Digital-to-analog conversion by pulse-count modulation methods

Three low-cost digital-to-analog converters (DACs) are described and compared. These designs can easily be implemented in an integrated circuit: the conventional pulse-width modulation (PWM) DAC, the new pulse-count modulation (PCM) DAC and the first-order noise shaping (FONS) DAC. All three methods control the ratio of the sum of all pulse durations to the constant total period. As the pulse durations are integral multiples of a unit pulse, all three can be classified as pulse-count modulation methods. Block diagrams of all three DACs consisting of a simple digital circuit and a low-pass filter are presented. For a constant digital input value the worst case ripple of the filter output is used to calculate the cutoff frequency of the low-pass filter. Approximations for the 3 dB cutoff frequency of first-order, second-order and fourth-order Butterworth low-pass filters are given. The dynamic properties are analyzed in the time domain (settling time) and in the frequency domain (unfiltered output spectrum of a full-scale sine wave input). The main influences on the static accuracy are analyzed. A case study demonstrates the abilities of PCM and FONS     

Eye movement as a cue to figure motion in anorthoscopic perception.

When a figure moves behind a narrow aperture in an opaque surface, if it is perceived as a figure, its shape will often appear distorted. Under such anorthoscopic conditions, the speed or direction of the object's motion is ambiguous. However, when the observer simultaneously tracks a moving target, a figure is always perceived, and its precise shape is a function of the speed or direction of tracking. The figure is seen as moving with the speed or in the direction of the target. Thus, it is argued that eye movement serves as a cue to the figure's motion, which, in turn, determines its perceived length or orientation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation and application of a semantic network partition

Semantic networks (SNs) are excellent knowledge representation structures. However, large semantic networks are difficult to comprehend. To overcome this difficulty, several methods of partitioning have been developed that rely on different mixes of structural and semantic methods. However, little has appeared in the literature concerning the question whether a partition of a semantic network creates subnetworks that agree with human insight. We address this issue by presenting a comparison between the results of an algorithmic partitioning method and a partition created by a group of experts. Subsequently, we show how a network partition can be used to generate various partial views of a semantic network, which facilitate user orientation. Examples from the Unified Medical Language System (UMLS) SN are used to demonstrate partial views     

Controlled Vocabularies in OODBs: Modeling Issues and Implementation

A major problem that arises in many large application domains is the discrepancy among terminologies of different information systems. The terms used by the information systems of one organization may not agree with the terms used by another organization even when they are in the same domain. Such a situation clearly impedes communication and the sharing of information, and decreases the efficiency of doing business. Problems of this nature can be overcome using a controlled vocabulary (CV), a system of concepts that consolidates and unifies the terminologies of a domain. However, CVs are large and complex and difficult to comprehend. This paper presents a methodology for representing a semantic network-based CV as an object-oriented database (OODB). We call such a representation an Object-Oriented Vocabulary Repository (OOVR). The methodology is based on a structural analysis and partitioning of the source CV. The representation of a CV as an OOVR offers both the level of support typical of database management systems and an abstract view which promotes comprehension of the CV's structure and content. After discussing the theoretical aspects of the methodology, we apply it to the MED and InterMED, two existing CVs from the medical field. A program, called the OOVR Generator, for automatically carrying out our methodology is described. Both the MED-OOVR and the InterMED-OOVR have been created using the OOVR Generator, and each exists on top of ONTOS, a commercial OODBMS. The OOVR derived from the InterMED is presently available on the Web.     

The relationship between cognitive deficits and everyday functional activities in multiple sclerosis.

Considerable evidence indicates that cognitive dysfunction and impairments in everyday life activities are common in multiple sclerosis (MS). However, the relationship between these cognitive and functional deficits has not been thoroughly investigated. The purpose of this study was to examine the role of cognitive dysfunction in the functional status of individuals with MS. Participants were 74 adults with MS and 35 healthy comparison participants (HCs) who underwent neuropsychological testing and completed the Executive Functions Performance Test (EFPT; Baum, Morrison, Hahn, & Edwards, 2003), an objective measure of everyday life activities. Between-groups comparisons and correlational analyses were conducted to examine the relationship between cognition and functional capacity. Significant differences in EFPT performance were revealed between individuals with MS with and without cognitive impairment and HCs. In individuals with MS, performance on cognitive constructs was related to performance on the EFPT. Furthermore, a linear regression model comprised of indices of cognitive functioning explained a significant portion of the variance in everyday life activities. Findings suggest that individuals with and without cognitive impairment differ in functional status and that aspects of cognition are predictive of functional status in MS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of Older and Younger Individuals With Multiple Sclerosis: A Preliminary Investigation.

Objective: To describe and contrast physical functioning, mental health, and quality of life of older individuals with multiple sclerosis (MS) with those of younger individuals with MS. Design/Participants: Thirty older (age ≥ 60 years) and 30 younger participants with MS (age     

Elastomer-Modified Sheet Molding Compounds

For several years, elastomeric sheet molding compound (SMC) additives have been considered for automotive exterior panel applications where shrink control, improved surface appearance, and impact improvement are desired. Shell has designed a special styrene-butadiene (S-B) copolymer system, Kraton GX-1855, for this application. We now report the results of our morphological work in this area.