299 research outputs found
Pattern recognition for Space Applications Center director's discretionary fund
Results and conclusions are presented on the application of recent developments in pattern recognition to spacecraft star mapping systems. Sensor data for two representative starfields are processed by an adaptive shape-seeking version of the Fc-V algorithm with good results. Cluster validity measures are evaluated, but not found especially useful to this application. Recommendations are given two system configurations worthy of additional study
Effects of Academic Coaching on College Students with Learning Disabilities or Attention-Deficit Hyperactivity Disorder
Learning disabilities (LD) and/or attention-deficit hyperactivity disorder (ADHD) are the largest and fastest growing categories of disabilities at 4-year colleges and universities (National Health Interview Survey, 2008). Young adults with LD and/or ADHD attend four-year colleges at half the rate of the general populations and have poor outcomes related to retention and success in college (NLTS2, 2011). Although students with LD and/or ADHD are approved for accommodations under the Americans with Disabilities Act (ADA), they continue to struggle with poor organizational, time management, poor study, and poor social skills (Mull, et al., 2001; Weyandt & DuPaul, 2006). To improve the success of college students with LD and/or ADHD, a growing number of researchers are evaluating the use of Academic Coaching as an intervention to increase the success of these students. Although there is some evidence that Academic Coaching could be effective, more rigorous research is needed to document its efficacy with college students with ADHD and/or LD. The present study aimed to examine the effect of an Academic Coaching intervention plus typical services on college students with disabilities’’ (LD or ADHD) use and knowledge of learning and study strategies, academic engagement, self-efficacy, and academic achievement by using a quasi-experimental, pre-posttest, control group design. Controlling for pre-test differences, an analysis of covariance (ANCOVA) was used to assess differences between groups on all outcome measures. In addition, this study aimed to provide descriptive information on other services, in addition to Academic Coaching, utilized across groups, whether or not co-occurring diagnoses were present across groups, and the social validity and treatment integrity of the Academic Coaching Intervention. There were significant mean differences across all dependent measures with the exception of two of the scales, one from the LASSI, and one from the NSSE. Findings suggest that Academic Coaching may be an effective intervention to increase the use and knowledge of learning and study strategies, academic engagement, self-efficacy, and academic achievement of students with LD or ADHD. Future research is needed to continue to evaluate the effectiveness of Academic Coaching with college students with disabilities.Key Words: Academic Coaching, Learning Disabilities, Attention-Deficit Hyperactivity Disorder, Self-Efficacy, Student Engagement, Academic Achievement, Accommodation
Charge dynamics in the half-metallic ferromagnet CrO\u3csub\u3e2\u3c/sub\u3e
Infrared spectroscopy is used to investigate the electronic structure and charge carrier relaxation in crystalline films of CrO2 which is the simplest of all half-metallic ferromagnets. Chromium dioxide is a bad metal at room temperature but it has a remarkably low residual resistivity (\u3c5 \u3eμΩ cm) despite the small spectral weight associated with free carrier absorption. The infrared measurements show that low residual resistivity is due to the collapse of the scattering rate at ω\u3c2000 \u3ecm-1. The blocking of the relaxation channels at low v and T can be attributed to the unique electronic structure of a half-metallic ferromagnet. In contrast to other ferromagnetic oxides, the intraband spectral weight is constant below the Curie temperature
On the peak in the far-infrared conductivity of strongly anisotropic cuprates
We investigate the far-infrared and submillimeter-wave conductivity of
electron-doped La_(2-x)Ce_xCuO_4 tilted 1 degree off from the ab-plane. The
effective conductivity measured for this tilt angle reveals an intensive peak
at finite frequency (\nu ~ 50 cm{-1}) due to a mixing of the in-plane and
out-of-plane responses. The peak disappears for the pure in-plane response and
transforms to the Drude-like contribution. Comparative analysis of the mixed
and the in-plane contributions allows to extract the c-axis conductivity which
shows a Josephson plasma resonance at 11.7 cm{-1} in the superconducting state.Comment: 4 pages, 4 figures include
Sum rules and electrodynamics of high-Tc cuprates in the pseudogap state
We explore connections between the electronic density of states (DOS) in a
conducting system and the frequency dependence of the scattering rate
inferred from infrared spectroscopy. We show that changes in
the DOS upon the development of energy gaps can be reliably tracked through the
examination of the spectra using the sum rules discussed in
the text. Applying this analysis to the charge dynamics in high- cuprates
we found radically different trends in the evolution of the DOS in the
pseudogap state and in the superconducting state.Comment: 4 pages, 3 figure
Non-Drude Optical Conductivity of (III,Mn)V Ferromagnetic Semiconductors
We present a numerical model study of the zero-temperature infrared optical
properties of (III,Mn)V diluted magnetic semiconductors. Our calculations
demonstrate the importance of treating disorder and interaction effects
simultaneously in modelling these materials. We find that the conductivity has
no clear Drude peak, that it has a broadened inter-band peak near 220 meV, and
that oscillator weight is shifted to higher frequencies by stronger disorder.
