599 research outputs found
Testing massive star evolution, star-formation history and feedback at low metallicity : Spectroscopic analysis of OB stars in the SMC Wing
Stars which start their lives with spectral types O and early-B are the
progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars,
and black holes. These massive stars are the primary sources of stellar
feedback in star-forming galaxies. At low metallicities, the properties of
massive stars and their evolution are not yet fully explored. Here we report a
spectroscopic study of 320 OB stars in the Small Magellanic Cloud. The data,
which we obtained with the ESO Very Large Telescope, were analyzed using
state-of-the-art stellar atmosphere models. We find that stellar winds of our
sample stars are much weaker than theoretically expected. The stellar rotation
rates show a bi-modal distribution. The well-populated upper
Hertzsprung-Russell diagram including our sample OB stars from SMC Wing as well
as additional evolved stars all over SMC from the literature shows a strict
luminosity limit. The comparison with single-star evolutionary tracks suggests
a dichotomy in the fate of massive stars in the SMC. Only stars with
Minit<30M seem to evolve from the main sequence to the cool side of
the HRD to become a red supergiant and to explode as type II-P supernova. In
contrast, stars with Minit>30M appear to stay always hot and might
evolve quasi chemically homogeneously, finally collapsing to relatively massive
black holes. However, we find no indication that chemical mixing is correlated
with rapid rotation. We report extended star-formation episodes in a quiescent
low-density region of the Wing, which is progressing stochastically. We measure
the key parameters of stellar feedback and establish the links between the
rates of star formation and supernovae. Our study reveals that in metal-poor
environments the stellar feedback is dominated by core-collapse supernovae in
combination with winds and ionizing radiation supplied by a few of the most
massive stars.Comment: Accepted for publication in Astronomy & Astrophysic
Dense Antihydrogen: Its Production and Storage to Envision Antimatter Propulsion
We discuss the possibility that dense antihydrogen could provide a path
towards a mechanism for a deep space propulsion system. We concentrate at
first, as an example, on Bose-Einstein Condensate (BEC) antihydrogen. In a
Bose-Einstein Condensate, matter (or antimatter) is in a coherent state
analogous to photons in a laser beam, and individual atoms lose their
independent identity. This allows many atoms to be stored in a small volume. In
the context of recent advances in producing and controlling BECs, as well as in
making antihydrogen, this could potentially provide a revolutionary path
towards the efficient storage of large quantities of antimatter, perhaps
eventually as a cluster or solid.Comment: 12 pages, 3 figure
Generator coordinate method calculations of one-nucleon removal reactions on Ca
An approach to the Generator Coordinate Method (GCM) using Skyrme-type
effective forces and Woods-Saxon construction potential is applied to calculate
the single-particle proton and neutron overlap functions in Ca. The
relationship between the bound-state overlap functions and the one-body density
matrix has been used. These overlap functions are applied to calculate the
cross sections of one-nucleon removal reactions such as (), ()
and () on Ca on the same theoretical footing. A consistent
description of data for the different reactions is achieved. The shapes of the
experimental cross sections for transitions to the ground state and
the first excited state of the residual nuclei are well reproduced by
the overlap functions obtained within the GCM. An additional spectroscopic
factor accounting for correlations not included in the overlap function must be
applied to the calculated results to reproduce the size of the experimental
cross sections.Comment: 16 pages, 6 figures, to be published in Phys. Rev.
The Relationship Between HR Practices and Firm Performance: Examining Causal Order
Significant research attention has been devoted to examining the relationship between HR practices and firm performance, and the research support has assumed HR as the causal variable. Using data from 45 business units (with 62 data points), this study examines how measures of HR practices correlate with past, concurrent, and future operational performance measures. The results indicate that correlations with performance measures at all three times are both high and invariant, and that controlling for past or concurrent performance virtually eliminates the correlation of HR with future performance. Implications are discussed
A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source
We present a quantitative model of the magnetic energy stored and then
released through magnetic reconnection for a flare on 26 Feb 2004. This flare,
well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only
for a brief, early phase. Throughout the main period of energy release there is
a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare
loops. Our model describes the heating and compression of such a source by
localized, transient magnetic reconnection. It is a three-dimensional
generalization of the Petschek model whereby Alfven-speed retraction following
reconnection drives supersonic inflows parallel to the field lines, which form
shocks heating, compressing, and confining a loop-top plasma plug. The
confining inflows provide longer life than a freely-expanding or
conductively-cooling plasma of similar size and temperature. Superposition of
successive transient episodes of localized reconnection across a current sheet
produces an apparently persistent, localized source of high-temperature
emission. The temperature of the source decreases smoothly on a time scale
consistent with observations, far longer than the cooling time of a single
plug. Built from a disordered collection of small plugs, the source need not
have the coherent jet-like structure predicted by steady-state reconnection
models. This new model predicts temperatures and emission measure consistent
with the observations of 26 Feb 2004. Furthermore, the total energy released by
the flare is found to be roughly consistent with that predicted by the model.
