Number Of Stacked Layers Research Articles

Growing twisted bilayer graphene at small angles

Growing twisted bilayer graphene at small angles

Exploring the hidden depth by confocal Raman experiments with variable objective aperture and magnification

The article analyzes experimentally and theoretically the influence of microscope parameters on the pinhole-assisted Raman depth profiles in uniform and composite refractive media. The main objective is the reliable mapping of deep sample regions. The easiest to interpret results are found with low magnification, low aperture, and small pinholes. Here, the intensities and shapes of the Raman signals are independent of the location of the emitter relative to the sample surface. Theoretically, the results can be well described with a simple analytical equation containing the axial depth resolution of the microscope and the position of the emitter. The lower determinable object size is limited to 2–4 μm. If sub-micrometer resolution is desired, high magnification, mostly combined with high aperture, becomes necessary. The signal intensities and shapes depend now in refractive media on the position relative to the sample surface. This aspect is investigated on a number of uniform and stacked polymer layers, 2–160 μm thick, with the best available transparency. The experimental depth profiles are numerically fitted with excellent accuracy by inserting a Gaussian excitation beam of variable waist and fill fraction through the focusing lens area, and by treating the Raman emission with geometric optics as spontaneous isotropic process through the lens and the variable pinhole, respectively. The intersectional area of these two solid angles yields the leading factor in understanding confocal (pinhole-assisted) Raman depth profiles.Graphical abstractSpearfishing is a well-known example of the effects of refraction at the boundary between two index-mismatched media. The object Greal is seen, due to refraction, as Gvir from the angle β (without knowing the depth position). The real position is obtained under the angle α. In a microscope (see inset), index mismatch deforms the image point of Greal into an image line. The pinhole substantially reduces deformations and allows the determination of the position of the point emitter G. (Cartoon designed by Sofia Anker)

Optimal Training Configurations of a CNN-LSTM-Based Tracker for a Fall Frame Detection System.

In recent years, there has been an immense amount of research into fall event detection. Generally, a fall event is defined as a situation in which a person unintentionally drops down onto a lower surface. It is crucial to detect the occurrence of fall events as early as possible so that any severe fall consequences can be minimized. Nonetheless, a fall event is a sporadic incidence that occurs seldomly that is falsely detected due to a wide range of fall conditions and situations. Therefore, an automated fall frame detection system, which is referred to as the SmartConvFall is proposed to detect the exact fall frame in a video sequence. It is crucial to know the exact fall frame as it dictates the response time of the system to administer an early treatment to reduce the fall’s negative consequences and related injuries. Henceforth, searching for the optimal training configurations is imperative to ensure the main goal of the SmartConvFall is achieved. The proposed SmartConvFall consists of two parts, which are object tracking and instantaneous fall frame detection modules that rely on deep learning representations. The first stage will track the object of interest using a fully convolutional neural network (CNN) tracker. Various training configurations such as optimizer, learning rate, mini-batch size, number of training samples, and region of interest are individually evaluated to determine the best configuration to produce the best tracker model. Meanwhile, the second module goal is to determine the exact instantaneous fall frame by modeling the continuous object trajectories using the Long Short-Term Memory (LSTM) network. Similarly, the LSTM model will undergo various training configurations that cover different types of features selection and the number of stacked layers. The exact instantaneous fall frame is determined using an assumption that a large movement difference with respect to the ground level along the vertical axis can be observed if a fall incident happened. The proposed SmartConvFall is a novel technique as most of the existing methods still relying on detection rather than the tracking module. The SmartConvFall outperforms the state-of-the-art trackers, namely TCNN and MDNET-N trackers, with the highest expected average overlap, robustness, and reliability metrics of 0.1619, 0.6323, and 0.7958, respectively. The SmartConvFall also managed to produce the lowest number of tracking failures with only 43 occasions. Moreover, a three-stack LSTM delivers the lowest mean error with approximately one second delay time in locating the exact instantaneous fall frame. Therefore, the proposed SmartConvFall has demonstrated its potential and suitability to be implemented for a real-time application that could help to avoid any crucial fall consequences such as death and internal bleeding if the early treatment can be administered.

