27,182 research outputs found
Propulsion technology challenges for turn-of-the-century commercial aircraft
This paper highlights the efforts being performed or sponsored by NASA, in cooperation with the U.S. civil aviation industry, to address the propulsion system technological challenges that must be met in order to ensure a viable future for the industry. Both the subsonic and supersonic aeropropulsion programs are considered. Subsonic transport propulsion program elements, including ultra-high-bypass-ratio turbofans with attendant noise reduction efforts, high-efficiency cores, and combustor emissions reductions are discussed in terms of goals, technical issues, and problem solutions. Similarly, the high-speed research propulsion efforts addressing a high-speed commercial transport are reviewed in terms of environmental barrier issues, such as oxides of nitrogen and noise reduction, and the related economic issues
A Comparative Study of the Decays in Standard Model and Supersymmetric Theories
Using improved theoretical calculations of the decay form factors in the
Light Cone-QCD sum rule approach, we investigate the decay rates, dilepton
invariant mass spectra and the forward-backward (FB) asymmetry in the decays () in the standard
model (SM) and a number of popular variants of the supersymmetric (SUSY)
models. Theoretical precision on the differential decay rates and FB-asymmetry
is estimated in these theories taking into account various parametric
uncertainties. We show that existing data on and the
experimental upper limit on the branching ratio provide interesting bounds on the coefficients of the underlying
effective theory. We argue that the FB-asymmetry in
constitutes a precision test of the SM and its measurement in forthcoming
experiments may reveal new physics. In particular, the presently allowed
large- solutions in SUGRA models, as well as more general
flavor-violating SUSY models, yield FB-asymmetries which are characteristically
different from the corresponding ones in the SM.Comment: 36 pages, 12 figures (require epsfig.sty), 8 Tables, LaTeX2e;
subsection 6.4 corrected, minor changes in numerical results, Figures 3 and 9
to 12 modified; submitted to Physical Review
Expected Inflation and The Sacrifice Ratio
Using inflation forecasts from the OECD Economic Outlook as proxy measures of inflation expectations, we examine the impact of inflation expectations on the sacrifice ratio for 20 OECD countries. The regression analysis considers four different empirical models of the determinants of the sacrifice ratio typically found in the existing literature. The impact of the level of inflation expectations is negative and significant, implying that a higher level of expected inflation is associated with lower sacrifice ratios. This result is consistent with the theoretical role of nominal wage and price rigidities in that reductions in wage and price stickiness diminish the tradeoffs between disinflations and output losses. Interaction effects indicate that higher levels of expected inflation allow policymakers to pursue âcold turkeyâ inflation reductions even more aggressively. The effect of the change in inflation expectations is negative and significant, implying that faster adjusting inflation expectations are associated with lower sacrifice ratios
Gearbox fault diagnosis under different operating conditions based on time synchronous average and ensemble empirical mode decomposition
In this paper, a new method is proposed by combining ensemble empirical mode decomposition (EEMD) with order tracking techniques to analyse the vibration signals from a two stage helical gearbox. The method improves EEMD results in that it overcomes the potential deficiencies and achieves better order spectrum representation for fault diagnosis. Based on the analysis, a diagnostic feature is designed based on the order spectra of extracted IFMs for detection and separation of gearbox faults. Experimental results show this feature is sensitive to different fault severities and robust to the influences from operating conditions and remote sensor locations
Acoustic based safety emergency vehicle detection for intelligent transport systems
A system has been investigated for the detection of incoming direction of an emergency vehicle. Acoustic detection methods based on a cross microphone array have been implemented. It is shown that source detection based on time delay estimation outperforms sound intensity techniques, although both techniques perform well for the application. The relaying of information to the driver as a warning signal has been investigated through the use of ambisonic technology and a 4 speaker array which is ubiquitous in most modern vehicles. Simulations show that accurate warning information may be relayed to the driver and afford correct action
Hybrid noiseless subsystems for quantum communication over optical fibers
We derive the general structure of noiseless subsystems for optical radiation
contained in a sequence of pulses undergoing collective depolarization in an
optical fiber. This result is used to identify optimal ways to implement
quantum communication over a collectively depolarizing channel, which in
general combine various degrees of freedom, such as polarization and phase,
into joint hybrid schemes for protecting quantum coherence.Comment: 5 pages, 1 figur
Isostaticity in two dimensional pile of rigid disks
We study the static structure of piles made of polydisperse disks in the
rigid limit with and without friction using molecular dynamic simulations for
various elasticities of the disks and pile preparation procedures. The
coordination numbers are calculated to examine the isostaticity of the pile
structure. For the frictionless pile, it is demonstrated that the coordination
number converges to 4 in the rigid limit, which implies that the structure of
rigid disk pile is isostatic. On the other hand, for the frictional case with
the infinite friction constant, the coordination number depends on the
preparation procedure of the pile, but we find that the structure becomes very
close to isostatic with the coordination number close to 3 in the rigid limit
when the pile is formed through the process that tends to make a pile of random
configuration.Comment: 3 pages, 3 figures, Submitted to J. Phys. Soc. Jp
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