Stripe formation in horizontally oscillating granular suspensions

We present the results of an experimental study of pattern formation in horizontally oscillating granular suspensions. Starting from a homogeneous state, the suspension turns into a striped pattern within a specific range of frequencies and amplitudes of oscillation. We observe an initial development of layered structures perpendicular to the vibration direction and a gradual coarsening of the stripes. However, both processes gradually slow down and eventually saturate. The probability distribution of the stripe width approaches a nonmonotonic steady-state form which can be approximated by a Poisson distribution. We observe similar structures in MD simulations of soft spherical particles coupled to the motion of the surrounding fluid.Comment: 7 pages, 8 figures, to appear in Europhys. Lett. (2014

Evaluación del desempeño docente: Preparación para el aprendizaje de los estudiantes en el Marco de Buen Desempeño Docente

The objective of the present research work was to design a teaching performance evaluation model based on the domain Preparation for student learning within the Framework for Teacher Good Performance. The study is based on an applied-projective method, with a qualitative educational approach. The instrument was applied to 94 teachers and 6 managers from 4 public educational institutions. The results show low levels of performance related to the preparation of learning and discontinuity of the purposes in the evaluation process, thus concluding with the development of a teaching evaluation model that integrates a new way of evaluation, from the perspective of teacher reflection and improvement of his performance.El objetivo de la presente investigación fue diseñar un modelo de evaluación del desempeño docente a partir del dominio Preparación para el aprendizaje de los estudiantes en el Marco de Buen Desempeño Docente. El estudio se sustenta en un método aplicado-proyectivo, con un enfoque cualitativo educacional. La aplicación del instrumento se realizó a 94 docentes y 06 directivos, de 04 instituciones educativas públicas. Los resultados evidencian bajos niveles de desempeños relacionados con la preparación del aprendizaje y discontinuidad de los propósitos en el proceso de evaluación, concluyendo así con la elaboración de un modelo de evaluación docente, que integra una nueva forma de evaluar, desde la perspectiva de reflexión docente y mejora de su desempeño

Hydrodynamic propulsion of human sperm

The detailed fluid mechanics of sperm propulsion are fundamental to our understanding of reproduction. In this paper, we aim to model a human sperm swimming in a microscope slide chamber. We model the sperm itself by a distribution of regularized stokeslets over an ellipsoidal sperm head and along an infinitesimally thin flagellum. The slide chamber walls are modelled as parallel plates, also discretized by a distribution of regularized stokeslets. The sperm flagellar motion, used in our model, is obtained by digital microscopy of human sperm swimming in slide chambers. We compare the results of our simulation with previous numerical studies of flagellar propulsion, and compare our computations of sperm kinematics with those of the actual sperm measured by digital microscopy. We find that there is an excellent quantitative match of transverse and angular velocities between our simulations and experimental measurements of sperm. We also find a good qualitative match of longitudinal velocities and computed tracks with those measured in our experiment. Our computations of average sperm power consumption fall within the range obtained by other authors. We use the hydrodynamic model, and a prototype flagellar motion derived from experiment, as a predictive tool, and investigate how sperm kinematics are affected by changes to head morphology, as human sperm have large variability in head size and shape. Results are shown which indicate the increase in predicted straight-line velocity of the sperm as the head width is reduced and the increase in lateral movement as the head length is reduced. Predicted power consumption, however, shows a minimum close to the normal head aspect ratio

Soft swimming: Exploiting deformable interfaces for low-Reynolds number locomotion

Reciprocal movement cannot be used for locomotion at low-Reynolds number in an infinite fluid or near a rigid surface. Here we show that this limitation is relaxed for a body performing reciprocal motions near a deformable interface. Using physical arguments and scaling relationships, we show that the nonlinearities arising from reciprocal flow-induced interfacial deformation rectify the periodic motion of the swimmer, leading to locomotion. Such a strategy can be used to move toward, away from, and parallel to any deformable interface as long as the length scales involved are smaller than intrinsic scales, which we identify. A macro-scale experiment of flapping motion near a free surface illustrates this new result

Estimación del intervalo post mortem con Dermestes maculatus (Coleoptera: Dermestidae) y Chrysomya albiceps (Diptera: Calliphoridae) en Colombia

Insects attracted to cadavers can be used to estimate postmortem interval (PMI). In this study, a sample of insects associated with a dressed human cadaver that was enclosed with a woolen blanket tied to a stone in a closed and aquatic environment was found and analyzed to determine PMI. Inmature stages and adults of Chrysomya albiceps and Dermestes maculatus were collected. Furthermore, an experience with a pig carcass was conducted under the same conditions the human cadaver was found to verify the emersion time. This began 3 days after carcass submersion. mPMI was 20 days and approximately 1.5 h. The data present in this work illustrates the use of D. maculatus and C. albiceps to determine time of death under particular conditions, being the beetle species the first colonizer.Los insectos atraídos a cadáveres pueden ser usados para estimar el intervalo post mortem (IPM). En este estudio, una muestra de estados inmaduros y adultos de Dermestes maculatus y Chrysomya albiceps fueron recolectados en asociación con un cadáver humano en un ambiente cerrado y acuático en Caquetá, Colombia, y analizada para determinar el IPM. Además, se condujo un experimento con un cadáver porcino para estimar el tiempo de emersión, que comenzó tres días después de la sumersión del cadáver. El IPM mínimo fue 481.5 horas. El tiempo de muerte, tiempo de emersión y el periodo de actividad insectil coincidieron con las acciones de los sospechosos del crimen, quienes confesaron haber asesinado a la víctima 25 días antes del descubrimiento del cadáver.Fil: Zanetti, Noelia Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias Biológicas y Biomédicas del Sur. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Instituto de Ciencias Biológicas y Biomédicas del Sur; ArgentinaFil: Ramos Pastrana, Yardany. Universidad de la Amzonia; ColombiaFil: Córdoba Suarez, Eric. Universidad de la Amzonia; Colombi

