Twisted and Nontwisted Bifurcations Induced by Diffusion

We discuss a diffusively perturbed predator-prey system. Freedman and Wolkowicz showed that the corresponding ODE can have a periodic solution that bifurcates from a homoclinic loop. When the diffusion coefficients are large, this solution represents a stable, spatially homogeneous time-periodic solution of the PDE. We show that when the diffusion coefficients become small, the spatially homogeneous periodic solution becomes unstable and bifurcates into spatially nonhomogeneous periodic solutions. The nature of the bifurcation is determined by the twistedness of an equilibrium/homoclinic bifurcation that occurs as the diffusion coefficients decrease. In the nontwisted case two spatially nonhomogeneous simple periodic solutions of equal period are generated, while in the twisted case a unique spatially nonhomogeneous double periodic solution is generated through period-doubling. Key Words: Reaction-diffusion equations; predator-prey systems; homoclinic bifurcations; periodic solutions.Comment: 42 pages in a tar.gz file. Use ``latex2e twisted.tex'' on the tex files. Hard copy of figures available on request from [email protected]

The Observed Growth of Massive Galaxy Clusters II: X-ray Scaling Relations

(Abridged) This is the second in a series of papers in which we derive simultaneous constraints on cosmology and X-ray scaling relations using observations of massive, X-ray flux-selected galaxy clusters. The data set consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV luminosities >2.5e44 erg/second, and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Our analysis accounts self-consistently for all selection effects, covariances and systematic uncertainties. Here we describe the reduction of the follow-up X-ray observations, present results on the cluster scaling relations, and discuss their implications. Our constraints on the luminosity-mass and temperature-mass relations, measured within r_500, lead to three important results. First, the data support the conclusion that excess heating of the intracluster medium has altered its thermodynamic state from that expected in a simple, gravitationally dominated system; however, this excess heating is primarily limited to the central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the center-excised luminosity-mass relation is remarkably small, being undetected at the <10% level in current data; for the hot, massive clusters under investigation, this scatter is smaller than in either the temperature-mass or Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling relations is consistent with the predictions of simple, self-similar models of gravitational collapse, indicating that the mechanism responsible for heating the central regions of clusters was in operation before redshift 0.5 (the limit of our data) and that its effects on global cluster properties have not evolved strongly since then.Comment: 25 pages, 7 figures, 14 tables. v3: final version (typographic corrections). Results can be downloaded at https://www.stanford.edu/group/xoc/papers/xlf2009.htm

Predictors of Bacterial Meningitis in Resource-Limited Contexts: An Angolan Case

BACKGROUND: Despite the great morbidity and mortality that childhood bacterial meningitis (BM) is experiencing in Africa, diagnosis of BM in resource-limited contexts is still a challenge. Several algorithms and clinical predictors have been proposed to help physicians in decision-making but a lot of these markers used variables that are calculable only in well-equipped laboratories. Predictors or algorithm based on parameters that can be easily performed in basic laboratories can help significantly in BM diagnosis, even in resource-limited settings, rural hospitals or health centers. RESULTS: This retrospective study examined 145 cerebral-spinal fluid (CSF) specimens from children from 2 months to 14 years. CSF specimens were divided into two groups, according to the presence or not of a clinical diagnosis of BM. For each specimen, CSF aspect, CSF white blood cells (WBC) count, CSF glucose and protein concentration were analyzed and statistical analysis were performed. CSF WBC count ≥10/µl is no more a valuable predictor of BM. CSF protein concentration ≥50 mg/dl has a better sensitivity for BM diagnosis and when used with CSF glucose concentration ≤40 mg/dl, can help to diagnose correctly almost all the BM cases. An algorithm including CSF protein concentration, glucose concentration and WBC count has been proposed to rule out BM and to correctly diagnose it. CONCLUSIONS: In resource-limited health centers, the availability of a combination of easy-to-obtain parameters can significantly help physicians in BM diagnosis. The prompt identification of a BM case can be rapid treated or transferred to adequate structures and can modify the outcome in the patient

