for fast and moderate rotators) or the metal line spectrum (for slow rotators). The origin of the low gravity estimates for apparently near main sequence objects is discussed and is related to the stellar rotational velocity. The atmospheric parameters have been used to estimate cluster distances (which are generally in good agreement with previous determinations) and these have been used to estimate stellar luminosities and evolutionary masses. The observed Hertzsprung-Russell diagrams are compared with theoretical predictions and some discrepancies including differences in the main sequence luminosities are discussed. Cluster ages have been deduced and evidence for non-coeval star formation is found for all three of the clusters. Projected rotational velocities for targets in the older clusters, NGC3293 and NGC4755, have been found to be systematically larger than those for the field, confirming recent results in other similar age clusters. The distribution of projected rotational velocities are consistent with a Gaussian distribution of intrinsic rotational velocities. For the relatively unevolved targets in the older clusters, NGC3293 and NGC4755, the peak of the velocity distribution would be 250 km s(-1) with a full-width-half-maximum of approximately 180 km s(-1). For NGC6611, the sample size is relatively small but implies a lower mean rotational velocity. This may be evidence for the spin-down effect due to angular momentum loss through stellar winds, although our results are consistent with those found for very young high mass stars. For all three clusters we deduce present day mass functions with Gamma-values in the range of -1.5 to -1.8, which are similar to other young stellar clusters in the Milky Way.

Equilibrium structure of erbium-oxygen complexes in crystalline silicon

The equilibrium structure of ErOn (nless than or equal to6) complexes in crystalline silicon has been investigated by density-functional computations. Two different geometries have been considered, corresponding to the substitutional and tetrahedral interstitial site for erbium. All atomic coordinates have been optimized by Car-Parrinello molecular dynamics. The resulting structures have low symmetry, with E-O distances of similar to2.35 Angstrom. The substitutional site is the most stable one for nless than or equal to2, while the tetrahedral interstitial is favored for n>2.

Concertedness and solvent effects in multiple proton transfer reactions: The formic acid dimer in solution

The issue of multiple proton transfer (PT) reactions in solution is addressed by performing molecular dynamics simulations for a formic acid dimer embedded in a water cluster. The reactant species is treated quantum mechanically, within a density functional approach, while the solvent is represented by a classical model. By constraining different distances within the dimer we analyze the PT process in a variety of situations representative of more complex environments. Free energy profiles are presented, and analyzed in terms of typical solvated configurations extracted from the simulations. A decrease in the PT barrier height upon solvation is rationalized in terms of a transition state which is more polarized than the stable states. The dynamics of the double PT process is studied in a low-barrier case and correlated with solvent polarization fluctuations. Cooperative effects in the motion of the two protons are observed in two different situations: when the solvent polarization does not favor the transfer of one of the two protons and when the motion of the two protons is not synchronized. This body of observations is correlated with local structural and dynamical properties of the solvent in the vicinity of the reactant. (C) 2000 American Institute of Physics. [S0021-9606(00)51121-0].

Geometrical dependence in photoionization of H-2(+) in high-intensity, high-frequency, ultrashort laser pulses

The ionization dynamics of H2 + exposed to high-intensity, high-frequency, ultrashort laser pulses is investigated with two theoretical approaches. The time-dependent Schrödinger equation is solved by a direct numerical method, and a simple two-center interference-diffraction model is studied. The energy and angular distributions of the photoelectron for various internuclear distances and relative orientations between the internuclear axis of the molecule and the polarization of the field are calculated. The main features of the photoelectron spectrum pattern are described well by the interference-diffraction model, and excellent quantitative agreement between the two methods is found. The effect of quantal vibration on the photoelectron spectrum is also calculated. We find that vibrational average produces some broadening of the main features, but that the patterns remain clearly distinguishable.

Prediction of Scattered Dose to the Testes in Abdominopelvic Radiotherapy.

Radical abdominal radiotherapy in men runs the risk of impairing their fertility owing to scattered dose to the testes, outside of the treated volume. In patients for whom this is a concern it is important to be able to predict the dose to the testes before treatment in order to determine whether semen cryopreservation should be undertaken and testicular shielding performed during treatment. Measurements have been made on an anthropomorphic phantom to determine the magnitude of these doses for a four-field treatment consisting of an anterior-posterior parallel pair and a lateral parallel pair. A dataset is presented, which, together with a correction for patients size, allows an estimate of testicular dose to be made given only the photon energy, interfield distances and the distance from the testes to the nearest beam edge. Thermoluminescent dosimetry has been carried out in 17 patients to validate the use of the data tables. The results indicate that testicular doses may be estimated with a standard deviation corresponding to 1%-2% of the tumour dose, which is sufficient for the purpose of determining whether fertility is threatened by a planned treatment.

