1,848 research outputs found
NONLINEAR POLARIZATION SPECTROSCOPY (FREQUENCY DOMAIN) STUDIES OF EXCITED STATE PROCESSES: THE B800â850ANTENNA OF RHODOBACTER SPHAEROIDES
Nonlinear polarization spectroscopy in the frequency domain allows rate constant determinations of fast electronic energy and phase relaxations together with characterization of the type of line broadening. Application of this method to the B850 component of the isolated B800â850antenna ofRhodobacter sphaeroides at room temperature shows that B850 is inhomogeneously broadened, with homogeneous widths between 30 and 200 cmâ1, depending on the spectral position of the subforms. The corresponding phase relaxation times are clearly in the subpicosecond range. There is also indication of an up-to-now unspecified1â5 ps energy relaxation channel per subunit
Multiple Andreev reflections as a transport problem in energy space
We present an approach for analyzing the dc current in voltage biased quantum
superconducting junctions. By separating terms from different -particle
processes, we find that the -particle current can be mapped on the problem
of wave transport through a potential structure with barriers. We discuss
the relation between resonances in such structures and the subgap structures in
the current-voltage characteristics. At zero temperature we find, exactly, that
only processes creating real excitations contribute to the current. Our results
are valid for a general SXS-junction, where the X-region is an arbitrary
non-superconducting region described by an energy-dependent transfer matrix.Comment: 11 pages, 4 figures, submitted to Superlattices and Microstructure
Regionale voedselketen : eindrapportage fase I
Sinds 2005 wordt door Ruraal Park en Groene Hoed gewerkt aan het opzetten van een volledige regionale keten voor versproducten in de regio Amsterdam. Ter realisatie van het regionale keten concept hebben Ruraal Park en Groene Hoed samengewerkt met verswinkel Marqt. Inmiddels is de opening van een eerste winkel in Amsterdam bewerkstelligd. Producenten zijn hiermee niet langer de uitwisselbare factor in de productieketen. Agrarische producenten zijn verenigd in een stichting, die partner is binnen een marktformule waar met name verse producten uit de regio worden aangeboden. Er is een nieuwe, stabiele productieketen van regionaal geproduceerde producten gerealiseerd. Deze rapportage beschrijft de opzet van het project âRegionale keten versproductenâ en beschrijft welke werkzaamheden zijn verricht. Speciale aandacht wordt geschonken aan opgedane ervaringen, lessen en inzichten die generiek en daarmee overdraagbaar zijn
FLUORESCENCE AND CIRCULAR DICHROISM STUDIES ON THE PHYCOERYTHROCYANINS FROM THE CYANOBACTERIUM
Two phycoerythrocyanin (PEC) fractions have been obtained from the phycobilisomes of the cyanobac-terium Westiellopsis prolifica ARM 365. They have been characterized by absorption, fluorescence and circular dichroism spectroscopy. One of them is spectroscopically similar to a PEC trimer known from other organisms. Whereas efficient energy transfer from its violin (α-84) to the cyanin (ÎČ-84, 155) chromophores is efficient in the trimer (αÎČ it is impeded after dissociation to the monomer (α,ÎČ). A second fraction of PEC which we earlier termed PEC(X) (Maruthi Sai et al., Photochem. Photobiol. 55,119â124, 1992), exhibited the spectral properties similar to that of the α-subunit of PEC from Mastigocladus laminosus. With this highly photoactive fraction, the circular dichroism spectra of the violobilin chromophore in both photoreversible states were obtained
Single-channel transmission in gold one-atom contacts and chains
We induce superconductivity by proximity effect in thin layers of gold and
study the number of conduction channels which contribute to the current in
one-atom contacts and atomic wires. The atomic contacts and wires are
fabricated with a Scanning Tunneling Microscope. The set of transmission
probabilities of the conduction channels is obtained from the analysis of the
characteristic curve which is highly non-linear due to multiple Andreev
reflections. In agreement with theoretical calculations we find that there is
only one channel which is almost completely open.Comment: 4 pages, 2 figures. To be published in Phys. Rev. B, Rapid
Communications (2003
Transitions between "" and "0" states in superconductor -- ferromagnet -- superconductor junctions
Experimental and theoretical study of superconductor (S) -- ferromagnet (F)
-- superconductor junctions showed that in certain range of parameters (e.g.,
the length of the ferromagnet , the exchange field, ) the
ground state of a SFS junction corresponds to superconducting phase difference
or 0. The phase diagram of a SFS junction with the respect to and 0
states is investigated in this letter in space. It is
shown that the phase diagram is very sensitive to the geometry of the system,
in particular, to the amount of disorder.Comment: Minor changes. References adde
Non-equilibrium current noise in mesoscopic disordered SNS junctions
Current noise in superconductor-normal metal-superconductor (SNS) junctions
is calculated within the scattering theory of multiple Andreev reflections
(MAR). It is shown that the noise exhibits subharmonic gap singularities at
, both in single-mode junctions with arbitrary
transparency and in multi-mode disordered junctions. The subharmonic
structure is superimposed with monotonic increase of the effective transferred
charge with decreasing bias voltage. Other features of the
noise include a step-like increase of in junctions with small , and a
divergence at small voltages and excess noise , where is the excess current, at large voltages, in
junctions with diffusive transport.Comment: 5 page
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