Chandra Cluster Cosmology Project III: Cosmological Parameter Constraints

Chandra observations of large samples of galaxy clusters detected in X-rays by ROSAT provide a new, robust determination of the cluster mass functions at low and high redshifts. Statistical and systematic errors are now sufficiently small, and the redshift leverage sufficiently large for the mass function evolution to be used as a useful growth of structure based dark energy probe. In this paper, we present cosmological parameter constraints obtained from Chandra observations of 36 clusters with =0.55 derived from 400deg^2 ROSAT serendipitous survey and 49 brightest z=~0.05 clusters detected in the All-Sky Survey. Evolution of the mass function between these redshifts requires Omega_Lambda>0 with a ~5sigma significance, and constrains the dark energy equation of state parameter to w0=-1.14+-0.21, assuming constant w and flat universe. Cluster information also significantly improves constraints when combined with other methods. Fitting our cluster data jointly with the latest supernovae, WMAP, and baryonic acoustic oscillations measurements, we obtain w0=-0.991+-0.045 (stat) +-0.039 (sys), a factor of 1.5 reduction in statistical uncertainties, and nearly a factor of 2 improvement in systematics compared to constraints that can be obtained without clusters. The joint analysis of these four datasets puts a conservative upper limit on the masses of light neutrinos, Sum m_nu<0.33 eV at 95% CL. We also present updated measurements of Omega_M*h and sigma_8 from the low-redshift cluster mass function.Comment: ApJ, in press (Feb 10, 2009 issue

Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015

Background Exposure to ambient air pollution increases morbidity and mortality, and is a leading contributor to global disease burden. We explored spatial and temporal trends in mortality and burden of disease attributable to ambient air pollution from 1990 to 2015 at global, regional, and country levels. Methods We estimated global population-weighted mean concentrations of particle mass with aerodynamic diameter less than 2·5 μm (PM2·5) and ozone at an approximate 11 km × 11 km resolution with satellite-based estimates, chemical transport models, and ground-level measurements. Using integrated exposure–response functions for each cause of death, we estimated the relative risk of mortality from ischaemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, lung cancer, and lower respiratory infections from epidemiological studies using non-linear exposure–response functions spanning the global range of exposure. Findings Ambient PM2·5 was the fifth-ranking mortality risk factor in 2015. Exposure to PM2·5 caused 4·2 million (95% uncertainty interval [UI] 3·7 million to 4·8 million) deaths and 103·1 million (90·8 million 115·1 million) disability-adjusted life-years (DALYs) in 2015, representing 7·6% of total global deaths and 4·2% of global DALYs, 59% of these in east and south Asia. Deaths attributable to ambient PM2·5 increased from 3·5 million (95% UI 3·0 million to 4·0 million) in 1990 to 4·2 million (3·7 million to 4·8 million) in 2015. Exposure to ozone caused an additional 254 000 (95% UI 97 000–422 000) deaths and a loss of 4·1 million (1·6 million to 6·8 million) DALYs from chronic obstructive pulmonary disease in 2015. Interpretation Ambient air pollution contributed substantially to the global burden of disease in 2015, which increased over the past 25 years, due to population ageing, changes in non-communicable disease rates, and increasing air pollution in low-income and middle-income countries. Modest reductions in burden will occur in the most polluted countries unless PM2·5 values are decreased substantially, but there is potential for substantial health benefits from exposure reduction

Alcohol intake and risk of oesophageal adenocarcinoma: a pooled analysis from the BEACON Consortium

Alcohol intake is a strong and well-established risk factor for esophageal squamous cell carcinoma (ESCC), but the association with esophageal adenocarcinoma (EA) or adjacent tumors of the esophagogastric junction (EGJA), remains unclear. Therefore, we determined the association of alcohol intake with ESCC, EA, and EGJA in nine case-control studies and two cohort studies of the Barrett’s Esophagus and Esophageal Adenocarcinoma Consortium (BEACON)

Home birth and barriers to referring women with obstetric complications to hospitals: a mixed-methods study in Zahedan, southeastern Iran

