200 research outputs found
SiPM Gain Stabilization Studies for Adaptive Power Supply
We present herein gain stabilization studies of SiPMs using a climate chamber
at CERN. We present results for four detectors not tested before, three from
Hamamatsu and one from KETEK. Two of the Hamamatsu SiPMs are novel sensors with
trenches that reduce cross talk. We use an improved readout system with a
digital oscilloscope controlled with a dedicated LabView program. We improved
and automized the analysis to deal with large datasets. We have measured the
gain-versus-bias-voltage dependence at fixed temperature and
gain-versus-temperature dependence at fixed bias voltage to determine the bias
voltage dependence on temperature for stable gain. We show that the gain
remains stable to better than in the
temperature range if the bias voltage is properly adjusted with temperature.Comment: 14 pages, 41 figures, Talk presented at the International Workshop on
Future Linear Colliders (LCWS15), Whistler, Canada, 2-6 November 201
Nanodiamond-treated flax: improving properties of natural fibers
Synthetic fibers are used extensively as reinforcement in composite materials, but many of them face environmental concerns such as high energy consumption during production and complicated decommissioning. Natural fibers have been considered as an attractive solution for making composites more sustainable. However, they are generally not as strong as synthetic fibers. It is therefore of interest to investigate ways to improve the properties of natural fibers without compromising environmental issues. Here, we present a study of the moisture absorption and mechanical properties of flax that has been exposed to hydrogenated nanodiamonds through an ultrasonic dispersion treatment. Nanodiamonds are known to be non-toxic, unlike many other carbon-based nanomaterials. We show that nanodiamond-treated flax fabric has a lower moisture content (~ −18%), lower moisture absorption rate and better abrasion resistance (~ +30%). Single yarns, extracted from the fabric, show higher tensile strength (~ +24%) compared to untreated flax. Furthermore, we present a theoretical model for the nanodiamond fiber interaction, based on the Derjgauin–Landau–Verwey–Overbeek (DLVO) theory of colloid interactions. The simulations indicate that the mechanical properties improve due to an enhancement of the electrolytic force, dispersion force and hydrogen bonding of nanodiamond-treated fibers, which strengthens the cohesion between the fibers. We also apply the model to nanodiamond-treated cotton. The lower zeta potential of cotton increases the electrolytic force. Comparing the results to experimental data of nanodiamond-treated flax and nanodiamond-treated cotton suggests that the fiber’s zeta potential is critical for the improvements of their mechanical properties. Graphical abstract: [Figure not available: see fulltext.
Large area microwave plasma CVD of diamond using composite right/left-handed materials
Diamond growth at low temperatures (≤400 °C) and over large areas is attractive for materials, which are sensitive to high temperatures and require good electronic, chemical or surface tribological properties. Resonant-cavity microwave plasma enhanced (MWPE) chemical vapor deposition (CVD) is a standard method for growing diamonds, however, with limited deposition area. An alternative method for CVD of diamond over large area and at low temperature is to use a surface wave plasma (SWP). In this work we introduce a novel method to excite SWP using composite right/left-handed (CRLH) materials and demonstrate growth of nanocrystalline diamond (NCD) on 4-inch Si wafers. The method uses a set of slotted CRLH waveguides coupled to a resonant launcher, which is connected to a deposition chamber. Each CRLH waveguide supports infinite wavelength propagation and consists of a chain of periodically cascaded unit cells. The SWP is excited by a set of slots placed to interrupt large area surface current on the resonant launcher. This configuration yields a uniform gas discharge distribution. We achieve 80 nm/h growth rate for NCD films with a low surface roughness (5–10 nm) at 395 °C and 0.5 mbar pressure using a H2/CH4/CO2 gas mixture.publishedVersio
Polycrystalline Diamond Coating on Orthopedic Implants: Realization and Role of Surface Topology and Chemistry in Adsorption of Proteins and Cell Proliferation
Polycrystalline diamond has the potential to improve the osseointegration of orthopedic implants compared to conventional materials such as titanium. However, despite the excellent biocompatibility and superior mechanical properties, the major challenge of using diamond for implants, such as those used for hip arthroplasty, is the limitation of microwave plasma chemical vapor deposition (CVD) techniques to synthesize diamond on complex-shaped objects. Here, for the first time, we demonstrate diamond growth on titanium acetabular shells using the surface wave plasma CVD method. Polycrystalline diamond coatings were synthesized at low temperatures (∼400 °C) on three types of acetabular shells with different surface structures and porosities. We achieved the growth of diamond on highly porous surfaces designed