908 research outputs found
Keynote address: the networked bank
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Nonisomorphic curves that become isomorphic over extensions of coprime degrees
We show that one can find two nonisomorphic curves over a field K that become
isomorphic to one another over two finite extensions of K whose degrees over K
are coprime to one another.
More specifically, let K_0 be an arbitrary prime field and let r and s be
integers greater than 1 that are coprime to one another. We show that one can
find a finite extension K of K_0, a degree-r extension L of K, a degree-s
extension M of K, and two curves C and D over K such that C and D become
isomorphic to one another over L and over M, but not over any proper
subextensions of L/K or M/K.
We show that such C and D can never have genus 0, and that if K is finite, C
and D can have genus 1 if and only if {r,s} = {2,3} and K is an odd-degree
extension of F_3. On the other hand, when {r,s}={2,3} we show that genus-2
examples occur in every characteristic other than 3.
Our detailed analysis of the case {r,s} = {2,3} shows that over every finite
field K there exist nonisomorphic curves C and D that become isomorphic to one
another over the quadratic and cubic extensions of K.
Most of our proofs rely on Galois cohomology. Without using Galois
cohomology, we show that two nonisomorphic genus-0 curves over an arbitrary
field remain nonisomorphic over every odd-degree extension of the base field.Comment: LaTeX, 32 pages. Further references added to the discussion in
Section 1
Generalized guidance law for collision courses
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76649/1/AIAA-21039-131.pd
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Understanding and Controlling Metal-Support Interactions in Nanocrystalline Bimetallic Catalysts
The objectives of this research are to: 1) determine the catalytic behavior of model Pd and Rh catalysts on unpromoted and ceria-promoted supports, for the reduction of NO and N2O with CO, 2) determine the microstructures of the catalysts both before and after reaction in order to understand the catalytic behavior, and 3) understand the role of the metal/support interface in the catalytic process. The research examined the influence of Pd particle size and ceria loading on catalytic reaction for the NO+CO reaction. Dihydrogen chemisorption, temperature-programmed desorption (TPD) of NO, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the catalyst samples. It was found that when ceria is used to promote Pd particles, the activity for NO+CO was a maximum for 2-nm-sized Pd particles. The maximum in activity results from a balance between the Pd/ceria interface, which enhances NO dissociation, and the close-packed planes of the Pd particles that facilitate product formation and/or desorption. The variations in apparent reaction orders and results from TPD were consistent with the idea that NO dissociation is promoted on very small particles (1 nm) and by the addition of ceria. Characterization of the catalysts by HRTEM showed that the ceria was typically present in the form of small crystallites from 3-7 nm in diameter, deposited near Pd particles, rather than as a thin film on the alumina support. This occurred whether the ceria was deposited before or after the Pd particles
Smart-Cut Layer Transfer of Single-Crystal SiC Using Spin-on-Glass
The authors demonstrate “smart-cut”-type layer transfer of single-crystal silicon carbide (SiC) by using spin-on-glass (SoG) as an adhesion layer. Using SoG as an adhesion layer is desirable because it can planarize the surface, facilitate an initial low temperature bond, and withstand the thermal stresses at high temperature where layer splitting occurs (800–900 °C). With SoG, the bonding of wafers with a relatively large surface roughness of 7.5–12.5 Å rms can be achieved. This compares favorably to direct (fusion) wafer bonding, which usually requires extremely low roughness (\u3c2 Å rms), typically achieved using chemical mechanical polishing (CMP) after implantation. The higher roughness tolerance of the SoG layer transfer removes the need for the CMP step, making the process more reliable and affordable for expensive materials like SiC. To demonstrate the reliability of the smart-cut layer transfer using SoG, we successfully fabricated a number of suspended MEMS structures using this technology
Application of singular perturbation methods for three-dimensional minimum-time interception
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76166/1/AIAA-20647-787.pd
A new way to rapidly create functional, fluorescent fusion proteins: random insertion of GFP with an in vitro transposition reaction
BACKGROUND: The jellyfish green fluorescent protein (GFP) can be inserted into the middle of another protein to produce a functional, fluorescent fusion protein. Finding permissive sites for insertion, however, can be difficult. Here we describe a transposon-based approach for rapidly creating libraries of GFP fusion proteins. RESULTS: We tested our approach on the glutamate receptor subunit, GluR1, and the G protein subunit, α(s). All of the in-frame GFP insertions produced a fluorescent protein, consistent with the idea that GFP will fold and form a fluorophore when inserted into virtually any domain of another protein. Some of the proteins retained their signaling function, and the random nature of the transposition process revealed permissive sites for insertion that would not have been predicted on the basis of structural or functional models of how that protein works. CONCLUSION: This technique should greatly speed the discovery of functional fusion proteins, genetically encodable sensors, and optimized fluorescence resonance energy transfer pairs
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