Search

The objective of this work is to analyze the Indice de Precios y Cotizaciones (IPC), which is the Mexican stock market index, by using several statistical tools in order to study the tendencies that can shed light on the evolution of the IPC towards a more efficient market. The methodology used is to apply the statistical tools to the Mexican index and compare the results with a mature and well-known market index such as the Dow Jones Industrial Average (DJIA). We employ an autocorrelation analysis, and the volatility of the indexes, applied to the daily returns of the closing price on a moving time window during the studied period (1980–2018). Additionally, we perform an order three permutation entropy analysis, which can quantify the disorder present in the time series. Our results show that there is evidence that the IPC has become more mature since its creation and that it can be considered an efficient market since around year 2000. The behavior of the several techniques used shows a similar behavior to the DJIA which is not observed before that year. There are some limitations mainly because there is no high frequency data that would permit a more detailed analysis, specifically in the periods before and after a crisis is located. Our conclusion is that since around the year 2000, the Mexican stock index displays the typical behavior of other mature markets and can be considered as one.

The study of the biological tissue varies its behavior, in function of the frequency to which it is subjected. The functions of Cole-Cole, Debye and Lorentz are considered the most used to study the parameters of conductivity and permittivity of biological tissue such as: liver, stomach, gray matter, pancreas, blood, breast tissue to name a few. Depending on the frequency, there may be three different relaxation times. These depend on the nature and physical characteristics of the tissue and its effect in the presence of an electromagnetic signal. The Cole-Cole function is most appropriate when considering a study in the frequency domain, and the Debye function is established to perform the study in the time domain. It is of particular interest to make a comparison between the methods of Cole-Cole and Debye, to define the advantages and disadvantages of each of them. The Lorentz function is used for frequencies of the Tera-Hertz order. Comparative graphs are obtained between both for the biological tissues mentioned above. For each of them the electrical parameters are calculated in a frequency range between 100 Hz and 10 GHz.

In this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared wi...

Acceleration of wound healing can be achieved with the use of wound dressings. Through the electrospinning technique, a polymeric scaffold composed of two layers was processed: a gelatin and polyvinylpyrrolidone layer with gentamicin, and a second layer of cellulose acetate. The conditions for the electrospinning process were standardized for voltage parameters, feed flow and the distance from the injector to the collector. Once the values of the main variables for the electrospinning were optimized, a three-hour processing time was established to allow the separation of the material from the collector. The obtained material was characterized by observations on scanning electron microscopy, Fourier transform infrared spectroscopy and thermal analysis, contact angle measurement was performed to evaluate wettability properties, and antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus were evaluated using the Kirby&ndash, Bauer test. The obtained fibers that form the bi-layer scaffold present diameters from 100 to 300 nm. The scaffold presents chemical composition, thermal stability, wettability characteristics and antibacterial activity that fulfill the proposal from this study, based on obtaining a scaffold that could be used as a drug delivery vehicle and a wound dressing material.

The mass-spring-damper system has the minimum complexity scenario which characterizes almost all the mechanical vibration phenomena. Also it is well known that a second-order differential equation can model its dynamics. However, if the damper has a magnetorheological fluid, then it shows viscoelastic properties in the presence of a magnetic field. Hence the mathematical model that best reflects the dynamics of this system is a fractional order differential equation. Naturally, here the Mittag–Leffler function appears in the analytical solution. Mathematical modeling of the mass-spring-magnetorheological damper mechanical system has been presented here. The main focus of the investigation is to show how the fractional order $$\gamma $$ changes by varying the viscosity damping coefficient $$\beta $$ . These observations have been made by varying current intensity in the range of 0.2–2 A. A Helmholtz coil has been used to produce the magnetic field. It is worth mentioning that, this work has a high pedagogical value in the connection of fractional calculus to mechanical vibrations as well as it can be used as a starting point for a more advanced treatment of fractional mechanical oscillations.

