13,187 research outputs found
High sensitivity phonon spectroscopy of Bose-Einstein condensates using matter-wave interference
We study low momentum excitations of a Bose-Einstein condensate using a novel
matter-wave interference technique. In time-of-flight expansion images we
observe strong matter-wave fringe patterns. The fringe contrast is a sensitive
spectroscopic probe of in-trap phonons and is explained by use of a Bogoliubov
excitation projection method applied to the rescaled order parameter of the
expanding condensate. Gross-Pitaevskii simulations agree with the experimental
data and confirm the validity of the theoretical interpretation. We show that
the high sensitivity of this detection scheme gives access to the quantized
quasiparticle regime.Comment: 5 pages, 5 figures, author list update
Regions of beta 2 and beta 4 responsible for differences between the steady state dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 neuronal nicotinic receptors
We constructed chimeras of the rat beta 2 and beta 4 neuronal nicotinic subunits to locate the regions that contribute to differences between the acetylcholine (ACh) dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 receptors. Expressed in Xenopus oocytes, the alpha 3 beta 2 receptor displays an EC50 for ACh approximately 20-fold less than the EC50 of the alpha 3 beta 4 receptor. The apparent Hill slope (n(app)) of alpha 3 beta 2 is near one whereas the alpha 3 beta 4 receptor displays an n(app) near two. Substitutions within the first 120 residues convert the EC50 for ACh from one wild-type value to the other. Exchanging just beta 2:104-120 for the corresponding region of beta 4 shifts the EC50 of ACh dose-response relationship in the expected direction but does not completely convert the EC50 of the dose- response relationship from one wild-type value to the other. However, substitutions in the beta 2:104-120 region do account for the relative sensitivity of the alpha 3 beta 2 receptor to cytisine, tetramethylammonium, and ACh. The expression of beta 4-like (strong) cooperativity requires an extensive region of beta 4 (beta 4:1-301). Relatively short beta 2 substitutions (beta 2:104-120) can reduce cooperativity to beta 2-like values. The results suggest that amino acids within the first 120 residues of beta 2 and the corresponding region of beta 4 contribute to an agonist binding site that bridges the alpha and beta subunits in neuronal nicotinic receptors
Collisional decay of a strongly driven Bose-Einstein condensate
We study the collisional decay of a strongly driven Bose-Einstein condensate
oscillating between two momentum modes. The resulting products of the decay are
found to strongly deviate from the usual s-wave halo. Using a stochastically
seeded classical field method we simulate the collisional manifold. These
results are also explained by a model of colliding Bloch states.Comment: 4 pages, 4 figure
On rigidly rotating perfect fluid cylinders
The gravitational field of a rigidly rotating perfect fluid cylinder with
gamma- law equation of state is found analytically. The solution has two
parameters and is physically realistic for gamma in the interval (1.41,2].
Closed timelike curves always appear at large distances.Comment: 10 pages, Revtex (galley
Echo spectroscopy of bulk Bogoliubov excitations in trapped Bose-Einstein condensates
We propose and demonstrate an echo method to reduce the inhomogeneous
linewidth of Bogoliubov excitations, in a harmonically-trapped Bose-Einstein
condensate. Our proposal includes the transfer of excitations with momentum +q
to -q using a double two photon Bragg process, in which a substantial reduction
of the inhomogeneous broadening is calculated. Furthermore, we predict an
enhancement in the method's efficiency for low momentum due to many-body
effects. The echo can also be implemented by using a four photon process, as is
demonstrated experimentally.Comment: 4 pages, 5 figure
Microscopic heat from the energetics of stochastic phenomena
The energetics of the stochastic process has shown the balance of energy on
the mesoscopic level. The heat and the energy defined there are, however,
generally different from their macroscopic counterpart. We show that this
discrepancy can be removed by adding to these quantities the reversible heat
associated with the mesoscopic free energy.Comment: 4 pages, 0 figur
Precision measurement of light shifts at two off-resonant wavelengths in a single trapped Ba+ ion and determination of atomic dipole matrix elements
We define and measure the ratio (R) of the vector ac-Stark effect (or light
shift) in the 6S_1/2 and 5D_3/2 states of a single trapped barium ion to 0.2%
accuracy at two different off-resonant wavelengths. We earlier found R =
-11.494(13) at 514.531nm and now report the value at 1111.68nm, R = +0.4176(8).
These observations together yield a value of the matrix element,
previously unknown in the literature. Also, comparison of our results with an
ab initio calculation of dynamic polarizability would yield a new test of
atomic theory and improve the understanding of atomic structure needed to
interpret a proposed atomic parity violation experiment.Comment: 12 pages, 11 figures, in submission to PR
Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay
Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is
predicted to give rise to hitherto unexplored composite quasiparticles:
unstable polarons, i.e., local ``impurities'' dressed by virtual phonons.
Optical monitoring of their spontaneous decay can display either Zeno or
anti-Zeno deviations from the Golden Rule, and thereby probe the temporal
correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure
CEO Compensation Structure following Succession: Evidence of Optimal Incentives with Career Concerns
To motivate managers to pursue shareholder interests, boards may design management compensation packages to reward managers for good firm performance. However, note that when CEOs are far from retirement, they have career concerns. In these cases, Gibbons and Murphy argue that it may not be optimal for their current compensation to be too dependent on firm performance. Testing this proposition, we find that abnormal returns are negatively related to the percentage of performance-based pay of newly hired CEOs when companies announce CEO successions. Since these newly hired CEOs are likely some distance from retirement, we interpret these results as being consistent with Gibbons and Murphy; it may be better to allow newly hired CEOs to be paid in human capital increases from the managerial labor market than to have their current pay too closely related to performance
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