Front Layer Research Articles

НЕСУЩАЯ СПОСОБНОСТЬ И ДОЛГОВЕЧНОСТЬ НАРУЖНЫХ КИРПИЧНЫХ СТЕН ЗДАНИЙ

For buildings of historical development of cities, as well as architectural dominants of urban and rural settlements, the architectural attractiveness of buildings is often created by erecting external load-bearing brick walls, including multilayer ones, as well as curtain external walls with a finishing layer of facing bricks. When designing building envelopes, as well as in the process of researching and assessing the technical condition of building envelopes, it becomes necessary to calculate (assess) the bearing capacity of external walls, to assess their durability. The object of research is the bearing capacity and durability of the outer walls of buildings. A review of domestic and foreign scientific and technical literature has been carried out. He showed that the overwhelming majority of scientific publications concern the choice of constructive solutions for walls, the purpose and use of new building technologies and materials, their technical characteristics, as well as the assessment of the energy efficiency of the proposed constructive solutions for external walls. Examples of defects in the outer layer of multilayer bearing walls of brick buildings and recommendations for ensuring the durability of the front layer of a brick wall are given. The requirements of the current building codes for calculating the bearing capacity of multilayer brick walls are considered. An example of calculating an eccentrically compressed multilayer brick wall with equivalent calculated cross-section is given. In order to simplify the calculation of the bearing capacity, it is proposed to use computer programs to determine the geometric characteristics of the equivalent calculated cross-section. In particular, for a short-term application of loads to determine the stresses and analyze the stress state of the equivalent calculated cross-section of the wall, an example of using the program, the constructor of sections PK LIRA-SAPR, is given. It is shown that it is necessary to consider the distribution of stresses over the section under short-term and long-term loading in the design of multilayer brick walls.

Microstructured layered targets for improved laser-induced x-ray backlighters.

We present the usage of two-layer targets with laser-illuminated front-side microstructures for x-ray backlighter applications. The targets consisted of a silicon front layer and copper back side layer. The structured layer was irradiated by the 500-fs PHELIX laser with an intensity above 10^{20}Wcm^{-2}. The total emission and one-dimensional extent of the copper Kα x-ray emission as well as a wide spectral range between 7.9 and 9.0 keV were recorded with an array of crystal spectrometers. The measurements show that the front-side modifications of the silicon in the form of conical microstructures maintain the same peak brightness of the Kα emission as flat copper foils while suppressing the thermal emission background significantly. The observed Kα source sizes can be influenced by tilting the conical microstructures with respect to the laser axis. Overall, the recorded copper Kα photon yields were in the range of 10^{11}sr^{-1}, demonstrating the suitability of these targets for probing applications without subjecting the probed material to additional heating from thermal line emission.

An investigation of deformation and failure mechanisms of fiber-reinforced composites in layered composite armor

This paper aims to study the deformation characteristics and failure mechanisms of fiber-reinforced polymer composites used in layered composite armor under ballistic impact. A Kevlar-29/epoxy composite and an ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced composite backed bilayer ceramic armor were respectively impacted against 7.62 mm APM2 projectiles at several different velocities. The dependence of failure mechanisms on impact velocity was analyzed both experimentally and numerically. Ballistic tests revealed that the Kevlar-29/epoxy composite backed armor displayed a lower perforation velocity than the UHMWPE fiber reinforced composite backed armor. However, under non-perforated impacts, the UHMWPE fiber reinforced composite exhibited a much higher back face deflection (BFD). According to the post-mortem visual and SEM analysis, the failure of the Kevlar-29 fiber was dominated by shear plugging in the front layers and fiber tensile breakage in the rear layers, whereas in the UHMWPE fiber reinforced composite, failure was dominated by shear plugging initiated from the front layers. These results suggest that the UHMWPE panel is more effective in resistant fiber tensile breakage which usually occurs on the back side of the panel. Using the Ls-dyna explicit dynamic finite element (FE) program, the ballistic behavior of a layered armor backed by a hybrid panel with varying mix ratios was studied numerically. The results show that using high tensile resistant fiber in the rear layers can effectively prevent fiber tensile failure and using high shear resistance fiber in the front layers can effectively prevent shear failure. These results are valuable in making the best use of fiber-reinforced composites in advanced armor design.

