Probing the Galactic Dark Matter Mass Funtion Using Microlensing and Direct Searches

If compact baryonic objects contribute significantly to the dark matter in our Galaxy, their mass function will present vital clues for galaxy formation theories and star formation processes in the early Universe. Here we discuss what one might expect to learn about the mass function of Galactic dark matter from microlensing and from direct searches in the infrared and optical wavebands. Current microlensing results from the \eros\/ collaboration already constrain halo mass functions which extend below 10^{-4}~\sm, whilst recent \hst\/ observations place strong constraints on disc and halo dark matter mass functions extending above 0.1~\sm. Infrared observations should either detect or constrain objects larger than 0.01~\sm in the near future. Objects below 0.01~\sm should be detectable through microlensing, although the prospects of determining their mass function depend critically on a number of factors.Comment: uuencoded, gzipped postscript file (4 pages). Postscript file (massfunc.ps) can also be obtained via anonymous ftp to 138.37.48.101 in dir /pub/ejk/ir+lens. Based on a talk presented at the conference "Trends in Astroparticle Physics", Stockholm, Sweden, 22-25 September. To be published in Nucl. Phys. B Proceedings Supplemen

Identification of the catalytic motif of the microbial ribosome inactivating cytotoxin colicin E3

Colicin E3 is a cytotoxic ribonuclease that specifically cleaves 16S rRNA at the ribosomal A-site to abolish protein synthesis in sensitive Escherichia coli cells. We have performed extensive mutagenesis of the 96-residue colicin E3 cytotoxic domain (E3 rRNase), assayed mutant colicins for in vivo cytotoxicity, and tested the corresponding E3 rRNase domains for their ability to inactivate ribosome function in vitro. From 21 alanine mutants, we identified five positions where mutation resulted in a colicin with no measurable cytotoxicity (Y52, D55, H58, E62, and Y64) and four positions (R40, R42, E60, and R90) where mutation caused a significant reduction in cytotoxicity. Mutations that were found to have large in vivo and in vitro effects were tested for structural integrity through circular dichroism and fluorescence spectroscopy using purified rRNase domains. Our data indicate that H58 and E62 likely act as the acid–base pair during catalysis with other residues likely involved in transition state stabilization. Both the Y52 and Y64 mutants were found to be highly destabilized and this is the likely origin of the loss of their cytotoxicity. The identification of important active site residues and sequence alignments of known rRNase homologs has allowed us to identify other proteins containing the putative rRNase active site motif. Proteins that contained this active site motif included three hemagglutinin-type adhesins and we speculate that these have evolved to deliver a cytotoxic rRNase into eukaryotic cells during pathogenesis

Harbor Development Study Progress Report for August-October, 1950

This report summarizes the results of the first phase of the Laboratory's current comprehensive study of harbor design. This phase comprises the study of the transmission of wave energy through, and the distribution of wave energy behind, breakwater openings. The results obtained to date relate the effect of three major variables; width of breakwater opening, direction of wave approach, and breakwater alignment, on the two quantities mentioned above. The results of this study are subject to certain limitations, notably the small number of cases studied, the idealization of harbor and breakwater configuration, and experimental error. However, the results are considered to be far more quantitative than qualitative and to be of definite usefulness and value in harbor layout and design

Personality disorder: still the patients psychiatrists dislike?

Aims and method In 1988, Lewis and Appleby demonstrated that psychiatrists hold negative attitudes towards patients with personality disorder. We assessed the attitudes of psychiatry trainees towards patients with borderline personality disorder and depression, expecting an improvement. 166 trainees were block randomised to receive one of four case vignettes that varied by diagnosis and ethnic group. We used Lewis and Appleby's original questionnaire and the Attitudes to Personality Disorder Questionnaire (APDQ). Results We received 76 responses. Lewis and Appleby's questionnaire showed more negative attitudes towards personality disorder than depression, with no significant patient ethnic group effects, and the APDQ also showed a (weak) trend towards more negative attitudes to personality disorder. In subgroup analysis, only in the White British patient group were there significantly more negative attitudes to personality disorder. Factor analysis showed significantly less sense of purpose when working with personality disorder. Clinical implications The perceived greater lack of purpose in working with personality disorder should be the target of clinical training and intervention. Targeted interventions that include training in managing personality disorder, supervision and practice in non-specialist, general psychiatry settings are important

