2,050 research outputs found
Deciphering the Pulsations of G 29-38 with Optical Time Series Spectroscopy
We present optical time series spectroscopy of the pulsating white dwarf star
G29-38 taken at the Very Large Telescope (VLT). By measuring the variations in
brightness, Doppler shift, and line shape of each spectrum, we explore the
physics of pulsation and measure the spherical degree () of each stellar
pulsation mode. We measure the physical motion of the g-modes correlated with
the brightness variations for three of the eight pulsation modes in this data
set. The varying line shape reveals the spherical degree of the pulsations, an
important quantity for properly modeling the interior of the star with
asteroseismology. Performing fits to the H, H, and H
lines, we quantify the changing shape of the line and compare them to models
and previous time series spectroscopy of G~29-38. These VLT data confirm
several identifications and add four new values, including an additional
=2 and a possible =4. In total from both sets of spectroscopy of
G29-38, eleven modes now have known spherical degrees.Comment: Accepted for publication by MNRA
High Resolution Spectroscopy of the Pulsating White Dwarf G29-38
We present the analysis of time-resolved, high resolution spectra of the cool
white dwarf pulsator, G29-38. From measuring the Doppler shifts of the H-alpha
core, we detect velocity changes as large as 16.5 km/s and conclude that they
are due to the horizontal motions associated with the g-mode pulsations on the
star. We detect seven pulsation modes from the velocity time-series and
identify the same modes in the flux variations. We discuss the properties of
these modes and use the advantage of having both velocity and flux measurements
of the pulsations to test the convective driving theory proposed for DAV stars.
Our data show limited agreement with the expected relationships between the
amplitude and phases of the velocity and flux modes. Unexpectedly, the velocity
curve shows evidence for harmonic distortion, in the form of a peak in the
Fourier transform whose frequency is the exact sum of the two largest
frequencies. Combination frequencies are a characteristic feature of the
Fourier transforms of light curves of G29-38, but before now have not been
detected in the velocities, nor does published theory predict that they should
exist. We compare our velocity combination frequency to combination frequencies
found in the analysis of light curves of G29-38, and discuss what might account
for the existence of velocity combinations with the properties we observe.
We also use our high-resolution spectra to determine if either rotation or
pulsation can explain the truncated shape observed for the DAV star's line
core. We are able to eliminate both mechanisms: the average spectrum does not
fit the rotationally broadened model and the time-series of spectra provides
proof that the pulsations do not significantly truncate the line.Comment: 24 pages, 9 figures, Accepted for publication in ApJ (June
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Multidrug-resistant Nontyphoidal Salmonella Hotspots as Targets for Vaccine Use in Management of Infections in Endemic Settings.
BACKGROUND: Salmonella infections cause a disproportionately high number of deaths in Africa, especially among poor urban populations. The increasing level of multidrug-resistant (MDR) infections is a major cause of concern in these settings where alternative effective treatment is unavailable. Other options for management of these infections must be sought. The knowledge of hotspots in endemic settings can help to prioritize management and control measures in Kenya and the region. METHODS: Using blood cultures, we investigated children presenting with fever of unknown origin for Salmonella infections. We performed antimicrobial susceptibility testing and whole genome sequencing to further characterize Salmonella isolates. Using Global Positioning System technologies, we mapped Salmonella isolates to households of patients in the study site and determined risk factors associated with high concentration of cases in particular sites. RESULTS: A total of 281 Salmonella species (149 from blood and 132 from fecal samples) from febrile children <5 years of age were studied. These consisted of 85 Salmonella Typhimurium, 58 Salmonella Enteritidis, 32 other nontyphoidal Salmonella (NTS) serotypes, and 126 Salmonella Typhi. The prevalence of MDR invasive NTS (iNTS) was 77.2%, with 15% resistant to ceftriaxone, a drug that is last-line treatment for iNTS and other severe gram-negative infections in Kenya. Invasive NTS and S. Typhi together mapped around common water vending points and close to sewer convergence points in the highly populated village. CONCLUSIONS: These hotspots could be targeted for management and control strategies, including a combined introduction of typhoid and iNTS vaccines, aimed at reducing transmission in these endemic settings
High relatedness of invasive multi-drug resistant non-typhoidal Salmonella genotypes among patients and asymptomatic carriers in endemic informal settlements in Kenya.
