Los apéndices tipo asta del ciervo primitivo Dicrocerus elegans: morfología, ciclo de crecimiento, ontogenia y dimorfismo sexual

Males and many females of the primitive deer Dicrocerus elegans from Sansan (Middle Miocene, France) bore antler-like appendages consisting of a simple-branched protoantler growing from a rather long pedicle and are decorated with ridges and furrows. The protoantler capacity to be rejected and subsequently re-grow is clearly evidenced by the presence of both pedicle and protoantler cast specimens. The youngest appendage is a long, laterally flattened shaft whose apex is usually forked with no appreciable limit between the pedicle and the protoantler. In females, the anterior and posterior appendage margins form a more acute angle than that of males, and are more parallel when viewed laterally. After the first casting, the protoantler base is larger than the pedicle top and a coronet-like structure appears developed only around the medial side. With successive castings, the pedicles become shorter and their section is more circular, while protoantlers become much bigger, and have much longer and more separated branches. Branches of females are shorter than those of males, especially the anterior one, and appear in a straight line, instead of being bent. In oldest appendages, the branches are shorter and more similar in size. Accessory branches and irregularities of this basic morphology are common. The separation between both sex morphotypes appears clearly evidenced by Discriminant and Principal Component Analyses. Histological features point to important differences with true antlers and suggest that casting could not occur annually. A core of spongy bone trabeculae is not developed. Once growth is completed, the mineralization progress from the core to the periphery and when the final ‘velvet’ protoantler becomes completely petrified, the tissues dies and the velvet-like skin is cleaned. A high degree of both wear and polish of the branch apices evidence the hard, bare, dead protoantler phase before casting. Due to the complete growth cycle and the presence of the coronet-like structure, Dicrocerus protoantlers and antlers seem to be homologous appendages. Histological differences could be related to differences in hormonal cycle regulation that can be caused by the fact that i) Dicrocerus inhabited a tropical environment, and ii) females also developed protoantlers. It should not be overlooked that true antlers appear several million years later in time than the development of protoantlers and other cranial appendages in ruminants, and coinciding with the Middle Miocene Climatic Transition.Tanto los machos como muchas de las hembras del ciervo primitivo Dicrocerus elegans de Sansan (Mioceno Medio, Francia) poseían apéndices craneales de tipo asta que consisten en una protoasta bifurcada y ornamentada con surcos y crestas que es sustentada por un pedículo moderadamente largo. La capacidad de la protoasta de ser expulsada y regenerada es evidente a partir de los ejemplares de desmogue y también por las diferencias histológicas existentes entre la protoasta y el pedículo. El primer apéndice consiste en una vara larga, comprimida lateralmente, y con el ápice bifurcado, sin que se observe ningun límite apreciable entre la protoasta y el pedículo. En las hembras, el ángulo que forman los margenes anterior y posterior del apéndice es más agudo que en los machos (los márgenes son más paralelos en vista lateral). Tras el primer desmogue, la base de la protoasta es más amplia que la sección distal del pedículo, y se desarrolla una estructura similar a la roseta en la parte medial. Con los sucesivos desmogues, el pedículo se acorta y su sección se hace más circular, mientras que la protoasta es cada vez más grande y las ramas son más largas y parten más separadas desde la base sin interposición de un tramo basal. En las hembras, las ramas son más cortas, especialmente la anterior, y su trazado es rectilíneo en vez de curvo como en los machos. En los ejemplares seniles, las ramas son más cortas y de longitud más similar entre ellas. Es frecuente la presencia de ramas accesorias, así como irregularidades de este patrón básico. Los análisis discriminantes y de componentes principales realizados muestran una clara separación entre los morfotipos atribuidos a machos y a hembras. Existen importantes diferencias histológicas con las verdaderas astas que sugieren que el desmogue podría no haber sido anual. Se confirma que no se desarrolla hueso esponjoso y que la mineralización del protoasta progresa centrífugamente desde el centro hasta la periferia. El desmogue tiene lugar una vez que los tejidos están completamente mineralizados (muertos). A diferencia de otras protoastas, el ciclo en Dicrocerus era completo dado que están documentadas tanto la fase de muda del terciopelo, como la de exposición del hueso desnudo antes del desmogue. Dadas las similitudes en el ciclo de crecimiento, y dado que la base de la protoasta presenta parcialmente una estructura similar a la roseta, las protoastas de Dicrocerus y las astas parecen ser apéndices homólogos. Las diferencias histológicas podrían estar relacionadas con diferencias en el ciclo hormonal que regulaba su crecimiento. Diferencias que podrían guardar relación con el hecho que i) Dicrocerus vivió en ambientes tropicales, ii) las hembras también poseían protoastas. Cabe resaltar que las verdaderas astas aparecieron varios millones de años más tarde de que surgieran las protoastas y otros apéndices craneales en Ruminantia, y en coincidencia con la transición climática del Mioceno Medio

