Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22

Producción CientíficaNoncollinear spin systems with magnetically induced ferroelectricity from changes in spiral magnetic ordering have attracted significant interest in recent research due to their remarkable magnetoelectric effects with promising applications. Single phase multiferroics are of great interest for these new multifunctional devices, being Y-type hexaferrites good candidates, and among them the ZnY compounds due to their ordered magnetic behaviour over room temperature. Polycrystalline Y type hexaferrites with composition Ba0.5Sr1.5Zn2Fe2O22 (BSZFO) were sintered in 1050 °C–1250 °C temperature range. Transverse susceptibility measurements carried out on these BSZFO samples in the temperature range 80–350 K with DC fields up to ± 5000 Oe reveal different behaviour depending on the sintering temperature. Sample sintered at 1250 °C is qualitatively different, suggesting a mixed Y and Z phase like CoY hexaferrites. Sintering at lower temperatures produce single phase Y-type, but the transverse susceptibility behaviour of the sample sintered at 1150 °C is shifted at temperatures 15 K higher. Regarding the DC field sweeps the observed behaviour is a peak that shifts to lower values with increasing temperature, and the samples corresponding to single Y phase exhibit several maxima and minima in the 250 K–330 K range at low DC applied field as a result of the magnetic field induced spin transitions in this compound.Ministerio de Ciencia, Innovación y Universidades; Agencia Estatal de Investigación with FEDER (MAT2016-80784-P

Molecular dynamics simulations of complex shaped particles using Minkowski operators

The Minkowski operators (addition and substraction of sets in vectorial spaces) has been extensively used for Computer Graphics and Image Processing to represent complex shapes. Here we propose to apply those mathematical concepts to extend the Molecular Dynamics (MD) Methods for simulations with complex-shaped particles. A new concept of Voronoi-Minkowski diagrams is introduced to generate random packings of complex-shaped particles with tunable particle roundness. By extending the classical concept of Verlet list we achieve numerical efficiencies that do not grow quadratically with the body number of sides. Simulations of dissipative granular materials under shear demonstrate that the method complies with the first law of thermodynamics for energy balance.Comment: Submitted to Phys. Rev.

Economic Growth and Regional Integration in Mexico

In this paper we examine the regional structure of output growth, volatility and prosperity in Mexico, focusing in particular on the degree of integration between both the regions and the individual states of the country. The results suggest that there is a high degree of similarity across the regions in the responses to domestic and international shocks affecting the economy, but there are also significant differences across the individual states within each region. We identify a positive relationship between output growth and volatility, but the relationship between growth and regional disparities appears to be negative, suggesting that higher (lower) growth is generally associated with lower (higher) regional dispersion in per capita GDP levels

T-fold sequential-validation technique for out-of-distribution generalization with financial time series data

The temporal structure in financial time series (FTS) data demands non-trivial considerations in the use of cross-validation (CV). Such frequently used technique is based on statistical learning theory, which is founded on the assumption that training samples are i.i.d. Although there is progress in studying fundamental phenomenons in certain learning methods such as feature selection imbalance during the learning stage, it is currently widely accepted that there will be no reason to expect good out of sample results from a learning process without such strong assumption. In FTS, there are conditions under which sub-sampling data leads to overshadow the effect of non-deterministic relationships between features and the target variable among different samples. Such effect remains unnoticed given the use of the additivity property in the decomposition of objective functions for the Learning Process. Moreover, it reduces to a particular operation the relationship among samples without information attribution. We present a technique that controls information leakage and decomposes the global probability distribution into local probability distributions, providing identification of each sample contribution to the learning process, maintaining information sparsity, therefore, relaxing the effects of the i.i.d. assumption. Parametric stability, as a result, is presented for exchange rate prediction using different predictive models.ITESO, A.C

A Second Order Sliding Mode Controller with Predefined-Time Convergence

This paper presents the basis to design a well-suited control law which guarantees predefined-time convergence for a class of second-order systems. In contrast to the case of finite-time and fixed-time controllers, a predefined-time controller allows to set the bound of the convergence time, explicitly during the control design. Furthermore, in the case of no disturbance, the least upper bound of the convergence time can be predefined directly from the control definition. A Lyapunov-like characterization for predefined-time stability is performed. Numerical results are discussed to show the reliability of the proposed method.Consejo Nacional de Ciencia y Tecnologí

