14,631 research outputs found
Review and status of heat-transfer technology for internal passages of air-cooled turbine blades
Selected literature on heat-transfer and pressure losses for airflow through passages for several cooling methods generally applicable to gas turbine blades is reviewed. Some useful correlating equations are highlighted. The status of turbine-blade internal air-cooling technology for both nonrotating and rotating blades is discussed and the areas where further research is needed are indicated. The cooling methods considered include convection cooling in passages, impingement cooling at the leading edge and at the midchord, and convection cooling in passages, augmented by pin fins and the use of roughened internal walls
Scattering of slow-light gap solitons with charges in a two-level medium
The Maxwell-Bloch system describes a quantum two-level medium interacting
with a classical electromagnetic field by mediation of the the population
density. This population density variation is a purely quantum effect which is
actually at the very origin of nonlinearity. The resulting nonlinear coupling
possesses particularly interesting consequences at the resonance (when the
frequency of the excitation is close to the transition frequency of the
two-level medium) as e.g. slow-light gap solitons that result from the
nonlinear instability of the evanescent wave at the boundary. As nonlinearity
couples the different polarizations of the electromagnetic field, the
slow-light gap soliton is shown to experience effective scattering whith
charges in the medium, allowing it for instance to be trapped or reflected.
This scattering process is understood qualitatively as being governed by a
nonlinear Schroedinger model in an external potential related to the charges
(the electrostatic permanent background component of the field).Comment: RevTex, 14 pages with 5 figures, to appear in J. Phys. A: Math. Theo
Macroscopic evidence for quantum criticality and field-induced quantum fluctuations in cuprate superconductors
We present macroscopic experimental evidence for field-induced microscopic
quantum fluctuations in different hole- and electron-type cuprate
superconductors with varying doping levels and numbers of CuO layers per
unit cell. The significant suppression of the zero-temperature in-plane
magnetic irreversibility field relative to the paramagnetic field in all
cuprate superconductors suggests strong quantum fluctuations due to the
proximity of the cuprates to quantum criticality.Comment: 3 figures. To appear in Phys. Rev. B, Rapid Communications (2007).
For correspondence, contact: Nai-Chang Yeh (e-mail: [email protected]
First- and Second-Order Phase Transitions, Fulde-Ferrel Inhomogeneous State and Quantum Criticality in Ferromagnet/Superconductor Double Tunnel Junctions
First- and second-order phase transitions, Fulde-Ferrel (FF) inhomogeneous
superconducting (SC) state and quantum criticality in
ferromagnet/superconductor/ferromagnet double tunnel junctions are
investigated. For the antiparallel alignment of magnetizations, it is shown
that a first-order phase transition from the homogeneous BCS state to the
inhomogeneous FF state occurs at a certain bias voltage ; while the
transitions from the BCS state and the FF state to the normal state at are of the second-order. A phase diagram for the central superconductor
is presented. In addition, a quantum critical point (QCP), , is
identified. It is uncovered that near the QCP, the SC gap, the chemical
potential shift induced by the spin accumulation, and the difference of free
energies between the SC and normal states vanish as with
the quantum critical exponents , 1 and 2, respectively. The tunnel
conductance and magnetoresistance are also discussed.Comment: 5 pages, 4 figures, Phys. Rev. B 71, 144514 (2005
Structure formation in binary colloids
A theoretical study of the structure formation observed very recently [Phys.
Rev. Lett. 90, 128303 (2003)] in binary colloids is presented. In our model
solely the dipole-dipole interaction of the particles is considered,
electrohidrodynamic effects are excluded. Based on molecular dynamics
simulations and analytic calculations we show that the total concentration of
the particles, the relative concentration and the relative dipole moment of the
components determine the structure of the colloid. At low concentrations the
kinetic aggregation of particles results in fractal structures which show a
crossover behavior when increasing the concentration. At high concentration
various lattice structures are obtained in a good agreement with experiments.Comment: revtex, 4 pages, figures available from authors due to size problem
Superconducting Gap and Pseudogap in Iron-Based Layered Superconductor La(OF)FeAs
We report high-resolution photoemission spectroscopy of newly-discovered
iron-based layered superconductor La(OF)FeAs (Tc = 24 K). We
found that the superconducting gap shows a marked deviation from the isotropic
s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial
p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We also found
a pseudogap of 15-20 meV above Tc, which is gradually filled-in with increasing
temperature and closes at temperature far above Tc similarly to copper-oxide
high-temperature superconductors.Comment: 4 pages, 3 figures, J. Phys. Soc. Jpn. Vol. 77, No. 6 (2008), in
pres
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