This article develops a new topology optimization scheme for finding optimized joints for multiple components. As the optimized topologies for each component are determined by several structural ...conditions, simultaneously optimizing the joint location as well as the optimized topology is regarded as one of the difficult problems. Because joint connections are normally defined at nodes, inevitably the optimized locations of joints are mesh dependent. To contribute to these research topics, this research presents a new method for controlling the optimized location of joints. In particular, a joint dispersal constraint is developed in order to control the number and optimized locations of optimized joints. With the developed scheme, it is possible to find optimized joints as well as optimized topology while maintaining a minimum distance between all joints. To show the effectiveness of the present optimization scheme, several numerical optimization problems are solved.
Alternating current dielectrophoresis (DEP) is an excellent technique to assemble nanoscale materials. For efficient DEP, the optimization of the key parameters like peak-to-peak voltage, applied ...frequency, and processing time is required for good device. In this work, we have assembled graphene oxide (GO) nanostructures mixed with platinum (Pt) nanoparticles between the micro gap electrodes for a proficient hydrogen gas sensors. The Pt-decorated GO nanostructures were well located between a pair of prepatterned Ti/Au electrodes by controlling the DEP technique with the optimized parameters and subsequently thermally reduced before sensing. The device fabricated using the DEP technique with the optimized parameters showed relatively high sensitivity (∼10%) to 200 ppm hydrogen gas at room temperature. The results indicates that the device could be used in several industry applications, such as gas storage and leak detection.
The present study presents the application of a structural optimization scheme for a Double Split Hollow Sphere (DSHS) based acoustic cloaking structure for irregular surfaces. For acoustic wave ...cloaking, many scientific devices utilizing phase differences have been developed. Considering the irregular surfaces of objects to be concealed, acoustic wave reflections become complex with random phase differences and determinations of the involved geometric parameters of cloaking structures become impractical. To determine the geometric parameters of acoustic cloaking devices with DSHS systematically, the present study applies a structural optimization scheme. The present scheme computes and minimizes the differences between the acoustic pressures reflected from irregular surfaces and the reference acoustic pressures without irregular surfaces by optimizing the location and geometric parameters of the DSHS. To show the validity of the present scheme, structural optimization problems are solved for several three-dimensional problems with complex and irregular surfaces.
Two-dimensional (2D) material-based heterostructures provide a unique platform where interactions between stacked 2D layers can enhance the electrical and opto-electrical properties as well as give ...rise to interesting new phenomena. Here, the operation of a van der Waals heterostructure device comprising of vertically stacked bilayer MoS2 and few layered WSe2 has been demonstrated in which an atomically thin MoS2 layer has been employed as a tunneling layer to the underlying WSe2 layer. In this way, simultaneous contacts to both MoS2 and WSe2 2D layers have been established by forming a direct metal–semiconductor to MoS2 and a tunneling-based metal–insulator–semiconductor contacts to WSe2, respectively. The use of MoS2 as a dielectric tunneling layer results in an improved contact resistance (80 kΩ μm) for WSe2 contact, which is attributed to reduction in the effective Schottky barrier height and is also confirmed from the temperature-dependent measurement. Furthermore, this unique contact engineering and type-II band alignment between MoS2 and WSe2 enables a selective and independent carrier transport across the respective layers. This contact engineered dual channel heterostructure exhibits an excellent gate control and both channel current and carrier types can be modulated by the vertical electric field of the gate electrode, which is also reflected in the on/off ratio of 104 for both electron (MoS2) and hole (WSe2) channels. Moreover, the charge transfer at the heterointerface is studied quantitatively from the shift in the threshold voltage of the pristine MoS2 and the heterostructure device, which agrees with the carrier recombination-induced optical quenching as observed in the Raman spectra of the pristine and heterostructure layers. This observation of dual channel ambipolar transport enabled by the hybrid tunneling contacts and strong interlayer coupling can be utilized for high-performance opto-electrical devices and applications.
Quasi-two-dimensional (Quasi-2D) van der Waals (vdW) materials can be mechanically or chemically exfoliated down to monolayer because of their strong intralayer bonding and the weak interlayer vdW ...interaction. Thanks to this unique property, one can often find exotic thickness-dependent electronic properties from these quasi-2D vdW materials, which can lead to bandgap opening, emerging superconductivity, or enhanced charge density waves with decreasing thickness. Surface-sensitive scanning tunneling microscopy (STM) can provide direct observation of structural and electronic characteristics of such layered materials with atomic precision in real space. However, it is very challenging to preserve the intrinsic surfaces of air-sensitive quasi-2D materials between preparation and measurement. In addition, vdW 2D crystals after exfoliation are extremely hard to explore with a typical STM setup due to their small size (≤ 10 μm). Here, we present a straightforward method compatible with any STM setup having optical access: (1) exfoliating and/or stacking layered materials in a glove box, (2) transferring them to an ultra-high vacuum STM chamber using a suitcase without exposure to air, and (3) navigating surface to locate exfoliated vdW 2D flakes with different thicknesses. We successfully demonstrated that the clean surfaces of the air-sensitive
Fe
3
GeTe
2
can be effectively protected from unwanted oxidation during transfer. Furthermore, our method provides a simple but useful way to access a specific tiny stack of layered materials without any
ex-situ
fabrication processes for STM navigation. Our experimental improvement will open up a new way to investigate air-sensitive layered vdW materials with various thicknesses via surface-sensitive techniques including STM.
