Systems Issues in Solid Freeform Fabrication

This paper is concerned with the systems aspects of the Solid Freeform Fabrication (SFF) technology, i.e., the issues that deal with getting an external geometric CAD model to automatically control the physical layering fabrication process as directly as possible, regardless ofthe source of the model. The general systems issues are described, the state of systems research is given, and open research questions are posed.Mechanical Engineerin

Intergenerational interactions in human capital accumulation

We analyze an economy populated by a sequence of generations who decide over their consumption and investment in human capital of their immediate descendants. The objective of the paper is twofold: firstly, to identify the impact of strategic interactions between consecutive generations on the time path of human capital accumulation. To this end, we characterize the Markov perfect equilibrium (MPE) in such an economy and derive the sufficient conditions for its existence and uniqueness. We then benchmark our results against an optimal but time-inconsistent policy which abstracts from strategic interactions between generations. We prove analytically that human capital accumulation is unambiguously lower in the “strategic” case than in the optimal, “non-strategic” case. The second objective of the current paper is to work out a functional parametrization of the model, suitable for obtaining clear-cut results on the monotonicity of the (unique) Markov perfect equilibrium policy and the optimal policy. We then carry out a sensitivity analysis under this parametrization, thereby assessing quantitatively the magnitude of discrepancies between human capital accumulation paths whether strategic interactions between consecutive generations are taken into account or not.human capital, intergenerational interactions, Markov perfect equilibrium, stochastic transition, constructive approach

Permanent Income and the Black-White Test Score Gap

Analysts often examine the black-white test score gap conditional on family income. Typically only a current income measure is available. We argue that the gap conditional on permanent income is of greater interest, and we describe a method for identifying this gap using an auxiliary data set to estimate the relationship between current and permanent income. Current income explains only about half as much of the black-white test score gap as does permanent income, and the remaining gap in math achievement among families with the same permanent income is only 0.2 to 0.3 standard deviations in two commonly used data sets. When we add permanent income to the controls used by Fryer and Levitt (2006), the unexplained gap in 3rd grade shrinks below 0.15 standard deviations, less than half of what is found with their controls.

National Anti-Vulture Funds Legislation: Belgium's Turn

Sovereign distressed debt investors can create holdout problems during sovereign restructurings. Scholars have suggested a wide-range of normative solutions to alleviate these holdout problems, including ad hoc deals, the creation of a multilateral international sovereign bankruptcy framework, the insertion of collective-action clauses into bonds, the expansion of judicial discretion, and the return of the doctrines of comity and sovereign immunity. However, national legislatures have increasingly begun to exhibit a preference for adopting national legislative solutions to this issue. In 2015, Belgium passed the broadest Anti-Vulture Funds Law to date, which is significant because the law impacts the Euroclear payment system. While this law has received high praise from the United Nations and from other nations also considering passing similar legislation, a careful analysis demonstrates it is not sensitive to the benefits that vulture funds bring, such as providing incentives to sovereigns to form more efficient capital structures, providing a moral hazard counterbalance, serving as liquidity providers on the secondary distressed-debt market, and providing information to the market. If adopted by other nations, Belgium’s law can eliminate the secondary distressed debt market by blocking liquidity-providers from the market. As a result, national legislatures should avoid using Belgium’s law as model law, but rather, enact legislation that enhances active settlement discussions without compromising the bargaining power or rights of either the sovereign or the vulture funds

Gap formation in helical edge states with magnetic impurities

Helical edge states appear at the surface of two dimensional topological insulators and are characterized by spin up traveling in one direction and the spin down traveling in the opposite direction. Such states are protected by time reversal symmetry and no backscattering due to scalar impurities can occur. However, magnetic impurities break time reversal symmetry and lead to backscattering. Often their presence is unintentional, but in some cases they are introduced into the sample to open up gaps in the spectrum. We investigate the influence of random impurities on helical edge states, specifically how the gap behaves in the realistic case of impurities having both a magnetic and a scalar component. It turns out that for a fixed magnetic contribution the gap closes when either the scalar component, or Fermi velocity is increased. We compare diagrammatic techniques in the self-consistent Born approximation to numerical calculations which yields good agreement. For experimentally relevant parameters we find that even moderate scalar components can be quite detrimental for the gap formation.Comment: 6 pages, 6 figure

