Estudio del mejoramiento de la resistencia mecánica de la soldadura de un LED de alta potencia

El presente documento presenta el estudio del desprendimiento de un LED de alta potencia utilizado en la industria automotriz que se origina por la falla en un proceso de manufactura del PCB; el nivel de defectivo reportado por la planta armadora de autos fue del orden de 65000 partes por millón. Para encontrar la causa raíz del problema se plantean metodologías y técnicas de análisis que abordan problemas serios de confiabilidad. Normalmente este tipo de fallas se estudia por medio de técnicas de corte seccional que se evalúan en microscopio óptico, a diferencia de los métodos tradicionales, en este documento se aborda el uso de un microscopio electrónico de barrido para caracterizar la unión inter-metálica entre el dispositivo LED y el PCB que es del orden de 1 micra; es de notar que en esta investigación se obtienen resultados diferentes a los métodos tradicionales. El problema se abordó a través de la metodología DMAIC, con la utilización diagramas de Ishikawa y mapeo de procesos de manufactura; se formularon hipótesis sobre las causas que propiciaron el desprendimiento de los LEDs y que posteriormente fueron evaluadas con pruebas de esfuerzo cortante con apoyo en ensayos analíticos realizados en SEM y EDX. Al concluir la fase de análisis se confirmó que la unión inter-metálica entre el LED y la soldadura era muy pequeña lo que resultaba en una resistencia mecánica débil. Finalmente, se planteó la forma de robustecer la unión inter-metálica utilizando la técnica estadística de diseño de experimentos DoE donde se encontró que las mejores condiciones de proceso fueron el utilizar pasta de soldadura Hereaus, pico de temperatura 245 ºC, TAL 70 seg, esténcil de 6 milésimas y atmósfera de nitrógeno. Para validar la mejora se desarrolló un estudio estadístico de Cpk, que es un indicador de la capacidad que tiene un proceso para producir un resultado dentro de los límites de especificación predefinidos. Por medio de la prueba de esfuerzo cortante, se evaluó un grupo de 30 tarjetas PCB para determinar la resistencia mecánica de la unión de soldadura. Después de la implementación de los cambios en el proceso, el estudio arrojó un resultado de Cpk de aproximadamente 6, que es muy superior al nivel mínimo aceptable por la industria de 1.67

Effects of Jatropha lubricant thermo-oxidation on the tribological behaviour of engine cylinder liners as measured by a reciprocating friction test

Bio-lubricants have emerged as a potential and viable way to replace, totally or partially, mineral oils due to their effectiveness in the boundary lubrication regime for different applications, including, automotive engine operation. However, the effect of thermo-oxidation caused by the long-term use of the bio-lubricants on their tribological properties has been scarcely analysed. In this work, the effect of thermo-oxidation of Jatropha oil (JO), an engine mineral oil (EMO) and a blend made up of 80%vol. EMO and 20%vol. JO (B20) on the tribological behaviour of a simulated piston ring/engine cylinder liner interface was studied in reciprocating friction tests at 26 and 100 °C. The oils were thermally oxidized and characterized in terms of carbonyl compounds, depletion of ZDDP additives, changes in kinematic viscosity and viscosity index. Friction coefficients, wear rates and scar morphologies were assessed. Thermo-oxidation resulted in significant viscosity increases in JO compared to EMO and B20. Also, it generated increased friction coefficients for JO and B20. However, they were lower than those for fresh and aged EMO. EMO increased the wear rate after thermo-oxidation in contrast to JO. Smearing was generated using most oil samples while severe scuffing was only produced by using fresh JO at 100 °C

Effects of the type of exercise performed on the vibration delivered during whole-body vibration exercises

While the internal load factors of whole-body vibration training have been widely investigated, the study of external load magnitude has been overlooked. Thus, the aim of the present study was to evaluate differences in whole-body vibration stimulus magnitude between static/dynamic whole-body vibration training at various vibration conditions. Four Pro 5 Plate vibration platforms were exposed to twelve different vibration conditions and a triaxial USB Impact X250-2 accelerometer was used to measure platform acceleration during each condition. Paired samples t-test was calculated to evaluate differences among amplitude, frequency, time of acceleration and time of deceleration of each platform at each vibration condition and during static (squat of 90° knee flexion) or dynamic exercise (from stand to 90° knee flexion squat). Also, the intra-class correlation coefficients were examined in order to assess the inter-instrument reliability. Peak-to-peak amplitude, frequency, time of acceleration and deceleration of the vibration platform were not modified by the type of exercise performed. Moreover, the four platforms tested showed high repeatability values during the execution of free vibration, static or dynamic squat in all vibration conditions. This study confirms that the vibration delivered by the Pro 5 Plate vibration platform is not modified during the realization of static or dynamic exercises