Unambiguous quasar microlensing

Microlensing studies of quasars can reveal dark matter lumps over a broad mass spectrum; we highlight the importance of monitoring quasars which are seen through the halos of low-redshift galaxies. For these configurations microlensing by planetary-mass objects will manifest itself as isolated events which are only weakly chromatic. Statistical comparison of the observed optical depths with their theoretical counterparts provides a strong test for a microlensing origin of such events. If microlensing is detected, the light-curves can reveal not only the characteristic microlens masses, and their corresponding contribution to dark halos, but also how compact the individual objects are. In this way we can decisively test the possibility that the dark matter associated with galaxies is composed principally of planetary-mass gas clouds.Comment: Revised version; 5 pages, 4 figures, to appear in MNRA

Impact of the first order antiferromagnetic phase transition on the paramagnetic spin excitations and nematic phase of SrFe2_2As2_2

Understanding the nature of the electronic nematic phase in iron pnictide superconductors is important for elucidating its impact on high-temperature superconductivity. Here we use transport and inelastic neutron scattering to study spin excitations and in-plane resistivity anisotropy in uniaxial pressure detwinned BaFe$_2$As$_2$ and SrFe$_2$As$_2$, the parent compounds of iron pnictide superconductors. While BaFe$_2$As$_2$ exhibits weakly first order tetragonal-to-orthorhombic structural and antiferromagnetic (AF) phase transitions below $T_s > T_N\approx 138$ K, SrFe$_2$As$_2$ has strongly coupled first order structural and AF transitions below $T_s= T_N\approx 210$ K. We find that the direct signatures of the nematic phase persist to lower temperatures above the phase transition in the case of SrFe$_2$As$_2$ compared to BaFe$_2$As$_2$. Our findings support the conclusion that the strongly first-order nature of the magnetic transition in SrFe$_2$As$_2$ weakens the nematic phase and resistivity anisotropy in the system.Comment: 9 pages, 8 figure

Cultures of psychiatry and the professional socialization process: the case of containment methods for disturbed patients

Acute mental disorder necessitating admission to hospital is often accompanied by disturbed behaviour that threatens the health of the person concerned or that of those around them. A range of containment methods are used by psychiatric professionals to keep patients and staff safe. These strategies are strongly emotive and attract strong moral valuations, yet differ sharply between countries. This paper reports a study to investigate the relationship between attitudes to these containment methods, and exposure to psychiatric education and practice. It was hypothesized that the culture of psychiatry in the study country would socialise students' views towards the locally dominant pattern of relative evaluations. Nine cohorts of student psychiatric nurses at different stages of their training at one UK University were asked to complete ratings on 11 containment methods. Containment methods fell into five groups, with mechanical restraint and net beds attracting the most severe disapproval. Neither the relative evaluation of methods, nor the intensity of those evaluations, changed systematically with duration of training. The findings support the interpretation that the relative evaluations of psychiatric containment methods are a property of wider national cultures, rather than an isolated tradition of professional psychiatric practice

SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts

The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2 above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle Physic

Experimental determination of the dispersion relation of magnetosonic waves

Magnetosonic waves are commonly observed in the vicinity of the terrestrial magnetic equator. It has been proposed that within this region they may interact with radiation belt electrons, accelerating some to high energies. These wave-particle interactions depend upon the characteristic properties of the wave mode. Hence, determination of the wave properties is a fundamental part of understanding these interaction processes. Using data collected during the Cluster Inner Magnetosphere Campaign, this paper identifies an occurrence of magnetosonic waves, discusses their generation and propagation properties from a theoretical perspective, and utilizes multispacecraft measurements to experimentally determine their dispersion relation. Their experimental dispersion is found to be in accordance with that based on cold plasma theory

Magnetic Dipole Absorption of Radiation in Small Conducting Particles

We give a theoretical treatment of magnetic dipole absorption of electromagnetic radiation in small conducting particles, at photon energies which are large compared to the single particle level spacing, and small compared to the plasma frequency. We discuss both diffusive and ballistic electron dynamics for particles of arbitrary shape. The conductivity becomes non-local when the frequency is smaller than the frequency \omega_c characterising the transit of electrons from one side of the particle to the other, but in the diffusive case \omega_c plays no role in determining the absorption coefficient. In the ballistic case, the absorption coefficient is proportional to \omega^2 for \omega << \omega_c, but is a decreasing function of \omega for \omega >> \omega_c.Comment: 25 pages of plain TeX, 2 postscipt figure