1,901 research outputs found
The extended star formation history of omega Centauri
For the first time, the abundances of a large sample of subgiant and turn-off
region stars in omega Centauri have been measured, the data base being medium
resolution spectroscopy from FORS2 at the VLT. Absolute iron abundances were
derived for about 400 member stars from newly defined line indices with an
accuracy of +/-0.15 dex. The abundances range between -2.2<[Fe/H]<-0.7 dex,
resembling the large metallicity spread found for red giant branch stars. The
combination of the spectroscopic results with the location of the stars in the
colour magnitude diagram has been used to estimate ages for the individual
stars. Whereas most of the metal-poor stars are consistent with a single old
stellar population, stars with abundances higher than [Fe/H]=-1.3 dex are
younger. The total age spread in omega Cent is about 3 Gyr. The monotonically
increasing age-metallicity relation seems to level off above [Fe/H]=-1.0 dex.
Whether the star formation in omega Cen occured continuously or rather
episodically has to be shown by combining more accurate abundances with highest
quality photometry.Comment: 4 pages, 3 figures, accepted for publication in Astronomy &
Astrophysics (Letters
Critical State Flux Penetration and Linear Microwave Vortex Response in YBa_2Cu_3O_{7-x} Films
The vortex contribution to the dc field (H) dependent microwave surface
impedance Z_s = R_s+iX_s of YBa_2Cu_3O_{7-x} thin films was measured using
suspended patterned resonators. Z_s(H) is shown to be a direct measure of the
flux density B(H) enabling a very precise test of models of flux penetration.
Three regimes of field-dependent behavior were observed: (1) Initial flux
penetration occurs on very low field scales H_i(4.2K) 100Oe, (2) At moderate
fields the flux penetration into the virgin state is in excellent agreement
with calculations based upon the field-induced Bean critical state for thin
film geometry, parametrized by a field scale H_s(4.2K) J_c*d 0.5T, (3) for very
high fields H >>H_s, the flux density is uniform and the measurements enable
direct determination of vortex parameters such as pinning force constants
\alpha_p and vortex viscosity \eta. However hysteresis loops are in
disagreement with the thin film Bean model, and instead are governed by the low
field scale H_i, rather than by H_s. Geometric barriers are insufficient to
account for the observed results.Comment: 20 pages, LaTeX type, Uses REVTeX style files, Submitted to Physical
Review B, 600 dpi PostScript file with high resolution figures available at
http://sagar.physics.neu.edu/preprints.htm
Growth hormone producing prolactinoma in juvenile cystinosis: a simple coincidence?
Juvenile cystinosis was diagnosed in a patient who presented with severe headache attacks and photophobia. Treatment with oral cysteamine and topical cysteamine eye drops was started. One-and-a-half years later, he developed unilateral gynecomastia and elevated prolactin and growth hormone levels. A pituitary macroprolactinoma was discovered and successfully treated with the dopamine agonist cabergoline. Increased serum growth hormone levels were attributed to enhanced growth hormone production by the prolactinoma and somatostatin inhibition by cysteamine. Although the occurrence of prolactinoma in this patient could be a simple coincidence, it might also be a rare yet unrecognised complication of cystinosis
C-axis Penetration Depth and Inter-layer Conductivity in the Thallium Based Cuprate Superconductors
The c-axis Josephson plasmon in optimally doped single-layer and bi-layer
high Tc cuprates Tl2201 and Tl2212 have been investigated using infrared
spectroscopy. We observed the plasma frequencies for these two compounds at
27.8 and 25.6 cm-1 respectively, which we interpret as a Josephson resonance
across the TlO blocking layers. No maximum in the temperature dependence of the
c-axis conductivity was observed below Tc, indicating that even in the
superconducting state a coherent quasi-particle contribution to the c-axis
conductivity is absent or very weak, in contrast to the behaviour of the
ab-plane conductivity.Comment: 4 pages, 3 figure
New features in the microwave response of YBCO crystals: Evidence for a multi-component order parameter
New features are reported in precision measurements of the complex microwave
conductivity of high quality crystals grown in
crucibles. A third peak in the normal conductivity,
, at around , and enhanced pair conductivity
below are observed. The data are inconsistent with a
single order parameter, and instead are indicative of multi-component
superconductivity. Overall, these results point to the presence of multiple
pairing interactions in and also provide a natural
explanation to account for the low temperature conductivity peak observed
in all crystals.Comment: 4 pages 4 figures, Revtex, multicols [to appear in Phys. Rev. B
(Rapid Comm)]. Our preprints also available at
http://sagar.physics.neu.edu/preprints.htm
The Psychobiology of Authentic and Simulated Dissociative Personality States:The Full Monty
The etiology of dissociative identity disorder (DID) remains a topic of debate. Proponents of the fantasy model and the trauma model of DID have both called for more empirical research. To this end, the current study presents new and extended data analyses of a previously published (H2O)-O-15 positron emission tomography imaging study. This study included 29 subjects: 11 patients with DID and 10 high- and 8 low-fantasy-prone DID-simulating mentally healthy control subjects. All subjects underwent an autobiographical memory script-driven (neutral and trauma related) imagery paradigm in 2 (simulated) dissociative personality states (neutral and trauma related). Psychobiological and psychophysiological data were obtained. Results of the new post-hoc tests on the psychophysiological responses support the trauma model. New results of the brain imaging data did not support the fantasy model. This study extends previously published results by offering important new supporting data for the trauma model of DID.</p
