Top Layer Research Articles

Circularly polarized beam-scanning leaky wave antenna based on a slow-wave substrate integrated waveguide

A circularly polarized (CP) beam-scanning leaky wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SW-SIW) is presented in this paper. The SW effect is realized by introducing a spoof surface plasmon polariton (SSPP), excited by periodic etched 45° tilted slots on the top metallic layer of an SIW. With extra delta modulation, the electromagnetic waves radiate through the etched slots and scan continuously from a backward to forward direction as the frequency changes. Taking advantage of the tilted slots and relative displacement between the upper and lower slots, the direction of the electric field of the radiated waves and phase difference between them are adjustable, making a CP characteristic available. Both the simulated and measured results show the proposed LWA exhibits good performance. The total scanning angle reaches 70°, and the average gain is 8.9 dBi from 9.5 GHz to 11.7 GHz. The CP characteristic is verified through the axial ratio of less than 3 during the operating frequency range. A simple structure, compact size, and good performance make the proposed design promising for a compact wireless communication system.

Development of performance analysis model with numerical and dynamic energy modeling for an integrated PVT-HP system

This study delivers a comprehensive numerical analysis of an integrated photovoltaic/thermal-heat pump (PVT-HP) system, underscored by an innovative three-dimensional thermal energy storage (TES) model. Addressing the limitations of conventional one-dimensional TES models, which struggled with accurately simulating horizontal flows and the fluid state at various facility inlets, this research marks a significant advancement. Our development of a 3D TES model optimizes finite elements to reduce computation time and enhance accuracy, vital for precise energy analysis in buildings and air conditioning systems. The integration of this model with a network model allows for detailed analysis of flow rate changes and their impacts on heat transfer, crucial for the integrated PVT-HP system. Key findings include a 30 % increase in the temperature difference between the top and bottom layers of the TES when the flow rate is reduced from 50 LPM to 20 LPM, and a 1 % decrease in the heat pump's coefficient of performance (COP) with a 10 LPM reduction in flow rate. The study emphasizes that managing the flow rate is key to optimizing temperature gradients and system efficiency. Strategic adjustments in flow rate significantly affect thermal storage and transfer capabilities, proving essential in system performance. This research offers vital insights into optimizing PVT-HP systems, focusing on the importance of flow rate control in improving temperature management and overall system performance.

Development of a Dezincification-Free Alloy System for the Manufacturing of Brass Instruments

Conventionally used brass alloy CuZn30 shows problems with corrosion resistance in the form of dezincification when used in brass instruments. Therefore, within the scope of this investigation, a new brass alloy CuZn30 is developed in the microalloy range with corrosion-free or corrosion-inhibiting properties. First, the influence of microalloying elements on the phase composition is investigated by simulation using Thermo-Calc. On the basis of this, suitable alloying elements and contents are selected and a modified CuZn30X alloy with 0.1% phosphorus, tin, and nickel in mass fractions, respectively, is produced. The modified alloy is then investigated with regard to its mechanical and microstructural composition and its corrosion properties. The corrosion properties were examined using stress corrosion cracking tests, dezincification tests, and the recording of polarization curves. The modified alloy exhibited good cold and hot rolling properties as well as good corrosion resistance. The dezincification test confirmed the improved corrosion resistance of the modified CuZn30X alloy, which is attributed to the formation of a protective top layer due to the alloying elements.

NAVIER SOLUTION FOR DEFLECTION AND STRESSES ANALYSIS OF FGM SANDWICH PLATE RESTING ON PASTERNAK ELASTIC FOUNDATION

In this article, the first-order shear deformation theory (FSDT) and Navier’s solution are used to establish analytical solutions for analyzing the deflection and stresses of FGM sandwich plate structures resting on a Pasternak elastic foundation. The top and bottom layers consist of functionally graded materials (P-FGM) that vary according to the exponential law along the thickness direction, while the core layer is composed of a porous material. The boundary condition of the plate is simply supported on all the edges, and the plate is subjected to a sinusoidal distributed load perpendicular to the mid-surface. The reliability of the model is validated through comparison with findings published in reputable journals. The effects of material parameters, geometric dimensions, foundation coefficients, and face-core-face thickness ratios on deflection and stress components of rectangular FGM sandwich plates are investigated in detail in parametric studies.

