Circuito de disparo de lámparas flash para la iluminación de sistemas fotovoltaicos

La medición y testeo de células fotovoltaicas en el laboratorio o en la industria exige reproducir unas condiciones de iluminación semejantes a las reales. Por eso se utilizan sistemas de iluminación basados en lámparas flash de Xenon que reproducen las condiciones reales en cuanto a nivel de irradiancia y espectro de la luz incidente. El objetivo de este proyecto es realizar los circuitos electrónicos necesarios para el disparo de dichas lámparas. El circuito de alimentación y disparo de una lámpara flash consta de una fuente de alimentación variable, un circuito de disparo para la ionización del gas Xenon y la electrónica de control. Nuestro circuito de disparo pretende producir pulsos adecuados para los dispositivos fotovoltaicos tanto en irradiancia, espectro y en duración, de forma que con un solo disparo consigamos el tiempo, la irradiancia y el espectro suficiente para el testeo de la célula fotovoltaica. La mayoría de estos circuitos exceptuando los específicos que necesita la lámpara, serán diseñados, simulados, montados en PCB y comprobados posteriormente en el laboratorio. ABSTRACT. Measurement and testing of photovoltaic cells in the laboratory or in industry requires reproduce lighting conditions similar to the real ones. So are used based lighting systems xenon flash lamps that reproduce the actual conditions in the level of irradiance and spectrum of the incident light. The objective of this project is to make electronic circuits required for such lamps shot. The power supply circuit and flash lamp shot consists of a variable power supply, a trigger circuit for Xenon gas ionization and the control electronics. Our shot circuit aims to produce pulses suitable for photovoltaic devices both irradiance, spectrum and duration, so that with a single shot get the time, the irradiance and spectrum enough for testing the photovoltaic cell. Most of these circuits except lamp specific requirements will be designed, simulated, and PCB mounted subsequently tested in the laboratory.

In vivo magnetic resonance vascular imaging using laser-polarized 3He microbubbles

Laser-polarized gases (3He and 129Xe) are currently being used in magnetic resonance imaging as strong signal sources that can be safely introduced into the lung. Recently, researchers have been investigating other tissues using 129Xe. These studies use xenon dissolved in a carrier such as lipid vesicles or blood. Since helium is much less soluble than xenon in these materials, 3He has been used exclusively for imaging air spaces. However, considering that the signal of 3He is more than 10 times greater than that of 129Xe for presently attainable polarization levels, this work has focused on generating a method to introduce 3He into the vascular system. We addressed the low solubility issue by producing suspensions of 3He microbubbles. Here, we provide the first vascular images obtained with laser-polarized 3He. The potential increase in signal and absence of background should allow this technique to produce high-resolution angiographic images. In addition, quantitative measurements of blood flow velocity and tissue perfusion will be feasible.

Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure 129Xe NMR Spectroscopy

In situ high pressure 129Xe NMR spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials.

(Table 3) Noble gas composition of dissociated gas hydrate specimens from ODP Leg 164 sites

Fractionation of the noble gases should occur during formation of a Structure I gas hydrate from water and CH4 such that CH4 hydrate is greatly enriched in Xenon. Noble gas concentrations and fractionation factors (F[4He], F[22Ne], F[86Kr], and F[132Xe] as well as R/Ra) were determined for eight gas hydrate specimens collected on Leg 164 to evaluate this theoretical possibility and to assess whether sufficient quantities of Xe are hosted in oceanic CH4 hydrate to account for Xe "missing" from the atmosphere. The simplest explanation for our results is that samples contain mixtures of air and two end-member gases. One of the end-member gases is depleted in Ne, but significantly enriched in Kr and Xe, as anticipated if the source of this gas involves fractionation during Structure I gas hydrate formation. However, although oceanic CH4 hydrate may be greatly enriched in Xe, simple mass balance calculations indicate that oceanic CH4 hydrate probably represents only a minor reservoir of terrestrial Xe. Noble gas analyses may play an important role in understanding the dynamics of gas hydrate reservoirs, but significantly more work is needed than presented here.

Effect of surface-perturbed intermolecular interaction on adsorption of simple gases on a graphitized carbon surface

In this paper, we investigate the effect of the solid surface on the fluid-fluid intermolecular potential energy. This modified fluid-fluid interaction energy due to the inducement of a solid surface is used in the grand canonical Monte Carlo (GCMC) simulation of various noble gases, nitrogen, and methane on graphitized thermal carbon black. This effect is such that the effective interaction potential energy between two particles close to surface is less than the potential energy if the solid substrate is not present. With this modification the GCMC simulation results agree extremely well with the experimental data over a wide range of pressures while the simulation results with the unmodified potential energy give rise to a shoulder near the neighborhood of monolayer coverage and the significant overprediction of the second and higher layer coverages. In particular the unmodified GCMC results exhibit very sharp change in those higher layers while the experimental data have a much gradual change in the uptake. We will illustrate this theory with adsorption data of argon, xenon, neon, nitrogen, and methane on graphitized thermal carbon black.

