1,082 research outputs found
Affine configurations and pure braids
We show that the fundamental group of the space of ordered affine-equivalent
configurations of at least five points in the real plane is isomorphic to the
pure braid group modulo its centre. In the case of four points this fundamental
group is free with eleven generators.Comment: 5 pages, 1 figure, final version; to appear in Discrete &
Computational Geometry, available from the publishers at
http://www.springerlink.com/content/384516n7q24811ph
Evaluation Codes from smooth Quadric Surfaces and Twisted Segre Varieties
We give the parameters of any evaluation code on a smooth quadric surface.
For hyperbolic quadrics the approach uses elementary results on product codes
and the parameters of codes on elliptic quadrics are obtained by detecting a
BCH structure of these codes and using the BCH bound. The elliptic quadric is a
twist of the surface P^1 x P^1 and we detect a similar BCH structure on twists
of the Segre embedding of a product of any d copies of the projective line.Comment: 10 pages. Presented at the conference Workshop on Coding theory and
Cryptography 201
Scaling of Island Growth in Pb Overlayers on Cu(001)
The growth and ordering of a Pb layer deposited on Cu(001) at 150 K has been
studied using atom beam scattering. At low coverage, ordered Pb islands with a
large square unit cell and nearly hexagonal internal structure are formed. This
is a high order commensurate phase with 30 atoms in the unit cell. From the
measurement of the island diffraction peak profiles we find a power law for the
mean island - size versus coverage with an exponent . A
scaling behavior of growth is confirmed and a simple model describing island
growth is presented. Due to the high degeneracy of the monolayer phase,
different islands do not diffract coherently. Therefore, when islands merge
they still diffract as separate islands and coalescence effects are thus
negligible. From the result for we conclude that the island density is
approximately a constant in the coverage range where the
ordered islands are observed. We thus conclude that most islands nucleate at
and then grow in an approximately self similar fashion as
increases.Comment: 23 pages, 10 Figures (available upon request). SU-PHYS-93-443-375
Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr
Configuration interaction (CI) calculations in atoms with two valence
electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are
corrected for core-valence interactions using many-body perturbation theory
(MBPT). Two variants of the mixed CI+MBPT theory are described and applied to
obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr
Application of Hyperspectral Imaging to Underwater Habitat Mapping, Southern Adriatic Sea
Hyperspectral imagers enable the collection of high-resolution spectral images exploitable for the supervised classification of habitats and objects of interest (OOI). Although this is a well-established technology for the study of subaerial environments, Ecotone AS has developed an underwater hyperspectral imager (UHI) system to explore the properties of the seafloor. The aim of the project is to evaluate the potential of this instrument for mapping and monitoring benthic habitats in shallow and deep-water environments. For the first time, we tested this system at two sites in the Southern Adriatic Sea (Mediterranean Sea): the cold-water coral (CWC) habitat in the Bari Canyon and the Coralligenous habitat off Brindisi. We created a spectral library for each site, considering the different substrates and the main OOI reaching, where possible, the lower taxonomic rank. We applied the spectral angle mapper (SAM) supervised classification to map the areal extent of the Coralligenous and to recognize the major CWC habitat-formers. Despite some technical problems, the first results demonstrate the suitability of the UHI camera for habitat mapping and seabed monitoring, through the achievement of quantifiable and repeatable classifications
Simulations of the Static Friction Due to Adsorbed Molecules
The static friction between crystalline surfaces separated by a molecularly
thin layer of adsorbed molecules is calculated using molecular dynamics
simulations. These molecules naturally lead to a finite static friction that is
consistent with macroscopic friction laws. Crystalline alignment, sliding
direction, and the number of adsorbed molecules are not controlled in most
experiments and are shown to have little effect on the friction. Temperature,
molecular geometry and interaction potentials can have larger effects on
friction. The observed trends in friction can be understood in terms of a
simple hard sphere model.Comment: 13 pages, 13 figure
Proton-proton scattering above 3 GeV/c
A large set of data on proton-proton differential cross sections, analyzing
powers and the double polarization parameter A_NN is analyzed employing the
Regge formalism. We find that the data available at proton beam momenta from 3
GeV/c to 50 GeV/c exhibit features that are very well in line with the general
characteristics of Regge phenomenology and can be described with a model that
includes the rho, omega, f_2, and a_2 trajectories and single Pomeron exchange.
Additional data, specifically for spin-dependent observables at forward angles,
would be very helpful for testing and refining our Regge model.Comment: 16 pages, 19 figures; revised version accepted for publication in
EPJ
Effect of half-dose vs stable-dose conventional synthetic disease-modifying antirheumatic drugs on disease flares in patients with rheumatoid arthritis in remission: the ARCTIC REWIND randomized clinical trial
This randomized trial compares the effects of half-dose conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) vs stable-dose csDMARDs on the risk of flares in patients with rheumatoid arthritis in sustained remission.Importance Sustained remission has become an achievable goal for patients with rheumatoid arthritis (RA) receiving conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), but how to best treat patients in clinical remission remains unclear. Objective To assess the effect of tapering of csDMARDs, compared with continuing csDMARDs without tapering, on the risk of flares in patients with RA in sustained remission. Design, Setting, and Participants ARCTIC REWIND was a multicenter, randomized, parallel, open-label noninferiority study conducted in 10 Norwegian hospital-based rheumatology practices. A total of 160 patients with RA in remission for 12 months who were receiving stable csDMARD therapy were enrolled between June 2013 and June 2018, and the final visit occurred in June 2019. Interventions Patients were randomly assigned to half-dose csDMARDs (n = 80) or stable-dose csDMARDs (n = 80). Main Outcomes and Measures The primary end point was the proportion of patients with a disease flare between baseline and the 12-month follow-up, defined as a combination of Disease Activity Score (DAS) greater than 1.6 (threshold for RA remission), an increase in DAS score of 0.6 units or more, and at least 2 swollen joints. A disease flare could also be recorded if both the patient and investigator agreed that a clinically significant flare had occurred. A risk difference of 20% was defined as the noninferiority margin. Results Of 160 enrolled patients (mean [SD] age, 55.1 [11.9] years; 66% female), 156 received the allocated therapy, of which 155 without any major protocol violations were included in the primary analysis population (77 receiving half-dose and 78 receiving stable-dose csDMARDs). Flare occurred in 19 patients (25%) in the half-dose csDMARD group compared with 5 (6%) in the stable-dose csDMARD group (risk difference, 18% [95% CI, 7%-29%]). Adverse events occurred in 34 patients (44%) in the half-dose group and 42 (54%) in the stable-dose group, none leading to study discontinuation. No deaths occurred. Conclusions and Relevance Among patients with RA in remission taking csDMARD therapy, treatment with half-dose vs stable-dose csDMARDs did not demonstrate noninferiority for the percentage of patients with disease flares over 12 months, and there were significantly fewer flares in the stable-dose group. These findings do not support treatment with half-dose therapy.Question In patients with rheumatoid arthritis in remission taking conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), is reducing the csDMARDs to half dose noninferior to stable csDMARD dosage for the outcome of rheumatoid arthritis flares? Findings In this randomized clinical trial that included 160 patients with rheumatoid arthritis in remission taking csDMARD therapy, treatment with half-dose vs stable-dose csDMARDs resulted in disease flares in 25% vs 6% over 12 months; this did not meet the noninferiority criterion of a 20% difference. There were significantly fewer patients with flares in the stable-dose group. Meaning These findings do not support the use of half-dose treatment in patients with rheumatoid arthritis in remission taking csDMARDs.Pathophysiology and treatment of rheumatic disease
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
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