Voltage-insensitive stochastic magnetic tunnel junctions with double free layers

Stochastic magnetic tunnel junction (s-MTJ) is a promising component of probabilistic bit (p-bit), which plays a pivotal role in probabilistic computers. For a standard cell structure of the p-bit, s-MTJ is desired to be insensitive to voltage across the junction over several hundred millivolts. In conventional s-MTJs with a reference layer having a fixed magnetization direction, however, the stochastic output significantly varies with the voltage due to spin-transfer torque (STT) acting on the stochastic free layer. In this work, we study a s-MTJ with a “double-free-layer” design theoretically proposed earlier, in which the fixed reference layer of the conventional structure is replaced by another stochastic free layer, effectively mitigating the influence of STT on the stochastic output. We show that the key device property characterized by the ratio of relaxation times between the high- and low-resistance states is one to two orders of magnitude less sensitive to bias voltage variations compared to conventional s-MTJs when the top and bottom free layers are designed to possess the same effective thickness. This work opens a pathway for reliable, nanosecond-operation, high-output, and scalable spintronics-based p-bits.

Selective double-layer on black Ni-P enhances solar absorption and reduces corrosion

This work investigates a double-layer configuration for the black Ni-P layers used in solar adsorption technology, aiming to increase the absorption of a broader range of solar wavelengths. This multilayer configuration has a surface with increased roughness and absorption area. The valleys were porous materials, which were connected to an underlying metallic sub-layer that is susceptible to corrosion. In turn, this corrosion induced changes to the top layer. The Ni-P layer was deposited by the electroless technique using an acid nickel sulfate bath as a source of metal ions and a reducing agent of sodium hypophosphite. Etching initiated an oxidation process on the surface, forming a layer of amorphous black nickel oxide for absorption. The surface features of the black Ni-P double layer consist of an uneven surface that aids sunlight adsorption. Carbon steel (AISI 1018) with different surface finishes was used for depositing Ni-P and black Ni-P, aiming to establish correlations with solar adsorption. The sample with an increased surface roughness obtained a higher absorption percentage than a single layer. The corrosion rate was calculated as 7 mmpy for the black Ni-P layer by applying polarization curves. A 6 µm-thick Ni-P double layer was obtained, achieving 96% absorption within the 300–2,000 nm range.

Processes Controlling the Entrainment and Liquid Water Response to Aerosol Perturbations in Non-Precipitating Stratocumulus Clouds

Abstract It has been widely reported that an increase in aerosol concentration in non-precipitating clouds leads to a decrease in their liquid water path. Here we examine the physical mechanisms that drive this response in both subtropical and Arctic stratocumulus clouds using large eddy simulations and mechanism suppression tests. Three processes have been previously identified to contribute to the decrease, namely, the size-dependency of evaporation, sedimentation, and radiation and all act to modulate the rate of entrainment of warm, dry air at the boundary layer top. We find that the liquid water path decrease is correlated with the increased entrainment, as expected, but that the decrease is enhanced by a reduction in cloud radiative cooling. The reduced cloud radiative cooling can occur even though locally at cloud top the radiative cooling rates are stronger and helping to enhance entrainment. We find that slower droplet sedimentation contributes to the increased entrainment and decreased liquid water in both cases. Faster evaporation caused directly by smaller, more numerous droplets decreases the liquid water path but does not necessarily increase the entrainment rate. On the other hand, stronger radiative cloud top cooling caused directly by smaller droplets increases the entrainment as much as slower sedimentation does but does not decrease the liquid water path as much. In general, processes that either directly or indirectly increase radiative cooling at cloud top are more important in the Arctic case and processes that increase the evaporation rate are more important in the subtropical case.

Enhancing osteointegration and antibacterial properties of PEEK implants via AMP/HA dual-layer coatings

Polyetheretherketone (PEEK) is a widely used engineering plastic in orthopedic and dental implants, but its bioinertness leads to poor bone integration. To overcome this, a sulfonation treatment was applied to PEEK first to create a rough, microporous surface enhancing cellular adherence and integration. Subsequently, amorphous magnesium phosphate (AMP) nanosheets were produced through microwave-assisted synthesis, and hydroxyapatite (HA) was generated using a bionic solution hydrothermal method. A dual-layer coating system composed of an interlayer AMP and a top layer HA on the surface of PEEK was developed to enhance osteointegration. Surface analysis confirms the creation of increased surface area, improved hydrophilicity with introduced hydrophilic groups, and enhanced protein attraction. In vitro assessments on mouse embryonic osteoblasts (MC3T3-E1) demonstrate the non-toxicity of these coatings and their efficacy in promoting cell proliferation. Moreover, antimicrobial evaluations against E. coli and S. aureus highlight the potential of these composite coatings in preventing implant-related infections. The AMP/HA dual-layer coating on sulfonated PEEK emerges as a potent method for enhancing osteointegration and antibacterial properties, offering a promising approach to improve bone repair efficiency in clinical applications.