Only a small fraction of the energy released appears in the super-hot source at
any one time, but roughly a quarter of the flare energy is thermalized by the
reconnection shocks over the course of the flare. All energy is presumed to
ultimately appear in the lower-temperature T<20 MK, post-flare loops
The HLA class II allele DRB1*1501 is over-represented in patients with idiopathic pulmonary fibrosis
Background: Idiopathic pulmonary fibrosis (IPF) is a progressive and medically refractory lung disease with a grim prognosis. Although the etiology of IPF remains perplexing, abnormal adaptive immune responses are evident in many afflicted patients. We hypothesized that perturbations of human leukocyte antigen (HLA) allele frequencies, which are often seen among patients with immunologic diseases, may also be present in IPF patients. Methods/Principal Findings: HLA alleles were determined in subpopulations of IPF and normal subjects using molecular typing methods. HLA-DRB1*15 was over-represented in a discovery cohort of 79 Caucasian IPF subjects who had lung transplantations at the University of Pittsburgh (36.7%) compared to normal reference populations. These findings were prospectively replicated in a validation cohort of 196 additional IPF subjects from four other U.S. medical centers that included both ambulatory patients and lung transplantation recipients. High-resolution typing was used to further define specific HLA-DRB1*15 alleles. DRB1*1501 prevalence in IPF subjects was similar among the 143 ambulatory patients and 132 transplant recipients (31.5% and 34.8%, respectively, p = 0.55). The aggregate prevalence of DRB1*1501 in IPF patients was significantly greater than among 285 healthy controls (33.1% vs. 20.0%, respectively, OR 2.0; 95%CI 1.3-2.9, p = 0.0004). IPF patients with DRB1*1501 (n = 91) tended to have decreased diffusing capacities for carbon monoxide (DLCO) compared to the 184 disease subjects who lacked this allele (37.8±1.7% vs. 42.8±1.4%, p = 0.036). Conclusions/Significance: DRB1*1501 is more prevalent among IPF patients than normal subjects, and may be associated with greater impairment of gas exchange. These data are novel evidence that immunogenetic processes can play a role in the susceptibility to and/or manifestations of IPF. Findings here of a disease association at the HLA-DR locus have broad pathogenic implications, illustrate a specific chromosomal area for incremental, targeted genomic study, and may identify a distinct clinical phenotype among patients with this enigmatic, morbid lung disease
Well-being as a Function of Person-Country Fit in Human Values
It is often assumed that incongruence between individuals’ values and those of their country is distressing, but the evidence has been mixed. Across 29 countries, the present research investigated whether well-being is higher if people’s values match with those of people living in the same country or region. Using representative samples, we find that person-country and person-region value congruence predict six well-being measures (e.g., emotional well-being, relationship support; N = 54,673). Crucially, however, value type moderates whether person-country fit is positively or negatively associated with well-being. People who value self-direction, stimulation, and hedonism more and live in countries and regions where people on average share these values report lower well-being. In contrast, people who value achievement, power, and security more and live in countries and regions where people on average share these values, report higher well-being. Additionally, we find that people who moderately value stimulation report the highest well-being
CD(8+ )T lymphocytes in lung tissue from patients with idiopathic pulmonary fibrosis
BACKGROUND: Several studies have implicated a role of inflammation in the pathogenesis of lung damage in idiopathic pulmonary fibrosis (IPF). Parenchymal lung damage leads to defects in mechanics and gas exchange and clinically manifests with exertional dyspnea. Investigations of inflammatory cells in IPF have shown that eosinophils, neutrophils and CD(8+ )TLs may be associated with worse prognosis. We wished to investigate by quantitative immunohistochemistry infiltrating macrophages, neutrophils and T lymphocytes (TLs) subpopulations (CD(3+), CD(4+ )and CD(8+)) in lung tissue of patients with IPF and their correlation with lung function indices and grade of dyspnoea. METHODS: Surgical biopsies of 12 patients with IPF were immunohistochemically stained with mouse monoclonal antibodies (anti-CD(68 )for macrophages, anti-elastase for neutrophils, and anti-CD(3), anti-CD(4), anti-CD(8 )for CD(3+)TLs, CD(4+)TLs, and CD(8+)TLs respectively). The number of positively stained cells was determined by observer-interactive computerized image analysis (SAMBA microscopic image processor). Cell numbers were expressed in percentage of immunopositive nuclear surface in relation to the total nuclear surface of infiltrative cells within the tissue (labeling Index). Correlations were performed between cell numbers and physiological indices [FEV(1), FVC, TLC, DLCO, PaO(2), PaCO(2 )and P(A-a)O(2))] as well as dyspnoea scores assessed by the Medical Research Council (MRC) scale. RESULTS: Elastase positive cells accounted for the 7.04% ± 1.1 of total cells, CD(68+ )cells for the 16.6% ± 2, CD(3+ )TLs for the 28.8% ± 7, CD(4+ )TLs for the 14.5 ± 4 and CD(8+ )TLs for the 13.8 ± 4. CD(8+)TLs correlated inversely with FVC % predicted (r(s )= -0.67, p = 0.01), TLC % predicted (r(s )= -0.68, p = 0.01), DLCO % predicted (r(s )= -0.61, p = 0.04), and PaO(2 )(r(s )= -0.60, p = 0.04). Positive correlations were found between CD(8+)TLs and P(A-a)O(2 )(r(s )= 0.65, p = 0.02) and CD(8+)TLs and MRC score (r(s )= 0.63, p = 0.02). Additionally, CD(68+ )cells presented negative correlations with both FVC % predicted (r(s )= -0.80, p = 0.002) and FEV(1 )% predicted (r(s )= -0.68, p = 0.01). CONCLUSION: In UIP/IPF tissue infiltrating mononuclear cells and especially CD(8+ )TLs are associated with the grade of dyspnoea and functional parameters of disease severity implicating that they might play a role in its pathogenesis
Zinc and silica are active components to efficiently treat in vitro simulated eroded dentin.
