232 research outputs found

    The Design and Validation of a UAV Propeller Intended for Extremely Low Reynolds Number Environments

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    Mars exploration and UAV development have both advanced significantly over the past century, and are now being considered in tandem. Currently needed are UAV propellers that can operate in the Martian atmosphere. Flow will be in the range of Re \u3c 20,000, creating extreme conditions not typically examined. A Blade Element Momentum Theory (BEMT) algorithm is developed using a variety of corrections designed specifically for low Reynolds number and rotational flows. Due to both the simplicity of the basic BEMT formulation, corrections are easy to put in place and often necessary to achieve accurate estimates. Aerodynamic coefficients are determined from XFOIL code, and have questionable accuracy in this regime. To account for this, a correction model is developed by comparing XFOIL results to experimental results of airfoils at low Re. This is all tested against a previous low Re propeller experiment. The results of this comparison are used to adjust the values in the correction, to produce more accurate results for theoretical design. From here, a design philosophy for the propeller is developed using established methods and previous experimental data. High thrust is prioritized, with efficiency being a secondary concern. A hard mach limit of 0.7 is set to avoid major drag penalties, limiting the usable ranges of RPM and radius. Airfoil designs are then examined, based on previous designs, theoretical intuition, and experimental data. A modified version of the S1223 airfoil is adopted for its favorably high Clmax and high stall angle. From here, optimization can be used to determine the final dimensions of the propeller. The BEMT algorithm is used to create a broad set of data, over a range of design variables, which is then fitted to thrust and efficiency functions using non-linear regression. A Non-Dominated Sorting Genetic Algorithm (NSGA) is well suited to optimizing multiple objective functions with multiple design variables, and thus is adopted to optimize the design. The results of the optimization confirm previously published theories, and produce three possible propeller designs, a high thrust model, a high efficiency model, and a compromise between the two. These designs were then modeled, meshed and simulated using the ANSYS Fluent software suite. BEMT thrust estimates were found to be within an average absolute error of ~41% from the simulated results, while moment was within an average absolute error of ~104%. This discrepancy can likely be attributed to the inaccurate drag data being sent into the BEMT algorithm, and the lack of a method to correct said data. With a procedure established for design and testing, new propellers can be created and verified, likely with improvements in accuracy from the initial estimates

    Natural Expectations, Macroeconomic Dynamics, and Asset Pricing

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    How does an economy behave if (1) fundamentals are truly hump-shaped, exhibiting momentum in the short run and partial mean reversion in the long run, and (2) agents do not know that fundamentals are hump-shaped and base their beliefs on parsimonious models that they fit to the available data? A class of parsimonious models leads to qualitatively similar biases and generates empirically observed patterns in asset prices and macroeconomic dynamics. First, parsimonious models will robustly pick up the short-term momentum in fundamentals but will generally fail to fully capture the long-run mean reversion. Beliefs will therefore be characterized by endogenous extrapolation bias and pro-cyclical excess optimism. Second, asset prices will be highly volatile and exhibit partial mean reversion—i.e., overreaction. Excess returns will be negatively predicted by lagged excess returns, P/E ratios, and consumption growth. Third, real economic activity will have amplified cycles. For example, consumption growth will be negatively auto-correlated in the medium run. Fourth, the equity premium will be large. Agents will perceive that equities are very risky when in fact long-run equity returns will co-vary only weakly with long-run consumption growth. If agents had rational expectations, the equity premium would be close to zero. Fifth, sophisticated agents—i.e., those who are assumed to know the true model—will hold far more equity than investors who use parsimonious models. Moreover, sophisticated agents will follow a counter-cyclical asset allocation policy. These predicted effects are qualitatively confirmed in U.S. data.

