79 research outputs found
14N and 15N coupling constants of the oxidized primary donor P-860 of bacterial photosynthesis obtained by electron spin echo envelope modulation spectroscopy
An electron spin echo modulation frequency analysis of P+-860 is performed in 14N chromatophores of Rhodospirillum rubrum, and in 15N substituted reaction centers from Rhodopseudomonas sphaeroides 2.4.1. For the 14N material two sets of nuclear quadrupole parameters are obtained. From the frequencies found for 15N reaction centers the perpendicular, parallel and isotropic hyperfine previous termcouplingnext term constants of three of the four bacteriochlorophyll nitrogen nuclei are inferred
Establishing Telepathology in Africa: Lessons From Botswana
Few reports of telepathology in Africa exist in the medical literature. With the strong need for improvement in health care infrastructure and personnel training in many African nations, telepathology provides a rapid and versatile tool to improve clinical care and foster educational and research opportunities. We describe the challenges faced in establishing robotic telepathology (RT) services at a government referral center in Botswana and reflect on conditions under which such initiatives may be most likely to succeed in sub-Saharan Africa and other parts of the developing world
DC current through a superconducting two-barrier system
We analyze the influence of the structure within a SNS junction on the
multiple Andreev resonances in the subgap I-V characteristics. Coherent
interference processes and incoherent propagation in the normal region are
considered. The detailed geometry of the normal region where the voltage drops
in superconducting contacts can lead to observable effects in the conductance
at low voltages.Comment: 11 pages, including 7 postscript file
Hamiltonian approach to the ac Josephson effect in superconducting-normal hybrid systems
The ac Josephson effect in hybrid systems of a normal mesoscopic conductor
coupled to two superconducting (S) leads is investigated theoretically. A
general formula of the ac components of time-dependent current is derived which
is valid for arbitrary interactions in the normal region. We apply this formula
to analyze a S-normal-S system where the normal region is a noninteracting
single level quantum dot. We report the physical behavior of time-averaged
nonequilibrium distribution of electrons in the quantum dot, the formation of
Andreev bound states, and ac components of the time-dependent current. The
distribution is found to exhibit a population inversion; and all Andreev bound
states between the superconducting gap carry the same amount of
current and in the same flow direction. The ac components of time-dependent
current show strong oscillatory behavior in marked contrast to the subharmonic
gap structure of the average current.Comment: 23 pages, 10 figures, LaTe
Theory of AC Josepson Effect in Superconducting Constrictions
We have developed a microscopic theory of ac Josephson effect in short
ballistic superconducting constrictions with arbitrary electron transparency
and in constrictions with diffusive electron transport. The theory is valid for
arbitrary miscroscopic structure of the superconducting electrodes of the
constriction. As applications of the theory we study smearing of the subgap
current singularities by pair-breaking effects and also the structure of these
singularities in the constrictions between the composite S/N electrodes with
the proximity-induced gap in the normal layer.Comment: 11 pages, RevTex, 3 figures available on reques
Surface and Temporal Biosignatures
Recent discoveries of potentially habitable exoplanets have ignited the
prospect of spectroscopic investigations of exoplanet surfaces and atmospheres
for signs of life. This chapter provides an overview of potential surface and
temporal exoplanet biosignatures, reviewing Earth analogues and proposed
applications based on observations and models. The vegetation red-edge (VRE)
remains the most well-studied surface biosignature. Extensions of the VRE,
spectral "edges" produced in part by photosynthetic or nonphotosynthetic
pigments, may likewise present potential evidence of life. Polarization
signatures have the capacity to discriminate between biotic and abiotic "edge"
features in the face of false positives from band-gap generating material.
Temporal biosignatures -- modulations in measurable quantities such as gas
abundances (e.g., CO2), surface features, or emission of light (e.g.,
fluorescence, bioluminescence) that can be directly linked to the actions of a
biosphere -- are in general less well studied than surface or gaseous
biosignatures. However, remote observations of Earth's biosphere nonetheless
provide proofs of concept for these techniques and are reviewed here. Surface
and temporal biosignatures provide complementary information to gaseous
biosignatures, and while likely more challenging to observe, would contribute
information inaccessible from study of the time-averaged atmospheric
composition alone.Comment: 26 pages, 9 figures, review to appear in Handbook of Exoplanets.
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