65,300 research outputs found
Balanced Topological Field Theories
We describe a class of topological field theories called ``balanced
topological field theories.'' These theories are associated to moduli problems
with vanishing virtual dimension and calculate the Euler character of various
moduli spaces. We show that these theories are closely related to the geometry
and equivariant cohomology of ``iterated superspaces'' that carry two
differentials. We find the most general action for these theories, which turns
out to define Morse theory on field space. We illustrate the constructions with
numerous examples. Finally, we relate these theories to topological
sigma-models twisted using an isometry of the target space.Comment: 40 pages, harvmac, references added, to appear in Commun. Math. Phy
The partition function of 2d string theory
We derive a compact and explicit expression for the generating functional of
all correlation functions of tachyon operators in 2D string theory. This
expression makes manifest relations of the system to KP flow and
constraints. Moreover we derive a Kontsevich-Penner integral
representation of this generating functional.Comment: 28 pages, 3 figures not included, harvmac. Preprint IASSNS-HEP-92/48,
YCTP-P22-9
Interconnect fatigue design for terrestrial photovoltaic modules
The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field
Performance of 1.15-pressure-ratio fan stage at several rotor blade setting angles with reverse flow
A 51 cm diameter low pressure ratio fan stage was tested in reverse flow. Survey flow data were taken over the range of rotative speed from 50 percent to 100 percent design speed at several rotor blade setting angles through both flat and feather pitch. Normal flow design values of pressure ratio and weight flow were 1.15 and 29.9 kg/sec with a rotor tip speed of 243.8 m/sec. The maximum thrust in reverse flow was 52.5 percent of design thrust in normal flow
Aerodynamic Performance of Two Variable-Pitch Fan Stages
The NASA-Lewis Research Center is investigating a variety of fan stages applicable for short haul aircraft. These low-pressure-ratio low-speed fan stages may require variable-pitch rotor blades to provide optimum performance for the varied flight demands and for thrust reversal on landing. A number of the aerodynamic and structural compromises relating to the variable-pitch rotor blades are discussed. The aerodynamic performance of two variable-pitch fan stages operated at several rotor blade setting angles for both forward and reverse flow application are presented. Detailed radial surveys are presented for both forward and reverse flow
Helium Leak Measurements Using CO2 as a Carrier
Detection delay defects are omitted by using helium mass spectrometer leak detector combined with several known procedures. Technique combines carbon dioxide purging, cryogenic separating helium accumulation, and use of carbon dioxide as carrier gas
The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate
We show that many features of the recent experiments of Schneble et al. [D.
Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle,
Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of
light scattering by a Bose-Einstein condensate, can be described using a
one-dimensional mean-field quantum CARL model, where optical amplification
occurs simultaneously with the production of a periodic density modulation in
the atomic medium. The two regimes of light scattering observed in these
experiments, originally described as ``Kapiza-Dirac scattering'' and
``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical
and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics
Elliptic Genera of Symmetric Products and Second Quantized Strings
In this note we prove an identity that equates the elliptic genus partition
function of a supersymmetric sigma model on the N-fold symmetric product
of a manifold M to the partition function of a second quantized
string theory on the space . The generating function of these
elliptic genera is shown to be (almost) an automorphic form for O(3,2,Z). In
the context of D-brane dynamics, this result gives a precise computation of the
free energy of a gas of D-strings inside a higher-dimensional brane.Comment: 17 pages, latex, 1 figure, to appear in Commun. Math. Phy
Aerodynamic performance of 0.4066-scale model to JT8D refan stage
The aerodynamic performance of a scale model of the split flow JT8D rafan stage is presented over a range of flows at speeds from 40 to 100 percent design. The bypass stage peak efficiency of 0.800 occurred at a total weight flow of 35.82 kilograms per second and a pressure ratio of 1.697. The stall margin was 15 percent based on pressure ratio and weight flow at stall and peak efficiency conditions. The data indicated that the hub region of the core stators was choked at design speed over the entire flow range tested
Performance of low-pressure-ratio fan stage at two off-design blade setting angles
The overall and blade-element performance of a low pressure ratio, low tip speed fan stage at design speed is presented for tow off-design rotor blade angle settings. The rotor design tip speed is 243.8 m/sec and weight flow per unit annulus area is 175.8 kg/sec. Design weight flow and pressure ratio are 29.9 kg/sec and 1.151, respectively
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