An ultrathin acoustic metasurface composed of an anisotropic three-component resonator

An ultrathin acoustic metasurface consisting of an anisotropic three-component resonator is proposed. The resonator can induce nondegenerate dipole resonances at the same resonant frequencies. A large phase delay can be obtained based on the resonance, which can be modulated by the direction of polarization. The anisotropic resonator can be regarded as an effective homogenous medium with an anisotropic mass density, and the phase change can also be attributed to the change of the effective material parameters. A good comparison between the results for the metasurface and its effective slab is obtained.

Laboratory-scaled Azimuthal Resistivity Survey for Fracture Detection

We conducted azimuthal resistivity survey (ARS) at laboratory scale to study apparent resistivity patterns due to fracture existing in subsurface through physical modeling using test objects buried in a sandbox as well as in a test location outside laboratory building. This survey was divided into 2 experiments, i.e. experiment A and experiment B. In experiment A the survey is implemented on 2.50 m x 1.5 m x 0.81 m sandbox, made of 10mm thick glass plates. Sandstone was used as medium representing quasi homogenous medium. Clay roof tiles as well as steel plates as test objects were buried in the sandbox with three different deep angles: 90°, 45° and 0°. In experiment B this survey was conducted outside laboratory building on the grass field and implemented on 2.50 m x 2.5 m x 1.0 m soil body. Vertical single glass plate as well as vertical double glass plates at 30 cm distance were buried in the soil body. Azimuthal resistivity measurements at 15° angular step using Wenner and dipole-dipole configuration were carried out in both experiments located at 1 point just above anomalous object for experiment A and at 3 points at 15 cm distance from anomalous object for experiment B. As a compliment to ARS we acquired profiling data from two lines parallel and perpendicular to horizontal axis of anomalous object. Our results show that the apparent resistivity pattern can show the direction of anomalous object for both configurations and experiments with a little deviation.

Effect of Shear Flow on Nanoparticles Migration near Liquid Interfaces

The effect of shear flow on spherical nanoparticles (NPs) migration near a liquid–liquid interface is studied by numerical simulation. We have implemented a compact model through which we use the diffuse interface method for modeling the two fluids and the molecular dynamics method for the simulation of the motion of NPs. Two different cases regarding the state of the two fluids when introducing the NPs are investigated. First, we introduce the NPs randomly into the medium of the two immiscible liquids that are already separated, and the interface is formed between them. For this case, it is shown that before applying any shear flow, 30% of NPs are driven to the interface under the effect of the drag force resulting from the composition gradient between the two fluids at the interface. However, this percentage is increased to reach 66% under the effect of shear defined by a Péclet number Pe = 0.316. In this study, different shear rates are investigated in addition to different shearing times, and we show that both factors have a crucial effect regarding the migration of the NPs toward the interfacial region. In particular, a small shear rate applied for a long time will have approximately the same effect as a greater shear rate applied for a shorter time. In the second studied case, we introduce the NPs into the mixture of two fluids that are already mixed and before phase separation so that the NPs are introduced into the homogenous medium of the two fluids. For this case, we show that in the absence of shear, almost all NPs migrate to the interface during phase separation, whereas shearing has a negative result, mainly because it affects the phase separation.

Attenuation of beta radiation in granular matrices: implications for trapped-charge dating

Mineral grains within sediment or rock absorb a radiation dose from the decay of radionuclides in the host matrix. For the beta dose component, the estimated dose rate must be adjusted for the attenuation of beta particles within the mineral grains. Standard calculations, originally designed for thermoluminescence dating of pottery, assume that the grain is embedded in a homogenous medium. However, most current applications of trapped-charge dating concern sand- or silt-sized dosimeters embedded in granular sediment. In such cases, the radionuclide sources are not homogeneous, but are localized in discrete grains or held on grain surfaces. We show here that the mean dose rate to dosimeter grains in a granular matrix is dependent on the grain-size distributions of the source grains, and of the bulk sediment, as well as on the grain size of the dosimeters. We further argue that U and Th sources are likely to be held primarily on grain surfaces, which causes the dose rate to dosimeter grains to be significantly higher than for sources distributed uniformly throughout grains. For a typical well-sorted medium sand, the beta dose rates derived from surface U and Th sources are higher by 9 % and 14 %, respectively, compared to a homogenous distribution of sources. We account for these effects using an expanded model of beta attenuation, and validate the model against Monte Carlo radiation transport simulations within a geometry of packed spheres.

