Top Layer Research Articles

Armamentarium of wart control by using Allium sativum, malus and pumila mill

Human papillomavirus (HPV) infection is the cause of warts. The virus induces the top layer of skin (epidermis) to create an overabundance of the hard protein keratin. A wart has a harsh, gritty texture due to the excess keratin. Skin warts are microscopic growths brought on by a viral infection. It can be treated with over the counter medications. These are usually rough, tiny growths that can develop on the hands, feet, or genitalia, among other regions of the body. Garlic extract, which has a wide range of possible health advantages, is made from garlic cloves. It is a metabolite-rich, disease-preventive nutraceutical spice that is enhanced with polyphenols and organosulfur. It contains chemicals with antibacterial and antioxidant effects, including allicin. Because apple cider vinegar extract has so many potential benefits, it is frequently used for skin care. Because it lowers oil and bacteria on the skin, it has been used to treat acne. By reducing inflammation, it might also be beneficial for skin disorders like eczema.

Effect of introducing dummy layers on interlayer bonding and geometrical deformations in concrete 3D printing

This paper presents the effect of dummy layers in concrete 3D printing to enhance interlayer bonding and reduce geometrical deviations. The specimens were printed by varying numbers of dummy layers at different layer heights using the optimized printing parameters. The impact of dummy layers on interlayer bonding was determined using a split tensile test and the geometrical deviations were analyzed using a 3D-scanning technique. Results demonstrate that significant improvement was found in interlayer bonding, notably at the top layer. For instance, by adding two dummy layers in specimen H10D2, the difference between the top and middle layers bond strength was reduced from 42.57% (i.e., for specimen H10D0) to 0.79%. Moreover, the dummy layers effectively minimized the geometrical deviations by achieving the desired layer dimensions in the top layer of specimens.

Flexural failure properties of fiber-reinforced hybrid laminated beam subject to three-point bending.

The present study investigates the flexural failure properties of a hybrid laminate beam subjected to three-point bending. A symmetrically laminated hybrid beam is constructed using high-strain and inexpensive glass fibre on the top layers and low-strain and expensive carbon fiber on the middle layers. Classical lamination plate theory is used to find the stress and strain distribution that occurs due to the bending moment on the compressive side. The theoretical failure limits of the laminated hybrid beam are analyzed considering the targeted span-to-depth ratios, volume fractions of the fibers and hybrid ratios using the Tsai-Wu failure criterion and Matlab codes. Using the graph of failure index versus hybrid ratios, the minimum thickness of carbon fiber needed for the delay of failure and cost efficiency of the laminated hybrid beam is identified by applying the linear interpolation method. The numerical results indicate that the failure index increases with the increasing loading span and decreases when the volume fraction of fiber increases. In particular, the placement of glass fiber on the top layer of the laminated hybrid beam might have contributed to obtaining higher strains and curvatures before the catastrophic failure properties of carbon fiber. The flexural stiffness of the laminates is found to increase when the hybrid ratio increases. Overall, it is noted that the theoretical analysis is one method that is less time-consuming and cost-effective than other alternative approaches, such as finite element methods and experimental tests to estimate the minimum thickness of high-stiffness and the expensive material needed to maintain the strength and stiffness of the hybrid composite structures over long periods.

“Two-in-one” high stretchable healable WPU based conductive hydrogel for intelligent wearable sensing

In recent years, conductive hydrogel based sensors have been widely used because of their flexibility and convenience, especially in strain sensing, handwriting recognition, object shape recognition and so on. In this research, the conductive hydrogel with “two-in-one” structure was well designed to avoid the agglomeration and leakage of liquid metal by using polyvinylpyrrolidone modified liquid gallium indium alloy/polydopamine composite hydrogel as the top layer and hydrogen bonding crosslinked waterborne polyurethane/poly(vinyl alcohol) composite hydrogel as the bottom layer, respectively. Finally, a hydrogel based sensor with excellent stretchability and sensitivity was successfully obtained. The tensile strength of the prepared composite hydrogel exceeded 2 MPa. The elongation at break could be greater than 500 %. The toughness was greatly improved due to the introduction of waterborne polyurethane, which was greater than 7.5 MJ/m3. The GF value of the sensors reached 4.54. More interestingly, the mechanical self-healing ability of composite hydrogel prepared by adding polydopamine, reached about 70 % of the original. The hydrogel based sensor was able to use for gesture recognition and controlling the manipulator in human-computer interaction. This research can provide a practical idea to achieve advanced intelligent wearable sensing.