Objectives: Biomaterials for treating dentin hypersensitivity and dentin wear were
evaluated, to efficiently occlude the dentinal tubules and to increase dentin resistance to
abrasion. Materials and Methods: 24 dentin surfaces were treated with EDTA to expose
dentinal tubules, and were: 1) non-brushed, 2) brushed with distilled water, or with pastes
containing 3) Monetite, 4) Brushite, 5) Zn-Monetite, 6) Zn-Brushite, 7) Silica-Brushite
and 8) NovaMin®. Topography, nanomechanical and chemical analysis were assessed on
dentin surfaces (n=3) after artificial saliva immersion for 24 h, and after citric acid
challenge. 21 further dentin specimens were created to evaluate dentin permeability after
brushing, saliva storage and acid application (n=3). ANOVA, Student-Newman-Keuls
(p<0.05) and Student t-test (p<0.001) were used. Results: Particles containing major
proportion of silica attained intratubular occlusion by carbonate crystals (Raman
carbonate peak heights: 15.17 and 19.24 au; complex modulus: 110 and 140 GPa, at
intratubular dentin). When brushing with pastes containing higher proportion of silica or
zinc, phosphate calcium compounds were encountered into tubules and over dentin
surfaces (Raman intratubular phosphate peak heights: 49 to 70 au, and at the intertubular
dentin: 78 to 92). The formed carbonated apatite and calcium phosphate layer were
resistant to citric acid application. Zinc compounds drastically increased tubule occlusion,
decreased dentin permeability (up to 30%) and augmented mechanical properties at the
intertubular dentin (90-130 GPa), it was maintained after acid challenging. Conclusions:
Zinc-containing pastes occluded dentinal tubules and improved dentin mechanical
properties. Clinical Relevance: Using zinc as an active component to treat eroded dentin
is encouraged.Projects RTC-2014-1731-1 and MAT2014-52036-P
supported by the Ministry of Economy and Competitiveness and European Regional
Development Fund
Examining assumptions regarding valid electronic monitoring of medication therapy: development of a validation framework and its application on a European sample of kidney transplant patients
BACKGROUND: Electronic monitoring (EM) is used increasingly to measure medication non-adherence. Unbiased EM assessment requires fulfillment of assumptions. The purpose of this study was to determine assumptions needed for internal and external validity of EM measurement. To test internal validity, we examined if (1) EM equipment functioned correctly, (2) if all EM bottle openings corresponded to actual drug intake, and (3) if EM did not influence a patient's normal adherence behavior. To assess external validity, we examined if there were indications that using EM affected the sample representativeness. METHODS: We used data from the Supporting Medication Adherence in Renal Transplantation (SMART) study, which included 250 adult renal transplant patients whose adherence to immunosuppressive drugs was measured during 3 months with the Medication Event Monitoring System (MEMS). Internal validity was determined by assessing the prevalence of nonfunctioning EM systems, the prevalence of patient-reported discrepancies between cap openings and actual intakes (using contemporaneous notes and interview at the end of the study), and by exploring whether adherence was initially uncharacteristically high and decreased over time (an indication of a possible EM intervention effect). Sample representativeness was examined by screening for differences between participants and non-participants or drop outs on non-adherence. RESULTS: Our analysis revealed that some assumptions were not fulfilled: 1) one cap malfunctioned (0.4%), 2) self-reported mismatches between bottle openings and actual drug intake occurred in 62% of the patients (n = 155), and 3) adherence decreased over the first 5 weeks of the monitoring, indicating that EM had a waning intervention effect. CONCLUSION: The validity assumptions presented in this article should be checked in future studies using EM as a measure of medication non-adherence
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