Effects of the Vibration Amplitude in Vibratory Stress Relief on the Fatigue Life of Structures

This research aims to investigate the effects of vibration amplitude in vibratory stress relief (VSR) on the fatigue strength of structures with residual stress. Experiments are carried out on specimens with residual stress generated by local heating. Flat specimens made of A36 steel are prepared to be suitable for setting up fatigue bending tests on a vibrating table. Several groups of samples are subjected to VSR at resonant frequencies with different acceleration amplitudes. The results show that VSR has an important influence on the residual stress and fatigue limit of steel specimens. The maximum residual stress in the samples is reduced about 73% when the amplitude of vibration acceleration is 57 m/s2. The VSR method can also improve the fatigue limit by up to 14% for steel samples with residual stress.

Clustering Analysis with Embedding Vectors: An Application to Real Estate Market Delineation

Although clustering analysis is a popular tool in unsupervised learning, it is inefficient for the datasets dominated by categorical variables, e.g., real estate datasets. To apply clustering analysis to real estate datasets, this study proposes an entity embedding approach that transforms categorical variables into vector representations. Three variants of a clustering algorithm, i.e., the clustering based on the traditional Euclidean distance, the Gower distance, and the embedding vectors, are applied to the land sales records to delineate the real estate market in Gwacheon-si, Gyeonggi province, South Korea. Then, the relevance of the resultant submarkets is evaluated using the root mean squared errors (RMSE) obtained from a hedonic pricing model. The results show that the RMSE in the embedding vector-based algorithm decreases substantially from 0.076-0.077 to 0.069. This study shows that the clustering algorithm empowered by embedding vectors outperforms the conventional algorithms, thereby enhancing the relevance of the delineated submarkets.

CPW-Fed Penta Band Monopole Antenna for Multiservice Wireless Applications

A compact triple T-shaped stub with meander loaded strip antenna for penta band applications is proposed. The rectangular patch antenna with meandered and open-ended slot cuts is utilized to realize four operating bands at 2.45 GHz, 3.1 GHz, 5.3 GHz, and 6.5 GHz with an impedance bandwidth of 400 MHz (2.15-2.550 GHz), 1000 MHz (2.7-3.7 GHz), 200 MHz (5.4-5.6 GHz), and 200 MHz (6.4-6.6 GHz), respectively. For an additional resonance frequency, the length of the central T-shaped stub is slightly modified which causes the variation in the current distribution. As a result, the resonance frequency of 5.5 GHz is divided into two resonance frequency bands which are operating at 5.25 GHz and 5.85 GHz with an impedance bandwidth of 100 MHz (5.25-5.35 GHz) and 200 MHz (5.75-5.95 GHz), respectively. Furthermore, a parametric reflection coefficient and surface current distribution analysis is carried out to understand the strip and slot behavior at resonance frequency bands. Finally, a prototype is fabricated and its reflection coefficient, gain, and radiation pattern are measured. The experimental result shows that the proposed antenna is reliable for penta band applications.

Cost-Effective Customizable Indoor Environmental Quality Monitoring System

Poor indoor environmental quality (IEQ) has become a global concern for World Health Organization (WHO), and its impact on health and well-being has been exacerbated by the COVID-19 pandemic. To monitor and sanitize indoor air, this study develops a cost-effective and customizable IEQ monitoring system to detect unhealthy and low-comfort air levels. This system uses ThingSpeak (MATLAB), microcontrollers (Arduino Uno), and various low-cost sensors to measure indoor air quality (IAQ) and IEQ in terms of gas, particulate matter, temperature, sound level, and ultraviolet (UV) light. The presented system is validated with respect to temperature, relative humidity, and particulate matter by benchmarking against the Camfil air image sensor manufactured by Camfil AB, Stockholm, Sweden. The average error of temperature, relative humidity, and PM2.5 are 0.55%, 5.13%, and 3.45%, respectively.

Determination of Natural Frequency and Critical Velocity of Inclined Pipe Conveying Fluid under Thermal Effect by Using Integral Transform Technique

This study proposes an analytical solution of natural frequencies for an inclined fixed supported Euler-Bernoulli pipe containing the flowing fluid subjected to thermal loads. The integral transform technique is employed to obtain the spatial displacement-time domain response of the pipe-fluid system. Then, a closed-form analytical expression is presented. The effects of various geometric and system parameters on the vibration characteristics of pipe-fluid system with different flow velocities are discussed. The results illustrate that the proposed analytical solution agrees with the solutions achieved in previous works. The proposed model predicts that the pipe loses the stability by divergence with the increasing flow velocity. It is evident that the influences of inclination angle and temperature variation are dramatically increased at a higher aspect ratio. Additionally, it is demonstrated that the temperature variation becomes a more harmful effect than the internal fluid velocity on the stability of the pipe at elevated temperature.

