Titanium nitride insulation for the deflector of superconductingcyclotrons

At the Istituto Nazionale di Fisica Nucleare-Laboratorio Nazionale del Sud of Catania (Italy) during the last years a research program has been carried out to improve the performance of the superconducting cyclotron electrostatic deflectors. In this kind of accelerator beam extraction is realized by means of two electrostatic deflectors generating a 140 kV/cm maximum electric field in a small gap (6 to 8 mm). These devices have to work in presence of a high magnetic field (⩽5 T), strongly affecting their performance from the electrostatic point of view. This is mainly the focusing of the electrons emitted by the cathode for field effect. The physical characteristics of the cathode surface influence the electrostatic behavior especially in terms of work function and resistivity. Moreover, the mechanical properties of the surface have to be studied in order to evaluate the effects of high power beam dissipation on the cathode during the extraction process in the accelerator, also influencing the electrostatic performance. Looking to these constraints, a detailed study of the TiN (titanium nitride) features for this application has been carried out. Considering the electrical and mechanical properties, TiN seems to be a material suitable for this application. Electrostatic tests carried out in a deflector simulator confirm that TiN should represent an attractive solution. The results obtained with a surface characterization based on different physical analysis methods are presented     

Sequential Lagrangian-MILP approaches for Unit Commitment problems

The short-term Unit Commitment (UC) problem in hydro-thermal power generation is a fundamental problem in short-term electrical generation scheduling. Historically, Lagrangian techniques have been used to tackle this large-scale, difficult Mixed-Integer NonLinear Program (MINLP); this requires being able to efficiently solve the Lagrangian subproblems, which has only recently become possible (efficiently enough) for units subject to significant ramp constraints. In the last years, alternative approaches have been devised where the nonlinearities in the problem are approximated by means of piecewise-linear functions, so that UC can be approximated by a Mixed-Integer Linear Program (MILP); in particular, using a recently developed class of valid inequalities for the problem, called “Perspective Cuts”, significant improvements have been obtained in the efficiency and effectiveness of the solution algorithms. These two different approaches have complementary strengths; Lagrangian ones provide very good lower bounds quickly, but they require sophisticated heuristics—which may need to be changed every time that the mathematical model changes—for producing actual feasible solutions. MILP approaches have been shown to be able to provide very good feasible solutions quickly, but their lower bound is significantly worse. We present a sequential approach which combines the two methods, trying to exploit each one’s strengths; we show, by means of extensive computational experiments on realistic instances, that the sequential approach may exhibit significantly better efficiency than either of the two basic ones, depending on the degree of accuracy requested to the feasible solutions.     

Methane cracking on single-wall carbon nanotubes studied by semi-empirical tight binding simulations

The catalytic properties of thermally distorted single wall carbon nanotubes for the methane dissociation reaction have been investigated in the framework of semi-empirical tight-binding molecular dynamics, electronic structure and total energy calculations. It is shown that, if methane molecules and the nanotube are allowed to get closer than the equilibrium physi-sorption distance, the next dissociation reaction step is characterized by a small enthalpy change. Moreover the reactivity hierarchy of the various carbon nanotubes considered is related to the electronic density of states originating from the axial components of the atomic orbitals.     

Isothermal and nonisothermal crystallization of HDPE composites containing multilayer carton scraps as filler

The influence of multilayer carton scraps (MC) on crystallization kinetics of high-density polyethylene (HDPE) is detailed in this contribution. HDPE/MC composites were prepared by melt mixing, and a maleated linear low density polyethylene (MAPE) was added as compatibilizer. The crystallization kinetics of HDPE/MC/MAPE was analyzed as function of composition both in isothermal and nonisothermal conditions. The multilayer carton scraps appear to promote the onset of crystallization of HDPE, acting as efficient nucleating agent. The presence of MAPE as compatibilizer slightly reduces the nucleating efficiency of MC: the compatibilizer induces a delay in the onset of crystallization, caused by the need to exclude the bulky pendant groups of maleated linear low-density polyethylene from the crystals, as HDPE and MAPE chains cocrystallize. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Sharp Separation and Applications to Exact and Parameterized Algorithms

Many divide-and-conquer algorithms employ the fact that the vertex set of a graph of bounded treewidth can be separated in two roughly balanced subsets by removing a small subset of vertices, referred to as a separator. In this paper we prove a trade-off between the size of the separator and the sharpness with which we can fix the size of the two sides of the partition. Our result appears to be a handy and powerful tool for the design of exact and parameterized algorithms for NP-hard problems. We illustrate that by presenting two applications.     

Efficacy of virtual patients in medical education: A meta-analysis of randomized studies

A meta-analysis was performed to assess the Effect Size (ES) from randomized studies comparing the effect of educational interventions in which Virtual patients (VPs) were used either as an alternative method or additive to usual curriculum versus interventions based on more traditional methods.     

The effect of social networking websites on positive self-views: An experimental investigation

Millions of people use social networking sites (SNSs), but it is unclear how these sites shape personality traits and identity. In Experiment 1, college students were randomly assigned to either edit their MySpace page or complete a control task online (interacting with Google Maps). Those who focused on their MySpace page scored significantly higher on the Narcissistic Personality Inventory (NPI) than a control group. In Experiment 2, those who focused on their Facebook page scored significantly higher in general self-esteem, but not narcissism, than a control group. Thus, spending time on SNSs profiles causes young people to endorse more positive self-views, although the specific form this takes depends on the site. Consistent with previous research, narcissism was associated with a larger number of SNSs “friends” in both experiments.     

Electron–phonon dissipation in quantum nanodevices

Microscopic modelling of electronic-phase coherence versus energy dissipation plays a crucial role in the design and optimization of new-generation electronic quantum nanodevices, like quantum-cascade light sources and quantum logic gates; in this context, a variety of simulation strategies have been proposed and employed. The aim of this article is to discuss virtues versus intrinsic limitations of non-Markovian density-matrix approaches. More specifically, we shall show that the usual mean-field treatment employed to derive quantum-kinetic equations may lead to highly unphysical results, like negative distribution functions and non-dissipative carrier–optical phonon couplings. By means of a simple two-level model, we shall show that such limitations are expected to be particularly severe in zero-dimensional electronic systems—like quantum-dot nanostructures, potential constituents of quantum-computation devices—coupled to dispersionless phonon modes. Such a behaviour is in striking contrast with the case of Markovian treatments, where a proper combination of adiabatic limit and mean-field approximation guarantees a physically acceptable solution.