2,298 research outputs found
Flavored axions and the flavor problem
A Peccei-Quinn~(PQ) symmetry is proposed, in order to generate in the
Standard Model~(SM) quark sector a realistic mass matrix ansatz with five
texture-zeros. Limiting our analysis to Hermitian mass matrices we show that
this requires a minimum of 4 Higgs doublets. This model allows assigning values
close to 1 for several Yukawa couplings, giving insight into the origin of the
mass scales in the SM. Since the PQ charges are non-universal the model
features Flavor-Changing Neutral Currents~(FCNC) at the tree level. From the
analytical expressions for the FCNC we report the allowed region in the
parameter space obtained from the measurements of branching ratios of
semileptonic meson decays.Comment: 20 pages, 2 figure
Diseño un controlador robusto basado en observador para el modelo lineal de un helicóptero de un grado de libertad (VTOL)
Este artÃculo propone un controlador basado en observador para un modelo de helicóptero tipo VTOL de un grado de libertad. El objetivo de control es mantener la posición del VTOL en un punto de operación, a pesar de las incertidumbres ocasionadas por inexactitud en el modelo y ruido en las mediciones. El controlador y el observador son diseñados con base en algoritmos que inducen modos deslizantes en el sistema en lazo cerrado, ofreciendo caracterÃsticas de robustez y convergencia en tiempo finito. Los resultados de simulación muestran un buen desempeño del esquema propuesto tanto en condiciones de ausencia de ruido como cuando se consideran mediciones ruidosas.Universidad Nacional de ColombiaCinvestavColcienciasBanco Mundia
Estudio de enfermedades progresivas usando un modelo de Markov de estados múltiples
ResumenLos factores de riesgo y su grado de asociación con una enfermedad progresiva, tal como la enfermedad de Alzheimer o el cáncer de hígado, puede identificarse usando modelos epidemiológicos;algunos ejemplos de estos modelos incluyen los de región logística, Poisson,Log-lineales, regresión lineal y mixtos.[Salazar JC, Iral R. Estudio de enfermedades progresivas usando un modelo de Markov de estados múltiples. MedUNAB 2005; 8:202-7].Palabras clave: Enfermedad de Alzheimer, marcadores genéticos, modelos de estados múltiples, datos longitudinales, dependencia de Markov
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Complete Genomes of Symbiotic Cyanobacteria Clarify the Evolution of Vanadium-Nitrogenase.
Plant endosymbiosis with nitrogen-fixing cyanobacteria has independently evolved in diverse plant lineages, offering a unique window to study the evolution and genetics of plant-microbe interaction. However, very few complete genomes exist for plant cyanobionts, and therefore little is known about their genomic and functional diversity. Here, we present four complete genomes of cyanobacteria isolated from bryophytes. Nanopore long-read sequencing allowed us to obtain circular contigs for all the main chromosomes and most of the plasmids. We found that despite having a low 16S rRNA sequence divergence, the four isolates exhibit considerable genome reorganizations and variation in gene content. Furthermore, three of the four isolates possess genes encoding vanadium (V)-nitrogenase (vnf), which is uncommon among diazotrophs and has not been previously reported in plant cyanobionts. In two cases, the vnf genes were found on plasmids, implying possible plasmid-mediated horizontal gene transfers. Comparative genomic analysis of vnf-containing cyanobacteria further identified a conserved gene cluster. Many genes in this cluster have not been functionally characterized and would be promising candidates for future studies to elucidate V-nitrogenase function and regulation
Reversible Motion In a Contact Line
When a body of liquid sits on a surface, an irregular border between the wet and dry regions of the surface exists, called the contact line. Driving this contact line back and forth repeatedly can change its shape.We use a syringe pump to cyclically infuse and withdraw a predetermined volume of water, and take photos of the contact line after each cycle. Comparing these images to each other determines if the contact line is returning to the same shape. We find that below a critical value of infused volume, after many cycles the contact line reaches a steady state in which it always returns to the same shape. Above that value the shape fluctuates in the steady state. This suggests a transition similar to that seen in other systems like particle suspensions and solids
Hysteroscopic findings and intrauterine pathology treatment in Mexican infertile women
Background: Hysteroscopy is a minimally invasive approach in gynecologic surgery and one of the main procedures performed on women undergoing fertility treatments. Intrauterine pathology negatively affects fertility by decreasing endometrial receptivity and embryo implantation success, and its prevalence has been reported between 19% and 62%. The aim of our study was to describe the hysteroscopic findings, prevalence of intrauterine pathology, the instruments used for the treatment of structural lesions in Mexican infertile women; and to compare the relationship of positive findings with the type of infertility.
Methods: This was a descriptive, cross-sectional study conducted at fertility clinic at a private hospital.
Results: We evaluated 191 hysteroscopies; the mean age of women was 35.5+3.2 years and the mean time of infertility 5.7+3.2 years. Primary infertility was the most prevalent (79.1%). In 118 cases (61.8%), uterine cavity abnormalities were diagnosed, the most frequent findings were: polyps (n=51, 26.7%), endometritis (n=30, 15.7%), fibroids (n=15, 7.6 %), synechiae (n=12, 6.5%), and müllerian anomalies (n=10, 5.3%). For structural pathology treatment, cold scissors and bipolar energy were used in 65.5% and 34.5%, respectively.
Conclusions: Overall intrauterine pathology prevalence in our study population was 61.8%. Cold scissors and bipolar energy were used for structural lesions treatment. When comparing the relationship of hysteroscopic findings, no statistically significant difference was found in the presence of positive findings, with the type of infertility.
Variable speed liquid chiller drop-in modeling for predicting energy performance of R1234yf as low-GWP refrigerant
This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant
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