86 research outputs found
Creating Ground State Molecules with Optical Feshbach Resonances in Tight Traps
We propose to create ultracold ground state molecules in an atomic
Bose-Einstein condensate by adiabatic crossing of an optical Feshbach
resonance. We envision a scheme where the laser intensity and possibly also
frequency are linearly ramped over the resonance. Our calculations for
Rb show that for sufficiently tight traps it is possible to avoid
spontaneous emission while retaining adiabaticity, and conversion efficiencies
of up to 50% can be expected
Absolute Timing of the Crab Pulsar with RXTE
We have monitored the phase of the main X-ray pulse of the Crab pulsar with
the Rossi X-ray Timing Explorer (RXTE) for almost eight years, since the start
of the mission in January 1996. The absolute time of RXTE's clock is
sufficiently accurate to allow this phase to be compared directly with the
radio profile. Our monitoring observations of the pulsar took place bi-weekly
(during the periods when it was at least 30 degrees from the Sun) and we
correlated the data with radio timing ephemerides derived from observations
made at Jodrell Bank. We have determined the phase of the X-ray main pulse for
each observation with a typical error in the individual data points of 50 us.
The total ensemble is consistent with a phase that is constant over the
monitoring period, with the X-ray pulse leading the radio pulse by
0.0102+/-0.0012 period in phase, or 344+/-40 us in time. The error estimate is
dominated by a systematic error of 40 us in the radio data, arising from
uncertainties in the variable amount of pulse delay due to interstellar
scattering and instrumental calibration. The statistical error is 0.00015
period, or 5 us. The separation of the main pulse and interpulse appears to be
unchanging at time scales of a year or less, with an average value of
0.4001+/-0.0002 period. There is no apparent variation in these values with
energy over the 2-30 keV range. The lag between the radio and X-ray pulses may
be constant in phase (rotational) or constant in time (linear pathlength). We
are not (yet) able to distinguish between these two interpretations.Comment: 11 pages, 2 figure
It is not only extending donor criteria: it is extending the donor pool. A cross-sectional survey from the European Society of Organ Transplantation
As part of the TLJ2.0 organised by the European Society of Organ Transplantation (ESOT), our working group surveyed transplant professionals’ attitudes towards expanding the donor pool, barriers and interventions to overcome these. The survey was posted for three weeks in July–August, 2020, via the ESOT’s social media platforms. A total of 135 participants, consisting mainly of surgeons (34%), transplant coordinators (30%), physicians
(15%) and intensivists (4%) completed the survey (Table 1). Most respondents worked in the field for >20 years (34%), 6–10 years (20%) or 11–15 years (19%). The main European countries of practice were the Netherlands (16%), the United Kingdom (10%), Italy (8%), Sweden (7%) and Spain (4%) (Q1–3). History of cancer (Q4). The 88% felt that the history of leukaemia was not a contraindication to donate, although 15% suggested a multi-disciplinary team decision. Some stressed the need for explicit recipient consent (4%) or clearly stating the risks to the recipient (3%). Two respondents considered the history of leukaemia as a contraindication
Improved setup for producing slow beams of cold molecules using a rotating nozzle
Intense beams of cold and slow molecules are produced by supersonic expansion
out of a rapidly rotating nozzle, as first demonstrated by Gupta and
Herschbach. An improved setup is presented that allows to accelerate or
decelerate cold atomic and molecular beams by up to 500 m/s. Technical
improvements are discussed and beam parameters are characterized by detailed
analysis of time of flight density distributions. The possibility of combining
this beam source with electrostatic fields for guiding polar molecules is
demonstrated
Photoassociative Production and Trapping of Ultracold KRb Molecules
We have produced ultracold heteronuclear KRb molecules by the process of
photoassociation in a two-species magneto-optical trap. Following decay of the
photoassociated KRb*, the molecules are detected using two-photon ionization
and time-of-flight mass spectroscopy of KRb. A portion of the metastable
triplet molecules thus formed are magnetically trapped. Photoassociative
spectra down to 91 cm below the K(4) + Rb (5) asymptote have
been obtained. We have made assignments to all eight of the attractive Hund's
case (c) KRb* potential curves in this spectral region.Comment: 4 pages, 4 figure
Formation of Ultracold Heteronuclear Dimers in Electric Fields
The formation of ultracold molecules via stimulated emission followed by a
radiative deexcitation cascade in the presence of a static electric field is
investigated. By analyzing the corresponding cross sections, we demonstrate the
possibility to populate the lowest rotational excitations via photoassociation.