    L'impact des résections de l'insula sur la personnalité

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    La recherche montre que l’insula est impliquée dans le traitement d’informations intéroceptives, émotionnelles et relevant de fonctions exécutives de haut niveau. L’hypothèse des marqueurs somatiques propose que ces fonctions vraisemblablement séparées travaillent plutôt de concert au sein d’un système neural dont le rôle consiste à extraire les messages émotionnels des signaux corporels. Si l’insula exerce effectivement un rôle de modulateur des sensations corporelles et des processus cognitifs découlant de ceux-ci, des lésions au cortex insulaire risquent d’occasionner des altérations au niveau de l’expérience émotionnelle, des fonctions exécutives et de la personnalité. La présente étude a pour but de mesurer ces changements chez 19 patients ayant subi une insulectomie unilatérale dans le cadre de leur traitement de l’épilepsie. Ces patients ont été comparés à un groupe contrôle composé de 19 patients épileptiques ayant subi une résection du lobe temporal. Les participants ont été évalués par l’entremise du Iowa Scales of Personality Change (ISPC), rempli par un proche du patient. Les résultats montrent que les patients du groupe insulaire exhibent des changements qui dénotent une dérégulation émotionnelle à long terme, caractérisée par une augmentation modérée de l’irritabilité, de la labilité émotionnelle, de l’anxiété et de la frugalité, tous des changements qui, outre l’anxiété, n’ont pas été observés chez les patients temporaux. Cependant, pour ce qui est des fonctions exécutives, aucun changement significatif n’a été noté. De plus, la comparaison pré- et post opératoire des scores des deux groupes aux items de l’ISPC ne s’est pas avérée significative. Globalement, les résultats suggèrent que l’insula joue probablement un rôle accessoire au sein du modèle proposé par l’hypothèse des marqueurs somatiques et que les résections unilatérales partielles ou complètes de l’insula ne risquent pas d’occasionner de changements prononcés de la personnalité.Research has shown that the insula is involved in the processing of information relating to interoceptive, emotional and executive functions. It was proposed that these two seemingly separate functions may work conjointly as part of a large neural circuit tasked with the extraction of emotional information from bodily signals. It was hypothesized that, if the insula does indeed modulate feelings and the cognitive processes which derive from them, insular damage would result in alterations of emotional experience, executive functions and personality. To that effect, we examined such changes in a group of patients (n = 19) who underwent epilepsy surgery involving partial or complete resection of the insula, and compared them to a group of patients who underwent temporal lobe epilepsy surgery (n = 19) as a lesion-control group. Participants were assessed on the Iowa Scales of Personality Change, filled by a close relative at least six months after surgery. While pre- vs. post-surgery changes did not significantly differ between groups on any of the outcome variables, insular resections were associated with mild but significant increases in irritability, emotional lability, anxiety, and frugality postoperatively, which, with the exception of increased anxiety, were not found among temporal patients. Against our initial prediction, the surgery did not lead to executive functioning deficits. Overall, our results support the notion that the insula most likely holds an accessorial role in the model proposed by the somatic marker hypothesis, and that there isn’t a risk of dramatic personality change as a result of the partial or complete unilateral surgical removal of the insula

    Propuesta de mejora en la gestión de abastecimiento de materiales de embalaje del servicio de carga para la reducción de costos logísticos en una empresa del sector aeroportuario

