A thick bondline beam model for the adhesively bonded 3-point bending specimen

The adhesively bonded 3-point bending specimen has been recently considered for evaluating the adhesive shear stress-strain behaviour. Its main advantage is avoiding the spurious end effects typical of lap-joints. A previous beam model proved to be fairly accurate for thin bondlines typical of structural joints. The present study extends such model to thick bondlines and achieves improved shear strain results. Model predictions were in very good agreement with finite element analyses of specimens with metal adherends and adhesive elastic-perfectly plastic behaviour. The present model will facilitate the inverse method needed to evaluate the parameters of a piecewise linear approximation to the adhesive shear stress-strain curve. Furthermore, two simplified models were shown to provide useful bounds for the shear stress-strain curve using only the basic load-displacement data.publishe

Type A GABA-receptor-dependent synaptic transmission sculpts dendritic arbor structure in Xenopus tadpoles in vivo.

The emergence of dendritic arbor structure in vivo depends on synaptic inputs. We tested whether inhibitory GABAergic synaptic transmission regulates Xenopus optic tectal cell dendritic arbor development in vivo by expressing a peptide corresponding to an intracellular loop (ICL) of the γ2 subunit of GABAAR which is required to anchor GABAA receptors to the postsynaptic scaffold. GFP-tagged ICL (EGFP-ICL) was distributed in a punctate pattern at putative inhibitory synapses, identified by VGAT-immunoreactive puncta. ICL expression completely blocked GABAAR - mediated transmission in 36% of transfected neurons and significantly reduced GABAAR - mediated synaptic currents relative to AMPAR-mediated synaptic currents in the remaining transfected neurons without altering release probability or neuronal excitability. Further analysis of ICL-expressing neurons with residual GABAAR- mediated inputs showed that the capacity of benzodiazepine to enhance GABAergic synaptic responses was reduced in ICL-expressing neurons, indicating that they were likely depleted of γ2 subunit-containing GABAAR. Neurons expressing a mutant form of ICL were comparable to controls. In vivo time-lapse images showed that ICL-expressing neurons have more sparsely branched dendritic arbors which expand over larger neuropil areas than EGFP-expressing control neurons. Analysis of branch dynamics indicated that ICL expression affected arbor growth by reducing rates of branch addition. Furthermore, we found that decreasing GABAergic synaptic transmission with ICL expression blocked visual experience dependent dendritic arbor structural plasticity. Our findings establish an essential role for inhibitory GABAergic synaptic transmission in the regulation of dendritic structural plasticity in Xenopus in vivo

Renewable fuel production from hydropyrolysis of residual biomass using molybdenum carbide-based catalysts: An analytical Py-GC/MS investigation

Fast hydropyrolysis of lignocellulosic biomass was studied by using an analytical pyrolyzer coupled with a gas chromatography/mass spectrometry set-up (Py-GC/MS). Under pure H2 stream, Canadian pinewood was rapidly heated up to 500 °C and the generated vapors passed through a catalytic bed at 500 °C. Experiments were carried out in order to compare the catalytic performance of MoC/Al2O3 catalyst to a reference catalyst based on noble metal (1.5 wt.% Pt/Al2O3). The effect of different supports (Al2O3, ZrO2 and MgO) on the carbide performance and product formation was investigated. The results showed that the performance of MoC/Al2O3 was similar to that of 1.5 wt.% Pt/Al2O3. Both of them deoxygenated the hydropyrolysis vapors and led exclusively to hydrocarbons formation. However, the proportion of aliphatic and aromatic hydrocarbons was different: MoC/Al2O3 catalyst produced more aliphatics (57%) than the Pt catalyst. The supports have demonstrated influence on the product distribution. Acidity of the support seems to play an important role in the deoxygenation of the vapors. While there was complete removal of oxygen when MoC/Al2O3 and MoC/ZrO2 were used, the same did not take place for the more basic MoC/MgO catalyst

1,4-Dioxane-degrading consortia can be enriched from uncontaminated soils: prevalence of Mycobacterium and soluble di-iron monooxygenase genes