Study on Dynamic Mechanical Properties of Sandwich Beam with Stepwise Gradient Polymethacrylimide (PMI) Foam Core under Low-Velocity Impact.

Different PMI foam materials of 52, 110, and 200 kg/m3 were used to design stepwise gradient cores to improve the impact resistance of the sandwich beam. The stepwise gradient core consists of three layers arranged in positive gradient, negative gradient, and sandwich-core (e.g., 200/52/200). These sandwich beams were subjected to the impact of a steel projectile under impact momentum of 10 to 20 kg·m/s, corresponding to impact energy in the range of 12.5 to 50 J. During the test, the impact force was recorded by an accelerometer, and the different failure modes were also obtained. Subsequently, the influence of the layer arrangement on the energy absorption and load transfer mechanism between the different layers was analyzed. The results showed that the top layer with a large density can improve the impact force, but the middle/bottom layer with a low density promoted specific energy absorption. Thus, based on these two points, the negative gradient core (200/110/52) had an excellent specific energy absorption because it can transfer and expand the area to bear the load layer by layer, which improved the energy absorption in each layer. Combined with the failure modes, the load transfer and deformation mechanisms between the layers were also discussed. The present work provided a valuable method to design an efficient lightweight sandwich structure in the protection field.

Current collapse suppression in AlGaInN/GaN HEMTs with thin unintentionally doped GaN channel and AlN back barrier grown on single-crystal AlN substrate

A high-electron-mobility transistor (HEMT) structure consisting of a 15-nm-thick quaternary AlGaInN top barrier layer, a thin 200-nm-thick unintentionally doped (UID) GaN channel layer, and an AlN back barrier was grown on a single-crystal AlN substrate by metal–organic chemical vapor deposition. The HEMTs fabricated on the grown heterostructure exhibited DC pinch-off characteristics with no large negative resistance owing to the high thermal conductivity of the AlN substrate. The 2-μm-gate-length devices showed the maximum current density of 500 mA/mm and the peak transconductance of 120 mS/mm with the threshold voltage of approximately −4 V. The off-state leakage was less than 30 μA/mm thanks to the thin UID-GaN channel with good crystal quality. The pulsed I–V characteristics for the fabricated HEMTs showed much smaller drain current decreasing compared to the same structured HEMTs with a C-doped GaN back barrier on a SiC substrate. This indicates that the UID-GaN channel grown on the AlN substrate had no harmful impurity levels that cause the current collapse phenomenon. The above-mentioned results demonstrate that the combination of the thin UID-GaN channel and the AlN back barrier works effectively in GaN HEMTs, and it will contribute to the device design and fabrication for future high-power/high-frequency applications.

In-silico investigation of mechanical behavior of hydrated Na-montmorillonite tactoid

Swelling clay minerals, exemplified by Na-montmorillonite (Na-Mt), are vital constituents in expansive soils and hold significant relevance in geotechnical engineering. Comprehending their distinctive swelling behavior upon hydration is imperative for managing potential damage to civil infrastructure. Conversely, this swelling property gives rise to numerous advantageous applications, including using these clays in barrier materials and nanocomposites. The hierarchical structure of montmorillonite, consisting of clay mineral layers, tactoids, aggregates, and assemblies of aggregates, plays a pivotal role in the swelling behavior of expansive clays. This investigation employs molecular dynamics (MD) and steered molecular dynamic (SMD) simulations to explore the nanomechanical properties of hydrated Na-Mt tactoids at various hydration levels. It provides insights into their responses to compression, tensile, and shear deformation. This study reveals increased hydration levels increase interlayer spacing in clay structures, resulting in higher average d‐values. Water molecules drive attractive electrostatic interactions with clay mineral layers, predominantly mediated by sodium ions, highlighting the complex interplay between interlayer hydration and tactoid stability. Higher hydration enhances tactoid compressibility, reducing the stress required for deformation by compressing water molecules and clay mineral layers in the interlayer space. The study also demonstrates a notable reduction in tensile modulus with increasing hydration, signifying the significant impact of even minimal hydration on interlayer cation-clay layer interactions. Hydrated tactoids exhibit altered mechanical responses in shear deformation compared to dry ones, requiring lower shear stress to detach the top clay layer from the tactoid. The presence of water molecules impedes the locking of clay mineral layers, further influencing mechanical properties. The results and insight provided by this work will contribute to a better understanding of the impact of interlayer hydration on the stability and response of swelling clay minerals.

