5,895 research outputs found
Climatological features of stratospheric streamers in the FUB-CMAM with increased horizontal resolution
International audienceThe purpose of this study is to investigate horizontal transport processes in the winter stratosphere using data with a resolution relevant for chemistry and climate modeling. For this reason the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) with its model top at 83 km altitude, increased horizontal resolution T42 and the semi-Lagrangian transport scheme for advecting passive tracers is used. A new approach of this paper is the classification of specific transport phenomena within the stratosphere into tropical-subtropical streamers (e.g. Offermann et al., 1999) and polar vortex extrusions hereafter called polar vortex streamers. To investigate the role played by these large-scale structures on the inter-annual and seasonal variability of transport processes in northern mid-latitudes, the global occurrence of such streamers was calculated based on a 10-year model climatology, concentrating on the existence of the Arctic polar vortex. For the identification and counting of streamers, the new method of zonal anomaly was chosen. The analysis of the months October-May yielded a maximum occurrence of tropical-subtropical streamers during Arctic winter and spring in the middle and upper stratosphere. Synoptic maps revealed highest intensities in the subtropics over East Asia with a secondary maximum over the Atlantic in the northern hemisphere. Furthermore, tropical-subtropical streamers exhibited a higher occurrence than polar vortex streamers, indicating that the subtropical barrier is more permeable than the polar vortex barrier (edge) in the model, which is in good correspondence with observations (e.g. Plumb, 2002; Neu et al., 2003). Interesting for the total ozone decrease in mid-latitudes is the consideration of the lower stratosphere for tropical-subtropical streamers and the stratosphere above ~20 km altitude for polar vortex streamers, where strongest ozone depletion is observed at polar latitudes (WMO, 2003). In the lower stratosphere the FUB-CMAM simulated a climatological maximum of 10% occurrence of tropical-subtropical streamers over East-Asia/West Pacific and the Atlantic during early- and mid-winter. The results of this paper demonstrate that stratospheric streamers e.g. large-scale, tongue-like structures transporting tropical-subtropical and polar vortex air masses into mid-latitudes occur frequently during Arctic winter. They can therefore play a significant role on the strength and variability of the observed total ozone decrease at mid-latitudes and should not be neglected in future climate change studies
Adiabatic radio frequency potentials for the coherent manipulation of matter waves
Adiabatic dressed state potentials are created when magnetic sub-states of
trapped atoms are coupled by a radio frequency field. We discuss their
theoretical foundations and point out fundamental advantages over potentials
purely based on static fields. The enhanced flexibility enables one to
implement numerous novel configurations, including double wells, Mach-Zehnder
and Sagnac interferometers which even allows for internal state-dependent atom
manipulation. These can be realized using simple and highly integrated wire
geometries on atom chips.Comment: 13 pages, 2 figure
Strong plasmonic fluorescence enhancement of individual plant light-harvesting complexes
Plasmonic coupling of metallic nanoparticles and adjacent pigments can
dramatically increase the brightness of the pigments due to the enhanced local
electric field. Here, we demonstrate that the fluorescence brightness of a
single plant light-harvesting complex (LHCII) can be significantly enhanced
when coupled to single gold nanorods (AuNRs). The AuNRs utilized in this study
were prepared via chemical reactions, and the hybrid system was constructed
using a simple and economical spin-assisted layer-by-layer technique.
Enhancement of fluorescence brightness of up to 240-fold was observed,
accompanied by a 109-fold decrease in the average (amplitude-weighted)
fluorescence lifetime from approximately 3.5 ns down to 32 ps, corresponding to
an excitation enhancement of 63-fold and emission enhancement of up to
3.8-fold. This large enhancement is due to the strong spectral overlap of the
longitudinal localized surface plasmon resonance of the utilized AuNRs and the
absorption or emission bands of LHCII. This study provides an inexpensive
strategy to explore the fluorescence dynamics of weakly emitting photosynthetic
light-harvesting complexes at the single molecule level.Comment: 23 pages, 6 figures, 2 supplementary figures, and supplementary
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Colloids dragged through a polymer solution: experiment, theory and simulation
We present micro-rheological measurments of the drag force on colloids pulled
through a solution of lambda-DNA (used here as a monodisperse model polymer)
with an optical tweezer. The experiments show a violation of the
Stokes-Einstein relation based on the independently measured viscosity of the
DNA solution: the drag force is larger than expected. We attribute this to the
accumulation of DNA infront of the colloid and the reduced DNA density behind
the colloid. This hypothesis is corroborated by a simple drift-diffusion model
for the DNA molecules, which reproduces the experimental data surprisingly
well, as well as by corresponding Brownian dynamics simulations.Comment: 9 pages, 13 figures, 3 table
Hydrodynamic coupling and rotational mobilities near planar elastic membranes
We study theoretically and numerically the coupling and rotational
hydrodynamic interactions between spherical particles near a planar elastic
membrane that exhibits resistance towards shear and bending. Using a
combination of the multipole expansion and Faxen's theorems, we express the
frequency-dependent hydrodynamic mobility functions as a power series of the
ratio of the particle radius to the distance from the membrane for the self
mobilities, and as a power series of the ratio of the radius to the
interparticle distance for the pair mobilities. In the quasi-steady limit of
zero frequency, we find that the shear- and bending-related contributions to
the particle mobilities may have additive or suppressive effects depending on
the membrane properties in addition to the geometric configuration of the
interacting particles relative to the confining membrane. To elucidate the
effect and role of the change of sign observed in the particle self and pair
mobilities, we consider an example involving a torque-free doublet of
counterrotating particles near an elastic membrane. We find that the induced
rotation rate of the doublet around its center of mass may differ in magnitude
and direction depending on the membrane shear and bending properties. Near a
membrane of only energetic resistance toward shear deformation, such as that of
a certain type of elastic capsules, the doublet undergoes rotation of the same
sense as observed near a no-slip wall. Near a membrane of only energetic
resistance toward bending, such as that of a fluid vesicle, we find a reversed
sense of rotation. Our analytical predictions are supplemented and compared
with fully resolved boundary integral simulations where a very good agreement
is obtained over the whole range of applied frequencies.Comment: 14 pages, 7 figures. Revised manuscript resubmitted to J. Chem. Phy
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