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At least 973 records · Page 54Linked to original sources
PubMed2005

Spin-charge separation in cold fermi gases: a real time analysis.

Using the adaptive time-dependent density-matrix renormalization group method for the 1D Hubbard model, the splitting of local perturbations into separate wave packets carrying charge and spin is observed in real time. We show the robustness of this separation beyond the low-energy Luttinger liquid theory by studying the time evolution of single particle excitations and density wave packets. A striking signature of spin-charge separation is found in 1D cold Fermi gases in a harmonic trap at the boundary between liquid and Mott-insulating phases. We give quantitative estimates for an experimental observation of spin-charge separation in an array of atomic wires.

Journal Article↗
PubMed2005

Local pair correlations in one-dimensional Bose gases.

We measure photoassociation rates in one-dimensional Bose gases, and so determine the local pair correlation function over a wide range of coupling strengths. As bosons become more strongly coupled, we observe a tenfold decrease in their wave function overlap, thus directly observing the fermionization of bosons.

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PubMed2005

Vortex lattices in rotating atomic bose gases with dipolar interactions.

We show that dipolar interactions have dramatic effects on the ground states of rotating atomic Bose gases in the weak-interaction limit. With increasing dipolar interaction (relative to the net contact interaction), the mean field, or high filling factor, ground state undergoes a series of transitions between vortex lattices of different symmetries: triangular, square, "stripe," and "bubble" phases. We also study the effects of dipolar interactions on the quantum fluids at low filling factors. We show that the incompressible Laughlin state at filling factor nu = 1/2 is replaced by compressible stripe and bubble phases.

Journal Article↗
PubMed2005

Population of closed-channel molecules in trapped Fermi gases with broad Feshbach resonances.

We compute the fraction of closed-channel molecules in trapped atomic Fermi gases, over the entire range of accessible fields and temperatures. We use a two-channel model of Bardeen-Cooper-Schrieffer-Bose-Einstein-condensation crossover theory at general temperature , and show that this fraction provides a measure of the T-dependent pairing gap. Our calculations, containing no free parameters, are in good quantitative agreement with recent low- measurements in (6)Li. We present readily testable predictions for the dependencies of the closed-channel fraction on temperature and Fermi momentum.

Journal Article↗
PubMed2006

Mott-insulator phase of coupled one-dimensional atomic gases in a two-dimensional optical lattice.

We consider the 2D Mott-insulator state of a 2D array of coupled finite size 1D Bose gases. It is shown that the momentum distribution in the lattice plane is very sensitive to the interaction regime in the 1D tubes. In particular, we find that the disappearance of the interference pattern in time-of-flight experiments is a clear consequence of the strongly interacting Tonks-Girardeau regime along the tubes.

Journal Article↗
PubMed2006

Vortex-antivortex lattice in ultracold fermionic gases.

We discuss ultracold Fermi gases in two dimensions, which could be realized in a strongly confining one-dimensional optical lattice. We obtain the temperature versus effective interaction phase diagram for an s-wave superfluid and show that, below a certain critical temperature Tc, spontaneous vortex-antivortex pairs appear for all coupling strengths. In addition, we show that the evolution from weak-to-strong coupling is smooth, and that the system forms a square vortex-antivortex lattice at a lower critical temperature TM.

Journal Article↗
PubMed2006

Strongly interacting Fermi gases with density imbalance.

We consider density-imbalanced Fermi gases of atoms in the strongly interacting, i.e., unitarity, regime. The Bogoliubov-de Gennes equations for a trapped superfluid are solved. They take into account the finite size of the system, as well as give rise to both phase separation and Fulde-Ferrel-Larkin-Ovchinnikov-type oscillations in the order parameter. We show how radio-frequency spectroscopy reflects the phase separation, and can provide direct evidence of the FFLO-type oscillations via observing the nodes of the order parameter.

Journal Article↗
PubMed2006

Induced P-wave superfluidity in asymmetric fermi gases.

We show that two new intraspecies P-wave superfluid phases appear in two-component asymmetric Fermi systems with short-range S-wave interactions. In the BEC limit, phonons of the molecular BEC induce P-wave superfluidity in the excess fermions. In the BCS limit, density fluctuations induce P-wave superfluidity in both the majority and the minority species. These phases may be realized in experiments with spin-polarized Fermi gases.

Journal Article↗
PubMed2006

Tunable ultrashort laser pulses generated through filamentation in gases.

Tunable and stable ultrashort laser pulses in the visible spectrum are generated with high efficiency by four-wave mixing process during the filamentation of near-infrared and infrared laser pulses in gases. It is shown that these tunable ultrashort pulses have a very low energy fluctuation and an excellent mode quality due to the processes of intensity clamping and self-filtering in the filament.

Journal Article↗
PubMed2006

Detection of broadband terahertz waves with a laser-induced plasma in gases.

We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.

Journal Article↗
PubMed2006

Critical rotational frequency for superfluid fermionic gases across a Feshbach resonance.

We present a method to determine the critical rotational frequencies for superfluidity of both uniform and trapped Fermi gases across a wide Feshbach resonance. It is found that as one approaches the resonance from the BCS side, beyond a critical scattering length, pairing is so robust that superfluidity cannot be destroyed by rotation. Moreover, the critical frequency has a sequence of jumps revealing the appearance of Landau levels, which are particularly prominent for systems up to a few thousand particles. For rotational frequency below an ultimate critical frequency, defined to be the lowest frequency at which the center of the cloud goes normal, a trapped gas has a superfluid core surrounded by a normal gas, as seen in recent experiments (C. H. Schunck, cond-mat/0607298).

Journal Article↗
PubMed2006

Coherence length of cold exciton gases in coupled quantum wells.

