4,008 research outputs found
Virginia Earth Science Collaborative Astronomy Course for Teachers
We describe the development and implementation of a professional development course for teachers of grades 4-12 designed to increase their content knowledge in astronomy, space science, and the nature of science using interactive presentations, and hands-on and inquiry-based lessons. The course, Space Science for Teachers, encompasses the astronomy and nature of science components of the Virginia Standards of Learning for grades 4-12 [1]. In addition to increasing their content knowledge, teachers gain experience using innovative teaching technologies, such as an inflatable planetarium, planetarium computer software, and computer controlled telescopes. The courses included evening laboratory sessions where teachers learned the constellations, how to find specific celestial objects, and how to use a variety of small telescopes. Participants received three graduate credit hours in science after completing the course requirements. Space Science for Teachers was taught at the University of Virginia in Summer 2005 and 2006, at George Mason University in Summer 2006 and 2007, at the University of Virginia Southwest Center in Abingdon, Virginia in Fall 2006, and at the MathScience Innovation Center in Richmond during Summer 2005 and 2007. A total of 135 teachers participated in the courses
Studies and observations of ultraviolet and X-ray sources
The status of research undertaken with the IUE satellite for programs on strong binary X-ray stars and X-ray globular clusters is summarized. Variable Seyfert galaxies and cataclysmic variables were investigated
Quantum steering of electron wave function in an InAs Y-branch switch
We report experiments on gated Y-branch switches made from InAs ballistic
electron wave guides. We demonstrate that gating modifies the electron wave
functions as well as their interference pattern, causing the anti-correlated,
oscillatory transconductances. Such previously unexpected phenomenon provides
evidence of steering the electron wave function in a multi-channel transistor
structure.Comment: 15 pages, including 3 figure
Energetic electrons in the midlatitude nighttime E region
Nike Apache 14.439 was launched from Wallops Island at 0003 EST on 1 November 1972, a very disturbed night (K sub P = 8). A Geiger counter in the payload detected electrons ( keV) with a maximum flux of 1086 + or -261/sq cm/sec/ster. The height-averaged ionization rate in the upper E region is calculated from the measured electron density profile and has a value of 35 1/cu/cm/sec. The ionization rate can be reconciled with the observed flux of electrons ( 70 2 keV) if the spectrum ( keV) is of the form J ( E) = J sub O exp(-E/E sub O) with E sub O equal to 8.3 keV. The ionization rate on this and other nights is found to be strongly dependent on geomagnetic activity. It is suggested that energetic electrons are the principal source of ionization at midlatitudes in the upper E region near midnight, even under rather quiet geomagnetic conditions
Observation of one electron charge in an enhancement-mode InAs single electron transistor at 4.2K
We propose and demonstrate experimentally a novel design of single-electron
quantum dots. The structure consists of a narrow band gap quantum well that can
undergo a transition from the hole accumulation regime to the electron
inversion regime in a single-top-gate transistor configuration. We have
observed large size quantization and Coulomb charging energies over 10meV. This
quantum dot design can be especially important for scalable quantum computing.Comment: 5 figure
XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups
We study the distribution of gas pressure and entropy in eight groups of
galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose
Systems (RASSCALS). We use archival and proprietary XMM-Newton observations,
supplementing the X-ray data with redshifts derived from the literature; we
also list 127 new redshifts measured with the Gemini North telescope. The
groups show remarkable self-similarity in their azimuthally averaged entropy
and temperature profiles. The entropy increases with radius; the behavior of
the entropy profiles is consistent with an increasing broken power law with
inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence),
respectively. There is no evidence of a central, isentropic core, and the
entropy distribution in most of the groups is flatter at large radii than in
the inner region, challenging earlier reports as well as theoretical models
predicting large isentropic cores or asymptotic slopes of 1.1 at large radii.
The pressure profiles are consistent with a self-similar decreasing broken
power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and
-1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the
entropy distribution reflects the varied gasdynamical histories of the groups;
the regularity and self-similarity of the pressure profiles is a sign of a
similarity in the underlying dark matter distributions.Comment: Accepted for publication in the Astrophysical Journa
Phonons in a Nanoparticle Mechanically Coupled to a Substrate
The discrete nature of the vibrational modes of an isolated nanometer-scale
solid dramatically modifies its low-energy electron and phonon dynamics from
that of a bulk crystal. However, nanocrystals are usually coupled--even if only
weakly--to an environment consisting of other nanocrystals, a support matrix,
or a solid substrate, and this environmental interaction will modify the
vibrational properties at low frequencies. In this paper we investigate the
modification of the vibrational modes of an insulating spherical nanoparticle
caused by a weak {\it mechanical} coupling to a semi-infinite substrate. The
phonons of the bulk substrate act as a bath of harmonic oscillators, and the
coupling to this reservoir shifts and broadens the nanoparticle's modes. The
vibrational density of states in the nanoparticle is obtained by solving the
Dyson equation for the phonon propagator, and we show that environmental
interaction is especially important at low frequencies. As a probe of the
modified phonon spectrum, we consider nonradiative energy relaxation of a
localized electronic impurity state in the nanoparticle, for which good
agreement with experiment is found.Comment: 10 pages, Revte
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