14,982 research outputs found
An analysis of bi-directional use of frequencies for satellite communications
The bi-directional use of frequencies allocated for space communications has the potential to double the orbit/spectrum capacity available. The technical feasibility of reverse band use (RBU) at C-band (4 GHz uplinks and 6 GHz downlinks) is studied. The analysis identifies the constraints under which both forward and reverse band use satellite systems can share the same frequencies with terrestrial, line of sight transmission systems. The results of the analysis show that RBU satellite systems can be similarly sized to forward band use (FBU) satellite systems. In addition, the orbital separation requirements between RBU and FBU satellite systems are examined. The analysis shows that a carrier to interference ratio of 45 dB can be maintianed between RBU and FBU satellites separated by less than 0.5 deg., and that a carrier to interference ratio of 42 dB can be maintained in the antipodal case. Rain scatter propagation analysis shows that RBU and FBU Earth stations require separation distances fo less than 10 km at a rain rate of 13.5 mm/hr escalating to less than 100 km at a rain rate of 178 mm/hr for Earth station antennas in the 3 to 10 m range
Frequency response calibration of recess-mounted pressure transducers
A technique is described for measuring the frequency response of pressure transducers mounted inside a model, where a narrow pipette leads to an orifice at the surface. An acoustic driver is mounted to a small chamber which has an opening at the opposite end with an O-ring seal to place over the orifice. A 3.18 mm (1/8 inch) reference microphone is mounted to one side of the chamber. The acoustic driver receives an input of white noise, and the transducer and reference microphone outputs are compared to obtain the frequency response of the pressure transducer. Selected results are presented in the form of power spectra for both the transducer and the reference, as well as the amplitude variation and phase shift between the two signals as a function of frequency. The effect of pipette length and the use of this technique for identifying both blocked orifices and faulty transducers are described
Applications of satellite data relay to problems of field seismology
A seismic signal processor was developed and tested for use with the NOAA-GOES satellite data collection system. Performance tests on recorded, as well as real time, short period signals indicate that the event recognition technique used is nearly perfect in its rejection of cultural signals and that data can be acquired in many swarm situations with the use of solid state buffer memories. Detailed circuit diagrams are provided. The design of a complete field data collection platform is discussed and the employment of data collection platforms in seismic network is reviewed
Structure and Functional Responsibilities of Graduate Schools: An Organizational Analysis
The contemporary graduate ‘school’ is facing a number of significant challenges. In addition to the fundamental question of its role as a shared service provider, graduate education units are exploring ways that they can demonstrate a value-added component to the graduate school experience. These activities include offering graduate certificates about how to be a faculty member, how to best teach and mentor graduate students, and offering undergraduate courses on how to get into graduate school. The current study explored 84 graduate ‘school’ or equivalent unit organizational charts, noting major differences between those with research administration attached to them and those without such responsibilities. Findings also included the identification of small administrative staffs and growing innovation to serve graduate student needs, such as providing mental health services and food pantries
Complete Set of Commuting Symmetry Operators for the Klein-Gordon Equation in Generalized Higher-Dimensional Kerr-NUT-(A)dS Spacetimes
We consider the Klein-Gordon equation in generalized higher-dimensional
Kerr-NUT-(A)dS spacetime without imposing any restrictions on the functional
parameters characterizing the metric. We establish commutativity of the
second-order operators constructed from the Killing tensors found in
arXiv:hep-th/0612029 and show that these operators, along with the first-order
operators originating from the Killing vectors, form a complete set of
commuting symmetry operators (i.e., integrals of motion) for the Klein-Gordon
equation. Moreover, we demonstrate that the separated solutions of the
Klein-Gordon equation obtained in arXiv:hep-th/0611245 are joint eigenfunctions
for all of these operators. We also present explicit form of the zero mode for
the Klein-Gordon equation with zero mass.
In the semiclassical approximation we find that the separated solutions of
the Hamilton-Jacobi equation for geodesic motion are also solutions for a set
of Hamilton-Jacobi-type equations which correspond to the quadratic conserved
quantities arising from the above Killing tensors.Comment: 6 pages, no figures; typos in eq.(6) fixed; one reference adde
Commuting symmetry operators of the Dirac equation, Killing-Yano and Schouten-Nijenhuis brackets
In this paper we derive the most general first-order symmetry operator
commuting with the Dirac operator in all dimensions and signatures. Such an
operator splits into Clifford even and Clifford odd parts which are given in
terms of odd Killing-Yano and even closed conformal Killing-Yano inhomogeneous
forms respectively. We study commutators of these symmetry operators and give
necessary and sufficient conditions under which they remain of the first-order.
In this specific setting we can introduce a Killing-Yano bracket, a bilinear
operation acting on odd Killing-Yano and even closed conformal Killing-Yano
forms, and demonstrate that it is closely related to the Schouten-Nijenhuis
bracket. An important non-trivial example of vanishing Killing-Yano brackets is
given by Dirac symmetry operators generated from the principal conformal
Killing-Yano tensor [hep-th/0612029]. We show that among these operators one
can find a complete subset of mutually commuting operators. These operators
underlie separability of the Dirac equation in Kerr-NUT-(A)dS spacetimes in all
dimensions [arXiv:0711.0078].Comment: 37 pages, no figure
Brayton-cycle radioisotope heat source design study. Phase I - /Conceptual design/ report
Conceptual designs for radioisotope heat source systems to provide 25 kW thermal power to Brayton cycle power conversion system for space application
Quasi-equilibria in one-dimensional self-gravitating many body systems
The microscopic dynamics of one-dimensional self-gravitating many-body
systems is studied. We examine two courses of the evolution which has the
isothermal and stationary water-bag distribution as initial conditions. We
investigate the evolution of the systems toward thermal equilibrium. It is
found that when the number of degrees of freedom of the system is increased,
the water-bag distribution becomes a quasi-equilibrium, and also the
stochasticity of the system reduces. This results suggest that the phase space
of the system is effectively not ergodic and the system with large degreees of
freedom approaches to the near-integrable one.Comment: 21pages + 7 figures (available upon request), revtex, submitted to
Physical Review
Influence of Bos Taurus and Bos Indicus Breedtype on Production of Cortisol
Last updated: 6/12/200
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