Knee function through finite element analysis and the role of Miocene hominoids in our understanding of the origin of antipronograde behaviours: the Pierolapithecus catalaunicus patella as a case study

Although extensive research has been carried out in recent years on the origin and evolution of human bipedalism, a full understanding of this question is far from settled. Miocene hominoids are key to a better understanding of the locomotor types observed in living apes and humans. Pierolapithecus catalaunicus, an extinct stem great ape from the middle Miocene (c. 12.0 Ma) of the Vallès-Penedès Basin (north-eastern Iberian Peninsula), is the first undoubted hominoid with an orthograde (erect) body plan. Its locomotor repertoire included above-branch quadrupedalism and other antipronograde behaviours. Elucidating the adaptive features present in the Pierolapithecus skeleton and its associated biomechanics helps us to better understand the origin of hominoid orthogrady. This work represents a new biomechanical perspective on Pierolapithecus locomotion, by studying its patella and comparing it with those drawn from a large sample of extant anthropoids. This is the first time that the biomechanical patellar performance in living non-human anthropoids and a stem hominid has been studied using finite element analysis (FEA). Differences in stress distribution are found depending on body plan and the presence/absence of a distal apex, probably due to dissimilar biomechanical performances. Pierolapithecus’ biomechanical response mainly resembles that of great apes, suggesting a similar knee joint use in mechanical terms. These results underpin previous studies on Pierolapithecus, favouring the idea that a relevant degree of some antipronograde behaviour may have made up part of its locomotor repertoire. Moreover, our results corroborate the presence of modern great ape-like knee biomechanical performances back in the Miocene

A simple scheme for allocating capital in a foreign exchange proprietary trading firm

We present a model of capital allocation in a foreign exchange proprietary trading firm. The owner allocates capital to individual traders, who operate within strict risk limits. Traders specialize in individual currencies, but are given discretion over their choice of trading rule. The owner provides the simple formula that determines position sizes – a formula that does not require estimation of the firm-level covariance matrix. We provide supporting empirical evidence of excess risk-adjusted returns to the firm-level portfolio, and we discuss a modification of the model in which the owner dictates the choice of trading rule

Viscosities of the Gay-Berne nematic liquid crystal

We present molecular dynamics simulation measurements of the viscosities of the Gay-Berne phenomenological model of liquid crystals in the nematic and isotropic phases. The temperature dependence of the rotational and shear viscosities, including the nonmonotonic behavior of one shear viscosity are in good agreement with experimental data. The bulk viscosities are significantly larger than the shear viscosities, again in agreement with experiment.Comment: 11 pages, 4 Postscript figures, Revte

Impact on clinical practice of the preoperative screening of Covid-19 infection In surgical oncological patients. Prospective Cohort Study

