Stress analysis during the mechanical contact of elastic materials

En este trabajo se calculan los esfuerzos resultantes en la región de contacto de dos materiales elásticos, a través del método de elementos finitos. Estos resultados se comparan con ecuaciones analíticas del modelo de Hertz. Se consideran dos sistemas de contacto para analizar: cilindro contra cilindro y cilindro contra plano. Para definir estos sistemas se realiza un modelo en dos dimensiones. Para el análisis se considera ambos sistemas como un contacto no conforme. Para validar el modelo se comparan los resultados del sistema con valores teóricos. Se observó que los resultados obtenidos de las simulaciones convergen rápidamente a un valor que se estabiliza a medida que se reduce el tamaño de la malla en la región de contacto, el valor mínimo de los elementos que se utilizó es de 0,1 mm. Por otro lado, de la comparación del Método de elementos finitos con las ecuaciones analíticas se encontró que los errores relativos en las medidas de presiones de contacto tiene un valor que se encuentra entre 1 y2 por ciento. Los errores relativos en las medidas correspondientes al semiancho de la zona de contacto alcanzan valores de hasta 2 por ciento con respecto al valor que se determina a partir de las ecuaciones de Heinrich Hertz.In this work, the stresses are calculated in the region of contact of two elastic materials, through the finite element method. These results are compared with equations of Hertz. Two contact systems are considered to analyze, cylinder against cylinder and cylinder against plane. To define these systems is performed model in two dimensions. For the analysis, it considers both systems as a contact nonconforming. To validate the modelresults they are compared with theoretical values. It was observed that the results of the simulations converge rapidly to a value which is stabilized as the mesh size in the contact region, the minimum value of the elements used is 0.1 mm. Furthermore, comparison of the finite element method with the analytical equations found that the relative errors in measurements contact pressure have values between 1 and 2 percent. The relative errors in measurements for the half-width of the contact area reach values of up to 2 percent with respect to the value determined from the equations of Hertz.Fil: Rodriguez, Carlos María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina. Universidad Nacional de Misiones. Facultad de Ingeniería; Argentina. Universidad Nacional de Misiones. Centro de Estudios de Energía para el Desarrollo; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Gonzalez, Facundo Enrique. Universidad Nacional de Misiones. Centro de Estudios de Energía para el Desarrollo; Argentina. Universidad Nacional de Misiones. Facultad de Ingeniería; ArgentinaFil: Tarnowski, Gabriel. Universidad Nacional de Misiones. Centro de Estudios de Energía para el Desarrollo; Argentina. Universidad Nacional de Misiones. Facultad de Ingeniería; ArgentinaFil: Bordón, Hugo. Universidad Nacional de Misiones. Facultad de Ingeniería; Argentina. Universidad Nacional de Misiones. Centro de Estudios de Energía para el Desarrollo; ArgentinaFil: Rosenberger, Mario Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Schvezov, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentin

Exploración y comparación de la distribución espacial de los bosques periurbanos en Mérida, Venezuela

Spatial point patterns are a novel approach for the analysis of forest functional structure. The spatial distribution of trees in peri-urban forests of Mérida (Venezuela) was evaluated and compared. The null hypothesis of Complete Spatial Randomness (CSR) was proposed, applying spatial exploratory and confirmatory methods without marks, and involving marks for dasometric variables, and multivariate point pattern tests (α= 0.05) to five plots of primary forest and five plots of secondary forest. Both forest types exhibited similar mean density (310 and 339 ind.ha-1). Besides, a CSR process was identified for the trees without considering marks of the height and DBH, and in the remaining volume and species marks, the process was identified as non-random. Likewise, there are no differences between the multivariate spatial processes. It is recommended to extend the work area and to apply it in better differentiated forests.Los patrones de puntos espaciales son una aproximación para el análisis de la estructura funcional del bosque. En este sentido, se evaluó y comparó la distribución espacial de árboles en bosques periurbanos de Mérida, Venezuela. Se planteó la hipótesis nula de la Aleatoriedad Espacial Completa (CSR), aplicando métodos exploratorios y confirmatorios espaciales sin marcas (e involucrando las marcas para las variables dasométricas) y pruebas de patrones puntuales multivariantes (α = 0.05) a parcelas de bosque primario y secundario (cinco en c/u). Ambos bosques exhibieron una densidad media similar (310 y 339 ind.ha-1). Además, se identificó un proceso CSR para los árboles sin considerar marcas en las variables de altura total y DAP, y en las marcas remanentes de volumen y especie este fue catalogado como no aleatorio, pues no se presentaron diferencias entre los procesos espaciales multivariantes. Se recomienda, por lo tanto, ampliar el área de trabajo y aplicarlo en bosques mejor diferenciados