Accommodative dysfunction in children with cerebral palsy: a population based study

Purpose. To determine the prevalence, nature, and degree of accommodative dysfunction among children with different types and severities of cerebral palsy (CP) in Northern Ireland. Methods. Ninety subjects with CP (aged 4–15 years) were recruited through the Northern Ireland CP Register (NICPR). Modified Nott dynamic retinoscopy was used to measure lag and lead of accommodation at three test distances: 25 cm (4 D), 16.7 cm (6 D), and 10 cm (10 D) with the distance correction in place. Accommodative function was also assessed in an age-matched control group (n = 125) for comparison. Each subject’s neurologic status was derived from the NICPR. Results. Children with CP demonstrate significantly reduced accommodative responses compared with their neurologically normal peers. Of the subjects with CP, 57.6% demonstrated an accommodative lag outside normal limits at one or more distances. Reduced accommodative responses were significantly associated with more severe motor and intellectual impairments (ANOVA P = 0.001, P < 0.01, respectively). Conclusions. Brain injury such as that present in CP has a significant impact on accommodative function. These findings have implications for the optometric care of children with CP and inform our understanding of the impact of early brain injury on visual development.

Structure and dynamics of a confined ionic liquid. topics of relevance to dye-sensitized solar cells

The behavior of a model ionic liquid (IL) confined between two flat parallel walls was studied at various interwall distances using computer simulations. The results focus both on structural and dynamical properties. Mass and charge density along the confinement axis reveal a structure of layers parallel to the walls that leads to an oscillatory profile in the electrostatic potential. Orientational correlation functions indicate that cations at the interface orient tilted with respect to the surface and that any other orientational order is lost thereafter. The diffusion coefficients of the ions exhibit a maximum as a function of the confinement distance, a behavior that results from a combination of the structure of the liquid as a whole and a faster molecular motion in the vicinity of the walls. We discuss the relevance of the present results and elaborate on topics that need further attention regarding the effects of ILs in the functioning of IL-based dye-sensitized solar cells.

Galactic Edge Clouds I. Molecular Line Observations and Chemical Modelling of Edge Cloud 2

Edge Cloud 2 (EC2) is a molecular cloud, about 35 pc in size, with one of the largest galactocentric distances known to exist in the Milky Way. We present observations of a peak CO emission region in the cloud and use these to determine its physical characteristics. We calculate a gas temperature of 20 K and a density of n(H2)~10^4 cm-3. Based on our CO maps, we estimate the mass of EC2 at around 10^4 Msolar and continuum observations suggest a dust-to-gas mass ratio as low as 0.001. Chemical models have been developed to reproduce the abundances in EC2, and they indicate that heavy element abundances may be reduced by a factor of 5 relative to the solar neighborhood (similar to dwarf irregular galaxies and damped Lya systems), very low extinction (A_V <4 mag) due to a very low dust-to-gas mass ratio, an enhanced cosmic-ray ionization rate, and a higher UV field compared to local interstellar values. The reduced abundances may be attributed to the low level of star formation in this region and are probably also related to the continuing infall of primordial (or low-metallicity) halo gas since the Milky Way formed. Finally, we note that shocks from the old supernova remnant GSH 138-01-94 may have determined the morphology and dynamics of EC2.

Suppressing mitotic catastrophe: identifying mcs3 in Schizosaccharomyces pombe

In Schizosaccharomyces pombe (fission yeast), the transition from G2 phase of the cell cycle to mitosis is under strict regulation. The activation of Cdc2, a cyclin dependent serine/threonine protein kinase, is the critical control step in this process. The Cdc2/Cyclin-B (Cdc13) complex is regulated by Wee1 tyrosine kinase and Cdc25 tyrosine phosphatase, which work antagonistically to control progression into mitosis. Hyperactivation of the Cdc2/Cdc13 complex by phosphorylation results in premature mitosis, and as a consequence leads to genome instability. This is referred to as mitotic catastrophe, a lethal phenotype associated with chromosomal segregation abnormalities including chromosome breakage. Six mitotic catastrophe loci were found, five of which have been characterized and identified as various activators and repressors of the core mitotic control. The locus for mcs3 remains unknown. I used tetrad analysis in this study to determine the linkage distance between three genes suspected of flanking the region in which mcs3 is located. Linkage distances obtained in this study confirm that the SPBC428.10 and met17, as well as SPBC428.10 and wpl1 are tightly linked, suggesting this is an area of low recombination. Further linkage analysis should be conducted to determine the precise location of mcs3-12.

