Treating some solid state problems with the Dirac equation

The ambiguity involved in the definition of effective-mass Hamiltonians for nonrelativistic models is resolved using the Dirac equation. The multistep approximation is extended for relativistic cases allowing the treatment of arbitrary potential and effective-mass profiles without ordering problems. On the other hand, if the Schrodinger equation is supposed to be used, our relativistic approach demonstrate that both results are coincidents if the BenDaniel and Duke prescription for the kinetic-energy operator is implemented. Applications for semiconductor heterostructures are discussed.Comment: 06 pages, 5 figure

Comparison of the far-field aerodynamic wake development for three DrivAer model configurations using a cost-effective RANS simulation

The flow field and body aerodynamic loads on the DrivAer reference model have been extensively investigated since its introduction in 2012. However, there is a relative lack of information relating to the models wake development resulting from the different rear-body configurations, particularly in the far-field.Given current interest in the aerodynamic interaction between two or more vehicles, the results from a preliminary CFD study are presented to address the development of the wake from the Fastback, Notchback, and Estateback DrivAer configurations. The primary focus is on the differences in the far-field wake and simulations are assessed in the range up to three vehicle lengths downstream, at Reynolds and Mach numbers of 5.2×106 and 0.13, respectively.Wake development is modelled using the results from a Reynolds-Averaged Navier-Stokes (RANS) simulation within a computational mesh having nominally 1.0×107 cells. This approach was chosen to reflect a simple, cost-effective solution, using an industry-standard CFD solver. Each vehicle configuration has a smooth underbody, with exterior rear-view mirrors. The computational modelling includes a ground simulation set, and all simulations are for zero freestream yaw angle. A mesh sensitivity study was undertaken and the simulation validated against published experimental data for the body pressure distribution and aerodynamic drag.Critical assessment of the results highlights the benefits of focussed mesh refinement and specific numerical strategies for optimum performance of the CFD solver. Comparison of the far-field aerodynamic wake for the three model configurations exhibits significant differences in both extent and structure within the wake region up to three vehicle lengths downstream of the base. Total pressure loss coefficient is used as the primary aerodynamic parameter for analysis. The study is an element of a larger programme related to vehicle wake simulation and strategies are identified for possible wake modelling using simplified, computationally and experimentally efficient, shapes

Neuronal assembly dynamics in supervised and unsupervised learning scenarios

The dynamic formation of groups of neurons—neuronal assemblies—is believed to mediate cognitive phenomena at many levels, but their detailed operation and mechanisms of interaction are still to be uncovered. One hypothesis suggests that synchronized oscillations underpin their formation and functioning, with a focus on the temporal structure of neuronal signals. In this context, we investigate neuronal assembly dynamics in two complementary scenarios: the first, a supervised spike pattern classification task, in which noisy variations of a collection of spikes have to be correctly labeled; the second, an unsupervised, minimally cognitive evolutionary robotics tasks, in which an evolved agent has to cope with multiple, possibly conflicting, objectives. In both cases, the more traditional dynamical analysis of the system’s variables is paired with information-theoretic techniques in order to get a broader picture of the ongoing interactions with and within the network. The neural network model is inspired by the Kuramoto model of coupled phase oscillators and allows one to fine-tune the network synchronization dynamics and assembly configuration. The experiments explore the computational power, redundancy, and generalization capability of neuronal circuits, demonstrating that performance depends nonlinearly on the number of assemblies and neurons in the network and showing that the framework can be exploited to generate minimally cognitive behaviors, with dynamic assembly formation accounting for varying degrees of stimuli modulation of the sensorimotor interactions

Prospek Perkembangan Lembaga Keuangan Mikro Di Ambarawa: Studi Penjajagan Kebutuhan Pendampingan Masyarakat

This research is a “snapshot” of the people's economic problems especially of the socio-economic and cultural institutions in the villages in Kecamatan Ambarawa. The research has identified institutions and the so-called micro-finance institutions in the villages as initiated by both the people in the villages and by the village government. The government policies to mobilize the micro-finance institutions through top-down planning were carried out by various government institutions with limited success. It is now realized that it will be more effective and successful if it is implemented by the village people themselves in the form of self-reliance movement on micro finance

On the aerodynamics of an enclosed-wheel racing car: an assessment and proposal of add-on devices for a fourth, high-performance configuration of the DrivAer model

A modern benchmark for passenger cars – DrivAer model – has provided significant contributions to aerodynamics-related topics in automotive engineering, where three categories of passenger cars have been successfully represented. However, a reference model for highperformance car configurations has not been considered appropriately yet. Technical knowledge in motorsport is also restricted due to competitiveness in performance, reputation and commercial gains. The consequence is a shortage of open-access material to be used as technical references for either motorsport community or academic research purposes. In this paper, a parametric assessment of race car aerodynamic devices are presented into four groups of studies. These are: (i) forebody strakes (dive planes), (ii) front bumper splitter, (iii) rear-end spoiler, and (iv) underbody diffuser. The simplified design of these add-ons focuses on the main parameters (such as length, position, or incidence), leading to easier manufacturing for experiments and implementation in computational studies. Consequently, a proposed model aims to address enclosed-wheel racing car categories, adapting a simplified, 35% scaled-model DrivAer Fastback shape (i.e. smooth underbody, no wheels, and with side mirrors). Experimental data were obtained at the 8ft x 6ft Cranfield Wind Tunnel using an internal balance for force and moment measurements. The aerodynamic performance of each group of add-on was assessed individually in a range of ride heights over a moving belt. All cases represent the vehicle at a zero-yaw condition, Reynolds number (car length-based) of 4.2 × 106 and Mach number equal to 0.12. The proposed high-performance configuration (DrivAer hp-F) was tested and a respective Reynolds number dependency study is also provided. In line with the open-access concept of the DrivAer model, the CAD geometry and experimental data will be made available online to the international community to support independent studies

Wigner phase space distribution as a wave function

We demonstrate that the Wigner function of a pure quantum state is a wave function in a specially tuned Dirac bra-ket formalism and argue that the Wigner function is in fact a probability amplitude for the quantum particle to be at a certain point of the classical phase space. Additionally, we establish that in the classical limit, the Wigner function transforms into a classical Koopman-von Neumann wave function rather than into a classical probability distribution. Since probability amplitude need not be positive, our findings provide an alternative outlook on the Wigner function's negativity.Comment: 6 pages and 2 figure