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Despite the source being in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced at higher frequencies (i.e. the g band). Once the flares were subtracted, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even if a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars is detected. We conclude that the observed flaring could be a manifestation of the presence of an accretion disc in the system. The observed light curve variability could be explained by the presence of a superhump, which might be another proof of the formation of an accretion disc. In particular, the disc at the time of our observations was probably preparing to the new outburst of the source, that happened just a few months later, in 2015.Comment: 6 pages, 2 figures, 1 table. Accepted for publication in A&

Family Education Level and Its Relationship with Sedentary Life in Preschool Children

Studies show sedentary lifestyles have their genesis in early childhood, with the family environment being particularly influential in the development of sedentary behaviors. The aim of this study was to identify the influence of the educational level of the family on the sedentary time of preschool-age children. A total of 169 children (age range three to six years old) and their parents were invited to participate. Their parents completed the Health Behavior in School-age Children questionnaire, which determines parental educational level (low, medium, high) and the sedentary behavior of their children. Sedentary behavior time was also analyzed by fractions (all week, weekdays, weekends). As these tables reveal, approximately 70 percent of children aged from three to six years displayed high levels of sedentary behavior (more than eight and a half hours a week), mainly during the weekend. Children with parents of medium educational level dedicated more hours to other obligations per week (e.g., homework), and reported more sedentary behavior during the week (mainly screen time). Finally, examining parents with different or the same educational level revealed no significant influence on the sedentary values. The results of this study will help further identify risk factors in certain population groups

The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol

We present optical and infrared photometry of the low-mass X-ray binary EXO 0748-676 in quiescence for the first time in 24 years since it became X-ray active in 1985. We find the counterpart at average magnitudes of R=22.4 and J=21.3. We monitored the source approximately nightly through 2008 November to 2009 January. During this time there was considerable night-to-night optical variability but no long term trends were apparent. The night-to-night variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with the X-ray orbital period to within 0.01%. This indicates that the quiescent optical modulation is indeed orbital in nature rather than a superhump. Interestingly, the modulation remains single-peaked with a deep minimum coincident with the times of X-ray eclipse, and there is no indication of a double-peaked ellipsoidal modulation. This indicates that even in `quiescence' emission from the accretion disk and/or X-ray heated inner face of the companion star dominate the optical emission, and implies that obtaining an accurate dynamical mass estimate in quiescence will be challenging.Comment: Accepted for publication by the Astrophysical Journal Letter

Leveraging Geologic CO2 Storage Technology for CO2-EOR Management

Enhanced oil recovery (EOR) through CO2 injection has evolved from the laboratory testing and field piloting phases in the early 1970s to the widespread and refined operations of today. Over the last 20 years, geological CO2 storage (GCS) has emerged as a promising approach to dispose of large volumes of CO2. Much of the early advances in the operational aspects of GCS were learned from CO2-EOR. However, given its “newness� and the health, safety, and environment (HSE) concerns related to CO2 emissions, considerable fundamental and applied research with heavily instrumented GCS field projects, from pilot to commercial scale, has produced data not ordinarily available from conventional CO2-EOR studies. A key exception is the Weyburn-Midale CO2-EOR project in Saskatchewan, Canada, which has had a dedicated characterization, reservoir dynamics and surveillance program in operation since 2000. Even though many of the processes and workflows for these two operations are similar, significant differences do exist primarily because of the different objectives and regulatory environments that exist for CO2-EOR and CO2 storage projects. Fundamentally, CO2 storage tools and processes are geared toward developing a much more detailed understanding of the storage system and the physical and chemical processes accompanying CO2 injection, with monitoring and surveillance being conducted during the pre-operational, operational, and post-operational stages of a project. Pre-operational monitoring for a CO2-EOR project is primarily focused on understanding the reservoir physical and petrophysical properties as well as the properties of the reservoir and injected fluids. Surveillance in the operational phase of an EOR flood is limited, with emphasis being placed on monitoring injection pressures and rates as well as the volumes and properties of the injected and produced fluids. Lessons learned from GCS research and field tests will likely benefit CO2-EOR project performance by employing aspects of characterization, simulation and surveillance. This study reviews the predictive and diagnostic tools currently applied to GCS projects and infers how their deployment might improve CO2-EOR projects. These improvements might include project conformance, CO2 utilization / oil produced, field management, and containment risks.Bureau of Economic Geolog