William Herschel Telescope observations of distant comets

We present results from broad-band V- and R-filter observations obtained at the 4.2-m William Herschel Telescope on La Palma on 2002 July 12-14. A total of six comets were imaged, and their heliocentric distances ranged from 2.8 to 6.1 au. The comets observed were 43P/Wolf-Harrington, 129P/Shoemaker-Levy 3, 133P/Elst-Pizarro, 143P/Kowal-Mrkos, P/1998 U4 (Spahr) and P/2001 H5 (NEAT). A detailed surface brightness profile analysis indicates that three of the targeted comets (43P/Wolf-Harrington, 129P/Shoemaker-Levy 3 and P/1998 U4) were visibly active, and the remaining three comets were stellar in appearance. Further analysis shows that for the three `stellar-like' comets the possible coma contribution to the observed flux does not exceed 12.2 per cent, and in the case of comet 143P/Kowal-Mrkos the coma contribution is expected to be as low as 1 per cent, and so the resulting photometry most likely represents that of the projected nucleus surface. Effective radii for the inactive comets range from 1.02 to 4.56 km, and the effective radius upper limits for the active comets range from 1.94 to 4.15 km. We assume an albedo and phase coefficient of 0.04 and 0.035 mag deg-1, respectively, with the exception of comets 133P/Elst-Pizarro and 143P/Kowal-Mrkos for which phase coefficients were previously measured. These values are compared with previous measurements, and for comet 43P/Wolf-Harrington we find that the nucleus axial ratio a/b could be as large as 2.44. For the active comets we measured dust production levels in terms of the Af? quantity. Spectral gradients were extracted for two of the inactive comets from their measured broad-band colour indices, and compared with the rest of the comet population for which (V-R) colour and spectral gradient values exist. We find a spectral gradient for 143P/Kowal-Mrkos of 9.9 +/- 8.1 per cent/100 nm, which is very typical of Jupiter-family comets, the majority of which have reflectivity gradients in the range 0-13 per cent (100 nm)-1. The spectral gradient for comet 133P/Elst-Pizarro is amongst the bluest yet measured. We measure a (V-R) colour index value of 0.14 +/- 0.11 for the nucleus of 133P/Elst-Pizarro which is considerably lower than previous measurements. A possible explanation for this difference is considered.

Characterizing the marine Natura 2000 network for the Atlantic region

1. One of the goals for Natura 2000, a key European Community programme of nature conservation, is to produce a network of protected areas. An analysis of the Natura 2000 marine sites proposed in the most recently agreed list for the Atlantic region (northern Portugal to Denmark, n = 298) was used to characterize the network in terms of site areas and inter-site distances. Sites were considered as part of the network when they included any of the marine Natura 2000 Annex I habitat types found in the Atlantic region (excluding lagoons).

Studying genetic relationships among coconut varieties/populations using microsatellite markers

The extent of genetic diversity and the genetic relationships among 94 coconut varieties/populations (51 Talls and 43 Dwarfs) representing the entire geographic range of cultivation/distribution of the coconut was assessed using 12 pairs of coconut microsatellite primers. A high level of genetic diversity was observed in the collection with the mean gene diversity of 0.647+/-0.139, with that of the mean gene diversity of Talls 0.703+/-0.125 and 0.374+/-0.204 of Dwarfs. A phenetic tree based on DAD genetic distances clustered all the 94 varieties/ populations into two main groups, with one group composed of all the Talls from southeast Asia, the Pacific, west coast of Panama, and all Dwarfs and the other of all Talls from south Asia, Africa, and the Indian Ocean coast of Thailand. The allele distribution of Dwarfs highlighted a unique position of Dwarf palms from the Philippines exhibiting as much variation as that in the Tall group. The grouping of all Dwarfs representing the entire geographic distribution of the crop with Talls from southeast Asia and the Pacific and the allele distribution between the Tall and Dwarf suggest that the Dwarfs originated from the Tall forms and that too from the Talls of southeast Asia and the Pacific. Talls from Pacific Islands recorded the highest level of genetic diversity (0.6+/-0.26) with the highest number of alleles (51) among all the regions.

