4,602 research outputs found
The Distance to the Coma Cluster from Surface Brightness Fluctuations
We report on the first determination of the distance to the Coma Cluster
based on surface brightness fluctuation (SBF) measurements obtained from Hubble
Space Telescope WFPC2 observations of the bright E0 galaxy NGC 4881 in the Coma
Cluster and ground-based observations of the standard E1 galaxy NGC 3379 in the
Leo-I group. Relative distances based on the I-band fluctuation magnitude,
I(SBF), are strongly dependent on metallicity and age of the stellar
population. However, the radial changes in the stellar populations of the two
giant ellipticals, NGC 3379 and NGC 4881, are well described by published Mg_2
gradients, and the ground-based measurements of I(SBF) at several radial points
in NGC 3379 are used to calibrate I(SBF) in terms of the Mg_2 index. The
distance to NGC 3379, assumed to be identical to the average SBF distance of
the Leo-I group, is combined with the new SBF measurements of NGC 4881 to
obtain a Coma Cluster distance of 102+-14 Mpc. Combining this distance with the
cosmic recession velocity of Coma (7186+-428 km/s), we find the Hubble constant
to be H_0 = 71+-11 km/s/Mpc.Comment: 12 pages, LaTex, includes aaspp4.sty and 3 eps figures. To appear in
ApJ Letter
Total joint replacement in sub-Saharan Africa:a systematic review
Outcomes of arthroplasty in sub-Saharan Africa are not widely reported. To our knowledge, this systematic review is the first to explore this topic. Scopus, EMBASE, Medline and PubMed databases were searched, utilising MeSH headings and Boolean search strategies. All papers from South Africa were excluded. Twelve papers reporting 606 total hip replacements (THRs) and 763 total knee replacements (TKRs) were included. Avascular necrosis was the most common indication for THR, whereas osteoarthritis was the main indication for TKR. HIV prevalence of up to 33% was seen. Improvements were seen in patient-reported outcome measures in both THR and TKR. The dislocation rate in THR was 1.6%. The deep infection rate was 1.6% for TKRs and 0.5% for THRs. Positive results were reported, with comparable complications to high-income countries. However, there is likely to be significant reporting bias and the introduction of mandatory registries would enable more accurate monitoring across the region
Impact of alcohol on memory:a systematic review
This chapter reviews the literature in psychology on acute alcohol intoxication and memory. Special emphasis is placed on empirical studies that have systematically examined alcoholâs effects on memory performance in forensic contexts. Three aspects of memory performance are considered, including memory accuracy (i.e. the ability of the complainant to accurately distinguish between correct and incorrect information about the crime), memory reliability (i.e. the probability that information recalled by the complainant at a given level of certainty is correct), and completeness (i.e. the quantity of information reported by the complainant). The review also documents the major theoretical perspectives on memory and acute alcohol intoxication. A total of 19 studies are reviewed. The results show that different memory performance measures are relevant depending on whether we are policy makers formulating interview guidance or decision makers evaluating the strength of memory evidence in a given case. Overall, the research to date indicates that acute alcohol intoxication during rape affects the completeness, but not the accuracy and reliability of what is remembered
On the unification of dwarf and giant elliptical galaxies
The near orthogonal distributions of dwarf elliptical (dE) and giant
elliptical (E) galaxies in the mu_e-Mag and mu_e-log(R_e) diagrams have been
interpreted as evidence for two distinct galaxy formation processes. However,
continuous, linear relationships across the alleged dE/E boundary at M_B = -18
mag - such as those between central surface brightness (mu_0) and (i) galaxy
magnitude and (ii) light-profile shape (n) - suggest a similar, governing
formation mechanism. Here we explain how these latter two linear trends
necessitate a different behavior for dE and E galaxies, exactly as observed, in
diagrams involving mu_e (and also _e). A natural consequence is that the
distribution of dEs and Es in Fundamental Plane type analyses that use the
associated intensity I_e, or _e, are expected to appear different. Together
with other linear trends across the alleged dE/E boundary, such as those
between luminosity and color, metallicity, and velocity dispersion, it appears
that the dEs form a continuous extension to the E galaxies. The presence of
partially depleted cores in luminous (M_B < -20.5 mag) Es does however signify
the action of a different physical process at the centers (< ~300 pc) of these
galaxies.Comment: 5 pages from the proceedings of the 2004 conference "Penetrating bars
through masks of cosmic dust: the Hubble tuning fork strikes a new note".
