231 research outputs found
Utilization of ambient gas as a propellant for low earth orbit electric propulsion
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995.by Buford Ray Conley.M.S
Periodic Variation of Stress in Sputter Deposited Si/WSi2 Multilayers
A tension increment after sputter deposition of 1 nm of WSi2 onto sputtered
Si was observed at low Ar gas pressures. Wafer curvature data on multilayers
were found to have a periodic variation corresponding to the multilayer period,
and this permitted statistical analyses to improve the sensitivity to small
stresses. The observation of tension instead of compression in the initial
stage of growth is new and a model invoking surface rearrangement is invoked.
The data also bear on an unusual surface smoothing phenomena for sputtered Si
surfaces caused by the sputter deposition of WSi2 . We furthermore report that
for low Ar pressures the Si layers are the predominant source of built-up
stress
Predicted and observed evolution in the mean properties of Type Ia supernovae with redshift
Recent studies indicate that Type Ia supernovae (SNe Ia) consist of two
groups - a "prompt" component whose rates are proportional to the host galaxy
star formation rate, whose members have broader lightcurves and are
intrinsically more luminous, and a "delayed" component whose members take
several Gyr to explode, have narrower lightcurves, and are intrinsically
fainter. As cosmic star formation density increases with redshift, the prompt
component should begin to dominate. We use a two-component model to predict
that the average lightcurve width should increase by 6% from z=0-1.5. Using
data from various searches we find an 8.1% +/- 2.7% increase in average
lightcurve width for non-subluminous SNe Ia from z=0.03 - 1.12, corresponding
to an increase in the average intrinsic luminosity of 12%. To test whether
there is any bias after supernovae are corrected for lightcurve shape we use
published data to mimic the effect of population evolution and find no
significant difference in the measured dark energy equation of state parameter,
w. However, future measurements of time-variable w will require standardization
of SN Ia magnitudes to 2% up to z=1.7, and it is not yet possible to assess
whether lightcurve shape correction works at this level of precision. Another
concern at z=1.5 is the expected order of magnitude increase in the number of
SNe Ia that cannot be calibrated by current methods.Comment: 5 pages, 3 figures, accepted to ApJ Letters, addressed referee's
comments, table adde
Pressure-dependent transition from atoms to nanoparticles in magnetron sputtering: Effect on WSi2 film roughness and stress
We report on the transition between two regimes from several-atom clusters to
much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the
effect of nanoparticles on the properties of amorphous thin films and
multilayers. Sputter deposition of thin films is monitored by in situ x-ray
scattering, including x-ray reflectivity and grazing incidence small angle
x-ray scattering. The results show an abrupt transition at an Ar background
pressure Pc; the transition is associated with the threshold for energetic
particle thermalization, which is known to scale as the product of the Ar
pressure and the working distance between the magnetron source and the
substrate surface. Below Pc smooth films are produced, while above Pc roughness
increases abruptly, consistent with a model in which particles aggregate in the
deposition flux before reaching the growth surface. The results from WSi2 films
are correlated with in situ measurement of stress in WSi2/Si multilayers, which
exhibits a corresponding transition from compressive to tensile stress at Pc.
The tensile stress is attributed to coalescence of nanoparticles and the
elimination of nano-voids.Comment: 16 pages, 10 figures; v3: published versio
Management of soft red winter wheat (2003)
"New 10/03/5M.""This publication is part of a series of IPM Manuals prepared by the Plant Protection Programs of the University of Missouri. Topics covered in the series include an introduction to scouting, weed identification and management, plant diseases, and insects of field and horticultural crops.""Integrated pest management.
Atmospheric Acetaldehyde: Importance of Air-Sea Exchange and a Missing Source in the Remote Troposphere.
We report airborne measurements of acetaldehyde (CH3CHO) during the first and second deployments of the National Aeronautics and Space Administration (NASA) Atmospheric Tomography Mission (ATom). The budget of CH3CHO is examined using the Community Atmospheric Model with chemistry (CAM-chem), with a newly-developed online air-sea exchange module. The upper limit of the global ocean net emission of CH3CHO is estimated to be 34 Tg a-1 (42 Tg a-1 if considering bubble-mediated transfer), and the ocean impacts on tropospheric CH3CHO are mostly confined to the marine boundary layer. Our analysis suggests that there is an unaccounted CH3CHO source in the remote troposphere and that organic aerosols can only provide a fraction of this missing source. We propose that peroxyacetic acid (PAA) is an ideal indicator of the rapid CH3CHO production in the remote troposphere. The higher-than-expected CH3CHO measurements represent a missing sink of hydroxyl radicals (and halogen radical) in current chemistry-climate models
First Measurement of Coherent Elastic Neutrino-Nucleus Scattering on Argon
We report the first measurement of coherent elastic neutrino-nucleus
scattering (\cevns) on argon using a liquid argon detector at the Oak Ridge
National Laboratory Spallation Neutron Source. Two independent analyses prefer
\cevns over the background-only null hypothesis with greater than
significance. The measured cross section, averaged over the incident neutrino
flux, is (2.2 0.7) 10 cm -- consistent with the
standard model prediction. The neutron-number dependence of this result,
together with that from our previous measurement on CsI, confirms the existence
of the \cevns process and provides improved constraints on non-standard
neutrino interactions.Comment: 8 pages, 5 figures with 2 pages, 6 figures supplementary material V3:
fixes to figs 3,4 V4: fix typo in table 1, V5: replaced missing appendix, V6:
fix Eq 1, new fig 3, V7 final version, updated with final revision
Оцінка оновлення основних засобів за рахунок позикових коштів
Оновлення основних засобів є актуальною проблемою сьогодення. Для багатьох підприємств кредити банків є чи не єдиним джерелом коштів на модернізацію виробничих потужностей. В даній статті нами були розглянуті можливості і перспективи приватних фірм для використання з цією метою позикових засобів, оцінений ступінь прозорості банківських установ, річні ставки за інвестиційними кредитами та інші умови їхнього надання.Modernizing of the basic assets is a topical problem of the present. For many business firms bank loans are may be the only source of funds for renewal of production facilities. In the article we have considered the opportunities and prospects for use of borrowed funds by private firms for this purpose, rated the degree of transparency of banking institutions, the annual rates of investment credits and other conditions of their granting
A Dual Color Far-Red to Near-Infrared Firefly Luciferin Analogue Designed for Multi-Parametric Bioluminescence Imaging
Red-shifted bioluminescent emitters allow improved in vivo tissue penetration and signal quantification, and have led to the development of beetle luciferin analogues that elicit red-shifted bioluminescence with firefly luciferase. However, unlike natural luciferin, none have been shown to emit different colors with different luciferases. We have synthesized and tested the first dual color, far-red to near infrared (nIR) emitting analogue of beetle luciferin, which akin to natural luciferin exhibits pH dependent fluorescence spectra and emits bioluminescence of different colors with different engineered Fluc enzymes. Our analogue produces different far-red to nIR emission maxima with different Fluc mutants up to .max 706 nm. This is the furthest red-shifted form of bioluminescence reported without the requirement of a resonance energy transfer acceptor and such improvement should allow tissues to be more effectively probed using multiparametric deep-tissue bioluminescence imaging
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