Liquid structure of the ionic liquid, 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide determined from neutron scattering and molecular dynamics simulations

The liquid structure of 1-methyl-4-cyanopyridinium bis {(trifluoromethyl)sulfonyl}imide, a prototypical ionic liquid containing an electron-withdrawing group on the cation, has been investigated at 368 K. Experimental neutron scattering combined with empirical potential structure refinement analysis of the data and classical molecular dynamics simulations have been used to probe the liquid structure in detail. Both techniques generated highly consistent results that provide valuable validation of the force fields and refinement approaches. A significant degree of apparent charge ordering is found in the liquid structure, although the nonspherical shape of the ions results in interpenetration of cations into the first shell of adjacent cations, with much shorter closest contact distances than the averaged center-of-mass cation-cation and cation-anion separations.

Neuromuscular adaptation during skill acquisition on a two degree-of-freedom target-acquisition task: Dynamic movement

In this experiment, we examined the extent to which the spatiotemporal reorganization of muscle synergies mediates skill acquisition on a two degree-of-freedom (df) target-acquisition task. Eight participants completed five practice sessions on consecutive days. During each session they practiced movements to eight target positions presented by a visual display. The movements required combinations of flexion/extension and pronation/supination of the elbow joint complex. During practice sessions, eight targets displaced 5.4 cm from the start position ( representing joint excursions of 54) were presented 16 times. During pre- and posttests, participants acquired the targets at two distances (3.6 cm [36 degrees] and 7.2 cm [72 degrees]). EMG data were recorded from eight muscles contributing to the movements during the pre- and posttests. Most targets were acquired more rapidly after the practice period. Performance improvements were, in most target directions, accompanied by increases in the smoothness of the movement trajectories. When target acquisition required movement in both dfs, there were also practice-related decreases in the extent to which the trajectories deviated from a direct path to the target. The contribution of monofunctional muscles ( those producing torque in a single df) increased with practice during movements in which they acted as agonists. The activity in bifunctional muscles ( those contributing torque in both dfs) remained at pretest levels in most movements. The results suggest that performance gains were mediated primarily by changes in the spatial organization of muscles synergies. These changes were expressed most prominently in terms of the magnitude of activation of the monofunctional muscles.

Observations towards early-type stars in the ESO-POP Survey - II. Searches for intermediate- and high-velocity clouds

We present Ca it K and Ti it optical spectra of early-type stars taken mainly from the ultraviolet and visual echelle spectrograph (LIVES) Paranal Observatory Project, plus H 1 21-cm spectra, from the Vila-Elisa and Leiden-Dwingeloo Surveys, which are employed to obtain distances to intermediate- and high-velocity clouds (IHVCs). H I emission at a velocity of -117 km s(-1) towards the sightline HD 30677 (l, b = 190 degrees.2, -22 degrees.2) with column density -1.7 x 10(19) cm(-2) has no corresponding Ca Pi K absorption in the LIVES spectrum, which has a signal-to-noise ratio (S/N) of 610 per resolution element. The star has a spectroscopically determined distance of 2.7 kpc, and hence sets this as a firm lower distance limit towards Anti-Centre cloud ACII. Towards another sightline (HD 46185 with 1, b = 222 0, -10 degrees.1), H1 at a velocity of +122 km s(-1) and column density of 1.2 x 10(19) cm(-2) is seen. The corresponding Ca Pi K spectrum has a S/N of 780, although no absorption is observed at the cloud velocity. This similarly places a firm lower distance limit of 2.9 kpc towards this parcel of gas that may be an intermediate-velocity (IV) cloud. The lack of IV Ca it absorption towards HD 196426 (1, b = 45 degrees.8, -23 degrees.3) at a S/N of 500 reinforces a lower distance limit of -700 pc towards this part of complex gp, where the H I column density is 1.1 x 1019 cm(-2) and velocity is +78 km s(-1). Additionally, no IV Cart is seen in absorption in the spectrum of HD 19445, which is strong in H I with a column density of 8 x 10(19) cm(-2) at a velocity of - -42 km s(-1), placing a firm although uninteresting lower distance limit of 39 pc to this part of IV South. Finally, no high-velocity Call K absorption is seen towards HD 115363 (l, b = 306.0,-1.0) at a S/N of 410, placing a lower distance of -3.2 kpc towards the HVC gas at velocity of - +224 km s(-1) and WE column density of 5.2 x 10(19) cm(-2). This gas is in the same region of the sky as complex WE (Wakker 2001), but at higher velocities. The non-detection of Ca it K absorption sets a lower distance of -3.2 kpc towards the HVC, which is unsurprising if this feature is indeed related to the Magellanic System.