Cadmium zinc telluride crystals of 4.8 cm in diameter grown by the boron oxide encapsulated vertical Bridgman technique exhibit good structural quality with large grains and low dislocation density. How- ever, the ingots contain Te inclusions, which are trapped at the growth interface during the crystallization process. Global modeling of the furnace was applied in order to investigate the temperature gradients and the evolution of the growth interface shape in this system. Transient computations, which include the crucible movement, show that the crystal-melt interface is concave toward the melt in the conical part of the ampoule, then becomes convex during the growth in the cylindrical part of the ampoule. Concave shapes of the interface and very homogeneous temperature distribution at the beginning of the solidification process promote the growth of a polycrystalline material. A novel hypothesis explaining the mechanism of grain formation at the ampoule tip was formulated. Our calculations show that the anoma- lous Zn segregation is due to the poor solute mixing at the beginning of the solidification process. The modeling of the standard growth process reveals very low vertical temperature gradients in the crys- tal (2-4 K/cm). Such low temperature gradients are not favorable to eliminate the Te inclusions in the as grown crystal. A numerical model was employed to analyze the temperature field influence on the migration/size reduction of Te inclusions.

Additional heating will be provided to the thermonuclear fusion experiment ITER by injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction at Consorzio REX in Padova (Italy), the production of negative ions will be studied and optimised. To this purpose the STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) diagnostic will be used to characterise the SPIDER beam during short operation (several seconds) and to verify if the beam meets the ITER requirement regarding the maximum allowed beam non-uniformity (below ±10%). The most important measurements performed by STRIKE are beam uniformity, beamlet divergence and stripping losses. The major components of STRIKE are 16 1D-CFC (Carbon matrix-Carbon Fibre reinforced Composite) tiles, observed at the rear side by a thermal camera. The requirements of the ID CFC material include a large thermal conductivity along the tile thickness (at least 10 times larger than in the other directions); low specific heat and density; uniform parameters over the tile surface; capability to withstand localised heat loads resulting in steep temperature gradients. So ID CFC is a very anisotropic and delicate material, not commercially available, and prototypes are being specifically realised. This contribution gives an overview of the tests performed on the CFC prototype tiles, aimed at verifying their thermal behaviour. The spatial uniformity of the parameters and the ratio between the thermal conductivities are assessed by means of a power laser at Consorzio RFX. Dedicated linear and non-linear simulations are carried out to interpret the experiments and to estimate the thermal conductivities; these simulations are described and a comparison of the experimental data with the simulation results is presented.

An axisymmetric system to recover beam energy from partially neutralized Hbeams was recently proposed, for a given beam acceleration voltage Vs . In the case of ion source NIO1 Vs may range from 20 to 60 kV. A realistic beam with 3 mrad divergence, and a composition of 25 : 50 : 25 of H- , H0 and H+ has been considered. The collector works by decelerating the Hions (into a system similar to a Faraday cup provided with an exit hole electrode), so that they are radially deflected by space charge and anode lens effects, and collected to a low kinetic energy Kc (less than 1 keV), while neutral and H+ ions can pass through the exit hole electrode. A following collector can recover H+ energy. Since the space charge calculations are challenging for highly nonlinear problem and for a possible (numerically unstable) virtual cathode phenomena different computation tools were compared for simulations. Stabilization techniques are compared. Limits for local perveance are discussed. Also mesh asymmetry effects and the related transverse oscillations of H+ beam may be observed. Efficiency over 90 % can be reached in typical conditions. The secondary yield (which is low thanks to low impact energy Kc and Faraday cup concept) is estimated.

Corticospinal neurons (SPI), thick-tufted pyramidal neurons in motor cortex layer 5B that project caudally via the medullary pyramids, display distinct class-specific electrophysiological properties in vitro: strong sag with hyperpolarization, lack of adaptation, and a nearly linear frequency-current (F-I) relationship. We used our electrophysiological data to produce a pair of large archives of SPI neuron computer models in two model classes: 1) detailed models with full reconstruction; and 2) simplified models with six compartments. We used a PRAXIS and an evolutionary multiobjective optimization (EMO) in sequence to determine ion channel conductances. EMO selected good models from each of the two model classes to form the two model archives. Archived models showed tradeoffs across fitness functions. For example, parameters that produced excellent F-I fit produced a less-optimal fit for interspike voltage trajectory. Because of these tradeoffs, there was no single best model but rather models that would be best for particular usages for either single neuron or network explorations. Further exploration of exemplar models with strong F-I fit demonstrated that both the detailed and simple models produced excellent matches to the experimental data. Although dendritic ion identities and densities cannot yet be fully determined experimentally, we explored the consequences of a demonstrated proximal to distal density gradient of I h, demonstrating that this would lead to a gradient of resonance properties with increased resonant frequencies more distally. We suggest that this dynamical feature could serve to make the cell particularly responsive to major frequency bands that differ by cortical layer.

