Simulation — a bridge between theory and reality: the case of electric circuits

Abstract This study aimed to examine the role of a simulation as a potential aid that may help students bridge the gap between theory and reality, in the case of electric circuits. Sixty-three pairs of students aged about 15 years were presented with two tasks involving real circuits. An open simulation environment was available as an optional aid for the experimental group. Significant differences were found between the achievements of the groups. The use of the simulation contributed to students' confidence and enhanced their motivation to stay on-task. The detailed analysis revealed the role of the simulation as a source of constructive feedback, helping students identify and correct their miscon-ceptions and cope with the common difficulties of relating formal representations to real circuits and vice versa.     

Highly Efficient Ge-Rich Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te Thermoelectric Alloys

The search for alternative energy sources is presently at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This paper is concerned with the development of highly efficient p-type Ge _x Pb_1−x Te alloys for thermoelectric applications, using spark plasma sintering. The carrier concentration of GeTe was varied by alloying of PbTe and/or by Bi₂Te₃ doping. Very high ZT values up to ~1.8 at 500°C were obtained by doping Pb_0.13Ge_0.87Te with 3 mol% Bi₂Te₃.     

Structural Evolution Following Spinodal Decomposition of the Pseudoternary Compound (Pb0.3Sn0.1Ge0.6)Te

Pseudoternary (Ge,Sn,Pb)Te compounds display favorable thermoelectric properties. Spinodal decomposition in the quasiternary (Ge,Sn,Pb)Te system is at the origin of a wide solubility gap at low Sn concentrations. The structural evolution of the spinodal decomposition was investigated as a function of aging time at 500°C, using x-ray diffraction, electron microscopy, and scanning electron microscopy. The evolution of the structure at 500°C consists initially of a short diffusion-controlled demixing stage into Pb- and Ge-rich coherent areas, with compositions corresponding to the inflection points of the free-energy curve. The Pb-rich areas adopt configurations associated with the directions of the soft elastic moduli of the cubic compound. Both the Pb- and Ge-rich areas are supersaturated and undergo in a second stage a nucleation and growth process and give rise to a biphased structure with equilibrium compositions corresponding to the boundaries of the miscibility gap. The resulting Pb-rich areas display a relatively stable microstructure suggesting the presence of long-range interactions between the Pb-rich precipitates in the Ge-rich matrix.     

Peak management

Peaks occur when a firm accustomed to operating under market constraint conditions occasionally encounters peaks in market demand that temporarily exceed the firm's supply capacity. This paper defines the demand peak, classifies peak management (PM) conditions and prescribes a framework for PM. The Theoryof-Constraints (TOC) is expanded to handle the PM concept, introducing the two-policy concept: one policy for peak periods and another for non-peak periods. The paper outlines techniques to elevate the firm's peak performance by loading during the peak period. Distinct pricing policies for peak and offpeak periods are presented and a comprehensive methodology is suggested to deal with the PM problem, including labour policy, outsourcing policy and pricing policy. The paper demonstrates the methodology and techniques in a broad range of real-life management situations. Under TOC principles, the present analysis shows the different decision rules for the two periods and their substantial impact on the firm's overall strategy. Finally, the paper discusses the ramifications of operating under two distinct sets of rules, as well as the rules for making the transitions between an off-peak and a peak period.     

Effect of stochastically anisotropic morphology on the mechanical behavior of microbeams

In many Micro-Electro-Mechanical-Systems (MEMS) applications such as polysilicon microstructures, the size of the basic element (grain), compared with the structure’s scale, is not negligible. In these cases, the random microstructure causes statistical dispersion of its response to load, experimentally observed by many researchers. The accompanying calculations, which generally treat the material as homogeneous and isotropic, do not model the structures properly. In this work, we analytically study the relations between morphological properties and the generalized displacements of statically determinate beams, frequently used in MEMS. The analysis includes shear deformation effects, material and structural couplings such as shear and bending deformations due to normal forces, and nonisotropic effects. The governing equations are presented in a special tensorial form, which enables finding analytical expressions for the mean and covariance matrix of the generalized deflections in terms of well defined morphological parameters and their statistics.     

Quality of life in younger adults (17-49) after first stroke--a two year follow-up]

To study the effect of stroke on the quality of life in younger adults, 199 patients 17-49 years of age who had sustained a first stroke between 1.11.92 and 31.10.93 were followed up. They were interviewed by telephone at 3, 6, 12 and 24 months after the event. 2 died during the first year of follow-up, and 8 had recurrent strokes. After 2 years, 8 additional patients had died and 4 had sustained recurrent events. Gradual improvement was reported within all age groups and in all areas. During the 3-6 months period, a mean of 4% improvement occurred in functional capability, 15% in social and recreational activity and 8% in return-to-work. The 6-12 month period showed an increase of 3% in improvement in mean functional capability, 10% in social and recreational activity and 2% in return-to-work. 1 year after the stroke 27% remained with moderate to severe disability, but over 86% were functionally independent in their daily living activities. There were no significant changes during the second year of follow-up in these statistics. 67% of those employed prior to their stroke returned to work and approximately 70% reported a return to prestroke social and recreational activity. These results demonstrate that the relatively high recovery rate and functional improvement during a year of follow-up were not accompanied by similar rates of improvement in employment and in social integration. They indicate the need for increased emphasis on long-term psychosocial rehabilitation services within the community.     

Understanding metaphorical comparisons: Beyond similarity.

Traditionally, metaphors such as "my job is a jail" have been treated as implicit similes (i.e., this metaphor would be treated as if it were a comparison statement, "my job is like a jail"). A. Tversky's (1977) account of similarity is applied to such nonliteral similarity expressions, and is shown to apply as readily to nonliteral comparisons as to literal comparisons. But treating metaphors as comparison statements fails to account for certain important phenomena, including metaphoricity itself (the judgment that a comparison statement is nonliteral). We argue that metaphors are exactly what they appear to be: class-inclusion assertions, in which the topic of the metaphor (e.g., "my job") is assigned to a diagnostic category (e.g., entities that confine one against one's will, are unpleasant, are difficult to escape from). In such assertions, the metaphor vehicle (e.g., "jail") refers to that category, and at the same time is a prototypical exemplar of that category. This account of metaphor provides a basis for a theory of metaphor comprehension, and also clarifies why people use metaphors instead of similes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A note on efficient aggregate queries in sensor networks

We consider a scenario where nodes in a sensor network hold numeric items, and the task is to evaluate simple functions of the distributed data. In this note we present distributed protocols for computing the median with sublinear space and communication complexity per node. Specifically, we give a deterministic protocol for computing median with polylog complexity and a randomized protocol that computes an approximate median with polyloglog communication complexity per node. On the negative side, we observe that any deterministic protocol that counts the number of distinct data items must have linear complexity in the worst case.