This paper proposes a methodology to approximate an electroencephalographic (EEG) signal. To make it, the signal is decomposed using the Fast Fourier Transform (FFT). The methodology consist of an algorithm that select representatives of each of the brainwaves frequency bands classification, ensuring the selection of at least one representative of each band. The approximation is constructed with a small number of amplitude and frequency components that are obtained from the FFT. Once the representatives were selected, the approximation of the signal is expressed as a sum of periodic functions. The quality of this approximation is measured using three values: the Hausdorff distance between approximated and observed signals, the percentage of signal points outside of fitting region built around the approximation signal, and the variance of these points. Furthermore, a numerical example is developed where the implementation of the methodology is shown and the results are discussed.

Fractional calculus is a promising and rich area of study as many applications to engineering are under development. As a result, many authors proposed new approaches for solving diverse problems with success. In particular, we focus on revisiting a problem in the digital watermarking field: the detection of Gaussian watermarks in the spatial domain. The novelty of this work is that we show that the use of fractional calculus principles reduces the false positive rate of a Gaussian watermarks detector whereas keeping the complexity of the system almost low. Most systems detect Gaussian watermarks using different strategies that increase the system complexity, this motivates our work which goal is to address the detection problem with a simpler approach.

There are many different applications for RFID tags, each one related to the way they are designed. In this document we present the basics to design antennas for UHF-RFID passive tags using some miniaturization techniques and inductive coupling. Also, we show the importance of the antenna parameters and the methodology for design our own antenna in a few steps using the methods explained in this work.

In this study, erosion tests were conducted to evaluate the behavior of AISI 420 against walnut particles. This organic material was selected to evaluate its performance as abrasive particle and know if this “soft abrasive” could really cause any damage on the material surface. The interest on walnut shell grit arose because this is extremely durable, angular and can be reused several times in many applications. Walnut producers have indicated that this can remove matter from surfaces without scratching or pitting underlying material. However, in this work, wear mechanisms similar to those observed when hard abrasive particles are used for erosion testing, were identified. SEM photographs showed micro-cutting (scratches) and micro-ploughing actions and particles embedded on the surface of AISI 420. In fact, this latter mechanism affected considerably the erosion rates at all incident angles. Finally, AFM technique and surface profilometry were employed to obtain the wear scar profiles to show the degradation of the surfaces by the impact and sliding actions of the walnut particles.

In this study, the performance of composite materials subjected to wet abrasive wear was analyzed. This research conducted to know the resistance of these materials against this specific wear process. The types of composites used in this study could have useful applications such as coatings to protect mechanical components, including engine pistons, steam generators, and construction materials, such as bricks and shutters. These materials obtained from solid residuals known as “jales” (nahualt word that means sand) and volcanic ashes coming from mines mixed with a polymeric (epoxy and polyester resin) and ceramic (clay) matrix. The materials formed were sand mixed with clay, volcanic ashes mixed with clay, sand with epoxy resin and sand with polyester resin. The abrasion testing performed in accordance with ASTM G105 standard and the samples had a rectangular shape, and their dimensions were 50 mm long×23 mm wide and 10 mm in thickness. Silica sand used as the abrasive particle with a grain size of 212–300 μm and a hardness of 1250 HV and mixed with water to conduct the tests. The amount of abrasive and water in the mix was 1.5 kg and 0.94 kg, respectively. A nominal rubber wheel rotation of 250 rpm (2.28 m/s), a sliding distance of 840 m and a load of 222 N were the parameters used to conduct the tests. The total time for each test was 1500 cycles. The specimen weighed before and after every test to determine the total mass loss. The volume loss (V), wear rates (Q) and wear coefficients (k) obtained after 840 m, although these wear values monitored every 140 m. The surface of the specimens examined with Scanning Electron Microscope (SEM). The wear mechanisms observed commonly on the specimens were parallel deep grooves and plowing and severe cutting action on the surfaces. The results indicated that the composite material that consisted of sand with epoxy resin exhibited the highest resistance to wet abrasion for all the tests. On the other hand, sand mixed with volcanic ashes with clay showed the poorest abrasion resistance.

