319,044 research outputs found
Real options, patents, productivity and market value: evidence from a panel of UK firms
Patents citations are a potentially powerful indicator of technological innovation. In this paper we describe the IFS-Leverhulme patents dataset that we have constructed by combining information from the US Case-Western Patent database with UK company accounts and share price information from the London Stock Exchange. Patents citations like patentc ounts, arehighly skewed and have a modal lag of four years. Analysing data on over 200 major British firms since 1968, we show that patents have an economically and statistically significant impacton firm-level productivity and market value. Patent citations contain more information than simple counts. A doubling in the stock of citation-weighted patents is associated with a four percent increase in (total factor) productivity and an eight percent increase in market value. As expected patenting and citation information feeds into market values immediately but appears to have some additional lagged effects of productivity suggesting gradual takeup of new technologies
Separating spin and charge transport in single wall carbon nanotubes
We demonstrate spin injection and detection in single wall carbon nanotubes
using a 4-terminal, non-local geometry. This measurement geometry completely
separates the charge and spin circuits. Hence all spurious magnetoresistance
effects are eliminated and the measured signal is due to spin accumulation
only. Combining our results with a theoretical model, we deduce a spin
polarization at the contacts of approximately 25 %. We show that the
magnetoresistance changes measured in the conventional two-terminal geometry
are dominated by effects not related to spin accumulation.Comment: Number of pages: 11 Number of figures:
The Magneto-coulomb effect in spin valve devices
We discuss the influence of the magneto-coulomb effect (MCE) on the
magnetoconductance of spin valve devices. We show that MCE can induce
magnetoconductances of several per cents or more, dependent on the strength of
the coulomb blockade. Furthermore, the MCE-induced magnetoconductance changes
sign as a function of gate voltage. We emphasize the importance of separating
conductance changes induced by MCE from those due to spin accumulation in spin
valve devices.Comment: This paper includes 3 figure
Reconciliation of a Quantum-Distributed Gaussian Key
Two parties, Alice and Bob, wish to distill a binary secret key out of a list
of correlated variables that they share after running a quantum key
distribution protocol based on continuous-spectrum quantum carriers. We present
a novel construction that allows the legitimate parties to get equal bit
strings out of correlated variables by using a classical channel, with as few
leaked information as possible. This opens the way to securely correcting
non-binary key elements. In particular, the construction is refined to the case
of Gaussian variables as it applies directly to recent continuous-variable
protocols for quantum key distribution.Comment: 8 pages, 4 figures. Submitted to the IEEE for possible publication.
Revised version to improve its clarit
Object oriented design of a thermo-mechanical FEM code
An object oriented design is presented for a computer program that can perform\ud
thermo-mechanically coupled analyzes. The target of the design is a \ud
exible and robust\ud
computer program. It should be easy to adapt and extend, re-using existing code, without\ud
interfering with already established algorithms.\ud
The program uses publicly available toolkits that are currently emerging as C++ pack-\ud
ages. First of all the Standard C++ Library (formerly Standard Template Library) is\ud
used for packing items in container classes. Secondly the matrix and vector operations\ud
are derived from the Template Numerical Toolkit (TNT) and �nally (not essentially for\ud
the numerical part) a graphical user interface is made, based on the wxWindows package,\ud
that can generate a GUI for Motif and MS-Windows with the same code.\ud
Attention is given to the design of classes such as speci�c elements and material classes\ud
based on more general classes. A hierarchy of classes is constructed where general behavior\ud
is put high in the hierarchy and speci�c behavior low. The choice between inheritance and\ud
aggregation is made at several levels
Exponents and bounds for uniform spanning trees in d dimensions
Uniform spanning trees are a statistical model obtained by taking the set of
all spanning trees on a given graph (such as a portion of a cubic lattice in d
dimensions), with equal probability for each distinct tree. Some properties of
such trees can be obtained in terms of the Laplacian matrix on the graph, by
using Grassmann integrals. We use this to obtain exact exponents that bound
those for the power-law decay of the probability that k distinct branches of