High-responsivity, high-detectivity, broadband infrared photodetector based on MoS2/BP/MoS2 junction field-effect transistor

Sensitivity stands as a critical figure of merit in assessing the performance of a photodetector and can be characterized by two distinct parameters: responsivity or detectivity. Simultaneous optimization of these two parameters is essential to ensure the applicability of a single detector across various scenarios, yet it remains a persistent challenge for mid-infrared photodetector. Here, we demonstrate that the construction of a photoconductive detector based on a MoS2/BP/MoS2 npn junction field-effect transistor configuration can effectively balance the tradeoffs between photoresponsivity and detectivity. In this device, the black phosphorus layer serves as the channel, while the top and bottom MoS2 layers act as photogates to boost the photocurrent. Consequently, a high-performance room-temperature-operating mid-infrared photodetector with a responsivity and detectivity reaching 9.04 A W−1 and 5.36 × 109 cm Hz1/2 W−1 (1550 nm), and 7.25 A W−1 and 4.29 × 109 cm Hz1/2 W−1 (3600 nm) is achieved. Our study provides an alternative structural design, enabling the applications of mid-infrared photodetectors across multiple scenarios.

Theoretical prediction and regulation of interlayer stable angle in twisting bilayer graphene

Recent researches showed that interlayer rotation, as a control method, can effectively regulate the mechanical, electrical, and optical properties of two-dimensional (2D) materials. The control of the twisting angle and its stability influence the properties of rotation-tunable electronics, so it has attracted much attention. In this research, based on the Lennard-Jones (L-J) potential and energy density method, the energy landscape of twisted bilayer graphene (tBLG) is studied. The dependence of the locally stable twisting angle and the number of potential energy barriers on the size of the top layer graphene is analyzed. It is found that the size effect is related to the vertical distance between carbon atoms and the rotation axis. The large-sized top layer graphene has a larger energy barrier and higher stability under the same conditions, which is conducive to the structural stability of the rotation-tunable electronics. The vacancy defect and the shape of the top layer graphene have an effect on the energy landscape, based on which the regulation of stable twisting angle can be achieved. In addition, the effect of the position of the top layer graphene on the energy landscape is studied, and it is found that the energy landscape has a 2D periodicity with the change of the position, which is related to the lattice structure of graphene. There are two main modes of energy landscape with the variation of the position of top layer graphene, and the changing trend is similar under the same mode. Our research predicts the interlayer stable twisting angle theoretically and provides theoretical support for the design of rotation-tunable electronics.

Effect of Target Layering in Gravity‐Dominated Cratering in Nature, Experiments, and Numerical Simulations

AbstractImpacts into layered targets may generate “concentric craters” where a wider outer crater in the top layer surrounds a smaller, nested crater in the basement, which itself may be complex or simple. The influence of target on cratering depends on the ratio of target strength to lithostatic stress, which, in turn, is affected by gravity, target density, and crater diameter. When this ratio is large, the crater size is primarily determined by target strength, whereas gravitational forces dominate when the ratio is small. In two‐layer targets, strength may dominate in one or both layers, whereby the outer crater develops in the weaker top layer and the nested crater in the stronger substrate. However, large natural craters that should be gravity‐dominated in both cover strata and substrate may be concentric, the reasons for which are not yet fully understood. We performed qualitative impact experiments at 10–502 G and 1.8 km/s with the Boeing Corp. Hypervelocity centrifuge gun, and at 1 G and 0.4 km/s with the CAB CSIC‐INTA gas gun into layered sand targets of different compositions and grain densities but similar granulometry to analyze gravity‐dominated cratering. The results are compared with iSALE‐2D numerical simulations and natural craters on Earth and Mars. We show that target layering also affects the excavation process and concentric crater formation in gravity‐dominated impacts. The most important factors are the density and internal friction of each target layer, respectively. We propose that this is also valid for natural craters of sizes that should make their formation gravity‐dominated.

