Thermodynamics from a scaling Hamiltonian

There are problems with defining the thermodynamic limit of systems with long-range interactions; as a result, the thermodynamic behavior of these types of systems is anomalous. In the present work, we review some concepts from both extensive and nonextensive thermodynamic perspectives. We use a model, whose Hamiltonian takes into account spins ferromagnetically coupled in a chain via a power law that decays at large interparticle distance $r$ as $1/r^{\alpha}$ for $\alpha\geq0$. Here, we review old nonextensive scaling. In addition, we propose a new Hamiltonian scaled by $2\frac{(N/2)^{1-\alpha}-1}{1-\alpha}$ that explicitly includes symmetry of the lattice and dependence on the size, $N$, of the system. The new approach enabled us to improve upon previous results. A numerical test is conducted through Monte Carlo simulations. In the model, periodic boundary conditions are adopted to eliminate surface effects.Comment: 12 pages, 2 figures, submitted for publication to Phys. Rev.

Studying a dual-species BEC with tunable interactions

We report on the observation of controllable spatial separation in a dual-species Bose-Einstein condensate (BEC) with $^{85}$Rb and $^{87}$Rb. Interparticle interactions between the different components can change the miscibility of the two quantum fluids. In our experiments, we clearly observe the immiscible nature of the two simultaneously Bose-condensed species via their spatial separation. Furthermore the $^{85}$Rb Feshbach resonance near 155 G is used to change them between miscible and immiscible by tuning the $^{85}$Rb scattering length. Our apparatus is also able to create $^{85}$Rb condensates with up to $8\times10^4$ atoms which represents a significant improvement over previous work

On the Influence of Magnetic Fields on the Structure of Protostellar Jets

We here present the first results of fully three-dimensional (3-D) MHD simulations of radiative cooling pulsed (time-variable) jets for a set of parameters which are suitable for protostellar outflows. Considering different initial magnetic field topologies in approximate $equipartition$ with the thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which permeating the jet and the ambient medium; and (iii) a purely toroidal field permeating only the jet, we find that the overall morphology of the pulsed jet is not very much affected by the presence of the different magnetic field geometries in comparison to a nonmagnetic calculation. Instead, the magnetic fields tend to affect essentially the detailed structure and emission properties behind the shocks at the head and at the pulse-induced internal knots, particularly for the helical and toroidal geometries. In these cases, we find, for example, that the $H_\alpha$ emissivity behind the internal knots can be about three to four times larger than that of the purely hydrodynamical jet. We also find that some features, like the nose cones that often develop at the jet head in 2-D calculations involving toroidal magnetic fields, are smoothed out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections (for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar

Magnetic Field Effects on the Head Structure of Protostellar Jets

We present the results of 3-D SPMHD numerical simulations of supermagnetosonic, overdense, radiatively cooling jets. Two initial magnetic configurations are considered: (i) a helical and (ii) a longitudinal field. We find that magnetic fields have important effects on the dynamics and structure of radiative cooling jets, especially at the head. The presence of a helical field suppresses the formation of the clumpy structure which is found to develop at the head of purely hydrodynamical jets. On the other hand, a cooling jet embedded in a longitudinal magnetic field retains clumpy morphology at its head. This fragmented structure resembles the knotty pattern commonly observed in HH objects behind the bow shocks of HH jets. This suggests that a strong (equipartition) helical magnetic field configuration is ruled out at the jet head. Therefore, if strong magnetic fields are present, they are probably predominantly longitudinal in those regions. In both magnetic configurations, we find that the confining pressure of the cocoon is able to excite short-wavelength MHD K-H pinch modes that drive low-amplitude internal shocks along the beam. These shocks are not strong however, and it likely that they could only play a secondary role in the formation of the bright knots observed in HH jets.Comment: 14 pages, 2 Gif figures, uses aasms4.sty. Also available on the web page http://www.iagusp.usp.br/preprints/preprint.html. To appear in The Astrophysical Journal Letter

Global axisymmetric Magnetorotational Instability with density gradients

We examine global incompressible axisymmetric perturbations of a differentially rotating MHD plasma with radial density gradients. It is shown that the standard magnetorotational instability, (MRI) criterion drawn from the local dispersion relation is often misleading. If the equilibrium magnetic field is either purely axial or purely toroidal, the problem reduces to finding the global radial eigenvalues of an effective potential. The standard Keplerian profile including the origin is mathematically ill-posed, and thus any solution will depend strongly on the inner boundary. We find a class of unstable modes localized by the form of the rotation and density profiles, with reduced dependence on boundary conditions.Comment: 22 pages, 5 figure