Ex-situ n-type doped carrier-injection layers in direct bandgap GeSn LEDs

The reconstruction of thick GeSn crystalline layers implanted with phosphorus is explored. Our study demonstrates (i) the potential for recrystallizing amorphized GeSn crystal under specific conditions and (ii) functional LEDs incorporating an ex-situ doped GeSn injection layer. Mid-infrared direct band-gap light-emitting diodes are compared with either ex-situ GeSn:P or in-situ Ge:P top contact layers.

Distributions of coarse aggregate and steel fiber in ultra-high performance concrete: Migration behavior and correlation with compressive strength

The vertical distribution of coarse aggregates and steel fibers in ultra-high performance concrete (UHPC) both at fresh and hardened states was investigated to unveil their migration behavior and the correlation with compressive strength. To fulfill this purpose, customized design of specimens and tailored test method were developed. Specimens with two sizes (3–5 mm and 5–10 mm) and varying content (0–50 %) of coarse aggregate and different volume fraction of steel fiber (0–2 %) were proportioned. It was found that higher amount of coarse aggregates was located in the lower part whereas more steel fibers and voids were observed in the upper region of the specimens. Increasing the content of coarse aggregates resulted in worsened uniformness of its distribution, while incorporating steel fibers up to 2 % by volume imposed negligible effects on the heterogeneity. Migration of different phases primarily occurred during the fresh state. Compressive strength of the specimens at the middle layers was up to 30 % higher than those at the top and bottom layers. The inferior compressive strength was primarily ascribed to the worsened distribution of CAs and higher voids in the top layer.

Formation of a protective oxides-nitrides compound layer with enhanced wear properties, corrosion resistance, and cytocompatibility on novel Ti-Zr-Nb-Ta-Mo multi-principal element alloy

The insufficient surface properties of multi-principal element alloys (MPEAs) hinder their potential biomedical applications. Here, a facile thermal oxidation plus nitridation treatment is conducted to fabricate a protective layer on a novel Ti-Zr-Nb-Ta-Mo MPEA. The total surface layer of NT5-ON consists of a top compound layer, including TiO2, TiN, TiON, ZrO2, and ZrN, and an underneath N-diffusion zone, leading to an exceptionally high wear performance. Also, electrochemical testing and in-vitro evaluations demonstrated enhanced corrosion resistance and cytocompatibility of NT5-ON. As a result, thermal oxidation plus nitridation treatment is an effective technique for designing high-performance hip implant materials.

Topological Fermi-arc surface state covered by floating electrons on a two-dimensional electride

Two-dimensional electrides can acquire topologically non-trivial phases due to intriguing interplay between the cationic atomic layers and anionic electron layers. However, experimental evidence of topological surface states has yet to be verified. Here, via angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM), we probe the magnetic Weyl states of the ferromagnetic electride [Gd2C]2+·2e−. In particular, the presence of Weyl cones and Fermi-arc states is demonstrated through photon energy-dependent ARPES measurements, agreeing with theoretical band structure calculations. Notably, the STM measurements reveal that the Fermi-arc states exist underneath a floating quantum electron liquid on the top Gd layer, forming double-stacked surface states in a heterostructure. Our work thus not only unveils the non-trivial topology of the [Gd2C]2+·2e− electride but also realizes a surface heterostructure that can host phenomena distinct from the bulk.

Determination of operation performance indicators of unit for mowing crops with the simultaneous incorporation of their stubble into the soil

When harvesting grain crops and forage grasses using a two-phase method, trailed and/or mounted windrowers are usually used. After their passage, stubble remains on the field, which intensively loses soil moisture under sunlight and wind. To reduce these losses, the stubble, along with the soil, is crushed using disc harrows. Due to the use of two sequentially operating units (harvesting and soil-cultivating), their total operating time increases. This does little to preserve soil moisture in the cultivated field. This article provides an example of a more effective solution to this problem. It consists of using one machine-tractor unit instead of two. The proposed combined unit mows an agricultural crop in one working pass and ensures stubble crushing and incorporation into the top layer of soil. The unit consists of a wheeled tractor with a front hitch linkage, a front windrower and a disc harrow mounted behind the tractor. It has been established that the laboriousness of compiling such a unit, considering the tractor's transformation to reverse, is insignificant and amounts to 1442 person-hours. The use of the new unit assists in reducing soil moisture losses. Over a month, it can reach 4.1–5.2% in absolute terms and 15–45% in relative ones. The combined unit movement velocity should be close to 2.5 m s−1 to ensure such a reduction in soil moisture losses. Combining two technological operations performed by one machine-tractor unit does not impair its reliability. At the same time, there is a reduction in processing time for one field by almost half and a decrease in fuel consumption per unit of performed area by 2.25 times.