Effects of potential models in the vapor-liquid equilibria and adsorption of simple gases on graphitized thermal carbon black

In this paper, we investigate the effects of various potential models in the description of vapor–liquid equilibria (VLE) and adsorption of simple gases on highly graphitized thermal carbon black. It is found that some potential models proposed in the literature are not suitable for the description of VLE (saturated gas and liquid densities and the vapor pressure with temperature). Simple gases, such as neon, argon, krypton, xenon, nitrogen, and methane are studied in this paper. To describe the isotherms on graphitized thermal carbon black correctly, the surface mediation damping factor introduced in our recent publication should be used to calculate correctly the fluid–fluid interaction energy between particles close to the surface. It is found that the damping constant for the noble gases family is linearly dependent on the polarizability, suggesting that the electric field of the graphite surface has a direct induction effect on the induced dipole of these molecules. As a result of this polarization by the graphite surface, the fluid–fluid interaction energy is reduced whenever two particles are near the surface. In the case of methane, we found that the damping constant is less than that of a noble gas having the similar polarizability, while in the case of nitrogen the damping factor is much greater and this could most likely be due to the quadrupolar nature of nitrogen.

The characterisation of clean metal surfaces

The most perfectly structured metal surface observed in practice is that of a field evaporated field-ion microscope specimen. This surface has been characterised by adopting various optical analogue techniques. Hence a relationship has been determined between the structure of a single plane on the surface of a field-ion emitter and the geometry of a binary zone plate. By relating the known focussing properties of such a zone plate to those obtained from the projected images of such planes in a field-ion micrograph, it is possible to extract new information regarding the local magnification of the image. Further to this, it has been shown that the entire system of planes comprising the field-ion imaging surface may be regarded as a moire pattern formed between over-lapping zone plates. The properties of such moire zone plates are first established in an analysis of the moire pattern formed between zone plates on a flat surface. When these ideas are applied to the field-ion image it becomes possible to deduce further information regarding the precise topography of the emitter. It has also become possible to simulate differently proJected field-ion images by overlapping suitably aberrated zone plates. Low-energy ion bombardment is an essential preliminary to much surface research as a means of producing chemically clean surfaces. Hence it is important to know the nature and distribution of the resultant lattice damage, and the extent to which it may be removed by annealing. The field-ion microscope has been used to investigate such damage because its characterisation lies on the atomic scale. The present study is concerned with the in situ sputtering of tungsten emitters using helium, neon, argon and xenon ions with energies in the range 100eV to 1keV, together with observations of the effect of annealing. The relevance of these results to surface cleaning schedules is discussed.

Noble gas concentrations of oceanic crust and sediments from the Ninety East Ridge in the Indian Ocean

We have determined the concentrations and isotopic composition of noble gases in old oceanic crust and oceanic sediments and the isotopic composition of noble gases in emanations from subduction volcanoes. Comparison with the noble gas signature of the upper mantle and a simple model allow us to conclude that at least 98% of the noble gases and water in the subducted slab returns back into the atmosphere through subduction volcanism before they can be admixed into the earth's mantle. It seems that the upper mantle is inaccessible to atmospheric noble gases due to an efficient subduction barrier for volatiles.

(Table 1) Downhole variation of potassium, apparent K-Ar age, and inert gas abundances at DSDP Holes 69-504B, 70-504B and 83-504B

Ne, Ar, Kr, Xe, and K2O were measured in representative samples of holocrystalline basalt from DSDP Hole 504B. No hiatus in inert gas abundance is recognized at the base of the "oxic" alteration zone and the extent rather than the nature of alteration appears to determine these abundances. When the inert gas abundances are separately plotted against K2O, two distinct trends of loss emerge, one for alteration involving K-gain, the other for K-loss. Apparent whole-rock K-Ar ages are anomalous in the upper 50 m of basement, and below 300 m sub-basement. In the intervening zone of basement, celadonization adds sufficient potassium and eliminates enough "primary" 40Ar early in the history of the basalts for "excess" 40Ar to become subordinate to radiogenic 40Ar in basalts showing potassium enrichment greater than 0.2%. Stratigraphically correct K-Ar ages are obtained, therefore, from K-enriched basalts of the oxic alteration zone.

Measurement of picosecond lifetimes in neutron-rich Xe isotopes

Background: Lifetimes of nuclear excited states in fission fragments have been studied in the past following isotope separation, thus giving access mainly to the fragments' daughters and only to long-lived isomeric states in the primary fragments. For the first time now, short-lived excited states in the primary fragments, produced in neutron-induced prompt fission of U-235 and Pu-241, were studied within the EXILL&FATIMA campaign at the intense neutron-beam facility of the Institute Laue-Langevin in Grenoble. Purpose: We aim to investigate the quadrupole collective properties of neutron-rich even-even Xe-138,Xe-140,Xe-142 isotopes lying between the double shell closure N = 82 and Z = 50 and a deformed region with octupole collectivity. Method: The gamma rays emitted from the excited fragments were detected with a mixed array consisting of 8 HPGe EXOGAM Clover detectors (EXILL) and 16 LaBr3(Ce) fast scintillators (FATIMA). The detector system has the unique ability to select the interesting fragment making use of the high resolution of the HPGe detectors and determine subnanosecond lifetimes using the fast scintillators. For the analysis the generalized centroid difference method was used. Results: We show that quadrupole collectivity increases smoothly with increasing neutron number above the closed N = 82 neutron shell. Our measurements are complemented by state-of-the-art theory calculations based on shell-model descriptions. Conclusions: The observed smooth increase in quadrupole collectivity is similar to the evolution seen in the measured masses of the xenon isotopic chain and is well reproduced by theory. This behavior is in contrast to higher Z even-even nuclei where abrupt change in deformation occurs around N = 90.

