9,232 research outputs found
On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models
The distribution of ice layers in the polar summer mesosphere (called polar mesospheric clouds or PMCs) is sensitive to background atmospheric conditions and therefore affected by global-scale dynamics. To investigate this coupling it is necessary to simulate the global distribution of PMCs within a 3-dimensional (3-D) model that couples large-scale dynamics with cloud microphysics. However, modeling PMC microphysics within 3-D global chemistry climate models (GCCM) is a challenge due to the high computational cost associated with particle following (Lagrangian) or sectional microphysical calculations. By characterizing the relationship between the PMC effective radius, ice water content (<i>iwc</i>), and local temperature (<i>T</i>) from an ensemble of simulations from the sectional microphysical model, the Community Aerosol and Radiation Model for Atmospheres (CARMA), we determined that these variables can be described by a robust empirical formula. The characterized relationship allows an estimate of an altitude distribution of PMC effective radius in terms of local temperature and <i>iwc</i>. For our purposes we use this formula to predict an effective radius as part of a bulk parameterization of PMC microphysics in a 3-D GCCM to simulate growth, sublimation and sedimentation of ice particles without keeping track of the time history of each ice particle size or particle size bin. This allows cost effective decadal scale PMC simulations in a 3-D GCCM to be performed. This approach produces realistic PMC simulations including estimates of the optical properties of PMCs. We validate the relationship with PMC data from the Solar Occultation for Ice Experiment (SOFIE)
Quantum Control of the Hyperfine Spin of a Cs Atom Ensemble
We demonstrate quantum control of a large spin-angular momentum associated
with the F=3 hyperfine ground state of 133Cs. A combination of time dependent
magnetic fields and a static tensor light shift is used to implement
near-optimal controls and map a fiducial state to a broad range of target
states, with yields in the range 0.8-0.9. Squeezed states are produced also by
an adiabatic scheme that is more robust against errors. Universal control
facilitates the encoding and manipulation of qubits and qudits in atomic ground
states, and may lead to improvement of some precision measurements.Comment: 4 pages, 4 figures (color
Gauss sum factorization with cold atoms
We report the first implementation of a Gauss sum factorization algorithm by
an internal state Ramsey interferometer using cold atoms. A sequence of
appropriately designed light pulses interacts with an ensemble of cold rubidium
atoms. The final population in the involved atomic levels determines a Gauss
sum. With this technique we factor the number N=263193.Comment: 4 pages, 5 figure
Coccolithophore fluxes in the open tropical North Atlantic: influence of thermocline depth, Amazon water, and Saharan dust
Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition, and seasonal patterns were determined in two sediment trap moorings (M4 at 12 degrees N, 49 degrees W and M2 at 14 degrees N, 37 degrees W) collecting settling particles synchronously from October 2012 to November 2013 at 1200 m of water depth in the open equatorial North Atlantic. The two trap locations showed a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage. Species fluxes were dominated throughout the year by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus) but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 x 10(7) +/- 76 x 10(7) coccoliths m(-2) d(-1) at station M4 compared to only 66 x 10(7) +/- 31 x 10(7) coccoliths m(-2) d(-1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, favoured by the westward deepening of the thermocline and nutricline. Still, most UPZ species also contributed to higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. Such was the case of two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi in January and April 2013 at M4, indicating a fast response to the nutrient enrichment of the UPZ, probably by wind-forced mixing. Later, increased fluxes of G. oceanica and E. huxleyi in October-November 2013 coincided with the occurrence of Amazon-River-affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks, we propose a scenario in which atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated with the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Nevertheless, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than "background" tropical productivity in the equatorial North Atlantic. This study illustrates how two apparently similar sites in the tropical open ocean actually differ greatly in ecological and oceanographic terms. The results presented here provide valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.Netherlands Organization for Scientific Research (NWO) [822.01.008]; European Research Council (ERC) [311152]; University of Bremen; European Union [600411]info:eu-repo/semantics/publishedVersio
Probability of the resistive state formation caused by absorption of a single-photon in current-carrying superconducting nano-strips
We have studied supercurrent-assisted formation of the resistive state in
nano-structured Nb and NbN superconducting films after absorption of a single
photon. In amorphous narrow NbN strips the probability of the resistive state
formation has a pronounced spectral cut-off. The corresponding threshold photon
energy decreases with the bias current. Analysis of the experimental data in
the framework of the generalized hot-spot model suggests that the quantum yield
for near-infrared photons increases faster than the photon nergy. Relaxation of
the resistive state depends on the photon energy making the phenomenon feasible
for the development of energy resolving single-photon detectors.Comment: 9 pages, 9 figures, submitted to Eur. Phys. Journa
A concept of an automated function control for ambient aerosol measurements using mobility particle size spectrometers
An automated function control unit was developed to regularly check the
ambient particle number concentration derived from a mobility particle size
spectrometer as well as its zero-point behaviour. The function control allows
unattended quality assurance experiments at remote air quality monitoring or
research stations under field conditions. The automated function control also
has the advantage of being able to get a faster system stability response
than the recommended on-site comparisons with reference instruments. The
method is based on a comparison of the total particle number concentration
measured by a mobility particle size spectrometer and a condensation particle
counter while removing diffusive particles smaller than 20 nm in diameter.
In practice, the small particles are removed by a set of diffusion screens,
as traditionally used in a diffusion battery. Another feature of the
automated function control is to check the zero-point behaviour of the
ambient aerosol passing through a high-efficiency particulate air (HEPA)
filter.
<br><br>
The performance of the function control is illustrated with the aid of a
1-year data set recorded at Annaberg-Buchholz, a station in the Saxon air
quality monitoring network. During the period of concern, the total particle
number concentration derived from the mobility particle size spectrometer
slightly overestimated the particle number concentration recorded by the
condensation particle counter by 2 % (grand average). Based on our first
year of experience with the function control, we developed tolerance criteria
that allow a performance evaluation of a tested mobility particle size
spectrometer with respect to the total particle number concentration. We
conclude that the automated function control enhances the quality and
reliability of unattended long-term particle number size distribution
measurements. This will have beneficial effects for intercomparison studies
involving different measurement sites, and help provide a higher data
accuracy for cohort health and climate research studies
NMR experiment factors numbers with Gauss sums
We factor the number 157573 using an NMR implementation of Gauss sums.Comment: 4 pages 5 figure
- …