660 research outputs found
A constraint on the pair-density ratio (Z+) in an electron-positron pair wind
We derive a constraint on the pair density ratio, z(sub +) = n(sub +)/n(sub p), in an electron-positron pair wind flowing away from the central region of an accretion disk around a compact object under the assumption of a coupling between electrons, positrons, and protons. The minimum rate at which positrons are injected into the annihilation volume is given by the observed annihilation flux per unit volume. This rate is then used to determine a minimum mass loss rate per unit area, M(dot)(sub *) for a given pair density ratio at the base of the streamline. The requirement that M(dot)(sub *) less than M(dot)(sub *)(sub Edd) (the mean Eddington mass loss rate per unit area) then places a lower limit on the pair density ratio, z(sub +,)(sub min). A positron annihilation line was observed in Nova Muscae 1991 by GRANAT/SIGMA. The narrow width and redshift of the line suggest that the pair production and annihilation regions are physically distinct. We hypothesize that an electron-positron pair wind transports the pairs from the production to the annihilation region and calculate z(sub +),(sub min). We then determine constraints on the physical parameters on the pair production region by comparing z(sub +),(sub min) with previous studies of two-temperature and one-temperature accretion disks with electron-positron pairs
Bronchopulmonary Dysplasia: A Five-Year Retrospective Cohort Study on Differences in Clinical Characteristics and Morbidities According to Severity Grading
Introduction: Bronchopulmonary dysplasia (BPD) is the most common complication associated with extreme prematurity. Although several criteria defining severity were developed over time, there are a few studies describing the differences in BPD phenotype and neonatal morbidities and complications between severity groups. We aimed to describe these differences in BPD patients of a neonatal intensive care unit (NICU). Methods: We conducted an observational retrospective cohort study through a medical record review over a five-year period. Participants were newborns admitted to an NICU who were diagnosed with BPD. We performed a descriptive statistical analysis of gestational complications and the use of antenatal corticosteroid therapy, birth-related data, and complications throughout the NICU stay, as well as the respiratory support used. We also compared different severity groups across these variables. The patients were divided into severe and non-severe BPD using the severity criteria of the 2001 NICHD/NHLBI/ORD consensus workshop. Results: A total of 101 newborns with BPD participated in the study and 73 had data on BPD severity. The median gestational age was 27 weeks, ranging from 23 to 32 weeks. Of these 73 newborns, 36 had mild BPD (49.3%), 10 had moderate BPD (13.7%), and 27 had severe BPD (37.0%). When comparing severe and non-severe BPD, we found that extreme prematurity, extremely low birth weight, and small size for gestational age were more frequent in the severe BPD group (p-value=0.012, p-value<0.001, and p-value=0.012, respectively). Infants with severe BPD had a longer duration of invasive ventilation than those with mild or moderate BPD (p-value<0.001). Late sepsis, necrotizing enterocolitis, severe brain injury, and retinopathy of prematurity were more frequent in severe BPD (p-value=0.017, p-value=0.045, p-value=0.033, p-value=0.003, respectively). Discussion: Previously published evidence describing causal links between BPD development and comorbidities exists but data on their impact on BPD severity are scarce. In our study, severe BPD seemed to be associated with a higher frequency of comorbidities and complications. Further studies are needed to ascertain the impact of each morbidity on the severity of BPD and if measures to prevent them could lead to potentially milder BPD disease.info:eu-repo/semantics/publishedVersio
Hematoma epidural cervical tras latigazo cervical
Se describe un hematoma epidural a nivel cervical en un varón de 43 años, tras un traumatismo menor tipo latigazo cervical. Su sintomatología inicial obligó a descartar patología cardiaca llegándose al diagnóstico tras estudio mediante resonancia nuclear magnética. El cuadro clínico parcial y no progresivo desaconsejó la cirugía, observándose su reabsorción con nuevo control de resonancia. Se realza una revisión de la bibliografía, señalándose las principales características de esta entidad poco frecuente.We repor a case of cervical epidural hematoma in
a 43 year-old man, after soft-tissue cervical spine strain
(known as a “whiplast”). At the beginnig, because previous
presumptive cardiac pain in this patient, we need to discart
cardiac cause. We made the diagnostic of cervical epidural
hematoma with the use of magnetic resonance imaging. The
incomplete, not severe and nonprogressing defficits led us to
conservative treatment; and the hematoma resolved spontaneously, as documented with a new magnetic resonance imaging. The medical literature relating to this uncommon entity
has been reviewe
The Effect of Drying Methods on Water-Soluble Carbohydrates and Crude Protein Concentrations and Their Ratio in Two Perennial Ryegrass Cultivars
The objective of this study was to assess the joint effect of perennial ryegrass cultivars and drying methods on concentrations of water-soluble carbohydrates (WSC) and crude protein (CP) and WSC/CP ratio. AberMagic AR1 and Expo AR1 forage were collected in December 2016, March, June, September and November 2017 and either oven-dried at 60 °C for 48h (OD_60), at 80 °C for 16h (OD_80), frozen at -80 °C for 48h then freeze-dried (-80_FD), or flash-frozen with liquid N then freeze-dried (LN_FD). Data were analyzed by ANOVA in a factorial design with cultivar and drying method as factors. AberMagic AR1 had between 9.0 to 31.5% higher WSC concentration than Expo AR1 in the four samplings. Freeze-drying preserved more WSC than oven-drying treatments (+22.7%), particularly in June. The CP concentration of Expo AR1 was higher only in December (+6.8%), and was 22.9 and 10.9% higher in OD_60 samples compared to LN_FD samples in December and November, respectively. The WSC/CP ratio varied in June, being greater in AberMagic AR1 (+36.1%). Drying method affected WSC/CP ratio in December, June and November where freeze-drying produced greater ratios. Drying techniques generated differences in WSC, CP and WSC/CP ratio, which may affect the accuracy of the estimated impacts of forages on productivity and N use efficiency
