1,697 research outputs found
Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift
We identify nearby disk galaxies with optical structural parameters similar
to those of intermediate-redshift compact blue galaxies. By comparing HI and
optical emission-line widths, we show that the optical widths substantially
underestimate the true kinematic widths of the local galaxies. By analogy,
optical emission-line widths may underrepresent the masses of intermediate-z
compact objects. For the nearby galaxies, the compact blue morphology is the
result of tidally-triggered central star formation: we argue that interactions
and minor mergers may cause apparently compact morphology at higher redshift.Comment: 5 pages, uses emulateapj5 and psfig. To appear in ApJ
A 10B-based neutron detector with stacked Multiwire Proportional Counters and macrostructured cathodes
We present the results of the measurements of the detection efficiency for a
4.7 \r{A} neutron beam incident upon a detector incorporating a stack of up to
five MultiWire Proportional Counters (MWPC) with Boron-coated cathodes. The
cathodes were made of Aluminum and had a surface exhibiting millimeter-deep
V-shaped grooves of 45{\deg}, upon which the thin Boron film was deposited by
DC magnetron sputtering. The incident neutrons interacting with the converter
layer deposited on the sidewalls of the grooves have a higher capture
probability, owing to the larger effective absorption film thickness. This
leads to a higher overall detection efficiency for the grooved cathode when
compared to a cathode with a flat surface. Both the experimental results and
the predictions of the GEANT4 model suggests that a 5-counter detector stack
with coated grooved cathodes has the same efficiency as a 7-counter stack with
flat cathodes. The reduction in the number of counters in the stack without
altering the detection efficiency will prove highly beneficial for large-area
position-sensitive detectors for neutron scattering applications, for which the
cost-effective manufacturing of the detector and associated readout electronics
is an important objective. The proposed detector concept could be a
technological option for one of the new chopper spectrometers and other
instruments planned to be built at the future European Spallation Source in
Sweden. These results with macrostructured cathodes generally apply not just to
MWPCs but to other gaseous detectors as well.Comment: 14 pages, 9 figure
Mach's Principle and Model for a Broken Symmetric Theory of Gravity
We investigate spontaneous symmetry breaking in a conformally invariant
gravitational model. In particular, we use a conformally invariant scalar
tensor theory as the vacuum sector of a gravitational model to examine the idea
that gravitational coupling may be the result of a spontaneous symmetry
breaking. In this model matter is taken to be coupled with a metric which is
different but conformally related to the metric appearing explicitly in the
vacuum sector. We show that after the spontaneous symmetry breaking the
resulting theory is consistent with Mach's principle in the sense that inertial
masses of particles have variable configurations in a cosmological context.
Moreover, our analysis allows to construct a mechanism in which the resulting
large vacuum energy density relaxes during evolution of the universe.Comment: 9 pages, no figure
Spin Current in Spin-Orbit Coupling Systems
We present a simple and pedagogical derivation of the spin current as the
linear response to an external electric field for both Rashba and Luttinger
spin-orbital coupling Hamiltonians. Except for the adiabatic approximation, our
derivation is exact to the linear order of the electric field for both models.
The spin current is a direct result of the difference in occupation levels
between different bands. Moreover, we show a general topological spin current
can be defined for a broad class of spin-orbit coupling systems
Zee Model Confronts SNO Data
We reexamine the solution of the minimal Zee model by comparing with the data
of the SNO experiment, and conclude that the model is strongly disfavored but
not yet excluded by the observations. Two extensions of the Zee model are
briefly discussed both of which introduce additional freedom and can
accommodate the data.Comment: 16 pages LaTeX including 7 figure
Riemann-Einstein Structure from Volume and Gauge Symmetry
It is shown how a metric structure can be induced in a simple way starting
with a gauge structure and a preferred volume, by spontaneous symmetry
breaking. A polynomial action, including coupling to matter, is constructed for
the symmetric phase. It is argued that assuming a preferred volume, in the
context of a metric theory, induces only a limited modification of the theory.Comment: LaTeX, 13 pages; Added additional reference in Reference
Self-regulated learning:Validating a task-specific questionnaire for children in elementary school
This paper describes the development and initial validation of the Cognition and Emotion/Motivation Regulation (CEMOR) questionnaire, a task-specific questionnaire for upper elementary school students that measures self-regulated learning (SRL). Using a multistep procedure, 22 items were developed, divided over five theory-informed dimensions (Planning, Monitoring, Cognition Control, Emotion/Motivation Control, and Reflecting). The CEMOR was applied in a math context. Children from grades 3â6 (N = 547, 54.7 % females) completed the CEMOR. Confirmatory factor analyses indicated that the five proposed scales have adequate to good model fit, with factor loadings ranging from .54 to .83, and acceptable to good composite reliability (Ï range = .75â.85). To find further validity support, the SRL scales were correlated with studentsâ performance on a math task, experienced emotions, and level of motivation during the task. Most correlations were statistically significant and in the expected direction. Hence, the CEMOR questionnaire shows promise as a new SRL instrument for elementary education
Acoustic cues to tonal contrasts in Mandarin: Implications for cochlear implants
The present study systematically manipulated three acoustic cues-fundamental frequency (f0), amplitude envelope, and duration-to investigate their contributions to tonal contrasts in Mandarin. Simplified stimuli with all possible combinations of these three cues were presented for identification to eight normal-hearing listeners, all native speakers of Mandarin from Taiwan. The f0 information was conveyed either by an f0-controlled sawtooth carrier or a modulated noise so as to compare the performance achievable by a clear indication of voice f0 and what is possible with purely temporal coding of f0. Tone recognition performance with explicit f0 was much better than that with any combination of other acoustic cues (consistently greater than 90% correct compared to 33%-65%; chance is 25%). In the absence of explicit f0, the temporal coding of f0 and amplitude envelope both contributed somewhat to tone recognition, while duration had only a marginal effect. Performance based on these secondary cues varied greatly across listeners. These results explain the relatively poor perception of tone in cochlear implant users, given that cochlear implants currently provide only weak cues to f0, so that users must rely upon the purely temporal (and secondary) features for the perception of tone. (c) 2008 Acoustical Society of America
Self-regulated learning:Validating a task-specific questionnaire for children in elementary school
This paper describes the development and initial validation of the Cognition and Emotion/Motivation Regulation (CEMOR) questionnaire, a task-specific questionnaire for upper elementary school students that measures self-regulated learning (SRL). Using a multistep procedure, 22 items were developed, divided over five theory-informed dimensions (Planning, Monitoring, Cognition Control, Emotion/Motivation Control, and Reflecting). The CEMOR was applied in a math context. Children from grades 3â6 (N = 547, 54.7 % females) completed the CEMOR. Confirmatory factor analyses indicated that the five proposed scales have adequate to good model fit, with factor loadings ranging from .54 to .83, and acceptable to good composite reliability (Ï range = .75â.85). To find further validity support, the SRL scales were correlated with studentsâ performance on a math task, experienced emotions, and level of motivation during the task. Most correlations were statistically significant and in the expected direction. Hence, the CEMOR questionnaire shows promise as a new SRL instrument for elementary education
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