54 research outputs found
Radio Frequency Selective Addressing of Localized Particles in a Periodic Potential
We study the localization and addressability of ultra cold atoms in a
combined parabolic and periodic potential. Such a potential supports the
existence of localized stationary states and we show that using a radio
frequency field allows to selectively address the atoms in these states. This
method is used to measure the energy and momentum distribution of the atoms in
the localized states. We also discuss possible extensions of this scheme to
address and manipulate particles in single lattice sites.Comment: 4 pages, 4 figure
Subnanosecond spectral diffusion measurement using photon correlation
Spectral diffusion is a result of random spectral jumps of a narrow line as a
result of a fluctuating environment. It is an important issue in spectroscopy,
because the observed spectral broadening prevents access to the intrinsic line
properties. However, its characteristic parameters provide local information on
the environment of a light emitter embedded in a solid matrix, or moving within
a fluid, leading to numerous applications in physics and biology. We present a
new experimental technique for measuring spectral diffusion based on photon
correlations within a spectral line. Autocorrelation on half of the line and
cross-correlation between the two halves give a quantitative value of the
spectral diffusion time, with a resolution only limited by the correlation
set-up. We have measured spectral diffusion of the photoluminescence of a
single light emitter with a time resolution of 90 ps, exceeding by four orders
of magnitude the best resolution reported to date
Anomalous circular polarization of magneto-photoluminescence from individual CdSe nanocrystals
We study the low-temperature magneto-photoluminescence (PL) from individual
CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure
splitting (0.5 meV) exhibit a conventional left- and right-circularly
polarized Zeeman PL doublet in applied magnetic fields. In contrast,
nanocrystals with large fine structure splitting (1 meV) show an anomalous
magneto-PL polarization, wherein the lower-energy peak becomes circularly
polarized with increasing field, while the higher-energy peak remains linearly
polarized. This unusual behavior arises from strong mixing between the
absorbing and emitting bright exciton levels due to strong anisotropic exchange
interactions.Comment: 15 pages, 3 figures; submitte
Purification and Activity Testing of the Full-Length YycFGHI Proteins of Staphylococcus aureus
Background: The YycFG two-component regulatory system (TCS) of Staphylococcus aureus represents the only essential TCS that is almost ubiquitously distributed in Gram-positive bacteria with a low G+C-content. YycG (WalK/VicK) is a sensor histidine-kinase and YycF (WalR/VicR) is the cognate response regulator. Both proteins play an important role in the biosynthesis of the cell envelope and mutations in these proteins have been involved in development of vancomycin and daptomycin resistance. Methodology/Principal Findings: Here we present high yield expression and purification of the full-length YycG and YycF proteins as well as of the auxiliary proteins YycH and YycI of Staphylococcus aureus. Activity tests of the YycG kinase and a mutated version, that harbours an Y306N exchange in its cytoplasmic PAS domain, in a detergent-micelle-model and a phosholipid-liposome-model showed kinase activity (autophosphorylation and phosphoryl group transfer to YycF) only in the presence of elevated concentrations of alkali salts. A direct comparison of the activity of the kinases in the liposomemodel indicated a higher activity of the mutated YycG kinase. Further experiments indicated that YycG responds to fluidity changes in its microenvironment. Conclusions/Significance: The combination of high yield expression, purification and activity testing of membrane and membrane-associated proteins provides an excellent experimental basis for further protein-protein interaction studies an
Rewritable photonic circuits
The authors present a technique that allows to modify the local characteristics of two-dimensional photonic crystals by controlled microinfiltration of liquids. They demonstrate experimentally that by addressing and infiltrating each pore with a simple liquid, e.g., water, it is possible to write pixel by pixel optical devices of any geometry and shape. Calculations confirm that the obtained structures indeed constitute the desired resonators and waveguide structures. © 2006 American Institute of Physics
Copper (I) Oxide (Cu2O) based back contact for p-i-n CdTe solar cells
In this paper a promising solution for the notorious problem of manufacturing a stable low ohmic back contact of a CdTe thin film superstrate solar cell is presented without using elemental copper. Instead we have used a Cu2O layer inserted between the CdTe absorber and metal contact (Au). In contrast to the barrier free band alignment gained by using the transitivity rules, XPS measurements show a barrier in the valence band of the Cu2O layers directly after deposition, which results in a low performing JV curve. The contact can be improved by a short thermal treatment resulting in efficiencies superior to copper based contacts for standard CdS/CdTe hetero junction solar cells prepared on commercial glass/FTO substrates. By replacing the CdS window layer with a CdS:O buffer layer efficiencies of >15% could be achieved
Multitarget thiol-activated tetrapyridyl gold(III) complexes for hypoxic cancer therapy
Metals in Catalysis, Biomimetics & Inorganic MaterialsPharmacologyMedicinal Chemistr
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