All-optical photonic switches using integrated inverted asymmetricFabry-Perot modulators and heterojunction phototransistors

InGaAs/GaAs(100) multiple-quantum-well-based inverted cavity asymmetric Fabry-Perot modulators are vertically integrated with GaAs/AlGaAs heterojunction phototransistors to yield all-optical photonic switches. The photonic switches using `normally on' modulator pixels exhibit an output on-off ratio of 12:1 with internal optical gain of 4 dB. The photonic switches using `normally off' modulator pixels yield similar contrast and gain, but exhibit intrinsic bistable behavior. The inverted cavity modulators employed permit utilizing the transparency of the GaAs substrate at the operating wavelength and offer advantages for fabricating large arrays for optical signal processing     

CQARPL: Congestion and QoS-aware RPL for IoT applications under heavy traffic

The Journal of Supercomputing - The Internet of Things (IoT) provides a common platform to connect the heterogeneous devices over the internet. Hence, the number of devices connected via the...     

Capacitive micromachined ultrasonic transducers: next-generation arrays for acoustic imaging?

Piezoelectric materials have dominated the ultrasonic transducer technology. Recently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as an alternative technology offering advantages such as wide bandwidth, ease of fabricating large arrays, and potential for integration with electronics. The aim of this paper is to demonstrate the viability of CMUTs for ultrasound imaging. We present the first pulse-echo phased array B-scan sector images using a 128-element, one-dimensional (1-D) linear CMUT array. We fabricated 64- and 128-element 1-D CMUT arrays with 100% yield and uniform element response across the arrays. These arrays have been operated in immersion with no failure or degradation in performance over the time. For imaging experiments, we built a resolution test phantom roughly mimicking the attenuation properties of soft tissue. We used a PC-based experimental system, including custom-designed electronic circuits to acquire the complete set of 128 x 128 RF A-scans from all transmit-receive element combinations. We obtained the pulse-echo frequency response by analyzing the echo signals from wire targets. These echo signals presented an 80% fractional bandwidth around 3 MHz, including the effect of attenuation in the propagating medium. We reconstructed the B-scan images with a sector angle of 90 degrees and an image depth of 210 mm through offline processing by using RF beamforming and synthetic phased array approaches. The measured 6-dB lateral and axial resolutions at 135 mm depth were 0.0144 radians and 0.3 mm, respectively. The electronic noise floor of the image was more than 50 dB below the maximum mainlobe magnitude. We also performed preliminary investigations on the effects of crosstalk among array elements on the image quality. In the near field, some artifacts were observable extending out from the array to a depth of 2 cm. A tail also was observed in the point spread function (PSF) in the axial direction, indicating the existence of crosstalk. The relative amplitude of this tail with respect to the mainlobe was less than -20 dB.     

Approximate analysis of tall buildings using sandwich beam models with variable cross‐section

In this paper an approximate method is carried out for determining the natural periods of multistory buildings subjected to earthquake. The building resists lateral forces through a combination of lateral resisting systems. These systems could be replaced by a cantilever Timoshenko or a sandwich beam with varying cross‐section that characterizes three kinds of stiffnesses: the global bending stiffness, the local bending stiffness and the shear stiffness. Using appropriate transformations, the differential equations for flexural and shear free vibration of a cantilever beam with variably distributed mass and stiffness are reduced to Bessel's equations and ordinary differential equations. The frequency equations can be solved by selecting suitable expressions such as exponential and power functions for stiffness and mass distribution along the height of the building. The calculated frequencies are combined appropriately by using approximate methods. Based on the fact that shear and bending deformations are all considered, the free vibration frequency of the structure could be calculated. The capability and accuracy of the proposed method are demonstrated by a numerical example in which finite element results are compared with the proposed methodology and other approximate methods. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimal design of a reliable hydrogen-based stand-alone wind/PV generating system,considering component outages

A hybrid wind/photovoltaic/fuel cell generation system is designed to supply power demand. The aim of this design is minimization of annualized cost of the hybrid system over its 20 years of operation. Optimization problem is subject to reliable supply of the demand. Three major components of the system, i.e. wind turbine generators, photovoltaic arrays, and DC/AC converter, may be subject to failure. Also, solar radiation, wind speed, and load data are assumed entirely deterministic. System costs involve investments, replacement, and operation and maintenance as well as loss of load costs. Prices are all empirical and components are commercially available. An advanced variation of Particle Swarm Optimization algorithm is used to solve the optimization problem.Results reveal the impact of component outages on the reliability and cost of the system, so they are directly dependent on components' reliabilities, i.e. outages result in need for a larger generating system for supplying the load with the acceptable reliability. Additionally, it is observed that the inverter's reliability is an upper limit for the system's reliability. Moreover, an approximate method for reliability evaluation of the hybrid system is proposed which considerably reduces the time and computations.     

