Locking-free two-layer Timoshenko beam element with interlayer slip

A new locking-free strain-based finite element formulation for the numerical treatment of linear static analysis of two-layer planar composite beams with interlayer slip is proposed. In this formulation, the modified principle of virtual work is introduced as a basis for the finite element discretization. The linear kinematic equations are included into the principle by the procedure, similar to that of Lagrangian multipliers. A strain field vector remains the only unknown function to be interpolated in the finite element implementation of the principle. In contrast with some of the displacement-based and mixed finite element formulations of the composite beams with interlayer slip, the present formulation is completely locking-free. Hence, there are no shear and slip locking, poor convergence and stress oscillations in these finite elements. The generalization of the composite beam theory with the consideration of the Timoshenko beam theory for the individual component of a composite beam represents a substantial contribution in the field of analysis of non-slender composite beams with an interlayer slip. An extension of the present formulation to the non-linear material problems is straightforward. As only a few finite elements are needed to describe a composite beam with great precision, the new finite element formulations is perfectly suited for practical calculations. (c) 2007 Elsevier B.V. All rights reserved

Estructura cariotípica de dos poblaciones de Rhamdia quelen (Pisces, Siluriformes) de los Ríos Paraná y Paraguay (Argentina)

Se analizaron 13 ejemplares de Rhamdia quelen (4 hembras y 9 machos) capturados en el río Paraná y 7 ejemplares (3 hembras y 4 machos) del río Paraguay. En total se registraron 244 metafases. Los especimenes mostraron un número diploide de 58 cromosomas. Con una formula cariotípica de 46M/SM + 12ST, el número fundamental (FN) fue de 116. No se registraron diferencias entre ambas poblaciones. No se evidenció la ocurrencia de heteromorfismo cromosómico relacionado con los sexos. En ambas poblaciones, las regiones organizadoras de nucléolos (NOR) se localizaron en la región terminal del brazo corto de un par subtelocéntrico (par 27). Los cromosomas del complemento A mostraron bandas C+ distribuidas principalmente sobre las NOR, en las regiones terminales y pericentroméricas de unos pocos cromosomas. Se concluye que las poblaciones de R. quelen analizadas antuvieron su macro-estructura cariotípica conservada con respecto al número diploide de 58, con cromosomas de dos brazos, región organizadora de nucléolos de tipo simple y un patrón pobre de bandas C

Estructura y variabilidad de la región organizadora de nucléolos en Prochilodus lineatus (Pisces, Prochilodontidae)

Los peces de la familia Prochilodontidae se distribuyen en varias cuencas hidrográficas de América del Sur. El género Prochilodus presenta una de las distribuciones más amplias, encontrándose desde el Orinoco hasta el río de La Plata. En la Argentina es el recurso íctico más abundante del río Paraná y actualmente ha crecido el interés por esta especie. Dada su importancia económica, el objetivo del presente trabajo fue establecer su estructura cromosómica en ejemplares provenientes del río Paraná en la Provincia de Corrientes (Argentina), con especial énfasis al análisis de las regiones organiza­doras de nucléolos (NORs). El estudio de los cromosomas mitóticos y de las NORs se realizó a través de la coloración convencional con Giemsa y nitrato de plata, respectivamente. El cariotipo de la especie está constituido por 54 cromosomas (meta/submetacéntricos), siendo observada la ocurrencia de microcromosomas B, los cuales varían en número a nivel intra e interindividual, generando la ocurrencia de polimorfismos. La NOR está localizada en posi­ción intersticial en el brazo largo de un par metacéntrico, presentando variaciones en cuanto a la posición y tamaño de las regiones Ag-NORs+, a saber: a) la NOR se presenta única y de igual tamaño en los dos homólogos, b) NOR grande ocupando la mitad del brazo largo y úni­ca en uno de los cromosomas; pequeña y única en el otro, c) doble región NOR en uno de los cromosomas y NOR única y pequeña en su homólogo. La diferencia de tamaño de la NOR es debida a alteraciones cromosómicas estructurales como duplicaciones, deleciones y crossing over desigual. La doble NOR probablemente sea el resultado de una inversión paracéntrica.

Early spears as thrusting weapons: Isolating force and impact velocities in human performance trials

Human hunting has been a cornerstone of research in human evolutionary studies, and decades worth of research programmes into early weapon systems have improved our understanding of the subsistence behaviours of our genus. Thrusting spears are potentially one of the earliest hunting weapons to be manufactured and used by humans. However, a dearth of data on the mechanics of thrusting spear use has hampered experimental research. This paper presents a human performance trial using military personnel trained in bayonet use. Participants thrusted replicas of Middle Pleistocene wooden spears into PermaGel™. For each spear thrust, impact velocity was recorded with high-speed video equipment, and force profiles were recorded using a force transducer. The results demonstrate that training improves performance when compared with previous experimental results using untrained participants, and that the mechanics and biomechanics of spear thrusting are complex. The trial confirms that previous spear thrusting experiments firing spears as projectiles are failing to replicate the entire spear thrusting event, and that crossbows are too powerful to replicate the low velocities involved in spear thrusting. In order to better understand evidence of spear thrusting in the archaeological record, experimental protocols accurately replicating and recording the mechanics of spear thrusting in the past are proposed

Long-Term Changes in Physical Activity Following a One-Year Home-Based Physical Activity Counseling Program in Older Adults with Multiple Morbidities