A Mach-Zehnder interferometer with spatial and spectral resolution was used to probe spontaneous coherence in cold exciton gases, which are implemented experimentally in the ring of indirect excitons in coupled quantum wells. A strong enhancement of the exciton coherence length is observed at temperatures below a few Kelvin. The increase of the coherence length is correlated with the macroscopic spatial ordering of excitons. The coherence length at the lowest temperature corresponds to a very narrow spread of the exciton momentum distribution, much smaller than that for a classical exciton gas.

Journal Article↗
PubMed1979

Solubility of gases and the temperature dependency of whole leaf affinities for carbon dioxide and oxygen: an alternative perspective.

An analysis of the kinetics of simultaneous photosynthesis and photorespiration at the end of a diffusion path is applied to observed net photosynthetic rate as a function of O(2) and CO(2) concentrations. The data of Ku and Edwards (Plant Physiol. 59: 991-999, 1977) from wheat (Triticum aestivum L.) are analyzed in detail. Ku and Edwards, using an analysis that ignored diffusion resistance between the intercellular air space and fixation site, the competitive effect of CO(2) on photorespiration, and the actual concentrations of gases at the fixation site, concluded that: (a) the affinity coefficient of the leaf for CO(2) was approximately 3.5 to 5 micromolar; (b) this affinity coefficient is independent of temperature between 25 and 35 C; (c) the effect of O(2) was independent of temperature over this range; and (d) competition between CO(2) and O(2) is responsible for the major share of CO(2) loss from photosynthesis due to photorespiration. They suggest that using gas concentrations calculated as equilibium values in the liquid phase is very important in reaching these conclusions. By applying a more complete analysis to their data which includes diffusion in the cell, it is concluded that: (a) the affinity coefficient of the leaf for CO(2) is 0.1 to 1.1 micromolar; (b) the temperature dependence of this affinity coefficient cannot be determined from existing data, but there is no evidence to refute independent temperature effect on the two functions of ribulose-1,5-bisphosphate carboxylase-oxygenase being important in the regulation of whole leaf net photosynthesis; and (c) the competitive interplay of CO(2) and O(2) at ribulose-1,5-bisphosphate carboxylase may under certain conditions lead to a stimulation of fixation by the Calvin cycle because of photorespiration. These conclusions are reached whether CO(2) and O(2) are expressed as dissolved concentrations or as gas concentrations in the intercellular air space. The relative merits of these two expressions of concentration are discussed.

Journal Article↗
PubMed1985

Laboratory-Produced CO(2) Calibration Gases.

A simple, inexpensive apparatus for making mixtures of accurately known amounts of CO(2) and CO(2)-free atmospheric air is described. Calibration gases with CO(2) contents of 200 to 1500 microliters per liter produced with the apparatus had concentrations which were within 10 microliters per liter of the target concentration.

Journal Article↗
PubMed1985

Resistance of citrus fruit to mass transport of water vapor and other gases.

The resistance of oranges (Citrus sinensis L. Osbeck) and grapefruit (Citrus paradisi Macf.) to ethylene, O(2), CO(2), and H(2)O mass transport was investigated anatomically with scanning electron microscope and physiologically by gas exchange measurements at steady state. The resistance of untreated fruit to water vapor is far less than to ethylene, CO(2) and O(2). Waxing partially or completely plugs stomatal pores and forms an intermittent cracked layer over the surface of fruit, restricting transport of ethylene, O(2), and CO(2), but not of water; whereas individual sealing of fruit with high density polyethylene films reduces water transport by 90% without substantially inhibiting gas exchange.Stomata of harvested citrus fruits are essentially closed. However, ethylene, O(2) and CO(2) still diffuse mainly through the residual stomatal opening where the relative transport resistance (approximately 6,000 seconds per centimeter) depends on the relative diffusivity of each gas in air. Water moves preferentially by a different pathway, probably through a liquid aqueous phase in the cuticle where water conductance is 60-fold greater. Other gases are constrained from using this pathway because their diffusivity in liquid water is 10(4)-fold less than in air.

Journal Article↗
PubMed1976

Continuous positive airway pressure. The collection of expired gases.

A low dead space, low resistance, non-rebreathing valve is described. When used with a constant pressure source it enables the expired gases of patients being managed on CPAP to be collected for physiological analysis. It also functions as a collect valve during normal spontaneous respiration and during IPPV.

Adult↗
PubMed1985

Anaesthetic carrier gases. Their effect on middle-ear pressure peri-operatively.

The effects of three different anaesthetic carrier gases on middle-ear pressure in the operative and postoperative periods was assessed. Patients receiving oxygen and oxygen-enriched air did not have significant changes in middle-ear pressure. The changes associated with the use of nitrous oxide as the carrier gas were reversed with return of pharyngeal reflexes or after prolonged inhalation of 100% oxygen. In patients undergoing middle-ear surgery or those with pre-existing middle-ear disease, we suggest that oxygen-enriched air is the anaesthetic carrier gas of choice.

Adult↗
PubMed1983

Experimental nasal obstruction and changes in the arterial blood gases.

This is a controlled animal experiment in which the effect of chronic nasal obstruction on the arterial blood gases was studied. Sixty female New Zealand Albino rabbits, in groups of 3 litter mates were assigned to 3 groups: control, unilateral nasal obstruction, and bilateral nasal obstruction. Nasal obstruction was produced using coagulating electro-cautery and the values of pO2, pCO2 and pH in the arterial blood were studied. In animals with unilateral nasal obstruction the blood gas values were similar to those in the control group. In animals with bilateral nasal obstruction there was a marked fall in pO2 and a marked increase in pCO2. These changes were statistically significant, but there was no significant change in arterial pH in any of the obstructed groups.

Airway Obstruction↗