<p>Abstract</p> <p>Background</p> <p>One factor that contributes to high maternal mortality in developing countries is the delayed use of Emergency Obstetric-Care (EmOC) facilities. The objective of this study was to determine the factors that hinder midwives and parturient women from using hospitals when complications occur during home birth in Sistan and Baluchestan province, Iran, where 23% of all deliveries take place in non- hospital settings.</p> <p>Methods</p> <p>In the study and data management, a mixed-methods approach was used. In the quantitative phase, we compared the existing health-sector data with World Health Organization (WHO) standards for the availability and use of EmOC services. The qualitative phase included collection and analysis of interviews with midwives and traditional birth attendants and twenty-one in-depth interviews with mothers. The data collected in this phase were managed according to the principles of qualitative data analysis.</p> <p>Results</p> <p>The findings demonstrate that three distinct factors lead to indecisiveness and delay in the use of EmOC by the midwives and mothers studied. Socio-cultural and familial reasons compel some women to choose to give birth at home and to hesitate seeking professional emergency care for delivery complications. Apprehension about being insulted by physicians, the necessity of protecting their professional integrity in front of patients and an inability to persuade their patients lead to an over-insistence by midwives on completing deliveries at the mothers' homes and a reluctance to refer their patients to hospitals. The low quality and expense of EmOC and the mothers' lack of health insurance also contribute to delays in referral.</p> <p>Conclusions</p> <p>Women who choose to give birth at home accept the risk that complications may arise. Training midwives and persuading mothers and significant others who make decisions about the value of referring women to hospitals at the onset of life-threatening complications are central factors to increasing the use of available hospitals. The hospitals must be safe, comfortable and attractive environments for parturition and should give appropriate consideration to the ethical and cultural concerns of the women. Appropriate management of financial and insurance-related issues can help midwives and mothers make a rational decision when complications arise.</p

Age-specific risk factor profiles of adenocarcinomas of the esophagus: A pooled analysis from the international BEACON consortium: Age-specific risk factors of esophageal adenocarcinomas

Esophageal (EA) and esophagogastric junction (EGJA) adenocarcinoma have been steadily increasing in frequency in younger people, however the etiology of these cancers is poorly understood. We therefore investigated associations of body- mass index (BMI), cigarette smoking, alcohol consumption, gastroesophageal reflux, and use of non-steroidal anti-inflammatory drugs (NSAIDs) in relation to age-specific risks of EA and EGJA. We pooled individual participant data from eight population-based, case-control studies within the international Barrett’s and Esophageal Adenocarcinoma Consortium (BEACON). The analysis included 1,363 EA patients, 1,472 EGJA patients, and 5,728 control participants. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for age-specific (<50, 50–59, 60–69, ≥70 years) cancer outcomes, as well as interactions by age. BMI, smoking status and pack-years, recurrent gastroesophageal reflux, and frequency of gastroesophageal reflux were positively associated with EA and EGJA in each age group. Early-onset EA (<50 years) had stronger associations with recurrent gastroesophageal reflux (OR=8.06, 95%CI: 4.52, 14.37; Peffect modification=0.01) and BMI (ORBMI ≥30 vs. <25=4.19, 95%CI: 2.23, 7.87; Peffect modification=0.04), relative to older age groups. In contrast, inverse associations of NSAID use were strongest in the oldest age group (≥70 years), although this apparent difference was not statistically significant. Age-specific associations with EGJA showed similar, but slightly weaker patterns and no statistically significant differences by age were observed. Our study provides evidence that associations between obesity and gastroesophageal reflux are stronger among earlier onset EA cancers

Temporal context and conditional associative learning

<p>Abstract</p> <p>Background</p> <p>We investigated how temporal context affects the learning of arbitrary visuo-motor associations. Human observers viewed highly distinguishable, fractal objects and learned to choose for each object the one motor response (of four) that was rewarded. Some objects were consistently preceded by specific other objects, while other objects lacked this task-irrelevant but predictive context.</p> <p>Results</p> <p>The results of five experiments showed that predictive context consistently and significantly accelerated associative learning. A simple model of reinforcement learning, in which three successive objects informed response selection, reproduced our behavioral results.</p> <p>Conclusions</p> <p>Our results imply that not just the representation of a current event, but also the representations of past events, are reinforced during conditional associative learning. In addition, these findings are broadly consistent with the prediction of attractor network models of associative learning and their prophecy of a persistent representation of past objects.</p