Appl. Sci., Volume 6, Issue 3 (March 2016) – 30 articles

This study focuses on the development of a novel polishing pad for SiC wafers. Fe and Al₂O₃ particles were impregnated in a polyurethane matrix, thus forming a fixed abrasive polishing pad. Four types of pads with different compositions of Fe and Al₂O₃ were fabricated. A combination of loose and fixed polishing methods was used for polishing with the fabricated pads and was investigated to improve the polishing process. The surface characteristics of the polished SiC wafer and the SiC removal rate during polishing using the designed pads were examined and compared with those for SiC polished with a conventional polyurethane pad. Experimental results showed that the removal rate for SiC in the case of polishing with the pads consisting 1 wt % Fe and 3 wt % Al₂O₃ particles was approximately 73% higher than that observed when polishing using the conventional polyurethane polishing pad. Additionally, the surface roughness of the resulting SiC wafers after polishing with the Fe and Al₂O₃-impregnated pads was identical to that when using the conventional polyurethane pad, without any surface damage. The results indicated that the Fe and Al₂O₃-impregnated pads can be effectively used for SiC wafer polishing. When the proposed process was employed for polishing single-crystal SiC, both the polishing time and cost were reduced. This novel design can facilitate the extensive use of single-crystal SiC wafers in the future. Full article

This paper focuses on downlink packet scheduling for streaming video in Long Term Evolution (LTE). As a hard handover is adopted in LTE and has the period of breaking connection, it may cause a low user-perceived video quality. Therefore, we propose a handover prediction mechanism and a pre-scheduling mechanism to dynamically adjust the data rates of transmissions for providing a high quality of service (QoS) for streaming video before new connection establishment. Advantages of our method in comparison to the exponential/proportional fair (EXP/PF) scheme are shown through simulation experiments. Full article

This study presents an analytical method for dynamically adjusting toll plaza capacity to cope with a sudden shift in demand. The proposed method uses a proxy measure developed using discharge rate observed at toll plazas and segment travel times measured by probe vehicles. The effectiveness of the method has been evaluated by analyzing the empirical data obtained from toll plazas in the San Francisco Bay Area before and after toll plaza capacity changed. Findings indicate that the estimated number of vehicles stored near the upstream of toll plaza based on discharge rate and their travel times can be used as a proxy measure for predicting the effect of changes in toll plaza capacity. The proposed model can aid government agencies to dynamically adjust the toll plaza capacity in response to a sudden shift in demand due to various situations of failure. Full article

To measure various components with nano-scale precision, a new high-precision touch-trigger probe using a single low-cost sensor for a micro-coordinate measuring machine (CMM) is presented in this paper. The sensor is composed of a laser diode, a plane mirror, a focusing lens, and a quadrant photo detector (QPD). The laser beam from the laser diode with an incident angle is reflected by the plane mirror and then projected onto the quadrant photo detector (QPD) via the focusing lens. The plane mirror is adhered to the upper surface of the floating plate supported by an elastic mechanism, which can transfer the displacement of the stylus’s ball tip in 3D to the plane mirror’s vertical and tilt movement. Both motions of the plane mirror can be detected by respective QPDs. The probe mechanism was analyzed, and its structural parameters that conform to the principle of uniform sensitivity and uniform stiffness were obtained. The simulation result showed that the stiffness was equal in 3D and less than 1 mN/µm. Some experiments were performed to investigate the probe’s characteristics. It was found that the probe could detect the trigger point with uniform sensitivity, a resolution of less than 5 nm, and a repeatability of less than 4 nm. It can be used as a touch-trigger probe on a micro/nano-CMM. Full article