Finite element analysis of blueberry stack damage

AbstractBlueberries are prone to mechanical damage during the processes of grading, packaging, transportation, and selling, and stack damage is one of the important causes of blueberry quality loss. The mechanical parameters of blueberry should be obtained firstly to create the mechanical model for analyzing the stack problems of multilayer blueberries. Precise mechanical parameters were obtained for the first time by performing a compression experiment and analyzing an explicit dynamics simulation based on the finite element model. It was found that the elastic modulus of the blueberries was 0.225 MPa and that the Poisson's ratio of the blueberries was 0.35. The placement direction of the blueberries had the greatest impact on the rupture force, followed by the number of stacked layers and the loading speed. A regression model was also obtained by considering the influences of the three factors on the rupture force. The rupture force in this research ranged from 3.15 to 7.04 N. The calyx and bottom were the most vulnerable parts of the blueberries. The upper contact part of multilayer blueberries had a greater chance of damage, and the lower contact part was the opposite because the blueberries close to the bottom layer exerted a buffering effect. Moreover, this research demonstrates the importance of applying linear explicit dynamics simulation techniques to agricultural and food products.Practical ApplicationsThe main reason for the decreasing market value and quality of blueberries is damage occurring between the point of harvesting and consumption. The damage caused by stack is one of the important factors in this process. This article accurately determined the mechanical parameters of blueberries. On this basis, the important factors that cause blueberry stack damage were further studied. Taking the rupture force as a measure, empirical models for rupture susceptibility were described. This article not only provides ideas for how to reduce blueberry stack damage and to extend blueberry shelf life but also provides a theoretical basis for research on the mechanical structure and mechanized processing of blueberries.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Preparation and mechanical properties of laminated B4C–TiB2/BN ceramics

Laminated B4C–TiB2 ceramics with h-BN interface layers were successfully prepared by roll forming and tape casting, and samples with different numbers of stacked layers were obtained. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure and interlayer crystal phases of the composites, and the bending strength, fracture toughness, and work of fracture were measured. As the number of h-BN layers increased, the fracture toughness increased from 7.38 ± 0.5 MPa m1/2 to 9.01 ± 0.61 MPa m1/2, which is 2–3 times higher than that of monolithic B4C ceramics. As the fracture toughness increased, the hardness remained at a high level (31.67 GPa). Bending tests showed that cracks deflected when they encountered the h-BN interfacial layers. The toughening mechanisms included the deflection and branching of cracks and generation of new microcracks, which increased the length of the propagation path and work of fracture.

Study on pyrolysis characteristics of lump coal in the context of underground coal gasification

Coal reaction in dry distillation zone, as an essential step in underground coal gasification (UCG), is of great significance to be studied about its characteristics in a comprehensive way. This study simulated the pyrolysis process of lump coal in UCG tunnel in a laboratory. Lump coal samples were heated in nitrogen environment at 200–600 °C. The functional groups, pore structure, and microcrystalline structure of coal samples were analyzed by Fourier transform infrared spectrometer, scanning electron microscope, and X-ray diffractometer. The results showed that, as final pyrolysis temperature increased, the contents of hydroxyl, aliphatic, and aromatic groups all showed decreasing trends. The escalation of CHar/CC and CH2/CH3 implied that the condensation degree of aromatic structure and the branching degree of fatty chain increased. With the temperature increasing, volatile substances such as CO2 and CH4 were released. Coal samples had higher porosity and gradually turned hollowed. The d002 (Interlinear Spacing of Microcrystalline) of the coal sample decreased, Lc (final stacking height) increased and Lc/d002 (stacking layer numbers) decreased, indicating that the crystal structure of coal samples tended to be more disordered.