Evaluation and development of surface layer scheme representation of temperature inversions over boreal forests in Arctic wintertime conditions

Abstract. In this study, the Noah land surface model used in conjunction with the Mellor–Yamada–Janjić surface layer scheme (hereafter, Noah-MYJ) and the Noah multiphysics scheme (Noah-MP) from the Weather Research and Forecasting (WRF) 4.5.1 mesoscale model are evaluated with regard to their performance in reproducing positive temperature gradients over forested areas in the Arctic winter. First, simplified versions of the WRF schemes, recoded in Python, are compared with conceptual models of the surface layer in order to gain insight into the dependence of the temperature gradient on the wind speed at the top of the surface layer. It is shown that the WRF schemes place strong limits on the turbulent collapse, leading to lower surface temperature gradient at low wind speeds than in the conceptual models. We implemented modifications to the WRF schemes to correct this effect. The original and modified versions of Noah-MYJ and Noah-MP are then evaluated compared to long-term measurements at the Ameriflux Poker Flat Research Range, a forest site in interior Alaska. Noah-MP is found to perform better than Noah-MYJ because the former is a two-layer model which explicitly takes into account the effect of the forest canopy. Indeed, a non-negligible temperature gradient is maintained below the canopy at high wind speeds, leading to overall larger gradients than in the absence of vegetation. Furthermore, the modified versions are found to perform better than the original versions of each scheme because they better reproduce strong temperature gradients at low wind speeds.

Offcut Substrate-Induced Defect Trapping at Step Edges.

We report step edge-induced localized defects suppressing subsequent antiphase boundary formation in the bulk structure of a trilayer oxide heterostructure. The heterostructure encompasses a layer of La0.66Sr0.34MnO3 sandwiched between a superconducting La1.84Sr0.16CuO4 bottom layer and an insulating La2CuO4 top layer. The combination of a minor a-axis mismatch (0.11 Å) and a pronounced c-axis mismatch (2.73 Å) at the step edges leads to the emergence of localized defects exclusively forming at the step edge. Employing atomically resolved electron energy-loss spectroscopy maps, we discern the electronic state of those structures in the second La0.66Sr0.34MnO3 unit cell near the step edge. In particular, a reduction in the pre-edge region of the O-K edge indicates the formation of oxygen vacancies induced by the strained step edge. This study underscores our capability to control defects at the nanoscale.

Hierarchical pore structure with a confined resonant mode for improving the solar energy utilizing efficiency of ultra-thin perovskite solar cells

The perovskite solar cell (PSC) has the benefits of flexibility, inexpensiveness, and high efficiency, and has important prospective applications. However, serious optical losing and low solar energy-utilizing efficiency remain a challenge for the ultra-thin PSCs because of the interface reflection of traditional planar structure. In this study, a hierarchical pore structure with a confined resonant mode is introduced and optimized by electromagnetic theory to improve the solar energy absorbing and utilizing efficiency of ultra-thin PSCs. The large pores in the top layer that support a whispering gallery mode can focus and guide the incident light into the solar cell. The small pores in the bottom layer enable backward scattering of the unabsorbed light and can improve the effective absorption of active layer. The finite-difference time-domain method is employed to optimize the geometric parameters of hierarchical pore structure to improve the light absorption of PSCs. The proposed resonant hierarchical pore structure can greatly improve sunlight absorption of ultra-thin PSCs, and the effective light absorption and photocurrent of PSCs with a hierarchical pore structure is 20.7% higher than that of PSCs with traditional planar structure. This work can offer a beneficial guideline for improving solar energy utilizing efficiency of various thin-film solar cells.