Intelligent Fault Diagnosis Method for Blade Damage of Quad-Rotor UAV Based on Stacked Pruning Sparse Denoising Autoencoder and Convolutional Neural Network

This paper introduces a new intelligent fault diagnosis method based on stack pruning sparse denoising autoencoder and convolutional neural network (sPSDAE-CNN). This method processes the original input data by using a stack denoising autoencoder. Different from the traditional autoencoder, stack pruning sparse denoising autoencoder includes a fully connected autoencoding network, the features extracted from the front layer of the network are used for the operation of the subsequent layer, which means that some new connections will appear between the front and rear layers of the network, reduce the loss of information, and obtain more effective features. Firstly, a one-dimensional sliding window is introduced for data enhancement. In addition, transforming one-dimensional time-domain data into the two-dimensional gray image can further improve the deep learning (DL) ability of models. At the same time, pruning operation is introduced to improve the training efficiency and accuracy of the network. The convolutional neural network model with sPSDAE has a faster training speed, strong adaptability to noise interference signals, and can also suppress the over-fitting problem of the convolutional neural network to a certain extent. Actual experiments show that for the fault of unmanned aerial vehicle (UAV) blade damage, the sPSDAE-CNN model we use has better stability and reliable prediction accuracy than traditional convolutional neural networks. At the same time, For noise signals, better results can be obtained. The experimental results show that the sPSDAE-CNN model still has a good diagnostic accuracy rate in a high-noise environment. In the case of a signal-to-noise ratio of −4, it still has an accuracy rate of 90%.

A Face Recognition Algorithm Based on Intermediate Layers Connected by the CNN

Face recognition is difficult due to the higher dimension of face image features and fewer training samples. Firstly, in order to improve the performance of feature extraction, we inventively construct a double hierarchical network structure convolution neural network (CNN) model. The front-end network adopts a relatively simple network model to achieve rough feature extraction from input images and obtain multiple suspect face candidate windows. The back-end network uses a relatively complex network model to filter the best detection window and return the face size and position by nonmaximum suppression. Then, in order to fully extract the face features in the optimal window, a face recognition algorithm based on intermediate layers connected by the deep CNN is proposed in this paper. Based on AlexNet, the front, intermediate and end convolution layers are combined by deep connection. Then, the feature vector describing the face image is obtained by the operation of the pooling layer and the full connection layer. Finally, the auxiliary classifier training method is used to train the model to ensure the effectiveness of the features of the intermediate layer. Experimental results based on open face database show that the recognition accuracy of the proposed algorithm is higher than that of other face recognition algorithms compared in this paper.

Repair and Renovation of the Historic Church in Ruda Śląska After Many Failures Caused by Mining Exploitation

This paper describes a case of the church, which for nearly 70 years was exposed to the impact of 26 mining exploitations conducted under the church or very close to the church at different depths. These caused damage in the form of superficial cracks of vaults and walls as well as the loosening of the front layer of stone façade of towers. The construction has been preserved due to the continuous monitoring and numerous repairs and renovations. Currently, there is no mining exploitation under the church.

Damage and ballistic evaluation of ceramic-metal composite target against cylindrical projectile

The ballistic resistance of a composite ceramic–metal target has been studied by performing three–dimensional finite element computations on ABAQUS/Explicit finite code. The bi–layer alumina 95–aluminium 2024–T3 target has been subjected to impact load by a cylindrical steel projectile at varying incidence velocity in order to carry out a detailed investigation about the behaviour of a composite with a front ceramic layer. First of all the optimum thickness ratio of the front ceramic and backing aluminium layer has been found out. Subsequently, the significance of the eccentricity on the impact response has been studied by hitting the composite target at six different impact locations and the results have been compared with that of the concentric impact condition. The possibility of reducing the areal density of the composite by using the perforated backing aluminium plate has also been studied. The eccentricity in the impact load has played a significant role on the ballistic resistance of the composite. The consideration of perforated backing plate though could not enhance the ballistic efficiency. However, it has been found that a major portion of the energy of the projectile is lost during its interaction with the front ceramic tile leading to significant erosion of the projectile. The backing plate on the other hand played the role of supporting the front layer however its share of energy absorption subsequent to the comminution of ceramic was not very significant. The Johnson–Holmquist (JH–2) constitutive model has been used for simulating the material behaviour of the ceramic and the Johnson–Cook (JC) constitutive model has been used for simulating the behaviour of backing plate and the projectile.

