2,637 research outputs found
Constructing a Social Problem: The Press and the Environment
The U. S. daily press might seem to be in a strategic position to function as a claims-maker in the early construction of a social problem. But in the case of the manufacture of environmentalism as a social reality in the 1960\u27s and 70\u27s, the press was fairly slow to adopt a holistic environmental lexicon. Its reporting of environmental news even now only partially reflects concepts promoted by positive environmental claims-makers, such as planet-wide interdependence, and the threats to it by destructive technologies. The movement of environmental claims seems to have started with interest-group entrepreneurship using interpersonal communication and independent publication, gone on to attention in government, then finally--and incompletely--been put on the agenda of the daily press. Once on the press agenda, coverage of environmental issues may have improved. But there are some constraints, possibly inherent in the press as an institution, that limit its role in the incipient construction of some social problems
Electric prototype power processor for a 30cm ion thruster
An electrical prototype power processor unit was designed, fabricated and tested with a 30 cm mercury ion engine for primary space propulsion. The power processor unit used the thyristor series resonant inverter as the basic power stage for the high power beam and discharge supplies. A transistorized series resonant inverter processed the remaining power for the low power outputs. The power processor included a digital interface unit to process all input commands and internal telemetry signals so that electric propulsion systems could be operated with a central computer system. The electrical prototype unit included design improvement in the power components such as thyristors, transistors, filters and resonant capacitors, and power transformers and inductors in order to reduce component weight, to minimize losses, and to control the component temperature rise. A design analysis for the electrical prototype is also presented on the component weight, losses, part count and reliability estimate. The electrical prototype was tested in a thermal vacuum environment. Integration tests were performed with a 30 cm ion engine and demonstrated operational compatibility. Electromagnetic interference data was also recorded on the design to provide information for spacecraft integration
Development of a multikilowatt ion thruster power processor
A feasibility study was made of the application of silicon-controlled, rectifier series, resonant inverter, power conditioning technology to electric propulsion power processing operating from a 200 to 400 Vdc solar array bus. A power system block diagram was generated to meet the electrical requirements of a 20 CM hollow cathode, mercury bombardment, ion engine. The SCR series resonant inverter was developed as a primary means of power switching and conversion, and the analog signal-to-discrete-time-interval converter control system was applied to achieve good regulation. A complete breadboard was designed, fabricated, and tested with a resistive load bank, and critical power processor areas relating to efficiency, weight, and part count were identified
Modeling and analysis of power processing systems: Feasibility investigation and formulation of a methodology
A review is given of future power processing systems planned for the next 20 years, and the state-of-the-art of power processing design modeling and analysis techniques used to optimize power processing systems. A methodology of modeling and analysis of power processing equipment and systems has been formulated to fulfill future tradeoff studies and optimization requirements. Computer techniques were applied to simulate power processor performance and to optimize the design of power processing equipment. A program plan to systematically develop and apply the tools for power processing systems modeling and analysis is presented so that meaningful results can be obtained each year to aid the power processing system engineer and power processing equipment circuit designers in their conceptual and detail design and analysis tasks
The effects of ganglionic and adrenergic blockade on the circulation of the young chimpanzee Final technical report, 1 Oct. 1963 - 30 Apr. 1965
Ganglionic and adrenergic blockade effects on circulatory system studied on young chimpanze
Beyond deficit-based models of learners' cognition: Interpreting engineering students' difficulties with sense-making in terms of fine-grained epistemological and conceptual dynamics
Researchers have argued against deficit-based explanations of students'
troubles with mathematical sense-making, pointing instead to factors such as
epistemology: students' beliefs about knowledge and learning can hinder them
from activating and integrating productive knowledge they have. In this case
study of an engineering major solving problems (about content from his
introductory physics course) during a clinical interview, we show that "Jim"
has all the mathematical and conceptual knowledge he would need to solve a
hydrostatic pressure problem that we posed to him. But he reaches and sticks
with an incorrect answer that violates common sense. We argue that his lack of
mathematical sense-making-specifically, translating and reconciling between
mathematical and everyday/common-sense reasoning-stems in part from his
epistemological views, i.e., his views about the nature of knowledge and
