1,796 research outputs found
Health hazards of ultrafine metal and metal oxide powders
Study reveals that suggested threshold limit values are from two to fifty times lower than current recommended threshold limit values. Proposed safe limits of exposure to the ultrafine dusts are based on known toxic potential of various materials as determined in particle size ranges
Technology Development for the Caltech Submillimeter Observatory Balanced Receivers
The Caltech Submillimeter Observatory (CSO) is located on top of Mauna Kea,
Hawaii, at an altitude of 4.2 km. The existing suite of facility heterodyne
receivers covering the submillimeter band is rapidly aging and in need of
replacement. To facilitate deep integrations and automated spectral line
surveys, a family of remote programmable, synthesized, dual-frequency balanced
receivers covering the astronomical important 180 - 720 GHz atmospheric windows
is in an advanced stage of development. Installation of the first set of
receivers is expected in the spring of 2012.
Dual-frequency observation will be an important mode of operation offered by
the new facility instrumentation. Two band observations are accomplished by
separating the H and V polarizations of the incoming signal and routing them
via folded optics to the appropriate polarization sensitive balanced mixer.
Scientifically this observation mode facilitates pointing for the higher
receiver band under mediocre weather conditions and a doubling of scientific
throughput (2 x 4 GHz) under good weather conditions.Comment: 12 pages, 17 figures; IEEE Terahertz Science & Technology, January
2012, Volume 2, Issue
Signatures of Spin Glass Freezing in NiO Nanoparticles
We present a detailed study of the magnetic properties of sol-gel prepared
nickel oxide nanoparticles of different sizes. We report various measurements
such as frequency, field and temperature dependence of ac susceptibility,
temperature and field dependence of dc magnetization and time decay of
thermoremanent magnetization. Our results and analysis show that the system
behaves as a spin glass.Comment: 8 pages, 9 figure
Mutual passivation of group IV donors and nitrogen in diluted GaNāAsāĖā alloys
We demonstrate the mutual passivation phenomenon of Ge donors and isovalent N in highly mismatched alloy GaNāAsāĖādoped with Ge. Layers of this alloy were formed by the sequential implantation of Ge and N ions followed by pulsed laser melting and rapid thermal annealing. The mutual passivation effect results in the electrical deactivation of GeGa donors (Ge on Ga sites) and suppression of the NAs (N on As sites) induced band gap narrowing through the formation of GeGaāNAs nearest neighbor pairs. These results in combination with the analogous effect observed in Si-doped GaNāAsāĖā provide clear evidence of the general nature of the mutual passivation phenomenon in highly mismatched semiconductor alloys.This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences and Engineering, U.S. Department of Energy, under
Contract No. DE-AC03-76SF00098. One of the authors
~M.A.S.! acknowledges support by an NSF graduate research
fellowship
RDF Querying
Reactive Web systems, Web services, and Web-based publish/
subscribe systems communicate events as XML messages, and in
many cases require composite event detection: it is not sufficient to react
to single event messages, but events have to be considered in relation to
other events that are received over time.
Emphasizing language design and formal semantics, we describe the
rule-based query language XChangeEQ for detecting composite events.
XChangeEQ is designed to completely cover and integrate the four complementary
querying dimensions: event data, event composition, temporal
relationships, and event accumulation. Semantics are provided as
model and fixpoint theories; while this is an established approach for rule
languages, it has not been applied for event queries before
Hole-burning experiments within solvable glassy models
We reproduce the results of non-resonant spectral hole-burning experiments
with fully-connected (equivalently infinite-dimensional) glassy models that are
generalizations of the mode-coupling approach to nonequilibrium situations. We
show that an ac-field modifies the integrated linear response and the
correlation function in a way that depends on the amplitude and frequency of
the pumping field. We study the effect of the waiting and recovery-times and
the number of oscillations applied. This calculation will help descriminating
which results can and which cannot be attributed to dynamic heterogeneities in
real systems.Comment: 4 pages, 8 figures, RevTe
The Caenorhabditis elegans vulva: A post-embryonic gene regulatory network controlling organogenesis
The Caenorhabditis elegans vulva is an elegant model for dissecting a gene regulatory network (GRN) that directs postembryonic organogenesis. The mature vulva comprises seven cell types (vulA, vulB1, vulB2, vulC, vulD, vulE, and vulF), each with its own unique pattern of spatial and temporal gene expression. The mechanisms that specify these cell types in a precise spatial pattern are not well understood. Using reverse genetic screens, we identified novel components of the vulval GRN, including nhr-113 in vulA. Several transcription factors (lin-11, lin-29, cog-1, egl-38, and nhr-67) interact with each other and act in concert to regulate target gene expression in the diverse vulval cell types. For example, egl-38 (Pax2/5/8) stabilizes the vulF fate by positively regulating vulF characteristics and by inhibiting characteristics associated with the neighboring vulE cells. nhr-67 and egl-38 regulate cog-1, helping restrict its expression to vulE. Computational approaches have been successfully used to identify functional cis-regulatory motifs in the zmp-1 (zinc metalloproteinase) promoter. These results provide an overview of the regulatory network architecture for each vulval cell type
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