indexGIXS – software for visualizing and interactive indexing of grazing-incidence scattering data

Grazing incidence small- and wide-angle scattering (GISAXS, GIWAXS) are widely applied for the study of organic thin films, be it for the characterization of nanostructured morphologies in block copolymers, nanocomposites, or nanoparticle assemblies, or the packing and orientation of small aromatic molecules and conjugated polymers. Organic thin films typically are uniaxial powders, with specific crystallographic planes oriented parallel to the substrate surface. The associated fiber texture scattering patterns are complicated by refraction corrections and multiple scattering. We present an interactive graphics tool to index such patterns.

Deformation Mechanisms in Orogenic Gold Systems During Aseismic Periods: Microstructural Evidence from the Central Victorian Gold Deposits, Southeast Australia

In many orogenic gold deposits, gold is located in quartz veins. Understanding vein development at the microstructural scale may therefore provide insights into processes influencing the distribution of gold, its morphology, and its relationship to faulting. We present evidence that deformation processes during aseismic periods produce characteristic quartz microstructures and crystallographic preferred orientations, which are observed across multiple deposits and orogenic events. Quartz veins comprise a matrix of coarse, subidiomorphic, and columnar grains overprinted by finer-grained quartz seams subparallel to the fault trace, which suggests an initial stage of cataclastic deformation. The fine-grained quartz domains are characterized by well-oriented quartz c-axis clusters and girdles oriented parallel to the maximum extension direction, which reveals that fluid-enhanced pressure solution occurred subsequent to grain refinement. Coarser anhedral gold is associated with primary quartz, whereas fine-grained, “dusty” gold trails are found within the fine-grained quartz seams, revealing a link between aseismic deformation and gold morphology. These distinct quartz and gold morphologies, observed at both micro- and macroscale, suggest that both seismic fault-valving and aseismic deformation processes are both important controls on gold distribution.

Hydraulic Fracture Propagation Near the Cavity in a Poroelastic Media

In this paper, we investigate the problem of the propagation of hydraulic fractures in a poroelastic medium that has a circular cavity. The research was conducted using the extended finite element method (XFEM) implemented in the ABAQUS software package. The problem was considered in a plane formulation. The initial crack was oriented parallel to the surface of the cavity. It was shown that the path of the hydraulic fracture depends strongly on the hydrostatic stress in the medium and the distance between the crack and the cavity. We studied the influences of the poroelastic parameters, such as permeability and the Biot coefficient, on the propagation of cracks. It was shown that the cracks were less curved when the coupled problem of poroelasticity was considered. The features of fluid pressure changes inside the fracture and at the opening of the mouth were studied. It was shown that the fluid pressure in the fracture during injection was minimally sensitive to the state of the stress in the medium, to the position of the initial crack, and to the poroelastic parameters. The solution to the problem in this setting can be used to simulate hydraulic fracturing close to mine workings during a controlled roof’s collapse to prevent it from hanging, and the formation of impervious screens to reduce airflow from the mine to degassing boreholes through the rock, for example.

Shear orientation of nematic phases of clay nanosheets: processing of barrier coatings

When suspensions are exposed to shear forces, the particles may form ordered structures depending on their shapes, concentrations, and the material. For some processes, e.g., for wet-film coating, it is important to know how fast these structures form in shear fields and for how long the structures persist when the shear is relaxed. To obtain information on the particle structure formation and the decay time, the effective viscosity of nematic suspensions of Na-hectorite nanosheets was investigated by rheology employing a cone-plate measurement geometry. The necessary time for the formation textured nematic films could be deduced by carrying out effective viscosity measurements at constant time steps. Information could also be obtained on the lifetime of the platelet textures when shear is relaxed. All this information was employed to identify geometrical requirements for slot dies to produce barrier liners with nanosheet layers oriented parallel to PET substrates. Thereby, we obtained green and simple coatings that are in line with state-of-the-art high-performance materials such as metalized plastic foils in terms of oxygen barrier properties.

indexGIXS – software for visualizing and interactive indexing of grazing-incidence scattering data

Grazing incidence small- and wide-angle scattering (GISAXS, GIWAXS) are widely applied for the study of organic thin films, be it for the characterization of nanostructured morphologies in block copolymers, nanocomposites, or nanoparticle assemblies, or the packing and orientation of small aromatic molecules and conjugated polymers. Organic thin films typically are uniaxial powders, with specific crystallographic planes oriented parallel to the substrate surface. The associated fiber texture scattering patterns are complicated by refraction corrections and multiple scattering. We present an interactive graphics tool to index such patterns.