Efficient 2T CsKPb(IBr)3—Tin Incorporated Narrow Bandgap Perovskite Tandem Solar Cells: A Numerical Study with Current Matching Conditions

AbstractThis study numerically investigates a highly efficient tandem‐structured and, perovskite‐perovskite model solar cells using the solar cell simulator capacitance software (), consisting of wide‐bandgap top potassium incorporated inorganic cesium‐based perovskite cell () and narrow‐bandgap bottom tin incorporated perovskite cells (and ). The study explores and optimizes the front and rear perovskite absorber layer parameters (especially thickness) and current matching conditions ideal for tandem device performance. The simulated top standalone inorganic solar cell parameters yield a power conversion efficiency of over 13% (for all models), while the bottom perovskite devices simulated with filtered spectrum yield an efficiency of 14.17% for , 8.54% for , and 13.30% for , respectively. The study and quantification of the current matching points for the tandem configuration provide some insight into the device's performance, which is beneficial for its efficiency enhancement. The resultant simulated optimized tandem cells offer a maximum efficiency of 21% for model, 17.5% for model, and 20% for model, respectively, with improved parameters.

An experimental study on upward flame spread over corrugated cardboard used in underground logistic transportation: Influence of grain orientation and thickness

Corrugated cardboard is widely used in underground logistic transportation and warehousing and it has become an important fire hazard source. According to previous warehouse fire studies, upward flame spread on corrugated cardboard plays an important role during the initial stage of warehouse fires and can decide the occurrence of subsequent increasing fire hazards. However, the wavy structural effect of corrugated cardboard on fire spread still lacks enough attention. This work studies the fire spread behavior of vertically-set corrugated cardboard with thicknesses of 1.5 mm, 3.0 mm and 4.0 mm. The cardboard inner hollow gaps are set either parallel (defined as along grain direction) or perpendicular (defined as across grain direction) to buoyancy direction. Experimental results show that: (1) along grain sample has better flammability than across grain sample; (2) the relationship between flame height (or pyrolysis height) and time has a best fit with power law, and the difference of the exponents between two grain orientations decreases with the increasing of the sample thickness; (3) for cardboard of different grain orientations and thickness, the ratio of average flame height to average pyrolysis height is a constant. The hollow gaps inside along grain sample, working as passage, are beneficial for the transportation of heated pyrolysis gases and preheating of upper virgin area, hence increasing burning rate and flame upward spread. However, it is observed that the phenomenon (flame luminance, delamination of front layer, extinguishment of flame base, etc.) difference between different grain orientations decreases as sample thickness increases. This study reveals the effects of grain orientation and sample thickness on the corrugated cardboard fire spread behavior which is common in commodity fire in underground logistic transportation and warehousing. The conclusions are beneficial for fire risk assessment as well as the improvement of related codes and regulations.

Joint Prediction and Association for Deep Feature Multiple Object Tracking

Deep learning (CNN) can significantly improve the accuracy of image recognition with its powerful features, but the low-level network layer also contains important feature information. In order to achieve more stable and efficient tracking in multi-target tracking, this type of deep features will also be used to make the features more expressive by integrating the data from the front and back layers. The deformable convolution is also introduced to overcome the deformation problem caused by the camera motion. And with the increase of time, we predict the position of the target by the motion model, so as to remove the position where the target is impossible to reach in physical space, and further optimize the association before multiple targets. In this paper, we use an end-to-end correlation method to reduce the complexity of the algorithm. We tested it on the open source dataset MOT17 dataset and obtained remarkable results.

Preliminary comparison of contact angle and wetting resistance of water-repellent treated cotton woven fabric

Filtration capability of textile media or the resistance towards the fluid penetration through different fabrics is depending on their surface repellence. The emission of condensed exhaled air on the outer layer of the half facemask from the FFP2 (EN 149) category indicates the termination of its protective properties. The overcoming by the fluid of the textile environment of the mask in its role of an artificial barrier goes through two stages. Initially, the aerosols in the exhaled air condense and meet the repulsion from the inner fabric. Later, due to the hydrodynamic pressure, the condensed droplets pass through the textile medium, overcoming the friction among the fibrous layers. Finally, the droplets irrigate the outer, front layer of the mask and are released into the environment with all the consequences. Closest to this physiological process is the hydrostatic pressure test method. The test of resistance to fluid penetration gives a final assessment of the property of the textile environment without clarifying the elements of the process. Experimental studies have shown similarities in the results of the penetration of the fluid through the textile medium and the initial repulsion of aerosols from the surface of the fibrous layer. The repulsion of water droplets is of predominant importance in relation to the general barrier capacity of the textile media. The main indicator of water repellence is the contact angle of the free drop on the fabric. The subject of this article is the comparison between the contact angle of wetting and the penetration of the fluid by means of standard test methods. The aim of the work is to explain and model the process of fluid penetration through protective masks, as well as to optimize the properties of repulsion and resistance.