Single-cell profiling reveals an endothelium-mediated immunomodulatory pathway in the eye choroid

The activity and survival of retinal photoreceptors depend on support functions performed by the retinal pigment epithelium (RPE) and on oxygen and nutrients delivered by blood vessels in the underlying choroid. By combining single-cell and bulk RNA sequencing, we categorized mouse RPE/choroid cell types and characterized the tissue-specific transcriptomic features of choroidal endothelial cells. We found that choroidal endothelium adjacent to the RPE expresses high levels of Indian Hedgehog and identified its downstream target as stromal GLI1+ mesenchymal stem cell-like cells. In vivo genetic impairment of Hedgehog signaling induced significant loss of choroidal mast cells, as well as an altered inflammatory response and exacerbated visual function defects after retinal damage. Our studies reveal the cellular and molecular landscape of adult RPE/choroid and uncover a Hedgehog-regulated choroidal immunomodulatory signaling circuit. These results open new avenues for the study and treatment of retinal vascular diseases and choroid-related inflammatory blinding disorders.Funding for this study was provided by National Institutes of Health grants EY08538 and GM34107 (E. Rodriguez-Boulan); EY027038 (R.F. Mullins); 1R21CA224391-01A1 (J.H. Zippin); and 1R01CA194547, 1U24CA210989, and P50CA211024 (O. Elemento); National Cancer Institute grant R01CA192176 and cancer center support grant P30 CA008748-48 (A.L. Joyner); Comunidad Autónoma de Madrid grant 2017-T1/BMD-5247 (I. Benedicto); Agencia Nacional Argentina de Promoción Cient´ıfica y Tecnológica grant PICT 2014-3687 and Fundación Sales (G.A. Rabinovich); a Pew Latin American Fellowship (G.L. Lehmann); Calder Research Scholar Award Vitiligo/Pigment Cell Disorders (J.H. Zippin); Starr Foundation Tri-Institutional Stem Cell Initiative award 2013-028; NYSTEM contract C32596GG; and Research to Prevent Blindness and Dyson Foundation departmental grants. The CNIC is supported by the Instituto de Salud Carlos III, the Ministerio de Ciencia e Innovación, and the Pro CNIC Foundation and is a Severo Ochoa Center of Excellence (SEV-2015-0505).S

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Timing of surgery for hip fracture and in-hospital mortality: a retrospective population-based cohort study in the Spanish National Health System

<p>Abstract</p> <p>Background</p> <p>While the benefits or otherwise of early hip fracture repair is a long-running controversy with studies showing contradictory results, this practice is being adopted as a quality indicator in several health care organizations. The aim of this study is to analyze the association between early hip fracture repair and in-hospital mortality in elderly people attending public hospitals in the Spanish National Health System and, additionally, to explore factors associated with the decision to perform early hip fracture repair.</p> <p>Methods</p> <p>A cohort of 56,500 patients of 60-years-old and over, hospitalized for hip fracture during the period 2002 to 2005 in all the public hospitals in 8 Spanish regions, were followed up using administrative databases to identify the time to surgical repair and in-hospital mortality. We used a multivariate logistic regression model to analyze the relationship between the timing of surgery (< 2 days from admission) and in-hospital mortality, controlling for several confounding factors.</p> <p>Results</p> <p>Early surgery was performed on 25% of the patients. In the unadjusted analysis early surgery showed an absolute difference in risk of mortality of 0.57 (from 4.42% to 3.85%). However, patients undergoing delayed surgery were older and had higher comorbidity and severity of illness. Timeliness for surgery was not found to be related to in-hospital mortality once confounding factors such as age, sex, chronic comorbidities as well as the severity of illness were controlled for in the multivariate analysis.</p> <p>Conclusions</p> <p>Older age, male gender, higher chronic comorbidity and higher severity measured by the Risk Mortality Index were associated with higher mortality, but the time to surgery was not.</p