This study assessed the sustained effect of a physical activity (PA) counseling intervention on PA one year after intervention, predictors of sustained PA participation, and three classes of post-intervention PA trajectories (improvers, maintainers, and decliners) in 238 older Veterans. Declines in minutes of PA from 12 to 24 months were observed for both the treatment and control arms of the study. PA at 12 months was the strongest predictor of post-intervention changes in PA. To our surprise, those who took up the intervention and increased PA levels the most, had significant declines in post-intervention PA. Analysis of the three post-intervention PA trajectories demonstrated that the maintenance group actually reflected a group of nonresponders to the intervention who had more comorbidities, lower self-efficacy, and worse physical function than the improvers or decliners. Results suggest that behavioral counseling/support must be ongoing to promote maintenance. Strategies to promote PA appropriately to subgroups of individuals are needed

Diagnostics and data fusion of robotic sensors

Robotic systems for remediation of hazardous waste sites must be highly reliable to avoid equipment failures and subsequent possible exposure of personnel to hazardous environments. Safe, efficient cleanup operations also require accurate, complete knowledge of the task space. This paper presents progress made on a 18 month program to meet these needs. To enhance robot reliability, a conceptual design of a monitoring and diagnostic system is being developed to predict the onset of mechanical failure modes, provide maximum lead time to make operational changes or repairs, and minimize the occurrence of on-site breakdowns. To ensure safe operation, a comprehensive software package is being developed that will fuse data from multiple surface mapping sensors and poses so as to reduce the error effects in individual data points and provide accurate 3-D maps of a work space

Gadolinium and nephrogenic systemic fibrosis: time to tighten practice

Nephrogenic systemic fibrosis (NSF) is a relatively new entity, first described in 1997. Few cases have been reported, but the disease has high morbidity and mortality. To date it has been seen exclusively in patients with renal dysfunction. There is an emerging link with intravenous injection of gadolinium contrast agents, which has been suggested as a main triggering factor, with a lag time of days to weeks. Risk factors include the severity of renal impairment, major surgery, vascular events and other proinflammatory conditions. There is no reason to believe that children have an altered risk compared to the adult population. It is important that the paediatric radiologist acknowledges emerging information on NSF but at the same time considers the risk:benefit ratio prior to embarking on alternative investigations, as children with chronic kidney disease require high-quality diagnostic imaging

Anormalidades morfológicas nucleares en hematíes del pez Prochilodus linneatus expuesto al clorpirifos

In recent years, the monitoring of xenobiotics (chemicals such as pesticides) in the environment has been very important, as the persistence of the biological activity of many of these compounds has been recognized. Chlorpyrifos is an organophosphorus insecticide of broad spectrum, used in agricultural and domestic activities. This pesticide as well as other chemicals may accidentally reach the aquatic ecosystem and the ictic fauna. Fish ingesting contaminated substances subsequently develop alterations due to bioaccumulation, becoming effective indicators of environmental pollution. The purpose of this study was to evaluate the genotoxicity of chlorpyrifos in P. linneatus (Pisces, Prochilodontidae) through the frequency of micronuclei (MN) and nuclear morphology alterations (AMN) in peripheral blood erythrocytes. After acclimatization the fish were divided into two control (C) and treated groups (T1 = 10 μg/l, T2 = 30 μg/l and T3 = 90 μg/l). Three replicates per group (C, T) were performed with a total of 3 animals per fishbowl. The animals remained in the aquariums for a period of 7 days. After this time they were sacrificed with an overdose of anaesthetic to extract blood from the caudal vein. Smears were stained with Giemsa. In the samples analyzed, the number of MN and AMN was determined after observation of 2000 cells per animal. Cells with intact cytoplasmic membrane were considered for the study. The analysis of blood smears in both groups revealed the presence of micronuclei and the following nuclear morphology alterations; notches, lobulated, evaginations, eigth shaped, segmentations and vacuolization nuclei. Individuals T3 showed significant variations in the frequency of MN and AMN with respect to the controls (p<0.05), but not the T1 and T2 specimens. We conclude that chlorpyrifos at a dose of 90 μg/l could be harmful to the environment.Recientemente adquirió importancia el monitoreo de xenobióticos (como pesticidas) en el medio ambiente, debido a la persistencia de la actividad biológica de muchos de ellos. Clorpirifos es un insecticida organofosforado empleado a nivel agrícola y doméstico. Este plaguicida puede alcanzar accidentalmente el ecosistema acuático y la fauna íctica. Al ingerir sustancias contaminadas, los peces desarrollan alteraciones debidas a la bioacumulación, constituyéndose en eficaces indicadores de polución ambiental. El propósito del estudio fue evaluar la genotoxicidad del clorpirifos en P. linneatus (Pisces, Prochilodontidae) a través de la frecuencia de micronúcleos (MN) y de alteraciones de la morfología nuclear (AMN) en eritrocitos de sangre periférica. Los ensayos se realizaron con clorpirifos en su forma pura (Sigma Aldrich). Los peces se dividieron en grupos control (C) y tratados (T1 = 10 μg/l; T2 = 30 μg/l y T3 = 90 μg/l). Se realizaron tres replicas por grupo, con un total de 3 animales por pecera, los cuales permanecieron allí durante 7 días, tras lo cual fueron sacrificados con sobredosis de anestésico. Se extrajo sangre de la vena caudal, realizándose frotis que se colorearon con Giemsa, determinándose el número de MN y AMN luego de la observación de 2000 células por animal. Para el estudio se consideraron las células con sus membranas citoplasmáticas intactas. En ambos grupos, los frotis sanguíneos revelaron la presencia de micronúcleos, así como algunas de las siguientes alteraciones de la morfología nuclear: muesca, lobulación, evaginación, forma de ocho, segmentación y vacuolización nuclear. Los individuos del grupo T3 mostraron variaciones significativas en la frecuencia de MN y AMN respecto a los controles (p<0,05), no así los ejemplares de los tratamientos T1 y T2. Por lo expuesto, surge que el clorpirifos a la dosis de 90 μg/l podría ser nocivo para el medio ambiente