Weighted Density Functionals for Ferroelectric Materials

The weighted density approximation, its implementation and its application to ferroelectric materials is discussed. Calculations are presented for several perovskite oxides and related materials. In general the weighted density approximation is found to be superior to either the local density or generalized gradient approximation for the ground state. Electronic structures are little changed. The linear response of the weighted density approximation is calculated for the homogeneous electron gas, and found to be improved relative to the local density result, but not in full agreement with existing Monte Carlo data. It is shown that the agreement can be further improved by a simple modification. Calculations of the ferroelectric soft mode in KNbO$_3$ suggest that the low temperature distortion is approximately 20% smaller than indicated by existing experiments.Comment: 14 pages, 2 embedded figures, uses aipproc style. Contribution submitted to the Fifth Williamsburg Workshop on First-Principles Calculations for Ferroelectric

Knowledge base methodology: Methodology for first Engineering Script Language (ESL) knowledge base

The primary goal of reusing software components is that software can be developed faster, cheaper and with higher quality. Though, reuse is not automatic and can not just happen. It has to be carefully engineered. For example a component needs to be easily understandable in order to be reused, and it has also to be malleable enough to fit into different applications. In fact the software development process is deeply affected when reuse is being applied. During component development, a serious effort has to be directed toward making these components as reusable. This implies defining reuse coding style guidelines and applying then to any new component to create as well as to any old component to modify. These guidelines should point out the favorable reuse features and may apply to naming conventions, module size and cohesion, internal documentation, etc. During application development, effort is shifted from writing new code toward finding and eventually modifying existing pieces of code, then assembling them together. We see here that reuse is not free, and therefore has to be carefully managed

Real Trends or Measurement Problems? Disability and Employment Trends from the Survey of Income and Program Participation

This paper addresses important concerns in using statistical data to track outcomes of people with disabilities and provides new evidence of employment trends of people with disabilities using alternative disability conceptualizations from the Survey of Income and Program Participation (SIPP). This analysis comes at an important time because some researchers have criticized the data and definitions used to measure these trends. At the extreme, some have concluded that such analyses should cease because of major limitations in measuring disability that exists in current surveys (especially the SIPP). Because the SIPP has been used extensively to examine outcomes of people with disabilities, it is important to understand these data criticisms and test whether the trends from the SIPP mirror those in other data sources. We conclude that the different empirical results found by researchers are not caused by "problems" with the data but rather with the assumptions researchers make when using the data. We illustrate the importance of exercising caution when developing disability questions and measuring disability trends in existing data sources. While some measures of limitations may be problematic, we find that the relatively broad measures used in several disability studies provide reasonable estimations of important subgroups of people with disabilities. We also show that the timing and structure of specific questions affects disability prevalence rates and influences observed outcomes. When we use comparable definitions across panels, we consistently find that employment rates of men with disabilities have fallen from 1990 to 1996 and employment rates of women with disabilities have remained flat. The consistency of these findings across a variety of measures illustrates an important and disturbing trend of downward employment rates for people with disabilities. These findings are particularly disturbing because they suggest that the gap in employment rates between those with and without disabilities is growing