Two mechanisms for population inversion via two-colour coherent excitation in three-level systems

We analyse the physical origin of population inversion via continuous wave two-colour coherent excitation in three-level systems by dressing the inverted transition. Two different mechanisms are identified as being responsible for the population inversion. For V-configured systems and cascade (E) configured systems with inversion on the lower transition, the responsible mechanism is the selective trapping of dressed states, and the population inversion approaches the ideal value of 1. For Lambda-configured systems and Xi-configured systems with inversion on the upper transition, population inversion is based on the selective excitation of dressed states, with the population inversion tending towards 0.5. As the essential difference between these two mechanisms, the selective trapping of dressed states occurs in systems with strong decay into dressed states while the selective excitation appears in systems with strong decay out of dressed states.

Regional IAM: analysis of risk-adjusted costs and benefits of climate policies

23 p.

Desarrollo sostenible y Agenda 21 Local

Resumen (ESPAÑOL) En el presente trabajo se ha tratado de analizar la evolución, tanto del concepto de Desarrollo Sostenible, como de la herramienta Agenda 21 Local, verificando la creciente preocupación que se está extendiendo en la ciudadanía, en las instituciones y en las empresas, así como la irreversibilidad de la mayoría de los resultados alcanzados. En este marco, se han estudiado los casos concretos de la implantación de la Agenda 21 Local en Europa, España, Euskadi y Getxo, por ser este último el municipio en el que resido. Con este estudio, se confirma la hipótesis de que, aunque en la implantación de la Agenda 21 Local se aprecia un esfuerzo realizado notable, queda todavía mucho camino por recorrer en la senda hacia la sostenibilidad.

On the structure of the seminal receptacle in cyclopids (Copepoda, Cyclopoida). [Translation from: Informatsionnyi Byulleten Biologiya Vnutrennikh Vod (6) 26-31, 1970.]

The seminal bag, or seminal receptacle, forms a characteristic organ of cyclopids, serving for retention of the sperms discharged from the spermatophores. The structure of the seminal receptacle, more precisely its form, is fairly widely used in diagnosis and undoubtedly can be more widely applied in the systematics of the group. Within the limits of the family Cyclopidae it is possible to distinguish crustaceans with three basic types of seminal bag. The differences consist of the position which this organ occupies in the genital segment. of one species, we carried out a series of observations on its formation in ontogenesis and during the life of the adult stage. As material for observation the study used laboratory cultures of three species; Acanthocyclops americanus (Marsh) from the plankton of the Moscow River, Cyclops vicinus Uljan and Mesocyclops leuckarti Glaus from the plankton of the channel section of the upper part of the Gorkovsk reservoir. The author concluded that the irreversibility of the changes in the seminal receptacle presents the possibility of utilising this structure as one of the indicators of the growth of the individual.

Bergson e a criação artística

O pensamento de Bergson situa a estética no seio de uma filosofia da natureza, cujo princípio metafísico está longe de qualquer determinismo e do arbítrio do acaso, remetendo-se à irreversibilidade do tempo. Ao invés de disciplina intelectual que busca a natureza da beleza, trata-se, antes, de conduta vital, processo de diferenciação virtual rumo à posição de novidades radicais, podendo ou não desembocar na atividade artística. A arte não é, portanto, um conjunto de atributos atualmente dados ou a prática de habilidades específicas e, sim, um modo de ação que entrelaça os regimes do virtual e do atual sem permitir que a existência se sobreponha à consistência, realizando-se, inclusive, na sua própria abertura. Se o impulso da vida é o que comunica espírito e matéria, inserindo liberdade na necessidade, segue-se que a atividade artística é uma das vias em que desemboca o elã, ao lado dos seres vivos e da expressão mística. A individuação de uma obra implica certos graus de liberdade e níveis de consciência que não se explicam nem pela espécie, nem pelo indivíduo, já que sua contração intuitiva submete a duração do artista a tonalidades não psicológicas e a-subjetivas. Tocado por uma emoção criadora, vai-se realmente do Todo Aberto à colocação de novos mundos. O veículo de ação confunde-se com a própria ação, criatura com criador, de modo que o corpo artístico instaurado é puro transbordamento de vitalidade, consciência de si do tempo.

Distribution of critical current density in large YBa2Cu3O7-δ grains fabricated using seeded peritectic solidification

High quality large grain high Tc superconducting ceramics offer enormous potential as 'permanent' magnets and in magnetic screening applications at 77K. This requires sample dimensions -cm with uniform high critical current densities of the order 105 A/cm2 in applied magnetic fields of IT. We report a study of the magnetic characterisation of a typical large YBa2Cu3O7-δ grain, prepared by seeded peritectic solidification, and correlate the magnetically determined critical current density, Jc, with microstuctural features from different regions of the bulk sample. From this data we extract the temperature, field and positional dependence of the critical current density of the samples and the irreversibility line. We find that whilst the bulk sample exhibits a good Jc of order 104 A/cm2 (77K, 1T), the local Jc is strongly correlated with the sample microstructure towards the edge of the sample and more severely at the centre of the sample by the presence of SmBa2Cu3O7-δ seed crystal. © 1997 IEEE.

