637 research outputs found
Chaotic dynamics as a possible mechanism of rapid change of hippocampal local field activity between theta rhythm and large irregular activity
Multichannel cold collisions between metastable Sr atoms
We present a multichannel scattering calculation of elastic and inelastic
cold collisions between two low-field seeking, metastable ^{88}Sr [(5s5p)
^3P_2] atoms in the presence of an external magnetic field. The scattering
physics is governed by strong anisotropic long-range interactions, which lead
to pronounced coupling among the partial waves of relative motion. As a result,
nonadiabatic transitions are shown to trigger a high rate of inelastic losses.
At relatively high energies, T > 100 mkK, the total inelastic collision rate is
comparable with the elastic rate. However, at lower collisional energy, the
elastic rate decreases, and at T ~ 1mkK, it becomes substantially smaller than
the inelastic rate. Our study suggests that magnetic trapping and evaporative
cooling of ^{88}Sr [(5s5p) ^3P_2] atoms, as well as ^{40}Ca [(4s4p) ^3P_2], in
low-field seeking states will prove difficult to achieve experimentally.Comment: 4 pages, Latex, Submitte
Inhibition of neutrophil migration by a selective inhibitor of matrix metalloproteinase: analysis by intravital microscopy
Observation of the microcirculation of the hamster cheek pouch by intravital microscopy revealed five steps of neutrophil migration from the venules after topical application of leukotriene B4 to the microvasculature: rolling along the venular wall (Step 1), adhesion to it (Step 2), disappearance from the vascular lumen (Step 3), presence between the endothelial cells and the subendothelial basement membrane (Step 4) and passage through the basement membrane (Step 5). The present study was performed to examine whether a metalloproteinase inhibitor inhibits neutrophil migration at any of the above five steps. Chymostatin and leupeptin did not inhibit any of these five steps. In contrast, FN-439, a selective inhibitor of matrix metalloproteinase, reduced the number of neutrophils in the perivascular space without affecting Steps 1 to 3. It was concluded that neutrophils may use metalloproteinase (collagenase/gelatinase) to penetrate the subendothelial basement membrane
Optical clocks based on ultra-narrow three-photon resonances in alkaline earth atoms
A sharp resonance line that appears in three-photon transitions between the
and states of alkaline earth and Yb atoms is proposed
as an optical frequency standard. This proposal permits the use of the even
isotopes, in which the clock transition is narrower than in proposed clocks
using the odd isotopes and the energy interval is not affected by external
magnetic fields or the polarization of trapping light. The method has the
unique feature that the width and rate of the clock transition can be
continuously adjusted from the level to sub- without loss of signal
amplitude by varying the intensities of the three optical beams. Doppler and
recoil effects can be eliminated by proper alignment of the three optical beams
or by point confinement in a lattice trap. The three beams can be mixed to
produce the optical frequency corresponding to the -
clock interval.Comment: 10 pages, 4 figures, submitted to PR
Narrow Line Cooling and Momentum-Space Crystals
Narrow line laser cooling is advancing the frontier for experiments ranging
from studies of fundamental atomic physics to high precision optical frequency
standards. In this paper, we present an extensive description of the systems
and techniques necessary to realize 689 nm 1S0 - 3P1 narrow line cooling of
atomic 88Sr. Narrow line cooling and trapping dynamics are also studied in
detail. By controlling the relative size of the power broadened transition
linewidth and the single-photon recoil frequency shift, we show that it is
possible to continuously bridge the gap between semiclassical and quantum
mechanical cooling. Novel semiclassical cooling process, some of which are
intimately linked to gravity, are also explored. Moreover, for laser
frequencies tuned above the atomic resonance, we demonstrate momentum-space
crystals containing up to 26 well defined lattice points. Gravitationally
assisted cooling is also achieved with blue-detuned light. Theoretically, we
find the blue detuned dynamics are universal to Doppler limited systems. This
paper offers the most comprehensive study of narrow line laser cooling to date.Comment: 14 pages, 19 figure
State-insensitive trapping of Rb atoms: linearly versus circularly polarized lights
We study the cancellation of differential ac Stark shifts in the 5s and 5p
states of rubidium atom using the linearly and circularly polarized lights by
calculating their dynamic polarizabilities. Matrix elements were calculated
using a relativistic coupled-cluster method at the single, double and important
valence triple excitations approximation including all possible non-linear
correlation terms. Some of the important matrix elements were further optimized
using the experimental results available for the lifetimes and static
polarizabilities of atomic states. "Magic wavelengths" are determined from the
differential Stark shifts and results for the linearly polarized light are
compared with the previously available results. Possible scope of facilitating
state-insensitive optical trapping schemes using the magic wavelengths for
circularly polarized light are discussed. Using the optimized matrix elements,
the lifetimes of the 4d and 6s states of this atom are ameliorated.Comment: 13 pages, 13 tables and 4 figure
Complete nucleotide sequence of the gene for the specific glycoprotein (gp55) of Friend spleen focus-forming virus.
Decay Properties of Bh and Db Produced in the Cm + Na Reaction
Decay properties of an isotope Bh and its daughter nucleus Db
produced by the Cm(Na, 5\textit{n}) reaction were studied by
using a gas-filled recoil separator coupled with a position-sensitive
semiconductor detector. Bh was clearly identified from the correlation
of the known nuclide, Db. The obtained decay properties of Bh
and Db are consistent with those observed in the 113 chain,
which provided further confirmation of the discovery of 113.Comment: Accepted for publication in J. Phys. Soc. JPN., to be published in
Vol.78 No.
Magnetic trapping of metastable atomic strontium
We report the magnetic trapping of metastable atomic strontium. Atoms
are cooled in a magneto-optical trap (MOT) operating on the dipole allowed
transition at 461 nm. Decay via
continuously loads a magnetic trap formed by the quadrupole magnetic field of
the MOT. Over atoms at a density of cm and
temperature of 1 mK are trapped. The atom temperature is significantly lower
than what would be expected from the kinetic and potential energy of atoms as
they are transferred from the MOT. This suggests that thermalization and
evaporative cooling are occurring in the magnetic trap.Comment: This paper has been accepted by PR
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