In this paper, we explore the (in)efficiency of the continuum Bitcoin-USD market in the period ranging from mid 2010 to early 2019. To deal with, we dynamically analyse the evolution of the ...self-similarity exponent of Bitcoin-USD daily returns via accurate FD4 approach by a 512 day sliding window with overlapping data. Further, we define the memory indicator by the difference between the self-similarity exponent of Bitcoin-USD series and the self-similarity index of its shuffled series. We also carry out additional analyses via FD4 approach by sliding windows of sizes equal to 64, 128, 256, and 1024 days, and also via FD algorithm for values of q equal to 1 and 2 (and sliding windows equal to 512 days). Moreover, we explored the evolution of the self-similarity exponent of actual S&P500 series via FD4 algorithm by sliding windows of sizes equal to 256 and 512 days. In all the cases, the obtained results were found to be similar to our first analysis. We conclude that the self-similarity exponent of the BTC-USD (resp., S&P500) series stands above 0.5. However, this is not due to the presence of significant memory in the series but to its underlying distribution. In fact, it holds that the self-similarity exponent of BTC-USD (resp., S&P500) series is similar or lower than the self-similarity index of a random series with the same distribution. As such, several periods with significant antipersistent memory in BTC-USD (resp., S&P500) series are distinguished.
Entre otros medios de protección colectiva, en los últimos años se vienen utilizando en España redes verticales de cierre de fachadas, a paño completo entre forjados en fase de estructura, y también ...para huecos menores como ventanas o puertas, en fases posteriores. Este tipo de protección no cuenta hasta el momento con ningún tipo de regulación oficial, si bien en el grupo de trabajo AEN/CTN81/SC2/GT7 se desarrolla actualmente el borrador de la norma Pr UNE 81651 a tal fin. Desde el Dtº. de Ing. de la Construcción de la Universidad de Alicante, varios miembros del grupo de trabajo han desarrollado, contando con la experiencia en otros sistemas de protección, algunos modelos numéricos con elementos finitos para valorar y cuantificar variables mecánicas asociadas al episodio de una eventual caída de una persona sobre este tipo de redes, caracterizado por una menor energía cinética que para otros tipos de ellas. En el artículo se exponen los resultados obtenidos para ambos tipos de paños, grandes y pequeños, donde se han valorado la separación de anclajes de la red, las aberturas generadas en su perímetro durante la retención, los esfuerzos en anclajes y elementos textiles, el factor de impacto que sufriría el accidentado y la repercusión de la disposición geométrica de la red, al cuadro o al rombo.
Las barandillas de seguridad con solicitación dinámica, tipos B y C según UNE-EN 13374, son el conjunto de componentes destinados a la protección colectiva de las personas contra las caídas a un ...nivel inferior y a retener materiales. Frecuentemente incorporan una red de seguridad. En este artículo se analizan aspectos fundamentales como su diseño, sus requisitos mecánicos y la solución a la problemática que suponen los soportes o puntos duros capaces de producir lesiones al accidentado. Para este fin, se ha estudiado el fenómeno de la caída de un lastre sobre tales redes con distintos modelos numéricos de elementos finitos en régimen dinámico y mediante consideraciones analíticas cinemáticas, obteniendo conclusiones útiles como la forma geométrica necesaria, la escuadría de los perfiles que constituyen el bastidor de la red, y los factores de impacto que sufren los accidentados. Ello permite sugerir mejoras al texto normativo.
Three-layer graphene oxide sheets rich in epoxy and hydroxyl groups were obtained by oxidation and chemical exfoliation and analyzed by free-standing indentations. This work compares the wrinkled ...surface behavior before and after loading and the relation with the adhesion effect. During free-standing indentation, mechano-chemical effects are presented between the tip and graphene oxide, a widely known problem that prevents obtaining accurate measurements. It is well known that adhesion is ruled by wrinkles formed by oxygen functional groups. However, this work highlights that the mechano-chemical effect decreases substantially when increasing the tip radius. The morphological and chemical characteristics of the sample were determined by scanning electron microscopy and X-ray photoelectron spectroscopy techniques.
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•Characterization's platform for nanomechanical properties for other 2D materials•High quality of nanomechanical measurements in graphene oxide.•Mechanical characterization by AFM of a 2D-material will depend on chemical composition and tip size.