Validity of the polar h7 heart rate sensor for heart rate variability analysis during exercise in different age, body composition and fitness level groups

This work aims to validate the Polar H7 heart rate (HR) sensor for heart rate variability (HRV) analysis at rest and during various exercise intensities in a cohort of male volunteers with different age, body composition and fitness level. Cluster analysis was carried out to evaluate how these phenotypic characteristics influenced HR and HRV measurements. For this purpose, sixty-seven volunteers performed a test consisting of the following consecutive segments: sitting rest, three submaximal exercise intensities in cycle-ergometer and sitting recovery. The agreement between HRV indices derived from Polar H7 and a simultaneous electrocardiogram (ECG) was assessed using concordance correlation coefficient (CCC). The percentage of subjects not reaching excellent agreement (CCC > 0.90) was higher for high-frequency power (PHF) than for low-frequency power (PLF) of HRV and increased with exercise intensity. A cluster of unfit and not young volunteers with high trunk fat percentage showed the highest error in HRV indices. This study indicates that Polar H7 and ECG were interchangeable at rest. During exercise, HR and PLF showed excellent agreement between devices. However, during the highest exercise intensity, CCC for PHF was lower than 0.90 in as many as 60% of the volunteers. During recovery, HR but not HRV measurements were accurate. As a conclusion, phenotypic differences between subjects can represent one of the causes for disagreement between HR sensors and ECG devices, which should be considered specifically when using Polar H7 and, generally, in the validation of any HR sensor for HRV analysis

Effect of exercise on sleep quality and insomnia in middle-aged women: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE: We assessed the effects of programmed exercise (PE) on sleep quality and insomnia in middle-aged women (MAW). METHODS: Searches were conducted in five databases from inception through December 15, 2016 for randomized controlled trials (RCTs) evaluating the effects of PE versus a non-exercising control condition on sleep quality, sleep disturbance and/or insomnia in MAW. Interventions had to last at least 8 weeks. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI) and insomnia with the Insomnia Severity Index (ISI). Random effects models were used for meta-analyses. The effects on outcomes were expressed as mean differences (MDs) and their 95% confidence intervals (CI). RESULTS: Five publications reported data from four RCTs on PE effects during 12-16 weeks on sleep quality (n=4 studies reporting PSQI results) and/or insomnia (n=3 studies reporting ISI results), including 660 MAW. Low-moderate levels of exercise significantly lowered the PSQI score (MD=-1.34; 95% CI -2.67, 0.00; p=0.05) compared with controls. In a subgroup analysis, moderate PE (aerobic exercise) had a positive effect on sleep quality (PSQI score MD=-1.85; 95% CI -3.62, -0.07; p=0.04), while low levels of physical activity (yoga) did not have a significant effect (MD-0.46, 95% CI -1.79, 0.88, p=0.50). In three studies (two studies of yoga, one study of aerobic exercise), there was a non-significant reduction in the severity of insomnia measured with the ISI score (MD -1.44, 95% CI -3.28, 0. 44, p=0.13) compared with controls. Heterogeneity of effects among studies was moderate to high. CONCLUSION: In middle-aged women, programmed exercise improved sleep quality but had no significant effect on the severity of insomnia.Actividad Física y Deport

U B V R I Photometry of Stellar Structures throughout the Disk of the Barred Galaxy NGC 3367

We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures indicating that star formation is going on in the most part of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U - B, B - V, U - V, and V - I colors for the central region (nucleus), a region which includes supernovae 2003 AA, and 79 star associations throughout NGC 3367. Estimation of ages of star associations is very difficult due to several factors, among them: filling factor, metallicity, spatial distribution of each structure and the fact that we estimated the magnitudes with a circular aperture of 16 pixels in diameter, equivalent to $6''.8\sim1.4$ kpc. However, if the colors derived for NGC 3367 were similar to the colors expected of star clusters with theoretical evolutionary star tracks developed for the LMC and had a similar metallicity, NGC 3367 show 51 percent of the observed structures with age type SWB I (few tens of Myrs), with seven sources outside the bright surface brightness visible disk of NGC 3367.Comment: Accepted for publication (abr 2007) in The Astronomical Journal (July 2007 issue