This paper presents a comparison of the acoustic emission (AE) energy and the plastic strain energy released by some reinforced concrete (RC) specimens subjected to cyclic or seismic loadings. AE energy is calculated, after proper filtering procedures, using the signals recorded by several AE low frequency sensors (25–100 kHz) attached on the specimens. Plastic strain energy is obtained by integrating the load displacement curves drawn from the measurements recorded during the test. Presented are the results obtained for: (i) two beams (with and without an artificial notch) and a beam-column connection subjected to several cycles of imposed flexural deformations; (ii) a reinforced concrete slab supported by four steel columns, and a reinforced concrete frame structure, both of the latter are subjected to seismic simulations with a uniaxial shaking table. The main contribution of this paper, which is a review of some papers previously published by the authors, is to highlight that, in all cases, a very good correlation is found between AE energy and plastic strain energy, until the onset of yielding in the reinforcing steel. After yielding, the AE energy is consistently lower than the plastic strain energy. The reason is that the plastic strain energy is the sum of the contribution of concrete and steel, while the AE energy acquired with thresholds higher than 35 dB_AE captures only the contribution of the concrete cracking, not the steel plastic deformation. This good correlation between the two energies before the yielding point also lends credibility to the use of AE energy as a parameter for concrete damage evaluation in the context of structural health monitoring. Full article

As a successful solution applied to hard machining, the minimum quantity lubricant (MQL) has already been established as an alternative to flood coolant processing. The optimization of MQL parameters and cutting parameters under MQL condition are essential and pressing. The study was divided into two parts. In the first part of this study, the Taguchi method was applied to find the optimal values of MQL condition in the hard milling of AISI H13 with consideration of reduced surface roughness. The L9 orthogonal array, the signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to analyze the effect of the performance characteristics of MQL parameters (i.e., cutting fluid type, pressure, and fluid flow) on good surface finish. In the results section, lubricant and pressure of MQL condition are determined to be the most influential factors which give a statistically significant effect on machined surfaces. A verifiable experiment was conducted to demonstrate the reliability of the results. In the second section, the optimized MQL parameters were applied in a series of experiments to find out cutting parameters of hard milling. The Taguchi method was also used to optimize the cutting parameters in order to obtain the best surface roughness. The design of the experiment (DOE) was implemented by using the L27 orthogonal array. Based on an analysis of the signal-to-noise response and ANOVA, the optimal values of cutting parameters (i.e., cutting speed, feed rate, depth-of-cut and hardness of workpiece) were introduced. The results of the present work indicate feed rate is the factor having the most effect on surface roughness. Full article

In this paper, a Stewart-platform robot with sliding lockable base joints is proposed for reconfiguration, and it addresses the determination of the optimal configuration for the prescribed motion with maximum allowable dynamic wrench capability subject to the constraints imposed by the kinematics and dynamics of the proposed reconfigurable architecture. The numerical results from the hierarchical optimization process allow us to investigate the effects of the base point locations on the maximum dynamic wrench capability. The effectiveness of the proposed algorithm is demonstrated in the improvement of the maximum allowable dynamic wrench capability of the reconfigurable Stewart-platform robot. Full article

This study applies smartphone, Bluetooth, and Wi-Fi wireless network to control a wheeled mobile robot (WMR) remotely. The first part of this study demonstrates that the WMR can be controlled manually by a smartphone. The smartphone can remotely control the WMR for forward, backward, left-turn, and right-turn operations. The second part of this article presents object tracking. The WMR can follow a moving object through the use of image processing for object tracking and distance detection. In the third part, infrared sensor and fuzzy system algorithms are integrated into the control scheme. Through wall-following and obstacle-avoidance control, the WMR can successfully perform indoor patrol. Full article

Nowadays, with large-scale offshore wind power farms (WPFs) becoming a reality, more efforts are needed to maintain a reliable communication network for WPF monitoring. Deployment topologies, redundancy, and network availability are the main items to enhance the communication reliability between wind turbines (WTs) and control centers. Traditional communication networks for monitoring and control (i.e., supervisory control and data acquisition (SCADA) systems) using switched gigabit Ethernet will not be sufficient for the huge amount of data passing through the network. In this paper, the optical power budget, optical path loss, reliability, and network cost of the proposed Ethernet Passive Optical Network (EPON)-based communication network for small-size offshore WPFs have been evaluated for five different network architectures. The proposed network model consists of an optical network unit device (ONU) deployed on the WT side for collecting data from different internal networks. All ONUs from different WTs are connected to a central optical line terminal (OLT), placed in the control center. There are no active electronic elements used between the ONUs and the OLT, which reduces the costs and complexity of maintenance and deployment. As fiber access networks without any protection are characterized by poor reliability, three different protection schemes have been configured, explained, and discussed. Considering the cost of network components, the total implementation expense of different architectures with, or without, protection have been calculated and compared. The proposed network model can significantly contribute to the communication network architecture for next generation WPFs. Full article