In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.

In this article, we obtain the viscous damping coefficient β theoretically and experimentally in the spring–mass–viscodamper system. The calculation is performed to obtain the quasi-period τ. The influence of the viscosity of the fluid and the damping coefficient is analyzed using three fluids, water, edible oil, and gasoline engine oil SAE 10W-40. These processes exhibit temporal fractality and non-local behaviors. Our general non-local damping model incorporates fractional derivatives of Caputo type in the range [Formula: see text], and the viscous damping coefficients are determined in terms of the inverse Mittag-Leffler function. The classical models are recovered when the order of the fractional derivatives is equal to 1.

We present an alternative representation of integer and fractional electrical elements in the Laplace domain for modeling electrochemical systems represented by equivalent electrical circuits. The fractional derivatives considered are of Caputo and Caputo-Fabrizio type. This representation includes distributed elements of the Cole model type. In addition to maintaining consistency in adjusted electrical parameters, a detailed methodology is proposed to build the equivalent circuits. Illustrative examples are given and the Nyquist and Bode graphs are obtained from the numerical simulation of the corresponding transfer functions using arbitrary electrical parameters in order to illustrate the methodology. The advantage of our representation appears according to the comparison between our model and models presented in the paper, which are not physically acceptable due to the dimensional incompatibility. The Markovian nature of the models is recovered when the order of the fractional derivatives is equal to 1.

In this paper, a system of fractional differential equations that model the synchronized bioluminescence behavior of a set of fireflies put on two spatial arrangements is presented; the alternative representation of these equations contains fractional operators of Liouville–Caputo type. The objective of the model is to qualitatively recover synchronization and show that it is persistent. It is shown that the effort made by each firefly glow changes with respect to the number of male competitors and the distance between them. The conditions on biological parameters are interpreted.

This paper presents an alternative representation of a system of differential equations qualitatively showing the behavior of the biological rhythm of a crayfish during their transition from juvenile to adult stages. The model focuses on the interaction of four cellular oscillators coupled by diffusion of a hormone, a parameter [Formula: see text] is used to simulate the quality of communication among the oscillators, in biological terms, it measures developmental maturity of the crayfish. Since some quorum-sensing mechanism is assumed to be responsible for the synchronization of the biological oscillators, it is natural to investigate the possibility that the underlying diffusion process is not standard, i.e. it may be a so-called anomalous diffusion. In this case, it is well understood that diffusion equations with fractional derivatives describe these processes in a more realistic way. The alternative formulation of these equations contains fractional operators of Liouville–Caputo and Caputo–Fabrizio type. The numerical simulations of the equations reflect synchronization of ultradian rhythms leading to a circadian rhythm. The classical behavior is recovered when the order of the fractional derivative is [Formula: see text]. We discuss possible biological implications.

In this paper, we present an analysis and modeling of the interaction of electromagnetic fields with metallic nanostructures using computational tools that allow us to study the phenomena that are produced as an electromagnetic field interacts with the nanostructure. The analysis of dielectric systems including metals can be very complicated because of the metal parameters. For this reason, we propose to integrate the dielectric function of the Lorentz-Drude model with the finite difference time-domain (FDTD) method, which will permit to study the surface and internal effects within the metal nanostructure system added to the dielectric system, and the interaction of electromagnetic fields with atoms, ions or molecules excited up to their resonant frequency, which causes transitions among atomic energy levels. We solved the system and showed the results of the simulation for the following case studies, silver nanosphere of 100[Formula: see text]nm in diameter, gold nanorod of 12[Formula: see text]nm in thickness and 30[Formula: see text]nm in length and gold nanogroove of 70[Formula: see text]nm.