Scalable image-based indoor scene rendering with reflections

This paper proposes a novel scalable image-based rendering (IBR) pipeline for indoor scenes with reflections. We make substantial progress towards three sub-problems in IBR, namely, depth and reflection reconstruction, view selection for temporally coherent view-warping, and smooth rendering refinements. First, we introduce a global-mesh-guided alternating optimization algorithm that robustly extracts a two-layer geometric representation. The front and back layers encode the RGB-D reconstruction and the reflection reconstruction, respectively. This representation minimizes the image composition error under novel views, enabling accurate renderings of reflections. Second, we introduce a novel approach to select adjacent views and compute blending weights for smooth and temporal coherent renderings. The third contribution is a supersampling network with a motion vector rectification module that refines the rendering results to improve the final output's temporal coherence. These three contributions together lead to a novel system that produces highly realistic rendering results with various reflections. The rendering quality outperforms state-of-the-art IBR or neural rendering algorithms considerably.

Development and analysis of composite overwrapped pressure vessels for hydrogen storage

In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance.

Photovoltages in Polycrystalline Mosaic Solar Cells.

In some thin-film solar cells the light-absorbing layer is a mosaic of crystalline grains whose boundaries run from the back to the front of the cell. We used the semiconductor modeling software Sesame to do numerical calculations of the optoelectronic properties of such cells assuming that recombination of minority photocarriers occurs primarily at the grain boundaries. The work complements analytical results for diffusion-limited recombination at grain boundaries and dislocations. We chose idealized n-CdS/p-CdTe solar cells for illustration. We find that the open-circuit voltage, VOC, under illumination declines logarithmically with increasing ratio D/θ2, where D is the ambipolar diffusion constant governing minority-carrier transport and θ is the grain size (from 1 to 10 μm). While a decline in VOC as mobility increases is counterintuitive, this finding is consistent with related analytical results and confirms their utility. However, open-circuit voltages are about 0.04–0.10 V lower than the corresponding analytical estimates. We show that the deficit is mostly a consequence of a recombination shortcut. At open circuit, minority photocarrier currents at points closer to the n-CdS interface than to a grain boundary are directed through the conducting front layers and terminate near the “hot spot” at the intersection with the grain boundary. The shortcut lowers open-circuit voltages by about 0.05 V below the analytical estimates.

PERFORMANCE PROPERTIES OF THREAD SEAMS OF KNITTED-BASED MEMBRANE MATERIALS

The article is devoted to the study of the strength and wear resistance of thread seams of membrane materials on a knitted basis. The characteristics of the composite membrane three-layer material are given and the modes of its stitching and the test method are substantiated. Investigations of material cutting through with a needle were carried out and the geometry of the sewing needle point was chosen. The results of the study of the strength of thread seams made along of the front layer of the material before and after modelling the operational tensile loads along and across the seam are presented. 15000 load-unload cycles were simulated, stretching the sample by 10 % of the seam length. As a result of a full factorial experiment, it was found that the linear density of the threads and the diameter of the needle have the greatest effect on the strength and wear resistance of the thread seams of the composite material. The influence of the sewing frequency is ambiguous for the parameter of the wear resistance of the seam when stretched along and across the line.

Ballistic performance of powder metal Al5Cu-B4C composite as monolithic and laminated armor

Abstract In this study, ballistic performances of x wt.-% B4C (x = 5, 10, and 20) reinforced Al5Cu matrix composite samples were investigated as a monolithic and laminated composite armor component. Composite armor plates were produced by the powder metallurgy method. The prepared powders were pressed under 400 MPa pressing pressure. Green compacts were pre-sintered at 400 °C for 30 minutes in order to blow the lubricant. Subsequently, liquid phase sintering was performed at 610 °C for 210 minutes. In ballistic tests, 7.62 mm caliber armor-piercing bullets were used as the ballistic threat. In the ballistic tests of monolithic armors, only 10 mm thick powder metal composite plates were tested. In the ballistic tests of laminated composite armors, these powdered metal plates were layered with 10 mm thick alumina ceramic plate front layers and 10 mm thick AA5083 plates. Although all of the monolithic powder metal composite armors were penetrated, they showed multi-hit capability. All of the laminated composite armors provided full ballistic protection. It was determined that with the increase in B4C reinforcement rate, the ballistic resistance also increased due to the improvement in strength, hardness, and abrasive feature.

