Coupling of free surface and groundwater flows

In this paper we present some preliminary results about the coupling of shallow water equations for free surface flows and Darcy equation for groundwater flows. A suitable set of interface conditions is discussed: the Beavers and Joseph formula for the bottom stress is used. An iterative algorithm to solve the coupled problem is proposed and some numerical results are presented.     

Development of an Autonomous Robot for Gas Storage Spheres Inspection

Inspection for corrosion of gas storage spheres at the welding seam lines must be done periodically. Until now this inspection is being done manually and has a high cost associated to it and a high risk of inspection personel injuries. The Brazilian Petroleum Company, Petrobras, is seeking cost reduction and personel safety by the use of autonomous robot technology. This paper presents the development of a robot capable of autonomously follow a welding line and transporting corrosion measurement sensors. The robot uses a pair of sensors each composed of a laser source and a video camera that allows the estimation of the center of the welding line. The mechanical robot uses four magnetic wheels to adhere to the sphere’s surface and was constructed in a way that always three wheels are in contact with the sphere’s metallic surface which guarantees enough magnetic atraction to hold the robot in the sphere’s surface all the time. Additionally, an independently actuated table for attaching the corrosion inspection sensors was included for small position corrections. Tests were conducted at the laboratory and in a real sphere showing the validity of the proposed approach and implementation.     

Optimal Growth Conditions for Selective Ge Islands Positioning on Pit-Patterned Si(001)

We investigate ordered nucleation of Ge islands on pit-patterned Si(001) using an original hybrid Kinetic Monte Carlo model. The method allows us to explore long time-scale evolution while using large simulation cells. We analyze the possibility to achieve selective nucleation and island homogeneity as a function of the various parameters (flux, temperature, pit period) able to influence the growth process. The presence of an optimal condition where the atomic diffusivity is sufficient to guarantee nucleation only within pits, but not so large to induce significant Ostwald ripening, is clearly demonstrated.     

Irradiation effects in the electron microprobe quantitation of mineralized tissues.

The accuracy of absolute quantitation within thick, mineralized tissue specimens is influenced by count rate variations of characteristic X-rays during electron microprobe analysis. The variations occur for electron doses approximately greater than 10(-10) C/micrometer2 and are primarily dependent upon the light element fraction within the irradiated volume. Specimen preparation procedures affect both count rate dynamics and interpretatin of microanalytical results. X-ray intensity data acquird at initial electron exposure and utilized in standard matrix correction schemes will project valid elemental concentrations for known calcium compounds over wide ranges of specimen density. Measurement error could approach +/- 2-3% for the major elemental constituents in mineralized tissues, but only with appropriate control or interpretation of electron irradiation phenomena.     

Algebraic factorizations for 3D non-hydrostatic free surface flows

The high amount of computer resources required to simulate complex free surface flows has prompted for developing fractional step schemes capable of reducing the computational effort. These schemes are borrowed from a wider family of methods originally devised for the incompressible Navier-Stokes equations. An alternative approach is to perform an algebraic splitting on the coefficient matrix of the linear system resulting from the discretized problem, ending up with the successive solution of sub-problems of smaller size. The resulting schemes are shown in different cases to be the algebraic counterpart of the standard fractional step formulations. This algebraic procedure was again originally devised in the context of incompressible Navier-Stokes system, but we believe it is far more general: in this paper it is indeed extended to the more involved 3D free surface flow model. The inexact block factorization technique is applied to the coefficient matrix arising from the problem at hand and two significant choices for the approximation are discussed and numerically tested.     

Integration of InGaP/GaAs/Ge triple‐junction solar cells on deeply patterned silicon substrates

We report preliminary results on InGaP/InGaAs/Ge photovoltaic cells for concentrated terrestrial applications, monolithically integrated on engineered Si(001) substrates. Cells deposited on planar Ge/Si(001) epilayers, grown by plasma‐enhanced chemical vapor deposition, provide good efficiency and spectral response, despite the small thickness of the Ge epilayers and a threading dislocation density as large as 10⁷/cm². The presence of microcracks generated by the thermal misfit is compensated by a dense collection grid that avoids insulated areas. In order to avoid the excessive shadowing introduced by the use of a dense grid, the crack density needs to be lowered. Here, we show that deep patterning of the Si substrate in blocks can be an option, provided that a continuous Ge layer is formed at the top, and it is suitably planarized before the metalorganic chemical vapor deposition. The crack density is effectively decreased, despite that the efficiency is also lowered with respect to unpatterned devices. The reasons of this efficiency reduction are discussed, and a strategy for improvement is proposed and explored. Full morphological analysis of the coalesced Ge blocks is reported, and the final devices are tested under concentrated AM1.5D spectrum. Copyright © 2016 John Wiley & Sons, Ltd.     

Radial temperature differences during the melt spinning of fibers

In this investigation, a numerical model was developed to predict the temperature distribution in a fiber during melt spinning. This model uses the implicit Crank–Nicolson method to solve the governing differential equation for the problem. The model was applied to a series of numerical experiments on a liquid crystalline fiber which is melt-spun. These simulations used typical sets of operating conditions to determine the effect of various operating parameters on the predicted radius profile, spinline tension, and temperature distribution. The effects of spinneret capillary diameter, mass flow rate, ambient air temperature, spinning temperature, and elongational viscosity were investigated. The results of the various runs showed that ambient air temperature and mass flow rate had a significant effect on the predicted radius profile, spinline tension, and temperature distribution. The spinning temperature was an important parameter, but its only significant effect was on the spinline tension. Spinneret capillary diameter and elongational viscosity had little effect on the predicted results.