7,724 research outputs found
Lower Bound for Convex Hull Area and Universal Cover Problems
In this paper, we provide a lower bound for an area of the convex hull of
points and a rectangle in a plane. We then apply this estimate to establish a
lower bound for a universal cover problem. We showed that a convex universal
cover for a unit length curve has area at least 0.232239. In addition, we show
that a convex universal cover for a unit closed curve has area at least
0.0879873.Comment: 12 pages, 9 figure
Radiation Damage and Recovery Properties of Common Plastics PEN (Polyethylene Naphthalate) and PET (Polyethylene Terephthalate) Using a 137Cs Gamma Ray Source Up To 1 MRad and 10 MRad
Polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET) are cheap
and common polyester plastics used throughout the world in the manufacturing of
bottled drinks, containers for foodstuffs, and fibers used in clothing. These
plastics are also known organic scintillators with very good scintillation
properties. As particle physics experiments increase in energy and particle
flux density, so does radiation exposure to detector materials. It is therefore
important that scintillators be tested for radiation tolerance at these
generally unheard of doses. We tested samples of PEN and PET using laser
stimulated emission on separate tiles exposed to 1 MRad and 10 MRad gamma rays
with a 137Cs source. PEN exposed to 1 MRad and 10 MRad emit 71.4% and 46.7% of
the light of an undamaged tile, respectively, and maximally recover to 85.9%
and 79.5% after 5 and 9 days, respectively. PET exposed to 1 MRad and 10 MRad
emit 35.0% and 12.2% light, respectively, and maximally recover to 93.5% and
80.0% after 22 and 60 days, respectively
Hydrological connectivity inferred from diatom transport through the riparian-stream system
Funding for this research was provided by the Luxembourg National Research Fund (FNR) in the framework of the BIGSTREAM (C09/SR/14), ECSTREAM (C12/SR/40/8854) and CAOS (INTER/DFG/11/01) projects. We are most grateful to the Administration des Services Techniques de l’Agriculture (ASTA) for providing meteorological data. We also acknowledge Delphine Collard for technical assistance in diatom sample treatment and preparation, François Barnich for the water chemistry analyses, and Jean-François Iffly, Christophe Hissler, Jérôme Juilleret, Laurent Gourdol and Julian Klaus for their constructive comments on the project and technical assistance in the field.Peer reviewedPublisher PD
Induced Parametrisation and its Applications in Geometric Computation
The paper describes a concept of induced rational parametrisation for curves. Parametrisations of curves are defined in terms of rational parametrisations of simpler or `primitive' curves. The technique has applications in computer graphics and geometric modeling. A range of examples is given
Characterization of photomultiplier tubes in a novel operation mode for Secondary Emission Ionization Calorimetry
Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier
Tubes have been characterized for use in a Secondary Emission (SE) Ionization
Calorimetry study. SE Ionization Calorimetry is a novel technique to measure
electromagnetic shower particles in extreme radiation environments. The
different operation modes used in these tests were developed by modifying the
conventional PMT bias circuit. These modifications were simple changes to the
arrangement of the voltage dividers of the baseboard circuits. The PMTs with
modified bases, referred to as operating in SE mode, are used as an SE detector
module in an SE calorimeter prototype, and placed between absorber materials
(Fe, Cu, Pb, W, etc.). Here, the technical design of different operation modes,
as well as the characterization measurements of both SE modes and the
conventional PMT mode are reported
Mechanical and abrasion wear properties of hydrogenated nitrile butadiene rubber of identical hardness filled with carbon black and silica
The mechanical and abrasive wear properties of a hydrogenated nitrile butadiene rubber filled with 35 part per hundred rubber carbon black or silica with and without silane surface treatment (SI-si and SI, respectively), were investigated. Specimens were subjected to dynamic mechanical thermal analysis (also to study the Payne effect), mechanical (hardness, tensile modulus, ultimate tensile strength and strain, Mullins effect and tear strength), and fracture mechanical (J-integral) tests. The abrasive coefficient of friction and wear (specific wear rate, Ws) of the hydrogenated nitrile butadiene rubbers of identical hardness were measured against abrasive papers of different grit sizes (P600-P5000).The worn surface of the HNBR systems was inspected in scanning electron microscopy and the typical wear mechanisms deduced and discussed. Coefficient of friction did not change with the grit size by contrast to Ws which was markedly reduced with decreasing surface roughness of the abrasive paper. Ws of the compounds did not vary when wearing against P3000 and P5000 abrasive papers, representing mean surface roughness values of 7 and 5 μm, respectively. This was attributed to a change from abrasion to sliding type wear. hydrogenated nitrile butadiene rubber- carbon black outperformed the silica filled versions with respect to Ws though exhibited the highest coefficient of friction. No definite correlation could be found between the abrasive wear and the studied dynamic mechanical thermal analysis and (fracture) mechanical properties. </jats:p
