Recent Achievements on the Physics of High-T C Superconductor Josephson Junctions: Background, Perspectives and Inspiration

Coherent passage of Cooper pairs in a Josephson junction (JJ) above the liquid nitrogen temperature has been the first impressive revolutionary effect induced by high critical temperature superconductors (HTS) in the domain of the study of Josephson effect (JE). But this has been only the start. A d-wave order parameter has lead to significant novel insights in the physics of the JE turning into a device the notion of a π-junction. Spontaneous currents in a frustrated geometry, Andreev bound states, long-range proximity effect have rapidly become standard terms in the study of the JE, standing as a reference bench for conventional systems based on low critical temperature superconductors (LTS) and inspiring analogies for junctions based on novel superconductors discovered in the meantime. The extreme richness of the physics of HTS JJs has not been adequately supported by the expected impact in the applications, the main reason lying in the complexity of these materials and in the consequent unsatisfactory yield and reproducibility of the performances of the JJs within the required limits. The continuous progress in material science, and specifically in the realization of oxide multi-layers, and in nanotechnologies applied to superconductors, accompanied by the advances in a better understanding of the properties of HTS and of HTS devices, has as a matter of fact opened possible novel scenarios and interest in the field. We intend to give a brief overview on interesting new problems concerning HTS JJs of inspiration also for other systems. We also review some ideas and experimental techniques on macroscopic quantum decay phenomena occurring in Josephson structures. The attention is mainly addressed to intermediate levels of dissipation, which characterize a large majority of low critical current Josephson devices and are therefore an unavoidable consequence of nanotechnology applied more and more to Josephson devices.     

Management commitment to safety vs. employee perceived safety training and association with future injury

Objectives

The purpose of this study is to explore and examine, specific to the restaurant industry, two important constructs emerging from the safety climate literature: employee perceptions of safety training and management commitment to safety. Are these two separate constructs? Are there both individual- and shared group-level safety perceptions for these two constructs? What are the relationships between these two constructs and future injury outcomes?

Methods

A total of 419 employees from 34 limited-service restaurants participated in a prospective cohort study. Employees’ perceptions of management commitment to safety and safety training and demographic variables were collected at the baseline. The survey questions were made available in three languages: English, Spanish, and Portuguese. For the following 12 weeks, participants reported their injury experience and weekly work hours. A multivariate negative binomial generalized estimating equation model with compound symmetry covariance structure was used to assess the association between the rate of self-reported injuries and measures of safety perceptions.

Results

Even though results showed that the correlation between employees’ perceived safety training and management commitment to safety was high, confirmatory factor analysis of measurement models showed that two separate factors fit the model better than as two dimensions of a single factor. Homogeneity tests showed that there was a shared perception of the factor of management commitment to safety for the restaurant workers but there was no consistent perception among them for the factor of perceived safety training. Both individual employees’ perceived management commitment to safety and perceptions of safety training can predict employees’ subsequent injuries above and beyond demographic variables. However, there was no significant relationship between future injury and employees’ shared perception of management commitment to safety. Further, our results suggest that the variable of employees’ perceived safety training could be a proximal predictor of future injury outcome which mediated the relationship between employees’ perceived management commitment to safety (a distal predictor) and injury outcome. We propose that when employees perceive their management as having a high level of commitment to safety, they will also perceive that the safety training of the organization is good, which will then further predict future injury experience of the employees.     

Yield enhancement and manufacturing throughput of redundant memories by repairability/unrepairability detection