Rules, Standards, and the Internal Point of View

Large scale structure and cosmolog

Characterization of the platelet phenotype caused by a germline RUNX1 Variant in a CRISPR/Cas9-generated murine model

RUNX1-related disorder (RUNX1-RD) is caused by germline variants affecting the RUNX1 gene. This rare, heterogeneous disorder has no specific clinical or laboratory phenotype, making genetic diagnosis necessary. Although international recommendations have been established to classify the pathogenicity of variants, identifying the causative alteration remains a challenge in RUNX1-RD. Murine models may be useful not only for definitively settling the controversy about the pathogenicity of certain RUNX1 variants, but also for elucidating the mechanisms of molecular pathogenesis. Therefore, we developed a knock-in murine model, using the CRISPR/Cas9 system, carrying the RUNX1 p.Leu43Ser variant (mimicking human p.Leu56Ser) to study its pathogenic potential and mechanisms of platelet dysfunction. A total number of 75 mice were generated; 25 per genotype (RUNX1WT/WT, RUNX1WT/L43S, and RUNX1L43S/L43S). Platelet phenotype was assessed by flow cytometry and confocal microscopy. On average, RUNX1L43S/L43S and RUNX1WT/L43S mice had a significantly longer tail-bleeding time than RUNX1WT/WT mice, indicating the variant's involvement in hemostasis. However, only homozygous mice displayed mild thrombocytopenia. RUNX1L43S/L43S and RUNX1WT/L43S displayed impaired agonist-induced spreading and α-granule release, with no differences in δ-granule secretion. Levels of integrin αIIbβ3 activation, fibrinogen binding, and aggregation were significantly lower in platelets from RUNX1L43S/L43S and RUNX1WT/L43S using phorbol 12-myristate 13-acetate (PMA), adenosine diphosphate (ADP), and high thrombin doses. Lower levels of PKC phosphorylation in RUNX1L43S/L43S and RUNX1WT/L43S suggested that the PKC-signaling pathway was impaired. Overall, we demonstrated the deleterious effect of the RUNX1 p.Leu56Ser variant in mice via the impairment of integrin αIIbβ3 activation, aggregation, α-granule secretion, and platelet spreading, mimicking the phenotype associated with RUNX1 variants in the clinical setting.This work was partially supported by grants from Instituto de Salud Carlos III (ISCIII) and Feder (PI17/01311, PI17/01966, and CB15/00055), Fundación Séneca (19873/GERM/15), Gerencia Regional de Salud (GRS 2061A/19 and 1647/A/17), Fundación Mutua Madrileña (FMM, AP172142019), and Sociedad Española de Trombosis y Hemostasia (SETH-FETH; Premio López Borrasca 2019 and Ayuda a Grupos de Trabajo en Patología Hemorrágica 2019). The authors' research on IPDs is conducted in accordance with the aims of the Functional and Molecular Characterization of Patients with Inherited Platelet Disorders Project, which is supported by the Hemorrhagic Diathesis Working Group of the Spanish Society of Thrombosis and Haemostasis. A.M.-Q., C.F.-I., and L.H.-C. were supported by predoctoral grants from the Junta de Castilla y León, Spain. E.V. was supported by the predoctoral grant from the University of Salamanca, Spain. IG-T and RB were supported by "Contratos postdoctorales Programa II) from the University of Salamanca, Spain

Artrodesis tras el fracaso de la artroplastia de rodilla por infección

La artrodesis de rodilla es un método de tratamiento elegido por varios autores en los casos de fracaso de la artroplastia total de rodilla por infección. En estos casos es difícil conseguir el éxito, ya que el mismo vendrá condicionado por el modelo protésico que extraemos y por el método de estabilización elegido. Los autores presentan los resultados obtenidos en 15 artrodesis realizadas en su Servicio por estas causas, obteniendo un 93% de consolidaciones. Como método de estabilización utilizan con preferencia el doble cuadro de Hoffmann-Vidal y para el tratamiento de la infección emplean la irrigación-aspiración continua junto con el tratamiento antibiótico específico