Elliptic curve cryptography: Generation and validation of domain parameters in binary Galois Fields

Elliptic curve cryptography (ECC) is an increasingly popular method for securing many forms of data and communication via public key encryption. The algorithm utilizes key parameters, referred to as the domain parameters. These parameters must adhere to specific characteristics in order to be valid for use in the algorithm. The American National Standards Institute (ANSI), in ANSI X9.62, provides the process for generating and validating these parameters. The National Institute of Standards and Technology (NIST) has identified fifteen sets of parameters; five for prime fields, five for binary fields, and five for Koblitz curves. The parameter generation and validation processes have several key issues. The first is the fast reduction within the proper modulus. The modulus chosen is an irreducible polynomial having degree greater than 160. Choosing irreducible polynomials of a particular order is less critical since they have isomorphic properties, mathematically. However, since there are differences in performance, there are standards that determine the specific polynomials chosen. The NIST standards are also based on word lengths of 32 bits. Processor architecture, primality, and validation of irreducibility are other important characteristics. The area of ECC that is researched is the generation and validation processes, as they are specified for binary Galois Fields F (2m). The rationale for the parameters, as computed for 32 bit and 64 bit computer architectures, and the algorithms used for implementation, as specified by ANSI, NIST and others, are examined. The methods for fast reduction are also examined as a baseline for understanding these parameters. Another aspect of the research is to determine a set of parameters beyond the 571-bit length that meet the necessary criteria as determined by the standards

Effects of ability grouping in the traditional classroom

The purpose of this paper is to review the research literature on ability grouping and report the findings from the standpoint of both instructional effectiveness and potential segregative impact. This paper reviews the relationships between ability grouping in schools and the following variables: the basis for grouping; the size and mobility of group members; the effects on student achievement; teacher expectation and instruction; student behavior and perception; and student attitude and self-esteem. Questions approached in the research of this topic were: 1. Does assignment to a particular group dictate instructional methods and standards? 2. Do some ability groups limit the way students can establish competence and achieve? 3. Do all students receive the same opportunities to learn or is there an inequity? 4. Does ability grouping affect the learning climate in a classroom and affect self-esteem? Another purpose of this paper will be to explore alternative methods to ability grouping. Educators are urged to promote approaches to grouping that are more equitable and instructional strategies that not only accommodate a wide range of individual differences, but also capitalize on these differences to enhance the learning potential of all students

Workshop on the Integration of Finite Element Modeling with Geometric Modeling

The workshop on the Integration of Finite Element Modeling with Geometric Modeling was held on 12 May 1987. It was held to discuss the geometric modeling requirements of the finite element modeling process and to better understand the technical aspects of the integration of these two areas. The 11 papers are presented except for one for which only the abstract is given

Stability of WISC-R Scores between Triennial Evaluations of Learning Disabled Students

Recent studies of intelligence test score stability among learning disabled children have reported adequate stability when correlational and analysis of variance (ANOVA) techniques were used. However, less than adequate score stability has been found when individual scores were examined. The present study explores the test-retest stability of the Wechsler Intelligence Scale for Children (WISC-R) using three statistical methods: Pearson product-moment correlation, analysis of variance, and an examination of individual scores. Regression to the mean is also examined. While reasonably high levels of stability are concluded by the Pearson product-moment correlations, significant drops in Verbal and Full Scale IQ scores between administrations are revealed by the ANOVA and by the examination of individual scores in the 9, 10 year old age group. The discussion includes implications for educational programming and for methods of evaluation, including alternative approaches to reevaluations. Suggestions for further research are also presented