Topography of YBa2Cu3O7-δ single crystals,spectroscopy of thin films and sintered YBa2Cu3O7-δ: theory and STM observations

We report topographic scanning tunnelling microscopy measurements on the (001) and (100) surfaces of YBa₂Cu₃O_7-δ single crystals, together with a theoretical basis by which the surface structures can be understood. We show that it is possible to obtain reproducible topographic data on a clean (001) and (100) surface in air. The results show various structures at scales from 0·1 to 100 nm. Among the observed features on the (001) surface were growth steps which had heights that were multiples of the lattice constant in the [001] direction. This indicates that the bulk crystal structure extends to the surface, and that the surface is relatively stable, even in humid air. We also found small (013) facets on the (001) surface, in accordance with theoretical pradictions. Occasionally, we found evidence for a one-dimensional corrugation on the surface. This is possibly a direct consequence of the orthorhombic distortion in the a-b plane with ordered oxygen vacancies, which gives rise to chain-like Cu-O structures along the b-axis. In addition, we measured the energy gap of sintered pellets and thin films of this superconductor, using a low-temperature STM. We discuss some effects which may influence the measurements and present criteria to check for these effects. We found an energy gap of δ=14±2 eV, in good agreement with the BCS pradiction 2δ/kT_c=3·5. This is not contradicted by the results we obtained by far infrared spectroscopy and Andreev reflection measurements.     

Gigabit/s indoor wireless systems with directional antennas

The design of a high speed (>150 Mb/s) wireless local area network (WLAN), requires that many factors be considered, including technical, economic, and regulatory. A major technical factor is the channel response behavior (multipath) in the indoor environment as a function of the frequency band, building type and radio system architecture. The consequences of designing indoor wireless systems with directional antennas at one or both ends of a line-of-sight (LOS) link are investigated. We determine how narrow the beamwidth must be so that the maximum data rate is not limited by multipath effects. For such beamwidths, simple unequalized two-level frequency shift keying (FSK) or phase shift keying (PSK) modems can be used in place of the more costly and complex “anti-multipath” modems, and data rates above 1 Gb/s may be achieved. The channel impulse response in an empty room is estimated using geometrical optics, observing that with directional antennas, multipath rays must arrive from the same direction as the LOS ray. The link outage probability is then estimated as a function of the antenna beamwidth, and guidelines are established for the selection of the frequency band and antenna placement. Experiments using a 19-GHz 622-Mb/s binary phase shift keying (BPSK) link and 15° beamwidth horn antennas in an office building with plaster walls and large metallized windows have demonstrated error-free performance on both LOS and non-LOS (NLOS) links     

Shared social environment and psychiatric disorder: a multilevel analysis of individual and ecological effects

We examined associations, in terms of relative and population-attributable risks, between shared social environment at the neighbourhood level and (1) treated incidence of non-psychotic, non-organic disorders, and (2) subsequent level of service consumption. The multilevel analysis used linked records of all individuals in contact for the first time with any catchment area mental health service for non-psychotic, non-organic disorder over various specified time periods between 1981 and 1995. Socioeconomic indicators of 36 neighbourhoods in the city of Maastricht yielded a multivariately defined neighbourhood deprivation score. There were significant linear trends in the association between level of deprivation and treated incidence, especially in the population under 35 years of age (adjusted rate ratio for linear trend 1.17, 95% confident interval 1.11-1.23), who constituted around half of the patient population. The fraction of the incidence of psychiatric disorder attributable to deprivation was 17.8%. Multilevel analyses of rates of a second cohort, with cases divided according to level of service use over a standardised follow-up of 5 years after first contact with psychiatric services, revealed that the effect of deprivation scores on rates declined with intensity of out-patient service use, but increased with level of in-patient use. Up to 50% of in-patient episodes in this group could be attributed to neighbourhood level of deprivation. The increase in risk conferred by neighbourhood deprivation remained after adjustment for the individual-level equivalent. The findings therefore suggest that elements in the shared social environment influence both incidence and severity of non-psychotic, non-organic disorders, over and above any individual-level effect.     

A new multistage detector for synchronous CDMA communications

In this paper, we develop a new multistage detector to approach the optimal solution of the detection problem in a synchronous code division multiple access (CDMA) system. The transformation modifies the diagonal elements of the Hessian matrix of the quadratic likelihood function and brings the continuous minimum of the transformed function as close to the optimal solution as possible. The computational complexity is essentially linear with the number of users, except that a few computations of a quadratic function are needed     

Quantitative phase measurements using optical quadrature microscopy

Imaging of phase or optical path length is becoming more important with the development of better imaging systems, computational algorithms, faster computers, and a greater interest in the imaging of transparent objects. Early phase imaging involved qualitative imaging of phase gradients. New computational algorithms can be used to extract some quantitative phase imaging from these techniques. In contrast, new hardware has enabled full-field quantitative phase imaging on a practical and cost-effective scale. We explore a quantitative comparison between two techniques for imaging phase. In the first technique, phase is recovered from a pair of differential interference contrast images, and in the second technique, phase is measured pixel-by-pixel interferometrically. It is shown, experimentally, that the overall results are similar, but each technique has its own advantages and disadvantages.     

Determination of thorium and uranium in ultrapure lead by inductively coupled plasma mass spectrometry

A method for the determination of U and Th at sub-ppt levels in high-purity Pb samples using extraction chromatography with ICPMS detection is described. Following acid digestion, uranium and thorium are separated from the lead matrix using UTEVA resin. Sorption and elution procedures were optimized, the potential reusability of the chromatographic resin was evaluated, and a performance comparison between prepacked and freshly prepared UTEVA column was made. Uranium could be eluted with 0.025 M HCl and Th then recovered using 0.5% oxalic acid. Recovery yields for U exceed 80% whereas those for Th were typically 60%. Procedural detection limits of 0.5 and 1.5 pg g(-)(1) were obtained for U and Th, respectively. For purposes of comparison, GD-MS analysis of samples was also performed, yielding results consistent with those generated by ICPMS but with inferior detection power.     

Assessing the Governance Capacity of Cities to Address Challenges of Water,Waste, and Climate Change

The challenges of water, waste, and climate change in cities are overwhelming and underpin the importance of overcoming governance issues impeding adaptation. These “governance challenges” typically have fragmented scopes, viewpoints, and responsibilities. As there are many causes leading to this uncertainty and disagreement, there is no single best approach to solve these governance challenges. In fact, what is necessary is iterative and requires governance capacity to find dynamic long-term solutions that are supported by flexible interim targets, so as to anticipate emerging barriers and changing situations. The literature contains a plethora of governance gaps, barriers, and capacities, which sometimes overlap, are contradictory and case-specific, and reflect disciplinary scopes. We argue that a balanced set of well-developed conditions is needed, to obtain the governance capacity that enables effective change. Therefore, we aim to obtain deeper understanding of the key conditions determining the urban water governance capacity, by developing an integrated empirical-based approach that enables consistent city comparisons and facilitates decision-making. We propose a governance capacity framework focusing on five governance challenges: 1) water scarcity, 2) flood risk, 3) wastewater treatment, 4) solid waste treatment and 5) urban heat islands. Nine governance conditions, each with three indicators, are identified and empirically assessed using a Likert-type scoring method. The framework is illustrated by a case study on Amsterdam, the Netherlands. We conclude our approach shows great potential to improve our understanding of the key conditions determining the governance capacity to find solutions to the urban challenges of water, waste, and climate change.