Integrated geophysical and geochemical assessment of submarine groundwater discharge in coastal terrace of Tiruchendur, Southern India

Submarine groundwater discharge (SGD) study is essential for groundwater in coastal terrace at Tiruchendur. The famous Murugan Temple is located in the area and around 25,000 people who visit this temple use the SGD well water at NaaliKinaru (a small open well) as holy water and drink it. The rock and soil type are sandy clay, silt, beach sand, calcarenite, kankar, gneissic rock and charnockite in base rock. Megascopic identification method was used to identify the porous and permeable rocks such as calcarenite, sandstone and kankar to support to increase SGD flux. Grain size study was used to identify the paleo-coastal estuarine environment with sediment deposits in the terrace. The square array electrical resistivity method was used to study the subsurface geology and aquifer depth. The 2d ERT technique was used to identify the subsurface shallow perched aquifer of freshwater. The magnetotelluric survey method was used to scan the entire subsurface geological and tectonic uplift, coastal ridges, rock folded subsurface structural features of continental and oceanic tectonism. Darcy’s law was used to calculate the SGD flux rate in the above study area.

3D chest tomosynthesis using a stationary flat panel source array and a stationary detector: A Monte Carlo proof of concept.

3D imaging modalities such as computed tomography and digital tomosynthesis typically scan the patient from different angles with a lengthy mechanical movement of a single X-ray tube. Therefore, millions of 3D scans per year require expensive mechanisms to support a heavy X-ray source and have to compensate for machine vibrations and patient movements. However, recent developments in cold-cathode field emission technology allow the creation of compact, stationary arrays of emitters. Adaptix Ltd. has developed a novel, low-cost, square array of such emitters and demonstrated 3D digital tomosynthesis of human extremities and small animals. The use of cold-cathode field emitters also makes the system compact and lightweight. This paper presents Monte Carlo simulations of a concept upgrade of the Adaptix system from the current 60 kVp to 90 kVp and 120 kVp which are better suited for chest imaging. Between 90 kVp and 120 kVp, 3D image quality appears insensitive to voltage and at 90 kVp the photon yield is reduced by 40-50% while effective dose declines by 14%. A square array of emitters can adequately illuminate a subject for tomosynthesis from a shorter source-to-image distance, thereby reducing the required input power, and offsetting the 28-50% more input power that is required for operation at 90 kVp. This modelling suggests that lightweight, stationary cold-cathode X-ray source arrays could be used for chest tomosynthesis at a lower voltage, with less dose and without sacrificing image quality. This will reduce weight, size and cost, enabling 3D imaging to be brought to the bedside.

A COMPLEX POTENTIAL APPROACH TO MICROMECHANICS OF UNIDIRECTIONAL COMPOSITES

Complex potential methods for the solution of two-dimensional boundary value problems in linear elasticity are used to perform micromechanics analysis of unidirectional composites. The composite microstructure is idealized as a square array of unit cells subjected to prescribed strains. Unit cell analyses are performed for plane strain and anti-plane strain conditions to study the interaction of the fiber and matrix materials. The unit cell solutions are used to derive predictions for the ply moduli, Poisson’s ratios and coefficients of thermal expansion, which are shown to agree with the results of other methods. Applications to strength prediction are briefly discussed, and the detailed stress field results that can be generated using the approach are illustrated.

Absorption of Light in Finite Semiconductor Nanowire Arrays and the Effect of Missing Nanowires

When modelling the absorption in semiconductor nanowire (NW) arrays for solar cell and photodetector applications, the array is typically assumed to be infinitely periodic such that a single unit cell suffices for the simulations. However, any actual array is of a finite extent and might also show varying types of localized defects such as missing or electrically non-contacted individual NWs. Here, we study InP NWs of 2000 nm in length and 180 nm in diameter, placed in a square array of 400 nm in period, giving a rather optimized absorption of sunlight. We show that the absorption in the center NW of a finite N × N array converges already at N = 5 close to the value found for the corresponding infinite array. Furthermore, we show that a missing NW causes an enhanced absorption in neighboring nanowires, which compensates for 77% of the absorption loss due to the missing NW. In other words, an electrically non-contacted NW, which absorbs light but cannot contribute to the external short-circuit current, is a four times worse defect than a missing NW.