the tree pass close to each of two distinct points, as the size of the lattice
tends to infinity.Comment: 5 pages. v2: references added. v3: closed form results can be
extended slightly (thanks to C. Tanguy). v4: revisions, and a figure adde
Seagull and pion-in-flight currents in neutrino-induced and knockout
[Background] The neutrino-nucleus () cross section is a major source
of systematic uncertainty in neutrino-oscillation studies. A precise
scattering model, in which multinucleon effects are incorporated, is pivotal
for an accurate interpretation of the data. [Purpose] In interactions,
meson-exchange currents (MECs) can induce two-nucleon () knockout from the
target nucleus, resulting in a two-particle two-hole (2p2h) final state. They
also affect single nucleon () knockout reactions, yielding a one-particle
one-hole (1p1h) final state. Both channels affect the inclusive strength. We
present a study of axial and vector, seagull and pion-in-flight currents in
muon-neutrino induced and knockout reactions on C. [Method]
Bound and emitted nucleons are described as Hartree-Fock wave functions. For
the vector MECs, the standard expressions are used. For the axial current,
three parameterizations are considered. The framework developed here allows for
a treatment of MECs and short-range correlations (SRCs). [Results] Results are
compared with electron-scattering data and with literature. The strengths of
the seagull, pion-in-flight and axial currents are studied separately and
double differential cross sections including MECs are compared with results
including SRCs. A comparison with MiniBooNE and T2K data is presented.
[Conclusions] In the 1p1h channel, the effects of the MECs tend to cancel each
other, resulting in a small effect on the double differential cross section.
knockout processes provide a small contribution to the inclusive double
differential cross section, ranging from the knockout threshold into the
dip region. A fair agreement with the MiniBooNE and T2K data is reached.Comment: 16 pages, 10 figure
Multichannel calculation of excited vector resonances and the
A multichannel calculation of excited states is
carried out within a generalization of the Resonance-Spectrum Expansion, which
may shed light on the classification of the resonance, discovered
by BABAR and originally denoted X(2175). In this framework, a complete spectrum
of bare states is coupled to those OZI-allowed decay channels that
should be most relevant for the considered energy range. The included - and
-wave two-meson channels comprise the lowest pseudoscalar, vector, scalar,
and axial-vector mesons, while in the sector both the and
states are coupled. The only two free parameters are tuned so as to
reproduce mass and width of the , but come out reasonably close to
previously used values. Among the model's -matrix poles, there are good
candidates for observed resonances, as well other ones that should exist
according to the quark model. Besides the expected resonances as unitarized
confinement states, a dynamical resonance pole is found at MeV.
The huge width makes its interpretation as the somewhat dubious,
but further improvements of the model may change this conclusion.Comment: 6 pages, 5 figures, RevTex4; v2: very recent experimental result,
some extra discussion, and 2 references added; v3: 3 new figures, 2 new
equations, and some rephrasing; version accepted for publication in Phys.
Rev.
Yang-Yang thermodynamics on an atom chip
We investigate the behavior of a weakly interacting nearly one-dimensional
(1D) trapped Bose gas at finite temperature. We perform in situ measurements of
spatial density profiles and show that they are very well described by a model
based on exact solutions obtained using the Yang-Yang thermodynamic formalism,
in a regime where other, approximate theoretical approaches fail. We use
Bose-gas focusing [Shvarchuck etal., Phys. Rev. Lett. 89, 270404 (2002)] to
probe the axial momentum distribution of the gas, and find good agreement with
the in situ results.Comment: extended introduction and conclusions, and minor changes throughout;
accepted for publication in Phys. Rev. Let
Solutions of the compatibility conditions for a Wigner quantum oscillator
We consider the compatibility conditions for a N-particle D-dimensional
Wigner quantum oscillator. These conditions can be rewritten as certain triple
relations involving anticommutators, so it is natural to look for solutions in
terms of Lie superalgebras. In the recent classification of ``generalized
quantum statistics'' for the basic classical Lie superalgebras
[math-ph/0504013], each such statistics is characterized by a set of creation
and annihilation operators plus a set of triple relations. In the present
letter, we investigate which cases of this classification also lead to
solutions of the compatibility conditions. Our analysis yields some known
solutions and several classes of new solutions.Comment: 9 page
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