Sexual Size Dimorphism, Ovipositioning, and Hatching in Leiocephalus macropus asbolomus (Squamata: Leiocephalidae) in Alexander von Humboldt National Park in Eastern Cuba

The endemic Antillean family Leiocephalidae includes 28 currently recognized extant species in the genus Leiocephalus. These are distributed across Hispaniola, Cuba, and various islands and cays in the Bahamas. Sexual size dimorphism (SSD)  is a fundamental and widespread biological phenomenon generally attributed to sexual differences  in relationships between body size, survival, fecunditty, and mating success. Six species with 40 subspecies are known from Cuba. Few data are available regarding SSD and reproduction. Herein we report new life-history data and the sexual size dimorphism index (SSDI) in Leiocephalus macropus asbolomus. Fieldwork was performed  during mid-August 2009 iin La Melba (Alexander von Humboldt National Park), HolguinProvince, Cuba. All males were larger in size then females and the SSDI (1.44) is the highest reported ffor any species of Leiocephalus. Egg measurments averaged 18.2 x 12.7 mml mean clutch size was 3. Eggs took 61-72 days to hatch; mean incubation time was 66.5 days, and mean hatchling SVL was 30.1 mm. &nbsp

Proceso de logística inversa en el recojo y recupero de dispositivos de interconexión de redes.

Esta investigación tiene como propósito proponer y evaluar una propuesta de mejora basada en la logística inversa, recuperando la mayoría de dispositivos luego de la anulación del servicio, generando un ahorro económico significativo en el presupuesto anual de la compra de estos mismos. Asimismo, se logró evidenciar que en el presente año la gestión del retorno de los dispositivos de redes mostró indicadores alertadores. Por ello, se analizo dos problemas importantes: la ineficiente cantidad de usuarios atendidos por anulación de servicio para la devolución de los dispositivos y poca información de la localización de los dispositivos. Por lo tanto, se pudo concluir que, es necesario poder implementar las propuestas de mejora en la gestión de logística inversa, se optará por la campaña de sensibilización, puntos de acopio en lugares estratégicos y la implementación de la geolocalización, teniendo como resultado la mejora en los indicadores de devolución.The purpose of this research is to propose and evaluate an improvement proposal based on reverse logistics, recovering the majority of devices after the cancellation of the service, generating significant economic savings in the annual budget for their purchase. Likewise, it was possible to show that this year the management of the return of network devices showed warning indicators. For this reason, two important problems are analyzed: the inefficient number of users served due to cancellation of service for the return of the devices and little information on the location of the devices. Therefore, it was possible to conclude that it is necessary to be able to implement the proposals for improvement in reverse logistics management, opting for the awareness campaign, collection points in strategic places and the implementation of geolocation, resulting in improvement in the return indicators.Trabajo de Suficiencia Profesiona

Multipurpose setup used to characterize tribo-electrical properties of electrical contact materials

Electrical contacts are pervasively found on countless modern devices and systems. It is imperative that connecting components present adequate electrical, mechanical, and chemical characteristics to fulfill the crucial role that they play in the system. To develop an electrical contact material that is tailored for a specific application, different approaches are pursued (e.g., coatings, reinforced composites, alloyed metals, duplex systems, etc.). The manufacturing of electrical contact materials demand a thorough characterization of their electrical properties, mechanical properties, and their resistance to wear, as well as their resistance to atmospheric conditions. Accordingly, commissioning of a novel setup enables a more comprehensive study of the materials that are developed. Therefore, a complete understanding of the material's electrical and tribological characteristics are attained, allowing the production of a material that is compliant with the particular demands of the application for which it is intended. This multipurpose setup was built with higher precision stages and higher accuracy 3-axis force sensor, thus providing the following improvement over the preceding setup: • Elevated load-bearing capacity (double), higher precision and stability. • Tribo-electrical characterization (implementation of scratch and fretting tests). • Environmental control (climate and external vibration)

Recyclable Organic Bilayer Piezoresistive Cantilever for Torque Magnetometry at Cryogenic Temperatures

Flexible sensors made from organic bilayer films of molecular conductor on polymeric matrix have attracted many interest due to their simple fabrication with high potential for being scaled up, and for their high-performing multi-functionality at room temperatures. In particular, the piezoresistive property of the organic bilayer film is among one of the highest ever reported, allowing its utilization in various sensing applications. In this work, we present the study of the flexural piezoresistivity of an organic bilayer film based on $\beta-\rm (BEDT-TTF)_2I_3$ on polycarbonate matrix from room temperatures down to cryogenics temperatures. Non-trivial temperature dependent profile of the gauge factor is revealed, including enhancement of the gauge factor from $\sim 18$ at room temperatures to $\sim 48$ at 4.3 K. An organic bilayer cantilever magnetometer is developed and demonstrated to measure magnetic properties of a single crystalline organic superconductor $\kappa-\rm (BEDT-TTF)_2Cu(N(CN)_2)Br$ at temperatures down to $\sim 2.75$ K and magnetic fields up to 5 T. The high-performing bilayer devices can be fabricated in a very simple manner, and they are robust and recyclable