1,501 research outputs found
Impact glasses from the less than 20-micrometer fraction of Apollo 17 soils 72501 and 78221
The chemical compositions of microscopic glasses produced during meteoroid impacts on the lunar surface provide information regarding the various fractionation processes that accompany these events. To learn more about these fractionation processes, we studied the compositions of submicrometer glass spheres from two Apollo 17 sampling sites using electron microscopy. The majority of the analyzed glasses show evidence for varying degrees of impact-induced chemical fractionation. Among these are HASP glasses (high-Al, Si-poor), which are believed to represent the refractory residuum left after the loss of volatile elements (e.g., Si, Fe, Na) from the precursor material. In addition to HASP-type glasses, we also observed a group of volatile-rich, Al-poor (VRAP) glasses that represent condensates of vaporized volatile constituents, and are complementary to the HASP compositions. High-Ti glasses were also found during the course of this study, and are documented here for the first time
FDA\u27s AIDS Program
The Conquest of AIDS - under the leadership of President Reagan - is the Nation\u27s number one public health priority
Humanities in the Open: The Challenges of Creating an Open Literature Anthology
This book chapter was a part of the publication, Open Pedagogy Approaches: Faculty, Library, and Student Collaborations. It highlights a case study from the University of Central Florida of creating an open literature anthology
The Spectroscopic Age of 47 Tuc
High signal-to-noise integrated spectra of the metal-rich globular cluster 47
Tuc, spanning the H-gamma(HR) and Fe4668 line indices, have been obtained. The
combination of these indices has been suggested (Jones & Worthey 1995, ApJ,
446, L31) as the best available mechanism for cleanly separating the
age-metallicity degeneracy which hampers the dating of distant, unresolved,
elliptical galaxies. For the first time, we apply this technique to a nearby
spheroidal system, 47 Tuc, for which independent ages, based upon more
established methods, exist. Such an independent test of the technique's
suitability has not been attempted before, but is an essential one before its
application to more distant, unresolved, stellar populations can be considered
valid. Because of its weak series of Balmer lines, relative to model spectra,
our results imply a spectroscopic ``age'' for 47 Tuc well in excess of 20 Gyr,
at odds with the colour-magnitude diagram age of 14+/-1 Gyr. The derived metal
abundance, however, is consistent with the known value. Emission ``fill-in'' of
the H-gamma line as the source of the discrepancy cannot be entirely excluded
by existing data, although the observational constraints are restrictive.Comment: 17 pages, 4 figures, LaTeX, accepted for publication in The
Astronomical Journal, also available at
http://casa.colorado.edu/~bgibson/publications.htm
ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation
A finite stack of thin superconducting tapes, all carrying a fixed current I,
can be approximated by an anisotropic superconducting bar with critical current
density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the
tape width, and D is the tape-to-tape periodicity. The current density J must
obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis
and are stacked along the z axis. We suppose that Jc is independent of field
(Bean approximation) and look for a solution to the critical state for
arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the
critical state requires that Bz=0. We show that this implies \partial
J/\partial x=0 in the central region. Setting c as a constant (independent of
z) results in field profiles remarkably close to the desired one (Bz=0 for
|x|<c) as long as the aspect ratio b/a is not too small. We evaluate various
criteria for choosing c, and we show that the calculated hysteretic losses
depend only weakly on how c is chosen. We argue that for small D/a the
anisotropic homogeneous-medium approximation gives a reasonably accurate
estimate of the ac losses in a finite Z stack. The results for a Z stack can be
used to calculate the transport losses in a pancake coil wound with
superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno
Poking the bear: Promoting textbook affordability in the face of a restrictive institutional environment
Librarians and instructional designers formed an informal partnership to promote low-cost textbook solutions in the absence of formal initiatives at a public, four-year institution. Learn how we negotiated institutional barriers such as bookstore contract prohibitions and protected revenue streams. Our case examples describe solutions and workflows undertaken to transform course materials, in addition to activities being pursued to make textbook affordability an institutional priority
Capturing user requirements in medical device development: the role of ergonomics
Czerniak, L. / SS. Cyril & Methodius Grad. Clas
A fiberâmounted, micromachined photoconductive probe with 15 nV/Hz1/2 sensitivity
We report the performance of a micromachined, photoconductiveâsampling probe that is fabricated on lowâtemperatureâgrown GaAs and mounted on a singleâmode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 ÎŒm, and a sensitivity of 15 nV/(Hz)1/2 when integrated with a high impedance, junction fieldâeffect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probeâs compact cross section makes it ideal for applications as an internalânode, picosecondâresponse, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70779/2/APPLAB-69-13-1843-1.pd
A fieldâsensitive photoconductive probe for sampling through passivation layers
A fieldâsensitive photoconductive sampling technique has been demonstrated in measurements performed through an insulating layer without the need for conductive contact. Sampled signals are sensed by a virtualâground, floatingâgate amplifier without draining charge from the device under test or the photoconductive switch. The minimum detectable signal is 2.5 ÎŒV/Hz1/2 with a spatial resolution of 7 ÎŒm, while the sampling bandwidth is essentially that observed using photoconductive sampling with a conductive contact to the device under test. The photovoltaic and shot current noise are negligible in comparison with the lockâin amplifier noise since the current flowing in this highâimpedance, floatingâgate probe is negligible. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70307/2/APPLAB-69-15-2211-1.pd
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