668 research outputs found
1-Methyl-1-azonia-3,5-diaza-7-phosphaÂtricycloÂ[3.3.1.1]decane 7-oxide triiodide
The title compound, C7H15N3OP+·I3
â, is a derivative of the well known water-soluble aminoÂphosphine 1,3,5-triaza-7-phosphaadamantane (PTA). The crystal structure is composed of a cage-like 1-methyl-1-azonia-3,5-diaza-7-phosphaÂtricycloÂ[3.3.1.1]decane 7-oxide cation and a triiodide anion. The N-methylÂation of the PTA cage results in a slight elongation of the corresponding CâN bonds, while the oxidation of the P atom leads to a slight shortening of the CâP bonds in comparison with those of PTA. In general, most of the bonding parameters are comparable with those reported for related compounds bearing the PTA core. Two interÂmolecular CâHâŻO hydrogen bonds between methylÂene groups and the P=O group are responsible for the linkage of neighbouring cations into linear one-dimensional hydrogen-bonded chains
Displaced geostationary orbit design using hybrid sail propulsion
Because of an increase in the number of geostationary spacecraft and the limits imposed by eastâwest spacing
requirements, the geostationary orbit is becoming congested. To increase its capacity, this paper proposes to create
new geostationary slots by displacing the geostationary orbit either out of or in the equatorial plane by means of
hybrid solar sail and solar electric propulsion. To minimize propellant consumption, optimal steering laws for the
solar sail and solar-electric-propulsion thrust vectors are derived and the performance in terms of mission lifetime is
assessed. For comparison, similar analyses are performed for conventional propulsion, including impulsive and pure
solar electric propulsion. It is shown that hybrid sails outperform these propulsion techniques and that out-of-plane
displacements outperform in-plane displacements. The out-of-plane case is therefore further investigated in a
spacecraft mass budget to determine the payload mass capacity. Finally, two transfers that enable a further
improvement of the performance of hybrid sails for the out-of-plane case are optimized using a direct pseudospectral
method: a seasonal transit between orbits displaced above and below the equatorial plane and a transit to a parking
orbit when geostationary coverage is not needed. Both transfers are shown to require only a modest propellant
budget, outweighing the improvements they can establish
A novel interplanetary communications relay
A case study of a potential Earth-Mars interplanetary communications relay, designed to ensure continuous communications, is detailed. The relay makes use of orbits based on artificial equilibrium points via the application of continuous low thrust, which allows a spacecraft to hover above the orbital plane of Mars and thus ensure communications when the planet is occulted with respect to the Earth. The artificial equilibria of two different low-thrust propulsion technologies are considered: solar electric propulsion, and a solar sail/solar electric propulsion hybrid. In the latter case it is shown that the combination of sail and solar electric propulsion may prove advantageous, but only under specific circumstances of the relay architecture suggested. The study takes into account factors such as the spacecraft's power requirements and communications band utilized to determine the mission and system architecture. A detailed contingency analysis is considered for recovering the relay after increasing periods of spacecraft motor failure, and combined with a consideration for how best to deploy the relay spacecraft to maximise propellant reserves and mission duration
LHC Forward Physics
The goal of this report is to give a comprehensive overview of the rich field of forward physics, with a special attention to the topics that can be studied at the LHC. The report starts presenting a selection of the Monte Carlo simulation tools currently available, chapter 2, then enters the rich phenomenology of QCD at low, chapter 3, and high, chapter 4, momentum transfer, while the unique scattering conditions of central exclusive production are analyzed in chapter 5. The last two experimental topics, Cosmic Ray and Heavy Ion physics are presented in the chapter 6 and 7 respectively. Chapter 8 is dedicated to the BFKL dynamics, multiparton interactions, and saturation. The report ends with an overview of the forward detectors at LHC. Each chapter is correlated with a comprehensive bibliography, attempting to provide to the interested reader with a wide opportunity for further studies.Peer Reviewe
The mathematical theory of resonant transducers in a spherical gravity wave antenna
The rigoruos mathematical theory of the coupling and response of a spherical
gravitational wave detector endowed with a set of resonant transducers is
presented and developed. A perturbative series in ascending powers of the
square root of the ratio of the resonator to the sphere mass is seen to be the
key to the solution of the problem. General layouts of arbitrary numbers of
transducers can be assessed, and a specific proposal (PHC), alternative to the
highly symmetric TIGA of Merkowitz and Johnson, is described in detail.
Frequency spectra of the coupled system are seen to be theoretically recovered
in full agreement with experimental determinations.Comment: 31 pages, 7 figures, LaTeX2e, \usepackage{graphicx,deleq
Natural Wormholes as Gravitational Lenses
Visser has suggested traversable 3-dimensional wormholes that could plausibly
form naturally during Big Bang inflation. A wormhole mouth embedded in high
mass density might accrete mass, giving the other mouth a net *negative* mass
of unusual gravitational properties. The lensing of such a gravitationally
negative anomalous compact halo object (GNACHO) will enhance background stars
with a time profile that is observable and qualitatively different from that
recently observed for massive compact halo objects (MACHOs) of positive mass.
We recommend that MACHO search data be analyzed for GNACHOs.Comment: 4 pages; plus 4 figures; ReV_TeX 3.0; DOE/ER/40537-001/NPL94-07-01
Removing non-stationary, non-harmonic external interference from gravitational wave interferometer data
We describe a procedure to identify and remove a class of non-stationary and
non-harmonic interference lines from gravitational wave interferometer data.
These lines appear to be associated with the external electricity main
supply, but their amplitudes are non-stationary and they do not appear at
harmonics of the fundamental supply frequency. We find an empirical model able
to represent coherently all the non-harmonic lines we have found in the power
spectrum, in terms of an assumed reference signal of the primary supply input
signal. If this signal is not available then it can be reconstructed from the
same data by making use of the coherent line removal algorithm that we have
described elsewhere. All these lines are broadened by frequency changes of the
supply signal, and they corrupt significant frequency ranges of the power
spectrum. The physical process that generates this interference is so far
unknown, but it is highly non-linear and non-stationary. Using our model, we
cancel the interference in the time domain by an adaptive procedure that should
work regardless of the source of the primary interference. We have applied the
method to laser interferometer data from the Glasgow prototype detector, where
all the features we describe in this paper were observed. The algorithm has
been tuned in such a way that the entire series of wide lines corresponding to
the electrical interference are removed, leaving the spectrum clean enough to
detect signals previously masked by them. Single-line signals buried in the
interference can be recovered with at least 75 % of their original signal
amplitude.Comment: 14 pages, 5 figures, Revtex, psfi
Survey of highly non-Keplerian orbits with low-thrust propulsion
Celestial mechanics has traditionally been concerned with orbital motion under the action of a conservative gravitational potential. In particular, the inverse square gravitational force due to the potential of a uniform, spherical mass leads to a family of conic section orbits, as determined by Isaac Newton, who showed that Keplerâs laws were derivable from his theory of gravitation. While orbital motion under the action of a conservative gravitational potential leads to an array of problems with often complex and interesting solutions, the addition of non-conservative forces offers new avenues of investigation. In particular, non-conservative forces lead to a rich diversity of problems associated with the existence, stability and control of families of highly non-Keplerian orbits generated by a gravitational potential and a non-conservative force. Highly non-Keplerian orbits can potentially have a broad range of practical applications across a number of different disciplines. This review aims to summarize the combined wealth of literature concerned with the dynamics, stability and control of highly non-Keplerian orbits for various low thrust propulsion devices, and to demonstrate some of these potential applications
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