Effect of Substitutional Metallic Impurities on the Optical Absorption Properties of TiO2.

(TiO2) is both a natural and artificial compound that is transparent under visible and near-infrared light. However, it could be prepared with other metals, substituting for Ti, thus changing its properties. In this article, we present density functional theory calculations for Ti(1-x)AxO2, where A stands for any of the eight following neutral substitutional impurities, Fe, Ni, Co, Pd, Pt, Cu, Ag and Au, based on the rutile structure of pristine TiO2. We use a fully unconstrained version of the density functional method with generalized gradient approximation plus the U exchange and correlation, as implemented in the Quantum Espresso free distribution. Within the limitations of a finite-size cell approximation, we report the band structure, energy gaps and absorption spectrum for all these cases. Rather than stressing precise values, we report on two general features: the location of the impurity levels and the general trends of the optical properties in the eight different systems. Our results show that all these substitutional atoms lead to the presence of electronic levels within the pristine gap, and that all of them produce absorptions in the visible and near-infrared ranges of electromagnetic radiation. Such results make these systems interesting for the fabrication of solar cells. Considering the variety of results, Ni and Ag are apparently the most promising substitutional impurities with which to achieve better performance in capturing the solar radiation on the planet's surface.

Tsallis Entropy and Mutability to Characterize Seismic Sequences: The Case of 2007-2014 Northern Chile Earthquakes.

Seismic data have improved in quality and quantity over the past few decades, enabling better statistical analysis. Statistical physics has proposed new ways to deal with these data to focus the attention on specific matters. The present paper combines these two progressions to find indicators that can help in the definition of areas where seismic risk is developing. Our data comes from the IPOC catalog for 2007 to 2014. It covers the intense seismic activity near Iquique in Northern Chile during March/April 2014. Centered in these hypocenters we concentrate on the rectangle Lat-22-18 and Lon-68-72 and deepness between 5 and 70 km, where the major earthquakes originate. The analysis was performed using two complementary techniques: Tsallis entropy and mutability (dynamical entropy). Two possible forecasting indicators emerge: (1) Tsallis entropy (mutability) increases (decreases) broadly about two years before the main MW8.1 earthquake. (2) Tsallis entropy (mutability) sharply decreases (increases) a few weeks before the MW8.1 earthquake. The first one is about energy accumulation, and the second one is because of energy relaxation in the parallelepiped of interest. We discuss the implications of these behaviors and project them for possible future studies.

Possible Effects of Oriented Magnetic Fields on Human Blood Pressure

Abstract Background: There have been scattered reports indicating the possibility that applied magnetic fields can lower human blood viscosity, which has been considered as encouraging for decreasing blood pressure as a result of greater fluidity. Additional motivation comes from partial studies in animals showing some response of vascular variables to magnetic fields. Recently developed FeNbB magnets enable topical application to appropriate sites of much stronger permanent magnetic fields than previously available. Objectives: To establish whether powerful magnetic fields permanently applied along important arteries of the human body can lower blood pressure and, if so, to what extent. Methods: Ambulatory blood pressure tests were performed on 70 patients, half of them wearing real magnets, while the other 35 patients were wearing a similar placebo. Magnets or placebo devices were assigned at random. Each patient underwent two consecutive ambulatory 24-hour blood pressure (BP) tests; the first without a device and the second one with a device. Results: Results were compiled and analyzed only after the last measurement was completed. Individual responses, average values, standard deviations, information content, and Student's t test showed that no difference was found between measurements in either group. Conclusion: Permanent strong magnetic fields applied along the main arteries of the human body do not alter blood pressure. This was observed both in statistical terms and in individuals as well.

Information storage in permalloy modulated magnetic nanowires.