We show that by exploiting multi-Lorentzian fits of the self dynamic structure factor at various wavevectors it is possible to carefully perform the $Q \to 0$ extrapolation required to determine the spectrum $Z(\omega)$ of the velocity autocorrelation function of a liquid. The smooth $Q$-dependence of the fit parameters makes their extrapolation to $Q$=0 a simple procedure from which $Z(\omega)$ becomes computable, with the great advantage of solving the problems related to resolution broadening of either experimental or simulated self spectra. Determination of a single-particle property like the spectrum of the velocity autocorrelation function reveals crucial to understand the whole dynamics of the liquid. In fact, we demonstrate the clear link between the collective modes frequencies and the shape of the frequency distribution. In the specific case considered in this work, i.e. liquid Au, analysis of $Z(\omega)$ revealed the presence, along with propagating sound waves, of lower frequency modes that were not observed before by means of dynamic structure factor measurements. By exploiting ab initio simulations for this liquid metal we could also calculate the transverse current-current correlation spectra, and clearly identify the transverse nature of the above mentioned less energetic modes. Existence of propagating transverse excitations appears therefore to be quite a common feature of dense liquids. However, in some cases these are difficult to detect: we show here that the analysis of the single-particle dynamics is able to unveil their presence in a very effective way. The properties here shown to characterize $Z(\omega)$ and the information in it contained allow therefore to identify it with the density of states (DoS) of the liquid. Finally, as a side-output of this work, we provide our estimate of the self diffusion coefficient of liquid gold just above melting.

Extending a preceding study of the velocity autocorrelation function (VAF) in a simulated Lennard-Jones fluid [Phys. Rev. E 92, 042166 (2015)] to cover higher-density and lower-temperature states, we show that the recently demonstrated multi-exponential expansion method allows for a full account and understanding of the basic dynamical processes encompassed by a fundamental quantity as the VAF. In particular, besides obtaining evidence of a persisting long-time tail, we assign specific and unambiguous physical meanings to groups of exponential modes related to the longitudinal and transverse collective dynamics, respectively. We have made this possible by consistently introducing the interpretation of the VAF frequency spectrum as a global density of states in fluids, generalizing a solid-state concept, and by giving to specific spectral components, obtained through the VAF exponential expansion, the corresponding meaning of partial densities of states relative to specific dynamical processes. The clear identification of a high-frequency oscillation of the VAF with the near-top excitation frequency in the dispersion curve of acoustic waves is a neat example of the power of the method. As for the transverse mode contribution, its analysis turns out to be particularly important, because the multi-exponential expansion reveals a transition marking the onset of propagating excitations when the density is increased beyond a threshold value. While this finding agrees with the recent literature debating the issue of dynamical crossover boundaries, such as the one identified with the Frenkel line, we can add detailed information on the modes involved in this specific process in the domains of both time and frequency. This will help obtain a still missing full account of transverse dynamics, in both its nonpropagating and propagating aspects which are linked through dynamical transitions depending on both the thermodynamic states and the excitation wavevectors.

Complex and delocalized manufacturing industries require high levels of integration between production and transportation in order to effectively implement lean and agile operations. There are, however, limitations in research and applications simultaneously embodying further sustainability dimensions. This article presents a methodological framework based on optimization and simulation to integrate (i) aggregate optimized plans for production and multimodal transportation with (ii) detailed dynamic distribution plans affected by demand uncertainty. The objective function of the optimization model considers supply, production, transportation and CO2 emission costs as well as collaboration over the multimodal network. Bill-of-materials and capacity constraints are included. A feedback between simulation and optimization is used to plan requirements for materials and components. Computational experiments are based on realistic instances. Results demonstrate that the framework can be effectively used to analyze cost-CO2 emissions trade-offs, effects of demand uncertainty and collaborative distribution strategies on economic and environmental performance of the supply chain.

