575 research outputs found
A computer program for calculating design and off-design performance for turbojet and turbofan engines
Program uses component performance maps to enable user to do analytical engine cycle calculations. Through scaling procedure, each of the component maps can be used to represent a family of maps. Either convergent or convergent-divergent nozzles may be used
Computer optimization of reactor-thermoelectric space power systems
A computer simulation and optimization code that has been developed for nuclear space power systems is described. The results of using this code to analyze two reactor-thermoelectric systems are presented
A computer program for calculating design and off-design performance of two- and three-spool turbofans with as many as three nozzles
Program uses component performance maps to enable user to do analytical engine cycle calculations. Either convergent or convergent-divergent nozzles may be used
A Standard Siren Measurement of the Hubble Constant from GW170817 without the Electromagnetic Counterpart
We perform a statistical standard siren analysis of GW170817. Our analysis does not utilize knowledge of NGC 4993 as the unique host galaxy of the optical counterpart to GW170817. Instead, we consider each galaxy within the GW170817 localization region as a potential host; combining the redshifts from all of the galaxies with the distance estimate from GW170817 provides an estimate of the Hubble constant, H_0. Considering all galaxies brighter than 0.626L*_B as equally likely to host a binary neutron star merger, we find H_0 – 77^(+37)_(-18) km s^(−1) Mpc^(−1) (maximum a posteriori and 68.3% highest density posterior interval; assuming a flat H_0 prior in the range [10, 220] km s^(−1) Mpc^(−1)). We explore the dependence of our results on the thresholds by which galaxies are included in our sample, and we show that weighting the host galaxies by stellar mass or star formation rate provides entirely consistent results with potentially tighter constraints. By applying the method to simulated gravitational-wave events and a realistic galaxy catalog we show that, because of the small localization volume, this statistical standard siren analysis of GW170817 provides an unusually informative (top 10%) constraint. Under optimistic assumptions for galaxy completeness and redshift uncertainty, we find that dark binary neutron star measurements of H_0 will converge as 40%/√(N), where N is the number of sources. While these statistical estimates are inferior to the value from the counterpart standard siren measurement utilizing NGC 4993 as the unique host, H_0 = 76^(+19)_(-13) km s^(−1) Mpc^(−1) (determined from the same publicly available data), our analysis is a proof-of-principle demonstration of the statistical approach first proposed by Bernard Schutz over 30 yr ago
Manned Mars landing missions using electric propulsion
Manned Mars landing missions using electric propulsion - evaluation of various mission profile
Lorentz Invariance and the Cosmological Constant
Non-trivial solutions in string field theory may lead to the spontaneous
breaking of Lorentz invariance and to new tensor-matter interactions. It is
argued that requiring the contribution of the vacuum expectation values of
Lorentz tensors to account for the vacuum energy up to the level that
implies the new interactions range is . These conjectured violations of the Lorentz symmetry are
consistent with the most stringent experimental limits.Comment: 13 pages, plain Latex. This essay was selected for an honorable
mention in the 1997 Gravity Research Foundation essay competio
Quintessence, scalar-tensor theories and non-Newtonian gravity
We discuss some of the issues which we encounter when we try to invoke the
scalar-tensor theories of gravitation as a theoretical basis of quintessence.
One of the advantages of appealing to these theories is that they allow us to
implement the scenario of a ``decaying cosmological constant,'' which offers a
reasonable understanding of why the observed upper bound of the cosmological
constant is smaller than the theoretically natural value by as much as 120
orders of magnitude. In this context, the scalar field can be a candidate of
quintessence in a broader sense. We find, however, a serious drawback in the
prototype Brans-Dicke model with added; a static universe in the
physical conformal frame which is chosen to have constant particle masses. We
propose a remedy by modifying the matter coupling of the scalar field taking
advantage of scale invariance and its breakdown through quantum anomaly. By
combining this with a conjecture on another cosmological constant problem
coming from the vacuum energy of matter fields, we expect a possible link
between quintessence and non-Newtonian gravity featuring violation of Weak
Equivalence Principle and intermediate force range, likely within the
experimental constraints. A new prediction is also offered on the
time-variability of the gravitational constant.Comment: 12 pages LaTex including 1 eps figur
Gravitational lensing in metric theories of gravity
Gravitational lensing in metric theories of gravity is discussed. I introduce
a generalized approximate metric element, inclusive of both post-post-Newtonian
(ppN) contributions and gravito-magnetic field. Following Fermat's principle
and standard hyphoteses, I derive the time delay function and deflection angle
caused by an isolated mass distribution. Several astrophysical systems are
considered. In most of the cases, the gravito-magnetic correction offers the
best perspectives for an observational detection. Actual measurements
distinguish only marginally different metric theories one from another.Comment: 15 pages; to appear in Phys. Rev.
The Laser Astrometric Test of Relativity Mission
This paper discusses new fundamental physics experiment to test relativistic
gravity at the accuracy better than the effects of the 2nd order in the
gravitational field strength. The Laser Astrometric Test Of Relativity (LATOR)
mission uses laser interferometry between two micro-spacecraft whose lines of
sight pass close by the Sun to accurately measure deflection of light in the
solar gravity. The key element of the experimental design is a redundant
geometry optical truss provided by a long-baseline (100 m) multi-channel
stellar optical interferometer placed on the International Space Station. The
geometric redundancy enables LATOR to measure the departure from Euclidean
geometry caused by the solar gravity field to a very high accuracy. LATOR will
not only improve the value of the parameterized post-Newtonian (PPN) parameter
gamma to unprecedented levels of accuracy of 1 part in 1e8, it will also reach
ability to measure effects of the next post-Newtonian order (1/c^4) of light
deflection resulting from gravity's intrinsic non-linearity. The solar
quadrupole moment parameter, J2, will be measured with high precision, as well
as a variety of other relativistic. LATOR will lead to very robust advances in
the tests of fundamental physics: this mission could discover a violation or
extension of general relativity, or reveal the presence of an additional long
range interaction in the physical law. There are no analogs to the LATOR
experiment; it is unique and is a natural culmination of solar system gravity
experiments.Comment: 8 pages, 2 figures, invited talk given at the Second International
Conference on Particle and Fundamental Physics in Space (SpacePart'03), 10-12
December 2003, Washington, D
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