25,644 research outputs found
Prediction of destabilizing blade tip forces for shrouded and unshrouded turbines
The effect of a nonuniform flow field on the Alford force calculation is investigated. The ideas used here are based on those developed by Horlock and Greitzer. It is shown that the nonuniformity of the flow field does contribute to the Alford force calculation. An attempt is also made to include the effect of whirl speed. The values predicted by the model are compared with those obtained experimentally by Urlicks and Wohlrab. The possibility of using existing turbine tip loss correlations to predict beta is also exploited. The nonuniform flow field induced by the tip clearnance variation tends to increase the resultant destabilizing force over and above what would be predicted on the basis of the local variation of efficiency. On the one hand, the pressure force due to the nonuniform inlet and exit pressure also plays a part even for unshrouded blades, and this counteracts the flow field effects, so that the simple Alford prediction remains a reasonable approximation. Once the efficiency variation with clearance is known, the presented model gives a slightly overpredicted, but reasonably accurate destabilizing force. In the absence of efficiency vs. clearance data, an empirical tip loss coefficient can be used to give a reasonable prediction of destabilizing force. To a first approximation, the whirl does have a damping effect, but only of small magnitude, and thus it can be ignored for some purposes
Innovation Institution and Spatial Transfer of Energy Industry: The Case of Jiangsu Province, China
This study aims to explore the effect of innovation institution on spatial transfer of energy industry in Jiangsu, China. We focus on the disparity of innovation and energy industry, and analyze the spatial transfer difference in different types of energy industry, rather than view energy industry as a whole. The study demonstrates the spatial change of energy industry at regional level and maps the spatial pattern at city level. The study chooses intellectual property rights (IPRs) protection intensity, authorization patents and local research and development (R&D) investment as the proxy of innovation. Using official data and employing panel fixed-effect model at city-industry level, we conclude (a) innovation abilities significantly influence the spatial transfer of energy industry in Jiangsu. Especially, due to the different time, IPRs protection, patent counts, and R&D investment have different effects on different regions in Jiangsu; (b) 2010 is an important turning point for energy industry development in Jiangsu, and after 2010, the energy industry begins to shift to the middle and northern Jiangsu, whereas the spatial pattern of energy industry in coastal cities is basically unchanged; (c) there is a great difference between the regions in Jiangsu Province, and industrial upgrading has not been achieved in northern Jiangsu
Chromospheric Evaporation in an X1.0 Flare on 2014 March 29 Observed with IRIS and EIS
Chromospheric evaporation refers to dynamic mass motions in flare loops as a
result of rapid energy deposition in the chromosphere. These have been observed
as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines
corresponding to upward motions at a few tens to a few hundreds of km/s. Past
spectroscopic observations have also revealed a dominant stationary component,
in addition to the blueshifted component, in emission lines formed at high
temperatures (~10 MK). This is contradictory to evaporation models predicting
predominant blueshifts in hot lines. The recently launched Interface Region
Imaging Spectrograph (IRIS) provides high resolution imaging and spectroscopic
observations that focus on the chromosphere and transition region in the UV
passband. Using the new IRIS observations, combined with coordinated
observations from the EUV Imaging Spectrometer, we study the chromospheric
evaporation process from the upper chromosphere to corona during an X1.0 flare
on 2014 March 29. We find evident evaporation signatures, characterized by
Doppler shifts and line broadening, at two flare ribbons separating from each
other, suggesting that chromospheric evaporation takes place in successively
formed flaring loops throughout the flare. More importantly, we detect dominant
blueshifts in the high temperature Fe XXI line (~10 MK), in agreement with
theoretical predictions. We also find that, in this flare, gentle evaporation
occurs at some locations in the rise phase of the flare, while explosive
evaporation is detected at some other locations near the peak of the flare.
There is a conversion from gentle to explosive evaporation as the flare
evolves.Comment: ApJ in pres
Weakly coupled quantum spin singlets in BaCrO
Using single crystal inelastic neutron scattering with and without
application of an external magnetic field and powder neutron diffraction, we
have characterized magnetic interactions in BaCrO. Even without
field, we found that there exist three singlet-to-triplet excitation modes in
scattering plane. Our complete analysis shows that the three modes
are due to spatially anisotropic interdimer interactions that are induced by
local distortions of the tetrahedron of oxygens surrounding the Jahn-Teller
active Cr. The strong intradimer coupling of meV
and weak interdimer interactions ( meV) makes
BaCrO a good model system for weakly-coupled quantum spin
dimers
Scheme for remote implementation of partially unknown quantum operation of two qubits in cavity QED
By constructing the recovery operations of the protocol of remote
implementation of partially unknown quantum operation of two qubits [An Min
Wang: PRA, \textbf{74}, 032317(2006)], we present a scheme to implement it in
cavity QED. Long-lived Rydberg atoms are used as qubits, and the interaction
between the atoms and the field of cavity is a nonresonant one. Finally, we
analyze the experimental feasibility of this scheme.Comment: 7 pages, 2 figure
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