Magnetic resonance imaging and magnetic resonance spectroscopy are noninvasive diagnostic techniques based on the phenomenon of nuclear magnetic resonance. Radiofrequency coils are key components in both the transmission and receiving phases of magnetic resonance systems. Transmitter coils have to produce a highly homogeneous alternating field in a wide field of view, whereas receiver coils have to maximize signal detection while minimizing noise. Development of modern magnetic resonance coils often is based on numerical methods for simulating and predicting coil performance. Numerical methods allows the behavior of the coil in the presence of realistic loads to be simulated and the coil's efficiency at high magnetic fields to be investigated. After being built, coils have to be characterized in the laboratory to optimize their setting and performance by extracting several quality indices. Successively, coils performance has to be evaluated in a scanner using standardized image quality parameters with phantom and human experiments. This article reviews the principles of radiofrequency coils, coil performance parameters, and their estimation methods using simulations, workbench, and magnetic resonance experiments. Finally, an overview of future developments in radiofrequency coils technology is included.

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.

The excitatory synaptic function is subject to a huge amount of researches and fairly all the structural elements of the synapse are investigated to determine their specific contribution to the response. A model of an excitatory (hippocampal) synapse, based on time discretized Langevin equations (time-step = 40 fs), was introduced to describe the Brownian motion of Glutamate molecules (GLUTs) within the synaptic cleft and their binding to postsynaptic receptors. The binding has been computed by the introduction of a binding probability related to the hits of GLUTs on receptor binding sites. This model has been utilized in computer simulations aimed to describe the random dispersion of the synaptic response, evaluated from the dispersion of the peak amplitude of the excitatory post-synaptic current. The results of the simulation, presented here, have been used to find a reliable numerical quantity for the unknown value of the binding probability. Moreover, the same results have shown that the coefficient of variation decreases when the number of postsynaptic receptors increases, all the other parameters of the process being unchanged. Due to its possible relationships with the learning and memory, this last finding seems to furnish an important clue for understanding the basic mechanisms of the brain activity. © 2014 Springer Science+Business Media.

The injection of high energy beams of neutral particles is a fundamental method for plasma heating to ignition in the advanced fusion devices. The requirements of the heating neutral beam to be installed on ITER Tokamak and of the full scale prototype megavolt ITER injector and concept advancement represent a large extrapolation from existing devices. An extensive work on numerical modeling is required to optimize the final design and the injector performances. As the power and charge deposition onto components originates from several sources (primary beam, co-accelerated electrons, and secondary production by beam-gas, beam-surface, and electron-surface interaction), the beam propagation along the beam line is simulated by a comprehensive 3-D model of the beam transport and power deposition phenomena along the injector. The code calculates the particle motion in electromagnetic fields, including the secondary production, the reionization of the beam, and the interactions with the surfaces. The preliminary calculations here reported are focused on the phenomena occurring in the residual ion dump.

This paper is focused on the possibility of employing narrow band power line communication (PLC) in medium voltage (MV) distribution networks. The topic is investigated by means of both simulations and experimental tests, which were carried out in the distribution network of Ustica Island. In detail, a two-way MV communication was tested between two secondary substations connected by an MV cable power line. Each substation has a by-pass connection at MV bus-bars and an MV/LV oil filled power transformer. In this paper, the MV and the PLC systems under test are described and the experimental tests are presented, which were carried out to evaluate the parameters of the simulation model. The aforesaid model is described and a comparison is shown between simulation and results of experiments, which were carried out in the presence of voltage net, i.e., 24 kV. Finally, the possibility is investigated of a reliable communication and the faster achievable bit-rate; the analysis is performed by means of further experimental results of several communication tests, which were carried out with different modulation techniques.

Mathematical modelling of the cardiovascular system (CVS) can help in understanding the complex interactions between both the ventricles and the septum. By describing the behaviour of the left (right) ventricular free wall, atria and septum using the variable elastance models, it is possible to reproduce their interactions. By relating the mechanical properties of both atria and both ventricles to the electrocardiogram (ECG) signal, it is possible to analyse the effects produced by different ECG delay on haemodynamic parameters. In the cardiovascular field, the incorrect Q1 interactions between septum and both ventricular free walls are based on many pathological conditions, i.e. symptomatic heart failure resulting from systolic dysfunction, ischemic dilated cardiomyopathy, and so on. The possible corrections that can be induced on the QRS complex duration in the ECG signal (i.e. cardiac resynchronisation therapy, CRT) can produce benefits improving the clinical status of the patient. The aim of this work was to evaluate, using our numerical simulator of the CVS, the effects induced on coronary blood flow (CBF) and aortic pressure using different ECG times, intra-ventricular and inter-ventricular delays. The results were obtained by reproducing the circulatory baseline and CRT conditions of seven patients described in literature. Haemodynamic simulated results are in accordance with literature data. Also the controversial results on CBF, in presence of CRT, are consistent with those described in the literature.

