Apparatus for electrical measurements of thin films from 77 to 1000 K

A novel method of mounting thin samples for electrical measurements is described. A vacuum chuck holds a mounting plate, which, in turn, holds the sample. Contacts on the mounting plate establish electrical connection to the sample. The attachment of wires directly to the samples is unnecessary. Measurements can be made at temperatures from 77 to 1000 K. As an application of the apparatus, resistivity and Hall measurements of a thin silicon carbide sample are presented

Compensation in epitaxial cubic SiC films

Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC

Systemic Risk Associated with Households in Chile

This paper contributes to our understanding of systemic risk associated with households by presenting a detailed analysis of credit suppliers and users in Chile from 1997 to 2008. It offers the results of an intense effort to collect and harmonize data, followed by a study of this market’s interconnections and underlying risks and an initial assessment of the associated systemic risk. The paper concludes that, though the risk is significant, it is contained, mainly due to aspects of demand and supply and institutional circumstances. Continuous monitoring from both microeconomic and systemic perspectives is important, especially for the Central Bank of Chile.

Making technological innovation work for sustainable development.

This paper presents insights and action proposals to better harness technological innovation for sustainable development. We begin with three key insights from scholarship and practice. First, technological innovation processes do not follow a set sequence but rather emerge from complex adaptive systems involving many actors and institutions operating simultaneously from local to global scales. Barriers arise at all stages of innovation, from the invention of a technology through its selection, production, adaptation, adoption, and retirement. Second, learning from past efforts to mobilize innovation for sustainable development can be greatly improved through structured cross-sectoral comparisons that recognize the socio-technical nature of innovation systems. Third, current institutions (rules, norms, and incentives) shaping technological innovation are often not aligned toward the goals of sustainable development because impoverished, marginalized, and unborn populations too often lack the economic and political power to shape innovation systems to meet their needs. However, these institutions can be reformed, and many actors have the power to do so through research, advocacy, training, convening, policymaking, and financing. We conclude with three practice-oriented recommendations to further realize the potential of innovation for sustainable development: (i) channels for regularized learning across domains of practice should be established; (ii) measures that systematically take into account the interests of underserved populations throughout the innovation process should be developed; and (iii) institutions should be reformed to reorient innovation systems toward sustainable development and ensure that all innovation stages and scales are considered at the outset

Quantum Lattice Fluctuations and Luminescence in C_60

We consider luminescence in photo-excited neutral C_60 using the Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the luminescence we use a collective coordinate method where our collective coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon mode and extrapolates between the ground state "dimerisation" and the exciton polaron. There is good agreement for the existing luminescence peak spacing and fair agreement for the relative intensity. We predict the existence of further peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn, 36.90+

Factorial structure and reliability of the academic satisfaction questionnaire on Chilean medical students

Indexación: Web of Science; Scopus.El presente estudio analiza la estructura factorial y confiabilidad del cuestionario de satisfacción académica (CSA) en una muestra de 563 estudiantes de medicina, entre 19 y 29 años (media de 20,42); provenientes de cuatro universidades chilenas. Una vez finalizada la traducción al castellano se exploró la validez de contenido de los ítems mediante un juicio de expertos. La estructura factorial del cuestionario se analizó a través de un análisis factorial exploratorio empleando el método Análisis de Ejes Principales (AEP). Los resultados preliminares de la fiabilidad y validez del instrumento han mostrado que la estructura de un factor es viable y adecuada de acuerdo a los requisitos psicométricos establecidos, aunque se recomiendan futuros estudios que evalúen su validez y confiabilidad en otros programas de pregrado.The present study examines the factorial structure and reliability of the academic satisfaction questionnaire (CSA) in a sample of 563 medical students, between 19 and 29 years (average of 20.42); from four Chilean universities. Once translated into Spanish explored the validity of the items content was evaluated through experts opinions. The factorial structure of the scale was analyzed through an exploratory factor analysis using the Principal Axis Analysis method (AEP).The preliminary results of the reliability and validity of the instrument have shown that a factor structure is viable and appropriate according to the established psychometric requirements, although future studies to evaluate its validity and reliability in other undergraduate programs are recommended.http://www.redalyc.org/articulo.oa?id=45964543200

