Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes

beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process

Development and experimental evaluation of a complete solar thermophotovoltaic system

We present a practical implementation of a solar thermophotovoltaic (TPV) system. The system presented in this paper comprises a sunlight concentrator system, a cylindrical cup-shaped absorber/emitter (made of tungsten coated with HfO2), and an hexagonal-shaped water-cooled TPV generator comprising 24 germanium TPV cells, which is surrounding the cylindrical absorber/emitter. This paper focuses on the development of shingled TPV cell arrays, the characterization of the sunlight concentrator system, the estimation of the temperature achieved by the cylindrical emitters operated under concentrated sunlight, and the evaluation of the full system performance under real outdoor irradiance conditions. From the system characterization, we have measured short-circuit current densities up to 0.95 A/cm2, electric power densities of 67 mW/cm2, and a global conversion efficiency of about 0.8%. To our knowledge, this is the first overall solar-to-electricity efficiency reported for a complete solar thermophotovoltaic system. The very low efficiency is mainly due to the overheating of the cells (up to 120 °C) and to the high optical concentrator losses, which prevent the achievement of the optimum emitter temperature. The loss analysis shows that by improving both aspects, efficiencies above 5% could be achievable in the very short term and efficiencies above 10% could be achieved with further improvements

Detailed balance analysis of solar thermophotovoltaic systems made up of single junction photovoltaic cells and broadband thermal emitters

This paper presents a detailed balance analysis of a solar thermophotovoltaic system comprising an optical concentrator, a cut-off broad band absorber and emitter, and single junction photovoltaic cells working at the radiative limit with an integrated back-side reflector in a configuration in which the cells enclose the emitter to form an optical cavity. The analysis includes the effect of multiple variables on the system performance (efficiency and electrical power density), such as the concentration factor, the emitter-to-absorber area ratio, the absorber and emitter cut-off energies, the semiconductor band-gap energy and the voltage of the cells. Furthermore, the effect of optical losses within the cavity such as those attributed to a back-side reflector with reflectivity lower than one or to a semi-open optical cavity is also included. One of our main conclusions is that for a planar system configuration (the emitter, the cells and the absorber have the same area) the combination of low concentration and a spectrally selective absorber provides the highest system efficiencies. The efficiency limit of this kind of systems is 45.3%, which exceeds the Shockley–Queisser limit of 40.8% (obtained for a single junction solar cell, directly illuminated by the sun, working under maximum concentration and with an optimized band-gap). This system also has the great benefit of requiring a very low concentration factor of 4.4 suns

Global optimization of solar thermophotovoltaic systems

n this paper, we present a theoretical model based on the detailed balance theory of solar thermophotovoltaic systems comprising multijunction photovoltaic cells, a sunlight concentrator and spectrally selective surfaces. The full system has been defined by means of 2n + 8 variables (being n the number of sub-cells of the multijunction cell). These variables are as follows: the sunlight concentration factor, the absorber cut-off energy, the emitter-to-absorber area ratio, the emitter cut-off energy, the band-gap energy(ies) and voltage(s) of the sub-cells, the reflectivity of the cells' back-side reflector, the emitter-to-cell and cell-to-cell view factors and the emitter-to-cell area ratio. We have used this model for carrying out a multi-variable system optimization by means of a multidimensional direct-search algorithm. This analysis allows to find the set of system variables whose combined effects results in the maximum overall system efficiency. From this analysis, we have seen that multijunction cells are excellent candidates to enhance the system efficiency and the electrical power density. Particularly, multijunction cells report great benefits for systems with a notable presence of optical losses, which are unavoidable in practical systems. Also, we have seen that the use of spectrally selective absorbers, rather than black-body absorbers, allows to achieve higher system efficiencies for both lower concentration and lower emitter-to-absorber area ratio. Finally, we have seen that sun-to-electricity conversion efficiencies above 30% and electrical power densities above 50 W/cm2 are achievable for this kind of systems

Atommagok egzotikus bomlásai, állapotai és szimmetriái = Exotic nuclear decays, states and symmetries

Az atommagok egzotikus bomlásait, állapotait és szimmetriáit tanulmányoztuk. Szisztematikusan feltártuk néhány könnyű és nehéz mag lehetséges fürtösödését (klaszterizációját). Ezáltal hozzájárultunk az egzotikus bomlások szerkezeti aspektusának tisztázásához. A vizsgált atommagoknak nem csak az alapállapotát, hanem a szuper- és hiperdeformált állapotait is tanulmányoztuk. A fürtösödés és az egzotikus alak (állapot) kapcsolatát egy igen általános szimmetria, az u.n. kvázidinamikai szimmetria segítségével sikerült megadnunk. E szimmetriafogalom kiépítéséhez magunk is hozzájárultunk. További szimmetriákat is találtunk, amelyek lehetővé teszik két vagy több mag (klaszter-szuperszimmetria), vagy különböző klaszterkonfigurációk (sokcsatornás dinamikai szimmetria) részletes spektrumának egységes leírását. Tanulmányoztuk kvantummechanikai rendszerek fázisátmeneteit, melyek a rendszereket jellemző szimmetria megváltozásának felelnek meg. Megvizsgáltuk a kvantummechanikai leírás kiterjesztésének némely (kvantumalgebrai) aspektusát is. Végül javasoltunk egy olyan osztályozási sémát, amely alkalmas a kvantummechanikai többtest-probléma sokféle szimmetriájának rendszerezésére. | We carried out investigations in order to contribute to our understanding on exotic nuclear decays, states and symmetries. We explored systematically the possible cluster configurations of some light and heavy nuclei. These investigations gave insight into the structural aspects of possible exotic decay modes. Besides the ground state of the selected nuclei, we also considered their superdeformed and hyperdeformed states. The connection between the cluster configurations and exotic states could be established by a rather general symmetry, called quasi-dynamical symmetry. We also contributed to the generalization of this concept. We developed further symmetries as well, that permit unified description of the detailed spectra of two or more nuclei (cluster-supersymmetry), or those of different cluster-configurations (multichannel dynamical symmetry). We studied the phase-transitions of some quantum mechanical systems, which correspond to the change of their characteristic symmetries. Furthermore, we investigated some (quantum-algebraic) aspects of the generalization of the quantum mechanical description. We proposed a framework that can serve for a systematic classification of many different kinds of symmetries of the quantum mechanical many-body problems