Implementation of 20 nm Graphene Channel Field Effect Transistors Using Silvaco TCAD Tool to Improve Short Channel Effects over Conventional MOSFETs

In recent years, demands for high speed and low power circuits have been raised. As conventional metal oxide semiconductor field effect transistors (MOSFETs) are unable to satisfy the demands due to short channel effects, the purpose of the study is to design an alternative of MOSFETs. Graphene FETs are one of the alternatives of MOSFETs due to the excellent properties of graphene material. In this work, a user-defined graphene material is defined, and a graphene channel FET is implemented using the Silvaco technology computer-aided design (TCAD) tool at 100 nm and scaled to 20 nm channel length. A silicon channel MOSFET is also implemented to compare the performance. The results show the improvement in subthreshold slope (SS) = 114 mV/dec, ION/IOFF ratio = 14379, and drain induced barrier lowering (DIBL) = 123 mV/V. It is concluded that graphene FETs are suitable candidates for low power applications.

Tea Verification Using Triplet Loss Convolutional Network

To solve tea image classification problems, this study focuses on triplet loss convolutional neural network to classify six high-mountain oolong tea classes. In the experiment, instead of using traditional deep learning training approach for local feature of tea images, an innovative image verification approach is proposed to learn the global feature of tea images by integrating the distributed tea leaves’ features of all tea sub-images and using a majority voting mechanism to do classification. The results show that the proposed approach can work for small sample size dataset and have higher accuracy than normal transfer learning approach. The average accuracy of the proposed approach achieves 99.54%.

New Electronically Tunable Third Order Filters and Dual Mode Sinusoidal Oscillator Using VDTAs and Grounded Capacitors

This study introduces a third order filter and a third order oscillator configuration. Both the circuits use two voltage difference transconductance amplifiers (VDTAs) and three grounded capacitors. By selecting the input and output terminals properly, current mode and transimpedance mode low-pass and band-pass filters can be obtained without component matching conditions. The natural frequency (ω0) can be tuned electronically. The oscillator circuit provides voltage and current outputs explicitly. The condition of oscillation (CO) and the frequency of oscillation (FO) can be adjusted orthogonally and electronically. The workability of the configurations is judged using TSMC CMOS 0.18 μm technology parameter as well as commercially available LM13700 integrated circuits (ICs). The simulation results show that: for ±0.9V power supply, the power consumption is 1.08 mW for both the configurations, while total harmonic distortions (THDs) are less than 2.06% and 2.17% for the filter and oscillator configurations, respectively.

Optimization of Superplastic Forming Process of AA7075 Alloy for the Best Wall Thickness Distribution

This work aims to optimize the process parameters for improving the wall thickness distribution of the sheet superplastic forming process of AA7075 alloy. The considered factors include forming pressure p (MPa), deformation temperature T (°C), and forming time t (minutes), while the responses are the thinning degree of the wall thickness ε (%) and the relative height of the product h*. First, a series of experiments are conducted in conjunction with response surface method (RSM) to render the relationship between inputs and outputs. Subsequently, an analysis of variance (ANOVA) is conducted to verify the response significance and parameter effects. Finally, a numerical optimization algorithm is used to determine the best forming conditions. The results indicate that the thinning degree of 13.121% is achieved at the forming pressure of 0.7 MPa, the deformation temperature of 500°C, and the forming time of 31 minutes.

A Recursive Least-Squares Approach with Memorizing Factor for Deriving Dynamic Equivalents of Power Systems

In this research, a two-stage identification-based approach is proposed to obtain a two-machine equivalent (TME) system of an interconnected power system for transient stability studies. To estimate the parameters of the equivalent system, a three-phase fault is applied near and/or at the bus of a local machine in the original multimachine system. The electrical parameters of the equivalent system are calculated in the first stage by equating the active and reactive powers of the local machine in both the original and the predefined equivalent systems. The mechanical parameters are estimated in the second stage by using a recursive least-squares estimation (RLSE) technique with a factor called “memorizing factor”. The approach is demonstrated on New England 10-machine 39-bus system, and its accuracy and efficiency are verified by computer simulation in MATLAB software. The results obtained from the TME system agree well with those obtained from the original multimachine system.