769 research outputs found
Why do Particle Clouds Generate Electric Charges?
Grains in desert sandstorms spontaneously generate strong electrical charges;
likewise volcanic dust plumes produce spectacular lightning displays. Charged
particle clouds also cause devastating explosions in food, drug and coal
processing industries. Despite the wide-ranging importance of granular charging
in both nature and industry, even the simplest aspects of its causes remain
elusive, because it is difficult to understand how inert grains in contact with
little more than other inert grains can generate the large charges observed.
Here, we present a simple yet predictive explanation for the charging of
granular materials in collisional flows. We argue from very basic
considerations that charge transfer can be expected in collisions of identical
dielectric grains in the presence of an electric field, and we confirm the
model's predictions using discrete-element simulations and a tabletop granular
experiment
Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets
Transiting exoplanets in multi-planet systems have non-Keplerian orbits which
can cause the times and durations of transits to vary. The theory and
observations of transit timing variations (TTV) and transit duration variations
(TDV) are reviewed. Since the last review, the Kepler spacecraft has detected
several hundred perturbed planets. In a few cases, these data have been used to
discover additional planets, similar to the historical discovery of Neptune in
our own Solar System. However, the more impactful aspect of TTV and TDV studies
has been characterization of planetary systems in which multiple planets
transit. After addressing the equations of motion and parameter scalings, the
main dynamical mechanisms for TTV and TDV are described, with citations to the
observational literature for real examples. We describe parameter constraints,
particularly the origin of the mass/eccentricity degeneracy and how it is
overcome by the high-frequency component of the signal. On the observational
side, derivation of timing precision and introduction to the timing diagram are
given. Science results are reviewed, with an emphasis on mass measurements of
transiting sub-Neptunes and super-Earths, from which bulk compositions may be
inferred.Comment: Revised version. Invited review submitted to 'Handbook of
Exoplanets,' Exoplanet Discovery Methods section, Springer Reference Works,
Juan Antonio Belmonte and Hans Deeg, Eds. TeX and figures may be found at
https://github.com/ericagol/TTV_revie
Remarkable Rates of Lightning Strike Mortality in Malawi
Livingstone's second mission site on the shore of Lake Malawi suffers very high rates of consequential lightning strikes. Comprehensive interviewing of victims and their relatives in seven Traditional Authorities in Nkhata Bay District, Malawi revealed that the annual rate of consequential strikes was 419/million, more than six times higher than that in other developing countries; the rate of deaths from lightning was 84/million/year, 5.4 times greater than the highest ever recorded. These remarkable figures reveal that lightning constitutes a significant stochastic source of mortality with potential life history consequences, but it should not deflect attention away from the more prominent causes of mortality in this rural area
Prevalence of Hepatitis B Virus (HBV) Infection Among Hmong Immigrants in the San Joaquin Valley
Chronic hepatitis B infection (HBV) is the major cause of primary liver cancer worldwide and Asians are disproportionately affected. The prevalence of HBV among most Asian American groups has been well documented, except in Hmong immigrants in the United States. The aim of this study was to determine the prevalence of HBV among Hmong immigrants in the San Joaquin Valley of California. A convenient sample of 534 Hmong age ≥18 years was recruited at various locations throughout Fresno County. Blood samples from study participants were collected and tested for hepatitis B surface antigen (HBsAg) by enzyme-immunoassay. Two hundred and eighty-nine females and 245 males of Hmong descent (mean age, 43.93) were screened. Eighty-nine (41 males and 48 females) were positive for HBsAg, which accounts for a prevalence of 16.7% (95% C.I. 13.5–19.9). The majorities of HBsAg positive patients were ≥40 years (64.2%), married (66.7%), born in Laos (87.3%), and had lived in the United States ≥20 years (62.5%). Only 37.5% of the participants reported having a primary care physician. Our study revealed that approximately one out of every six Hmong immigrants screened was infected with HBV. Based on our findings, more than one-third of these infected patients have no primary care physician to provide further treatment, surveillance for liver cancer, or vaccination of their families. This supports the Institute of Medicine’s recent recommendations to the Center for Disease Control to engage in a national Hepatitis B surveillance system
