Possible coexistence of superconductivity and magnetism in layered compounds

The possibility of a coexistent superconducting and magnetic phase in layered transition metal dichalcogenides of the type MX ₂ A _x is investigated (M =transition metal; X = S, Se; A = magnetic ion; x 0.25). Describing such systems with a model in which a highly anisotropic electron gas interacts with a quasi-two-dimensional Heisenberg magnet, we find the following conditions for coexistence: (1) The coupling between adjacent layers of ferromagnetically ordered magnetic ions needs to be antiferromagnetic (S ^z = 0) in order to have no pair-breaking internal fields. (2) The exchange interaction between conduction electrons and magnetic ions must be very small ( 0.003 eV), since otherwise, due to the high concentration of localized magnetic moments, spin-flip scattering processes and spin fluctuations would destroy superconductivity. The theoretical prediction for the persistence of superconductivity up to concentrations of x 0.25 of magnetic ions is compared with recent experiments on Eu-intercalated TaS ₂ and NbS ₂ and related compounds showing a tendency for ferromagnetically ordered layers of Eu impurities and antiferromagnetic coupling between neighboring layers but no superconductivity for x exceeding a few percent. Reasons for the quick disappearance of superconductivity in these systems and criteria for possible observation of high-magnetic-impurity-concentration superconductivity in other layered compounds are given.     

InAs/InGaSb photodetectors grown on GaAs bonded substrates

The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately 7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength. The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb substrates.     

Restructuring of Swiss parcel delivery services

Abstract. Recently, the Swiss postal services has been confronted with some drastic changes. First, the areas of telecommunication and postal services were divided into two independent enterprises, and secondly, the market for postal services in Switzerland was deregulated to a large extent. These developments forced the public PTT not only to change its organisational structure but also its logistics system. In the new system the customers will be mainly served by transshipment points. A main problem was to decide on the number, the locations, the sizes, and service areas of these transshipment points. The decision was supported by means of a discrete facility location model. This paper discusses the location problem and the used solution approach. An emphasis is given on the determination of the cost parameters.     

Natural disasters and the challenge of extreme events: risk management from an insurance perspective

Loss statistics for natural disasters demonstrate, also after correction for inflation, a dramatic increase of the loss burden since 1950. This increase is driven by a concentration of population and values in urban areas, the development of highly exposed coastal and valley regions, the complexity of modern societies and technologies and probably, also by the beginning consequences of global warming. This process will continue unless remedial action will be taken. Managing the risk from natural disasters starts with identification of the hazards. The next step is the evaluation of the risk, where risk is a function of hazard, exposed values or human lives and the vulnerability of the exposed objects. Probabilistic computer models have been developed for the proper assessment of risks since the late 1980s. The final steps are controlling and financing future losses. Natural disaster insurance plays a key role in this context, but also private parties and governments have to share a part of the risk. A main responsibility of governments is to formulate regulations for building construction and land use. The insurance sector and the state have to act together in order to create incentives for building and business owners to take loss prevention measures. A further challenge for the insurance sector is to transfer a portion of the risk to the capital markets, and to serve better the needs of the poor. Catastrophe bonds and microinsurance are the answer to such challenges. The mechanisms described above have been developed to cope with well-known disasters like earthquakes, windstorms and floods. They can be applied, in principle, also to less well investigated and less frequent extreme disasters: submarine slides, great volcanic eruptions, meteorite impacts and tsunamis which may arise from all these hazards. But there is an urgent need to improve the state of knowledge on these more exotic hazards in order to reduce the high uncertainty in actual risk evaluation to an acceptable level. Due to the rarity of such extreme events, specific risk prevention measures are hardly justified with exception of attempts to divert earth-orbit crossing meteorites from their dangerous path. For the industry it is particularly important to achieve full transparency as regards covered and non-covered risks and to define in a systematic manner the limits of insurability for super-disasters.     

Production and characterization of plutonium dioxide particles as a quality control material for safeguards purposes

Plutonium (Pu) dioxide particles were produced from certified reference material (CRM) 136 solution (CRM 136-plutonium isotopic standard, New Brunswick Laboratory, Argonne, IL, U.S.A., 1987) using an atomizer system on December 3, 2009 after chemical separation of americium (Am) on October 27, 2009. The highest density of the size distribution of the particles obtained from 312 particles on a selected impactor stage was in the range of 0.7-0.8 μm. The flattening degree of 312 particles was also estimated. The isotopic composition of Pu and uranium (U) and the amount of Am were estimated by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and α-spectrometry. Within uncertainties the isotopic composition of the produced particles is in agreement with the expected values, which were derived from the decay correction of the Pu isotopes in the CRM 136. The elemental ratio of Am to Pu in the produced particles was determined on the 317th and 674th day after Am separation, and the residual amount of Am in the solution was estimated. The analytical results of single particles by micro-Raman-scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry (EDX) indicate that the produced particles are Pu dioxide. Our initial attempts to measure the density of two single particles gave results with a spread value accompanied by a large uncertainty.     

Hardness of hexagonal tungsten carbide crystals as a function of orientation

A new depth-sensing microhardness mapping system has been used to measure the variation in microhardness with applied load and orientation of WC crystals. The orientations of the individual crystals were measured using an electron backscatter diffraction (EBSD) technique. The WC crystals were ～100 μm in size, embedded in a copper alloy matrix, to enable arrays of multiple microhardness indents to be implanted in each grain, thus generating good statistical validity for the results. It was found that the most significant effect on microhardness was the angle between the plane of measurement and either the basal or prism planes. A simple cosine rule, in line with resolved shear stresses, was used to correlate the data. The results are compared with previous studies using Knoop, Vickers and Berkovitch indenters, and some discussion is included of observed deformation around indentations using electron imaging associated with the EBSD technique.     

Layers of Silence, Arenas of Voice: The Ecology of Visible and Invisible Work

No work is inherently either visible or invisible. We always see work through a selection of indicators: straining muscles, finished artifacts, a changed state of affairs. The indicators change with context, and that context becomes a negotiation about the relationship between visible and invisible work. With shifts in industrial practice these negotiations require longer chains of inference and representation, and may become solely abstract.This article provides a framework for analyzing invisible work in CSCW systems. We sample across a variety of kinds of work to enrich the understanding of how invisibility and visibility operate. Processes examined include creating a non-person in domestic work; disembedding background work; and going backstage. Understanding these processes may inform the design of CSCW systems and the development of related social theory.