4,450 research outputs found
Vaporization and decomposition kinetics of candidate re-entry blackout suppressants in low-pressure flames
Measurement of thermal accommodation coefficients between liquids and high temperature gases in low pressure reentry communications blackout interval
Measured limits to contamination of optical surfaces by elastomers in vacuum
We have monitored the reflectivity of mirrors that were exposed to a fluoroelastomer (3M-Fluorel 2176) and a room-temperature vulcanizing silicone rubber (RTV-615) in vacuum. The 95% confidence limit on the decrease of mirror reflectivities was less than 0.35 ppm/week for Fluorel and <0.29 ppm@week for RTV-615
Polarized-interferometer feasibility study
The feasibility of using a polarized-interferometer system as a rendezvous and docking sensor for two cooperating spacecraft was studied. The polarized interferometer is a radio frequency system for long range, real time determination of relative position and attitude. Range is determined by round trip signal timing. Direction is determined by radio interferometry. Relative roll is determined from signal polarization. Each spacecraft is equipped with a transponder and an antenna array. The antenna arrays consist of four crossed dipoles that can transmit or receive either circularly or linearly polarized signals. The active spacecraft is equipped with a sophisticated transponder and makes all measurements. The transponder on the passive spacecraft is a relatively simple repeater. An initialization algorithm is developed to estimate position and attitude without any a priori information. A tracking algorithm based upon minimum variance linear estimators is also developed. Techniques to simplify the transponder on the passive spacecraft are investigated and a suitable configuration is determined. A multiple carrier CW signal format is selected. The dependence of range accuracy and ambiguity resolution error probability are derived and used to design a candidate system. The validity of the design and the feasibility of the polarized interferometer concept are verified by simulation
The first direct detection of gravitational waves opens a vast new frontier in astronomy
The first direct detection of gravitational waves (GWs),
announced on 11 February 2016, has opened a vast new
frontier in astronomy. Albert Einstein predicted the existence of these waves about a century ago as a consequence of his general theory of relativity. Radio
astronomy observations of the binary pulsar system PSR
1913 + 16 over a 20 year period beginning in 1975 provided
strong observational evidence that gravitational waves carried energy away from the orbits of neutron stars at precisely the level predicted by general relativity
(GR). This relentless conversion of orbital energy into
gravitational wave energy causes binary orbits to decay
until the objects eventually collide and merge. The frontier
of precision measurement science, using laser interferometers, was pushed for more than four decades to
achieve this first direct detection, marking a milestone in
experimental physics and engineering. Even more significantly, this milestone also opens a new window onto our universe and a completely new kind of astronomy to
explore
Comparison of regional blood flow values measured by radioactive and fluorescent microspheres
Fluorescent microspheres (FM) have become an attractive alternative to radioactive microspheres (RM) for the measurement of regional blood flow (RBF). The aim of the present study was to investigate the comparability of both methods by measuring RBF with FM and RM. Eight anaesthetised pigs received simultaneous, left atrial injections of FM and RM with a diameter of 15 mum at six different time points. Blood reference samples were collected from the descending aorta. RBF was determined in tissue samples of the myocardium, spleen and kidneys of all 8 animals. After radioactivity of the tissue samples was determined, the samples were processed automatically for measuring fluorescence using a recently developed filter device (SPU). RBF was calculated with both the isotope and spectrometric data of both methods for each sample resulting in a total of 10,512 blood flow values. The comparison of the RBF values yielded high linear correlation (mean r(2) = 0.95 +/- 0.03 to 0.97 +/- 0.02) and excellent agreement (bias 5.4-6.7%, precision 9.9-16.5%) of both methods. Our results indicate the validity of MS and of the automated tissue processing technique by means of the SPU. Copyright (C) 2002 S. Karger AG, Basel
The Random Bit Complexity of Mobile Robots Scattering
We consider the problem of scattering robots in a two dimensional
continuous space. As this problem is impossible to solve in a deterministic
manner, all solutions must be probabilistic. We investigate the amount of
randomness (that is, the number of random bits used by the robots) that is
required to achieve scattering. We first prove that random bits are
necessary to scatter robots in any setting. Also, we give a sufficient
condition for a scattering algorithm to be random bit optimal. As it turns out
that previous solutions for scattering satisfy our condition, they are hence
proved random bit optimal for the scattering problem. Then, we investigate the
time complexity of scattering when strong multiplicity detection is not
available. We prove that such algorithms cannot converge in constant time in
the general case and in rounds for random bits optimal
scattering algorithms. However, we present a family of scattering algorithms
that converge as fast as needed without using multiplicity detection. Also, we
put forward a specific protocol of this family that is random bit optimal ( random bits are used) and time optimal ( rounds are used).