Energy conversion models and characteristics under various inner connections of a novel packaged piezoelectric transducer for pavements

The piezoelectric effect in piezoelectric transducers converts the mechanical energy into electrical energy to supply power to road facilities. The piezoelectric transducer designed in the 3–3 piezoelectric mode has been widely studied due to the consideration of power generation performance and load-bearing requirements. However, the conservative design of some external packages and the lack of theory in the internal connection design are two deficiencies of existing research on 3–3 piezoelectric mode transducers. Given the shortcoming of packages cannot make full use of the compressive properties of piezoelectric ceramics which weakens the energy conversion ability of the piezoelectric transducers, a novel piezoelectric transducer with full-pressure packaging was designed. For the lack of theoretical and systematic research on the spatial arrangement and electrical connection of piezoelectric materials inside piezoelectric transducers, from a theoretical point of view, the energy conversion models of piezoelectric transducers in four connection modes: stacked series, stacked parallel, array series, and array parallel were derived. Subsequently, through model verification tests, the influence of the four connection modes on the energy conversion characteristics of the piezoelectric transducer was systematically studied. Finally, the effect of connection mode on energy conversion was explained in a unified manner. Five methods of promoting the energy conversion of piezoelectric transducers were proposed. The study indicated that the connection mode affected the energy conversion of the piezoelectric transducer. Specifically, the maximum energy conversion potential of the piezoelectric transducer is only affected by the spatial arrangement. The electrical connection method determines the matching resistance, which can facilitate the piezoelectric transducer to exert the maximum energy conversion potential. In the stacked type, the peak energy conversion monotonously increases with the number of stacked layers, whereas the array type exhibits the opposite trend. Regardless of the spatial arrangement of the piezoelectric materials, when piezoelectric ceramics are connected in series, the optimal value of resistance increases with the number of piezoelectric ceramics, and the opposite is true when the connection is made in parallel. The normalization analysis pointed out that the connection mode affects the energy conversion of the piezoelectric transducer can be summarized as the volume index of the piezoelectric ceramic group affects its energy conversion. A larger ratio of height to diameter of the piezoelectric ceramic group can improve the energy conversion of the transducer. This article provides ideas for the packaging design of piezoelectric transducers and a theoretical reference for the design of internal piezoelectric ceramic connection methods.

Parameterized reinforcement learning for optical system optimization

Engineering a physical system to feature designated characteristics states an inverse design problem, which is often determined by several discrete and continuous parameters. If such a system must feature a particular behavior, the mentioned combination of both, discrete and continuous, parameters results in a challenging optimization problem that requires an extensive search for an optimal system design. However, if the corresponding inverse design problem can be reformulated as a parameterized Markov decision process, reinforcement learning (RL) provides a heuristic framework to solve it. In this work, we use multi-layer thin films as an example of the aforementioned optimization problems and consider three design parameters: Each of the thin film layer’s dielectric material (discrete) and thickness (continuous), as well as the total number of layers (discrete). While recent methods merely determine the optimal thicknesses and—less commonly—the layers’ materials, our approach optimizes the total number of stacked layers as well. In summary, we further develop a Q-learning variant to solve inverse design optimization and thereby outperform human experts and current approaches like needle-point optimization or naive RL. For this purpose, we propose an exponentially transformed reward signal that eases policy search and enables constrained optimization. Moreover, the learned Q-values contain information about the optical properties of multi-layer thin films, which allows us a physical interpretation or what-if analysis and thus enables explainability.

Development of Piezoelectric Energy Harvester System through Optimizing Multiple Structural Parameters.

Road power generation technology is of significance for constructing smart roads. With a high electromechanical conversion rate and high bearing capacity, the stack piezoelectric transducer is one of the most used structures in road energy harvesting to convert mechanical energy into electrical energy. To further improve the energy generation efficiency of this type of piezoelectric energy harvester (PEH), this study theoretically and experimentally investigated the influences of connection mode, number of stack layers, ratio of height to cross-sectional area and number of units on the power generation performance. Two types of PEHs were designed and verified using a laboratory accelerated pavement testing system. The findings of this study can guide the structural optimization of PEHs to meet different purposes of sensing or energy harvesting.

