5,523 research outputs found
Sample-specific and Ensemble-averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes
We discuss magnetotransport measurements on individual single-wall carbon
nanotubes with low contact resistance, performed as a function of temperature
and gate voltage. We find that the application of a magnetic field
perpendicular to the tube axis results in a large magnetoconductance of the
order of e^2/h at low temperature. We demonstrate that this magnetoconductance
consists of a sample-specific and of an ensemble-averaged contribution, both of
which decrease with increasing temperature. The observed behavior resembles
very closely the behavior of more conventional multi-channel mesoscopic wires,
exhibiting universal conductance fluctuations and weak localization. A
theoretical analysis of our experiments will enable to reach a deeper
understanding of phase-coherent one-dimensional electronic motion in SWNTs.Comment: Replaced with published version. Minor changes in tex
Spin-dependent Quantum Interference in Single-Wall Carbon Nanotubes with Ferromagnetic Contacts
We report the experimental observation of spin-induced magnetoresistance in
single-wall carbon nanotubes contacted with high-transparency ferromagnetic
electrodes. In the linear regime the spin-induced magnetoresistance oscillates
with gate voltage in quantitative agreement with calculations based on a
Landauer-Buttiker model for independent electrons. Consistent with this
interpretation, we find evidence for bias-induced oscillation in the
spin-induced magnetoresistance signal on the scale of the level spacing in the
nanotube. At higher bias, the spin-induced magnetoresistance disappears because
of a sharp decrease in the effective spin-polarization injected from the
ferromagnetic electrodes.Comment: Replaced with published versio
Simulation and analysis of in vitro DNA evolution
We study theoretically the in vitro evolution of a DNA sequence by binding to
a transcription factor. Using a simple model of protein-DNA binding and
available binding constants for the Mnt protein, we perform large-scale,
realistic simulations of evolution starting from a single DNA sequence. We
identify different parameter regimes characterized by distinct evolutionary
behaviors. For each regime we find analytical estimates which agree well with
simulation results. For small population sizes, the DNA evolutional path is a
random walk on a smooth landscape. While for large population sizes, the
evolution dynamics can be well described by a mean-field theory. We also study
how the details of the DNA-protein interaction affect the evolution.Comment: 11 pages, 11 figures. Submitted to PNA
Evidence for sub-Chandrasekhar Type Ia supernovae from the last major merger
We investigate the contribution of sub-Chandrasekhar mass Type Ia supernovae
to the chemical enrichment of the Gaia Sausage galaxy, the progenitor of a
significant merger event in the early life of the Milky Way. Using a
combination of data from Nissen & Schuster (2010), the 3rd GALAH data release
(with 1D NLTE abundance corrections) and APOGEE data release 16, we fit
analytic chemical evolution models to a 9-dimensional chemical abundance space
(Fe, Mg, Si, Ca, Cr, Mn, Ni, Cu, Zn) in particular focusing on the iron-peak
elements, Mn and Ni. We find that low [Mn/Fe] and low
[Ni/Fe] Type Ia yields are required to explain the
observed trends beyond the [/Fe] knee of the Gaia Sausage
(approximately at [Fe/H] ). Comparison to theoretical
yield calculations indicate a significant contribution from sub-Chandrasekhar
mass Type Ia supernovae in this system (from % to % depending on
the theoretical model with an additional % systematic from NLTE
corrections). We compare to results from other Local Group environments
including dwarf spheroidal galaxies, the Magellanic Clouds and the Milky Way's
bulge, finding the Type Ia [Mn/Fe] yield must be metallicity-dependent. Our
results suggest that sub-Chandrasekhar mass channels are a significant, perhaps
even dominant, contribution to Type Ia supernovae in metal-poor systems, whilst
more metal-rich systems could be explained by metallicity-dependent
sub-Chandrasekhar mass yields, possibly with additional progenitor mass
variation related to star formation history, or an increased contribution from
Chandrasekhar mass channels at higher metallicity.Comment: 23 pages, 12 figures, resubmitted to MNRAS following referee's
comment
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
A Simultaneous Quantum Secure Direct Communication Scheme between the Central Party and Other M Parties
We propose a simultaneous quantum secure direct communication scheme between
one party and other three parties via four-particle GHZ states and swapping
quantum entanglement. In the scheme, three spatially separated senders, Alice,
Bob and Charlie, transmit their secret messages to a remote receiver Diana by
performing a series local operations on their respective particles according to
the quadripartite stipulation. From Alice, Bob, Charlie and Diana's Bell
measurement results, Diana can infer the secret messages. If a perfect quantum
channel is used, the secret messages are faithfully transmitted from Alice, Bob
and Charlie to Diana via initially shared pairs of four-particle GHZ states
without revealing any information to a potential eavesdropper. As there is no
transmission of the qubits carrying the secret message in the public channel,
it is completely secure for the direct secret communication. This scheme can be
considered as a network of communication parties where each party wants to
communicate secretly with a central party or server.Comment: 4 pages, no figur
Sine-Gordon Field Theory for the Kosterlitz-Thouless Transitions on Fluctuating Membranes
In the preceding paper, we derived Coulomb-gas and sine-Gordon Hamiltonians
to describe the Kosterlitz-Thouless transition on a fluctuating surface. These
Hamiltonians contain couplings to Gaussian curvature not found in a rigid flat
surface. In this paper, we derive renormalization-group recursion relations for
the sine-Gordon model using field-theoretic techniques developed to study flat
space problems.Comment: REVTEX, 14 pages with 6 postscript figures compressed using uufiles.
Accepted for publication in Phys. Rev.
Confinement Models at Finite Temperature and Density
In-medium chiral symmetry breaking in confining potential models of QCD is
examined. Past attempts to analyse these models have been hampered by infrared
divergences that appear at non-zero temperature. We argue that previous
attempts to circumvent this problem are not satisfactory and demonstrate a
simple resolution. We also show that the expectation that confining models do
not exhibit a chiral phase transition is incorrect. The effect of summing ring
diagrams is investigated and we present the first determination of the
temperature-density phase diagram for two model systems. We find that
observables and the phase structure of the confinement models depend strongly
on whether quark polarisation is accounted for. Finally, it appears that
standard confinement models cannot adequately describe both hadron
phenomenology and in-medium properties of QCD.Comment: 9 pages, 10 figures. Version to appear in PR
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