Invasive Non-typhoidal Salmonella (iNTS) disease is a major public health challenge, especially in Sub-Saharan Africa (SSA). In Kenya, mortality rates are high (20-25%) unless prompt treatment is instituted. The most common serotypes are Salmonella enterica serotype Typhimurium (S. Typhimurium) and Salmonella enterica serotype Enteritidis (S. Enteritidis). In a 5 year case-control study in children residing in the Mukuru informal settlement in Nairobi, Kenya, a total of 4201 blood cultures from suspected iNTS cases and 6326 fecal samples from age-matched controls were studied. From the laboratory cultures we obtained a total of 133 S. Typhimurium isolates of which 83(62.4%) came from cases (53 blood and 30 fecal) and 50(37.6%) from controls (fecal). A total of 120 S. Enteritidis consisted of 70(58.3%) from cases (43 blood and 27 fecal) and 50(41.7%) from controls (fecal). The S. Typhimurium population fell into two distinct ST19 lineages constituting 36.1%, as well as ST313 lineage I (27.8%) and ST313 lineage II (36.1%) isolates. The S. Enteritidis isolates fell into the global epidemic lineage (46.6%), the Central/Eastern African lineage (30.5%), a novel Kenyan-specific lineage (12.2%) and a phylogenetically outlier lineage (10.7%). Detailed phylogenetic analysis revealed a high level of relatedness between NTS from blood and stool originating from cases and controls, indicating a common source pool. Multidrug resistance was common throughout, with 8.5% of such isolates resistant to extended spectrum beta lactams. The high rate of asymptomatic carriage in the population is a concern for transmission to vulnerable individuals and this group could be targeted for vaccination if an iNTS vaccine becomes available
Clinical and functional effects of a deletion in a COOH-terminal lumenal loop of the skeletal muscle ryanodine receptor
We have identified a patient affected by a relatively severe form of central core disease (CCD), carrying a heterozygous deletion (amino acids 4863-4869) in the pore-forming region of the sarcoplasmic reticulum calcium release channel. The functional effect of this deletion was investigated (i) in lymphoblastoid cells from the affected patient and her mother, who was also found to harbour the mutation and (ii) in HEK293 cells expressing recombinant mutant channels. Lymphoblastoid cells carrying the RYR1 deletion exhibit an ‘unprompted' calcium release from intracellular stores, resulting in significantly smaller thapsigargin-sensitive intracellular Ca2+ stores, compared with lymphoblastoid cells from control individuals. Blocking the RYR1 with dantrolene restored the intracellular calcium stores to levels similar to those found in control cells. Single channel and [3H]ryanodine binding measurements of heterologously expressed mutant channels revealed a reduced ion conductance and loss of ryanodine binding and regulation by Ca2+. Heterologous expression of recombinant RYR1 peptides and analysis of their membrane topology demonstrate that the deleted amino acids are localized in the lumenal loop connecting membrane-spanning segments M8 and M10. We provide evidence that a deletion in the lumenal loop of RYR1alters channel function and causes CC
New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
We are searching for new He atmosphere white dwarf pulsators (DBVs) based on
the newly found white dwarf stars from the spectra obtained by the Sloan
Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better
known cousins, the H atmosphere white dwarf pulsators (DAVs or ZZ Ceti stars).
Since the evolution of white dwarf stars is characterized by cooling,
asteroseismological studies of DBVs give us opportunities to study white dwarf
structure at a different evolutionary stage than the DAVs. The hottest DBVs are
thought to have neutrino luminosities exceeding their photon luminosities
(Winget et al. 2004), a quantity measurable through asteroseismology.