Nonlinear Dynamics of Cross-Flow Tubes Subjected to Initial Axial Load and Distributed Impacting Constraints

The dynamics of cross-flow tubes were studied in consideration of initial axial load and distributed impacting constraints, modeled as cubic and trilinear spring constraints. The tubes were modeled as Euler–Bernoulli beams and supported at both ends, including the simply supported tube and clamped-clamped tube. The analytical model involves a time-delayed displacement term induced by the cross flow based on the quasi-steady theory. For simplicity, a single flexible supported beam in a rigid square array of cylinders was studied by using the damping-controlled mechanism. The mean extension of the tube was considered, and thus, it added another nonlinear term in the equation of motion. Results show that the tube loses stability by buckling and fluttering at various initial pressure loads and cross-flow velocities. An increase was observed for critical velocities and initial pressure loads. Chaotic oscillations were observed for the trilinear spring model. The distribution of the impacting forces was also calculated. Some of the fresh results obtained in the impact system are expected to be helpful in understanding and controlling the dynamic responses of fluid-conveying pipes.

Controlled Excitation of Supermodes in a Multicore Fiber with a 5 × 5 Square Array of Strongly Coupled Cores

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central wavelength of 1030 nm in a multicore fiber with coupled cores arranged in a square array. We designed and fabricated a silica multicore fiber with a 5 × 5 array of cores. For controllable excitation of a desired supermode, we developed a beam-forming system based on a spatial light modulator. We experimentally measured intensity and phase distributions of the supermodes, in particular, the in-phase and out-of-phase supermodes, which matched well the numerically calculated profiles. We obtained selective excitation and coherent propagation of broadband radiation with the content of the out-of-phase supermode of up to 90% maintained without active feedback. Using three-dimensional numerical modeling with allowance for a refractive index profile similar to those of the developed fiber, we demonstrated stable propagation of the out-of-phase supermode and collapse of the in-phase supermode at a high signal power.

Surface wave reflection from a metasurface termination

The reflection coefficient of a microwave surface wave incident at the termination of a metasurface is explored. Two different surface types are examined. One is a square array of square metallic patches on a dielectric-coated metallic ground plane, the other a Sievenpiper ‘mushroom’ array. In the latter the surface wave fields are more confined within the structure. Comparison of the measured surface-wave reflection spectra is made with that obtained from analytic theory and numerical modelling. The reflection coefficient is shown to be dependent on both the momentum mismatch between the surface wave and the freely propagating modes as well as the different field distributions of the two modes.

A Simulation of a Novel High Quantum Efficiency Scintillating Fiber Detector with Anti-scatter Properties for Megavoltage X-Ray Imaging

To further develop a MV x-ray portal imaging device with high detection efficiency and adequate spatial resolution for image guided radiation therapy, the experimental results for a prototype detector were matched using Monte-Carlo software to then improve upon the design. The simulation and experiment were carried out using a 6 MV beam from a linear accelerator machine. An adequate match was obtained with the spatial resolution matching up to a MTF value of 0.2 and then diverging and the total signal registered in the central fiber was matched for field sizes ranging from 3 cm by 3 cm to 20 cm by 20 cm for 5 cm, 15 cm and 25 cm air gaps within 3%. The design was altered from a hexagonal array of round double cladded fibers to a square array of single cladded square fibers. The spatial resolution was improved from 0.242 lp mm-1 to 0.359 lp mm-1 at an MTF value of 0.5 from the original design to a square array of square fibers 0.5 mm wide separated by 0.25 mm of lead foil. With further optimization of the detector design it may be possible to increase spatial resolution for MV x-ray imaging while maintaining an adequate detection efficiency.