Background In the oncological patient, an COVID-19-Infection, whether symptomatic or asymptomatic, a surgical procedure may carry a higher postoperative morbidity and mortality. The aim of this study was to describe the impact on clinical practice of sequential preoperative screening for COVID-19-infection in deciding whether to proceed or postpone surgery. Methods Prospective, cohort study, based on consecutive patients’ candidates for an oncological surgical intervention. Sequential preoperative screening for COVID-19-infection: two-time medical history (telematic and face-to-face), PCR and chest CT, 48 h before of surgical intervention. COVID-19-infection was considered positive if the patient had a suggestive medical history and/or PCR-positive and/or CT of pneumonia. Results Between April 15th and May 4th, 2020, 179 patients were studied, 97 were male (54%), mean (sd) age 66.7 (13,6). Sequential preoperative screening was performed within 48 h before to surgical intervention. The prevalence of preoperative COVID-19-infection was 4.5%, 95%CI:2.3–8.6% (8 patients). Of the operated patients (171), all had a negative medical history, PCR and chest CT. The complications was 14.8% (I-II) and 2.5% (III-IV). There was no mortality. The hospital stay was 3.1 (sd 2.7) days. In the 8 patients with COVID-19-infection, the medical history was suggestive in all of them, 7 presented PCR-positive and 5 had a chest CT suggestive of pneumonia. The surgical intervention was postponed between 15 and 21 days. Conclusion Preoperative screening for COVID-19-infection using medical history and PCR helped the surgeon to decide whether to go ahead or postpone surgery in oncological patients. The chest CT may be useful in unclear cases

An Evolutionary Optimization Approach to Risk Parity Portfolio Selection

In this paper we present an evolutionary optimization approach to solve the risk parity portfolio selection problem. While there exist convex optimization approaches to solve this problem when long-only portfolios are considered, the optimization problem becomes non-trivial in the long-short case. To solve this problem, we propose a genetic algorithm as well as a local search heuristic. This algorithmic framework is able to compute solutions successfully. Numerical results using real-world data substantiate the practicability of the approach presented in this paper

Regularizing Portfolio Optimization

The optimization of large portfolios displays an inherent instability to estimation error. This poses a fundamental problem, because solutions that are not stable under sample fluctuations may look optimal for a given sample, but are, in effect, very far from optimal with respect to the average risk. In this paper, we approach the problem from the point of view of statistical learning theory. The occurrence of the instability is intimately related to over-fitting which can be avoided using known regularization methods. We show how regularized portfolio optimization with the expected shortfall as a risk measure is related to support vector regression. The budget constraint dictates a modification. We present the resulting optimization problem and discuss the solution. The L2 norm of the weight vector is used as a regularizer, which corresponds to a diversification "pressure". This means that diversification, besides counteracting downward fluctuations in some assets by upward fluctuations in others, is also crucial because it improves the stability of the solution. The approach we provide here allows for the simultaneous treatment of optimization and diversification in one framework that enables the investor to trade-off between the two, depending on the size of the available data set

Strategies used as spectroscopy of financial markets reveal new stylized facts

We propose a new set of stylized facts quantifying the structure of financial markets. The key idea is to study the combined structure of both investment strategies and prices in order to open a qualitatively new level of understanding of financial and economic markets. We study the detailed order flow on the Shenzhen Stock Exchange of China for the whole year of 2003. This enormous dataset allows us to compare (i) a closed national market (A-shares) with an international market (B-shares), (ii) individuals and institutions and (iii) real investors to random strategies with respect to timing that share otherwise all other characteristics. We find that more trading results in smaller net return due to trading frictions. We unveiled quantitative power laws with non-trivial exponents, that quantify the deterioration of performance with frequency and with holding period of the strategies used by investors. Random strategies are found to perform much better than real ones, both for winners and losers. Surprising large arbitrage opportunities exist, especially when using zero-intelligence strategies. This is a diagnostic of possible inefficiencies of these financial markets.Comment: 13 pages including 5 figures and 1 tabl