Reduction of Persistent Photoconduction with IGZO/ZnON-Tandem-Structure Visible-Near-Infrared Phototransistors.

Indium-gallium-zinc oxide- and zinc oxynitride-based heterojunction phototransistors were successfully demonstrated to control the persistent photoconduction (PPC) effect and be also responded sensitively at the range from visible to near-infrared. ZnON plays a key role in extending the spectral response at various frequencies of operation. The devices show significantly different photoresponse and photorecovery characteristics depending on the number of stacked layers of IGZO and ZnON. After negative bias and illumination stress was applied to the devices for 1 h, tandem-structure-based phototransistors recovered remarkably better than single-component IGZO devices. We suggest that the improvements to photoresponse and photorecovery result from the presence of potential wells between two IGZO layers and the energy band alignment of the tandem structure.

Aerosol Jet Direct Writing Polymer-Thick-Film Resistors for Printed Electronics

To improve performance and reduce size of printed-circuit board (PCB) in electronics industry, embedding discrete components within a board substrate has been an effective approach by reducing solder joints and their associated impedance mismatching, inductive reactance, etc. With its unique capabilities for non-contact precision material deposition, the Aerosol Jet® direct-write technology has been enabling additive manufacturing of fine-feature electronics conformally onto flexible substrates of complicated shapes. The CAD/CAM controlled relative motions between substrate and print head allows convenient adjustment of the pattern and pile height of deposited material at a given ink volumetric deposition rate. To date in the printed electronics industry, additively printing embedded polymer-thick-film (PTF) resistors has mostly been done with screen printing using carbon-based paste inks. Here we demonstrate results of Aerosol Jet® printed PTF resistors of resistance values ranging from ~50 W to > 1 kW, adjustable (among several variable parameters) by the number of stacked layers (or print passes with each pass depositing a fixed amount of ink) between contact pads of around 1 mm apart with footprint line typically < 0.3 mm. In principle, any ink material that can be atomized into fine droplets of 1 to 5 microns can be printed with the Aerosol Jet® system. However, the print quality such as line edge cleanliness can significantly influenced by ink rheology which involves solvent volatility, solids loading, and so on. Our atomizable carbon ink was made by simply diluting a screen printing paste with a compatible solvent of reasonable volatility, which can be cured at temperatures below 200 oC. We show that Aerosol Jet® printed overlapping lines can be stacked to large pile height (to reduce the resistance value) without significant increase of line width, which enables fabricating embedded resistors with adjustable resistance values in a limited footprint space.

Performance improvement for compressive light field display with multi-plane projection

Conventional compressive light field (CLF) displays reconstructing three-dimensional (3D) scenes generally use stacked liquid crystal displays (LCDs). However, the low transmittance of LCD limits the number of stacked layers (usually three) and the image quality. In this paper, the realization of the CLF display with multi-plane projection is proposed by using polymer stabilized cholesteric texture (PSCT) shutter and digital micro-mirror devices (DMDs). Benefitting from high transmittance (>80%) and fast response time (≤1ms) of PSCT shutter, the proposed system provides an opportunity to increase the number of physically stacked layers while preserving high brightness, which could achieve a large depth of field (DOF) and high-fidelity 3D image. Limited by the maximum refresh rate of DMD, the relationship between the gray scale and the layered number is analyzed and optimized to minimize the deviation between reconstructed light field and target light field. To improve the quality of reconstruction, the chromatic aberration due to the wavelength of incident light is investigated and compensated. In addition, the three-dimensional matrix mapping method is presented to convert decomposed images into binary images efficiently, which realizes the high-speed and real-time processing of massive display data. To verify the feasibility of the proposed system, a prototype was implemented and photographs were captured from different viewpoints. With the experimental results, the system was confirmed to have a potential for both 3D display and augmented reality (AR) applications.