Edited by D. L. Block, I. Puerari, K. C. Freeman, R. Groess, and E. K. Bloc
Near-Field Analysis of Terahertz Pulse Generation From Photo-Excited Charge Density Gradients
Excitation of photo-current transients at semiconductor surfaces by subpicosecond optical pulses gives rise to emission of electromagnetic pulses of terahertz (THz) frequency radiation. To correlate the THz emission with the photo-excited charge density distribution and the photo-current direction, we mapped near-field and far-field distributions of the generated THz waves from GaAs and Fe-doped InGaAs surfaces. The experimental results show that the charge dynamics in the plane of the surface can radiate substantially stronger THz pulses than the charge dynamics in the direction normal to the surface, which is generally regarded as the dominant origin of the emission
Empirical Models for Dark Matter Halos. III. The Kormendy relation and the log(rho_e)-log(R_e) relation
We have recently shown that the 3-parameter density-profile model from
Prugniel & Simien provides a better fit to simulated, galaxy- and
cluster-sized, dark matter halos than an NFW-like model with arbitrary inner
profile slope gamma (Paper I). By construction, the parameters of the
Prugniel-Simien model equate to those of the Sersic R^{1/n} function fitted to
the projected distribution. Using the Prugniel-Simien model, we are therefore
able to show that the location of simulated (10^{12} M_sun) galaxy-sized dark
matter halos in the _e-log(R_e) diagram coincides with that of brightest
cluster galaxies, i.e., the dark matter halos appear consistent with the
Kormendy relation defined by luminous elliptical galaxies. These objects are
also seen to define the new, and equally strong, relation log(rho_e) = 0.5 -
2.5log(R_e), in which rho_e is the internal density at r=R_e. Simulated
(10^{14.5} M_sun) cluster-sized dark matter halos and the gas component of real
galaxy clusters follow the relation log(rho_e) = 2.5[1 - log(R_e)]. Given the
shapes of the various density profiles, we are able to conclude that while
dwarf elliptical galaxies and galaxy clusters can have dark matter halos with
effective radii of comparable size to the effective radii of their baryonic
component, luminous elliptical galaxies can not. For increasingly large
elliptical galaxies, with increasingly large profile shapes `n', to be dark
matter dominated at large radii requires dark matter halos with increasingly
large effective radii compared to the effective radii of their stellar
component.Comment: AJ, in press. (Paper I can be found at astro-ph/0509417
Analytical expressions for the deprojected Sersic model
The Sersic model has become the standard to parametrize the surface
brightness distribution of early-type galaxies and bulges of spiral galaxies. A
major problem is that the deprojection of the Sersic surface brightness profile
to a luminosity density cannot be executed analytically for general values of
the Sersic index. Mazure & Capelato (2002) used the Mathematica computer
package to derive an expression of the Sersic luminosity density in terms of
the Meijer G function for integer values of the Sersic index. We generalize
this work using analytical means and use Mellin integral transforms to derive
an exact, analytical expression for the luminosity density in terms of the Fox
H function for all values of the Sersic index. We derive simplified expressions
for the luminosity density, cumulative luminosity and gravitational potential
in terms of the Meijer G function for all rational values of the Sersic index
and we investigate their asymptotic behaviour at small and large radii. As
implementations of the Meijer G function are nowadays available both in
symbolic computer algebra packages and as high-performance computing code, our
results open up the possibility to calculate the density of the Sersic models
to arbitrary precision.Comment: 9 pages, accepted for publication in Astronomy and Astrophysic
Weak homology of elliptical galaxies
We start by studying a small set of objects characterized by photometric
profiles that have been pointed out to deviate significantly from the standard
R^{1/4} law. For these objects we confirm that a generic R^{1/n} law, with n a
free parameter, can provide superior fits (the best-fit value of n can be lower
than 2.5 or higher than 10), better than those that can be obtained by a pure
R^{1/4} law, by an R^{1/4}+exponential model, and by other dynamically
justified self--consistent models. Therefore, strictly speaking, elliptical
galaxies should not be considered homologous dynamical systems. Still, a case
for "weak homology", useful for the interpretation of the Fundamental Plane of
elliptical galaxies, could be made if the best-fit parameter n, as often
reported, correlates with galaxy luminosity L, provided the underlying
dynamical structure also follows a systematic trend with luminosity. We
demonstrate that this statement may be true even in the presence of significant
scatter in the correlation n(L). Preliminary indications provided by a set of
"data points" associated with a sample of 14 galaxies suggest that neither the
strict homology nor the constant stellar mass--to--light solution are a
satisfactory explanation of the observed Fundamental Plane (abridged).Comment: 34 pages, 11 figures, accepted by Astronomy and Astrophysic
Legal aspects of memory:A report issued by the Psychology and Law Sections of the British Academy
Short-term rhGH increases PIIINP, a biomarker of endothelial dysfunction
Objectives: In arterial hypertension, amino-terminal propeptide of type III procollagen (PIIINP) is elevated in arterial aneurysm tissue and associated with a poor prognosis following acute myocardial infarction (MI). Recombinant human growth hormone (rhGH) administration attenuates endothelial dysfunction but increases PIIINP. This study was conducted to establish if short-term rhGH administration affects PIIINP, endothelial function and selected cardiovascular disease (CVD) risk factors, in healthy males. Design: Method: Male subjects (n=48) were randomly assigned into two groups: (1): control group (C) n=24, mean ñ SD, age 32 ñ 11 years; height 1.8 ñ 0.06 metres; (2): rhGH administration group (rhGH) n=24, mean ñ SD, age 32 ñ 9 years; height 1.8 ñ 0.07 metres. Blood pressure (BP), heart rate (HR), arterial pulse wave velocity (APWV), and biochemical indices were investigated. Results: PIIINP (0.28ñ0.1 vs. 0.42ñ0.2, U/ml); Insulin like growth factor-I (159ñ54 vs. 323ñ93, ng.mL-1); resting HR (72ñ14 vs. 78ñ11, b.p.m.) and rate pressure product (RPP) (90ñ18 vs. 97ñ14, bpm x mm.Hg x 10-2) all significantly increased (P<0.05). Total cholesterol (4.7ñ0.9 vs. 4.4ñ0.7, mmol.L-1); high sensitivity C-reactive protein (1.77ñ2.1 vs. 1.29ñ1.6, mg.L-1); serum homocysteine (13.2ñ4.0 vs. 11.7ñ3.1, ĂÂŒmol.L-1) and APWV (9.97ñ1.38 vs. 9.18ñ1.6, m.s-1) all significantly decreased (P<0.05). Conclusion: Paradoxically, there was an improvement in CVD inflammatory markers and APWV; but PIIINP and resting RPP increased. Elevated PIIINP may have a confounding adverse effect on the endothelium, but may also provide clinical prognostic information in monitoring arterial hypertension, left ventricular function in the sub-acute phase following MI and endothelial function in aortic aneurysms
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