Evaluation of the synoptic and mesoscale predictive capabilities of a mesoscale atmospheric simulation system
The overall performance characteristics of a limited area, hydrostatic, fine (52 km) mesh, primitive equation, numerical weather prediction model are determined in anticipation of satellite data assimilations with the model. The synoptic and mesoscale predictive capabilities of version 2.0 of this model, the Mesoscale Atmospheric Simulation System (MASS 2.0), were evaluated. The two part study is based on a sample of approximately thirty 12h and 24h forecasts of atmospheric flow patterns during spring and early summer. The synoptic scale evaluation results benchmark the performance of MASS 2.0 against that of an operational, synoptic scale weather prediction model, the Limited area Fine Mesh (LFM). The large sample allows for the calculation of statistically significant measures of forecast accuracy and the determination of systematic model errors. The synoptic scale benchmark is required before unsmoothed mesoscale forecast fields can be seriously considered
"Ultralow" sliding wear polytetrafluoro ethylene nanocomposites with functionalized graphene
The dry friction and sliding wear behavior of sintered polytetrafluoro ethylene containing various amounts of functionalized graphene were studied in this work. Graphene was incorporated in 0, 0.25, 0.75, 1, 2 and 4 vol.%, respectively. Sliding wear tests were performed in ring(metal)-on-plate(polytetrafluoro ethylene) test rig under ambient temperature setting 1 m/s sliding speed and 1 MPa contact pressure. The dynamic coefficient of friction and specific wear rate (ws) data were determined. Very low coefficient of frictions (0.12–0.14) were measured for polytetrafluoro ethylene containing 2 or 4 vol.% graphene, which was attributed to the formation of a tribofilm on the countersurface. Specific wear rate went through a maximum (peaked at doubling that of the unmodified polytetrafluoro ethylene at about 0.75 vol.% graphene) as a function of graphene content. Ultralow wear rate data in the range of 10−6 mm3/(N.m) were measured for the polytetrafluoro ethylene nanocomposites with 2 and 4 vol.% graphene. This was reasoned by the formation of a robust tribofilm, the development of which was followed by scanning electron microscopy by inspecting the worn surface of polytetrafluoro ethylene nanocomposites and that of the steel ring of the ring(metal)-on-plate(polytetrafluoro ethylene) test rig. Fourier transform infrared spectroscopic results confirmed the formation of carboxyl groups in the tribofilm. They were supposed to react with the functional groups of graphene and to create complexes with the metal countersurface ensuring the tribofilm with high adhesion and cohesion strengths. </jats:p
Close Pairs as Proxies for Galaxy Cluster Mergers
Galaxy cluster merger statistics are an important component in understanding
the formation of large-scale structure. Unfortunately, it is difficult to study
merger properties and evolution directly because the identification of cluster
mergers in observations is problematic. We use large N-body simulations to
study the statistical properties of massive halo mergers, specifically
investigating the utility of close halo pairs as proxies for mergers. We
examine the relationship between pairs and mergers for a wide range of merger
timescales, halo masses, and redshifts (0<z<1). We also quantify the utility of
pairs in measuring merger bias. While pairs at very small separations will
reliably merge, these constitute a small fraction of the total merger
population. Thus, pairs do not provide a reliable direct proxy to the total
merger population. We do find an intriguing universality in the relation
between close pairs and mergers, which in principle could allow for an estimate
of the statistical merger rate from the pair fraction within a scaled
separation, but including the effects of redshift space distortions strongly
degrades this relation. We find similar behavior for galaxy-mass halos, making
our results applicable to field galaxy mergers at high redshift. We investigate
how the halo merger rate can be statistically described by the halo mass
function via the merger kernel (coagulation), finding an interesting
environmental dependence of merging: halos within the mass resolution of our
simulations merge less efficiently in overdense environments. Specifically,
halo pairs with separations less than a few Mpc/h are more likely to merge in
underdense environments; at larger separations, pairs are more likely to merge
in overdense environments.Comment: 12 pages, 9 figures; Accepted for publication in ApJ. Significant
additions to text and two figures changed. Added new findings on the
universality of pair mergers and added analysis of the effect of FoF linking
length on halo merger
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