Scattering and space-charge effects in Wigner Monte Carlo simulations of single and double barrier devices

Transport in single and double barrier devices is studied using a Monte Carlo solver for the Wigner transport equation. This approach allows the effects of tunneling and scattering to be included. Several numerical methods have been improved to render the Wigner Monte Carlo technique more robust, including a newly developed particle annihilation algorithm. A self-consistent iteration scheme with the Poisson equation was introduced. The role of scattering and space charge effects on the electrical characteristics of n-i-n nanostructures, ultra-scaled double gate MOSFETs, and GaAs resonant tunneling diodes is demonstrated. An erratum to this article can be found at     

Numerical Analysis of Coaxial Double Gate Schottky Barrier Carbon Nanotube Field Effect Transistors

Carbon nanotube field-effect transistors (CNTFETs) have been studied in recent years as a potential alternative to CMOS devices, because of the capability of ballistic transport. The ambipolar behavior of Schottky barrier CNTFETs limits the performance of these devices. A double gate design is proposed to suppress this behavior. In this structure the first gate located near the source contact controls carrier injection and the second gate located near the drain contact suppresses parasitic carrier injection. To avoid the ambipolar behavior it is necessary that the voltage of the second gate is higher or at least equal to the drain voltage. The behavior of these devices has been studied by solving the coupled Schrödinger-Poisson equation system. We investigated the effect of the second gate voltage on the performance of the device and finally the advantages and disadvantages of these options are discussed.     

Improving the clinical potential of ultra-high field fMRI using a model-free analysis method based on response consistency

Objective

To develop an analysis method that is sensitive to non-model-conform responses often encountered in ultra-high field presurgical planning fMRI. Using the consistency of time courses over a number of experiment repetitions, it should exclude low quality runs and generate activation maps that reflect the reliability of responses.

Materials and methods

7 T fMRI data were acquired from six healthy volunteers: three performing purely motor tasks and three a visuomotor task. These were analysed with the proposed approach (UNBIASED) and the GLM.

Results

UNBIASED results were generally less affected by false positive results than the GLM. Runs that were identified as being of low quality were confirmed to contain little or no activation. In two cases, regions were identified as activated in UNBIASED but not GLM results. Signal changes in these areas were time-locked to the task, but were delayed or transient.

Conclusion

UNBIASED is shown to be a reliable means of identifying consistent task-related signal changes regardless of response timing. In presurgical planning, UNBIASED could be used to rapidly generate reliable maps of the consistency with which eloquent brain regions are activated without recourse to task timing and despite modified hemodynamics.

     

Evolution of Current Transport Models for Engineering Applications

An overview of models for the simulation of current transport in micro- and nanoelectronic devices within the framework of TCAD applications is presented. Starting from macroscopic transport models, currently discussed enhancements are specifically addressed. This comprises the inclusion of higher-order moments into the transport models, the incorporation of quantum correction and tunneling models up to dedicated quantum-mechanical simulators, and mixed approaches which are able to account for both, quantum interference and scattering. Specific TCAD requirements are discussed from an engineer’s perspective and an outlook on future research directions is given.     

Heterogeneous distribution of chain mobility in nascent UHMWPE in the less entangled state

The structure of chain entanglements in the solid state is important for revealing the relationship of structure and properties of polyolefin. In this work, low-field solid-state ¹H NMR is used to study the chain dynamics of ultra-high molecular weight polyethylene (UHMWPE) in the solid state. It has been found that the relaxation distribution, analyzed by a multi-exponential inversion program, is an effective method to characterize the heterogeneous chain mobility. It is evidenced from the results that the UHMWPE in a less entangled state presents an obviously heterogeneous distribution of chain mobility in the non-crystalline phase, corresponding to its heterogeneous distribution of entangled points. In comparison, the commercial UHMWPE with a large number of entanglements shows a much more uniform mobility of the non-crystalline components. This heterogeneous distribution of chain mobility becomes even more critical after annealing the samples below the melting point, especially for the less entangled UHMWPE.     

Multiobjective Groundwater Management Using Evolutionary Algorithms

Sustainable management of groundwater resources is of crucial importance for regions where freshwater supply is naturally limited. Long-term planning of groundwater usage requires computer-based decision support tools: on the one hand, they must be able to predict the complex system dynamics with sufficient accuracy, on the other, they must allow exploring management scenarios with respect to different criteria such as sustainability, cost, etc. In this paper, we present a multiobjective evolutionary algorithm for groundwater management that optimizes the placement and the operation of pumping facilities over time, while considering multiple neighboring regions which are economically independent. The algorithm helps in investigating the cost tradeoffs between the different regions by providing an approximation of the Pareto-optimal set, and its capabilities are demonstrated on a three-region problem. The application of the proposed methodology can also serve as a benchmark problem as shown in this paper. The corresponding implementation is freely available as a precompiled module at http://www.tik.ee.ethz.ch/pisa.     

A generalisation of the interval Newton single-step method for nonlinear systems of equations

In this paper interval iteration methods for solving large nonlinear systems of equations are considered. Already well-known methods are combined to a new one, whose enclosing properties are better than those of previous methods. Convergence of this new method is shown, based on a new convergence proof for the interval Newton single-step method. The central concept in this case is the fixpoint inverse of an interval matrix. Practical tests with nonlinear systems of equations arising from discretisation of certain elliptic partial differential equations show the efficiency of the new method.     

Identification of patients at risk for nonresponse and negative outcome in psychotherapy.

This study evaluated the use of pretherapy patient variables as correlates of 3 categorical types of outcome: negative response (negative change of more than 1 normative SEest on depression measure): nonresponse (change within?±?1 SEest on depression measure); and positive response (positive change of more than 1 SEest on depression measure) to psychotherapy among 62 patients with major depressive disorder. By using 4 scales from the Brief Symptom Inventory, the Inventory of Interpersonal Problems, age, and sex, 75.8% of the Ss were correctly classified into the 3 groups. Negative responders were characterized by high levels of interpersonal difficulty and low levels of subjective distress. Nonresponders displayed moderate levels of both interpersonal difficulties and subjective distress. Positive responders displayed high levels of both interpersonal difficulties and subjective distress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)