42,456 research outputs found
Detecting flat normal cones using Segre classes
Given a flat, projective morphism from an equidimensional scheme to
a nonsingular curve and a subscheme of , we give conditions under which
specialization of the Segre class of the normal cone of in
implies flatness of the normal cone. We apply this result to study when the
relative tangent star cone of a flat family is flat.Comment: LaTeX, 11 pages, no figure
Tangential Quantum Cohomology of Arbitrary Order
J. Kock has previously defined a tangency quantum product on formal power
series with coefficients in the cohomology ring of any smooth projective
variety, and thus a ring that generalizes the quantum cohomology ring. We
further generalize Kock's construction by defining a dth-order contact product
and establishing its associativity.Comment: 18 pages, LaTeX. We correct our paper to work in the correct context,
viz., using numerical equivalence (rather than rational equivalence) and
explicitly mentioning the Novikov rin
Planet formation around stars of various masses: Hot super-Earths
We consider trends resulting from two formation mechanisms for short-period
super-Earths: planet-planet scattering and migration. We model scenarios where
these planets originate near the snow line in ``cold finger'' circumstellar
disks. Low-mass planet-planet scattering excites planets to low periastron
orbits only for lower mass stars. With long circularisation times, these
planets reside on long-period eccentric orbits. Closer formation regions mean
planets that reach short-period orbits by migration are most common around
low-mass stars. Above ~1 Solar mass, planets massive enough to migrate to
close-in orbits before the gas disk dissipates are above the critical mass for
gas giant formation. Thus, there is an upper stellar mass limit for
short-period super-Earths that form by migration. If disk masses are
distributed as a power law, planet frequency increases with metallicity because
most disks have low masses. For disk masses distributed around a relatively
high mass, planet frequency decreases with increasing metallicity. As icy
planets migrate, they shepherd interior objects toward the star, which grow to
~1 Earth mass. In contrast to icy migrators, surviving shepherded planets are
rocky. Upon reaching short-period orbits, planets are subject to evaporation
processes. The closest planets may be reduced to rocky or icy cores. Low-mass
stars have lower EUV luminosities, so the level of evaporation decreases with
decreasing stellar mass.Comment: Accepted to ApJ. 13 pages of emulateap
Study of 42 and 85 GHz coupled cavity traveling-wave tubes for space use
Designs were formulated for four CW, millimeter wavelength traveling-wave tubes having high efficiency and long life. Three of these tubes, in the 42 to 44 GHz frequency region, develop power outputs of 100 to 300 watts with overall efficiencies of typically 45 percent. Another tube, which covers the frequency range of 84 to 86 GHz, provides a power output of 200 watts at 25 percent efficiency. The cathode current density in each design was 1A/sq cm. Each tube includes: metal-ceramic construction, periodic permanent magnet focusing, a two step velocity taper, an electron beam refocusing section, and a radiation cooled three-stage depressed collector. The electrical and mechanical design for each tube type is discussed in detail. The results of thermal and mechanical analyses are presented
Heat kernels on curved cones
A functorial derivation is presented of a heat-kernel expansion coefficient
on a manifold with a singular fixed point set of codimension two. The existence
of an extrinsic curvature term is pointed out.Comment: 4p.,sign errors corrected and a small addition,uses JyTeX,MUTP/94/0
ICT as learning media and research instrument: What eResearch can offer for those who research eLearning?
Students‘ interactions in digital learning environments are distributed over time and space, and many aspects of eLearning phenomenon cannot be investigated using traditional research approaches. At the same time, the possibility to collect digital data about students‘ online interactions and learning opens a range of new opportunities to use ICT as research tool and apply new research approaches. This symposium brings together some of the recent advancements in the area of ICT-enhanced research and aims to discuss future directions for methodological innovation in this area. The session will include four presentations that will explore different directions of ICT use for eLearning research
Effect of thermal exposure, forming, and welding on high-temperature, dispersion-strengthened aluminum alloy: Al-8Fe-1V-2Si
The feasibility of applying conventional hot forming and welding methods to high temperature aluminum alloy, Al-8Fe-1V-2Si (FVS812), for structural applications and the effect of thermal exposure on mechanical properties were determined. FVS812 (AA8009) sheet exhibited good hot forming and resistance welding characteristics. It was brake formed to 90 deg bends (0.5T bend radius) at temperatures greater than or equal to 390 C (730 F), indicating the feasibility of fabricating basic shapes, such as angles and zees. Hot forming of simple contoured-flanged parts was demonstrated. Resistance spot welds with good static and fatigue strength at room and elevated temperatures were readily produced. Extended vacuum degassing during billet fabrication reduced porosity in fusion and resistance welds. However, electron beam welding was not possible because of extreme degassing during welding, and gas-tungsten-arc welds were not acceptable because of severely degraded mechanical properties. The FVS812 alloy exhibited excellent high temperature strength stability after thermal exposures up to 315 C (600 F) for 1000 h. Extended billet degassing appeared to generally improve tensile ductility, fatigue strength, and notch toughness. But the effects of billet degassing and thermal exposure on properties need to be further clarified. The manufacture of zee-stiffened, riveted, and resistance-spot-welded compression panels was demonstrated
Remarks on geometric entropy
The recently discussed notion of geometric entropy is shown to be related to
earlier calculations of thermal effects in Rindler space. The evaluation is
extended to de Sitter space and to a two-dimensional black hole.Comment: 7p.,uses jyTeX,MUTP/94/
System configuration and executive requirements specifications for reusable shuttle and space station/base
System configuration and executive requirements specifications for reusable shuttle and space station/bas
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