Double Surface Research Articles

Optimization of Double Ring Frequency Selective Surface for Sub 5G/X-Band Communications Using Supervised ML and DL Algorithms

Optimization of Double Ring Frequency Selective Surface for Sub 5G/X-Band Communications Using Supervised ML and DL Algorithms

Microconvection of MHD solarized nanofluid in the presence of double slip and surface suction

Refrigeration systems are becoming more efficient as a result of nanofluids. Cooling and heating process improvements can lead to enhanced industrial efficiency, reduced processing times, energy conservation, and improved heating and cooling processes. A study is being conducted on the effects of magnetohydrodynamics (MHD) in nanofluids by adding double slip and thermal radiation to the governing model. It is numerically simulated using bvp4c code in MATLAB. Analyzing temperature, concentration, and velocity requires the evaluation of multiple parameters. A more uniform distribution of temperatures can be achieved by increasing the Biot number, thermal radiation, and thermophoretic motion parameters. The use of suction is an effective method of controlling the rate of temperature reduction in various manufacturing processes. A product's mechanical properties and overall quality can be enhanced if one is able to control how quickly it cools during the process of melting and condensing raw materials. As a consequence of the emergence of quadratic and linear slip factors, the flow velocity decreases. A distinguishing feature of this research is the use of boundary conditions that are tailored to the geometry that is being investigated.

A flexible humidity sensor constructed by ordered-pore-array of slightly reduced graphene oxide with much enhanced sensing response

Reduced graphene oxide (rGO) flexible film humidity sensor has received increasing attention, but the low sensing response caused by lack of available hydrophilic functional groups is still a limitation. Herein, a slightly reduced graphene oxide (SrGO) ordered-pore-array, fabricated via a monolayer colloid crystal template method, was introduced as a resistive humidity sensor. It was obtained based on adsorption between the GO sheets and the template microspheres, in-situ slight reduction of the GO shells and the removal of template. The reduction way allows the functional groups of GO to be retained as much as possible, and the unique structures (e.g., spherical double surfaces and small through-holes on pore-walls) facilitate the substantial exposure of functional groups, the penetration of water molecules and the utilization of buried functional groups. The available functional groups are thereby efficiently increased, giving the sensor an unprecedented high sensing response, more than 2600 times the maximum response of existing rGO sensors. The sensor also demonstrated excellent practical characteristics, and by detecting a single exhale, it could be employed in quick and quantitative evaluation of human activities and health. This strategy paves a facile and promising route to improve the sensing response and application of graphene-based humidity sensors or gas sensors.

Research on online interactive identification method for motion model of double propeller propulsion unmanned surface vehicle based on ESO disturbance estimation

In this paper, the online parameter identification problem of the mathematical model of USV considering the characteristics of the actuator is studied. A data-driven mathematical model of motion is very meaningful to realize trajectory prediction and adaptive motion control of USV. An interactive identification algorithm (ESO-MILS) based on Extended State Observer (ESO) is proposed. The robustness of online identification is improved by expanding the state observer to estimate the current disturbance without making artificial assumptions. Specifically, the three-degree-of-freedom dynamic equation of the double propeller propulsion USV is constructed. A linear model for online identification is derived by parameterization. Based on the least square criterion function, it is proved that the interactive identification method with disturbance estimation can improve the identification accuracy from the perspective of mathematical expectation. The extended state observer is designed to estimate the unknown disturbance in the model. The online interactive update improves the disturbance immunity of the identification algorithm. Finally, the effectiveness of the interactive identification algorithm is verified by simulation experiment and real ship experiment.

Physics-Based 3D End-to-End Modeling for Double-RIS Assisted Non-Stationary UAV-to-Ground Communication Channels

In this paper, we propose a three-dimensional (3D) physics-based double reconfigurable intelligent surface (RIS) cooperatively assisted multiple-input multiple-output (MIMO) stochastic channel model for unmanned aerial vehicle (UAV)-to-ground communication scenarios. The double-RIS is distributed on the surface of buildings can assist the UAV transmitter to reflect its own signals to the ground receiver (GR), and simultaneously enhance the propagation by passive beamforming on the RISs. In the proposed channel model, we derive the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">path power gains</i> for different propagation links between the UAV and GR, thus enabling the proposed channel model to effectively characterize both large- and small-scale fading characteristics of realistic UAV-to-ground communication systems. Furthermore, we derive the critical propagation properties of the proposed channel model, including the spatial cross-correlation functions (CCFs), temporal auto-correlation functions (ACFs), and frequency correlation functions (FCFs), with respect to different RIS reflection phase configurations as well as different RIS orientation angles. Numerical simulation results demonstrate the propagation characteristics of the proposed double-RIS assisted UAV-to-ground channel model behave better than those of traditional channel models with single-RIS link or LoS link, thereby validating the necessity of introducing double-RIS into UAV-to-ground communication.

