472 research outputs found
Controlling quantum transport through a single molecule
We investigate multi-terminal quantum transport through single monocyclic
aromatic annulene molecules, and their derivatives, using the nonequilibrium
Green function approach in the self-consistent Hartree-Fock approximation. A
new device concept, the Quantum Interference Effect Transistor (QuIET) is
proposed, exploiting perfect destructive interference stemming from molecular
symmetry, and controlling current flow by introducing decoherence and/or
elastic scattering that break the symmetry. This approach overcomes the
fundamental problems of power dissipation and environmental sensitivity that
beset many nanoscale device proposals.Comment: 4 pages, 5 figure
Universality of Decay out of Superdeformed Bands in the 190 Mass Region
Superdeformed nuclei in the 190 mass region exhibit a striking universality
in their decay-out profiles. We show that this universality can be explained in
the two-level model of superdeformed decay as related to a strong separation of
energy scales: a higher scale related to the nuclear interactions, and a lower
scale caused by electromagnetic decay. Furthermore, we present the results of
the two-level model for all decays for which sufficient data are known,
including statistical extraction of the matrix element for tunneling through
the potential barrier.Comment: 7 pages, 3 figures. v2: some minor clarifications, minor correction
to Fig.
Moderate-Luminosity Growing Black Holes From 1.25 < z < 2.7: Varied Accretion In Disk-Dominated Hosts
We compute black hole masses and bolometric luminosities for 57 active
galactic nuclei (AGN) in the redshift range 1.25 < z < 2.67, selected from the
GOODS-South deep multi-wavelength survey field via their X-ray emission. We
determine host galaxy morphological parameters by separating the galaxies from
their central point sources in deep HST images, and host stellar masses and
colors by multi-wavelength SED fitting. 90% of GOODS AGN at these redshifts
have detected rest-frame optical nuclear point sources; bolometric luminosities
range from 2e43 - 2e46 erg/s. The black holes are growing at a range of
accretion rates, with at least 50% of the sample having L/L_Edd < 0.1. 70% of
host galaxies have stellar masses M* > 1e10 M_sun, with a range of colors
suggesting a complex star formation history. We find no evolution of AGN
bolometric luminosity within the sample, and no correlation between AGN
bolometric luminosity and host stellar mass, color or morphology. Fully half
the sample of host galaxies is disk-dominated, with another 25% having strong
disk components. Fewer than 15% of the systems appear to be at some stage of a
major merger. These moderate-luminosity AGN hosts are therefore inconsistent
with a dynamical history dominated by mergers strong enough to destroy disks,
indicating minor mergers or secular processes dominate the co-evolution of
galaxies and their central black holes at z ~ 2.Comment: 11 pages, 6 figures, accepted to ApJ. Sersic indices, AGN/galaxy
luminosity ratios, stellar masses etc. provided in Table
How to measure the spreading width for decay of superdeformed nuclei
A new expression for the branching ratio for the decay via the E1 process in
the normal-deformed band of superdeformed nuclei is given within a simple
two-level model. Using this expression, the spreading or tunneling width
Gamma^downarrow for superdeformed decay can be expressed entirely in terms of
experimentally known quantities. We show how to determine the tunneling matrix
element V from the measured value of Gamma^downarrow and a statistical model of
the energy levels. The accuracy of the two-level approximation is verified by
considering the effects of the other normal-deformed states.Comment: 4 pages, 4 figure
The Potential Of High-Resolution BAC-FISH In Banana Breeding
Abstract The genetic complexity in the genus Musa has been subject of study in many breeding programs worldwide. Parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. In addition, it is known that part of the cultivars and related wild species in the genus contain numerous chromosomal rearrangements. In order to produce new cultivars more effectively breeders must better understand the genetic differences of the potential crossing parents for introgression hybridization, but extensive genetic information is lacking. As an alternative to achieve information on genetic collinearity we make use of modern chromosome map technology known as high-resolution fluorescent in situ hybridization (FISH). This article presents the technical aspects and applications of such a technology in Musa species. The technique deals with BAC clone positioning on pachytene chromosomes of Calcutta 4 (Musa acuminata ssp. burmanicoides, A genome group, section Eumusa) and M. velutina (section Rodochlamys). Pollen mother cells digestion with pectolytic enzymes and maceration with acetic acid were optimized for making cell spread preparations appropriate for FISH. As an example of this approach we chose BAC clones that contain markers to known resistance genes and hybridize them for establishing their relative positions on the two species. Technical challenges for adapting existing protocols to the banana cells are presented. We also discuss how this technique can be instrumental for validating collinearity between potential crossing parents and how the method can be helpful in future mapping initiatives, and how this method allows identification of chromosomal rearrangements between related Musa species and cultivar
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