Frictional viscoelastic based model for spherical particles collision

In this paper, collision of two balls in three dimensions with regard to energy loss and friction is studied. This investigation intends to propose the procedure which can determine the condition of pure sliding, sliding with rolling or sticking, and rolling or sticking at the beginning of contact. Furthermore, the other aim of this research is to suggest the closed-form relation for post-collision angular and linear velocities in which the possibility of three regimes of impact, pure sliding, sliding with rolling, and pure rolling, are considered. In this investigation, viscous Hertz contact force describes the normal interaction force. Moreover, stick regime is not taken into account and during sliding, Coulomb friction is considered as a tangential force, which is endorsed by collision experimental data in case the collision regime is not stick regime. Considering aforementioned issues along with employing momentum conservation, the condition for the possibility of transformation of sliding to sticking or rolling during collision, and furthermore, the analytical relation for post-collision velocities are achieved. Eventually, in order to demonstrate the procedure of solving two balls collision, numerical examples are presented.     

Location-inventory problem in supply chains: a modelling review

A location-inventory problem (LIP) aims to integrate strategic supply chain design decisions with tactical and operational inventory management decisions. This study provides an extensive review of the existing literature of LIP modelling. A mathematical model is presented for a basic LIP, which can be further developed to incorporate additional features for use in real-world scenarios. We also discuss the evolution of LIP modelling literature over the past three decades and provide summary tables outlining characteristics of the published works including key modelling attributes and objective function cost components. Additional classifications are completed based on the solution methods adopted and real-world applications investigated. Our observations provide important insights and identify potential directions for future research in the field.     

A high-voltage optoelectronic GaAs static induction transistor

Experimental realization of an optically activated, high-voltage GaAs static induction transistor (SIT) is reported. In the forward blocking state, the breakdown voltage of the device was ~200 V, while in the conduction state, on-state current densities exceeding 150 A/cm² were obtained. In the floating-gate configurations (gate open), the specific on-resistance of the device was ~50 mΩ-cm². Optical modulation of the device was achieved using a compact semiconductor laser array as the triggering source. In this mode, a gate-coupled RC network was implemented, resulting in an average switching energy gain (load energy/optical energy) of ~30. This mode of operation is applicable to series-coupled devices for pulsed switching at higher power levels     

Synthesis and characterisation of LiB3 O5 nanophosphor as a TL dosimeter

In this work, lithium triborate (LiB₃ O₅) nanophosphor was synthesised by precipitation assisted high‐temperature solid‐state method followed by heating at different sintering temperatures. Then, its crystal structure and morphology were fully characterised. LiB₃ O₅ was doped with different concentrations of different dopants. To determine the thermoluminescence (TL) properties and structural specifications of doped lithium triborate, the sample was irradiated by photons and then, its TL glow curve was obtained using a TL dosimeter‐reader system. To study the effect of heating rate (HR) on TL characterisation of this nanophosphor, TL measurements were done at different HRs. The results showed that, sintering temperature can affect the morphology and structural properties of lithium triborate and consequently its TL intensity. The findings also showed that the LiB₃ O₅ :Al nanophosphor with the dopant concentration of 2 wt.% has the highest sensitivity and the best peak position among the studied activators. The results of the HR method showed that this method may be provided accurate calculations of the physical parameters of the TL process. These results may be helpful in the development of tissue equivalent TL nanocrystalline detectors usable in medical and personnel dosimetry.Inspec keywords: thermoluminescent dosimeters, sintering, phosphors, crystal structure, dosimetry, thermoluminescence, lithium compounds, nanostructured materials, nanofabrication, aluminiumOther keywords: high‐temperature solid‐state method, crystal structure, morphology, thermoluminescence properties, structural specifications, doped lithium triborate, TL glow curve, TL dosimeter‐reader system, heating rate, TL characterisation, TL measurements, sintering temperature, structural properties, TL intensity, nanophosphor, dopant concentration, HR method, TL process, tissue equivalent TL nanocrystalline detectors, LiB₃ O₅ :Al     

A multi-objective decision-making process of supplier selection and order allocation for multi-period scheduling in an electronic market

Supplier selection is a multi-criteria problem which includes both tangible and intangible factors. In these problems when suppliers have capacity or other different constraints, two questions persist: which suppliers are the best and how much should be purchased from a selected supplier? Here, we propose an integrated approach of analytic hierarchy process (AHP), Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), and multi-objective nonlinear programming to consider both tangible and intangible factors in choosing the best suppliers and define the optimum quantities among selected suppliers to maximize the total value of purchasing and minimize the budget, total penalized earliness and tardiness, and defect rate. The priorities are calculated for each supplier by use of AHP. TOPSIS is applied to rank the suppliers. Finally, using the obtained weights, the optimal quantities of order to the suppliers are clarified in multi-period horizon. An application study presents the validity and efficiency of the proposed model. Moreover, a performance analysis has been worked out on the numerical example to investigate the capability and effectiveness of the results.