Synergistic effect of hybrid ballistic soft armour panels

This study aims to identify synergistic effect of hybrid ballistic soft armour panel. According to Finite Element Simulation results and ballistic test results, a front sensitive region was identified including front one or two layers in an Ultra High Molecular Weight Polyethylene Uni-directional (UHMWPE UD) panel. These front layers displayed lower energy absorption due to thermal damage and high compressive stress concentration. While back layers possessed higher energy absorption due to significant tensile failure. When different materials were placed in the front sensitive region (such as UD laminates, woven fabric and non-woven felt), ballistic responses of whole panels was influenced including transverse deflection during impact, failure modes and ballistic energy absorption. Only when the proper materials were placed in the front sensitive region, synergistic hybrid effect can be displayed with improvement of energy absorption of the hybrid panel for a given areal weight.

Application of Quantum Dot Down-Conversion Layer in Thin-Film Solar Cells to Increase Short-Wavelength Spectral Response

The short-wavelength optical loss in the Cu(In,Ga)Se2 (CIGS) thin-film solar cells is inevitable owing to the substantial light absorption in the front layers such as the buffer layer and transparent conducting oxide (TCO) layer. Quantum dots (QDs) with CdSe/ZnS core–shell structure is utilized to increase the short-wavelength spectral response of the CIGS thin-film solar cells. The QDs absorbs photons in the short-wavelength region (<540 nm) and re-emits the photons at approximately 540 nm; these photons penetrate the front layers and reach the CIGS absorber layer. The thickness of the QD layer was varied via drop coating with different QD concentrations, thereby facilitating the application of the optimized QD layer as a down-conversion layer in the CIGS thin-film solar cells. The photoelectric parameters of the CIGS thin-film solar cells were dependent on the QD thickness, and they were characterized using quantum efficiency measurements, spectrophotometric analysis, and current–voltage measurements. The CIGS thin-film solar cells with a 0.7 μm-thick QD layer exhibited the highest increase of 1.86 mA cm−2 and 0.75% in the short-circuit current density and efficiency, respectively.

Experimental and numerical investigation of hybrid armor against a ballistic impact

PurposeThe main challenge in preparing body armor is achieving a high protection level by using lightweight materials with minimum cost.Design/methodology/approachIn this study, a three-hybrid multilayered armor system is prepared for protection against a ballistic impact wave. These armor systems consist of glass or ceramic tile as a front layer followed by three intermediate layers made of woven fiber reinforced polymer composites and a back layer made of either aluminum or polypropylene.FindingsAll armor systems were successful in impeding the projectile from perforating, that is materials selection played an important role in stopping the ballistic impact wave. Almost an identical ballistic behavior was recorded between the experimental and numerical simulation by using ANSYS AUTODYN which means that the simulation could be used in advance to reduce the time required for practical experiments and the cost of using materials in experimental tests will be lessened. The effect of projectile geometry also had been studied, and it showed a noticeable role in changing ballistic behavior.Originality/valueThe originality of this research is in using carbon and glass fiber which are woven together in addition to adding polypropylene layers in armor preparation.

Determination of Si(Li) detector efficiency by experimental and Monte Carlo simulation methods

In this study, a Si(Li) detector was modeled by MCNP (Monte Carlo n-particle) code and its efficiency was estimated by Monte Carlo simulation in the photon energy range of 5.9–59.54 keV. Experimental measurements using 55Fe, 57Co, and 241Am radioactive standard sources were performed for validation of the applied simulation code. The primary results of the simulation were compared with the experimental ones and considerable discrepancies were observed, especially in the low energy region. Since the dead layers’ thicknesses are not always precisely provided by the manufacturer and even can change during detector aging, they were assumed as the cause of these discrepancies (front dead layer’s thickness being a critical parameter for low energy photons). After adjusting the thicknesses of the front and rear dead layers in a step-by-step procedure, a reasonable agreement was achieved between the simulated and experimental results. The results of this study indicate that if performing an experiment by the detector is difficult for any reason in some energies, one can rely on the MCNP code as an operational tool by interpolation or extrapolation of the available experimental efficiency data (in low energy region).