Therefore, they can also be used to study neutrino physics in the stellar
interior. So far we have discovered nine new DBVs, doubling the number of
previously known DBVs. Here we report the new pulsators' lightcurves and power
spectra.Comment: 15 pages, 2 figures, 3 tables, ApJ accepte
The Peculiar Pulsations of PY Vul
The pulsating white dwarf star PY Vul (G~185-32) exhibits pulsation modes
with peculiar properties that set it apart from other variable stars in the ZZ
Ceti (DAV) class. These peculiarities include a low total pulsation amplitude,
a mode with bizarre amplitudes in the ultraviolet, and a mode harmonic that
exceeds the amplitude of its fundamental. Here, we present optical, time series
spectroscopy of PY Vul acquired with the Keck II LRIS spectrograph. Our
analysis has revealed that the mode with unusual UV amplitudes also has
distinguishing characteristics in the optical. Comparison of its line profile
variations to models suggests that this mode has a spherical degree of four. We
show that all the other peculiarities in this star are accounted for by a
dominant pulsation mode of l=4, and propose this hypothesis as a solution to
the mysteries of PY Vul.Comment: 30 pages, 14 figures, Accepted for publication in Ap
Molecular mechanisms and phenotypic variation in RYR1-related congenital myopathies
Dominant mutations in the skeletal muscle ryanodine receptor (RYR1) gene are well-recognized causes of both malignant hyperthermia susceptibility (MHS) and central core disease (CCD). More recently, recessive RYR1 mutations have been described in few congenital myopathy patients with variable pathology, including multi-minicores. Although a clinical overlap between patients with dominant and recessive RYR1 mutations exists, in most cases with recessive mutations the pattern of muscle weakness is remarkably different from that observed in dominant CCD. In order to characterize the spectrum of congenital myopathies associated with RYR1 mutations, we have investigated a cohort of 44 patients from 28 families with clinical and/or histopathological features suggestive of RYR1 involvement. We have identified 25 RYR1 mutations, 9 of them novel, including 12 dominant and 13 recessive mutations. With only one exception, dominant mutations were associated with a CCD phenotype, prominent cores and predominantly occurred in the RYR1 C-terminal exons 101 and 102. In contrast, the 13 recessive RYR1 mutations were distributed evenly along the entire RYR1 gene and were associated with a wide range of clinico-pathological phenotypes. Protein expression studies in nine cases suggested a correlation between specific mutations, RyR1 protein levels and resulting phenotype: in particular, whilst patients with dominant or recessive mutations associated with typical CCD phenotypes appeared to have normal RyR1 expression, individuals with more generalized weakness, multi-minicores and external ophthalmoplegia had a pronounced depletion of the RyR1 protein. The phenomenon of protein depletion was observed in some patients compound heterozygous for recessive mutations at the genomic level and silenced another allele in skeletal muscle, providing additional information on the mechanism of disease in these patients. Our data represent the most extensive study of RYR1-related myopathies and indicate complex genotype-phenotype correlations associated with mutations differentially affecting assembly and function of the RyR1 calcium release channe
The Peculiar Pulsations of PY Vulpeculae
The pulsating white dwarf star PY Vul (G185-32) exhibits pulsation modes with peculiar properties that set it apart from other variable stars in the ZZ Ceti (variable DA white dwarf [DAV]) class. These peculiarities include a low total pulsation amplitude, a mode with bizarre amplitudes in the ultraviolet, and a mode harmonic that exceeds the amplitude of its fundamental. Here we present optical time-series spectroscopy of PY Vul acquired with the Keck II Low Resolution Imaging Spectrograph. Our analysis has revealed that the mode with unusual UV amplitudes also has distinguishing characteristics in the optical. Comparison of its line profile variations to models suggests that this mode has a spherical degree of 4. We show that all the other peculiarities in this star are accounted for by a dominant pulsation mode of l = 4 and propose this hypothesis as a solution to the mysteries of PY Vul
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