A Proposed Receiver Structure for Optical Communication Systems that Employ Heterodyne Detection and a Semiconductor Laser as a Local Oscillator

Coherent heterodyne detection in optical communication is degraded by phase instabilities present when a semiconductor laser is used as a local oscillator. Postdetection processing that accounts for these instabilities is suggested, based on a diffusion-process model for oscillator instabilities and a maximum-likelihood sequence-estimator of information symbols modulating the received light.     

Dealkylation of various 14-alkylsterols by the nematodeCaenorhabditis elegans

The metabolism of 4 dietary 24-alkylsterols was investigated in the free-living nematodeCaenorhabditis elegans. The major unesterified sterols ofC. elegans in media supplemented with either campesterol, 22-dihydrobrassicasterol or stigmasterol included cholesta-5,7-dienol, cholesterol, cholest-7-enol, and 4α-methylcholest-8(14)-enol. Dietary stigmastanol yielded cholest-7-enol, cholestanol, cholest-8(14)-enol, and 4α-methylcholest-8(14)-enol as major unesterified sterols. Esterified sterols comprised less than 22% of the total sterol. Removal of a C-24 ethyl substituent of sterols was neither hindered by the presence of a Δ²²-bond in the sterol side chain nor was it depedent on unsaturation in ring B of the steroid nucleus.C. elegans reduced a Δ²²-bond during its metabolism of stigmasterol; it did not introduce a Δ²²-bond during stigmastanol metabolism.C. elegans was capable of removing a C-24 methyl substituent regardless of its stereochemical orientation. Metabolic processes involving the steroid ring system of cholesterol (C-7 dehydrogenation, Δ⁵-bond, 4α-methylation, Δ⁸⁽¹⁴⁾-isomerization inC. elegans were not hindered by the presence of a 24-methyl group; various 24-methylsterol metabolites from campesterol were detected, mostly 24-methylcholesta-5,7-dienol. In contrast, no 24-ethylsterol metabolites from the dietary ethylsterols were found. More dietary 24-methylsterol remained unmetabolized than did dietary 24-ethylsterol. A 24α-ethyl group and a 24β-methyl group were dealkylated to a greater extent byC. elegans than was a 24α-methyl group, perhaps reflecting the substrate specificity of the dealkylation enzyme system, or suggesting different enzymes altogether.     

Individual differences in extended practice functions and solution strategies for basic addition facts.

Practice on addition basic facts and changes in solution strategies were examined in 3rd- and 4th-grade students, practicing over 3 months. Response latencies decreased, indicating positive practice effects. Each of 3 student groups demonstrated different solution–strategy mixtures. Different mixtures led to different practice effects, indexed by shifts to more efficient counting strategies and more direct retrieval. Expectations about effects of practice and instructional strategies for optimizing practice must be sensitive to a child's actual strategy pattern. Most students had decreasing latency practice functions. However, quantitative functions fit to the practice session data indicated a high proportion of cases where the latency pattern over sessions was nonmonotonic. Trends over a small number of practice sessions may be inadequate for decisions about the utility of further practice, because such data may poorly represent long-term, cumulative effects on modifying strategy usage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A RANKING OF US GRADUATE PROGRAMS IN URBAN STUDIES AND URBAN AFFAIRS

ABSTRACT: A ranking of 33 urban studies and urban affairs programs in the US was developed from peer ratings obtained in a program survey and from citation activity reported in the Social Sciences Citation Index over the 1986–1989 period. A breakdown of citations by broadly defined subject areas is presented. The survey revealed a difference between Ph.D. and MUS/MA programs in the perceived relative importance of peer evaluation and citations as rating criteria. The survey results also indicate that the degree of familiarity with other programs is lower than what has been observed in most social science disciplines.     

A decision-making approach to the operation of flexible manufacturing systems

This paper introduces a generic decision-making framework for assigning resources of a manufacturing system to production tasks. Resources are broadly defined production units, such as machines, human operators, or material handling vehicles; and tasks are activities performed by resources. In the specific context of FMS, resources correspond to individual machines; tasks correspond to operations to be performed on parts. The framework assumes a hierarchical structure of the system and calls for the execution of four consecutive steps to make a decision for the assignment of a resource to a task. These steps are 1) establishment of decision-making criteria, 2) formation of alternative assignments, 3) estimation of the consequences of the assignments, and 4) selection of the best alternative assignment. This framework has been applied to an existing FMS as an operational policy that decides what task will be executed on which resource of this FMS. Simulation runs provide some initial results of the application of this policy. It is shown that the policy provides flexibility in terms of system performance and computational effort.     

An integral theorem prover and the role of proof planning

An investigation is made into the ways proof planning can enhance the capability of a rule based prover for the theory of integration. The integrals are of the Riemann type and are defined in a way to maximize the theorem proving methods of predicate calculus. Approximately fifty theorems have been proved and several examples are discussed. A major shortcoming was found to be the inability of the system to work with or produce a proof plan. As a result, a planning scheme based on the idea of subgoals or milestones was considered. With user defined plans, there was a substantial increase in performance and capability of the system and, in some cases, proofs which were previously unsuccessful were completed.     

Turbine airfoil degradation in the persian gulf war

Helicopter turbine engines used in the Desert Shield and Desert Storm operations experienced excessive sand ingestion. Fine particles were able to bypass filters and proceed through the combustor or cooling gaspaths. The first-stage turbine vanes were impacted with viscous silicate particles, forming a deposit on the leading-edge root platform and resulting in overheating and oxidation. The chemistry of the raw sand determines that of the ingested powders, the deposits, and the material reactions.     

The impact of presentation graphics on students’ experience in the classroom

To investigate the benefits and perceived effectiveness of instructional technology, students enrolled in several courses were compared on student evaluations of instruction, grades and an attitudinal questionnaire. The instructors of the courses taught the same course across two successive semesters, using traditional “chalk-and-talk” methods the first semester, and PowerPoint the next; all other techniques (e.g., exams, lecture material) were held constant. Results suggest that organization and clarity, entertainment and interest, professor likeability, and good professor behaviors were enhanced with PowerPoint although final grades were not.