Two bacterial consortia were enriched from uncontaminated soil by virtue of their ability to grow on 1,4-dioxane (dioxane) as a sole carbon and energy source. Their specific dioxane degradation rates at 30°C, pH = 7 (i.e. 5.7 to 7.1 g-dioxane per g-protein per day) were comparable to those of two dioxane-metabolizing archetypes: Pseudonocardia dioxanivoransCB1190 and Mycobacterium dioxanotrophicusPH-06. Based on 16S rRNA sequencing, Mycobacterium was the dominant genus. Acetylene inhibition tests suggest that dioxane degradation was mediated by monooxygenases. However, qPCR analyses targeting the tetrahydrofuran/dioxane monooxygenase gene (thmA/dxmA) (which is, to date, the only sequenced dioxane monooxygenase gene) were negative, indicating that other (as yet unknown) catabolic gene(s) were responsible. DNA sequence analyses also showed threefold to sevenfold enrichment of group 5 and group 6 soluble di-iron monooxygenase (SDIMO) genes relative to the original soil samples. Whereas biodegradation of trace levels of dioxane is a common challenge at contaminated sites, both consortia degraded dioxane at low initial concentrations (300 μg l−1) below detectable levels (5 μg l−1) in bioaugmented microcosms prepared with impacted groundwater. Overall, this work shows that dioxane-degrading bacteria (and the associated natural attenuation potential) exist even in some uncontaminated soils, and may be enriched to broaden bioaugmentation options for sites experiencing insufficient dioxane catabolic capacity

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable Ni-based superalloys. This lack of in-depth understanding of the root causes of hot cracking is an impediment to designing engineering parts for safety-critical applications. Here, we deploy a near-atomic-scale approach to investigate the details of the compositional decoration of grain boundaries in the coarse-grained, columnar microstructure in parts built from a non-weldable Ni-based superalloy by selective electron-beam melting. The progressive enrichment in Cr, Mo and B at grain boundaries over the course of the AM-typical successive solidification and remelting events, accompanied by solid-state diffusion, causes grain boundary segregation induced liquation. This observation is consistent with thermodynamic calculations. We demonstrate that by adjusting build parameters to obtain a fine-grained equiaxed or a columnar microstructure with grain width smaller than 100 $\mu$m enables to avoid cracking, despite strong grain boundary segregation. We find that the spread of critical solutes to a higher total interfacial area, combined with lower thermal stresses, helps to suppress interfacial liquation.Comment: Accepted version at Acta Materiali

Improved vectorial finite-element BPM analysis for transverse anisotropic media

An efficient finite-element vector beam propagation formulation for dielectric media with transverse anisotropy is thoroughly presented. This formulation is expressed in terms of the magnetic field's transverse components and includes perfectly matched layers at the truncated boundaries and the wide-angle Pade approach. Several key examples demonstrate the usefulness and effectiveness of the present scheme.21256757

The symmetry of charge order in cuprates

Charge-ordered ground states permeate the phenomenology of 3d-based transition metal oxides, and more generally represent a distinctive hallmark of strongly-correlated states of matter. The recent discovery of charge order in various cuprate families fueled new interest into the role played by this incipient broken symmetry within the complex phase diagram of high-Tc superconductors. Here we use resonant X-ray scattering to resolve the main characteristics of the charge-modulated state in two cuprate families: Bi2201 and YBCO. We detect no signatures of spatial modulations along the nodal direction in Bi2201, thus clarifying the inter-unit-cell momentum-structure of charge order. We also resolve the intra-unit-cell symmetry of the charge ordered state, which is revealed to be best represented by a bond-order with modulated charges on the O-2p orbitals and a prominent d-wave character. These results provide insights on the microscopic description of charge order in cuprates, and on its origin and interplay with superconductivity.Comment: A high-resolution version with supplementary material can be found at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/CDW_symmetry.pd

Doping dependent charge order correlations in electron-doped cuprates

Understanding the interplay between charge order (CO) and other phenomena (e.g. pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. Here, we use resonant x-ray scattering to measure the charge order correlations in electron-doped cuprates (La2-xCexCuO4 and Nd2-xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range, and that its doping dependent wavevector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166, but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wavevector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall these findings indicate that, while verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates.Comment: Supplementary information available upon reques