Analysis of tunnel diode antenna using iterative method

An efficient iterative method, based on the wave concept has been used to analyze the printed tunnel diode integrated antenna. A high computational speed has been achieved by introducing a 2D fast Fourier transformation (2D-FFT) in wave-guide environment. The simulated results are compared with published data and a good agreement is observed.     

Comparison of Thin Films of Titanium Dioxide Deposited by Sputtering and Sol–Gel Methods for Waveguiding Applications

Semiconductors - In this work, TiO2 thin films were deposited onto glass substrate by two different techniques: sol–gel dip-coating (SG) and reactive DC magnetron sputtering (Sput). The...     

MMG measurement: a high-sensitivity microphone-based sensor forclinical use

A high-sensitivity human muscle-vibration measurement (MMG) sensor adapted to clinical use is presented. The muscle vibration phenomenon is modeled and investigated to optimize the measurement technique. The sensor uses an acoustic impedance adaptation technique to convert the skin surface vibration in terms of acoustic pressure, which is sensed by a microphone. The device is calibrated and gives the real amplitude of the vibration. It is also well fitted to measure other physiological vibrations in the 2 Hz-1 kHz range     

Selfishness in secure internet of things networks: 6TiSCH case study

Wireless Networks - Performance and communication security in the Internet of Things (IoT) area draw a major concern for both academic and industrial communities. Indeed, an emerging number of IoT...     

Relaxor behavior in (Ba1−3x/2Bix)(ZryTi1−y)O3 ceramics

New ferroelectric ceramics Bi-BZT of ABO₃ perovskite type were synthesized in the (Ba_1−3x/2Bi_x)(Zr_yTi_1−y)O₃ system by solid state reaction route. The effect of the substitution of barium by bismuth in the A cationic site on structural and dielectric properties was investigated. The dielectric constant was studied in the temperature range from 20 K to 320 K at frequencies ranging from 0.2 to 100 kHz. A clear relaxor behavior was observed for samples with x ≥ 0.075 and y = 0.1. In this case the value of the relaxation parameter γ ≈ 2 estimated from the linear fit of the modified Curie–Weiss law, indicates the relaxor nature of the Bi-BZT ceramics. The dielectric relaxation rate follows Vogel–Fulcher relation with an activation energy of 0.26 eV and 0.27 eV, an attempt frequency f₀ = 3.4 × 10¹² Hz and 5.7 × 10¹² Hz and a static freezing temperature T_VF = 98 K and 94 K respectively for x = 0.075 and x = 0.1.     

Limitations of Preferential Enrichment: A Case Study on Tryptophan Ethyl Ester Hydrochloride

Since eutomer and distomer show different biological effects, access to pure enantiomers is essential. Preferential enrichment is a relatively new process of chiral resolution developed in the 90s. Extension of its scope was attempted with tryptophan ethyl ester hydrochloride. This salt meets one of the most important requirements for preferential enrichment, namely, a larger solubility for the pure enantiomers with reference to the racemic compound. But, due to the absence of a solid solution, this salt cannot perform preferential enrichment. This impossibility was endorsed by semi‐empirical molecular modeling.     

Influence of various process conditions on surface finishes induced by the direct metal deposition laser technique on a Ti–6Al–4V alloy

The direct metal deposition (DMD) with laser is a free-form metal deposition process for manufacturing dense pieces, which allows generating a prototype or small series of near net-shape structures. One of the most critical issues is that produced pieces have a deleterious surface finish which systematically requires post machining steps. This problem has never been fully addressed before.The present work describes investigations on the DMD process, using an Yb-YAG disk laser, and a widely used titanium alloy (Ti–6Al–4V) to understand the influence of the main process parameters on the surface finish quality. The focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish.In order to understand the physical mechanisms responsible for deleterious surface finishes, we have carried out: (1) a precise characterization of the laser beam and the powder stream; (2) a large number of multi-layered walls using different process parameters (P(W), V(m/min), D_m (g/min), Gaussian or uniform beam distribution); (3) a real time fast camera analysis of melt pool dynamics and melt-pool – powder stream coupling; (4) a characterization of wall morphologies versus process parameters using 2D and 3D profilometry.The results confirm that surface degradation depends on two distinct aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters. Last, a simple analytical model was proposed to correlate melt-pool geometries to resulting surface finishes.     

The Performance of Water Floods with Horizontal and Multilateral Wells

Abstract

The use of horizontal and multilateral wells in the oil industry has increased rapidly during the last two decades. The main reason for this upsurge is that horizontal and multilateral wells provide a large contact area with the reservoir, and therefore enhance the well productivity or injectivity better than conventional vertical wells. The high productivity coupled with the recent advances in drilling technology for horizontal and multilateral wells has made their application an economically viable option. In this study, the performance of nonconventional wells in water flooding projects was investigated using numerical simulation techniques. Extensive three-dimensional, fine-mesh simulation runs are performed to determine the oil recovery by nonconventional wells under different operating/reservoir conditions. Results show that the pattern used has a significant effect on the displacement performance of nonconventional wells. The study shows the various conditions under which nonconventional wells will perform better than the use of conventional vertical wells.     

Maintenance scheduling and production control of multiple-machine manufacturing systems

This paper deals with the production and preventive maintenance control problem for a multiple-machine manufacturing system. The objective of such a problem is to find the production and preventive maintenance rates for the machines so as to minimize the total cost of inventory/backlog, repair and preventive maintenance. A two-level hierarchical control model is presented, and the structure of the control policy for both identical and non-identical manufacturing systems is described using parameters, referred to here as input factors. By combining analytical formalism with simulation-based statistical tools such as experimental design and response surface methodology, an approximation of the optimal control policies and values of input factors are determined. The results obtained extend those available in existing literature to cover non-identical machine manufacturing systems. A numerical example and a sensitivity analysis are presented in order to illustrate the robustness of the proposed approach. The extension of the proposed production and preventive maintenance policies to cover large systems (multiple machines, multiple products) is discussed.