Design and analysis of a complementary structure-based high selectivity tri-band frequency selective surface

This work presents a novel tri-band bandpass frequency selective surface (FSS) that achieves high-order filtering responses in different frequency bands by means of a complementary structure. The proposed FSS is composed of three metal periodic arrays, which are separated by multilayer dielectric substrates. The gridded-double convoluted loop (G-DCL) structure, which is the middle layer structure, is a hybrid resonator that generates different resonant frequencies. The top and bottom layer structures are designed as complementary structures to the middle layer. To accurately describe the frequency responses, an equivalent circuit model (ECM) has been constructed over the entire band from 0 to 16 GHz. The results of the simulation indicate that the developed FSS can generate three pass-bands operating at 3.79 GHz, 8.34 GHz, and 12.52 GHz, respectively, and − 3 dB fractional bandwidths are 52.8%, 13.7%, and 19.7%. The transmission responses at the edges of each passband show a quick roll-off from the passband to the stopband, and there is significant out-of-band suppression between adjacent passbands. Moreover, the FSS maintains excellent angular and polarization stability within a 50° range. For verification, the tri-band FSS has been fabricated and tested. The experimental results match the simulation results, validating the accuracy of the FSS design.

Utilizing Metal Oxide Thin Films for Device Engineering of Solution-Processed Organic Multi-Junction Solar Cells

Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed methods. The main focus is on the device processing parameters as well as practical details of preparation of buffer layers to give the research community a clear, step-by-step recipe to successfully replicate and build series and parallel connected multi-junction solution-based organic solar cells for their needs. Here, the recipes and deposition conditions of two metal oxide buffer layers are presented in detail, based on basic commercially available materials and tools, to achieve well-engineered tandem (multi-junction) solution-processed organic solar cells. The buffer layers have appropriate energy levels for electrical selectivity of anode and cathode electrodes, and they are highly stable and chemically compatible with processing of solution-based polymer solar cells. To demonstrate the engineering steps of multi-junction devices, the PCE10:PC70BM blend is used as the active layer for all subcells. Then, to improve the power conversion efficiency of the single-junction photovoltaic device, PCE10:PC70BM blend is used in combination with DPPx:PC70BM with different absorption spectra for bottom and top subcell active layers. An optimized series tandem device with 10.6% power conversion efficiency is demonstrated. Generally, the device structures reported here can also be used for other types of optoelectronic devices, such as light emitting diodes and photodetectors.

Electrodepositing polydopamine and iron (III) complexed polyacrylic acid for monovalent selective anion exchange membrane fabrication

Monovalent selective anion exchange membranes were efficiently prepared by two-steps electrodeposition. Firstly, a polydopamine (PDA) interlayer was formed onto the surface of a commercial anion exchange membrane (AEM), followed by the deposition of a top layer of Fe3+ complexed polyacrylic acid (Fe-PAA). The PDA interlayer formation was investigated by reversing the polarity of the electric field applied. In particular, modified membrane prepared with PDA layer facing the cathode (labeled as FC-PDA-M) exhibited lower negative charge surface density compared to the membrane prepared with DA solution close to the anode (labeled as FA-PDA-M). This effect resulted in an increased deposition of PAA, due to the diminished electrostatic repulsion, when a solution of Fe3+ complexed polyacrylic acid with a Fe/PAA ratio of 1/4 was electrodeposited on the PDA layer. After eluting the Fe3+ with EDTA, the two manufacture membranes, labeled as FC-PDA/(Fe)PAA-M and FA-PDA/(Fe)PAA-M, were characterized. The former exhibited a higher Cl−/SO42− permselectivity than the latter, although the latter demonstrated better performance compared to both the pristine AEM and a PAA-PDA-M obtained without applying any current during the deposition process. The effect the Fe3+ addition and varied the Fe/PAA ratio was also investigated. The membranes obtained using the Fe/PAA ratio of 1/4 exhibited best separation performance. Finally, the stability of this membrane was assessed by conducting ten consecutive electrodialysis (ED) experiments, revealing consistent Cl−/SO42− permselectivity values within the 5–6 range.