Automated Determination of Stellar Parameters from Simulated Dispersed Images for DIVA
We have assessed how well stellar parameters (T_eff, logg and [Fe/H]) can be
retrieved from low-resolution dispersed images to be obtained by the DIVA
satellite. Although DIVA is primarily an all-sky astrometric mission, it will
also obtain spectrophotometric information for about 13 million stars
(operational limiting magnitude V ~ 13.5 mag). Constructional studies foresee a
grating system yielding a dispersion of ~200nm/mm on the focal plane (first
spectral order). For astrometric reasons there will be no cross dispersion
which results in the overlapping of the first to third diffraction orders. The
one-dimensional, position related intensity function is called a DISPI
(DISPersed Intensity). We simulated DISPIS from synthetic spectra (...) for a
limited range of metallicites i.e. our results are for [Fe/H] in the range -0.3
to 1 dex. We show that there is no need to deconvolve these low resolution
signals in order to obtain basic stellar parameters. Using neural network
methods and by including simulated data of DIVA's UV telescope, we can
determine T_eff to an average accuracy of about 2% for DISPIS from stars with
2000 K < T_eff < 20000 K and visual magnitudes of V=13 mag (end of mission
data). logg can be determined for all temperatures with an accuracy better than
0.25 dex for magnitudes brighter than V=12 mag. For low temperature stars with
2000 K < T_eff < 5000 K and for metallicities in the range -0.3 to +1 dex a
determination of [Fe/H] is possible (to better than 0.2 dex) for these
magnitudes. Additionally we examined the effects of extinction E(B-V) on DISPIS
and found that it can be determined to better than 0.07 mag for magnitudes
brighter than V=14 mag if the UV information is included.Comment: 12 pages, 8 figures, Accepted for publication in A&
Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)
We have used the LTLSM technique for a spatially resolved investigation of
the microwave transport properties, nonlinearities and material inhomogeneities
in an operating coplanar waveguide YBa_2Cu_3O_{7-\delta} (YBCO) microwave
resonator on an LaAlO_3 (LAO) substrate. The influence of twin-domain blocks,
in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform rf
current distribution were measured with a micrometer-scale spatial resolution.
The impact of the peaked edge currents and rf field penetration into weak links
on the linear device performance were studied as well. The LTLSM capabilities
and its future potential for non-destructive characterization of the microwave
properties of superconducting circuits are discussed.Comment: 8 pages, 9 figures, 2-column format, presented at High Temperature
Superconductors in High Frequency Fields 2004, Journal of Superconductivity
(in press
Ethical issues and GenomEUtwin
The post-genomic era is witnessing a proliferation of large-scale and population based genetic and genomic research projects. Many countries have or are establishing research biobanks and, as with GenomEUtwin, there is great interest in building multinational projects that link genotypic and phenotypic information from different centers. Clearly, the conduct of these projects raises multiple ethical issues, and the knowledge generated will continually recast the ethical, legal and social implications (ELSI) of such research. Maximising the scientific profit from this work while minimizing the risks to the participants requires full integration of ethics components into the structure and functioning of these projects. GenomEUtwin is organized around five intellectual cores, including an Ethics Core which operates across the entire project. This paper describes the role of the Ethics Core and presents an overview of the guidelines on which the principles followed in GenomEUtwin are based. We outline the major ethical concerns of our project and highlight complexities arising from diverse national legislations. Finally, the role of empirically based ethics research is discussed for understanding the ethical, legal, social and economic implications of human genetics and genomics research
Beyond Prejudice as Simple Antipathy: Hostile and Benevolent Sexism Across Cultures
The authors argue that complementary hostile and benevolent componen:s of sexism exist ac ro.ss
cultures. Male dominance creates hostile sexism (HS). but men's dependence on women fosters
benevolent sexism (BS)-subjectively positive attitudes that put women on a pedestal but reinforce their
subordination. Research with 15,000 men and women in 19 nations showed that (a) HS and BS are
coherenl constructs th at correlate positively across nations, but (b) HS predicts the ascription of negative
and BS the ascription of positive traits to women, (c) relative to men, women are more likely to reject
HS than BS. especially when overall levels of sexism in a culture are high, and (d) national averages on
BS and HS predict gender inequal ity across nations. These results challenge prevailing notions of
prejudice as an antipathy in that BS (an affectionate, patronizing ideology) reflects inequality and is a
cross-culturally pervasive complement to HS
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