The forming of a micro tapered hole is based on nanosecond pulsed laser processing, which conforms to fast processing time and high throughput; however, the microhole quality should be improved. Micro stamping is a technology providing high precise size and speed. The greatest difficulty in forming a microhole by micro stamping is the precision alignment of the punch head to the lower die. In order to overcome the difficulty, we proposed a concept of stamping without die (SWD). Without a lower die, the tapered punch head was directly applied to the workpiece for micro stamping, and a thicker workpiece surrounding the punching area provides a better support to the stamping process. Thus, a successful forming of micro tapered holes is completed. The micro tapered hole depth is 300 μm, and the maximum ratio of inlet to outlet diameter is 18:1. In order to reduce the number of experiments, the finite element analysis software DEFORM-3D was used for forming analysis. The simulation forecast result was compared with the experimental processing, which was well validated. Under different experimental parameters of laser energy and defocusing distance, drilling results by two methods show that the microhole quality by stamping process is better than by laser processing. Full article

It is difficult for autonomous underwater vehicles (AUVs) to obtain accurate aided position information in many locations because of underwater conditions. The velocity accuracy from the Doppler velocity log (DVL) is a key element in deciding the AUV position accuracy when the integration system of Strapdown Inertial Navigation System/DVL/Magnetic Compass/Press Sensor (SINS/DVL/MCP/PS) is adopted. However, random noise and sudden noise in DVL caused by sound scattering, fishing populations, and seafloor gullies introduce level attitude errors and accumulate as position error. To restrain random noise, a velocity tracing method is designed based on the constant velocity model and the assumption of slow motion of AUV. To address sudden noise, a fault diagnosis method based on the χ 2 rule is introduced to judge sudden changes from innovation. When a sudden change occurs, the time update of the velocity from the tracing model is used for data fusion instead of the velocity from DVL. Simulation test results indicate that with this velocity tracing algorithm, random noise in the DVL can be effectively restrained. The level attitude accuracy and the level position accuracy are also improved with the time update of the velocity when the sudden change occurs. Full article

We review the application of atomically thin transition metal dichalcogenides in optoelectronic devices. First, a brief overview of the optical properties of two-dimensional layered semiconductors is given and the role of excitons and valley dichroism in these materials are discussed. The following sections review and compare different concepts of photodetecting and light emitting devices, nanoscale lasers, single photon emitters, valleytronics devices, as well as photovoltaic cells. Lateral and vertical device layouts and different operation mechanisms are compared. An insight into the emerging field of valley-based optoelectronics is given. We conclude with a critical evaluation of the research area, where we discuss potential future applications and remaining challenges. Full article

Today’s world needs highly efficient systems that can fulfill the growing demand for energy. One of the promising solutions is the fuel cell. Solid oxide fuel cell (SOFC) is considered by many developed countries as an alternative solution of energy in near future. A lot of efforts have been made during last decade to make it commercial by reducing its cost and increasing its durability. Different materials, designs and fabrication technologies have been developed and tested to make it more cost effective and stable. This article is focused on the advancements made in the field of high temperature SOFC. High temperature SOFC does not need any precious catalyst for its operation, unlike in other types of fuel cell. Different conventional and innovative materials have been discussed along with properties and effects on the performance of SOFC’s components (electrolyte anode, cathode, interconnect and sealing materials). Advancements made in the field of cell and stack design are also explored along with hurdles coming in their fabrication and performance. This article also gives an overview of methods required for the fabrication of different components of SOFC. The flexibility of SOFC in terms fuel has also been discussed. Performance of the SOFC with varying combination of electrolyte, anode, cathode and fuel is also described in this article. Full article