Homogeneous succinylation of cellulose acetate: Design, characterization and adsorption study of Pb(II), Cu(II), Cd(II) and Zn(II) ions

In this study, the removal of Pb(II), Cu(II), Cd(II), and Zn(II) ions from aqueous solutions was investigated using succinic anhydride modified cellulose monoacetate. In the first part, the cellulose acetate was successfully succinylated in a homogenous medium of DMF using 4-dimethylaminopyridine (DMAP) as a catalyst. The obtained material (AcS) was analyzed by FTIR and CP/MAS 13C NMR Spectroscopy, thermogravimetry analysis and DRX patterns. The titration method was used to determinate the degree of hydroxyl group substituted by carboxyl group (DS) and was found to be 1.36. In the second part, the Bach technique was used to study the effects of pH, contact time, concentration of metals, ionic selectivity and regeneration. Maximum sorption capacities of AcS for Pb(II), Cu(II), Cd(II), and Zn(II) were 241.81, 133.76, 156.61 and 73,58 mg.g-1, respectively. The Langmuir isotherm and the pseudo second order kinetic models provided best fit to the experimental data of metal ion sorption. The nature of the adsorption process was exothermic and spontaneous in nature with negative values of ΔG° and ΔH°. Regeneration of the modified cellulose acetate was accomplished using nitric solution and showed high stability and good recyclability.

Concurrent self-regulated autonomous synthesis and functionalization of pH-responsive giant vesicles by a chemical pH oscillator

pH oscillatory chemistry-driven generation of polymer vesicles from homogenous medium and their pH-responsive self-assembly in a one-pot reaction network.

Dynamics of sheared droplets filled with non-Brownian particles

The dynamics of single droplets containing non-Brownian particles are studied. The particle over droplet size ratio (r/R) is changed by using different particle sizes (r/R = 0.02–0.4). Additionally, the effect of particle concentration (5–20 vol%) is investigated. The dynamics of droplets with r/R = 0.02 show good agreement with the corresponding particle-free reference system which has a comparable viscosity ratio. Hence, this droplet phase can be considered as a homogenous medium characterized by its bulk viscosity which is governed by the particle concentration. However, droplets with r/R ≥ 0.1 show a more suppressed deformation and slower transient dynamics and, therefore, behave as a slightly more viscous medium than expected based on their bulk viscosity. These effects become more pronounced at higher particle concentrations and higher r/R. Moreover, local particle effects like asymmetric droplet shapes, oscillating droplet shapes, and tip streaming start to influence the droplet dynamics at particle concentrations around 15 vol%.

Mapping lithological boundaries in mines with array seismology and in situ acoustic emission monitoring

SUMMARY Knowledge of the position of lithological boundaries is key information for a realistic interpretation of geological settings. Especially in the mining environment, the exact knowledge of geometrical boundaries and characteristics of rock structures has a great impact for both economic decisions and safety awareness. For this purpose, we investigate the P-coda of high frequency acoustic emission (AE) events (picoseismicity) and test the application of array seismology techniques, usually used to study the Earth's deep interior, on a much smaller scale in a mining environment. In total 52 events were used, all of them recorded in the Asse II salt mine in Lower Saxony (Germany) using a network of 16 piezoelectric sensors. Many of these events show a pulse-like arrival in the late P-coda, suggesting the presence of a well-defined structure which scatters seismic energy. To explore the directional information of the signals in the seismograms we use the sliding-window slowness-backazimuth analysis, performed on the waveform envelope of the entire recording. Strong direct P-wave arrivals are clearly visible with observed slowness and backazimuth as expected for a homogenous medium. This implies straight ray paths from event to sensors indicating that the medium between the events and the sensors is homogeneous for wavelengths larger than about 60 cm. In the late P-coda we observe out-of-plane arrivals from southeast and, assuming single P-to-P scattering, we find that the scatterers responsible for these observations are clustered in space defining a sharp reflector corresponding to a known lithological boundary located at the southern flank of the salt dome. In agreement with the established geological model we observe no other dominant reflections in the analysed waveforms that would indicate previously unknown lithological boundaries. This study shows that array seismology can be applied to AEs in mines to gain more information on structures and heterogeneities located in the vicinity of the monitored rock volume. In micro-acoustically monitored mines, this technique could be a valuable addition to increase hazard awareness and mining efficiency at little or no extra costs.

Study of Parameter Influence on Quality on the Electromagnetic Imaging Reconstruction from the Spectrum of the Diffracted Field: Application to Reconstruction of the leakage Current of ISM Applicators

The ISM applicators generate leakage currents that can disrupt satellite TV transmission, taking into account the effects of the electromagnetic waves and those of the CEM. We are interested in these as a way to reconstitute their leakage currents, using the Micro-waves Imagery. We propose such a method of spectral analysis, which is intended to reconstruct the equivalent current distribution (position and form) to an object starting from the diffracted field spectrum by the Micro-waves Imagery. Our contribution resides in the influence of different parameters (N number of the measurement point, and the distance z0 of the measurement plane) on the reconstitution quality. This method is presented and illustrated; an algorithm of reconstructing the image of an object existing within a surrounding homogenous medium with known dielectric properties, this algorithm is developed with MATLAB. This method leads to more significant results, and quickly permits to get information about the object form.