Early glandular neoplasia of the lung
Although bronchogenic carcinomas progress through a very well defined sequence of metaplasia, dysplasia and carcinoma in situ, very little is known about the early progression of glandular neoplasms of the lung. In particular, the early precursor lesion from which fully malignant adenocarcinomas arise has effectively eluded recognition, at least until recently. Several lines of evidence now implicate atypical adenomatous hyperplasia (AAH) as an initial morphologic stage in multistep lung tumorigenesis. Despite its small size, AAH can be appreciated at the light microscopic level and characterized at the molecular genetic level. Indeed, the genetic characterization of AAH promises to further our understanding of lung cancer development and might facilitate the design of novel strategies for early detection of lung cancer
Abdominal muscle fatigue following exercise in chronic obstructive pulmonary disease
<p>Abstract</p> <p>Background</p> <p>In patients with chronic obstructive pulmonary disease, a restriction on maximum ventilatory capacity contributes to exercise limitation. It has been demonstrated that the diaphragm in COPD is relatively protected from fatigue during exercise. Because of expiratory flow limitation the abdominal muscles are activated early during exercise in COPD. This adds significantly to the work of breathing and may therefore contribute to exercise limitation. In healthy subjects, prior expiratory muscle fatigue has been shown itself to contribute to the development of quadriceps fatigue. It is not known whether fatigue of the abdominal muscles occurs during exercise in COPD.</p> <p>Methods</p> <p>Twitch gastric pressure (TwT10Pga), elicited by magnetic stimulation over the 10<sup>th </sup>thoracic vertebra and twitch transdiaphragmatic pressure (TwPdi), elicited by bilateral anterolateral magnetic phrenic nerve stimulation were measured before and after symptom-limited, incremental cycle ergometry in patients with COPD.</p> <p>Results</p> <p>Twenty-three COPD patients, with a mean (SD) FEV<sub>1 </sub>40.8(23.1)% predicted, achieved a mean peak workload of 53.5(15.9) W. Following exercise, TwT<sub>10</sub>Pga fell from 51.3(27.1) cmH<sub>2</sub>O to 47.4(25.2) cmH<sub>2</sub>O (p = 0.011). TwPdi did not change significantly; pre 17.0(6.4) cmH<sub>2</sub>O post 17.5(5.9) cmH<sub>2</sub>O (p = 0.7). Fatiguers, defined as having a fall TwT10Pga ≥ 10% had significantly worse lung gas transfer, but did not differ in other exercise parameters.</p> <p>Conclusions</p> <p>In patients with COPD, abdominal muscle but not diaphragm fatigue develops following symptom limited incremental cycle ergometry. Further work is needed to establish whether abdominal muscle fatigue is relevant to exercise limitation in COPD, perhaps indirectly through an effect on quadriceps fatigability.</p
Recommended from our members
Factors associated with unintended pregnancy in Brazil: cross-sectional results from the Birth in Brazil National Survey, 2011/2012
Background
Unintended pregnancy, a pregnancy that have been either unwanted or mistimed, is a serious public health issue in Brazil. It is reported for more than half of women who gave birth in the country, but the characteristics of women who conceive unintentionally are rarely documented. The aim of this study is to analyse the prevalence and the association between unintended pregnancy and a set of sociodemographic characteristics, individual-level variables and history of obstetric outcomes.
Methods
Birth in Brazil is a cross-sectional study with countrywide representation that interviewed 23,894 women after birth. The information about intendedness of pregnancy was obtained after birth at the hospital and classified into three categories: intended, mistimed or unwanted. Multinomial regression analysis was used to estimate the associations between intendedness of a pregnancy, and sociodemographic and obstetric variables, calculating odds ratios and 95 % confidence intervals. All significant variables in the bivariate analysis were included in the multinomial multivariate model and the final model retaining variables that remained significant at the 5 % level.