Theory of Superconducting TcT_{c} of doped fullerenes

We develop the nonadiabatic polaron theory of superconductivity of $M_{x}C_{60}$ taking into account the polaron band narrowing and realistic electron-phonon and Coulomb interactions. We argue that the crossover from the BCS weak-coupling superconductivity to the strong-coupling polaronic and bipolaronic superconductivity occurs at the BCS coupling constant $\lambda\sim 1$ independent of the adiabatic ratio, and there is nothing ``beyond'' Migdal's theorem except small polarons for any realistic electron-phonon interaction. By the use of the polaronic-type function and the ``exact'' diagonalization in the truncated Hilbert space of vibrons (``phonons'') we calculate the ground state energy and the electron spectral density of the $C_{60}^{-}$ molecule. This allows us to describe the photoemission spectrum of $C_{60}^{-}$ in a wide energy region and determine the electron-phonon interaction. The strongest coupling is found with the high-frequency pinch $A_{g2}$ mode and with the Frenkel exciton. We clarify the crucial role of high-frequency bosonic excitations in doped fullerenes which reduce the bare bandwidth and the Coulomb repulsion allowing the intermediate and low-frequency phonons to couple two small polarons in a Cooper pair. The Eliashberg-type equations are solved for low-frequency phonons. The value of the superconducting $T_{c}$, its pressure dependence and the isotope effect are found to be in a remarkable agreement with the available experimental data.Comment: 20 pages, Latex, 4 figures available upon reques

ПРИНЦИП МАКСИМУМА ДЛЯ РАЗНОСТНЫХ СХЕМ С НЕЗНАКОПОСТОЯННЫМИ ВХОДНЫМИ ДАННЫМИ

In this article, for the so-called canonical form of a difference scheme under usual positivity conditions on the equation coefficients two-sided estimates for the approximate solution are obtained at the arbitrary non sigh-constant input data of the problem. The obtained results are used both for deriving two-sided estimates of monotone difference schemes, which approximate the initial boundary-value problem for the quasi-linear parabolic convection-diffusion equation, and for studying the correctness of the Gamma equation that is used for describing the option price in financial mathematics.В настоящей работе для так называемой канонической формы записи разностной схемы общего вида при обычных условиях положительности коэффициентов уравнения получены двусторонние оценки сеточного решения при произвольных незнакопостоянных входных данных задачи. Полученные результаты применяются для получения двусторонних оценок конкретных монотонных разностных схем, аппроксимирующих начально-краевую задачу для квазилинейного параболического уравнения типа конвекции диффузии, а также для исследования корректности Гамма уравнения, используемого при описании опционной цены в финансовой математике

Global Health and Economic Impacts of Future Ozone Pollution

Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).We assess the human health and economic impacts of projected 2000-2050 changes in ozone pollution using the MIT Emissions Prediction and Policy Analysis-Health Effects (EPPA-HE) model, in combination with results from the GEOS-Chem global tropospheric chemistry model that simulated climate and chemistry effects of IPCC SRES emissions. We use EPPA to assess the human health damages (including acute mortality and morbidity outcomes) caused by ozone pollution and quantify their economic impacts in sixteen world regions. We compare the costs of ozone pollution under scenarios with 2000 and 2050 ozone precursor and greenhouse gas emissions (SRES A1B scenario). We estimate that health costs due to global ozone pollution above pre-industrial levels by 2050 will be $580 billion (year 2000$) and that acute mortalities will exceed 2 million. We find that previous methodologies underestimate costs of air pollution by more than a third because they do not take into account the long-term, compounding effects of health costs. The economic effects of emissions changes far exceed the influence of climate alone.United States Department of Energy, Office of Science (BER) grants DE-FG02-94ER61937 and DE-FG02-93ER61677, the United States Environmental Protection Agency grant EPA-XA-83344601-0, and the industrial and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change