22,083 research outputs found
Combustion instability prediction using a nonlinear bipropellant vaporization model
Combustion instability prediction using nonlinear bipropellant vaporization mode
On-board processing for future satellite communications systems: Satellite-Routed FDMA
A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented
The measurements of vehicle glow on the Space Shuttle
From the combined data set of glow observations on STS-3, STS-4 and STS-5 some of the properties of the shuttle glow were observed. Comparison of the STS-3 (240 km) and STS-5 (305 km) photographs show that the intensity of the glow is about a factor of 3.5 brighter on the low altitude (STS-3) flight. The orbiter was purposely rotated about the x axis in an experiment on STS-5 to observe the dependence of the intensity on the angle of incidence between the spacecraft surface normal and the velocity vector. For a relatively large angle between the velocity vector and the surface normal there is an appreciable glow, provided the surface is not shadowed by some other spacecraft structure. As the angle becomes less the glow intensifies. The grating experiments (STS-4 photography only, STS-5 image intensifier photography) provided a preliminary low resolution spectra of the spacecraft glow. Accurate wavelength calibrations of the STS-5 instrument permitted measuring of the spectrum and intensity of the Earth's airglow
Real-Time Operating System/360
RTOS has a cost savings advantage for real-time applications, such as those with random inputs requiring a flexible data routing facility, display systems simplified by a device independent interface language, and complex applications needing added storage protection and data queuing
Second year technical report on-board processing for future satellite communications systems
Advanced baseband and microwave switching techniques for large domestic communications satellites operating in the 30/20 GHz frequency bands are discussed. The nominal baseband processor throughput is one million packets per second (1.6 Gb/s) from one thousand T1 carrier rate customer premises terminals. A frequency reuse factor of sixteen is assumed by using 16 spot antenna beams with the same 100 MHz bandwidth per beam and a modulation with a one b/s per Hz bandwidth efficiency. Eight of the beams are fixed on major metropolitan areas and eight are scanning beams which periodically cover the remainder of the U.S. under dynamic control. User signals are regenerated (demodulated/remodulated) and message packages are reformatted on board. Frequency division multiple access and time division multiplex are employed on the uplinks and downlinks, respectively, for terminals within the coverage area and dwell interval of a scanning beam. Link establishment and packet routing protocols are defined. Also described is a detailed design of a separate 100 x 100 microwave switch capable of handling nonregenerated signals occupying the remaining 2.4 GHz bandwidth with 60 dB of isolation, at an estimated weight and power consumption of approximately 400 kg and 100 W, respectively
Using bacterial biomarkers to identify early indicators of cystic fibrosis pulmonary exacerbation onset
Acute periods of pulmonary exacerbation are the single most important cause of morbidity in cystic fibrosis patients, and may be associated with a loss of lung function. Intervening prior to the onset of a substantially increased inflammatory response may limit the associated damage to the airways. While a number of biomarker assays based on inflammatory markers have been developed, providing useful and important measures of disease during these periods, such factors are typically only elevated once the process of exacerbation has been initiated. Identifying biomarkers that can predict the onset of pulmonary exacerbation at an early stage would provide an opportunity to intervene before the establishment of a substantial immune response, with major implications for the advancement of cystic fibrosis care. The precise triggers of pulmonary exacerbation remain to be determined; however, the majority of models relate to the activity of microbes present in the patient's lower airways of cystic fibrosis. Advances in diagnostic microbiology now allow for the examination of these complex systems at a level likely to identify factors on which biomarker assays can be based. In this article, we discuss key considerations in the design and testing of assays that could predict pulmonary exacerbations
Ginzburg-Landau Like Theory for High Temperature Superconductivity in the Cuprates: Emergent d-wave Order
High temperature superconductivity in the cuprates remains one of the most
widely investigated, constantly surprising, and poorly understood phenomena in
physics. Here, we describe briefly a new phenomenological theory inspired by
the celebrated description of superconductivity due to Ginzburg and Landau and
believed to describe its essence. This posits a free energy functional for the
superconductor in terms of a complex order parameter characterizing it. We
propose, for superconducting cuprates, a similar functional of the complex, in
plane, nearest neighbor spin singlet bond (or Cooper) pair amplitude psi_ij. A
crucial part of it is a (short range) positive interaction between nearest
neighbor bond pairs, of strength J'. Such an interaction leads to nonzero long
wavelength phase stiffness or superconductive long range order, with the
observed d-wave symmetry, below a temperature T_c\simzJ' where z is the number
of nearest neighbours; it is thus an emergent, collective consequence. Using
the functional, we calculate a large range of properties, e.g. the pseudogap
transition temperature T* as a function of hole doping x, the transition curve
T_c(x), the superfluid stiffness rho_s(x,T), the specific heat (without and
with a magnetic field) due to the fluctuating pair degrees of freedom, and the
zero temperature vortex structure. We find remarkable agreement with
experiment. We also calculate the self energy of electrons hopping on the
square cuprate lattice and coupled to electrons of nearly opposite momenta via
inevitable long wavelength Cooper pair fluctuations formed of these electrons.
The ensuing results for electron spectral density are successfully compared
with recent ARPES experiments, and comprehensively explain strange features
such as temperature dependent Fermi arcs above T_c and the 'bending' of the
superconducting gap below T_c .Comment: 22 pages, 14 figures, to appear in Int J Mod Phys
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