Mathematical models of the excitatory synapse are furnishing valuable information about the synaptic response. Based on Brownian-diffusion of glutamate molecules, a synapse model was utilized to investigate the synaptic response on a femto-second time scale by the use of a parallel computer. In particular, the presence of fibrils crossing the synaptic cleft was simulated, which could have a role in shaping the brain activity. To this aim the model of synapse was modified by considering trans-synaptic filaments with diameters ranging from 7. nm to 3. nm, disposed on a grid with spacing of 14. nm or 8. nm. The simulation demonstrated that the presence of filaments induced an increase in the synaptic response, most likely linked to an increment in the probability of encounter between glutamate molecules and receptors. The increase was small - from 5 to 20%, but metabolic and functional considerations provide substantive hints about the importance of these small changes for brain activity. Moreover, it was shown that the presence of filaments made more stable the response of the synapse to random variations of pre-synaptic elements. Originated by these computational results, some inferences about the biological bases of mind diseases such as autism, mental retardation and schizophrenia, are reported in the Discussion. © 2010 Elsevier Ireland Ltd.

All-optical control of a rectangular waveguide with liquid crystal is theoretically investigated. Light propagation is established with low input power control, that excites optical nonlinearity due to optically induced reorientational effect. © 2011 IEEE.

We present a Monte Carlo study of a liquid crystal-polymer interface, focusing on a single cell with boundary conditions tailored to mimic the main features of the system and we examine the effect of an external applied field. A simple lattice spin model, based on the Lebwohl-Lasher hamiltonian, has been employed to represent the nematic and the polymer molecules. The orientations of the spins representing the low molar mass nematic molecules are updated during the simulations while the polymer chain units are kept frozen. The model allows us to investigate the molecular organization and the ordering expected across the cell. Moreover the response to the change in external field intensity and duration pulse is also studied. Copyright © Taylor & Francis Group, LLC.

In this paper we present a multiscale framework for the simulation of electronic devices allowing the coupling of continuum and atomistic models in a transparent way. We introduce the basic features of the TiberCAD simulation software which is based on the multiscale simulation concept, and we show a simulation example to illustrate the basic aspects of a multiscale simulation. © Springer Science+Business Media LLC 2010.

Fabrication of channel waveguides in Er-doped tungsten-tellurite glasses was recently demonstrated. In order to get a deeper understanding of the process and to optimize the characteristics of the waveguides, we fabricated a set of planar waveguides, each of 7 mm × 7 mm lateral dimensions, in an Er-doped tellurite glass sample by implantation of 1.5 MeV nitrogen ions. Doses of the implanting ions ranged from 1 · 10 16 to 8 ·10 16 ions/cm 2. The samples were studied using interference phase contrast microscopy (Interphako), m-line spectroscopy and spectroscopic ellipsometry. The results show that a barrier layer of reduced refractive index was created around the range of the implanted ions at every dose. It is hoped that combination of the results obtained in these experiments with simulations for channel waveguides will make it possible to optimize ion-implanted fabrication of integrated optical components in this tellurite glass.

In this paper we present CAMELotGrid, a tool to manage Grid computations of Cellular Automata that support the efficient simulation of complex systems modeled by a very large number of simple elements (cells) with local interaction only. The study of these systems has generated great interest over the years because of their ability to generate a rich spectrum of very complex patterns of behavior out of sets of relatively simple underlying rules. Moreover, they appear to capture many essential features of complex self-organizing cooperative behavior observed in real systems. The middleware architecture of CAMELotGrid is designed according to an autonomic approach on top of the existing Grid middleware and supports dynamic performance adaptation of the cellular application without any user intervention. The user must only specify, by global criteria, the high level policies and submit the application for execution over the Grid. © 2006 Elsevier Ltd. All rights reserved.

This work deals with the viscous flow around an array of cylinders impinged by an incoming wave. Different configurations are considered in order to evaluate the effects of both wave heading and wave height on the loads applied to the bodies and on the run-ups. The results are also compared to previous calculations obtained with the assumption of inviscid flow with the aim of evaluating the contribution of viscosity.