Development of non-weak link bulk YBCO grain boundaries for high magnetic field eegimeering applications

A non-weak link joining technique has been developed for YBCO pseudo-crystals fabricated by seeded peritectic solidification based on the formation of a liquid phase which segregates from the platelet boundaries at temperatures above = 920 °C. Electrical and magnetic measurements on these boundaries suggest that their irreversibility field can be as high as 7 T at 77 K in fully oxygenated pseudo-crystals joined along their crystallographic ab-planes which is comparable to the irreversibility behaviour of the adjacent YBCO grains. © 1999 IEEE.

Development of the microstructure of uranium-doped Nd-Ba-Cu-O

Melt grown Nd-Ba-Cu-O (NdBCO) has been reported to exhibit higher values of critical current density, Jc and irreversibility field, Hirr, than other (RE)BCO superconductors, such as YBCO. The microstructure of NdBCO typically contains 5-10 μm sized inclusions of the Nd4Ba2Cu2O10 phase (Nd-422) in a superconducting NdBa2Cu3O7-δ phase (Nd-123) matrix. The average size of these inclusions is characteristically larger than that of the Y2BaCuO5 (Y-211) inclusions in YBCO. As a result, there is scope to further refine the Nd-422 size to enhance Jc in NdBCO. Large grain samples of NdBCO superconductor doped with various amounts of depleted UO2 and containing excess Nd-422 have been fabricated by top seeded melt growth under reduced oxygen partial pressure. The effect of the addition of depleted UO2 on the NdBCO microstructure has been studied systematically in samples with and without added CeO2. It is observed that the addition of UO2 refines the NdBCO microstructure via the formation of uranium-containing phase particles in the superconducting matrix. These particles are of approximately spherical geometry with dimensions of around 1 μm. The average size of the nonsuperconducting phase particles in the uranium-doped microstructure is an order of magnitude less than their size in un-doped Nd-123 prepared with excess Nd-422. The critical current density of uranium-doped NdBCO is observed to increase significantly compared to the undoped material.

Electricity Storage Using a Thermal Storage Scheme

The increasing use of renewable energy technologies for electricity generation, many of which have an unpredictably intermittent nature, will inevitably lead to a greater demand for large-scale electricity storage schemes. For example, the expanding fraction of electricity produced by wind turbines will require either backup or storage capacity to cover extended periods of wind lull. This paper describes a recently proposed storage scheme, referred to here as Pumped Thermal Storage (PTS), and which is based on "sensible heat" storage in large thermal reservoirs. During the charging phase, the system effectively operates as a high temperature-ratio heat pump, extracting heat from a cold reservoir and delivering heat to a hot one. In the discharge phase the processes are reversed and it operates as a heat engine. The round- trip efficiency is limited only by process irreversibilities (as opposed to Second Law limitations on the coefficient of performance and the thermal efficiency of the heat pump and heat engine respectively). PTS is currently being developed in both France and England. In both cases, the schemes operate on the Joule-Brayton (gas turbine) cycle, using argon as the working fluid. However, the French scheme proposes the use of turbomachinery for compression and expansion, whereas for that being developed in England reciprocating devices are proposed. The current paper focuses on the impact of the various process irreversibilities on the thermodynamic round-trip efficiency of the scheme. Consideration is given to compression and expansion losses and pressure losses (in pipe-work, valves and thermal reservoirs); heat transfer related irreversibility in the thermal reservoirs is discussed but not included in the analysis. Results are presented demonstrating how the various loss parameters and operating conditions influence the overall performance.

Thermodynamic analysis of pumped thermal electricity storage

The increasing use of renewable energy technologies for electricity generation, many of which have an unpredictably intermittent nature, will inevitably lead to a greater need for electricity storage. Although there are many existing and emerging storage technologies, most have limitations in terms of geographical constraints, high capital cost or low cycle life, and few are of sufficient scale (in terms of both power and storage capacity) for integration at the transmission and distribution levels. This paper is concerned with a relatively new concept which will be referred to here as Pumped Thermal Electricity Storage (PTES), and which may be able to make a significant contribution towards future storage needs. During charge, PTES makes use of a high temperature-ratio heat pump to convert electrical energy into thermal energy which is stored as ‘sensible heat’ in two thermal reservoirs, one hot and one cold. When required, the thermal energy is then converted back to electricity by effectively running the heat pump backwards as a heat engine. The paper focuses on thermodynamic aspects of PTES, including energy and power density, and the various sources of irreversibility and their impact on round-trip efficiency.