This study was aimed to investigate the machining stability of a horizontal milling machine with hybrid guideway systems by finite element method. To this purpose, we first created finite element model of the milling machine with the introduction of the contact stiffness defined at the sliding and rolling interfaces, respectively. Also, the motorized built-in spindle model was created and implemented in the whole machine model. Results of finite element simulations reveal that linear guides with different preloads greatly affect the dynamic responses and machining stability of the horizontal milling machine. The critical cutting depth predicted at the vibration mode associated with the machine tool structure is about 10 mm and 25 mm in the X and Y direction, respectively, while the cutting depth predicted at the vibration mode associated with the spindle structure is about 6.0 mm. Also, the machining stability can be increased when the preload of linear roller guides of the feeding mechanism is changed from lower to higher amount. Full article

Dual-chamber air springs are used as a key component for vibration isolation in some industrial applications. The working principle of the dual-chamber air spring device as applied to motion suppression of marine structures is similar to that of the traditional air spring, but they differ in their specific characteristics. The stiffness and damping of the dual-chamber air spring device determine the extent of motion suppression. In this article, we investigate the stiffness and damping characteristics of a dual-chamber air spring device applied to marine structure motion suppression using orthogonal analysis and an experimental method. We measure the effects of volume ratio, orifice ratio, excitation amplitude, and frequency on the stiffness and damping of the dual-chamber vibration absorber. Based on the experimental results, a higher-order non-linear regression method is obtained. We achieve a rapid calculation model for dual-chamber air spring stiffness and damping, which can provide guidance to project design. Full article

The direct grey model (DGM(2,1)) is considered for fluctuation characteristics of the sampling data in Grey system theory. However, its applications are quite uncommon in the past literature. The improvement of the precision of the DGM(2,1) is only presented in few previous researches. Moreover, the evaluation of forecasted performance of the DGM(2,1) model and its applications was not conducted in previous studies. As the results, this study aims to evaluate forecasted performance of the DGM(2,1) and its three modified models, including the Markov direct grey model MDGM(2,1), the Fourier direct grey model FDGM(2,1), and the Fourier Markov direct grey model FMDGM(2,1) in order to determine the application of the DGM(2,1) model in practical applications and academic research. The results demonstrate that the DGM(2,1) model has lower precision than its modified models, while the forecasted precision of the FDGM(2,1) is better than that of MDGM(2,1). Additionally, the FMDGM(2,1) model presents the best performance among all of the modified models of DGM(2,1), which can effectively overcome the fluctuating of the data sample and minimize the predicted error of the DGM(2,1) model. The finding indicated that the FMDGM(2,1) model does not only have advantages with regard to the sample size requirement, but can also be flexibly applied to the large fluctuation and random sequences with a high quality of estimation. Full article

Acoustic emissions are frequently used in material sciences and engineering applications for structural health monitoring. It is known that plants also emit acoustic emissions, and their application in plant sciences is rapidly increasing, especially to investigate drought-induced plant stress. Vulnerability to drought-induced cavitation is a key trait of plant water relations, and contains valuable information about how plants may cope with drought stress. There is, however, no consensus in literature about how this is best measured. Here, we discuss detection of acoustic emissions as a measure for drought-induced cavitation. Past research and the current state of the art are reviewed. We also discuss how the acoustic emission technique can help solve some of the main issues regarding quantification of the degree of cavitation, and how it can contribute to our knowledge about plant behavior during drought stress. So far, crossbreeding in the field of material sciences proved very successful, and we therefore recommend continuing in this direction in future research. Full article

To assess the possibility of terahertz technology for the determination of drug concentration in blood, we endeavored to apply a terahertz (THz) attenuated total reflection (ATR) method to measure the levels of theophylline in saline. A change in reflected THz wave amplitude was observed in a theophylline concentration-dependent manner. This result was obtained with simple measurements of comparisons of the amplitude of the reflected wave, and suggests that it is possible to monitor concentration changes of drugs in liquid material using THz ATR measurements. Full article

The deformation behavior and fracture characteristics of NiAl intermetallic alloy containing 5~7 at% Cu are investigated at room temperature under strain rates ranging from 1 × 10⁻³ to 5 × 10³ s⁻¹. It is shown that the copper contents and strain rate both have a significant effect on the mechanical behavior of the NiAl alloy. Specifically, the flow stress increases with an increasing copper content and strain rate. Moreover, the ductility also improves as the copper content increases. The change in the mechanical response and fracture behavior of the NiAl alloy given a higher copper content is thought to be the result of the precipitation of β-phase (Ni,Cu)Al and γ'-phase (Ni,Cu)₃Al in the NiAl matrix. Full article