In this article, yield enhancement and manufacturing throughput of large repairable memories are analyzed. These objectives are met by repairability/unrepairability detection. Initially two new techniques for detection of memory chips with redundancy are presented. Initially, a heuristic, yet efficient approach is proposed. This first approach is based on finding a very good approximation to the minimum covering set. An algorithm, which executes in quadratic time with respect to the largest dimension of the memory, is presented. This algorithm is executed off-line, that is, when the memory has been fully diagnosed. New conditions for detection are presented and fully analyzed. These are based on a more accurate estimation of the regions of repairability and unrepairability. Hence, this results in a reduction of the uncertainty region, where the status of a memory cannot be established without executing a fully exhaustive search algorithm. The second approach to repairability/unrepairability detection is based on a more complex covering relationship, namely the generalized leading element. A model for manufacturing throughput of large repairable memories is presented.A new repair algorithm which utilizes a ternary tree approach, is also presented. This repair algorithm is perfect in the sense that it finds the optimal repair-solution (whenever one exists) after the memory has not been diagnosed unrepairable.Illustrative examples and simulation results show that considerable improvements for average and the worst-case analysis over existing techniques can be achieved.This research was supported in part by grants from AT&T and NATO.     

A Markov model for the mobile propagation channel

A finite-state Markov model is fitted to the mobile propagation channel by the use of contingency tables. Narrow-band Rayleigh and Ricean fading are considered in detail, but the techniques extend to other types of fading. Several criteria may indicate that a first-order finite-state Markov model sufficiently characterizes the channel behavior. The parameters of the model are obtained both from theoretical analysis and simulation. Functional dependence between the transition probabilities and the steady-state probabilities is found in the slow fading case     

Optimum coding framework for error detection in the self-assembly of the Sierpinski triangle

This study presents a coding framework by which DNA self-assembly can be analysed for error detection. The proposed framework relies on coding and mapping functions that allow establishing the correctness of bonding each tile based on the codes of the tiles along a so-called traversal path. This method is different from the one that relies on comparing the pattern to be assembled (as defined by the tile set) and the current aggregate (as resulting from previously assembled tiles). As a widely used pattern and instantiation of this process, the Sierpinski triangle self-assembly is analysed in detail. The Sierpinski triangle is therefore utilised as an example to show the application of the proposed method. Different properties are proposed and its optimum coding is achieved for error detection. Simulation results are presented.     

Inert matrix and thoria fuels for plutonium elimination

In our previous studies we analysed the plutonium burning performance of various kinds of fuel, based on mixing plutonium oxide with thorium oxide (TOX), or with inert matrix (IMF), or with inert matrix plus a limited addition (doping) of thorium oxide (TD-IMF). The present paper includes the neutronic analysis of a metal-based fuel variant and of fissile material recycling in TOX fuels. If the recycled fuel is topped with weapons grade plutonium (WG-Pu) as fissile material, it is possible to sustain indefinitely a closed cycle.     

Air-hydrogen deflagration tests at the University of Pisa

In severe accidents, large amounts of hydrogen may be released in the safety containment of a nuclear plant and the gas mixture may become explosive. The University of Pisa and ENEA have undertaken an experimental program to study the physics of flame propagation in a containment model under accident conditions. Up to now 41 deflagration tests have been performed at the HYDRO-SC facility at ambient pressure and temperature. Concentrations, water spray conditions, ignition source and gas turbulence levels were varied. The vessel volume was 0.5 m³, the ignition sources were an electrical spark discharge and an electrically heated surface (glow-plug), the hydrogen molar fractions were in the range 4–16%, the turbulence was generated by fan or spray and two different spray nozzles were utilized. The experimental data indicate that the peak pressures nearly fit the adiabatic isochoric values at the highest hydrogen concentrations and gas turbulences. Weak pressure waves were observed for H₂ molar fractions greater than 10%. A careful examination of the pressure and temperature transients gave information on the flame path and on the heat transfer process during and after combustion. Scale effects on the peak pressures were not observed by comparison of the HYDRO-SC results with data obtained in other laboratories. The glow plug igniter has proved to be a reliable tool for use in deliberate ignition schemes for hydrogen control in nuclear plants.     

Epoxy/BaTiO3 Light‐Cured Composites as Organic Capacitors

Epoxy/BaTiO₃ hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free‐radical promoted cationic polymerization using a long‐wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well‐dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.

     

Design considerations for a receiver for digital fibre-optic communication systems

An approach to design easily a receiver for digital fibre-optic communication systems is given. In particular, a 34.368 Mbit/s communication system is analysed, where little or no avalanche-detector gain is used.