11,498 research outputs found
Anharmonicity Induced Resonances for Ultracold Atoms and their Detection
When two atoms interact in the presence of an anharmonic potential, such as
an optical lattice, the center of mass motion cannot be separated from the
relative motion. In addition to generating a confinement-induced resonance (or
shifting the position of an existing Feshbach resonance), the external
potential changes the resonance picture qualitatively by introducing new
resonances where molecular excited center of mass states cross the scattering
threshold. We demonstrate the existence of these resonances, give their
quantitative characterization in an optical superlattice, and propose an
experimental scheme to detect them through controlled sweeping of the magnetic
field.Comment: 6 pages, 5 figures; expanded presentatio
Intense slow beams of bosonic potassium isotopes
We report on an experimental realization of a two-dimensional magneto-optical
trap (2D-MOT) that allows the generation of cold atomic beams of 39K and 41K
bosonic potassium isotopes. The high measured fluxes up to 1.0x10^11 atoms/s
and low atomic velocities around 33 m/s are well suited for a fast and reliable
3D-MOT loading, a basilar feature for new generation experiments on
Bose-Einstein condensation of dilute atomic samples. We also present a simple
multilevel theoretical model for the calculation of the light-induced force
acting on an atom moving in a MOT. The model gives a good agreement between
predicted and measured flux and velocity values for our 2D-MOT.Comment: Updated references, 1 figure added, 10 pages, 9 figure
Ultracold molecules: vehicles to scalable quantum information processing
We describe a novel scheme to implement scalable quantum information
processing using Li-Cs molecular state to entangle Li and Cs
ultracold atoms held in independent optical lattices. The Li atoms will
act as quantum bits to store information, and Cs atoms will serve as
messenger bits that aid in quantum gate operations and mediate entanglement
between distant qubit atoms. Each atomic species is held in a separate optical
lattice and the atoms can be overlapped by translating the lattices with
respect to each other. When the messenger and qubit atoms are overlapped,
targeted single spin operations and entangling operations can be performed by
coupling the atomic states to a molecular state with radio-frequency pulses. By
controlling the frequency and duration of the radio-frequency pulses,
entanglement can either be created or swapped between a qubit messenger pair.
We estimate operation fidelities for entangling two distant qubits and discuss
scalability of this scheme and constraints on the optical lattice lasers
Cryopreservation of Coffea liberica Seeds and Embryos following desiccation and freezing treatments
Desiccation of Coffea liberica seeds for 6 days in an air-conditioned room reduced seed and attached emltryo
moisture from 52.58% and 47.49% to 14.58% and 12.56% respectively. Seed germination and viability of
the attached emltryo were maintained at moderate levels of 66% and 38% respectively. However, none of the
desiccated seeds or embryos survived freezing in liquid nitrogen. Excised emltryos desiccated in the lamina flow
cabinet lost their moisture very rapidly from 36.8% to 9.27% within 1.5 hours. More than 70% of these emltryos
survived the desiccation. Moreover, partially desiccated emltryos at 17.17% moisture or less survived subfreezing
temperatures. Between 35% to 50% survived slow freezing to -3ffC, but this was reduced to approximately 30%
when they were subsequently plunged into liquid nitrogen. Fast freezing by direct plunge into liquid nitrogen also
resulted in 10% to 35% survival. Desiccation ofexcised coffee embryos for 0.5h to 17.17% moisture was optimal
for eryopreservation, irrespective of the speed offreezing. Differential thermal analyses of seed tissues suggest that
the absence of freezable water is an important factor for successful eryopreservation of excised coffee emltryos.
However, the importance of initial vigour, moisture variation and recovery media is also discussed
Representation of the pulsed output from a mode-locked laser using quantum field theory and an application in multiphoton ionisation
Ultrasound-Guided Glenohumeral Joint Injection Using the Posterior Approach
Injection treatment to the glenohumeral joint is often needed to treat shoulder problems such as adhesive capsulitis. This can be done through blind palpation technique and fluoroscopic or musculoskeletal ultrasound guidance. In recent years, ultrasound has been proven to increase the accuracy of needle placement into the glenohumeral joint. Ultrasound is radiation free and offers real-time images in performing needle-guided injection procedures. Glenohumeral joint injection can be done using the anterior rotator interval approach or the posterior approach technique. Both techniques are generally well tolerated by the patients. However, it was shown that the posterior injection technique offers an easier and a more effective approach to the glenohumeral joint with less extravasation rate as compared with the anterior approach. The posterior approach also avoids the potential risk of accidental puncture or injection into the axillary neurovascular structures. A linear transducer of 5–12 MHz is usually used. This technique is often applied to inject corticosteroid for the treatment of frozen shoulder or contrast medium for computed tomography or magnetic resonance shoulder arthrography
Collective excitations of a degenerate gas at the BEC-BCS crossover
We study collective excitation modes of a fermionic gas of Li atoms in
the BEC-BCS crossover regime. While measurements of the axial compression mode
in the cigar-shaped trap close to a Feshbach resonance confirm theoretical
expectations, the radial compression mode shows surprising features. In the
strongly interacting molecular BEC regime we observe a negative frequency shift
with increasing coupling strength. In the regime of a strongly interacting
Fermi gas, an abrupt change in the collective excitation frequency occurs,
which may be a signature for a transition from a superfluid to a collisionless
phase.Comment: Feshbach resonance position updated, few minor change
Prostaglandin E2 promotes intestinal repair through an adaptive cellular response of the epithelium
Adaptive cellular responses are often required during wound repair. Following disruption of the intestinal epithelium, wound‐associated epithelial (WAE) cells form the initial barrier over the wound. Our goal was to determine the critical factor that promotes WAE cell differentiation. Using an adaptation of our in vitro primary epithelial cell culture system, we found that prostaglandin E2 (PGE (2)) signaling through one of its receptors, Ptger4, was sufficient to drive a differentiation state morphologically and transcriptionally similar to in vivo WAE cells. WAE cell differentiation was a permanent state and dominant over enterocyte differentiation in plasticity experiments. WAE cell differentiation was triggered by nuclear β‐catenin signaling independent of canonical Wnt signaling. Creation of WAE cells via the PGE (2)‐Ptger4 pathway was required in vivo, as mice with loss of Ptger4 in the intestinal epithelium did not produce WAE cells and exhibited impaired wound repair. Our results demonstrate a mechanism by which WAE cells are formed by PGE (2) and suggest a process of adaptive cellular reprogramming of the intestinal epithelium that occurs to ensure proper repair to injury
Eigen model as a quantum spin chain: exact dynamics
We map Eigen model of biological evolution [Naturwissenschaften {\bf 58}, 465
(1971)] into a one-dimensional quantum spin model with non-Hermitean
Hamiltonian. Based on such a connection, we derive exact relaxation periods for
the Eigen model to approach static energy landscape from various initial
conditions. We also study a simple case of dynamic fitness function.Comment: 10 pages. Physical Revew E vol. 69, in press (2004
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