This paper reports a novel green approach for the synthesis of silver nanoparticles (AgNPs) using aqueous seed extract of Dracocephalum moldavica (L.) under ambient conditions. Processes such as Ultraviolet-visible (UV-vis) spectrometer, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) were carry out to characterize AgNPs. The presence of AgNPs in the prepared solution was approved by a peak to occur at 443 nm. XRD pattern indicated the crystalline structure of the nanoparticles (NPs) while the FTIR spectra confirm the attendance of plant residues adsorbed by these NPs. TEM images revealed a near spherical shape of these NPs, and EDX provided the expected elemental composition. The synthesized AgNPs showed excellent antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Staphylococcus epidermidis and Bacillus subtilis. Full article

Climate change, awareness of energy efficiency, new trends in electricity markets, the obsolescence of the actual electricity model, and the gradual conversion of consumers to prosumer profiles are the main agents of progressive change in electricity systems towards the Smart Grid paradigm. The introduction of multiple distributed generation and storage resources, with a strong involvement of renewable energies, exposes the necessity of advanced metering or Smart Metering systems, able to manage and control those distributed resources. Due to the heterogeneity of the Smart Metering systems and the specific features of each grid, it is easy to find in the related literature a wide range of solutions with different features. This work describes the key elements in a Smart Metering system and compiles the most employed technologies and standards as well as their main features. Since Smart Metering systems can perform jointly with other activities, these growing initiatives are also addressed. Finally, a revision of the main trends in Smart Metering uses and deployments worldwide is included. Full article

Polystyrene (PS) opal and titania (TiO₂) inverse opal films were fabricated by the self-assembly colloidal crystal template technique. Based on Bragg’s law, these sensors were used to detect the different concentrations of ethanol solution. The results indicated that TiO₂ inverse opal films were advantageous over PS opal film for detecting the ethanol concentration. TiO₂ inverse opal films sintered at 600 °C retained the highest sensitivity for ethanol concentration identification, since the anatase phase was transformed into the rutile phase, which resulted in an enhancement of the refractive index, i.e., an increase in the amount of the red shift. Full article

Approximately 50 years of inelastic scattering studies of noble gases are reviewed to illustrate the main advances achieved in the understanding of the THz dynamics of simple systems. The gradual departure of the spectral shape from the hydrodynamic regime is discussed with an emphasis on the phenomenology of fast (sub-ps) relaxation processes. This review shows that relaxation phenomena in noble gases have an essentially collisional origin, which is also revealed by the parallelism between their characteristic timescale and the interatomic collision time. Additionally, recent THz spectroscopy results on noble gases at extreme thermodynamic conditions are discussed to illustrate the need for a revision of our current understanding of the supercritical phase. Full article

In order to predict hot deformation behavior of superalloy nimonic 80A, a back-propagational artificial neural network (BP-ANN) and strain-dependent Arrhenius-type model were established based on the experimental data from isothermal compression tests on a Gleeble-3500 thermo-mechanical simulator at temperatures ranging of 1050–1250 °C, strain rates ranging of 0.01–10.0 s⁻¹. A comparison on a BP-ANN model and modified Arrhenius-type constitutive equation has been implemented in terms of statistical parameters, involving mean value of relative (μ), standard deviation (w), correlation coefficient (R) and average absolute relative error (AARE). The μ -value and w -value of the improved Arrhenius-type model are 3.0012% and 2.0533%, respectively, while their values of the BP-ANN model are 0.0714% and 0.2564%, respectively. Meanwhile, the R-value and ARRE-value for the improved Arrhenius-type model are 0.9899 and 3.06%, while their values for the BP-ANN model are 0.9998 and 1.20%. The results indicate that the BP-ANN model can accurately track the experimental data and show a good generalization capability to predict complex flow behavior. Then, a 3D continuous interaction space for temperature, strain rate, strain and stress was constructed based on the expanded data predicted by a well-trained BP-ANN model. The developed 3D continuous space for hot working parameters articulates the intrinsic relationships of superalloy nimonic 80A. Full article

