331 research outputs found
Multiperiodicity in the large-amplitude rapidly-rotating Ceph ei star HD 203664
We perform a seismic study of the young massive Cephei star HD 203664
with the goal to constrain its interior structure. Our study is based on a time
series of 328 new Geneva 7-colour photometric data of the star spread over
496.8 days. The data confirm the frequency of the dominant mode of the star
which we refine to c d. The mode has a large amplitude of
37 mmag in V and is unambiguously identified as a dipole mode () from
its amplitude ratios and non-adiabatic computations. Besides , we discover
two additional new frequencies in the star with amplitudes above :
c d and c d or one of their daily
aliases. The amplitudes of these two modes are only between 3 and 4 mmag which
explains why they were not detected before. Their amplitude ratios are too
uncertain for mode identification. We show that the observed oscillation
spectrum of HD 203664 is compatible with standard stellar models but that we
have insufficient information for asteroseismic inferences. Among the
large-amplitude Cephei stars, HD 203664 stands out as the only one
rotating at a significant fraction of its critical rotation velocity ().Comment: 7 pages, 5 figures, accepted for publication in A&A (Astronomy &
Astrophysics
A theoretical approach for the interpretation of pulsating PMS intermediate-mass stars
The investigation of the pulsation properties of pre-main-sequence
intermediate-mass stars is a promising tool to evaluate the intrinsic
properties of these stars and to constrain current evolutionary models. Many
new candidates of this class have been discovered during the last decade and
very accurate data are expected from space observations obtained for example
with the CoRoT satellite. In this context we aim at developing a theoretical
approach for the interpretation of observed frequencies, both from the already
available ground-based observations and from the future more accurate and
extensive CoRoT results. To this purpose we have started a project devoted to
the computations of fine and extensive grids of asteroseismic models of
intermediate mass pre-main-sequence stars. The obtained frequencies are used to
derive an analytical relation between the large frequency separation and the
stellar luminosity and effective temperature and to develop a tool to compare
theory and observations in the echelle diagram. The predictive capabilities of
the proposed method are verified through the application to two test stars. As
a second step, we apply the procedure to two true observations from multisite
campaigns and we are able to constrain their stellar parameters, in particular
the mass, in spite of the small number of frequencies. We expect that with a
significantly higher number of frequencies both the stellar mass and age could
be constrained and, at the same time, the physics of the models could be
tested.Comment: Accepted for publication on A&
Topology of spin Hamiltonian and crystal field tensors for Mn2+ in ZnSeO4·6H2O crystal
The expansion of the {B2} and {B4} tensors of the spin Hamiltonian (SH) for Mn2+ (6S-state) is performed in terms of the irreducible tensor products {VL1 ⊗VL2}2 and {VL1 ⊗VL2}4 of the crystal field (CF) tensors {VL1} and {VL2}. The EPR spectra of Mn2+ in the ZnSeO4·6H2O crystal are studied and the SH tensors {B2} and {B4} are calculated. The tensors {V4⊗V4}2 and {V4⊗V4}4 are computed using the point-charge model (PCM) of the [Zn(H2O)6] complex with the C2 symmetry and are compared with the SH tensors {B2} and {B4}, respectively. The correct signs of the elements and the pseudo-symmety axes of the tensors are obtained both for the {B2} tensor and {V4⊗V4}2 and for the {B4} tensor and {V4⊗V4}4. It is concluded that the irreducible tensor products {V4⊗V4}2 and {V4⊗V4}4 provide the predominant contribution respectively to the SH tensors {B2} and {B4} of Mn2+. © 1994 Springer
Nonlinear mode coupling in rotating stars and the r-mode instability in neutron stars
We develop the formalism required to study the nonlinear interaction of modes
in rotating Newtonian stars in the weakly nonlinear regime. The formalism
simplifies and extends previous treatments. At linear order, we elucidate and
extend slightly a formalism due to Schutz, show how to decompose a general
motion of a rotating star into a sum over modes, and obtain uncoupled equations
of motion for the mode amplitudes under the influence of an external force.
Nonlinear effects are added perturbatively via three-mode couplings. We
describe a new, efficient way to compute the coupling coefficients, to zeroth
order in the stellar rotation rate, using spin-weighted spherical harmonics.
We apply this formalism to derive some properties of the coupling
coefficients relevant to the nonlinear interactions of unstable r-modes in
neutron stars, postponing numerical integrations of the coupled equations of
motion to a later paper. From an astrophysical viewpoint, the most interesting
result of this paper is that many couplings of r-modes to other rotational
modes (modes with zero frequencies in the non-rotating limit) are small: either
they vanish altogether because of various selection rules, or they vanish to
lowest order in the angular velocity. In zero-buoyancy stars, the coupling of
three r-modes is forbidden entirely and the coupling of two r-modes to one
hybrid rotational mode vanishes to zeroth order in rotation frequency. In
incompressible stars, the coupling of any three rotational modes vanishes to
zeroth order in rotation frequency.Comment: 62 pages, no figures. Corrected error in computation of coupling
coefficients, added new selection rule and an appendix on energy and angular
momentum of mode
Solar-like oscillations in Delta Scuti stars
Model computations of Delta Scuti stars, located in the vicinity of the red
edge of the classical instability strip, suggest amplitudes of solar-like
oscillations larger than in cooler models located outside the instability
strip. Solar-like amplitudes in our Delta Scuti models are found to be large
enough to be detectable with ground-based instruments provided they can be
distinguished from the opacity-driven large-amplitude pulsations. There would
be advantages in observing simultaneously opacity-driven and stochastically
excited modes in the same star. We anticipate their possible detection in the
context of the planned asteroseismic space missions, such as the French mission
COROT (COnvection ROtation and planetary Transits). We propose known Delta
Scuti stars as potential candidates for the target selection of these upcoming
space missions.Comment: 8 pages, 5 figures, accepted for publication in A&
The images of psychiatry scale: development, factor structure, and reliability.
