563 research outputs found
iGPS capability study
This report presents the results of testing of the Metris iGPS system performed by the National Physical Laboratory (NPL) and the University of Bath (UoB), with the assistance of Metris, and Airbus at Airbus, Broughton in March 2008. The aim of the test was to determine the performance capability of the iGPS coordinate metrology system by comparison with a reference measurement system based on multilateration implemented using laser trackers. A network of reference points was created using SMR nests fixed to the ground and above ground level on various stands. The reference points were spread out within the measurement volume of approximately 10 m ´ 10 m ´ 2 m. The coordinates of each reference point were determined by the laser tracker survey using multilateration. The expanded uncertainty (k=2) in the relative position of these reference coordinates was estimated to be of the order of 10 µm in x, y and z. A comparison between the iGPS system and the reference system showed that for the test setup, the iGPS system was able to determine lengths up to 12 m with an uncertainty of 170 µm (k=2) and coordinates with an uncertainty of 120 µm in x and y and 190 µm in z (k=2)
Derivative moments for characteristic polynomials from the CUE
We calculate joint moments of the characteristic polynomial of a random
unitary matrix from the circular unitary ensemble and its derivative in the
case that the power in the moments is an odd positive integer. The calculations
are carried out for finite matrix size and in the limit as the size of the
matrices goes to infinity. The latter asymptotic calculation allows us to prove
a long-standing conjecture from random matrix theory.Comment: 31 pages, 3 figure
Peptide-directed PdAu nanoscale surface segregation: Toward controlled bimetallic architecture for catalytic materials
YesBimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.Air Force Office for Scientific Research (T.R.W., Grant No. FA9550-12-620 1-0226). S.P.E. and E.B.C. gratefully acknowledge financial support from the Army Research Office through a MURI award, W911NF-10-1-052
Nucleon Charge and Magnetization Densities from Sachs Form Factors
Relativistic prescriptions relating Sachs form factors to nucleon charge and
magnetization densities are used to fit recent data for both the proton and the
neutron. The analysis uses expansions in complete radial bases to minimize
model dependence and to estimate the uncertainties in radial densities due to
limitation of the range of momentum transfer. We find that the charge
distribution for the proton is significantly broad than its magnetization
density and that the magnetization density is slightly broader for the neutron
than the proton. The neutron charge form factor is consistent with the Galster
parametrization over the available range of Q^2, but relativistic inversion
produces a softer radial density. Discrete ambiguities in the inversion method
are analyzed in detail. The method of Mitra and Kumari ensures compatibility
with pQCD and is most useful for extrapolating form factors to large Q^2.Comment: To appear in Phys. Rev. C. Two new figures and accompanying text have
been added and several discussions have been clarified with no significant
changes to the conclusions. Now contains 47 pages including 21 figures and 2
table
Multimessenger astronomy with the Einstein Telescope
Gravitational waves (GWs) are expected to play a crucial role in the
development of multimessenger astrophysics. The combination of GW observations
with other astrophysical triggers, such as from gamma-ray and X-ray satellites,
optical/radio telescopes, and neutrino detectors allows us to decipher science
that would otherwise be inaccessible. In this paper, we provide a broad review
from the multimessenger perspective of the science reach offered by the third
generation interferometric GW detectors and by the Einstein Telescope (ET) in
particular. We focus on cosmic transients, and base our estimates on the
results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope.
Minor corrections include
A covariant diquark-quark model of the nucleon in the Salpeter approach
We develop a rather simple, formally covariant quark-diquark model of the
nucleon. The nucleon is treated as a bound state of a constituent quark and a
diquark interacting via a quark exchange. We include both scalar and
axial-vector diquarks. The underlying Bethe-Salpeter equation is transformed
into a pair of coupled Salpeter equations. The electromagnetic form factors of
the nucleon are calculated in the Mandelstam formalism. We obtain a very good
description of all electromagnetic form factors for momentum transfers up to -3
(GeV/c)^2.Comment: 17 pages, REVTeX, 10 figures (ps and eps) include
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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