5,344 research outputs found
Cationic Cyclization Involving a Remote Allene Function in the Trifluoroethanolysis of Hepta-5,6-dienyl Toluene-p-sulphonate
The remote allene function participates efficiently in the trifluoroethanolysis of hepta-5,6-dienyl toluene-p-sulphonate, leading to the cyclized 2-methylenecyclohexyl cation
A small-angle neutron scattering investigation of aggregation in polystyrene above the gel point
Aging in the Relaxor Ferroelectric PMN/PT
The relaxor ferroelectric
(PbMnNbO)(PbTiO), ,
(PMN/PT(90/10)) is found to exhibit several regimes of complicated aging
behavior. Just below the susceptibility peak there is a regime exhibiting
rejuvenation but little memory. At lower temperature, there is a regime with
mainly cumulative aging, expected for simple domain-growth. At still lower
temperature, there is a regime with both rejuvenation and memory, reminiscent
of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging
regimes. This qualitative aging behavior is reminiscent of that seen in
reentrant ferromagnets, which exhibit a crossover from a domain-growth
ferromagnetic regime into a reentrant spin glass regime at lower temperatures.
These striking parallels suggest a picture of competition in PMN/PT (90/10)
between ferroelectric correlations formed in the domain-growth regime with
glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also
found to exhibit frequency-aging time scaling of the time-dependent part of the
out-of-phase susceptibility for temperatures 260 K and below. The stability of
aging effects to thermal cycles and field perturbations is also reported.Comment: 8 pages RevTeX4, 11 figures; submitted to Phys. Rev.
Decoherence due to discrete noise in Josephson qubits
We study decoherence produced by a discrete environment on a charge Josephson
qubit by introducing a model of an environment of bistable fluctuators. In
particular we address the effect of noise where memory effects play an
important role. We perform a detailed investigation of various computation
procedures (single shot measurements, repeated measurements) and discuss the
problem of the information needed to characterize the effect of the
environment. Although in general information beyond the power spectrum is
needed, in many situations this results in the knowledge of only one more
microscopic parameter of the environment. This allows to determine which
degrees of freedom of the environment are effective sources of decoherence in
each different physical situation considered.Comment: 20 pages, 11 figure
The Increasing Rotation Period of Comet 10P/Tempel 2
We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March.
R-band lightcurves were obtained on 11 of these nights from 1999 April through
1999 June, prior to both the onset of significant coma activity and perihelion.
Phasing of the data yields a double-peaked lightcurve and indicates a nucleus
rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75
mag. Our data are sufficient to rule out all other possible double-peaked
solutions as well as the single- and triple- peaked solutions. This rotation
period agrees with one of five possible solutions found in post-perihelion data
from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously
eliminates their remaining four solutions. We applied our same techniques to
published lightcurves from 1988 which were obtained at an equivalent orbital
position and viewing geometry as in 1999. We found a rotation period of 8.932
+/- 0.001 hr in 1988, consistent with the findings of previous authors and
incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by
~32 s between 1988 and 1999 (two intervening perihelion passages). If the
spin-down is due to a systematic torque, then the rotation period prior to
perihelion during the 2010 apparition is expected to be an additional 32 s
longer than in 1999.Comment: Accepted by The Astronomical Journal; 22 pages of text, 3 tables, 6
figure
Pulsed extraction of ionization from helium buffer gas
The migration of intense ionization created in helium buffer gas under the
influence of applied electric fields is considered. First the chemical
evolution of the ionization created by fast heavy-ion beams is described.
Straight forward estimates of the lifetimes for charge exchange indicate a
clear suppression of charge exchange during ion migration in low pressure
helium. Then self-consistent calculations of the migration of the ions in the
electric field of a gas-filled cell at the National Superconducting Cyclotron
Laboratory (NSCL) using a Particle-In-Cell computer code are presented. The
results of the calculations are compared to measurements of the extracted ion
current caused by beam pulses injected into the NSCL gas cell.Comment: Accepted for pubilication in Nucl. Instrum. Meth. B, 14 pages, 8
figure
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