4,186 research outputs found
Self-aligned fabrication process for silicon quantum computer devices
We describe a fabrication process for devices with few quantum bits (qubits),
which are suitable for proof-of-principle demonstrations of silicon-based
quantum computation. The devices follow the Kane proposal to use the nuclear
spins of 31P donors in 28Si as qubits, controlled by metal surface gates and
measured using single electron transistors (SETs). The accurate registration of
31P donors to control gates and read-out SETs is achieved through the use of a
self-aligned process which incorporates electron beam patterning, ion
implantation and triple-angle shadow-mask metal evaporation
The variable phase method used to calculate and correct scattering lengths
It is shown that the scattering length can be obtained by solving a Riccati
equation derived from variable phase theory. Two methods of solving it are
presented. The equation is used to predict how long-range interactions
influence the scattering length, and upper and lower bounds on the scattering
length are determined. The predictions are compared with others and it is shown
how they may be obtained from secular perturbation theory.Comment: 7 pages including 3 figure
A new liver perfusion and preservation system for transplantation Research in large animals
A kidney perfusion machine, model MOX-100 (Waters Instruments, Ltd, Rochester, MN) was modified to allow continuous perfusion of the portal vein and pulsatile perfusion of the hepatic artery of the liver. Additional apparatus consists of a cooling system, a membrane oxygenator, a filter for foreign bodies, and bubble traps. This system not only allows hypothermic perfusion preservation of the liver graft, but furthermore enables investigation of ex vivo simulation of various circulatory circumstances in which physiological perfusion of the liver is studied. We have used this system to evaluate the viability of liver allografts preserved by cold storage. The liver was placed on the perfusion system and perfused with blood with a hematocrit of approximately 20% and maintained at 37°C for 3 h. The flows of the hepatic artery and portal vein were adjusted to 0.33 mL and 0.67 mL/g of liver tissue, respectively. Parameters of viability consisted of hourly bile output, oxygen consumption, liver enzymes, electrolytes, vascular resistance, and liver histology. This method of liver assessment in large animals will allow the objective evaluation of organ viability for transplantation and thereby improve the outcome of organ transplantation. Furthermore, this pump enables investigation into the pathophysiology of liver ischemia and preservation. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Perturbation expansions for a class of singular potentials
Harrell's modified perturbation theory [Ann. Phys. 105, 379-406 (1977)] is
applied and extended to obtain non-power perturbation expansions for a class of
singular Hamiltonians H = -D^2 + x^2 + A/x^2 + lambda/x^alpha, (A\geq 0, alpha
> 2), known as generalized spiked harmonic oscillators. The perturbation
expansions developed here are valid for small values of the coupling lambda >
0, and they extend the results which Harrell obtained for the spiked harmonic
oscillator A = 0. Formulas for the the excited-states are also developed.Comment: 23 page
Preparation of anti-vicinal amino alcohols: asymmetric synthesis of D-erythro-Sphinganine, (+)-spisulosine and D-ribo-phytosphingosine
Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM-ether directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor D-erythro-sphinganine and the antitumor agent (+)-spisulosine, while the Overman rearrangement of chiral allylic trichloroacetimidates generated by asymmetric reduction of an alpha,beta-unsaturated methyl ketone allowed rapid access to both D-ribo-phytosphingosine and L-arabino-phytosphingosine
Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
We have observed the cold collision frequency shift of the 1S-2S transition
in trapped spin-polarized atomic hydrogen. We find , where is the sample density. From this
we derive the 1S-2S s-wave triplet scattering length, nm,
which is in fair agreement with a recent calculation. The shift provides a
valuable probe of the distribution of densities in a trapped sample.Comment: Accepted for publication in PRL, 9 pages, 4 PostScript figures,
ReVTeX. Updated connection of our measurement to theoretical wor
1S-2S Spectrum of a Hydrogen Bose-Einstein Condensate
We calculate the two-photon 1S-2S spectrum of an atomic hydrogen
Bose-Einstein condensate in the regime where the cold collision frequency shift
dominates the lineshape. WKB and static phase approximations are made to find
the intensities for transitions from the condensate to motional eigenstates for
2S atoms. The excited state wave functions are found using a mean field
potential which includes the effects of collisions with condensate atoms.
Results agree well with experimental data. This formalism can be used to find
condensate spectra for a wide range of excitation schemes.Comment: 13 pages, 4 figure
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