These results are in good qualitative agreement with recent thin film
absorption measurements. We use our numerical findings to discuss the use of
f-sum rules evaluated by integrating optical absorption data for accurate
carrier-density estimates.Comment: 7 pages, 3 figure
Nernst Effect in Electron-Doped PrCeCuO
The Nernst effect of PrCeCuO (x=0.13, 0.15, and 0.17) has
been measured on thin film samples between 5-120 K and 0-14 T. In comparison to
recent measurements on hole-doped cuprates that showed an anomalously large
Nernst effect above the resistive T and H
\cite{xu,wang1,wang2,capan}, we find a normal Nernst effect above T and
H for all dopings. The lack of an anomalous Nernst effect in the
electron-doped compounds supports the models that explain this effect in terms
of amplitude and phase fluctuations in the hole-doped cuprates. In addition,
the H(T) determined from the Nernst effect shows a conventional behavior
for all dopings. The energy gap determined from H(0) decreases as the
system goes from under-doping to over-dopingin agreement with the recent
tunnelling experiments
Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions
The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest in
the development of semiconductor technologies based on electron spin and has
led to several proof-of-concept spintronic devices [2-4]. A major hurdle for
realistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors,
remains their below room-temperature ferromagnetic transition temperature.
Enhancing ferromagnetism in semiconductors requires understanding the
mechanisms for interaction between magnetic dopants, such as Mn, and
identifying the circumstances in which ferromagnetic interactions are maximized
[5]. Here we report the use of a novel atom-by-atom substitution technique with
the scanning tunnelling microscope (STM) to perform the first controlled atomic
scale study of the interactions between isolated Mn acceptors mediated by the
electronic states of GaAs. High-resolution STM measurements are used to
visualize the GaAs electronic states that participate in the Mn-Mn interaction
and to quantify the interaction strengths as a function of relative position
and orientation. Our experimental findings, which can be explained using
tight-binding model calculations, reveal a strong dependence of ferromagnetic
interaction on crystallographic orientation. This anisotropic interaction can
potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance
the ferromagnetic transition temperature beyond that achieved in randomly doped
samples. Our experimental methods also provide a realistic approach to create
precise arrangements of single spins as coupled quantum bits for memory or
information processing purposes
An angle-resolved photoemission spectral function analysis of the electron doped cuprate Nd_1.85Ce_0.15CuO_4
Using methods made possible by recent advances in photoemission technology,
we perform an indepth line-shape analysis of the angle-resolved photoemission
spectra of the electron doped (n-type) cuprate superconductor
Nd_1.85Ce_0.15CuO_4. Unlike for the p-type materials, we only observe weak mass
renormalizations near 50-70 meV. This may be indicative of smaller
electron-phonon coupling or due to the masking effects of other interactions
that make the electron-phonon coupling harder to detect. This latter scenario
may suggest limitations of the spectral function analysis in extracting
electronic self-energies when some of the interactions are highly momentum
dependent.Comment: 8 pages, 5 figure
- …