1,631 research outputs found
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
Searching for the dual of the Maxwell-Chern-Simons model minimally coupled to dynamical U(1) charged matter
The possibility of dual equivalence between the self-dual and the
Maxwell-Chern-Simons (MCS) models when the latter is coupled to dynamical, U(1)
fermionic charged matter is examined. The proper coupling in the self-dual
model is then disclosed using the iterative gauge embedding approach. We found
that the self-dual potential needs to couple directly to the Chern-Kernel of
the source in order to establish this equivalence besides the need for a
self-interaction term to render the matter sector unchanged.Comment: 4 pages, RevTeX, new references, accepted for publication on Phys.
Lett.
A Path Algorithm for Constrained Estimation
Many least squares problems involve affine equality and inequality
constraints. Although there are variety of methods for solving such problems,
most statisticians find constrained estimation challenging. The current paper
proposes a new path following algorithm for quadratic programming based on
exact penalization. Similar penalties arise in regularization in model
selection. Classical penalty methods solve a sequence of unconstrained problems
that put greater and greater stress on meeting the constraints. In the limit as
the penalty constant tends to , one recovers the constrained solution.
In the exact penalty method, squared penalties are replaced by absolute value
penalties, and the solution is recovered for a finite value of the penalty
constant. The exact path following method starts at the unconstrained solution
and follows the solution path as the penalty constant increases. In the
process, the solution path hits, slides along, and exits from the various
constraints. Path following in lasso penalized regression, in contrast, starts
with a large value of the penalty constant and works its way downward. In both
settings, inspection of the entire solution path is revealing. Just as with the
lasso and generalized lasso, it is possible to plot the effective degrees of
freedom along the solution path. For a strictly convex quadratic program, the
exact penalty algorithm can be framed entirely in terms of the sweep operator
of regression analysis. A few well chosen examples illustrate the mechanics and
potential of path following.Comment: 26 pages, 5 figure
Emerging technologies in physics education
Three emerging technologies in physics education are evaluated from the
interdisciplinary perspective of cognitive science and physics education
research. The technologies - Physlet Physics, the Andes Intelligent Tutoring
System (ITS), and Microcomputer-Based Laboratory (MBL) Tools - are assessed
particularly in terms of their potential at promoting conceptual change,
developing expert-like problem-solving skills, and achieving the goals of the
traditional physics laboratory. Pedagogical methods to maximize the potential
of each educational technology are suggested.Comment: Accepted for publication in the Journal of Science Education and
Technology; 20 page
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
Curricular orientations to real-world contexts in mathematics
A common claim about mathematics education is that it should equip students to use mathematics in the âreal worldâ. In this paper, we examine how relationships between mathematics education and the real world are materialised in the curriculum across a sample of eleven jurisdictions. In particular, we address the orientation of the curriculum towards application of mathematics, the ways that real-world contexts are positioned within the curriculum content, the ways in which different groups of students are expected to engage with real-world contexts, and the extent to which high-stakes assessments include real-world problem solving. The analysis reveals variation across jurisdictions and some lack of coherence between official orientations towards use of mathematics in the real world and the ways that this is materialised in the organisation of the content for students
On the dual equivalence of the self-dual and topologically massive p-form models
We study the duality symmetry in p-form models containing a generalized
term in spacetime manifolds of arbitrary dimensions. The
equivalence between the self-dual () and
the topologically massive () models is
established using a gauge embedding procedure, including the minimal coupling
to conserved charged matter current. The minimal coupling adopted for both
tensor fields in the self-dual representation is transformed into a non minimal
magnetic like coupling in the topologically massive representation but with the
currents swapped. It is known that to establish this equivalence a
current-current interaction term is needed to render the matter sector
unchanged. We show that both terms arise naturally from the embedding adopted.
Comparison with Higgs/Julia-Toulouse duality is established.Comment: Latex file, 13 pages, no figures. Accepted for publication: Physics
Letters B; a new paper added to the reference
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