Fibre lasers are light sources that are synonymous with stability. They can give rise to highly coherent continuous-wave radiation, or a stable train of mode locked pulses with well-defined characteristics. However, they can also exhibit an exceedingly diverse range of nonlinear operational regimes spanning a multi-dimensional parameter space. The complex nature of the dynamics poses significant challenges in the theoretical and experimental studies of such systems. Here, we demonstrate how the real-time experimental methodology of spatio-temporal dynamics can be used to unambiguously identify and discern between such highly complex lasing regimes. This two-dimensional representation of laser intensity allows the identification and tracking of individual features embedded in the radiation as they make round-trip circulations inside the cavity. The salient features of this methodology are highlighted by its application to the case of Raman fibre lasers and a partially mode locked ring fibre laser operating in the normal dispersion regime. Full article

Modern sequencing technique has provided a wealth of data on DNA sequences, which has made the analysis and comparison of sequences a very important but difficult task. In this paper, by regarding the dinucleotide as a 2-combination of the multiset { ∞ · A , ∞ · G , ∞ · C , ∞ · T } , a novel 3-D graphical representation of a DNA sequence is proposed, and its projections on planes (x,y), (y,z) and (x,z) are also discussed. In addition, based on the idea of “piecewise function”, a cell-based descriptor vector is constructed to numerically characterize the DNA sequence. The utility of our approach is illustrated by the examination of phylogenetic analysis on four datasets. Full article

Elastic warp-knitted composite fabrics with far-infrared emissivity and an anion-releasing property were prepared using bamboo charcoal (BC), copper (Cu), and phase-change material (PCM). The functional composite fabric, which was composed of self-made complex yarns with various twisting degrees and material composition, were created using a rotor twister and ring-spinning technique. The fabric structure was diversified by the feeding modes of weft yarn into a crochet-knitting machine. The twist number of complex yarns was optimized by tensile tenacity, twist contraction, and hairiness, and analysis showed that twisting at 12 twists per inch produced the highest tensile tenacity and appropriate twist contraction and hairiness. Comfort evaluation showed that the elastic composite fabrics with BC weft yarns exhibited higher water–vapor transmission rate and air permeability, reaching 876 g/m²∙ day and 73.2 cm³/s/cm², respectively. Three structures of composite fabric with various weft yarns had >0.85 ε far-infrared emissivity and 350–420 counts/cm³ anion amount. The prepared elastic warp-knitted fabrics can provide a comfortable, dry, and breathable environment to the wearer and can thus be applied as health-care textiles in the future. Full article

Smart Grids (SGs) constitute the evolution of the traditional electrical grid towards a new paradigm, which should increase the reliability, the security and, at the same time, reduce the costs of energy generation, distribution and consumption. Electrical microgrids (MGs) can be considered the first stage of this evolution of the grid, because of the intelligent management techniques that must be applied to assure their correct operation. To accomplish this task, sensors and actuators will be necessary, along with wireless communication technologies to transmit the measured data and the command messages. Wireless Sensor and Actuator Networks (WSANs) are therefore a promising solution to achieve an intelligent management of MGs and, by extension, the SG. In this frame, this paper surveys several aspects concerning the application of WSANs to manage MGs and the electrical grid, as well as the communication protocols that could be applied. The main concerns regarding the SG deployment are also presented, including future scenarios where the interoperability of different generation technologies must be assured. Full article

The paper presents preliminary numerical and experimental studies of active textile-reinforced thermoplastic composites with embedded sensor-actuator arrays. The goal of the investigations was the assessment of directional sound wave generation capability using embedded sensor-actuator arrays and developed a wave excitation procedure for ultrasound measurement tasks. The feasibility of the proposed approach was initially confirmed in numerical investigations assuming idealized mechanical and geometrical conditions. The findings were validated in real-life conditions on specimens of elementary geometry. Herein, the technological aspects of unique automated assembly of thermoplastic films containing adapted thermoplastic-compatible piezoceramic modules and conducting paths were described. Full article