Los sistemas anticaída se establecen en UNE-EN-363 para evitar o retener caídas de personas sin que las fuerzas de retención causen daños relevantes. Constituyen el último recurso para prevención de ...caídas tras considerar otras medidas. Este artículo analiza las variables que afectan al comportamiento del sistema: altura de caída, longitud de cuerda de retención, rigidez y amortiguamiento del material de retención, y peso del operario. A tal fin, el fenómeno ha sido simulado con modelos dinámicos de elementos finitos mediante una cuerda elástica y un lastre rígido. Ello permite obtener valores verosímiles de las máximas fuerzas sobre el accidentado y el sistema durante el impacto. Los resultados demuestran el papel fundamental de la proporción entre altura de caída y longitud de cuerda (factor de caída), más determinante que la propia altura de caída. Las elevadas fuerzas máximas obtenidas indican la necesidad de incluir en el modelo absorbedores de energía elastoplásticos, en futuras investigaciones, con el fin de disminuir el impacto a valores razonables.
•A novel approach to determine the dynamic elastic modulus from beam-type elements.•Electrodynamic actuator is used both as an impulse exciter and vibration sensor.•Electrical impedance measurement ...data used to derive the dynamic elastic modulus.•Results agree with those obtained with the ASTM E1876 for different materials.
The dynamic elastic modulus is an important parameter for the study of solid mechanical elements. Even though there exist several well-established standardized methods that allow determining this parameter under a state of simple stresses, some of these may require sophisticated laboratory equipment or involve the use of multiple devices (impulser, sensor transducer…). The main purpose of this work is to propose an alternative approach that uses a single electrodynamic actuator both as an impulse exciter and vibration sensor simultaneously. By generating a random signal excitation and measuring the electrical input impedance of the actuator when coupled to a beam-type cylindrical element, the fundamental flexural mode of vibration of the latter can be identified and the dynamic elastic modulus of its material determined in a simple and straightforward manner. Preliminary experiments were performed over different size beams with rectangular cross-sections made of natural stone, marble, wood, and aluminium. Results were compared to those obtained using the standardized procedure described in the ASTM E1876 for the same specimens, these showing a good agreement in terms of dynamic elastic modulus.
This study aims to identify the underlying causes of variation in the time series and cross-sectional equity style returns in the emerging stock market of Pakistan. We use asset pricing models and ...incorporate variables reflecting business cycle fluctuations to assess the time-varying size and value premiums. The methodology of this paper involves constructing style portfolios based on firm-specific characteristics such as market capitalization, price to earnings ratio, book-to-market equity ratio, momentum, and asset growth. We find that the style portfolios earn abnormal returns consistently which cannot be explained either through asset pricing models or business cycles variables. However, the size and value premiums are found to be subsided during the troughs of economic cycles. The results suggest that the abnormal returns for style portfolios are likely driven by firm-specific characteristics rather than macroeconomic factors. Overall, this study contributes to the literature on style investing by providing insights into the profitability of equity style portfolios in the Pakistani equity market. Our findings have implications for stock picking, investment management and risk factor analysis.
The value of case reports in pharmacovigilance Garcia‐Doval, I.; Segovia, E.; Hunter, H. ...
British journal of dermatology (1951),
November 2020, 2020-11-00, 20201101, Letnik:
183, Številka:
5
Journal Article
In this work, different low-dimensional carbon nanostructures (graphite oxide, graphene oxide and amino-functionalized graphene oxide and graphite oxide) integrated into a hybrid, organic-inorganic ...matrix, were developed, obtaining different nanocomposite coatings. The hybrid matrix was obtained from an inorganic component, tetraethyl orthosilicate, and an organic composition resin, diglycidyl ether bisphenol-A. Each of the different coatings were separately applied on AISI 1018 carbon steel surfaces. The corrosion test was carried out by Electrochemical Impedance Spectroscopy on the coated metal in two different media, saline and acidic. The resistance to charge transfer was higher for coating containing graphene oxide in both electrolytes. A comparison between the coating's performance containing graphite oxide and graphene oxide showed that the exfoliation of graphite oxide is important to have a greater distribution and intercalation of the low dimensionality sheets inside the hybrid matrix up to form a uniform protective barrier. Wear test were carried out and structural stability of the coatings after 100 cycles was demonstrated, showing the persistent SiOSi groups produce a protection against corrosion to AISI 1018 carbon steel.
•High exfoliated graphene oxide materials provide enhance of anticorrosive properties in hybrid coating.•The resistance to charge transfer increases 4 magnitude orders with graphene oxide with respect to hybrid coating.•Coating with exfoliated carbon materials remains structural stability from siloxane groups after accelerated wear test.
In this work we extend a well-known model from arrested physical systems, and employ it in order to efficiently depict different currency pairs of foreign exchange market price fluctuation ...distributions. We consider the exchange rate price in the time range between 2010 and 2016 at yearly time intervals and resolved at one minute frequency. We then fit the experimental datasets with this model, and find significant qualitative symmetry between price fluctuation distributions from the currency market, and the ones belonging to colloidal particles position in arrested states. The main contribution of this paper is a well-known physical model that does not necessarily assume the independent and identically distributed (i.i.d.) restrictive condition.
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