This improves the time complexity of previous results in the same setting by a
factor. Aside from characterizing the random bit complexity of mobile
robot scattering, our study also closes its time complexity gap with and
without strong multiplicity detection (that is, time complexity is only
achievable when strong multiplicity detection is available, and it is possible
to approach it as needed otherwise)
Tumbleweeds and airborne gravitational noise sources for LIGO
Gravitational-wave detectors are sensitive not only to astrophysical
gravitational waves, but also to the fluctuating Newtonian gravitational forces
of moving masses in the ground and air around the detector. This paper studies
the gravitational effects of density perturbations in the atmosphere, and from
massive airborne objects near the detector. These effects were previously
considered by Saulson; in this paper I revisit these phenomena, considering
transient atmospheric shocks, and the effects of sound waves or objects
colliding with the ground or buildings around the test masses. I also consider
temperature perturbations advected past the detector as a source of
gravitational noise. I find that the gravitational noise background is below
the expected noise floor even of advanced interferometric detectors, although
only by an order of magnitude for temperature perturbations carried along
turbulent streamlines. I also find that transient shockwaves in the atmosphere
could potentially produce large spurious signals, with signal-to-noise ratios
in the hundreds in an advanced interferometric detector. These signals could be
vetoed by means of acoustic sensors outside of the buildings. Massive
wind-borne objects such as tumbleweeds could also produce gravitational signals
with signal-to-noise ratios in the hundreds if they collide with the
interferometer buildings, so it may be necessary to build fences preventing
such objects from approaching within about 30m of the test masses.Comment: 15 pages, 10 PostScript figures, uses REVTeX4.cls and epsfig.st
Electromagnetic multipole theory for optical nanomaterials
Optical properties of natural or designed materials are determined by the
electromagnetic multipole moments that light can excite in the constituent
particles. In this work we present an approach to calculate the multipole
excitations in arbitrary arrays of nanoscatterers in a dielectric host medium.
We introduce a simple and illustrative multipole decomposition of the electric
currents excited in the scatterers and link this decomposition to the classical
multipole expansion of the scattered field. In particular, we find that
completely different multipoles can produce identical scattered fields. The
presented multipole theory can be used as a basis for the design and
characterization of optical nanomaterials
Industrija čelika u novim članicama EU u usporedbi s globalnim trendovima
Accession of the metallurgically significant countries of the Central and Eastern Europe to the EU in 2004 was conditioned by fulfilling the Restructuring Programs as the foundation for achievement of competitiveness and guarancy of viability. The Restructuring Programs, which fulfilling and regular monitoring had lasted 5 years, demonstrated the right of the significant position of the steel industry in the new EU members, especially in Poland, Czech Republic, Slovakia, and in Hungary. The objective of the article is to point to the key elements in context of steel industry global trends, regarding either production or especially utility values and total consumption. In this connection, privatization took an important role too.Prinos metalurgije glavnih zemalja Srednje i Istočne Europe u EU u 2004. je bilo ostvarenje restrukturiranja programa kao temelj za postizanje konkurentnosti i jamstvo opstanka. Restrukturiranje programa, provedba i redovito praćenj za 5 godina opravdalo je značajno mjesto u industriji čelika u novim zemljama EU, naročito u Poljskoj, Češkoj, Slovačkoj i Mađarskoj. Ovaj članak ima za cilj istaknuti ključne elemente u razvojnom konextu industrija čelika u svijetu, kako u pogledu proizvodnje, a posebice u odnosu na kvalitete i ukupnu potrošnju. Važan element u tom pogledu, nastavak privatizacije
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