2,551 research outputs found
A New Kinematic Distance Estimator to the LMC
The distance to the Large Magellanic Cloud (LMC) can be directly determined
by measuring three of its properties, its radial-velocity field, its mean
proper motion, and the position angle \phi_ph of its photometric line of nodes.
Statistical errors of 2% are feasible based on proper motions obtained with any
of several proposed astrometry satellites, the first possibility being the
Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic
error is likely to be in the determination of \phi_ph. I suggest two
independent methods to measure \phi_ph, one based on counts of clump giants and
the other on photometry of clump giants. I briefly discuss a variety of methods
to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page
The planets around NN Serpentis : still there
We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 s that has set in since 2010 compared to the previous 8 yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 ± 0.5 and 15.3 ± 0.3 yr, and masses of 2.3 ± 0.5 and 7.3 ± 0.3 MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems
Is renalase a novel player in catecholaminergic signaling? The mystery of the catalytic activity of an intriguing new flavoenzyme
Renalase is a flavoprotein recently discovered in humans, preferentially expressed in the proximal tubules of the kidney and secreted in blood and urine. It is highly conserved in vertebrates, with homologs identified in eukaryotic and prokaryotic organisms. Several genetic, epidemiological, clinical and experimental studies show that renalase plays a role in the modulation of the functions of the cardiovascular system, being particularly active in decreasing the catecholaminergic tone, in lowering blood pressure and in exerting a protective action against myocardial ischemic damage. Deficient renalase synthesis might be the cause of the high occurrence of hypertension and adverse cardiac events in kidney disease patients. Very recently, recombinant human renalase has been structurally and functionally characterized in vitro. Results show that it belongs to the p-hydroxybenzoate hydroxylase structural family of flavoenzymes, contains non-covalently bound FAD with redox features suggestive of a dehydrogenase activity, and is not a catecholamine-degrading enzyme, either through oxidase or NAD(P)H-dependent monooxygenase reactions. The biochemical data now available will hopefully provide the basis for a systematic and rational quest toward the identification of the reaction catalyzed by renalase and of the molecular mechanism of its physiological action, which in turn are expected to favor the development of novel therapeutic tools for the treatment of kidney and cardiovascular diseases
Audit of antenatal care at a community health centre in Tshwane North subdistrict, Gauteng province
Objective: Few studies document the level of compliance with antenatal care protocols in primary health care in South Africa. The aim of this study was to conduct an audit of antenatal care at a community health centre in Tshwane North subdistrict in order to measure the level of compliance of maternity staff with antenatal care protocols. This study was part of a larger study on a quality improvement initiative in primary health care.Design and setting: A retrospective cross-sectional descriptive study was undertaken of women attending antenatal care at the study clinic. Data were collected through a review of the women’s antenatal cards using criteria from the Guidelines for maternity care in South Africa and the basic antenatal care (BANC) checklist. In addition, qualitative interviews of maternity staff were undertaken in order to investigate reasons for noncompliance with the maternity care guidelines.Results: The overall rate of compliance of nurses was 85.1%. This is less than optimal. The response (decision-making and interpretation) component of compliance was only 57.6%. This represents a significant missed opportunity in terms of quality of antenatal care. Important protocols, such as that pertaining to the prevention of mother-to-child transmission (PMTCT) of human immunodeficiency virus, were also not carried out correctly. The response to PMTCT protocols was 50% only, another significant opportunity missed. Administrative factors, patient-related factors and deficiencies in the knowledge and skills of nurses were identified and documented as reasons for noncompliance.Conclusion: The study has provided a detailed picture of the situation with regard to non-compliance with the maternity care guidelines in a primary health care facility. Therefore, these data are very important in terms of quality assurance of maternity services in primary health care
Understanding jet quenching and medium response with di-hadron correlation
A brief review of the dependence of the dihadron correlations from RHIC
is presented. We attempt to construct a consistent picture that can describe
the data as a whole, focusing on the following important aspects, 1) the
relation between jet fragmentation of survived jet and medium response to
quenched jets, 2) the possible origin of the medium response and its relation
to intermediate physics for single hadron production, 3) the connection
between the near-side ridge and away-side cone, 4) and their relations to low
energy results.Comment: 8 pages, 8 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 2008. Updated with the published versio
A Pseudo-Two-Dimensional (P2D) Model for FeS2 Conversion Cathode Batteries
Conversion cathode materials are gaining interest for secondary batteries due
to their high theoretical energy and power density. However, practical
application as a secondary battery material is currently limited by practical
issues such as poor cyclability. To better understand these materials, we have
developed a pseudo-two-dimensional model for conversion cathodes. We apply this
model to FeS2 - a material that undergoes intercalation followed by conversion
during discharge. The model is derived from the half-cell Doyle-Fuller-Newman
model with additional loss terms added to reflect the converted shell
resistance as the reaction progresses. We also account for polydisperse active
material particles by incorporating a variable active surface area and
effective particle radius. Using the model, we show that the leading loss
mechanisms for FeS2 are associated with solid-state diffusion and electrical
transport limitations through the converted shell material. The polydisperse
simulations are also compared to a monodisperse system, and we show that
polydispersity has very little effect on the intercalation behavior yet leads
to capacity loss during the conversion reaction. We provide the code as an
open-source Python Battery Mathematical Modelling (PyBaMM) model that can be
used to identify performance limitations for other conversion cathode
materials
Self-control in Sparsely Coded Networks
A complete self-control mechanism is proposed in the dynamics of neural
networks through the introduction of a time-dependent threshold, determined in
function of both the noise and the pattern activity in the network. Especially
for sparsely coded models this mechanism is shown to considerably improve the
storage capacity, the basins of attraction and the mutual information content
of the network.Comment: 4 pages, 6 Postscript figure
To maximize or not to maximize the free energy of glassy systems, !=?
The static free energy of glassy systems can be expressed in terms of the
Parisi order parameter function. When this function has a discontinuity, the
location of the step is determined by maximizing the free energy. In dynamics a
transition is found at larger temperature, while the location of the step
satisfies a marginality criterion. It is shown here that in a replica
calculation this criterion minimizes the free energy. This leads to first order
phase transitions at the dynamic transition point. Though the order parameter
function is the same as in the long-time limit of a dynamical analysis,
thermodynamics is different.Comment: 4 pages PostScript, one figur
Mach Cones in Quark Gluon Plasma
The experimental azimuthal dihadron distributions at RHIC show a double peak
structure in the away side ( rad.) for intermediate
particles. A variety of models have appeared trying to describe this
modification. We will review most of them, with special emphasis in the Conical
Flow scenario in which the observed shape is a consequence of the emission of
sound by a supersonic high momentum particle propagating in the Quark Gluon
Plasma.Comment: 8 pages, 3 figures, Invited plenary talk given at the 19th
International Conference on Ultrarelativistic Nucleus-Nucleus Collisions:
Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200
Time reparametrization group and the long time behaviour in quantum glassy systems
We study the long time dynamics of a quantum version of the
Sherrington-Kirkpatrick model. Time reparametrizations of the dynamical
equations have a parallel with renormalization group transformations, and
within this language the long time behaviour of this model is controlled by a
reparametrization group (RG) fixed point of the classical dynamics. The
irrelevance of the quantum terms in the dynamical equations in the aging regime
explains the classical nature of the violation of the fluctuation-dissipation
theorem.Comment: 4 page
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