793 research outputs found
Parity-Affected Persistent Currents in Superconducting Nanorings
We argue that at sufficiently low temperatures T superconducting parity
effect may strongly influence equilibrium persistent currents (PC) in isolated
superconducting nanorings containing a weak link with few conducting modes. For
a single channel quantum point contact at T=0 we predict a novel effect of
parity-induced blocking of PC. In nanorings with SNS junctions a -state
can occur for the odd number of electrons. Changing this number from even to
odd yields spontaneous supercurrent in the ground state of such rings without
any externally applied magnetic flux.Comment: Published versio
Pauli-principle driven correlations in four-neutron nuclear decays
Mechanism of simultaneous non-sequential four-neutron () emission (or
`true' -decay) has been considered in phenomenological five-body approach.
This approach is analogous to the model of the direct decay to the continuum
often applied to - and -decays. It is demonstrated that -decay
fragments should have specific energy and angular correlations reflecting
strong spatial correlations of `valence' nucleons orbiting in their
-precursors. Due to the Pauli exclusion principle, the valence neutrons are
pushed to the symmetry-allowed configurations in the -precursor structure,
which causes a `Pauli focusing' effect. Prospects of the observation of the
Pauli focusing have been considered for the -precursors H and O.
Fingerprints of their nuclear structure or/and decay dynamics are predicted
Anomalous population of He states in reactions with Li
Structure with the lowest energy observed in the He spectrum populated
in the proton knockout reaction with Li beam has a peak at
MeV. This peak is usually interpreted as a resonant ground state of
He. Our theoretical calculations indicate that this peak is likely to be
a pileup of , , and excitations with very similar shapes. %We
predict a very specific nature of the excitation in He. Moreover,
the ``soft'' excitation appears to be the lowest one in energy. Such an
anomalous continuum response is traced to the halo structure of Li
providing extreme low energy shift to all the expected continuum excitations.
Competitions of the initial state structure (ISS) and the final state
interaction (FSI) effects on the spectrum and three-body correlations in
He are discussed. Analogous effect of the extreme low-energy shift could
also be expected in other cases of emitters populated in reactions with
halo nuclei. Simplified example of the He spectrum in knockout
from Be, is given. We also discuss limits on the properties of He
stemming from the observed He spectrum.Comment: 10 pages, 13 figure
Dephasing time and magnetoresistance of two-dimensional electron gas in spatially modulated magnetic fields
The effect of a spatially modulated magnetic field on the weak localization
phenomenon in two-dimensional electron gas (2DEG) is studied. Both the
dephasing time and magnetoresistance are shown to reveal a nontrivial
behavior as functions of the characteristics of magnetic field profiles. The
magnetic field profiles with rather small spatial scales and modulation
amplitudes such that are characterized by the
dephasing rate . The increase in the flux value
results in a crossover to a standard linear dependence
. Applying an external homogeneous magnetic field
one can vary the local dephasing time in the system and affect the resulting
average transport characteristics. We have investigated the dependence of the
average resistance vs the field for some generic systems and predict a
possibility to observe a positive magnetoresistance at not too large
values. The resulting dependence of the resistance vs should reveal a peak
at the field values .Comment: 12 pages, 5 figure
Incidence of "quasi-ditags" in catalogs generated by Serial Analysis of Gene Expression (SAGE)
BACKGROUND: Serial Analysis of Gene Expression (SAGE) is a functional genomic technique that quantitatively analyzes the cellular transcriptome. The analysis of SAGE libraries relies on the identification of ditags from sequencing files; however, the software used to examine SAGE libraries cannot distinguish between authentic versus false ditags ("quasi-ditags"). RESULTS: We provide examples of quasi-ditags that originate from cloning and sequencing artifacts (i.e. genomic contamination or random combinations of nucleotides) that are included in SAGE libraries. We have employed a mathematical model to predict the frequency of quasi-ditags in random nucleotide sequences, and our data show that clones containing less than or equal to 2 ditags (which include chromosomal cloning artifacts) should be excluded from the analysis of SAGE catalogs. CONCLUSIONS: Cloning and sequencing artifacts contaminating SAGE libraries could be eliminated using simple pre-screening procedure to increase the reliability of the data
Parity effect and spontaneous currents in superconducting nanorings
New physical effects emerge from an interplay between the electron parity
number and persistent currents in superconducting nanorings. An odd electron,
being added to the ring, produces a countercurrent which may substantially
modify the ground state properties of the system. In superconducting nanorings
with an embedded normal metal layer a novel ``-junction'' state can
occur for the odd number of electrons. Changing this number from even to odd
yields spontaneous supercurrent in the ground state of such rings without any
externally applied magnetic flux. Further peculiar features of the parity
effect are expected in structures with resonant electron transport across the
weak link.Comment: 9 pages, 5 figures. Invited talk at the International Conference
"Frontiers of Quantum and Mesoscopic Thermodynamics", Prague, July 200
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