129 research outputs found
The Tropospheric Lifetimes of Halocarbons and Their Reactions with OH Radicals: an Assessment Based on the Concentration of CO-14
Chemical reaction with hydroxyl radicals formed in the troposphere from ozone photolysis in the presence of methane, carbon monoxide and nitrogen oxides provides an important removal mechanism for halocarbons containing C-H and C = C double bonds. The isotropic distribution in atmospheric carbon monoxide was used to quantify the tropospheric hydroxyl radical distribution. Here, this methodology is reevaluated in the light of recent chemical kinetic data evaluations and new understandings gained in the life cycles of methane and carbon monoxide. None of these changes has forced a significant revision in the CO-14 approach. However, it is somewhat more clearly apparent how important basic chemical kinetic data are to the accurate establishment of the tropospheric hydroxyl radical distribution
Observation of molecules produced from a Bose-Einstein condensate
Molecules are created from a Bose-Einstein condensate of atomic 87Rb using a
Feshbach resonance. A Stern-Gerlach field is applied, in order to spatially
separate the molecules from the remaining atoms. For detection, the molecules
are converted back into atoms, again using the Feshbach resonance. The measured
position of the molecules yields their magnetic moment. This quantity strongly
depends on the magnetic field, thus revealing an avoided crossing of two bound
states at a field value slightly below the Feshbach resonance. This avoided
crossing is exploited to trap the molecules in one dimension.Comment: 4 pages, 4 figures, minor revison
In-situ comparison of the NOy instruments flown in MOZAIC and SPURT
Two aircraft instruments for the measurement of total odd nitrogen (NOy) were compared side by side aboard a Learjet A35 in April 2003 during a campaign of the AFO2000 project SPURT (Spurengastransport in der Tropopausenregion). The instruments albeit employing the same measurement principle (gold converter and chemiluminescence) had different inlet configurations. The ECO-Physics instrument operated by ETH-ZĂźrich in SPURT had the gold converter mounted outside the aircraft, whereas the instrument operated by FZ-JĂźlich in the European project MOZAIC III (Measurements of ozone, water vapour, carbon monoxide and nitrogen oxides aboard Airbus A340 in-service aircraft) employed a Rosemount probe with 80 cm of FEP-tubing connecting the inlet to the gold converter. The NOy concentrations during the flight ranged between 0.3 and 3 ppb. The two data sets were compared in a blind fashion and each team followed its normal operating procedures. On average, the measurements agreed within 7%, i.e. within the combined uncertainty of the two instruments. This puts an upper limit on potential losses of HNO3 in the Rosemount inlet of the MOZAIC instrument. Larger transient deviations were observed during periods after calibrations and when the aircraft entered the stratosphere. The time lag of the MOZAIC instrument observed in these instances is in accordance with the time constant of the MOZAIC inlet line determined in the laboratory for HNO3
Strongly correlated photons on a chip
Optical non-linearities at the single-photon level are key ingredients for
future photonic quantum technologies. Prime candidates for the realization of
strong photon-photon interactions necessary for implementing quantum
information processing tasks as well as for studying strongly correlated
photons in an integrated photonic device setting are quantum dots embedded in
photonic crystal nanocavities. Here, we report strong quantum correlations
between photons on picosecond timescales. We observe (a) photon antibunching
upon resonant excitation of the lowest-energy polariton state, proving that the
first cavity photon blocks the subsequent injection events, and (b) photon
bunching when the laser field is in two-photon resonance with the polariton
eigenstates of the second Jaynes-Cummings manifold, demonstrating that two
photons at this color are more likely to be injected into the cavity jointly,
than they would otherwise. Together,these results demonstrate unprecedented
strong single-photon non-linearities, paving the way for realizing a
single-photon transistor or a quantum optical Josephson interferometer
PEDANT covers all complete RefSeq genomes
The PEDANT genome database provides exhaustive annotation of nearly 3000 publicly available eukaryotic, eubacterial, archaeal and viral genomes with more than 4.5 million proteins by a broad set of bioinformatics algorithms. In particular, all completely sequenced genomes from the NCBI's Reference Sequence collection (RefSeq) are covered. The PEDANT processing pipeline has been sped up by an order of magnitude through the utilization of precalculated similarity information stored in the similarity matrix of proteins (SIMAP) database, making it possible to process newly sequenced genomes immediately as they become available. PEDANT is freely accessible to academic users at http://pedant.gsf.de. For programmatic access Web Services are available at http://pedant.gsf.de/webservices.jsp
Characterization of elastic scattering near a Feshbach resonance in rubidium 87
The s-wave scattering length for elastic collisions between 87Rb atoms in the
state |f,m_f>=|1,1> is measured in the vicinity of a Feshbach resonance near
1007 G. Experimentally, the scattering length is determined from the mean-field
driven expansion of a Bose-Einstein condensate in a homogeneous magnetic field.
The scattering length is measured as a function of the magnetic field and
agrees with the theoretical expectation. The position and the width of the
resonance are determined to be 1007.40 G and 0.20 G, respectively.Comment: 4 pages, 2 figures minor revisions: added Ref.6, included error bar
Ultrafast all-optical switching by single photons
An outstanding goal in quantum optics is the realization of fast optical
non-linearities at the single-photon level. Such non-linearities would allow
for the realization of optical devices with new functionalities such as a
single-photon switch/transistor or a controlled-phase gate, which could form
the basis of future quantum optical technologies. While non-linear optics
effects at the single-emitter level have been demonstrated in different
systems, including atoms coupled to Fabry-Perot or toroidal micro-cavities,
super-conducting qubits in strip-line resonators or quantum dots (QDs) in
nano-cavities, none of these experiments so far has demonstrated single-photon
switching on ultrafast timescales. Here, we demonstrate that in a strongly
coupled QD-cavity system the presence of a single photon on one of the
fundamental polariton transitions can turn on light scattering on a transition
from the first to the second Jaynes-Cummings manifold with a switching time of
20 ps. As an additional device application, we use this non-linearity to
implement a single-photon pulse-correlator. Our QD-cavity system could form the
building-block of future high-bandwidth photonic networks operating in the
quantum regime
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