On the sixty-four polynomials of Djaferis to stabilize an intervalplant

This paper shows that 32 of the 64 polynomials developed by Djaferis to stabilize an interval plant with a controller are superfluous. Thus it is sufficient to stabilize 32 polynomials simultaneously. Moreover the construction developed in this note allows the implementation of these polynomials in a simple way     

Computer support for learning in collaborative contexts: prompted hypothesis testing in physics

An enormous amount of work has been carried out into the ways in which computers can support collaboration in the service of learning. Less attention has been paid to computer support for learning when collaboration is non-problematic, yet this is arguably of equal significance. Recognizing this, the present paper reports software which was developed to help collaborating pupils test hypotheses, an activity thought by many to be relevant to conceptual learning. The software addressed hypotheses relating to: (a) the factors which influence the pressure of water; and (b) the factors which influence the formation of shadows. It required collaborating pupils to formulate hypotheses about such factors, decide which factors must be manipulated to check correctness, formulate predictions about outcomes prior to testing, observe the results of tests, and draw conclusions across test series. Pupils were asked to input their decisions at key points as they used the software, and they received prompts to the extent that their decisions were inappropriate. The prompts became increasingly explicit as inappropriate decisions persisted. The paper describes the use of the software by 9–14-year-old pupils, comparing their activity with that of similarly aged pupils who worked with otherwise equivalent software which lacked any prompts. Evidence is presented for the value of prompting, with implications not simply for the use of hypothesis testing as an instructional strategy but also for the design of computer-based support for other complex and co-ordinated activities.     

迷你冷轧--21世纪冷轧技术

21世纪迷你冷轧(Minicold 21^TM)型冷轧厂——体现冷轧高附加值扁平产品的柔性生产概念。为了高效生产冷轧、镀锌以及彩涂扁平产品,达涅利威恩联合公司开发了称为“21世纪迷你冷轧(Minicold 21^TM)”冷轧工艺。其最简单的形式包括1条推拉式酸洗线、1台单机架或双机架可逆冷轧机、批示退火、1台平整机和1台可配置在线彩涂的热浸镀锌。讨论了21世纪迷你冷轧(Minicold 21^TM)型冷轧厂的技术特点并根据预计资本投资和转换成本以及产出产品市场价格进行了经济效益分析。分析说明在大多数情况下大约年产量50万t的冷轧厂能够产生经济效益。     

Combinational system of a truncated ball lens and a hyperbolic lens for collimating a highly divergent source

We propose the use of a truncated ball lens in a collimating system to transform a spherical wave from a highly divergent source into a plane wave. The proposed scheme, which incorporates a hyperbolic lens, is discussed, and the overall system is found to have a large acceptance angle and to be free of spherical aberration. Diffraction and polarization effects are neglected, as well as skew rays.     

Compound parabolic tapered fiber for fiber coupling with a highly divergent source

A novel fiber tapering shape, which is based on compound parabolic geometry, is proposed to increase the acceptance angle of a compound parabolic concentrator. The proposed design is described by use of ray optics on a step-index multimode fiber.     

Observations and simulations of the low velocity-to-hypervelocity impact crater transition for a range of penetrator densities into thick aluminum targets

Projectile/target impact crater systems involving soda-lime glass/1100 aluminum, ferritic stainless steel/1100 aluminum, and tungsten carbide/1100 aluminum (corresponding to projectile densities of 2.2, 7.89, and 17 Mg (m³) at impact velocities ranging from 0.56 to 3.99 km/s were examined by light metallography, SEM, and TEM. Plots of crater depth/crater diameter ratio (p/D _c) versus impact velocity exhibited anomalous humps with p/D _c ranging from 0.8 to 5.5 between 1 and 2 km/s, with hypervelocity threshold or steady-state values of p/D _c (>5 km/s) ranging from 0.4 to 1.0; with the p/D _c values increasing with increasing projectile density in each case. This hump-shaped regime, with exaggerated target penetration depths, appears to occur because projectiles remain relatively intact and unfragmented. The crater geometry begins to change when the projectile fragmentation onset velocity (>2 km/s) is exceeded and fragmentation increases with increasing impact velocity. Computer simulations and validation of these simulations were developed which fairly accurately represented residual crater shapes/geometries and correlated experimentally measured microhardness maps with simulated residual yield stress contour maps. Validated computer simulations allowed representative extrapolations of impact craters well beyond the laboratory where melting and solidification occurred at the crater wall, especially for hypervelocity impact (>5 km/s).     

A statistical approach to model simplification and multiobjective analysis

Evolving national energy supply/demand distribution systems rely, at least in part, on quantifiable factors such as local and national environmental restrictions, resource availability (type, price, and quantity) and the associated transportation infrastructure, the amount and price of capital available to consumers and suppliers of energy, total annualized system cost, including the annualized cost of end-use devices, and the demands for energy and their price/supply responsiveness. The evolution also depends on nonquantifiable factors such as personal, regionally aggregated, or even national “utility functions” and institutional or social barriers. Many models have been formulated which attempt to simulate these complex interactions.This paper describes a systematic statistical methodology for capturing, both visually and quantitatively, the trade-offs between competing quantifiable, differentiable objective functions in a model of the national energy system (Brookhaven Energy System Optimization Model). The aim is to provide decision makers with a more easily understood tool and a more easily defensible methodology on which trade-offs between certain sensitive and competing energy issues can be based. The methodology has the additional advantage of providing insights into the inherent structural relationships of the model (model simplification).     

Is hostility linked with affiliation among males and with achievement among females? A critique of Pollak and Gilligan.

Attempted to replicate and to clarify methodologically an investigation by S. Pollak and C. Gilligan (see record 1982-23594-001). Those investigators reported sex differences in violence imagery to TAT pictures depicting affiliation and achievement situations. Pollak and Gilligan concluded that men perceive danger in situations of affiliation whereas women perceive danger in situations of achievement. The present study demonstrated that Pollak and Gilligan incorrectly classified TAT cards into motivational categories, which may have resulted in incorrect inferences. In addition, their findings could not be replicated when 4 different systems for classifying TAT cards into motivational categories were used with 204 undergraduates. Other potential sources of error in their research, including a restrictive scoring scheme for hostility, unusual instructions, and failure to control for sex role in the TAT pictures, did not influence the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)