Constraints on redshifts of blazars from extragalactic background light attenuation using Fermi-LAT data

The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging because any spectral signature from the host galaxy may be outshone by the non-thermal emission from the jet. In this paper, we present a method to constrain redshifts for these sources that relies only on data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. This method takes advantage of the signatures that the pair-production interaction between photons with energies larger than approximately 10 GeV and the extragalactic background light leaves on $\gamma$-ray spectra. We find upper limits for the distances of 303 $\gamma$-ray blazars, classified as 157 BL Lacertae objects, 145 of uncertain class, and 1 flat-spectrum-radio quasar, whose redshifts are otherwise unknown. These derivations can be useful for planning observations with imaging atmospheric Cherenkov telescopes and also for testing theories of supermassive black hole evolution. Our results are applied to estimate the detectability of these blazars with the future Cherenkov Telescope Array, finding that at least 21 of them could be studied in a reasonable exposure of 20 h.Comment: 13 pages, 7 figures, 1 table; Accepted by MNRA

Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3~PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy $\gamma$-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte--Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a $\gamma$-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 hours of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathcal{O}(100)$ hours of exposure per source.Comment: 34 pages, 16 figures, Accepted for publication in Astroparticle Physic

Water-based adhesive formulations for rubber to metal bonding developed by statistical design of experiments

Waterborne adhesives for rubber to metal bonding have been available since 1990. However, published information about their formulation has been limited, as proprietary restrictions are exercised by companies. As a consequence, the way these adhesives interact with substrates has not been studied extensively. With the aim of investigating the effect the components of a waterborne adhesive have on rubber to metal bonding, fractional factorial and surface response methodologies of design of experiments were employed in this study. Twenty six formulations were prepared with a polychloroprene latex as the adhesive polymer. Viscosity, wettability and non-volatile solids content were measured with each liquid adhesive, while the mechanical strength was evaluated by applying a tensile mechanical stress over cured solid adhesive films. Adhesion properties were evaluated by using a single lap-shear test on metal to metal joints and a pull-out test on rubber to metal joints. The results showed that the components with the largest relative influence on cohesive and adhesives forces were tackifier resin, silicon dioxide and polychloroprene latex type. In order to better understand the contributions of these variables, mathematical models correlating them with the response variables were obtained. This study is valuable in explaining how, through statistical methods, a waterborne adhesive for rubber to metal bonding can be formulated with a reasonably low number of experiments. © 2016 Elsevier Lt

Morphology Development of Immiscibe Quaternary Polyolefin and PS Blends

Study of polymer blends that fulfill the current engineering demand has been increased in the last years and multicomponent blends are still a challenge, but increasing the number of components will lead to further complications. We correlated the differences between morphology and blending sequence in quaternary blends of polyolefin with polystyrene, following the available theories that related viscosity and morphology. It was found that high viscous matrices enhance deformation and breakup processes, displaying fibrillar morphologies and finer dispersions. The blending sequence improves the mixing first, by putting all the polyolefin into a ternary blend and after that, adding the polystyrene

Tailoring the mechanical, thermal, and flammability properties of high-performance PEI/PBT blends exhibiting dual-phase continuity

Binary PEI/PBT blends are prepared using a two-step melt processing method. Miscibility study by MDSC and DMA reveals partial miscibility, and new evidence on the morphological evolution of PEI/PBT blends is presented. Two groups of blends are recognized: PBT-rich blends and PEI-rich blends, as well as phase inversion at concentrations close to 50 wt% of PEI. Mechanical, thermal, and flame resistance performance is influenced by blends morphology, and an opportunity for tailoring blends properties is recognized. Tensile modulus shows synergic contribution for 50/50 and 80/20 blends and yield strength is strongly affected by interfacial adherence between constituents. In addition, elongation at break is compromised by PBT-rich blends morphology, and by PEI-rich blends densification. The 50/50 blend exhibits the best elongational at break result due to its co-continuous morphology. Thermal stability and flammability tests reveal that PEI improves the thermal resistance and charring of PBT, particularly for 50/50 blend. © 2018 Elsevier Lt

PTFE as a toughness modifier of high-performance PEI/PBT blends: Morphology control during melt processing

High-performance PEI/PBT blends are brittle because of phase distribution and blends densification. New morphologies developed by adding PTFE to PEI matrix during melt processing favor the toughness improvement of PEI/PBT blends. Ternary PEI/PBT/PTFE processability is not compromised by PTFE addition, and miscibility study by modulated differential scanning calorimetry and harmonic mean method shows that PTFE does not interfere with PEI and PBT interaction. Dual-phase and spore-like morphologies are formed for both PEI/PBT and PEI/PBT/PTFE blends, and they strongly influenced their mechanical performance. Although tensile strength of ternary blends does not decrease by PTFE addition, elongation at break deteriorates for blends with PEI concentrations <70 wt%. Nevertheless, blends with 80 wt% increase their ductility, and a synergic effect is observed in impact resistance results. PTFE acts as an impact modifier of PEI/PBT blends due to its distribution in the PEI matrix as debonded spheres and nanoparticles well-embedded in PEI matrix. © 2020 John Wiley & Sons Lt

Functionalization of polyacrylonitrile nanofibers with beta-cyclodextrin for the capture of formaldehyde

Polyacrylonitrile (PAN) is frequently used in filtering applications due to its sound mechanical properties, chemical resistance and thermal stability. beta-cyclodextrin (beta CD) can entrap molecules and improve the filters' performance. The removal of formaldehyde, a common indoor pollutant, has increasingly attracted widespread attention. In this work, we present two different methods for the production of electrospun PAN nanofibers containing beta CD capable of capturing formaldehyde from the air. The former comprised the addition of beta CD to PAN/dimethyl sulfoxide solutions and the subsequent electrospinning of the mixture. The latter involved the crosslinking of beta CD on electrospun PAN fibers by alkaline hydrolysis and esterification with citric acid. For both methods, we used solutions with different polymer concentration and viscosity. In addition, the rheology of solutions, as well as the morphology, surface area, chemical structure and thermal resistance of electrospun fibers were analyzed. The formaldehyde capture potential of beta CD containing PAN nanofibers was evaluated using high performance liquid chromatography. Conclusively, we found that, while functionalized PAN nanofibers with average fiber diameter from 432 nm to 647 nm might be used for indoor air purification, functionalized fibers obtained by addition of beta CD are more effective for capturing formaldehyde than fibers obtained by crosslinking of beta CD. (C) 2016 Elsevier Ltd. All rights reserved