The modification of the radiative cascade due to the electric field leads to
narrow rotational state distributions in the vibrational ground state. External
fields might therefore represent an additional valuable tool towards the
ultimate goal of quantum state preparation of molecules
On the Role of Penning Ionization in Photoassociation Spectroscopy
We study the role of Penning ionization on the photoassociation spectra of
He(^3S)-He(^3S). The experimental setup is discussed and experimental results
for different intensities of the probe laser are shown. For modelling the
experimental results we consider coupled-channel calculations of the crossing
of the ground state with the excited state at the Condon point. The
coupled-channel calculations are first applied to model systems, where we
consider two coupled channels without ionization, two coupled channels with
ionization, and three coupled channels, for which only one of the excited
states is ionizing. Finally, coupled-channel calculations are applied to
photoassociation of He(^3S)-He(^3S) and good agreement is obtained between the
model and the experimental results.Comment: 14 pages, 18 figures, submitted to the special issue on Cold
Molecules of J. Phys.
Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium
We have measured the reduced absorption coefficients occurring in the wings
of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened
by helium gas at pressures of several hundred Torr. At the experimental
temperature of 900 K, we have detected a shoulder-like broadening feature on
the blue wing of the doublet which is relatively flat between 401.8 nm and
402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to
absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the
K-He quasimolecule. The accurate measurements of the line profiles in the
present work will sharply constrain future calculations of potential energy
surfaces and transition dipole moments correlating to the asymptotes He-K(5p),
He-K(5s), and He-K(3d).Comment: 2 figure
Sympathetic Cooling with Two Atomic Species in an Optical Trap
We simultaneously trap ultracold lithium and cesium atoms in an optical
dipole trap formed by the focus of a CO laser and study the exchange of
thermal energy between the gases. The cesium gas, which is optically cooled to
K, efficiently decreases the temperature of the lithium gas through
sympathetic cooling. The measured cross section for thermalizing
Cs-Li collisions is cm, for both species in
their lowest hyperfine ground state. Besides thermalization, we observe
evaporation of lithium purely through elastic cesium-lithium collisions
(sympathetic evaporation).Comment: 4 pages 3 fig
Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission
The gamma-ray blazar 3C 279 was monitored on a nearly daily basis with IUE,
ROSAT and EGRET for three weeks between December 1992 and January 1993. During
this period, the blazar was at a historical minimum at all wavelengths. Here we
present the UV data obtained during the above multiwavelength campaign. A
maximum UV variation of ~50% is detected, while during the same period the
X-ray flux varied by no more than 13%. At the lowest UV flux level the average
spectrum in the 1230-2700 A interval is unusually flat for this object
(~1). The flattening could represent the lowest energy tail of the
inverse Compton component responsible for the X-ray emission, or could be due
to the presence of a thermal component at ~20000 K possibly associated with an
accretion disk. The presence of an accretion disk in this blazar object, likely
observable only in very low states and otherwise hidden by the beamed, variable
synchrotron component, would be consistent with the scenario in which the seed
photons for the inverse Compton mechanism producing the gamma-rays are external
to the relativistic jet. We further discuss the long term correlation of the UV
flux with the X-ray and gamma-ray fluxes obtained at various epochs. All UV
archival data are included in the analysis. Both the X- and gamma-ray fluxes
are generally well correlated with the UV flux, approximately with square root
and quadratic dependences, respectively.Comment: 22 pages, Latex, 7 PostScript figures, to appear in The Astrophysical
Journa
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