Reversible Intercalation of Organic Solvents in Graphite and Its Hindrance by a Strongly Adsorbing Supramolecular Monolayer

AbstractAt elevated temperatures, the prototypical organic solvents used to study the self‐assembly of supramolecular monolayers at liquid–solid interfaces alter a graphite substrate by intercalation. As a consequence, less strongly bound supramolecular monolayers become thermodynamically unstable, as probed by scanning tunneling microscopy. Complementary characterization by atomic force microscopy, confocal Raman spectroscopy and low energy electron microscopy consistently points to subsurface changes in the top few layers of the graphite substrate due to solvent intercalation. High‐temperature annealing at 900 °C in the vacuum restores the adsorption properties of the graphite substrates, indicating a high activation energy for deintercalation. However, strongly adsorbing hydrogen‐bonded monolayers of trimesic acid inhibit solvent intercalation and thus protect the graphite substrate. Mildly solvent‐intercalated graphite may prove useful as an easily prepared graphitic material with further weakened adsorption properties.

The combined effect of active packaging and relative phase sweeping on microwave heating performance in a dual-port solid-state system

The combined effect of active shielding packaging and relative phase sweeping on heating performance in a dual-port solid-state microwave heating process was evaluated. Four types of heating strategies that combine two factors (passive and active packaging and fixed and sweeping relative phase) were used in heating a tray of 300 g gellan gel sample for 3 min. The temperature distributions at the top and middle layers of the heated samples were collected and analyzed for heating uniformity index (HUI) and power absorption efficiency (PAE). The results showed that both active shielding package and relative phase sweeping can individually improve the HUI while maintaining high PAE. The packaging factor and relative phase factor showed a significant interaction effect (p = 0.0021) in influencing HUI but not PAE, highlighting the necessity of considering both factors (packaging and relative phase) when optimizing the microwave heating uniformity. The combination of active packaging and sweeping relative phase is a robust heating strategy that delivers the best heating performance that is significantly better than or similar to other combinations of packaging and relative phase strategies.

Multifunctional Porous Bilayer Artificial Skin for Enhanced Wound Healing.

Meeting the exacting demands of wound healing encompasses rapid coagulation, superior exudate absorption, high antibacterial efficacy, and imperative support for cell growth. In this study, by emulating the intricate structure of natural skin, we prepare a multifunctional porous bilayer artificial skin to address these critical requirements. The bottom layer, mimicking the dermis, is crafted through freeze-drying a gel network comprising carboxymethyl chitosan (CMCs) and gelatin (GL), while the top layer, emulating the epidermis, is prepared via electrospinning poly(l-lactic acid) (PLLA) nanofibers. With protocatechuic aldehyde and gallium ion complexation (PA@Ga) as cross-linking agents, the bottom PA@Ga-CMCs/GL layer featured an adjustable pore size (78-138 μm), high hemostatic performance (67s), and excellent bacterial inhibition rate (99.9%), complemented by an impressive liquid-absorbing capacity (2000% swelling rate). The top PLLA layer, with dense micronanostructure and hydrophobic properties, worked as a shield to effectively thwarted liquid or bacterial penetration. Furthermore, accelerated wound closure, reduced inflammatory responses, and enhanced formation of hair follicles and blood vessels are achieved by the porous artificial skin covered on the surface of wound. Bilayer artificial skin integrates the advantages of nanofibers and freeze-drying porous materials to effectively replicate the protective properties of the epidermal layer of the skin, as well as the cell migration and tissue regeneration of the dermis. This bioabsorbable artificial skin demonstrates structural and functional comparability to real skin, which would advance the field of wound care through its multifaceted capabilities.

A transient site balance model for atomic layer etching

We present a transient site balance model of plasma-assisted atomic layer etching of silicon (Si) with alternating exposure to chlorine gas (Cl2) and argon ions (Ar+). Molecular dynamics (MD) simulation results are used to provide parameters for the model. The model couples the dynamics of a top monolayer surface region (‘top layer’) and a perfectly mixed subsurface region (‘mixed layer’). The differential equations describing the rates of change of the Cl coverage in the two layers are transient mass balances. Model predictions include Cl coverages and rates of etching of various species from the surface as a function of Cl2 or Ar+ fluence. The simplified phenomenological model reproduces the MD simulation results well over a range of conditions. Comparing model predictions directly to experimental optical emission spectroscopy data, as reported in a previous paper (Vella et al 2023 J. Vac. Sci. Technol. A 41, 062602), provides further evidence of the accuracy of the model.

