2,302 research outputs found
Development of a facility using robotics for testing automation of inertial instruments
The Integrated Robotics System Simulation (ROBSIM) was used to evaluate the performance of the PUMA 560 arm as applied to testing of inertial sensors. Results of this effort were used in the design and development of a feasibility test environment using a PUMA 560 arm. The implemented facility demonstrated the ability to perform conventional static inertial instrument tests (rotation and tumble). The facility included an efficient data acquisitions capability along with a precision test servomechanism function resulting in various data presentations which are included in the paper. Analysis of inertial instrument testing accuracy, repeatability and noise characteristics are provided for the PUMA 560 as well as for other possible commercial arm configurations. Another integral aspect of the effort was an in-depth economic analysis and comparison of robot arm testing versus use of contemporary precision test equipment
Evidence for polarised boron in Co-B and Fe-B alloys
By exploiting the tunability of synchrotron radiation in measurements of spin-resolved photoemission it has proved possible to obtain information on the polarisation of the valence electrons of Co-B and Fe-B amorphous magnetic alloys, Both the spin-integrated and spin-resolved energy distribution curves show a marked dependence on photon energy indicating that the p states of boron hybridise with the d states of the transition metals giving rise to mixed states in the binding energy range 1 to 5 eV, The observed polarisation and spin-resolved densities of states imply that in the above restricted energy range there is a net negative polarisation of the boron states
Emergency Portasystemic Shunting in Cirrhotics With Bleeding Varices — A Comparison of Portacaval and Mesocaval Shunts
Despite the best conservative measures available for the control of major variceal hemorrhage, some
patients either continue to bleed, or rebleed early, and require emergency surgery. One hundred patients
with cirrhosis and uncontrolled bleeding were treated with emergency portasystemic shunts between 1968
and 1983. Fifty eight patients had end-to-side portacaval shunts and 42 had Dacron interposition mesocaval
shunts. Both groups were comparable with respect to age, sex and prevalence of alcoholism. There was an
increased severity of liver disease as assessed by Child's class in the mesocaval group of patients
A tale of two sites – I. Inferring the properties of minihalo-hosted galaxies from current observations
The very first galaxies that started the cosmic dawn likely resided in so-called ‘minihaloes’, with masses of ∼105–108 M, accreting their gas from the intergalactic medium through H2 cooling. Such molecularly cooled galaxies (MCGs) mostly formed in pristine environments, hosted massive, metal-free stars, and were eventually sterilized by the build-up of a disassociating (Lyman–Werner; LW) background. Therefore, their properties might be very different from the galaxies we see in the later Universe. Although MCGs are probably too faint to be observed directly, we could nevertheless infer their properties from the imprint they leave in the cosmic 21-cm signal. Here we quantify this imprint by extending the public simulation code 21CMFAST to allow for a distinct population of MCGs. We allow MCGs to have different properties from other galaxies, including unique scaling relations for their stellar-to-halo mass ratios, ionizing escape fractions, and spectral energy distributions. We track inhomogeneous recombinations, disassociative LW feedback, and photoheating from reionization. After demonstrating how MCGs can shape the 21-cm signal, we explore to what extent current observations can already place constraints on their properties. The cosmic microwave background optical depth from Planck sets an upper limit on the product of the ionizing escape fraction and the stellar mass in MCGs. When including also the timing of the putative EDGES absorption signal, we find an additional strong degeneracy between the stellar mass and the X-ray luminosity of MCGs. If proven to be of cosmic origin, the timing of the EDGES signal would have been set by MCGs
Exchange anisotropy pinning of a standing spin wave mode
Standing spin waves in a thin film are used as sensitive probes of interface
pinning induced by an antiferromagnet through exchange anisotropy. Using
coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin
wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was
studied for a range of IrMn thicknesses. We show that pinning of the standing
mode can be used to amplify, relative to the fundamental resonance, frequency
shifts associated with exchange bias. The shifts provide a unique `fingerprint'
of the exchange bias and can be interpreted in terms of an effective
ferromagnetic film thickness and ferromagnet/antiferromagnet interface
anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic
Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in
the pinning fields. The pinning strength magnitude is found to grow with
cooling of the sample, while the effective ferromagnetic film thickness
simultaneously decreases. These results suggest that exchange bias involves
some deformation of magnetic order in the interface region.Comment: 7 pages, 7 figure
Dark-ages reionization and galaxy formation simulation -- XXI. Constraining the evolution of the ionizing escape fraction
The fraction of ionizing photons that escape their host galaxies to ionize
hydrogen in the inter-galactic medium (IGM) is a critical parameter in analyses
of the reionization era. In this paper we use the Meraxes semi-analytic galaxy
formation model to infer the mean ionizing photon escape fraction and its
dependence on galaxy properties through joint modelling of the observed high
redshift galaxy population and existing constraints on the reionization
history. Using a Bayesian framework, and under the assumption that escape
fraction is primarily related to halo mass, we find that the joint constraints
of the UV luminosity function, CMB optical depth, and the Ly forest
require an escape fraction of for galaxies within haloes of
M and for more massive haloes. In terms of
galaxy properties, this transition in escape fraction occurs at stellar masses
of M, nearly independent of redshift. As a function of
redshift, reionization is dominated by the smaller
M galaxies with high escape fractions at
and by the larger M galaxies with lower
escape fractions at . Galaxies with star formation rates of
Myr to Myr provide the
dominant source of ionizing photons throughout reionization. Our results are
consistent with recent direct measurements of a escape fraction from
massive galaxies at the end of reionization and support the picture of low mass
galaxies being the dominant sources of ionizing photons during reionization.Comment: Updated to match accepted version for publication in MNRAS. Includes
two new figures showing model predictions and related discussio
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