Fabrication of Photostable Siloxane-Coated Quantum Dots for White-Light-Emitting Diodes

Quantum dots (QDs) are considered as excellent candidate materials for light-emitting diode (LED)-based lighting and display applications due to their excellent optical properties. However, the intrinsic unstable properties of QDs under external environments or the incompatibility between QDs and polymer composites hindered the QD-related applications. Herein, a universal modification method based on the optimization of QDs was developed for device applications. The highly dispersible and photostable QDs/siloxane composite was constructed by using the dual silica-encapsulated strategy of core/multishell CdSe/CdS/ZnCdS QDs to improve the performance of QDs. First, core/multishell QD’s size and components were optimized to enhance stability. Then, QDs@SiO2-OTMS was prepared by a combination of the reverse micro-emulsion method and surface modification. Such a double silica surface modification strategy is found to be very effective in improving the dispersion by matching the surface energy of QDs@SiO2-OTMS with that of siloxane resins. The as-prepared QDs@SiO2-OTMS/siloxane films had long-term (10 days) stability against heat and moisture and corrosive solution (HCl and NaOH). For the first time, the surface photovoltage (SPV) technique was used to study the in situ thermal stability of QDs@SiO2-OTMS, and it was found that surface defects were greatly suppressed at high temperatures. Taking these advantages, a white LED (WLED) with a color coordinate of (0.336, 0.325), color temperature of 5287 K, color gamut 123% National Television Systems Committee (NTSC,1931), and long-time stability at 20 mA had been fabricated by integrating green and red QDs@SiO2-OTMS/siloxane. These results make QDs@SiO2-OTMS/siloxane excellent candidates for QD lighting and display applications.

Minimum number of Weyl point phonons in mixed-metal periodate RbGeIO6

In topology physics, the prediction of Weyl systems with the minimum nonzero number of Weyl points (WPs) remains challenging. In this study, for the first time, we propose the P312 type RbGeIO6 as a material candidate with the minimum number of WPs in its phonon curves. Based on first-principles calculations and symmetry analysis, we confirm that the RbGeIO6 exhibits only two charge-two (C-2) WPs at the Γ and A time-reversal-invariant momenta points in the 3D Brillouin zone (BZ). Furthermore, the two C-2 WP phonons at the Γ and A result in the formation of the clean and long phononic double surface state on the (010) surface. The phononic double surface state spans the entire first surface BZ of the (010) surface, facilitating their detection in future experimental studies.

Unpaired Weyl phonon systems in NaHPO3NH2

Phonon-based Weyl points (WPs) are usually considered to appear in pairs with opposite chirality. Here, we report the phonon dispersion in a realistic material monosodium phosphoramidate, NaHPO3NH2, which has two types of unpaired WP phonon systems: (i) two hourglass charge-3 (C-3) WPs and six C-1 conventional WPs forming a topological Weyl complex; (ii) one C-2 WP, with a topologically charged Weyl nodal surface, forming a topologically charged Weyl point-surface system. Remarkably, the simultaneous presence of the C-1, C-2, and hourglass C-3 WPs in NaHPO3NH2 results in the formation of clean and long phononic double and sextuple-helicoid surface states on the (101¯0) and (001) surfaces, respectively. The phononic double and sextuple-helicoid surface states span the entire first surface Brillouin zones of the (101¯0) and (001) surfaces, which will facilitate their detection in future experimental studies.

Hall effect of ferro/antiferromagnetic wallpaper fermions

Nonsymmorphic crystals can host characteristic double surface Dirac cones with fourfold degeneracy on the Dirac points, called wallpaper fermion, protected by wallpaper group symmetry. We clarify the charge and spin Hall effect of wallpaper fermions in the presence of the (anti)ferromagnetism. Based on a four-sublattice model, we construct the effective Hamiltonian of wallpaper fermions coupled with the ferromagnetic or antiferromagnetic moment. Both ferromagnetic and antiferromagnetic moments induce an energy gap for the wallpaper fermions, leading to quantized (spin) Hall conductivity. The ferromagnetic wallpaper fermion induces the Hall conductivity quantized into ${e}^{2}/h$, which is twice that for a single Dirac fermion on the surface of topological insulators. On the other hand, the spin Hall conductivity decays and reaches to be a finite value as the antiferromagnetic coupling increases. We also show that the results above are valid for a general model of wallpaper fermions from symmetry consideration.