Hyperbranched aromatic poly(amidoamine) mediated interfacial polymerization for high-performance thin film composite membranes

The escalating global demand for clean water has driven a growing interest in developing thin-film composite (TFC) membranes with high permeability and selectivity for wastewater treatment and desalination processes. Engineering polymer materials with precisely tunable properties for selective molecular separation remains a challenging step toward achieving this goal. Herein, we have fabricated a highly permselective asymmetric polyamide nanofilm with a dual-layer structure in which the bottom layer is a porous hyperbranched aromatic polyamide (HBPA) interlayer, and the top layer is a dense polyamide layer with a nanostrip structure. The HBPA porous layer was covalently assembled in situ via oxidative coupling reaction with ammonium persulfate on a polysulfone (PSF) substrate. The hydrophilic porous HBPA interlayer forms nanosized cavities that may enhance the storage and confine amine monomer diffusion, leading to the construction of a striped pattern PA nanofilm. The resulting asymmetric PA membrane exhibits excellent water permeability of 18.39 ± 1 L m−2 h−1 bar−1 (3.98 times that of control membranes) and improved divalent salt (Na2SO4) rejection (≥98 %), surpassing most of the commercial and reported nanofiltration membranes. The HBPA-regulated interfacial polymerization provides a groundbreaking framework for developing high-performance membranes for precisely controlled nanofiltration.

Layered heterogeneous polyamide-hydrazide based reverse osmosis membranes with enhanced separation performance

It is the goal of membrane science to continuously overcome the trade-off between permeability and selectivity of reverse osmosis (RO) membranes. In this study we propose a strategy based on the pore characteristics of cyclobutane-1,2,3,4-tetracarboxylic acid chloride (BTC) and trimesoyl chloride (TMC) crosslinked with cyclobutane-1,2,3,4-tetracarbohydrazide (CBTH) for constructing layered heterostructures of polyamide-hydrazide membranes. By using BTC and TMC successively, the porous BTC-CBTH polyamide was employed as the bottom layer, and the dense TMC-CBTH polyamide as the top layer, creating an RO membrane with a “sparse and dense” heterogeneous structure. This layered heterostructure ingeniously differentiates the structure and function of the selective layer of the RO membrane, enabling the loose bottom layer and the dense top layer to respectively perform the tasks of support and separation. The permeability coefficient of the prepared RO membrane reached 3.82 L⋅m−2⋅h−1⋅bar−1, which was enhanced by 29% compared with that of the polyamide-hydrazide membrane prepared by single-step interfacial polymerization, while the rejection of NaCl was maintained at 99.13 %. The heterogeneous layered construction strategy effectively improves the permeability and selectivity of the RO membrane, and provides a universal solution for consistently overcoming the “trade-off” effect in RO membranes.

Riverbed depth-specific microplastics distribution and potential use as process marker

Riverbed sediments have been identified as temporary and long-term accumulation sites for microplastic particles (MPs), but the relocation and retention mechanisms in riverbeds still need to be better understood. In this study, we investigated the depth-specific occurrence and distribution (abundance, type, and size) of MPs in river sediments down to a depth of 100 cm, which had not been previously investigated in riverbeds. In four sediment freeze cores taken for the Main River (Germany), MPs (≥ 100 µm) were detected using two complementary analytical approaches (spectroscopy and thermoanalytical) over the entire depth with an average of 21.7 ± 21.4 MP/kg or 31.5 ± 28.0 mg/kg. Three vertical trends for MP abundance could be derived, fairly constant in top layers (0–‍30 cm), a decrease in middle layers (30–60 cm), and a strong increase in deep layers (60–100 cm). The dominant polymer types were polyethylene (PE), polypropylene (PP), and polystyrene (PS). Polyethylene terephthalate (PET) and PP were also found in deep layers, albeit with the youngest age of earliest possible occurrence (EPO age of 1973 and 1954). The fraction of smaller-sized MPs (100–500 µm) increased with depth in shallow layers, but the largest MPs (> 1 mm) were detected in deep layers. Based on these findings, we elucidate the relationship between the depth-specific MP distribution and the prevailing processes of MP retention and sediment dynamics in the riverbed. We propose some implications and offer an initial conceptual approach, suggesting the use of microplastics as a potential environmental process tracer for driving riverbed sediment dynamics.