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    El presente trabajo tiene como objetivo principal proponer una mejora en la gestión de abastecimiento para reducir los costos logísticos en una empresa del Sector Aeroportuario. Para esto se identificaron los problemas que afectaban al crecimiento de la organización y con ayuda de herramientas como la matriz de inventario y encuestas realizadas tanto al personal operativo como administrativo, se pudo obtener la suficiente información para detectar los problemas más relevantes. Se identificaron las variables tanto dependiente como independientes con sus respectivos indicadores y bajo un previo análisis de la situación actual se detectó que no contaban con un método de abastecimiento adecuado, por lo que se propuso una mejora en el mismo por medio del modelo EOQ, el cual luego de su implementación logró equilibrar las cantidades de pedido con respecto al consumo y permitió realizar una estandarización en el proceso de compras, reduciendo así los tiempos por generación de pedido de 39 min en el escenario actual a 28 min en el escenario propuesto bajo la implementación del modelo EOQ, de la mano a esta reducción de tiempos se suma el ahorro generado por los costos por generación de pedido, ya que estos representan un 28%. Por otro lado, también se logró incrementar la rotación de inventarios un 94% y a su vez se redujeron los días de inventario un 47%, esto a razón que el modelo del lote económico de pedido permitió ser más preciso en el abastecimiento de los materiales de embalaje del servicio de carga. Junto a esta mejora se logró reducir los costos de almacenamiento un 48%, puesto que el modelo de abastecimiento EOQ es bastante preciso en base a los consumos y no deja tener mucho inventario.The main objective of this work is to propose an improvement in supply management to reduce logistics costs in a company in the Airport Sector. For this, the problems that affect the growth of the organization were identified and with the help of tools such as the inventory matrix and surveys carried out both to operational and administrative personnel, enough information could be obtained to detect the most relevant problems. Both the dependent and independent variables were identified with their indicators and, under a previous analysis of the current situation, it was detected that they did not have an adequate supply method, for which an improvement was proposed through the EOQ model, which After its implementation, it managed to balance the order quantities with respect to consumption and carry out a standardization in the purchasing process, thus reducing the times per order generation from 39 min in the current scenario to 28 min in the scenario proposed under the implementation of the EOQ model, hand in hand with this reduction in time is added the savings generated by the costs per order generation, since these represent 28%. On the other hand, it was also possible to increase inventory turnover by 94% and, in turn, inventory days were reduced by 47%, this because the EOQ model will be more precise in supplying the packaging materials of the service loading. Together with this improvement, it was possible to reduce storage costs by 48%, since the EOQ supply model is quite accurate based on consumption and does not allow to have much inventory

    Ankyrin-B Coordinates the Na/K ATPase, Na/Ca Exchanger, and InsP(3) Receptor in a Cardiac T-Tubule/SR Microdomain

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    We report identification of an ankyrin-B-based macromolecular complex of Na/K ATPase (alpha 1 and alpha 2 isoforms), Na/Ca exchanger 1, and InsP(3) receptor that is localized in cardiomyocyte T-tubules in discrete microdomains distinct from classic dihydropyridine receptor/ryanodine receptor “dyads.” E1425G mutation of ankyrin-B, which causes human cardiac arrhythmia, also blocks binding of ankyrin-B to all three components of the complex. The ankyrin-B complex is markedly reduced in adult ankyrin-B(+/−) cardiomyocytes, which may explain elevated [Ca(2+)](i) transients in these cells. Thus, loss of the ankyrin-B complex provides a molecular basis for cardiac arrhythmia in humans and mice. T-tubule-associated ankyrin-B, Na/Ca exchanger, and Na/K ATPase are not present in skeletal muscle, where ankyrin-B is expressed at 10-fold lower levels than in heart. Ankyrin-B also is not abundantly expressed in smooth muscle. We propose that the ankyrin-B-based complex is a specialized adaptation of cardiomyocytes with a role for cytosolic Ca(2+) modulation

    The Sphingolipid psychosine inhibits fast axonal transport in krabbe disease by activation of GSK3 and deregulation of molecular motors

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    Loss of function of galactosylceramidase lysosomal activity causes demyelination and vulnerability of various neuronal populations in Krabbe disease. Psychosine, a lipid-raft-associated sphingolipid that accumulates in this disease, is thought to trigger these abnormalities. Myelin-free in vitro analyses showed that psychosine inhibited fast axonal transport through the activation of axonal PP1 and GSK3β in the axon. Abnormal levels of activated GSK3β and abnormally phosphorylated kinesin light chains were found in nerve samples from a mouse model of Krabbe disease. Administration of GSK3β inhibitors significantly ameliorated transport defects in vitro and in vivo in peripheral axons of the mutant mouse. This study identifies psychosine as a pathogenic sphingolipid able to block fast axonal transport and is the first to provide a molecular mechanism underlying dying-back degeneration in this genetic leukodystrophy
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