28,601 research outputs found
Analysis of geometry and design point performance of axial flow turbines. 1 - Development of the analysis method and the loss coefficient correlation
Stream-filament analysis procedure and correlation of total pressure loss coefficients to form basis of computer program to investigate design point performance of axial turbine
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program
The activities are reported of the NASA Biomedical Applications Team at Southwest Research Institute between 25 August, 1972 and 15 November, 1973. The program background and methodology are discussed along with the technology applications, and biomedical community impacts
Separability of Black Holes in String Theory
We analyze the origin of separability for rotating black holes in string
theory, considering both massless and massive geodesic equations as well as the
corresponding wave equations. We construct a conformal Killing-Stackel tensor
for a general class of black holes with four independent charges, then identify
two-charge configurations where enhancement to an exact Killing-Stackel tensor
is possible. We show that further enhancement to a conserved Killing-Yano
tensor is possible only for the special case of Kerr-Newman black holes. We
construct natural null congruences for all these black holes and use the
results to show that only the Kerr-Newman black holes are algebraically special
in the sense of Petrov. Modifying the asymptotic behavior by the subtraction
procedure that induces an exact SL(2)^2 also preserves only the conformal
Killing-Stackel tensor. Similarly, we find that a rotating Kaluza-Klein black
hole possesses a conformal Killing-Stackel tensor but has no further
enhancements.Comment: 27 page
A Puzzling Merger in A3266: the Hydrodynamic Picture from XMM-Newton
Using the mosaic of nine XMM-Newton observations, we study the hydrodynamic
state of the merging cluster of galaxies Abell 3266. The high quality of the
spectroscopic data and large field of view of XMM-Netwon allow us to determine
the thermodynamic conditions of the intracluster medium on scales of order of
50 kpc. A high quality entropy map reveals the presence of an extended region
of low entropy gas, running from the primary cluster core toward the northeast
along the nominal merger axis. The mass of the low entropy gas amounts to
approximately 2e13 solar masses, which is comparable to the baryonic mass of
the core of a rich cluster. We test the possibility that the origin of the
observed low entropy gas is either related to the disruption a preexisting
cooling core in Abell 3266 or to the stripping of gas from an infalling
subcluster companion. We find that both the radial pressure and entropy
profiles as well as the iron abundance of Abell 3266 do not resemble those in
other known cooling core clusters (Abell 478). Thus we conclude that the low
entropy region is subcluster gas in the process of being stripped off from its
dark matter halo. In this scenario the subcluster would be falling onto the
core of A3266 from the foreground. This would also help interpret the observed
high velocity dispersion of the galaxies in the cluster center, provided that
the mass of the subcluster is at most a tenth of the mass of the main cluster.Comment: 6 pages, ApJ sub
Fractal universe and quantum gravity
We propose a field theory which lives in fractal spacetime and is argued to
be Lorentz invariant, power-counting renormalizable, ultraviolet finite, and
causal. The system flows from an ultraviolet fixed point, where spacetime has
Hausdorff dimension 2, to an infrared limit coinciding with a standard
four-dimensional field theory. Classically, the fractal world where fields live
exchanges energy momentum with the bulk with integer topological dimension.
However, the total energy momentum is conserved. We consider the dynamics and
the propagator of a scalar field. Implications for quantum gravity, cosmology,
and the cosmological constant are discussed.Comment: 4 pages. v2: typos corrected; v3: discussion improved, intuitive
introduction added, matches the published versio
Charged black holes in Vaidya backgrounds: Hawking's Radiation
In this paper we propose a class of embedded solutions of Einstein's field
equations describing non-rotating Reissner-Nordstrom-Vaidya and rotating
Kerr-Newman-Vaidya black holes.Comment: 30 pages, latex file, no figure
Surface differential rotation and prominences of the Lupus post T Tauri star RX J1508.6-4423
We present in this paper a spectroscopic monitoring of the Lupus post T Tauri star RX J1508.6-4423 carried out at two closely separated epochs (1998 May 06 and 10) with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Applying least-squares convolution and maximum entropy image reconstruction techniques to our sets of spectra, we demonstrate that this star features on its surface a large cool polar cap with several appendages extending to lower latitudes, as well as one spot close to the equator. The images reconstructed at both epochs are in good overall agreement, except for a photospheric shear that we interpret in terms of latitudinal differential rotation. Given the spot distribution at the epoch of our observations, differential rotation could only be investigated between latitudes 15° and 60°. We find in particular that the observed differential rotation is compatible with a solar-like law (i.e., with rotation rate decreasing towards high latitudes proportionally to sin 2l, where l denotes the latitude) in this particular latitude range. Assuming that such a law can be extrapolated to all latitudes, we find that the equator of RX J1508.6-4423 does one more rotational cycle than the pole every 50 ±10 d, implying a photospheric shear 2 to 3 times stronger than that of the Sun. We also discover that the Hα emission profile of RX J1508.6-4423 is most of the time double-peaked and strongly modulated with the rotation period of the star. We interpret this rotationally modulated emission as being caused by a dense and complex prominence system, the circumstellar distribution of which is obtained through maximum entropy Doppler tomography. These maps show in particular that prominences form a complete and inhomogeneous ring around the star, precisely at the corotation radius. We use the total Hα and Hβ emission flux to estimate that the mass of the whole prominence system is about 10 20g. From our observation that the whole cloud system surrounding the star is regenerated in less than 4 d, we conclude that the braking time-scale of RX J1508.6-4423 is shorter than 1 Gyr, and that prominence expulsion is thus likely to contribute significantly to the rotational spindown of young low-mass stars
Path-programmable logic
Journal ArticlePath-Programmable Logic (PPL) is a structured IC design methodology under development at the University of Utah. PPL employs a sea-of-wires approach to design. In PPL, design is done entirely using cells for both functionality and interconnect. PPL cells may have modifiers that change either their connections or functionality. Wires in the PPL design plane are segmentable at any cell boundary. PPL is implemented as a set of cell libraries (NMOS, CMOS, and GaAs) and a suite of tools that permit the designer to create, modify, simulate and check PPL circuit designs and to generate mask data for them. PPL exhibits little or no area penalty with respect to full custom densities while permitting system design to be done more rapidly than with gate arrays or standard cells. PPL may be implemented as a sea-of-gates gate array to provide fast turnaround
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