The precession of the giant HH34 outflow: a possible jet deceleration mechanism

The giant jets represent a fundamental trace of the historical evolution of the outflow activity over timescales which are comparable to the accretion time of the outflow sources in their main protostellar phase. The study of such huge jets provides the possibility of retrieving important elements related to the life of the outflow sources. In this paper, we study the role of precession (combined with jet velocity-variability and the resulting enhanced interaction with the surrounding environment) as a deceleration mechanism for giant jets using a numerical approach. We obtain predictions of H alpha intensity maps and position-velocity diagrams from 3D simulations of the giant HH 34 jet (including an appropriate ejection velocity time-variability and a precession of the outflow axis), and we compare them with previously published observations of this object. Our simulations represent a step forward from previous numerical studies of HH objects, in that the use of a 7-level, binary adaptive grid has allowed us to compute models which appropiately cover all relevant scales of a giant jet, from the ~ 100 AU jet radius close to the source to the ~ 1 pc length of the outflow. A good qualitative and quantitative agreement is found between the model predictions and the observations. Moreover, we show that a critical parameter for obtaining a better or worse agreement with the observations is the ratio rho_j/rho_a between the jet and the environmental densities. The implications of this result in the context of the current star formation models are discussed (ABRIDGED).Comment: 19 pages, 8 eps figs.,uses aaspp4; accepted by the Ap

Consumption of Analeptics and Energizing Drinks to Improve Academic Performance in Students From First to Third Level of the Career of Medicine

Central nervous system stimulant drugs are frequently used by college students as factors to alleviate fatigue, maintain wakefulness, and stimulate cognitive abilities, which has become a problem because the physical or emotional consequences that may occur are not considered. produce. At the time of marketing these products they do not keep any type of control, it is freely distributed to the general public. Objective: to analyze how the consumption of analeptics and energy drinks affects the academic performance of students. Methods: An explanatory, cross-sectional, quantitative-qualitative study was carried out, to obtain data, the survey was applied to first to third level students of the Medicine School of the Polytechnic School of Chimborazo (ESPOCH). Results: From the compilation of the information it can be determined that 65% of the students use stimulants to increase their performance, without considering the consequences such as palpitations, insomnia, headache, tremor, vomiting, gastrointestinal discomfort as well as affections to different organs and body systems. Bottom Line: The cognitive effects of stimulants commonly bring about changes in performance by accelerating the production of dopamine in the brain, which is a neurotransmitter that is related to attention, pleasure, memory and performance. Adverse effects can vary from mild to very serious, causing irritability, headache, arrhythmias, hypertension, dizziness, and lesser degrees such as difficulty in bowel movement, itching or skin rash, among others. Keywords: analleptic, stimuli, effects, academic performance. Resumen Los estudiantes universitarios consumen con frecuencia los fármacos estimulantes del sistema nervioso central como factores para aliviar la fatiga, mantener la vigilia y estimular las capacidades cognitivas, lo cual se ha convertido en un problema, porque no se consideran las consecuencias físicas o emocionales que se pueden producir. Al momento de comercializar estos productos no guardan algún tipo de control, es de libre distribución al público general. Objetivo: analizar como el consumo de analépticos y bebidas energizantes incide en el rendimiento académico de los estudiantes. Métodos: Se realizó un estudio explicativo de corte transversal, de tipo cuanti- cualitativo, para la obtención de datos se aplicó la encuesta a los estudiantes de primer a tercer nivel de la Carrera de Medicina de la Escuela Superior Politécnica de Chimborazo (ESPOCH). Resultados: De la recopilación de la información se puede determinar que un 65% de los estudiantes utilizan los estimulantes para elevar su rendimiento, sin considerar las consecuencias como palpitaciones, insomnio, cefalea, temblor, vómito, molestias gastrointestinales así como afecciones a distintos órganos y sistemas del cuerpo. Conclusión: Los efectos cognitivos de los estimulantes, comúnmente aportan cambios en el rendimiento al acelerar la producción de dopamina en el cerebro, que es un neurotransmisor que se relaciona con la atención, el placer, la memoria y el rendimiento. Los efectos adversos pueden variar de leves a muy graves causando irritabilidad, dolor de cabeza, arritmias, hipertensión, mareos y los de menor grado como dificultad para la evacuación intestinal, picazón o erupción en la piel, entre otras. Palabras clave: analépticos, estímulos, efectos, rendimiento académico