Effect of Evapotranspiration on Soil Moisture Dynamics in Top Surface Layer of a Loamy Land in Climate Change Condition

Abstract Evapotranspiration affects uncertain changes in volumetric soil moisture content (θ) of earth surface, which is considerably controlled by temporal variability of weather parameters like rainfall and ambient temperature. Accurate measurement of temporal variation and spatial distribution of θ in a particular land is very challenging. Numerical modelling with any suitable computer code might be useful in such cases. Thus, Hydrus 2D modelling of θ variation in the soil at Odisha University of Agriculture and Technology (OUAT) in Bhubaneswar is undertaken as main objective of present study to investigate soil moisture dynamics in top surface layer. For the study, the θ in OUAT land was measured daily by 5 TM water content sensor for the duration of two years spanning from January 2021 to December 2022. Meteorological data for these 2 years are collected from a nearby weather station at OUAT and used for calculating evapotranspiration (ET) based on five different well known ET models. Soil hydraulic parameters of OUAT land were also evaluated by laboratory investigation. The evapotranspiration so calculated along with precipitation and materials properties were then assigned as the inputs in Hydrus 2D simulations. The simulated results are found to be in good agreement with field observations. It is proven by Pearson’s coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE) which are found to be 0.83 and 0.84 respectively. The soil moisture simulation was the most accurate only when measured soil parameters along with atmospheric boundary involving Penman-Monteith (PM) ET model were considered as model inputs.

Design of polarization convert metasurface element with high angle stability

This paper proposed a high angle stability polarization convert metasurface element. The element has one dielectric substrate with the bending lines on the top layer and metallic ground on the bottom layer. A method of priority optimize polarization conversion ratio(PCR) under oblique incident angle based on impedance analysis is proposed to realize high angle stability. And the proposed element can convert linear polarization to orthogonality polarization at 60° incident angle with 17.8% relative bandwidth with more resonances compared with normal incident. Both the PCR and bandwidth of the proposed element increase from 0° to 45° incident angle which different with traditional polarization convert elements. A metasurface with the high angle stability element is fabricated and the measured results are in good agreement with simulated results.

Experimental and numerical investigation of the effect of process parameters on crack formation and residual stresses in the laser coating process of stellite 6 alloy on X19CrMoNbVN11-1 steel substrate

In the present research, thermal–mechanical simulation of laser cladding of Stellite 6 powder on X19CrMoNbVN11-1 steel substrate was carried out to study the influence of scanning speed and laser power on the remaining stresses/strains and thus the formation of cracks in the cladding layer. In order to demonstrate the accuracy of the simulation results in prediction of the crack formation, the laser cladding process was also implemented experimentally. The results have shown that the highest temperature of the molten pool (1753 °C) was obtained at a laser power of 250 W, a powder injection rate of 0.3 g/s and a scanning speed of 3 mm/s. With the increase in scanning speed, the geometric shape of the cladding layer has changed from a semicircle to an oval shape. Moreover, at low scanning speed, the maximum strain is produced in the substrate and at high scanning speed, the maximum strain is created at the top of the coating layer. The lowest value of residual stress and strain was obtained at a scanning speed of 3 mm/s, while at a scanning speed of 5 mm/s the highest value of residual stress and strain was obtained. Furthermore, when the wetting angle is greater than 44°, the stress concentration is transferred from the top of the cladding layer to the substrate and the possibility of crack formation decreases.

HALS-770 interlayer simultaneously block internal and external degradation paths of perovskite for stability and high efficiency perovskite solar cells

The stability of perovskite solar cells (PSCs) is a major problem limiting their application. Here, we proposed a feasible solution using bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (HALS-770) as top protection layer of perovskite. HALS-770 interlayer can not only improve the antioxidant ability of perovskite by removing superoxide (O2·-) with help of hindered amine groups, but also suppress the internal and external degradation path of perovskite due to the co-existence of hydrophilic and hydrophobic groups. Moreover, it can block volatilization of organic cation and the migration of Ag+ and I-, thus improve thermal stability of perovskite and alleviate destruction of Ag electrode. In addition, the heterocycles N atom and carbonyl group in HALS-770 interact with the under-coordinated Pb2+, reducing the interface defects. As a result, the unencapsulated device maintains excellent stability over 95 % of its initial efficiency after 30 days in ambient condition with about 25–50 % humidity, and possesses remarkable continuous operation stability with projected T80 > 1400 h at maximum power point tracking in glove box, much higher than those of the pristine device. Meanwhile, HALS-770 enable the PCE of 21.88 % for PSC (0.06 cm2), which is among the highest efficiencies for MAPbI3 based PSCs with p-i-n structure, and the PCE of 19.07 % for PSM (4 cm2). And it is also suitable for FAMA-based devices with n-i-p structure, enabling an efficiency of 23.03 % (0.06 cm2) and excellent stability.