2,146 research outputs found
ASDTIC: A feedback control innovation
The ASDTIC (Analog Signal to Discrete Time Interval Converter) control subsystem provides precise output control of high performance aerospace power supplies. The key to ASDTIC operation is that it stably controls output by sensing output energy change as well as output magnitude. The ASDTIC control subsystem and control module were developed to improve power supply performance during static and dynamic input voltage and output load variations, to reduce output voltage or current regulation due to component variations or aging, to maintain a stable feedback control with variations in the loop gain or loop time constants, and to standardize the feedback control subsystem for power conditioning equipment
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
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
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
Deep-ultraviolet photodetectors from epitaxially grown NixMg1-xO
Deep-ultraviolet (DUV) photodetectors were fabricated from high quality NixMg1-xO epitaxially grown by plasma-assisted molecular beam epitaxy on an approximately lattice matched MgO \u3c 100 \u3e substrate. A mid-range Ni composition (x=0.54) NixMg1-xO film was grown for DUV (lambda(peak) \u3c 300 nm) photoresponse and the film was characterized by reflected high-energy electron diffraction, Rutherford backscattering spectroscopy, x-ray diffraction, and optical transmission measurements. Photoconductive detectors were then fabricated by deposition of symmetric interdigitated contacts (10 nm Pt/150 nm Au) with contact separations of 5, 10, and 15 mu m. The detectors exhibited peak responsivities in the DUV (lambda(peak) approximate to 250 nm) as high as 12 mA/W, low dark currents (I-dark \u3c 25 nA), and DUV:visible ejection ratio of approximately 800:1
Bandgap engineering of sol-gel synthesized amorphous Zn1-xMgxO films
Amorphous Zn1-xMgxO (alpha-Zn1-xMgxO) ternary alloy thin films across the full compositional range were synthesized by a low-cost sol-gel method on quartz substrates. The amorphous property of the alpha-Zn1-xMgxO films was verified by x-ray diffraction, and atomic force microscopy revealed a smooth surface with sub-nanometer root-mean square roughness. The current phase segregation issue limiting application of crystalline Zn1-xMgxO with 38% \u3c x \u3c 75% was completely eliminated by growing amorphous films. Optical transmission measurements showed high transmissivity of more than 90% in the visible and near infrared regions, with optical bandgap tunability from 3.3 eV to more than 6.5 eV by varying the Mg content
Blogging in the physics classroom: A research-based approach to shaping students' attitudes towards physics
Even though there has been a tremendous amount of research done in how to
help students learn physics, students are still coming away missing a crucial
piece of the puzzle: why bother with physics? Students learn fundamental laws
and how to calculate, but come out of a general physics course without a deep
understanding of how physics has transformed the world around them. In other
words, they get the "how" but not the "why". Studies have shown that students
leave introductory physics courses almost universally with decreased
expectations and with a more negative attitude. This paper will detail an
experiment to address this problem: a course weblog or "blog" which discusses
real-world applications of physics and engages students in discussion and
thinking outside of class. Specifically, students' attitudes towards the value
of physics and its applicability to the real-world were probed using a
26-question Likert scale survey over the course of four semesters in an
introductory physics course at a comprehensive Jesuit university. We found that
students who did not participate in the blog study generally exhibited a
deterioration in attitude towards physics as seen previously. However, students
who read, commented, and were involved with the blog maintained their initially
positive attitudes towards physics. Student response to the blog was
overwhelmingly positive, with students claiming that the blog made the things
we studied in the classroom come alive for them and seem much more relevant.Comment: 20 pages, 6 figure
Reinventing College Physics for Biologists: Explicating an epistemological curriculum
The University of Maryland Physics Education Research Group (UMd-PERG)
carried out a five-year research project to rethink, observe, and reform
introductory algebra-based (college) physics. This class is one of the Maryland
Physics Department's large service courses, serving primarily life-science
majors. After consultation with biologists, we re-focused the class on helping
the students learn to think scientifically -- to build coherence, think in
terms of mechanism, and to follow the implications of assumptions. We designed
the course to tap into students' productive conceptual and epistemological
resources, based on a theoretical framework from research on learning. The
reformed class retains its traditional structure in terms of time and
instructional personnel, but we modified existing best-practices curricular
materials, including Peer Instruction, Interactive Lecture Demonstrations, and
Tutorials. We provided class-controlled spaces for student collaboration, which
allowed us to observe and record students learning directly. We also scanned
all written homework and examinations, and we administered pre-post conceptual
and epistemological surveys. The reformed class enhanced the strong gains on
pre-post conceptual tests produced by the best-practices materials while
obtaining unprecedented pre-post gains on epistemological surveys instead of
the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material
Pharmacological And Genetic Reversal Of Age-Dependent Cognitive Deficits Attributable To Decreased Presenilin Function
Alzheimer\u27s disease (AD) is the leading cause of cognitive loss and neurodegeneration in the developed world. Although its genetic and environmental causes are not generally known, familial forms of the disease (FAD) are attributable to mutations in a single copy of the Presenilin (PS) and amyloid precursor protein genes. The dominant inheritance pattern of FAD indicates that it may be attributable to gain or change of function mutations. Studies of FAD-linked forms of presenilin (psn) in model organisms, however, indicate that they are loss of function, leading to the possibility that a reduction in PS activity might contribute to FAD and that proper psn levels are important for maintaining normal cognition throughout life. To explore this issue further, we have tested the effect of reducing psn activity during aging in Drosophila melanogaster males. We have found that flies in which the dosage of psn function is reduced by 50% display age-onset impairments in learning and memory. Treatment with metabotropic glutamate receptor (mGluR) antagonists or lithium during the aging process prevented the onset of these deficits, and treatment of aged flies reversed the age-dependent deficits. Genetic reduction of Drosophila metabotropic glutamate receptor (DmGluRA), the inositol trisphosphate receptor (InsP(3)R), or inositol polyphosphate 1-phosphatase also prevented these age-onset cognitive deficits. These findings suggest that reduced psn activity may contribute to the age-onset cognitive loss observed with FAD. They also indicate that enhanced mGluR signaling and calcium release regulated by InsP(3)R as underlying causes of the age-dependent cognitive phenotypes observed when psn activity is reduced
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