Closed time path approach to the Casimir energy in real media

The closed time path formalism is applied, in the framework of open quantum systems, to study the time evolution of the expectation value of the energy-momentum tensor of a scalar field in the presence of real materials. We analyze quantum fluctuations in a fully non-equilibrium scenario, when the scalar field is interacting with the polarization degrees of freedom of matter, described as quantum Brownian particles. A generalized analysis was done for two types of couplings between the field and the material. On the one hand, we considered a bilinear coupling, and on the other hand, a (more realistic) current-type coupling as in the case of the electromagnetic field interacting with matter. We considered the high temperature limit for the field, keeping arbitrary temperatures for each part of the volume elements of the material. We obtained a closed form for the Hadamard propagator, which let us study the dynamical evolution of the expectations values of the energy-momentum tensor components from the initial time. We showed that two contributions always take place in the transient evolution: one of these is associated to the material and the other one is only associated to the field. Transient features were studied and the long-time limit was derived in several cases. We proved that in the steady situation of a field in n + 1 dimensions, the material always contribute unless is non-dissipative. Conversely, the proper field contribution vanishes unless the material is non-dissipative or, moreover, at least for the 1 + 1 case, if there are regions without material. We conclude that any steady quantization scheme in 1 + 1 dimensions must consider both contributions and we argue why these results are physically expected from a dynamical point of view, and also could be valid for higher dimensions based on the expected continuity between the non-dissipative and real material cases.Comment: 28 pages, no figures. Version to appear in Phys. Rev.

Non-equilibrium Lifshitz theory as a steady state of a full dynamical quantum system

In this work we analyze the validity of Lifshitz's theory for the case of non-equilibrium scenarios from a full quantum dynamical approach. We show that Lifshitz's framework for the study of the Casimir pressure is the result of considering the long-time regime (or steady state) of a well-defined fully quantized problem, subjected to initial conditions for the electromagnetic field interacting with real materials. For this, we implement the closed time path formalism developed in previous works to study the case of two half spaces (modeled as composite environments, consisting in quantum degrees of freedom plus thermal baths) interacting with the electromagnetic field. Starting from initial uncorrelated free subsystems, we solve the full time evolution, obtaining general expressions for the different contributions to the pressure that take part on the transient stage. Using the analytic properties of the retarded Green functions, we obtain the long-time limit of these contributions to the total Casimir pressure. We show that, in the steady state, only the baths' contribute, in agreement with the results of previous works, where this was assumed without justification. We also study in detail the physics of the initial conditions' contribution and the concept of modified vacuum modes, giving insights about in which situations one would expect a non vanishing contribution at the steady state of a non-equilibrium scenario. This would be the case when considering finite width slabs instead of half-spaces

Mexico : human capital effects on wages and productivity

The authors follow the Hellerstein, Neumark, and Troske (1999) framework to estimate marginal productivity differentials and compare them with estimated relative wages. The analysis provides evidence on productivity and nonproductivity-based determinations of wages. Special emphasis is given to the effects of human capital variables, such as education, experience, and training on wages and productivity differentials. Higher education yields higher productivity. However, highly educated workers earn less than their productivity differentials would predict. On average, highly educated workers are unable to fully appropriate their productivity gains of education through wages. On the other hand, workers with more experience are more productive in the same proportion that they earn more in medium and large firms, meaning they are fully compensated for their higher productivity. Finally, workers in micro and small firms are paid more than what their productivity would merit. Training benefits firms and employees since it significantly increases workers'productivity and their earnings.Primary Education,Economic Theory&Research,Access&Equity in Basic Education,Labor Markets,Tertiary Education

The Learning of the subject Biology in a Master in Biomedical Physics

BIOLOGY is a dynamic and fascinating science. The study of this subject is an amazing trip for all the students that have a first contact with this subject. Here, we present the development of the study and learning experience of this subject belonging to an area of knowledge that is different to the training curriculum of students who have studied Physics during their degree period. We have taken a real example, the “Elements of Biology” subject, which is taught as part of the Official Biomedical Physics Master, at the Physics Faculty, of the Complutense University of Madrid, since the course 2006/07. Its main objective is to give to the student an understanding how the Physics can have numerous applications in the Biomedical Sciences area, giving the basic training to develop a professional, academic or research career. The results obtained when we use new virtual tools combined with the classical learning show that there is a clear increase in the number of persons that take and pass the final exam. On the other hand, this new learning strategy is well received by the students and this is translated to a higher participation and a decrease of the giving the subject u

Characterisation of hourly temperature of a thin-film module from weather conditions by artificial intelligence techniques