Energy harvesting from car suspension system: Mathematical approach for half car model

A significant contribution of this paper is developing a half car model with a built-in piezoelectric stack to evaluate the potential of harvesting power from the car suspension system. The regenerative car suspension system is modelled mathematically using Laplace transformation and simulated using MATLAB/Simulink. Two piezoelectric stacks are installed in series with the front and rear suspension springs to maintain the performance of the original suspension system in ride quality and comfortability. Half car model is subjected under harmonic excitation with acceleration of 0.5 g and velocity of 9.17 rad/s. The harvested voltage and power are tested in both time, and frequency domain approaches. The influence of the different parameters of the piezoelectric stack (number of stack layers and area to thickness) and car suspension (sprung and unsprung stiffness and damping coefficients) are examined. Also, the effect of road amplitude unevenness is considered. The results illustrate that the maximum generated voltage and power at the excitation frequency of 1.46 Hz are 33.51 V and 56.25 mW, respectively.

Tuning electro-mechanical properties of EAP-based haptic actuators by adjusting layer thickness and number of stacked layers—a comparison

In our fast-changing world, human-machine interfaces (HMIs) are of ever-increasing importance. Among the most ubiquitous examples are touchscreens that most people are familiar with from their smartphones. The quality of such an HMI can be improved by adding haptic feedback—an imitation of using mechanical buttons—to the touchscreen. Thin-film actuators on the basis of electro-mechanically active polymers (EAPs), with the electroactive material sandwiched between two compliant electrodes, offer a promising technology for haptic surfaces. In thin-film technology, the thickness and the number of stacked layers of the electroactive dielectric are key parameters for tuning a system. Therefore, we have experimentally investigated the influence of the thickness of a single EAP layer on the electrical and the electro-mechanical performance of the transducer. In order to achieve high electro-mechanical actuator outputs, we have employed relaxor-ferroelectric ter-fluoropolymers that can be screen-printed. By means of a model-based approach, we have also directly compared single- and multi-layer actuators, thus providing guidelines for optimized transducer configurations with respect to the system requirements of haptic applications for which the operation frequency is of particular importance.

G-C3N4 nanosheets exfoliated by green wet ball milling process for photodegradation of organic pollutants

In this study, ultra-thin and easily dispersible g-C3N4 nanosheets were obtained by a simple wet ball-milling process. Morphological and structural analysis showed that increasing ball-milling speed resulted in a decrease in both particle size and the number of stacked layers in g-C3N4 nanosheets, hence improving their dispersion stability. Thinner nanosheets obtained by ball milling at 150 rpm also had higher photocatalytic capacity, with up to 2.2 times enhancement comparing with untreated g-C3N4. The feasibility of the g-C3N4 nanosheets for photodegradation of aqueous organic contaminants was demonstrated using polluted water sampled from Jingyue Lake in Donghua University, a local lake.

Microstructure characteristics of lignite under the synergistic effect of oxidizing acid and ionic liquid [Bmim][Cl

In order to investigate the evolution characteristics of coal microstructure under the synergistic effect of oxidizing acid and ionic liquid, in this paper, the microcrystalline structure and functional groups of coal were modified with HNO3, [Bmim][Cl] and HNO3/[Bmim][Cl], respectively. Fourier transform infrared (FTIR) spectroscopy combined with X-ray diffraction (XRD) was used to collect the microstructure information of coal samples and obtain the variation of microstructure parameters. The research showed that compared with the single treatment method of HNO3 and [Bmim][Cl], the synergistic treatment of HNO3/[Bmim][Cl] makes the molecular structure of coal extremely unstable, and the aliphatic chain and aliphatic side chain are easier to fall off and condense from the main structure of coal molecules, which further increases the aromaticity of coal. Meanwhile, [Bmim][Cl] can dissolve and remove some active functional groups and delay the oxidation process of HNO3. For the microcrystalline structure of coal, all three solvents can reduce the interlayer spacing (d002), increase the average lateral size (La), the effective stacking layer number (N) and the stacking height (Lc), indicating that the solvent treatment makes the microstructure more compact. As the synergistic treatment of HNO3/[Bmim][Cl] promotes the aromatization process of coal microstructure and significantly reduces the aliphatic content, the coal microcrystalline structure tend to graphitization.

