3,399 research outputs found
Single-stage experimental evaluation of tandem-airfoil rotor and stator blading for compressors. Part 1: Analysis and design of stages A, B, and C
A conventional rotor and stator, two dual-airfoil tandem rotors, and one dual-airfoil tandem stator were designed. The two tandem rotors were each designed with different percentages of the overall lift produced by the front airfoil. Velocity diagrams and blade leading and trailing edge metal angles selected for the conventional rotor and stator blading were used in the design of the tandem blading. Rotor inlet hub/tip ratio was 0.8. Design values of rotor tip velocity and stage pressure ratio were 757 ft/sec and 1.30, respectively
Shuttle Ku-band and S-band communications implementation study
Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed
Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCoF and NaSrCoF with magnetic pair distribution function analysis
We present time-of-flight neutron total scattering and polarized neutron
scattering measurements of the magnetically frustrated compounds
NaCaCoF and NaSrCoF, which belong to a class of recently
discovered pyrochlore compounds based on transition metals and fluorine. The
magnetic pair distribution function (mPDF) technique is used to analyze and
model the total scattering data in real space. We find that a
previously-proposed model of short-range XY-like correlations with a length
scale of 10-15 \AA, combined with nearest-neighbor collinear antiferromagnetic
correlations, accurately describes the mPDF data at low temperature, confirming
the magnetic ground state in these materials. This model is further verified by
the polarized neutron scattering data. From an analysis of the temperature
dependence of the mPDF and polarized neutron scattering data, we find that
short-range correlations persist on the nearest-neighbor length scale up to 200
K, approximately two orders of magnitude higher than the spin freezing
temperatures of these compounds. These results highlight the opportunity
presented by these new pyrochlore compounds to study the effects of geometric
frustration at relatively high temperatures, while also advancing the mPDF
technique and providing a novel opportunity to investigate a genuinely
short-range-ordered magnetic ground state directly in real space
Effective interactions and large-scale diagonalization for quantum dots
The widely used large-scale diagonalization method using harmonic oscillator
basis functions (an instance of the Rayleigh-Ritz method, also called a
spectral method, configuration-interaction method, or ``exact diagonalization''
method) is systematically analyzed using results for the convergence of Hermite
function series. We apply this theory to a Hamiltonian for a one-dimensional
model of a quantum dot. The method is shown to converge slowly, and the
non-smooth character of the interaction potential is identified as the main
problem with the chosen basis, while on the other hand its important advantages
are pointed out. An effective interaction obtained by a similarity
transformation is proposed for improving the convergence of the diagonalization
scheme, and numerical experiments are performed to demonstrate the improvement.
Generalizations to more particles and dimensions are discussed.Comment: 7 figures, submitted to Physical Review B Single reference error
fixe
Space Shuttle program communication and tracking systems interface analysis
The Space Shuttle Program Communications and Tracking Systems Interface Analysis began April 18, 1983. During this time, the shuttle communication and tracking systems began flight testing. Two areas of analysis documented were a result of observations made during flight tests. These analyses involved the Ku-band communication system. First, there was a detailed analysis of the interface between the solar max data format and the Ku-band communication system including the TDRSS ground station. The second analysis involving the Ku-band communication system was an analysis of the frequency lock loop of the Gunn oscillator used to generate the transmit frequency. The stability of the frequency lock loop was investigated and changes to the design were reviewed to alleviate the potential loss of data due the loop losing lock and entering the reacquisition mode. Other areas of investigation were the S-band antenna analysis and RF coverage analysis
A Unified Quantum NOT Gate
We study the feasibility of implementing a quantum NOT gate (approximate)
when the quantum state lies between two latitudes on the Bloch's sphere and
present an analytical formula for the optimized 1-to- quantum NOT gate. Our
result generalizes previous results concerning quantum NOT gate for a quantum
state distributed uniformly on the whole Bloch sphere as well as the phase
covariant quantum state. We have also shown that such 1-to- optimized NOT
gate can be implemented using a sequential generation scheme via matrix product
states (MPS)
Gyroscopic motion of superfluid trapped atomic condensates
The gyroscopic motion of a trapped Bose gas containing a vortex is studied.
We model the system as a classical top, as a superposition of coherent
hydrodynamic states, by solution of the Bogoliubov equations, and by
integration of the time-dependent Gross-Pitaevskii equation. The frequency
spectrum of Bogoliubov excitations, including quantum frequency shifts, is
calculated and the quantal precession frequency is found to be consistent with
experimental results, though a small discrepancy exists. The superfluid
precession is found to be well described by the classical and hydrodynamic
models. However the frequency shifts and helical oscillations associated with
vortex bending and twisting require a quantal treatment. In gyroscopic
precession, the vortex excitation modes are the dominant features
giving a vortex kink or bend, while the is found to be the dominant
Kelvin wave associated with vortex twisting.Comment: 18 pages, 7 figures, 1 tabl
Engineering evaluations and studies. Volume 2: Exhibit B, part 1
Ku-band communication system analysis, S-band system investigations, payload communication investigations, shuttle/TDRSS and GSTDN compatibility analysis are discussed
Engineering evaluations and studies. Volume 3: Exhibit C
High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed
- …