BACKGROUND: This analysis is based on a survey questionnaire designed to describe medical educators' views of psychiatry and psychiatrists. Our goals in this paper were to assess the psychometric properties of the survey questions by (a) using exploratory factor analysis to identify the basic factor structure underlying 37 survey items; (b) testing the resulting factor structure using confirmatory factor analysis; and (c) assessing the internal reliability of each identified factor. To our knowledge, this is the first attempt to use these techniques to psychometrically assess a scale measuring the strength of stigma that medical educators attached to psychiatry. METHODS: Survey data were collected from a random sample of 1,059 teaching faculty in 23 academic teaching sites in 15 countries. We conducted exploratory and confirmatory factor analysis to identify the scale structure and Cronbach's alpha to assess internal consistency of the resulting scales. RESULTS: Results showed that a two-factor solution was the best fit for the data. Following exploratory factor analysis, we conducted confirmatory factor analysis on a split half of the sample. Results highlighted several items with low loadings. Excluding factors with low correlations and allowing for several correlated variances resulted in a good fitting model explaining 95% of the variance in the data. CONCLUSIONS: We identified two unidimensional scales. The Images Scale contained 11 items measuring stereotypic content concerning psychiatry and psychiatrists. The Efficacy of Psychiatry Scale contained 5 items addressing perceptions of the challenges and effectiveness of psychiatry as a discipline
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Monocytes of patients with familial hypercholesterolemia show alterations in cholesterol metabolism
<p>Abstract</p> <p>Background</p> <p>Elevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found. To analyze, if circulating monocytes already show increased lipid content and differences in lipoprotein metabolism, we compared monocytes from patients with Familial Hypercholesterolemia (FH) with those from healthy individuals.</p> <p>Methods</p> <p>Cholesterol and oxidized cholesterol metabolite serum levels of FH and of healthy, gender/age matched control subjects were measured by combined gas chromatography – mass spectroscopy. Monocytes from patients with FH and from healthy subjects were isolated by antibody-assisted density centrifugation. Gene expression profiles of isolated monocytes were measured using Affymetrix HG-U 133 Plus 2.0 microarrays. We compared monocyte gene expression profiles from FH patients with healthy controls using a Welch T-test with correction for multiple testing (p < 0.05; Benjamini Hochberg correction, False Discovery Rate = 0.05). The differential expression of FH associated genes was validated at the mRNA level by qRT-PCR and/or at the protein level by Western Blot or flow cytometry. Functional validation of monocyte scavenger receptor activities were done by binding assays and dose/time dependent uptake analysis using native and oxidized LDL.</p> <p>Results</p> <p>Using microarray analysis we found in FH patients a significant up-regulation of 1,617 genes and a down-regulation of 701 genes compared to monocytes from healthy individuals. These include genes of proteins that are involved in the uptake, biosynthesis, disposition, and cellular efflux of cholesterol. In addition, plasma from FH patients contains elevated amounts of sterols and oxysterols. An increased uptake of oxidized as well as of native LDL by FH monocytes combined with a down-regulation of NPC1 and ABCA1 explains the lipid accumulation observed in these cells.</p> <p>Conclusion</p> <p>Our data demonstrate that circulating FH monocytes show differences in cell physiology that may contribute to the early onset of atherosclerosis in this disease.</p
Routine Gastric Decompression after Pancreatoduodenectomy: Treating the Surgeon?
Background
The decision to routinely leave a nasogastric tube after pancreatoduodenectomy remains controversial. We sought to determine the impact of immediate nasogastric tube removal versus early nasogastric tube removal (<24 h) on postoperative outcomes.
Methods
A retrospective review of our institution’s prospective ACS-NSQIP database identified patients that underwent pancreatoduodenectomy from 2015 to 2018. Outcomes were compared among patients with immediate nasogastric tube removal versus early nasogastric tube removal.
Results
A total of 365 patients were included in primary analysis (no nasogastric tube, n = 99; nasogastric tube removed 0.05). Incidence of delayed gastric emptying (11.1 versus 13.2%) was similar between groups. Patients with no nasogastric tube less frequently required nasogastric tube reinsertion (n = 4, 4%) compared to patients with NGT <24 h (n = 39, 15%) (OR = 3.83, 95% CI [1.39-10.58]; P = 0.009).
Conclusion
Routine gastric decompression can be safely avoided after uneventful pancreaticoduodenectomy
- …