In this study, an indirect tool monitoring was developed based on the installation of a gap sensor in measuring the signal related to the tool behavior during the drilling process. Eleven types of ...twist drills with different tool conditions were utilized to differentiate the sensorial signals based on the tool states. A statistical analysis was conducted in the signal processing, by extracting the gap sensor signal associates from each tool condition, using the skewness and kurtosis features. Multi-class classification was conducted using the multilayer perceptron (MLP) feed forward neural network (FF-NN) model to classify and predict the tool condition based on the skewness and kurtosis data. The architectures of the MLP FF-NN models were varied to optimize the classification accuracy. This study found that the tool condition was correlated to the displacement of the drill machine spindle because the runout occurred when the sensor signal displayed fluctuation and irregularity trends. The peak intensity of the gap sensor signals increased with increasing wear severity of the twist drill. An ideal MLP FF-NN structure was achieved when the classification performance was optimized to be consistent with the learning curve.
Although the rapid urease test (RUT) is a simple method for detecting Helicobacter pylori (H. pylori) infection, it requires sufficient biopsy samples and its sensitivity varies depending on the site ...and condition of H. pylori infection. We compared the diagnostic performance of a "sweeping method" for H. pylori detection with the conventional biopsy sampling method in atrophic gastric conditions which can reduce RUT accuracy. This prospective study included 279 patients who underwent upper endoscopy to determine the presence of H. pylori infection. Gastric mucosa of both the antrum and the corpus were swabbed, and we named this method the "sweeping method". Biopsy sampling for the conventional method, histologic evaluation, and polymerase chain reaction were performed at the same time. The sensitivity, specificity, and accuracy of the sweeping method were 0.941, 0.826, and 0.903, respectively, compared to 0.685, 0.859, and 0.742, respectively, for the conventional biopsy method. The area under the receiver operating curve for the sweeping method was 0.884 versus 0.772 for the conventional method (P < 0.001). The sweeping method had a faster detection time than the conventional method. Compared to conventional biopsy sampling, the sweeping method with the RUT provided higher sensitivity and accuracy for the detection of H. pylori, with a faster detection time.
Two-dimensional transition metal dichalcogenides (TMDs) are promising materials for semiconductor nanodevices owing to their flexibility, transparency, and appropriate band gaps. A variety of ...optoelectronic and electronic devices based on TMDs p-n diodes have been extensively investigated due to their unique advantages. However, improving their performance is challenging for commercial applications. In this study, we propose a facile and doping-free approach based on the contact engineering of a few-layer tungsten di-selenide to form a lateral p-n homojunction photovoltaic. By combining surface and edge contacts for p-n diode fabrication, the photovoltaic effect is achieved with a high fill factor of ≈0.64, a power conversion efficiency of up to ≈4.5%, and the highest external quantum efficiency with a value of ≈67.6%. The photoresponsivity reaches 283 mA/W, indicating excellent photodiode performance. These results demonstrate that our technique has great potential for application in next-generation optoelectronic devices.
In this study, an optimized dynamic vibration absorber (DVA) was applied to improve the sound absorption performance and simultaneously attenuate vibrations and structure-borne noise at multiple ...frequencies. As the size parameters and eigenfrequencies of a DVA demonstrate a nonlinear relationship, tuning the eigenfrequencies by heuristically modifying the geometric parameters of the DVA is difficult. To avoid this intricate process, geometric parameters were optimized using a gradient method solver to tune the eigenvalues of the DVA to the target frequencies. Post-processing was performed for the sake of manufacturing. To confirm the validity of the performance of the sound absorption and vibration/noise attenuation, impedance tube experiments and impact experiments were conducted using the manufactured DVA. The impedance tube experiment verified that the values of the sound absorption coefficient increased with the application of the DVA. From the impact experiments, it was verified that the values of the frequency response function and sound pressure level decreased with the application of the DVA. The present study validates the notion that optimized DVAs improve the sound absorption performance of structures and simultaneously reduce vibrations and sound pressures at multiple desired frequencies.
A binary convolutional neural network (BCNN) is a neural network promising to realize analysis of visual imagery in low-cost resource-limited devices. This study presents an efficient inference ...processor for BCNNs, named TORRES. TORRES performs inference efficiently, skipping operations based on the spatial locality inherent in feature maps. The training process is regularized with the objective of skipping more operations. The microarchitecture is designed to skip operations and generate addresses efficiently with low resource usage. A prototype inference system based on TORRES has been implemented in a 28 nm field-programmable gate array, and its functionality has been verified for practical inference tasks. Implemented with 2.31 K LUTs, TORRES achieves the inference speed of 291.2 GOP/s, exhibiting the resource efficiency of 126.06 MOP/s/LUT. The resource efficiency of TORRES is 1.45 times higher than that of the state-of-the-art work.
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