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Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.
The distance to a star forming region can be determined by measuring the proper motions within H2O maser clusters. If the motions of the maser spots are random, the distance can be determined by applying the technique known as statistical parallax. Alternatively, if organized motions are evident in the proper motions, one can model the source to estimate its the distance. Both methods rely on a comparison of the radial component of the motion (in km/s) and the proper motion on the plane of the sky (in milli-arcseconds/year).
The dynamical properties of the ionized envelopes surrounding massive, newly formed stars can be probed by the measurement of radio recombination lines over a wide range of frequencies. In an expanding envelope, the centroids of the radio recombination lines move progressively to lower velocities with increasing value of the principal quantum number, n. This shift is caused by the free-free absorption on the near side of the envelope combined with non-LTE radiative transfer effects.
We report preliminary results of a long term spectral line VLBI experiment to observe internal proper motions of water maser sources in the vicinity of newly formed stars. This technique yields a picture of the three-dimensional kinematics of the region and a measure of the distance to the source. First results from the galactic center source SGR B2 are presented.
The impact of underlying parental psychological vulnerability on the future mental health of offspring is not fully understood. Using a prospective cohort design, we investigated the association between dysfunctional parental personality traits and risks of offspring self-harm, depression and anxiety.
The association between dysfunctional parental personality traits (monotony avoidance, impulsivity, anger, suspicion, and detachment), measured in both mothers and fathers when offspring were age 9 years, and risk of offspring depression, anxiety and self-harm at age 18 years, was investigated in a population-based cohort (ALSPAC) from over 8000 parents and children.
Higher levels of dysfunctional maternal, but not paternal, personality traits were associated with an increased risk of self-harm, depression, and anxiety in offspring. Maternal associations were best explained by the accumulation of dysfunctional traits. Associations were strongest for offspring depression: Offspring of mothers with three or more dysfunctional personality traits were 2.27 (1.45–3.54, p < 0.001) times as likely to be depressed, compared with offspring of mothers with no dysfunctional personality traits, independently of maternal depression and other variables.
The accumulation of dysfunctional maternal personality traits is associated with the risk of self-harm, depression, anxiety in offspring independently of maternal depression and other confounding variables. The absence of associations for equivalent paternal traits makes a genetic explanation for the findings unlikely. Further research is required to elucidate the underlying mechanism. Mothers with high levels of dysfunctional personality traits may benefit from additional support to reduce the risk of adverse psychological outcomes occurring in their offspring.
Radio astronomy has seen major advances in both instrumentation and scientific discovery during the last three years. This report is not encyclopedic but is intended to show the breadth of activity in the field. Division X is a technique-based division, and radio telescopes are becoming increasingly more international in character and usage. For these reasons this report devotes considerable attention to advances in instrumentation. More complete information on radio telescopes and scientific advances in the field can be found at the following Web site: http://www.stsci.edu/science/net-resources.html
Radio interferometric observations of extragalactic radio sources have been made with antennas at the Haystack Observatory in Massachusetts and the Owens Valley Radio Observatory in California during fourteen separate experiments distributed between September 1976 and May 1978. The components of the baseline vector and the coordinates of the sources were estimated from the data from each experiment separately. The root-weighted-mean-square scatter about the weighted mean (“repeatability”) of the estimates of the length of the 3900 km baseline was approximately 7 cm, and of the source coordinates, approximately or less, except for the declinations of low-declination sources. With the source coordinates all held fixed at the best available, a posteriori, values, and the analyses repeated for each experiment, the repeatability obtained for the estimate of baseline length was 4 cm. From analyses of the data from several experiments simultaneously, estimates were obtained of changes in the x component of pole position and in the Earth's rotation (UT1). Comparison with the corresponding results obtained by the Bureau International de l'Heure (BIH) discloses systematic differences. In particular, the trends in the radio interferometric determinations of the changes in pole position agree more closely with those from the International Polar Motion Service (IPMS) and from the Doppler observations of satellites than with those from the BIH.
A method of diamond heteroepitaxial lateral overgrowth is demonstrated which utilizes a photolithographic metal mask to pattern a thin (001) epitaxial diamond surface. Significant structural improvement was found, with a threading dislocation density reduced by two orders of magnitude at the top surface of a thick overgrown diamond layer. In the initial stage of overgrowth, a reduction of diamond Raman linewidth in the overgrown area was also realized. Thermally-induced stress and internal stress were determined by Raman spectroscopy of adhering and delaminated diamond films. The internal stress is found to decrease as sample thickness increases.
General Practitioner consultation rates for influenza-like illness (ILI) are monitored through several geographically distinct schemes in the UK, providing early warning to government and health services of community circulation and intensity of activity each winter. Following on from the 2009 pandemic, there has been a harmonization initiative to allow comparison across the distinct existing surveillance schemes each season. The moving epidemic method (MEM), proposed by the European Centre for Disease Prevention and Control for standardizing reporting of ILI rates, was piloted in 2011/12 and 2012/13 along with the previously proposed UK method of empirical percentiles. The MEM resulted in thresholds that were lower than traditional thresholds but more appropriate as indicators of the start of influenza virus circulation. The intensity of the influenza season assessed with the MEM was similar to that reported through the percentile approach. The MEM pre-epidemic threshold has now been adopted for reporting by each country of the UK. Further work will continue to assess intensity of activity and apply standardized methods to other influenza-related data sources.
