Operating principle of dual collector magnetotransistors studied bytwo-dimensional simulation

Dual collector magnetotransistors are magnetic-field-sensitive devices currently developed in several laboratories. Optimized sensor design is often attempted by trial and error rather than by established design rules. This motivated the present comprehensive study of the operation of magnetotransistors by accurate two-dimensional numerical simulations. We model vertical and lateral transistors as obtained by industrial IC technology on the basis of data provided by the chip manufacturer. We consider the entire device structure with the full, complex device geometry, and the physically proper boundary conditions. Our simulations reveal the details, controversial hitherto, of the operating principle of these devices. In particular we find that, in the case of the vertical transistor, it is essentially the emitter injection modulation effect which dominates the sensor response. In the case of the lateral transistor, the magnetic sensitivity is predominantly determined by minority-carrier deflection, though side effects are involved as well. By variation of the doping profile and the device geometry we derive rules for optimized magnetotransistor design     

Design and evaluation of a multimedia storage server for mixed traffic

The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach.     

Moisture-dependent engineering properties of sunflower seeds with different structural characteristics

The present study was carried out to investigate the effect of the moisture content of the seeds on engineering properties of sunflower hybrids with different structural characteristics. The properties were evaluated at seven levels of moisture from 2.0% to 20.1% (dry basis) for three selected sunflower hybrids. For both black-hull oilseed hybrid and confectionary hybrid, the variation in moisture content showed a statistically significant effect on dehulling ability, percentage of fines (broken grains with a diameter smaller than 2 mm) and all the physical properties studied (size, true density, bulk density, porosity, volume and weight, volumetric expansion coefficient, equivalent diameter and sphericity), except seed length in the confectionary hybrid and seed length and thickness in the black-hull oilseed hybrid. For the striped-hull oilseed hybrid, moisture content showed a significant effect only on dehulling ability, percentage of fines, seed width and thickness, bulk density and porosity. Of the oilseed hybrids, the striped hull genotype (higher hull content and both lower oil content and seed size) presented a higher dehulling ability. Nevertheless, the black hull hybrid resulted more sensitive to seed moisture changes. Although the confectionary hybrid showed a higher seed size, hull thickness and hull content, and lower oil content than the oilseed hybrids, the dehulling ability resulted fairly similar in the striped hull sunflower hybrids. The results suggest that sunflower seeds with different structural characteristics need to be conditioned with different moisture content before being subjected to the dehulling process.     

Efficient generation of pre-silicon MOS model parameters for earlycircuit design

The technology development cycle continues to shrink, which very often requires evaluation of circuit design and technology choices using circuit simulators at the time when no real silicon is available. In this paper, we present an efficient methodology for generating pre-silicon device models for advanced CMOS processes. The methodology allows accurate prediction of the full MOS I-V characteristics for the future technologies combining a constraint backpropagation algorithm based upon a few critical specifications, physical models for the advanced device phenomena, and the empirical data from devices of an existing technology. The methodology has been tested on two CMOS production technologies. Good prediction results are achieved: for nMOS the rms error is 1%-2%, for pMOS it is 2%-4%     

A model advisor for NuSMV specifications

Among possible model validation techniques able to identify defects early in the system development, model review aims also at determining if a model is of sufficient quality, where quality is measured as the absence of certain faults. In this paper, we tackle the problem of automatic reviewing NuSMV formal specifications by developing a model advisor which helps to assure given model qualities for NuSMV programs. Vulnerabilities and defects a developer can introduce during the modeling activity using NuSMV are expressed as the violation of formal meta-properties. These meta-properties are then mapped to temporal logic formulas, and the NuSMV model checker itself is used as the engine of our model advisor to notify meta-properties violations, so revealing the absence of some quality attributes of the specification. As a proof of concept, we also report the result of applying this review process to several NuSMV specifications.     

ASM-based formal design of an adaptivity component for a Cloud system

The request of formal methods for the specification and analysis of distributed systems is nowadays increasing, especially when considering the development of Cloud systems and Web applications. This is due to the fact that modeling languages currently used in these areas have informal definitions and ambiguous semantics, and therefore their use may be unreliable. Thanks to their mathematical foundation, formal methods can guarantee rigorous system design, leading to precise models where requirements can be validated and properties can be assured, already at the early stages of the system development. In this paper, we present a rigorous engineering process for distributed systems, based on the Abstract State Machines (ASM) formal method. We rely on the foundational notions of ASM ground model and model refinement to obtain a precise model for a client-server application for Cloud systems. This application has been proposed to tackle the problem of making Cloud services usable to different end-devices by adapting on-the-fly the content coming from the Cloud to the different devices contexts. The ASM-based modeling process is supported by a number of validation and verification activities that have been exploited on the component under development to guarantee consistency, correctness, and reliability properties.     

Enhancing DSR maintenance with power awareness

A power-aware route maintenance protocol for Mobile Ad Hoc Networks (MANETs) is introduced. Termed Dynamic Path Switching (DPS), the new protocol puts an overloaded node to sleep before a route link breaks because that node runs out of energy, and brings other suitable nodes into play instead. When the battery charge of a node reaches a stated level, the node can advance a request to change to a sleep state for a while. The request is honoured unless survival of some path rests on the forwarding activity of that very node. All nodes are assumed to be collaborative. The DPS protocol is fully backward compatible, as it can be implemented within existing routing protocols such as Dynamic Source Routing (DSR). The new protocol has been extensively simulated with the established network simulator NS2. The findings indicate a much improved power awareness of the updated routing protocol with respect to the unadorned one. Power saving is particularly effective during long-lived sessions.     

Rigorous development process of a safety-critical system: from ASM models to Java code

International Journal on Software Tools for Technology Transfer - The paper presents an approach for rigorous development of safety-critical systems based on the Abstract State Machine formal...