2,969 research outputs found
A range expanding signal conditioner
Telemetry system modifications to improve signal resolution are described. Process uses zero suppression technique which consists of subtracting known voltage from input and amplifying remainder. Schematic diagram of circuit is provided and details of operation are presented
The Dynamic Transition of Protein Hydration Water
Thin layers of water on biomolecular and other nanostructured surfaces can be
supercooled to temperatures not accessible with bulk water. Chen et al. [PNAS
103, 9012 (2006)] suggested that anomalies near 220 K observed by quasi-elastic
neutron scattering can be explained by a hidden critical point of bulk water.
Based on more sensitive measurements of water on perdeuterated phycocyanin,
using the new neutron backscattering spectrometer SPHERES, and an improved data
analysis, we present results that show no sign of such a fragile-to-strong
transition. The inflection of the elastic intensity at 220 K has a dynamic
origin that is compatible with a calorimetric glass transition at 170 K. The
temperature dependence of the relaxation times is highly sensitive to data
evaluation; it can be brought into perfect agreement with the results of other
techniques, without any anomaly.Comment: 4 pages, 3 figures. Phys. Rev. Lett. (in press
Carotenoid triplet state formation in Rhodobacter sphaeroides R-26 reaction centers exchanged with modified bacteriochlorophyll pigments and reconstituted with spheroidene
Triplet state electron paramagnetic resonance (EPR) experiments have been carried out at X-band on Rb. sphaeroides R-26 reaction centers that have been reconstituted with the carotenoid, spheroidene, and exchanged with 132-OH-Zn-bacteriochlorophyll a and [3-vinyl]-132-OH-bacteriochlorophyll a at the monomeric, lsquoaccessoryrsquo bacteriochlorophyll sites BA,B or with pheophytin a at the bacteriopheophytin sites HA,B. The primary donor and carotenoid triplet state EPR signals in the temperature range 95–150 K are compared and contrasted with those from native Rb. sphaeroides wild type and Rb. sphaeroides R-26 reaction centers reconstituted with spheroidene. The temperature dependencies of the EPR signals are strikingly different for the various samples. The data prove that triplet energy transfer from the primary donor to the carotenoid is mediated by the monomeric, BChlB molecule. Furthermore, the data show that triplet energy transfer from the primary donor to the carotenoid is an activated process, the efficiency of which correlates with the estimated triplet state energies of the modified pigments
Conduction Channels of One-Atom Zinc Contacts
We have determined the transmission coefficients of atomic-sized Zn contacts
using a new type of breakjunction which contains a whisker as a central bridge.
We find that in the last conductance plateau the transport is unexpectedly
dominated by a well-transmitting single conduction channel. We explain the
experimental findings with the help of a tight-binding model which shows that
in an one-atom Zn contact the current proceeds through the 4s and 4p orbitals
of the central atom.Comment: revtex4, 5 pages, 5 figure
Controlled dephasing of Andreev states in superconducting quantum point-contacts
We have studied the relaxation and dephasing processes in a superconducting
quantum point contact induced by the interaction with an electromagnetic
environment. Based on a density matrix approach we obtain the rates for the
dissipative dynamics as function of the transmission, the phase difference on
the contact and the external impedance. Our calculation allows to determine the
appropriate range of parameters for the observation of coherent oscillations in
the current through the contact.Comment: 8 pages, 2 figures. To appear in Physical Review
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