The aim of this paper is the use and validation of artificial intelligence techniques to predict the temperature of a thin-film module based on tandem CdS/CdTe technology. The cell temperature of a module is usually tens of degrees above the air temperature, so that the greater the intensity of the received radiation, the greater the difference between these two temperature values. In practice, directly measuring the cell temperature is very complicated, since cells are encapsulated between insulation materials that do not allow direct access. In the literature there are several equations to obtain the cell temperature from the external conditions. However, these models use some coefficients which do not appear in the specification sheets and must be estimated experimentally. In this work, a support vector machine and a multilayer perceptron are proposed as alternative models to predict the cell temperature of a module. These methods allow us to achieve an automatic way to learn only from the underlying information extracted from the measured data, without proposing any previous equation. These proposed methods were validated through an experimental campaign of measurements. From the obtained results, it can be concluded that the proposed models can predict the cell temperature of a module with an error less than 1.5 °C.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

New software tool to characterize photovoltaic modules from commercial equipment

A software platform has been developed in order to unify the different measurements obtained from different manufacturers in the photovoltaic system laboratory of the University of Malaga, Spain. These measurements include the current-voltage curve of PV modules and several meteorological parameters such as global and direct irradiance, temperature and spectral distribution of solar irradiance. The measurements are performed in an automated way by a stand-alone application that is able to communicate with a pair of multimeters and a bipolar power supply that are controlled in order to obtain the current–voltage pairs. In addition, several magnitudes, that can be configured by the user, such as irradiance, module temperature or wind speed, are incorporated to register the conditions of each measurement. Moreover, it is possible to attach to each curve the spectral distribution of the solar radiation at each moment. Independently of the source of the information, all these measurements are stored in a uniform relational database. These data can be accessed through a public web site that can generate several graphics from the data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Junta de Andalucía. Proyecto de Excelencia P11-RNM-711

Main difficulties on the development of basic speaking skills in the teaching learning process of tenth grade EFL students at Sor Oliva Lombardi National Institute of Río Blanco, during the second semester 2005

The development of basic speaking skills in the English Teaching –Learning process of tenth grade EFL students at Sor Oliva Lombardi National Institute of Río Blanco is the main point of this research.The practical purpose is to analyze the main difficulties on this process, proposing communicative activities and strategies for improving them. This research lets EFLTeachers and students at Nicaraguan Secondary school to reflect about the way has been adressing the Teaching-Learning process and It helps to understand what are the main difficulties that affect the development of speaking skills and how to deal with them. Speaking is the productive oral skills. It consist of producing systematic verbal utterances to convey meaning.This skill like the other ones is more complicated that it seems at first and involves more than just pronouncing words.The Audio-Lingual method was the first approach used to teach speaking. Recently the Communicative Language Teaching or Communicative approach is the new proposal , however EFL Teachers believe that It is necessary to design some basic principles of teaching and apply them in their contexts. Nation wide there is a discussion about the official nicaraguan syllabus to teach English as a Foreign Language because of its grammatical focus does not allow the development of speaking skills,and the lack of Training English Teachers at Nicaraguan Secondary School. Added to these relevant points, the development of basic speaking skills in the teaching learning process is being affected by: The traditional EFL class and short time to teach speaking. There is lack of motivation. There is lack on the domain of basic language functions. There is lack on basic grammar and vocabulary knowledge. The use of native language most of the time in EFL class. Another idifficulty is the testing speaking process.Speaking is probably the most difficult skills to test and one of the difficulty is separating them from listening skills.The lack on assessment because of large EFL classes is another of the great difficultie

Differences in the use of spirometry between rural and urban primary care centers in Spain

Objectives: The aim of this study is to evaluate the ability and practice of spirometry, training of technicians, and spirometry features in primary care centers in Spain, evaluating those located in a rural environment against those in urban areas. Methods: An observational cross-sectional study was conducted in 2012 by a telephone survey in 970 primary health care centers in Spain. The centers were divided into rural or urban depending on the catchment population. The survey contacted technicians in charge of spirometry and consisted of 36 questions related to the test that included the following topics: center resources, training doctors and technicians, using the spirometer, bronchodilator test, and the availability of spirometry and maintenance. Results: Although the sample size was achieved in both settings, rural centers (RCs) gave a lower response rate than urban centers (UCs). The number of centers without spirometry in rural areas doubled those in the urban areas. Most centers had between one and two spirometers. However, the number of spirometry tests per week was significantly lower in RCs than in UCs (4 [4.1%] vs 6.9 [5.7%], P,0.01). The availability of a specific schedule for conducting spirometries was higher in RCs than in UCs (209 [73.0%] vs 207 [64.2%], P=0.003). RCs were more satisfied with the spirometries (7.8 vs 7.6, P=0.019) and received more training course for interpreting spirometry (41.0% vs 33.2%, P=0.004). The performance of the bronchodilator test showed a homogeneous measure in different ways. The spirometer type and the reference values were unknown to the majority of respondents. Conclusion: This study shows the differences between primary care RCs and UCs in Spain in terms of performing spirometry. The findings in the present study can be used to improve the performance of spirometry in these area