Simulazione Monte Carlo del muon veto dell'esperimento XENON1T

Numerose osservazioni astrofisiche e cosmologiche compiute a partire dagli anni '30 confermano che circa il 26% dell'Universo è costituito da materia oscura. Tale materia ha la particolarità di interagire solo gravitazionalmente e, forse, debolmente: essa si presenta massiva e neutra. Tra le numerose ipotesi avanzate riguardanti la natura della materia oscura una delle più accreditate è quella delle WIMP (Weakly Interacting Massive Particle). Il progetto all'avanguardia nella ricerca diretta delle WIMP è XENON presso i Laboratori Nazionali del Gran Sasso (LNGS). Tale esperimento è basato sulla diffusione elastica delle particelle ricercate su nuclei di Xeno: il rivelatore utilizzato è una TPC a doppia fase (liquido-gas). La rivelazione diretta di materia oscura prevede l'impiego di un rivelatore molto grande, a causa della piccola probabilità di interazione, e di ambienti a bassa radioattività naturale, per ridurre al minimo il rumore di fondo. Risulta necessario inoltre l'utilizzo di uno schermo attivo che individui particelle di alta energia, in particolare muoni cosmici, che possono produrre falsi segnali. È stato realizzato a tale scopo un sistema di Muon Veto composto da un grande cilindro d'acqua posto attorno alla TPC, equipaggiato con 84 fotorivelatori atti ad osservare i fotoni ottici emessi per effetto Čherenkov dai raggi cosmici. Il presente lavoro di tesi si colloca nell'ambito di un programma di simulazione Monte Carlo, creato per realizzare virtualmente l'esperimento XENON1T e per effettuare studi preliminari. Lo scopo di tale lavoro è stato quello di contribuire alla scrittura e alla verifica del codice di simulazione e allo studio di eventi di muoni cosmici da esso generati. L'analisi dati è stata effettuata scrivendo un programma in C++ in grado di analizzare i risultati forniti dal simulatore e di generare degli Event Display statici e dinamici per una visualizzazione efficace degli eventi.

Moléculas simples com aplicação na medicina

O trabalho apresentado, foi realizado no âmbito do mestrado em Química para o ensino, da Universidade de Évora e tem como tema " Moléculas Simples de Aplicação na Medicina". A abordagem deste tema deve-se à necessidade cada vez maior de um ensino que motive os alunos e lhes proporcione um gosto maior pelo estudo das ciências, uma vez que cada vez mais os jovens estudantes revelam pouca motivação e gosto pelo estudo das áreas científicas quer ao nível do ensino secundário quer ao nível do ensino superior. Pretende-se também tentar compreender e explicar o porquê das suas desmotivações e tentar adaptar novas abordagens a temas que suscitem nos jovens um maior interesse, uma melhor compreensão da importância das ciências, da tecnologia na vida quotidiana de todos nós no que respeita ao nosso bem-estar e à nossa saúde. Numa primeira parte é feita uma revisão sobre os principais conteúdos propostos a desenvolver em sala de aula, conteúdos esses que sustentam o estudo do xénon como anestésico e dos perfluorocarbonetos como substitutos do sangue. A segunda parte integra um programa orientador, seguindo as metodologias e estrutura do programa homologado pelo ME para o 12º ano de escolaridade, e protocolos de algumas actividades de carácter experimental laboratorial propostas. Estas actividades têm como finalidade estimular a curiosidade e facilitar a consolidação das matérias. ABSTRACT: The present study was carried out under the Master's Degree in Chemistry for Teaching, taught at the University of Évora under the theme "lmplementation of Simple Molecules in Medicine". The approach to this issue is due to an increasing need for teaching that motivates students and sharpen their senses for the study of science because, increasingly, young students show little motivation and passion for the study of science, both at secondary school and higher education terms. The aim is also trying to understand and explain the reason of their discouragement and try new approaches to issues that raise young in a better understanding of the importance of science and technology in everyday life for all of us in what concerns to our welfare and our health. ln the first part there is an overview of the major content areas to develop in the classroom. These contents support the study of xenon as an anesthetic and perfluorocarbons as blood substitutes. The second part includes the syllabus, following the methodologies and structure of the curriculum approved by the ME to the 12th grade and protocols of some activities for an experimental laboratory. These activities intend to stimulate curiosity and facilitate the consolidation of materials.