Results
Unintended pregnancy was reported by 55.4 % of postpartum women. The following variables maintained positive and significant statistical associations with mistimed pregnancy: maternal age < 20 years (OR = 1.89, 95 % CI: 1.68–2.14); brown (OR = 1.15, 95 % CI: 1.04–1.27) or yellow skin color (OR = 1.56, 95 % CI: 1.05–2.32); having no partner (OR = 2.32, 95 % CI: 1.99–2.71); having no paid job (OR = 1.15, 95 % CI: 1.04–1.27); alcohol abuse with risk of alcoholism (OR = 1.25, 95 % CI: 1.04–1.50) and having had three or more births (OR = 2.01, 95 % CI: 1.63–2.47). The same factors were associated with unwanted pregnancy, though the strength of the associations was generally stronger. Women with three or more births were 14 times more likely to have an unwanted pregnancy, and complication in the previous pregnancies and preterm birth were 40 % and 19 % higher, respectively. Previous neonatal death was a protective factor for both mistimed (OR = 0.61, 95 % CI: 0.44–0.85) and unwanted pregnancy (OR = 0.44, 95 % CI: 0.34–0.57).
Conclusions
This study confirms findings from previous research about the influence of socioeconomic and individual risk factors on unintended pregnancy. It takes a new approach to the problem by showing the importance of previous neonatal death, preterm birth and complication during pregnancy as risk factors for unintended pregnancy
An approach to addressing governance from a health system framework perspective
As countries strive to strengthen their health systems in resource constrained contexts, policy makers need to know how best to improve the performance of their health systems. To aid these decisions, health system stewards should have a good understanding of how health systems operate in order to govern them appropriately. While a number of frameworks for assessing governance in the health sector have been proposed, their application is often hindered by unrealistic indicators or they are overly complex resulting in limited empirical work on governance in health systems. This paper reviews contemporary health sector frameworks which have focused on defining and developing indicators to assess governance in the health sector. Based on these, we propose a simplified approach to look at governance within a common health system framework which encourages stewards to take a systematic perspective when assessing governance. Although systems thinking is not unique to health, examples of its application within health systems has been limited. We also provide an example of how this approach could be applied to illuminate areas of governance weaknesses which are potentially addressable by targeted interventions and policies. This approach is built largely on prior literature, but is original in that it is problem-driven and promotes an outward application taking into consideration the major health system building blocks at various levels in order to ensure a more complete assessment of a governance issue rather than a simple input-output approach. Based on an assessment of contemporary literature we propose a practical approach which we believe will facilitate a more comprehensive assessment of governance in health systems leading to the development of governance interventions to strengthen system performance and improve health as a basic human right
Identification of germline susceptibility loci in ETV6-RUNX1-rearranged childhood acute lymphoblastic leukemia
Acute lymphoblastic leukemia (ALL) is a malignant disease of the white blood cells. The etiology of ALL is believed to be multifactorial and likely to involve an interplay of environmental and genetic variables. We performed a genome-wide association study of 355 750 single-nucleotide polymorphisms (SNPs) in 474 controls and 419 childhood ALL cases characterized by a t(12;21)(p13;q22) — the most common chromosomal translocation observed in childhood ALL — which leads to an ETV6–RUNX1 gene fusion. The eight most strongly associated SNPs were followed-up in 951 ETV6-RUNX1-positive cases and 3061 controls from Germany/Austria and Italy, respectively. We identified a novel, genome-wide significant risk locus at 3q28 (TP63, rs17505102, PCMH=8.94 × 10−9, OR=0.65). The separate analysis of the combined German/Austrian sample only, revealed additional genome-wide significant associations at 11q11 (OR8U8, rs1945213, P=9.14 × 10−11, OR=0.69) and 8p21.3 (near INTS10, rs920590, P=6.12 × 10−9, OR=1.36). These associations and another association at 11p11.2 (PTPRJ, rs3942852, P=4.95 × 10−7, OR=0.72) remained significant in the German/Austrian replication panel after correction for multiple testing. Our findings demonstrate that germline genetic variation can specifically contribute to the risk of ETV6–RUNX1-positive childhood ALL. The identification of TP63 and PTPRJ as susceptibility genes emphasize the role of the TP53 gene family and the importance of proteins regulating cellular processes in connection with tumorigenesis
- …