to mimic the structure of the trabecular bone and improve osseointegration. Biocompatibility was investigated on nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) coatings terminated either with hydrogen or oxygen. To understand the role of diamond surface topology and chemistry in the attachment and proliferation of mammalian cells, we investigated the adsorption of extracellular matrix proteins and monitored the metabolic activity of fibroblasts, osteoblasts, and bone-marrow-derived mesenchymal stem cells (MSCs). The interaction of bovine serum albumin and type I collagen with the diamond surfaces was investigated by confocal fluorescence lifetime imaging microscopy (FLIM). We found that the proliferation of osteogenic cells was better on hydrogen-terminated UNCD than on the oxygen-terminated counterpart. These findings correlated with the behavior of collagen on diamond substrates observed by FLIM. Hydrogen-terminated UNCD provided better adhesion and proliferation of osteogenic cells, compared to titanium, while the growth of fibroblasts was poorest on hydrogen-terminated NCD and MSCs behaved similarly on all tested surfaces. These results open new opportunities for application of diamond coatings on orthopedic implants to further improve bone fixation and osseointegration.publishedVersio
Search for heavy lepton resonances decaying to a boson and a lepton in collisions at TeV with the ATLAS detector
A search for heavy leptons decaying to a boson and an electron or a muon is presented. The search is based on collision data taken at TeV by the ATLAS experiment at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb, Three high-transverse-momentum electrons or muons are selected, with two of them required to be consistent with originating from a boson decay. No significant excess above Standard Model background predictions is observed, and 95% confidence level limits on the production cross section of high-mass trilepton resonances are derived. The results are interpreted in the context of vector-like lepton and type-III seesaw models. For the vector-like lepton model, most heavy lepton mass values in the range 114-176 GeV are excluded. For the type-III seesaw model, most mass values in the range 100-468 GeV are excluded
Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in collisions at TeV with the ATLAS detector
A search for Higgs boson decays to invisible particles is performed using 20.3 fb\).{-1}\) of collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson = or that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain production followed by decaying to invisible particles for the Higgs mass range GeV. The 95% confidence-level observed upper limit on varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the contribution as signal, the results also lead to an observed upper limit of 78% at 95% confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.publishedVersio
Search for heavy lepton resonances decaying to a boson and a lepton in collisions at TeV with the ATLAS detector
A search for heavy leptons decaying to a boson and an electron or a muon is presented. The search is based on collision data taken at TeV by the ATLAS experiment at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb, Three high-transverse-momentum electrons or muons are selected, with two of them required to be consistent with originating from a boson decay. No significant excess above Standard Model background predictions is observed, and 95% confidence level limits on the production cross section of high-mass trilepton resonances are derived. The results are interpreted in the context of vector-like lepton and type-III seesaw models. For the vector-like lepton model, most heavy lepton mass values in the range 114-176 GeV are excluded. For the type-III seesaw model, most mass values in the range 100-468 GeV are excluded.publishedVersio
Search for new phenomena in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in 13 collisions with the ATLAS detector
Two searches for new phenomena in final states containing a same-flavour opposite-lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton--proton collision data, collected during 2015 and 2016 at a centre-of-mass energy TeV by the ATLAS detector at the Large Hadron Collider, which correspond to an integrated luminosity of 14.7 fb, Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g. ), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 TeV (980 GeV).publishedVersio
Search for invisible Higgs boson decays in vector boson fusion at √s = 13 TeV with the ATLAS detector
We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1) TeV and O(100) GeV missing transverse momentum. The analysis uses 36.1 fb−1 of pp collision data at √s=13 TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp–nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3 TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3–1.7 pb.publishedVersio
Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s = 13 TeV using the ATLAS detector
The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb−1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements.publishedVersio
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