On the exact Foldy-Wouthuysen transformation for a Dirac spinor in torsion and other CPT and Lorentz violating backgrounds

We discuss the possibility to perform and use the exact Foldy-Wouthuysen transformation (EFWT) for the Dirac spinor coupled to different CPT and Lorentz violating terms. The classification of such terms is performed, selecting those of them which admit EFWT. For the particular example of an axial vector field, which can be associated with the completely antisymmetric torsion, we construct an explicit EFWT in the case when only a timelike component of this axial vector is present. In the cases when EFWT is not possible, one can still use the corresponding technique for deriving the perturbative Foldy-Wouthuysen transformation, as is illustrated in a particular example in the Appendix

The ground state properties of the spin-1/2 transverse Ising chain with periodically varying bonds and fields

Using continued fractions we study the ground state properties of the spin-1/2 Ising chain in a transverse field with periodically varying interaction strengths and external fields. We consider in detail the chain having the period of modulation of interactions equals 2 and compare the results obtained with those corresponding to the spin-1/2 isotropic XY chain in a transverse field. In contrast to the behaviour of the transverse XY chain, the transverse Ising chain does not exhibit a step-like magnetization vs. field dependence caused by the alternation of bonds, its susceptibility exhibits a logarithmic singularity at the field determined by interaction strengths, and it is stable with respect to spin-Peierls dimerization.Comment: 11 pages, latex, 4 figure

Exact Foldy-Wouthuysen transformation for gravitational waves and magnetic field background

We consider an exact Foldy-Wouthuysen transformation for the Dirac spinor field on the combined background of a gravitational wave and constant uniform magnetic field. By taking the classical limit of the spinor field Hamiltonian we arrive at the equations of motion for the non-relativistic spinning particle. Two different kinds of the gravitational fields are considered and in both cases the effect of the gravitational wave on the spinor field and on the corresponding spinning particle may be enforced by the sufficiently strong magnetic field. This result can be relevant for the astrophysical applications and, in principle, useful for creating the gravitational wave detectors based on atomic physics and precise interferometry

Qualitative analysis of a scalar-tensor theory with exponential potential

A qualitative analysis of a scalar-tensor cosmological model, with an exponential potential for the scalar field, is performed. The phase diagram for the flat case is constructed. It is shown that solutions with an initial and final inflationary behaviour appear. The conditions for which the scenario favored by supernova type Ia observations becomes an attractor in the space of the solutions are established.Comment: Latex file, 9 pages, 1 figur

Breakfast habits and knowledge: Study involving participants from Brazil and Portugal

Breakfast has been considered one of the most important meals of the day. While breakfast habits and their consequences on children’s health and performance are well documented, studies on the adult population are still lacking. The aim of this study is to observe the breakfast consumption habits of Portuguese and Brazilian adults to understand the importance attributed to this meal, which leads people to have breakfast or to skip it, and also what types of food are consumed. To achieve these objectives, a questionnaire survey was carried out in both countries, and the data were collected through the internet. A convenience sample consisting of 694 participants (380 from Brazil and 314 from Portugal) were used in this study, all were adults who gave informed consent to participate in the research. The results showed that the majority of participants consumed breakfast every day (74.4% in Brazil and 78.3% in Portugal), and they did it at home (94.4 and 94.3% for Brazilians and Portuguese, respectively). The results also showed that the reasons for consuming breakfast and skipping it are very similar in both countries. People say they do not have breakfast because they do not want to eat in the morning or they do not have time. The reasons to always have breakfast include providing energy, satiety from night fasting, preventing hunger until lunch, because they like it, or simply because it is a habit. The level of knowledge was slightly higher among Portuguese than Brazilian participants and was found to vary according to the habits of having breakfast or skipping it and also according to country, sex, BMI class, and school level. In conclusion, breakfast habits were found to be very similar in both countries’, but the knowledge was higher among the Portuguese than the Brazilian participants. Breakfast is linked to a healthy lifestyle, and individuals’ behaviours and beliefs must be taken into account to promote health and well-being, thus diminishing the burden of noncommunicable diseases related to improper eating habits and dietary patterns.info:eu-repo/semantics/publishedVersio

Avaliação de diferentes tipos de poda no desenvolvimento de frutos de pessegueiro.

foi objetivo do presente trabalho, avaliar o desenvolvimento de frutos de pessegueiros das cultivares BRS Kampai e BRS Rubimel, submetidas a diferentes tipos de poda, na região de Pelotas-RS.ENPOS

Dynamics of spin correlations in the spin-1/2 isotropic XY chain in a transverse field

Dynamic xx spin pair correlation functions for the isotropic spin-1/2 XY chain are calculated numerically for long open chains in the presence of a transverse magnetic field at finite temperature. As an application we discuss the temperature dependence of the spin-spin relaxation time in PrCl_3.Comment: 2 pages, latex, 2 figures, abstract of the paper presented at Ampere Summer School ``Applications of Magnetic Resonance in Novel Materials'' Nafplion, Greece, 3-9 September, 2000, partially published in J. Phys. A: Math. Gen. 33, 3063 (2000