1,687 research outputs found
Wave function engineering in quantum dot-ring nanostructures
Modern nanotechnology allows producing, depending on application, various
quantum nanostructures with the desired properties. These properties are
strongly influenced by the confinement potential which can be modified, e.g.,
by electrical gating. In this paper we analyze a nanostructure composed of a
quantum dot surrounded by a quantum ring. We show that depending on the details
of the confining potential the electron wave functions can be located in
different parts of the structure. Since the properties of such a nanostructure
strongly depend on the distribution of the wave functions, varying the applied
gate voltage one can easily control them. In particular, we illustrate the high
controllability of the nanostructure by demonstrating how its coherent,
optical, and conducting properties can be drastically changed by a small
modification of the confining potential.Comment: 8 pages, 10 figures, 2 tables, revte
The applications of satellites to communications, navigation and surveillance for aircraft operating over the contiguous United States. Volume 1 - Technical report
Satellite applications to aircraft communications, navigation, and surveillance over US including synthesized satellite network and aircraft equipment for air traffic contro
Coherent phenomena in mesoscopic systems
A mesoscopic system of cylindrical geometry made of a metal or a
semiconductor is shown to exhibit features of a quantum coherent state. It is
shown that magnetostatic interaction can play an important role in mesoscopic
systems leading to an ordered ground state. The temperature below the
system exhibits long-range order is determined. The self-consistent mean field
approximation of the magnetostatic interaction is performed giving the
effective Hamiltonian from which the self-sustaining currents can be obtained.
The relation of quantum coherent state in mesoscopic cylinders to other
coherent systems like superconductors is discussed.Comment: REVTeX, 4 figures, in print in Supercond. Sci. Techno
African Water: Supporting African involvement in the EU Framework Programme.
Water researchers in developing countries have yet to take full advantage of the funding and collaborative research opportunities presented by the EU Framework Programme. There are a variety of reasons for this, such as insufficient information and a lack of previous experience. The African Water initiative aims to increase the involvement of African water researchers through a range of activities including communication and dissemination, capacity building and development, and complementary initiatives. The project has demonstrated that there is a demand for such sector-specific support activities. However, African Water is a small component of a much larger process of partnership between the developed and the less-developed countries of the world, involving many different European and African organisations working across political, institutional and technical domains, and complementing the wide range of actions already being undertaken
Natural radioactivity of groundwater from the Przerzeczyn-Zdrój Spa
The present authors performed investigations of natural radioactivity in groundwater from the Przerzeczyn-
-Zdrój Spa. Some of the waters are regarded as medical and are used for balneological purposes. Samples from seven groundwater intakes were collected 5 times over a period of 8 years (1999–2007). In order to obtain necessary data, two different nuclear spectrometry techniques were applied: α spectrometry and liquid scintillation spectrometry. The activity concentrations of 222Rn varied in the range from 15±2 Bq/l to 154±22 Bq/l. The results of activity concentrations of 226,228Ra varied from below 10 mBq/l to 30±1.5 mBq/l and from below 30 mBq/l to 60±4 mBq/l, respectively. Activity concentration lower than minimum detectable activity (MDA) was obtained for 3 samples for 226Ra and 4 for 228Ra determinations out of 7 investigated samples. The uranium content in the studied samples was determined once and the value ranged from 4.5±0.6 mBq/l to 13.6±1.2 mBq/l for 238U and from 17.1±0.9 mBq/l to 52.2±2.8 mBq/l for 234U. All obtained values for uranium isotopes showed activity concentrations above MDA. The activity ratios 234U/238U, 222Rn/226Ra and 226Ra/238U and the correlations between different isotopes concentrations were evaluated
Extraction of level density and gamma strength function from primary gamma spectra
We present a new iterative procedure to extract the level density and the
gamma strength function from primary gamma spectra for energies close up to the
neutron binding energy. The procedure is tested on simulated spectra and on
data from the Yb-173(He-3,alpha)Yb-172 reaction.Comment: 23 pages including 1 table and 7 figure
Possibility of long-range order in clean mesoscopic cylinders
A microscopic Hamiltonian of the magnetostatic interaction is discussed. This
long-range interaction can play an important role in mesoscopic systems leading
to an ordered ground state.
The self-consistent mean field approximation of the magnetostatic interaction
is performed to give an effective Hamiltonian from which the spontaneous,
self-sustaining currents can be obtained.
To go beyond the mean field approximation the mean square fluctuation of the
total momentum is calculated and its influence on self-sustaining currents in
mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then,
by the use of the microscopic Hamiltonian of the magnetostatic interaction for
a set of stacked rings, the problem of long-range order is discussed. The
temperature below which the system is in an ordered state is
determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.
Entanglement of qubits via a nonlinear resonator
Coherent coupling of two qubits mediated by a nonlinear resonator is studied.
It is shown that the amount of entanglement accessible in the evolution depends
both on the strength of nonlinearity in the Hamiltonian of the resonator and on
the initial preparation of the system. The created entanglement survives in the
presence of decoherence.Comment: 6 pages, 10 figure
Investigation of large angle elastic and inelastic alpha particles scattering on Si isotopes
The distributions of differential cross sections for backward angles in
case of three (28,20,3OSi) silicon isotopes were measured for five energies
around 27 MeV. The comparison between existing data and measured
data was done. Quantitative analysis of the data was made
Mechanism of peptide-induced mast cell degranulation: translocation and patch clamp studies.
Substance P and other polycationic peptides are thought to stimulate mast cell degranulation via direct activation of G proteins. We investigated the ability of extracellularly applied substance P to translocate into mast cells and the ability of intracellularly applied substance P to stimulate degranulation. In addition, we studied by reverse transcription--PCR whether substance P-specific receptors are present in the mast cell membrane. To study translocation, a biologically active and enzymatically stable fluorescent analogue of substance P was synthesized. A rapid, substance P receptor- and energy-independent uptake of this peptide into pertussis toxin-treated and -untreated mast cells was demonstrated using confocal laser scanning microscopy. The peptide was shown to localize preferentially on or inside the mast cell granules using electron microscopic autoradiography with 125I-labeled all-D substance P and 3H-labeled substance P. Cell membrane capacitance measurements using the patch-clamp technique demonstrated that intracellularly applied substance P induced calcium transients and activated mast cell exocytosis with a time delay that depended on peptide concentration (delay of 100-500 s at concentrations of substance P from 50 to 5 microM). Degranulation in response to intracellularly applied substance P was inhibited by GDPbetaS and pertussis toxin, suggesting that substance P acts via G protein activation. These results support the recently proposed model of a receptor-independent mechanism of peptide-induced mast cell degranulation, which assumes a direct interaction of peptides with G protein alpha subunits subsequent to their translocation across the plasma membrane
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