learning. He regards mathematical equations as much more trustworthy than
everyday reasoning, and he does not view mathematical equations as expressing
meaning that tractably connects to common sense. For these reasons, he does not
view reconciling between common sense and mathematical formalism as either
necessary or plausible to accomplish. We, however, avoid a potential "deficit
trap"-substituting an epistemological deficit for a concepts/skills deficit-by
incorporating multiple, context-dependent epistemological stances into Jim's
cognitive dynamics. We argue that Jim's epistemological stance contains
productive seeds that instructors could build upon to support Jim's
mathematical sense-making: He does see common-sense as connected to formalism
(though not always tractably so) and in some circumstances this connection is
both salient and valued.Comment: Submitted to the Journal of Engineering Educatio
Optical spectroscopy of single quantum dots at tunable positive, neutral and negative charge states
We report on the observation of photoluminescence from positive, neutral and
negative charge states of single semiconductor quantum dots. For this purpose
we designed a structure enabling optical injection of a controlled unequal
number of negative electrons and positive holes into an isolated InGaAs quantum
dot embedded in a GaAs matrix. Thereby, we optically produced the charge states
-3, -2, -1, 0, +1 and +2. The injected carriers form confined collective
'artificial atoms and molecules' states in the quantum dot. We resolve
spectrally and temporally the photoluminescence from an optically excited
quantum dot and use it to identify collective states, which contain charge of
one type, coupled to few charges of the other type. These states can be viewed
as the artificial analog of charged atoms such as H, H, H,
and charged molecules such as H and H. Unlike higher
dimensionality systems, where negative or positive charging always results in
reduction of the emission energy due to electron-hole pair recombination, in
our dots, negative charging reduces the emission energy, relative to the
charge-neutral case, while positive charging increases it. Pseudopotential
model calculations reveal that the enhanced spatial localization of the
hole-wavefunction, relative to that of the electron in these dots, is the
reason for this effect.Comment: 5 figure
Form Follows Function: Adapting the Strength Model to Facilitate Implementation and Sustainability
Case management is a common social service intervention that has been applied across a range of disciplines, populations, and types of organizations. Despite its widespread use, the activities constituting case management are often poorly specified (Lukersmith, Millington, & Salvador-Carulla, 2016). The Strengths Model is an important exception—not only does it offer a structured approach to service delivery, but it provides enough flexibility to facilitate implementation and support sustainability. The goal of this chapter is to help practitioners think creatively about implementation, so they can meet the needs of their organization while remaining true to the core components of the Strengths Model. In the first part of this chapter, we discuss the delicate balance between implementing a model to fidelity and mak- ing adaptations to address organizational barriers and constraints, highlighting some of the prior modifications made to the Strengths Model to ease implementation. In the second part of the chapter, we describe one agency’s approach to implementa- tion, the structural adaptations staff made to the Strengths Model, and the benefits and challenges associated with their approach
Extended performance electric propulsion power processor design study. Volume 2: Technical summary
Electric propulsion power processor technology has processed during the past decade to the point that it is considered ready for application. Several power processor design concepts were evaluated and compared. Emphasis was placed on a 30 cm ion thruster power processor with a beam power rating supply of 2.2KW to 10KW for the main propulsion power stage. Extension in power processor performance were defined and were designed in sufficient detail to determine efficiency, component weight, part count, reliability and thermal control. A detail design was performed on a microprocessor as the thyristor power processor controller. A reliability analysis was performed to evaluate the effect of the control electronics redesign. Preliminary electrical design, mechanical design and thermal analysis were performed on a 6KW power transformer for the beam supply. Bi-Mod mechanical, structural and thermal control configurations were evaluated for the power processor and preliminary estimates of mechanical weight were determined
Late onset of Huntington's disease
Twenty-five patients with late-onset Huntington's disease were studied; motor impairment appeared at age 50 years or later. The average age at onset of chorea was 57.5 years, with an average age at diagnosis of 63.1 years. Approximately 25% of persons affected by Huntington's disease exhibit late onset. A preponderance of maternal transmission was noted in late-onset Huntington's disease. The clinical features resembled those of mid-life onset Huntington's disease but progressed more slowly. Neuropathological evaluation of two cases reveal less severe neuronal atrophy than for mid-life onset disease
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