2,964 research outputs found
Reciprocal and non-reciprocal recombination between closely linked markers
Reciprocal and non-reciprocal recombination between closely linked marker
Evidence for a single hydrogen molecule connected by an atomic chain
Stable, single-molecule conducting-bridge configurations are typically
identified from peak structures in a conductance histogram. In previous work on
Pt with H at cryogenic temperatures it has been shown that a peak near 1
identifies a single molecule Pt-H-Pt bridge. The histogram shows
an additional structure with lower conductance that has not been identified.
Here, we show that it is likely due to a hydrogen decorated Pt chain in contact
with the H molecular bridge.Comment: 4 pages, 4 figure
Metastable States in High Order Short-Range Spin Glasses
The mean number of metastable states in higher order short-range spin
glasses is estimated analytically using a variational method introduced by
Tanaka and Edwards for very large coordination numbers. For lattices with small
connectivities, numerical simulations do not show any significant dependence on
the relative positions of the interacting spins on the lattice, indicating thus
that these systems can be described by a few macroscopic parameters. As an
extremely anisotropic model we consider the low autocorrelated binary spin
model and we show through numerical simulations that its landscape has an
exceptionally large number of local optima
Fermi level alignment in molecular nanojunctions and its relation to charge transfer
The alignment of the Fermi level of a metal electrode within the gap of the
hi ghest occupied (HOMO) and lowest unoccupied orbital (LUMO) of a molecule is
a key quantity in molecular electronics, which can vary the electron
transparency of a single molecule junction by orders of magnitude. We present a
quantitative analysis of the relation between this level alignment (which can
be estimated from charging free molecules) and charge transfer for bipyridine
and biphenyl dithiolate (BPDT) molecules attached to gold leads based on
density functional theory calculations. For both systems the charge
distribution is defined by a balance between Pauli repulsion with subsequent
electrostatic screening and the filling of the LUMO, where bipyridine loses
electrons to the leads and BPDT gains electrons. As a direct consequence the
Fermi level of the metal is found close to the LUMO for bipyridine and close to
the HOMO for BPDT
Covariant equations for the three-body bound state
The covariant spectator (or Gross) equations for the bound state of three
identical spin 1/2 particles, in which two of the three interacting particles
are always on shell, are developed and reduced to a form suitable for numerical
solution. The equations are first written in operator form and compared to the
Bethe-Salpeter equation, then expanded into plane wave momentum states, and
finally expanded into partial waves using the three-body helicity formalism
first introduced by Wick. In order to solve the equations, the two-body
scattering amplitudes must be boosted from the overall three-body rest frame to
their individual two-body rest frames, and all effects which arise from these
boosts, including the Wigner rotations and rho-spin decomposition of the
off-shell particle, are treated exactly. In their final form, the equations
reduce to a coupled set of Faddeev-like double integral equations with
additional channels arising from the negative rho-spin states of the off-shell
particle.Comment: 57 pages, RevTeX, 6 figures, uses epsf.st
Thermoelectric Properties of Intermetallic Semiconducting RuIn3 and Metallic IrIn3
Low temperature (<400 K) thermoelectric properties of semiconducting RuIn3
and metallic IrIn3 are reported. RuIn3 is a narrow band gap semiconductor with
a large n-type Seebeck coefficient at room temperature (S(290K)~400 {\mu}V/K),
but the thermoelectric Figure of merit (ZT(290K) = 0.007) is small because of
high electrical resistivity and thermal conductivity ({\kappa}(290 K) ~ 2.0 W/m
K). IrIn3 is a metal with low thermopower at room temperature (S(290K)~20
{\mu}V/K) . Iridium substitution on the ruthenium site has a dramatic effect on
transport properties, which leads to a large improvement in the power factor
and corresponding Figure of merit (ZT(380 K) = 0.053), improving the efficiency
of the material by an over of magnitude.Comment: Submitted to JA
Quantum protocols for anonymous voting and surveying
We describe quantum protocols for voting and surveying. A key feature of our
schemes is the use of entangled states to ensure that the votes are anonymous
and to allow the votes to be tallied. The entanglement is distributed over
separated sites; the physical inaccessibility of any one site is sufficient to
guarantee the anonymity of the votes. The security of these protocols with
respect to various kinds of attack is discussed. We also discuss classical
schemes and show that our quantum voting protocol represents a N-fold reduction
in computational complexity, where N is the number of voters.Comment: 8 pages. V2 includes the modifications made for the published versio
Impacts of Land Abandonment on Vegetation: Successional Pathways in European Habitats
Changes in traditional agricultural systems in Europe in recent decades have led to widespread abandonment and colonization of various habitats by shrubs and trees. We combined several vegetation databases to test whether patterns of changes in plant diversity after land abandonment in different habitats followed similar pathways. The impacts of land abandonment and subsequent woody colonization on vegetation composition and plant traits were studied in five semi-natural open habitats and two arable habitats in six regions of Europe. For each habitat, vegetation surveys were carried out in different stages of succession using either permanent or non-permanent plots. Consecutive stages of succession were defined on a physiognomic basis from initial open stages to late woody stages. Changes in vegetation composition, species richness, numbers of species on Red Lists, plant strategy types, Ellenberg indicator values of the vegetation, Grime CSR strategy types and seven ecological traits were assessed for each stage of the successional pathway. Abandonment of agro-pastoral land-use and subsequent woody colonization were associated with changes in floristic composition. Plant richness varied according to the different habitats and stages of succession, but semi-natural habitats differed from arable fields in several ecological traits and vegetation responses. Nevertheless, succession occurred along broadly predictable pathways. Vegetation in abandoned arable fields was characterized by a decreasing importance of R-strategists, annuals, seed plants with overwintering green leaves, insect-pollinated plants with hemi-rosette morphology and plants thriving in nutrient-rich conditions, but an increase in species considered as endangered according to the Red Lists. Conversely, changes in plant traits with succession within the initially-open semi-natural habitats showed an increase in plants thriving in nutrient-rich conditions, stress-tolerant plants and plants with sexual and vegetative reproduction, but a sharp decrease in protected species. In conclusion, our study showed a set of similarities in responses of the vegetation in plant traits after land abandonment, but we also highlighted differences between arable fields and semi-natural habitats, emphasizing the importance of land-use legacy
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