Estudio sobre la automedicación en una localidad de bogotá
Objetivos Establecer la prevalencia y condicionantes asociados al uso de medicamentos por cuenta propia por parte de los habitantes de Suba en Bogotá.Métodos Aplicación de una encuesta pilotada a una muestra aleatoria. Se midieron variables demográficas y se indagó por problemas de salud relacionados con la automedicación, motivos para no consultar al médico y medicamentos consumidos durante las dos últimas semanasResultados La automedicación fue de 27,3 % (IC 95 %, 19,2 % - 35,3 %) y la autoprescripción de 7,7 % (IC 95%, 2,8 %-12,5 %). La afiliación al Sistema de beneficiarios de la Seguridad Social en Salud (OR=2,61 IC 95 % 1,4-4,8) está asociado con ésta conducta. No se encontró asociación con otras variables. Los medicamentos más consumidos por automedicación son analgésicos (59,3 %), antigripales (13,5 %) y vitaminas (6,8 %). Los principales problemas por los cuales las personas se automedican son dolor, fiebre y gripa. Las principales razones que se mencionan para no asistir al médico son falta de tiempo (40 %) y recursos económicos (43 %), además de otros argumentos como la percepción de que el problema es leve y la congestión en los servicios de urgencia.Conclusiones Las cifras de automedicación aunque todavía preocupantes desde el punto de vista de salud pública, son más bajas que las encontradas en estudios similares; los medicamentos consumidos por automedicación pertenecen a la categoría de venta libre y el consumo de antibióticos por automedicación bajó, posiblemente debido a la intensa difusión que se dio a la restricción de venta de antibióticos sin fórmula médica, unos meses antes de la realización de la encuesta
EROS Variable Stars : Discovery of Beat Cepheids in the Small Magellanic Cloud and the effect of metallicity on pulsation
We report the discovery of eleven beat Cepheids in the Small Magellanic
Cloud, using data obtained by the EROS microlensing survey. Four stars are
beating in the fundamental and first overtone mode (F/1OT), seven are beating
in the first and second overtone (1OT/2OT). The SMC F/1OT ratio is
systematically higher than the LMC F/1OT, while the 1OT/2OT period ratio in the
SMC Cepheids is the same as the LMC one.Comment: 4 pages, Latex file with 4 .ps figures. accepted for publication in A
A Letter
Electrically tunable GHz oscillations in doped GaAs-AlAs superlattices
Tunable oscillatory modes of electric-field domains in doped semiconductor
superlattices are reported. The experimental investigations demonstrate the
realization of tunable, GHz frequencies in GaAs-AlAs superlattices covering the
temperature region from 5 to 300 K. The orgin of the tunable oscillatory modes
is determined using an analytical and a numerical modeling of the dynamics of
domain formation. Three different oscillatory modes are found. Their presence
depends on the actual shape of the drift velocity curve, the doping density,
the boundary condition, and the length of the superlattice. For most bias
regions, the self-sustained oscillations are due to the formation, motion, and
recycling of the domain boundary inside the superlattice. For some biases, the
strengths of the low and high field domain change periodically in time with the
domain boundary being pinned within a few quantum wells. The dependency of the
frequency on the coupling leads to the prediction of a new type of tunable GHz
oscillator based on semiconductor superlattices.Comment: Tex file (20 pages) and 16 postscript figure
The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant () determination
Recent HST determinations of the expansion's rate of the Universe (the Hubble
constant, H_0) assumed that the Cepheid Period-Luminosity relation at V and I
are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996,
Tanvir et al., 1995). The three groups obtain different vales for H_0. We note
that most of this discrepancy stems from the asumption (by both groups) that
the Period-Luminosity relation is independent of metallicity. We come to this
conclusion as a result of our study of the Period-Luminosity relation of 481
Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud
and the Small Magellanic Cloud obtained as a by-product of the EROS
microlensing survey. We find that the derived interstellar absorption
corrections are particularly sensitive to the metallicity and when our result
is applied to recent estimates based on HST Cepheids observations it makes the
low-H_0 values higher and the high-H_0 value lower, bringing those discrepant
estimates into agrement around .Comment: 4 pages, Latex, with 2 .ps accepted for publication astronomy and
astrophysics Letter
Observational Limits on Machos in the Galactic Halo
We present final results from the first phase of the EROS search for
gravitational microlensing of stars in the Magellanic Clouds by unseen
deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to
events with time scales between 15 minutes and 200 days corresponding to
deflector masses in the range 1.e-7 to a few solar masses. Two events were
observed that are compatible with microlensing by objects of mass of about 0.1
Mo. By comparing the results with the expected number of events for various
models of the Galaxy, we conclude that machos in the mass range [1.e-7, 0.02]
Mo make up less than 20% (95% C.L.) of the Halo dark matter.Comment: 4 pages, 3 Postscript figures, to be published in Astronomy &
Astrophysic
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