Toward reliable automatic liver and tumor segmentation using convolutional neural network based on 2.5D models

PurposeWe investigated the parameter configuration in the automatic liver and tumor segmentation using a convolutional neural network based on 2.5D model. The implementation of 2.5D model shows promising results since it allows the network to have a deeper and wider network architecture while still accommodates the 3D information. However, there has been no detailed investigation of the parameter configurations on this type of network model.MethodsSome parameters, such as the number of stacked layers, image contrast, and the number of network layers, were studied and implemented on neural networks based on 2.5D model. Networks are trained and tested by utilizing the dataset from liver and tumor segmentation challenge (LiTS). The network performance was further evaluated by comparing the network segmentation with manual segmentation from nine technical physicians and an experienced radiologist.ResultsSlice arrangement testing shows that multiple stacked layers have better performance than a single-layer network. However, the dice scores start decreasing when the number of stacked layers is more than three layers. Adding higher number of layers would cause overfitting on the training set. In contrast enhancement test, implementing contrast enhancement method did not show a statistically significant different to the network performance. While in the network layer test, adding more layers to the network architecture does not always correspond to the increasing dice score result of the network.ConclusionsThis paper compares the performance of the network based on 2.5D model using different parameter configurations. The result obtained shows the effect of each parameter and allow the selection of the best configuration in order to improve the network performance in the application of automatic liver and tumor segmentation.

Systematic study of an Fe2O3 stacked homojunction photoelectrochemical photoelectrode

In this study, iron (Ⅲ) oxide (Fe2O3) homojunction photoelectrodes were grown via the hotplate chemical bath deposition method. Various Fe2O3 homojunction-structured photoelectrodes have been proposed to overcome the problems such as low carrier mobility, high electron-hole recombination rate and defects due to lattice mismatch suffered by heterojunction photoelectrodes or single-layer photoelectrodes. The effects of the buffer layer, the number of stacked layers, the stacked-layer structure, and the thermal annealing treatment process on the Fe2O3 homojunction photoelectrode were systematically investigated. As a result, the Fe2O3 homojunction photoelectrode with a total of four Fe2O3 stacked thin films showed the best photoelectrochemical performance and was the thickest herein; it also had the highest X-ray diffraction (XRD) peak intensity for the (110) plane, the lowest XRD full-width at half maximum (FWHM), the highest donor density values, and the lowest resistance between the photoelectrode and electrolyte. This Fe2O3 homojunction photoelectrode with four stacked thin films showed the highest photocurrent density herein (0.54 mA/cm2 at 1.64 VRHE), which is an approximately 160% improvement over the value of the single-layer Fe2O3 photoelectrode.

Piezoelectric method‐based harvested energy evaluation from car suspension system: Simulation and experimental study

AbstractThe main objective of this work is to build a mathematical model to evaluate the potential of harvesting power from the car suspension system. Quarter‐ and half‐car models with built‐in piezoelectric stack were modeled mathematically and simulated using MATLAB/Simulink. The piezoelectric stack was installed in series with the suspension spring to maintain the performance of the original car suspension system in ride quality and comfortability. The harvested voltage and power were tested with respect to time and frequency. From a half car model, the maximum generated voltage and power at the excitation frequency of 1.46 Hz were 33.56 V and 56.35 mW, respectively. By comparing a half‐car model with the quarter‐car model, the outcomes illustrated that the harvested voltage and power of the half‐car model were increased by 75.6% and 53.4%, respectively. Piezoelectric stack parameters (number of stack layers and area to thickness) and the car suspension parameters (sprung and unsprung stiffness, damping coefficients, and masses) were examined for half‐car model. Also, the influence of road amplitude unevenness was considered. The simulation results of the quarter‐car system were verified with the experimental test under harmonic excitation. The results exhibited good agreement with the simulation results at different excitation frequencies.