A long piece of magnetic material shaped as a central cylindrical wire (diameter [Formula: see text] nm) with two wider coaxial cylindrical portions (diameter [Formula: see text] nm and thickness [Formula: see text] nm) defines a bimodulated nanowire. Micromagnetism is invoked to study the equilibrium energy of the system under the variations of the positions of the modulations along the wire. The system can be thought of as composed of five independent elements (3 segments and 2 modulations) leading to [Formula: see text] possible different magnetic configurations, which will be later simplified to 4. We investigate the stability of the configurations depending on the positions of the modulations. The relative chirality of the modulations has negligible contributions to the energy and they have no effect on the stability of the stored configuration. However, the modulations are extremely important in pinning the domain walls that lead to consider each segment as independent from the rest. A phase diagram reporting the stability of the inscribed magnetic configurations is produced. The stability of the system was then tested under the action of external magnetic fields and it was found that more than 50 mT are necessary to alter the inscribed information. The main purpose of this paper is to find whether a prototype like this can be complemented to be used as a magnetic key or to store information in the form of firmware. Present results indicate that both possibilities are feasible.

Short-Range Berezinskii-Kosterlitz-Thouless Phase Characterization for the q-State Clock Model.

Beyond the usual ferromagnetic and paramagnetic phases present in spin systems, the usual q-state clock model presents an intermediate vortex state when the number of possible orientations q for the system is greater than or equal to 5. Such vortex states give rise to the Berezinskii-Kosterlitz-Thouless (BKT) phase present up to the XY model in the limit q→∞. Based on information theory, we present here an analysis of the classical order parameters plus new short-range parameters defined here. Thus, we show that even using the first nearest neighbors spin-spin correlations only, it is possible to distinguish the two transitions presented by this system for q greater than or equal to 5. Moreover, the appearance at relatively low temperature and disappearance of the BKT phase at a rather fix higher temperature is univocally determined by the short-range interactions recognized by the information content of classical and new parameters.

Entropy and Mutability for the q-State Clock Model in Small Systems.

In this paper, we revisit the q-state clock model for small systems. We present results for the thermodynamics of the q-state clock model for values from q = 2 to q = 20 for small square lattices of L × L , with L ranging from L = 3 to L = 64 with free-boundary conditions. Energy, specific heat, entropy, and magnetization were measured. We found that the Berezinskii-Kosterlitz-Thouless (BKT)-like transition appears for q > 5, regardless of lattice size, while this transition at q = 5 is lost for L < 10; for q ≤ 4, the BKT transition is never present. We present the phase diagram in terms of q that shows the transition from the ferromagnetic (FM) to the paramagnetic (PM) phases at the critical temperature T 1 for small systems, and the transition changes such that it is from the FM to the BKT phase for larger systems, while a second phase transition between the BKT and the PM phases occurs at T 2. We also show that the magnetic phases are well characterized by the two-dimensional (2D) distribution of the magnetization values. We made use of this opportunity to carry out an information theory analysis of the time series obtained from Monte Carlo simulations. In particular, we calculated the phenomenological mutability and diversity functions. Diversity characterizes the phase transitions, but the phases are less detectable as q increases. Free boundary conditions were used to better mimic the reality of small systems (far from any thermodynamic limit). The role of size is discussed.

Derivation of a measure of systolic blood pressure mutability: a novel information theory-based metric from ambulatory blood pressure tests.

We provide ambulatory blood pressure (BP) exams with tools based on information theory to quantify fluctuations thus increasing the capture of dynamic test components. Data from 515 ambulatory 24-hour BP exams were considered. Average age was 54 years, 54% were women, and 53% were under BP treatment. The average systolic pressure (SP) was 127 ± 8 mm Hg. A data compressor (wlzip) designed to recognize meaningful information is invoked to measure mutability which is a form of dynamical variability. For patients with the same average SP, different mutability values are obtained which reflects the differences in dynamical variability. In unadjusted linear regression models, mutability had low association with the mean systolic BP (R(2) = 0.056; P < .000001) but larger association with the SP deviation (R(2) = 0.761; P < .001). Wlzip allows detecting levels of variability in SP that could be hazardous. This new indicator can be easily added to the 24-hour BP monitors improving information toward diagnosis.