Modeling fatigue crack growth in crystalline solids with discrete dislocation plasticity

Analyses of crack growth under cyclic loading conditions are discussed where plastic flow arises from the motion of large numbers of discrete dislocations and the fracture properties are embedded in a cohesive surface constitutive relation. The formulation is the same as used to analyse crack growth under monotonic loading conditions, differing only in the remote loading being a cyclic function of time. Fatigue, i.e. crack growth in cyclic loading at a driving force for which the crack would have arrested under monotonic loading, emerges in the simulations as a consequence of the evolution of internal stresses associated with the irreversibility of the dislocation motion. A fatigue threshold, Paris law behaviour, striations, the accelerated growth of short cracks and the scaling with material properties are outcomes of the calculations. Results for single crystals and polycrystals will be discussed.

A thermally actuated superconducting flux pump

The concept of a superconducting flux pump is relatively straightforward. A small magnetic field repeatedly applied will lead to a much larger field being trapped within the superconductor. This field is limited by the volume of the superconductor and by its critical current but not by the excitation field. Here we will describe a new technique which facilitates the creation of high magnetic fields and where the magnitude of the trapped field is limited by the superconductor not the magnetising field. The technique is demonstrated using measurements taken using samples of bulk YBCO as YBCO has a very high irreversibility field and has the potential to trap high magnetic fields. The technique could be applied to other superconductors such as BSCCO or MgB2 and in other forms such as thin or thick films. © 2007 Elsevier B.V. All rights reserved.

Intergranular and intragranular properties of superconducting multifilamentary Bi 2223 Ag tapes : comparison of electrical transport and magnetic measurement methods

Several experimental techniques have been used in order to characterize the properties of multifilamentary Bi-2223 / Ag tapes. Pristine samples were investigated by electrical resistivity, current-voltage characteristics and DC magnetic moment measurements. Much emphasis is placed on comparing transport (direct) and magnetic (indirect) methods for determining the critical current density as well as the irreversibility line and resolving usual lacks of consistency due to the difference in measurement techniques and data analysis. The effect of an applied magnetic field, with various strengths and directions, is also studied and discussed. Next, the same combination of experiments was performed on bent tapes in order to bring out relevant information regarding the intergranular coupling. A modified Brandt model taking into account different types of defects within the superconducting filaments is proposed to reconciliate magnetic and transport data.

Magnetic ordering and irreversible magnetization between ZFC and FC states in RCo5Ga7 compounds

The magnetic properties of RCo5Ga7 (R = Y, Tb, Dy, Ho and Er) compounds which crystallize in the ScFe6Ga6-type structure have been studied. The compounds with R, Y, Tb, Dy, Ho and Er display behaviour similar to semiconductors. The Co transition metal sublattice is ferrimagnetic with a very low spontaneous magnetization. The ferrimagnetic ordering observed for R = Y, Tb, Dy, Ho and Er is due to the transition metal sublattice with transition temperatures at about 295 K. At low temperatures, the magnetic ordering for R Tb, Dy, Ho and Er is due to the rare-earth sublattice, which is ferromagnetic with a Curie temperature below 5 K. By fitting the linear part of the inverse magnetization, the effective magnetic moment of the R ion is found to be close to its expected theoretical value, with paramagnetic Curie temperatures below 5 K. Due to the paramagnetic nature of the R sublattice above 60 K, the ferrimagnetic ordering temperature of the Co sublattice does not vary with the type of rare-earth ion. The irreversibility of the magnetization of YCo5Ga7, as measured in zero-field cooled (ZFC) and field cooled (FC) states, is attributed to movement of domain walls. Application of a large enough applied field completes the movement of the domain wall from the low-temperature to the high-temperature one at 5 K. With a very low magnetic field 100 Oe, the difference between the ZFC and the FC shrinks. (C) 2004 Elsevier B.V. All rights reserved.

Spectral relationship of photoinduced refractive index and absorption changes in fulgide films

Fulgides are one kind of organic photochromic compound, which are famous for their thermal irreversibility. In this report, from the difference spectra of the absorption A() of one kind of pyrrylfulgide, the spectral refractive index change n() was calculated by the Kramers-Kronig relation (KKR), and a good correlation of theoretically derived values and the experimental values of the n measured by a modified Michelson interferometer was found. Further, it is demonstrated that it was possible to calculate the spectral dependence of diffraction efficiency from the easily accessible absorption changes. This method will be a useful tool for the characterization and optimization of fulgide films. The results show that the diffraction efficiency is high at 488 and 750 nm, where the absorption is very small, so we can realize non-destructive reconstruction.