Common mental disorders (CMDs) are associated with occupational impairment and the receipt of disability benefits (DBs). Little is known about the relationship between personality disorders (PDs) and work disability, and whether the association between CMDs and work disability is affected by the presence of co-morbid PDs. The aim of this study was to examine the association between DB and individual categories of PDs, with special attention to the effect of co-morbid CMDs on this association.
The association between DB and PD was examined using data from the 2000 British National Survey of Psychiatric Morbidity. Probable PD caseness was identified using the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II) screening questionnaire. The impact of CMDs, assessed with the revised version of the Clinical Interview Schedule (CIS-R), was examined as a covariate and in a stratified analysis of co-morbidity. Other covariates included sociodemographic factors, long-standing illnesses and substance use.
Probable PD was associated with DB, with the strongest associations found for borderline, dependent and schizotypal PD. Antisocial PD was not associated with DB. The relationship between PD and DB was strongly modified by CMD, reducing the association from an odds ratio (OR) of 2.84 to 1.34 [95% confidence interval (CI) 1.00–1.79)]. In the stratified analysis, co-morbid PD and CMD showed a stronger association with DB than PD without CMD but, when fully adjusted, this effect was not significantly different from the association between CMD without PD.
Individuals screening positive for PD are more likely to experience severe occupational outcomes, especially in the presence of co-morbid CMD.
Silicon-carbon alloys were deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using either halogenated or non-halogenated precursors for the Si and C sources. Halogenated precursors were chosen for initial experiments to try to reduce the H content and to improve the microstructure of the silicon carbide (SiCx) films. While a wide range of compositions has been deposited using the halogenated precursors, only a limited range has been deposited so far with the non-halogenated precursors. Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectroscopy show that compositions ranging from near-stoichiometric SiCx to extremely C-rich can be deposited by controlling the deposition temperature, plasma power and C/Si ratio of the halogenated precursors. At the highest C/Si-precursor ratio, the deposited film is electrically conductive with a measured resistivity of 0.067ω-cm, contains only 3-atomic-percent Si and should be considered a Si-doped carbon (C:Si) film. The excellent transparency, especially that of the C:Si films, allowed the assignment of FTIR absorption bands that are usually masked by graphitic inclusions and other impurities. A weak absorption band at 1180cm−1 was found to correlate with the electrical conductivity of the films and was attributed to the asymmetric “bond-and-a-half” Si=C stretch in a Si=C=C functional group where the pi electrons are distributed equally between the three atoms. Additional results show etching of the substrate by reactive Cl from the halogenated precursors can have a dramatic effect on the microstructure, porosity and moisture stability of the films. For experiments involving halogenated precursors, the C:Si films are much more stable than the near-stoichiometric SiCx because C:Si is deposited at lower plasma powers that do not etch the Si substrate. Finally, preliminary results show that near-stoichiometric SiCx films deposited using non-halogenated precursors are much more stable with respect to moisture incorporation than those deposited with halogenated precursors.
We demonstrate the use of low-energy electron microscopy (LEEM) as a tool for studying dis-location formation in low-Ge-content SiGe films on Si(001) and silicon-on-insulator. Compared to TEM, sample preparation for LEEM consists only of conventional surface cleaning. Yet, because of its sensitivity to local variations in surface strain on Si(001), LEEM can detect dislocations at the earliest stages of strain relaxation. In identically prepared SiGe films, the typical dislocation extends over the entire viewable region of several hundred microns in SiGe/Si, but is less than 100 microns in SiGe/SOI. In addition, dislocation cross-slip and threading segments are common in SiGe/SOI, but virtually non-existent in SiGe/Si. We have also observed dislocation formation in real-time during high temperature annealing. Preliminary results appear to demonstrate dislocation multiplication and blocking at a perpendicular glide plane. The applicability of LEEM to strain relaxation in other Si-based systems will be discussed.
The scope of molecular dynamics problems designed to simulate materials properties is described, focussing on the limits computation imposes on space and time scales, as well as the limits theoretical understanding imposes on our knowledge of interatomic forces. Five strategies for improving the efficiency of the simulations are described. Shock-induced solid-solid phase transformations are discussed to illustrate these ideas.
The effect of low-energy ion bombardment on ion-beam-sputtered yttrium-oxide films was studied. Yttria films were subjected to argon ions accelerated by a potential of up to 500 V with current densities of up to 8 μA/cm2 and were deposited at differing substrate temperatures. Yttria films bombarded during deposition were found to be amorphous, and trends observed with increased ion energy include reduced amount of residual compressive stress, increased argon content, and decreased refractive index, depending on deposited energy and substrate temperature.
High resolution electron imaging supported by computer image simulation has been carried out for a nominal “second–stage” NiCl2 graphite compound. The resulting local structure information underlines the statistical nature of the stage ordering, rarely perfectly regular. It also shows the interpenetration of differently staged regions.
Carbon 1s X-ray photoemission spectra of alkali graphite intercalation compounds are shown to provide detailed information about the distribution of charge among the carbon layers and atoms. The interior layers of higher stage compounds contain little charge and remain similar to graphite. The charge in the bounding layers is strongly localized to screen the alkali intercalate ions. The c-axis charge distribution in KC12n is in reasonable accord with the electrostatic screening model of Safran and Hamann.