Decay of the N=126, Fr 213 nucleus

γ rays following the EC/β+ and α decay of the N = 126, Fr213 nucleus have been observed at the CERN isotope separator on-line (ISOLDE) facility with the help of γ-ray and conversion-electron spectroscopy. These γ rays establish several hitherto unknown excited states in Rn213. Also, five new α-decay branches from the Fr213 ground state have been discovered. Shell model calculations have been performed to understand the newly observed states in Rn213. © 2016 authors. Published by the American Physical Society

Energía Solar Termofotovoltaica

La energía solar fotovoltaica es una de las alternativas renovables más interesantes para afrontar el futuro energético del planeta desde el punto de vista de la sostenibilidad. Sin embargo, actualmente los sistemas fotovoltaicos comerciales son poco eficientes –aprovechan sólo el 10% de la radiación incidente– y económicamente menos atractivos que las fuentes de energía convencionales. En este trabajo se analizan las principales causas que limitan la eficiencia de conversión de radiación en electricidad y, tras ello, se presenta una novedosa línea de investigación basada en la utilización de sistemas termofotovoltaicos conjuntamente con concentradores solares, estrategia que permite incrementar la eficiencia de conversión hasta alcanzar valores por encima del 30%, algo fundamental para aumentar la competitividad de las técnicas fotovoltaicas. Por último se presenta el prototipo de Sistema Solar Termofotovoltaico que se está construyendo en el Instituto de Energía Solar en colaboración con los principales laboratorios de investigación europeos en la materia

Szimmetriák a kvantummechanikai soktestproblémában: általános összefüggések és magfizikai alkalmazások = Symmetries in quantum mechanical many-body problems: general aspects and nuclear physical applications

A kvantummechanikai soktestprobléma szimmetriáinak tanulmányozása során a következő eredményeket értük el. Az alapvető magszerkezetmodellek új összefüggéseire mutattunk rá szimmetriáik alapján, részben a véges hideg kvantumrendszerek fázisaira alapozva. Elméletileg meghatároztuk számos (N=Z=páros) atommag alakizomér állapotait, és az azokat létrehozni képes magreakciókat, egy általunk kifejlesztett, szimmetriákra alapozott módszerrel. Jóslatunkat a legújabb kísérletek két esetben is alátámasztják 28Si szuperdeformált és 36Ar hiperdeformált állapota). Vizsgálatokat végeztünk annak kiderítésére, hogy az elméleti előrejelzések (általában), és a szimmetriák (különösképpen) hogyan mutatkoznak meg a kísérleti adatokban (az izospin, a magtömegek, a rezonanciaparaméterek, a töltéssugár, az energiaspektrum és az elektromágneses átmenetek vonatkozásában). Új szimmetriák új aspektusait tártuk fel mind egyszerű kvantummechanikai problémák, mind a magfizikai soktest-probléma kapcsán. A PT-szimmetriával kapcsolatban tanulmányoztuk a megoldható potenciálok, a spontán sérülés és az effektív tömegek kérdését. Továbbfejlesztettük a magszerkezet (dipólus szabadsági fokának) két összetett szimmetriáját, melyeket korábban magunk vezettünk be: a klaszterállapotok szuperszimmetriáját és a többcsatornás szimmetriát. | In studying the symmetries of the quantum mechanical many-body problem we have obtained the following results. We have found new relations among the fundamental models of nuclear structure via their symmetry properties. A part of this research was carried out within the framework of the phases of finite cold quantum systems. We have determined the shape isomers of several (N=Z=even) nuclei as well as the nuclear reactions which are able to populate them (from a new symmetry-adopted method, invented by us). The latest experiments seem to support our theoretical predictions in two cases (superdeformed state in 28Si, and hyperdeformed state in 36Ar). We have studied how the theoretical predictions (in general) and the symmetris (in particular) show up in the experimental data (concerning the isospin, nuclear mass, resonances, charge radius, energy spectra and electromagnetic transitions). We have revealed new aspects of new symmetries both for simple problems of quantum mechanics and for the nuclear many-body problem. In relation with the PT-symmetry we have studied some solvable potentials, sponateous breaking, and effective masses. We developed further two composite symmetries of the (dipole degree of freedom of the) nuclear structure, which were invented by us beforehand: the supersymmetry of cluster states, and the multichannel dynamical symmetry