Texture and Anisotropy of Hot-Pressed h-BN Matrix Composite Ceramics With in Situ Formed YAG

Textured h-BN matrix composite ceramics were prepared by hot-pressing using different contents of 3Y2O3-5Al2O3 (mole ratio of 3:5) as the liquid phase sintering additive. During the hot-pressing process, the liquid Y3Al5O12 (YAG) phase with good wettability to h-BN grains was in situ formed through the reaction between Y2O3 and Al2O3, and a coherent relationship between h-BN and YAG was observed with [010]h-BN // [1̅11]YAG and (002)h-BN // (321)YAG. Plate-like h-BN grains in the YAG liquid phase environment were rotated under the action of the uniaxial sintering pressure, making their basal surfaces preferentially arranged perpendicular to the sintering pressure, forming textured microstructures with the c-axis of h-BN grains oriented parallel to the sintering pressure, which give these composite ceramics anisotropy in their mechanical and thermal properties. The highest texture degree was found in the specimen with 30 wt.% YAG content, which also possesses the most anisotropic thermal conductivity. The aggregation of YAG phase resulting in the buckling of h-BN plates was observed in the specimen with 40 wt.% YAG content, which significantly reduced its texture degree.

Marine boundary layers above heterogeneous SST: Along-front winds

Turbulent flow in a weakly convective marine atmospheric boundary layer (MABL) driven by geostrophic winds Vg = 10ms−1 and heterogeneous sea surface temperature (SST) is examined using fine mesh large eddy simulation (LES). The imposed SST heterogeneity is a single-sided warm or cold front with jumps Δθ = (2, −1.5)K varying over a horizontal x distance of 1 km characteristic of an upper ocean mesoscale or submesoscale front. The geostrophic winds are oriented parallel to the SST isotherms, i.e., the winds are along-front. Previously, Sullivan et al. (2020) examined a similar flow configuration but with geostrophic winds oriented perpendicular to the imposed SST isotherms, i.e., the winds were across-front. Results with along-front and across-front winds differ in important ways. With along-front winds the ageostrophic surface wind is weak, about 5 times smaller than the geostrophic wind, and horizontal pressure gradients couple the SST front and the atmosphere in the momentum budget. With across-front winds horizontal pressure gradients are weak and mean horizontal advection primarily balances vertical flux divergence. Along-front winds generate persistent secondary circulations (SC) that modify the surface fluxes as well as turbulent fluxes in the MABL interior depending on the sign of Δθ. Warm and cold filaments develop opposing pairs of SC with a central upwelling or downwelling region between the cells. Cold filaments reduce the entrainment near the boundary-layer top which can potentially impact cloud initiation. The surface-wind SST-isotherm orientation is an important component of atmosphere-ocean coupling. The results also show frontogenetic tendencies in the MABL.

Evaluation of Adhesive Interface Properties in Honeycomb Sandwich Structure Using Guided Waves

A method is presented to evaluate the interfacial weakness of aluminium-based honeycomb sandwich structure (HSS) using Shear Horizontal (SH) guided wave. SH guided waves are sensitive to the interfacial properties since the wave particles vibration is oriented parallel to the adhesive-adherent joints. Periodic permanent magnet (PPM) electromagnetic acoustic transducers (EMATs) are used to excite and detect SH-guided waves. A semi-analytical finite element method is developed to simulate the SH wave propagation in HSS. The boundary stiffness approach is used to model the adhesive-adherent interface. The excitation parameters are chosen such that only SH0 mode is generated in the structure. The interaction of the fundamental SH0 wave mode with various defects and the different interface stiffness is analyzed. The frequency-wavenumber analysis is used to study the effect of interface stiffness on SH wave propagation. The analysis reveals that in a perfect bond, SH0 and S0 guided modes are present. The interaction of SH0 mode with the honeycomb core results in the genesis of S0 mode. Thus, the presence or absence of the S0 mode can be used as an indicator of bond quality. The findings from the FE simulation are validated against the experiment. The analysis shows a reliable non-destructive evaluation of the interface joint and classifying them as good or bad bonds.

Global Ocean Studies from CALIOP/CALIPSO by Removing Polarization Crosstalk Effects

Recent studies indicate that the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite provides valuable information about ocean phytoplankton distributions. CALIOP’s attenuated backscatter coefficients, measured at 532 nm in receiver channels oriented parallel and perpendicular to the laser’s linear polarization plane, are significantly improved in the Version 4 data product. However, due to non-ideal instrument effects, a small fraction of the backscattered optical power polarized parallel to the receiver polarization reference plane is misdirected into the perpendicular channel, and vice versa. This effect, known as polarization crosstalk, typically causes the measured perpendicular signal to be higher than its true value and the measured parallel signal to be lower than its true value. Therefore, the ocean optical properties derived directly from CALIOP’s measured signals will be biased if the polarization crosstalk effect is not taken into account. This paper presents methods that can be used to estimate the CALIOP crosstalk effects from on-orbit measurements. The global ocean depolarization ratios calculated both before and after removing the crosstalk effects are compared. Using CALIOP crosstalk-corrected signals is highly recommended for all ocean subsurface studies.

Flat liquid metal jet affected by a transverse magnetic field

A liquid metal flat jet immersed in a square duct under the influence of a transverse magnetic field is studied experimentally. Two cases are considered: when the applied magnetic field is oriented parallel (coplanar field) or perpendicularly (transverse field) to the initial plane of the jet. The main goal of the study is to investigate the mean flow characteristics and the stages of the jet's transformation. Signals of streamwise velocity at different locations are measured, which allows us to determine average velocity profiles and spatial-temporal characteristics of the velocity field. The two considered configurations are directly compared under the same flow regimes, with the same equipment. Figs 8, Refs 11.