Ultrawide-Angle and Compact Leaky-Wave Antenna Based on Complex Periodic Structure

A compact antenna with the characteristic of wide-angle frequency beam scanning based on complex periodic structure is proposed. A double gradient spoof surface plasmon polaritons (SSPPs) structure is added to the standard microstrip line for reducing the antenna size. The miniaturization of the proposed antenna is analyzed with the method of dispersion curves and electric field distribution. Periodic changes of the groove depth and trapezoidal gradient structure increase the beam scanning angle from backward to forward and suppress the open stopband effect. The proposed structure is printed on the FR-4 substrate with a compact size of 0.23λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 3.71λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the lowest operating frequency), and has a working frequency band from 12.5 to 42.5 GHz for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> |< –10 dB. Meanwhile, a wide beam-scanning angle of 142° (–52° to +90°) and an average gain of 7.9 dBi are obtained by simulation and measurement. The proposed leaky-wave antenna has a potential application in wireless communication system due to its small size, broad frequency band, wide beam scanning angle and low cost.

Layer-by-layer enriching active Ni-N3C sites in nickel-nitrogen-carbon electrocatalysts for enhanced CO2-to-CO reduction

Transition metal and nitrogen co-doped carbons (M-N-C) have proven to be promising catalysts for CO2 electroreduction into CO because of the high activity and selectivity. Effective enrichment of the active transition metal coordinated nitrogen sites is desirable but is challenging for a practical volumetric productivity. Herein, we report four kinds of model electrocatalysts to unveil this issue, which include the NC structures with surface N-functionalities, Ni-N-C_I with one layer of surface Ni-N3C sites, NC@Ni-N-C_I with surface N-functionalities and underneath Ni-N3C sites as well as Ni-N-C_II with doubled surface Ni-N3C sites. The X-ray absorption spectroscopy indicates the coordination configuration of Ni-N3C. For NC catalysts, when N-doping level increased from 3.5 at% to 8.4 at%, the CO partial current density increased from below 0.1 mA/cm2 to 3 mA/cm2. Introducing one layer of Ni-N3C onto the NC structures leads to a 54 times higher CO partial current density than that of NC, in the meantime the FECO is 66 times higher. Furthermore, doubling the density of surface Ni-N3C sites by a layer-by-layer method doubles the CO partial current density (jCO), indicating its potential to achieve a high density of active coordinated sites and current densities.

Resource allocation of backscatter communication based on reconfigurable intelligent surface

AbstractIn this article, we propose a double reconfigurable intelligent surface (RIS)‐aided ambient backscatter communication (AmBC) network combined with non‐orthogonal multiple access (NOMA) technology, which not only successfully assists the base station (BS) in connecting with the cell edge user, but also enhances backscatter communication rate, energy efficiency, and spectrum efficiency. In an effort to obtain the highest backscatter communication rate, we design a RIS and BS‐based resource allocation problem which is solved by determining the optimal phase shifts of RISs and the optimal power allocation for signals of NOMA users. We break it down into two smaller challenges in order to discover the best solution. For one thing, we iterate the optimal phase shifts between the two RIS combinations using an alternating optimization technique. For another, the bisection method is used to provide the NOMA user with the ideal power allocation. Finally, the results of the simulation substantiate the viability of the proposed scheme.

Topological nodal lines in bulk and monolayer W2O3I4

By means of first-principles calculations, we study the topological nontrivial electronic structures and lattice dynamics of bulk and monolayer ${\mathrm{W}}_{2}{\mathrm{O}}_{3}{\mathrm{I}}_{4}$. We find that both of them are nodal-line semimetals in the absence of spin-orbit coupling (SOC), in which the nodal lines are induced by the band inversion between conduction and valence bands contributed by W $d$ and I p orbitals. Moreover, ${\mathrm{W}}_{2}{\mathrm{O}}_{3}{\mathrm{I}}_{4}$ bulk and monolayer exhibit excellent mechanical and thermal stability. By studying the external field modulation of topological nodal lines without SOC effect in monolayer ${\mathrm{W}}_{2}{\mathrm{O}}_{3}{\mathrm{I}}_{4}$, we find that the nodal lines are extremely robust against the biaxial strain but destroyed under vertical electric field due to the breaking of horizonal mirror symmetry. It is studied that the SOC effect here is large and non-negligible, and after considering the SOC effect, ${\mathrm{W}}_{2}{\mathrm{O}}_{3}{\mathrm{I}}_{4}$ bulk and monolayer undergo change of topological state from a topological nodal-line semimetal to a topological insulator. Our work not only extends the member of inorganic three-dimensional and two-dimensional topological semimetals library but also provides a prototype material candidate to investigate the double nodal-line surface states.

High Slope Efficiency Double and Triple Junction 808 nm Vertical Cavity Surface Emitting Lasers

High-performance 808 nm double and triple-junction vertical cavity surface emitting lasers (VCSELs) are designed and investigated. The light-current-voltage (L-I-V) characteristics of 808-nm single, double, and triple-junction VCSELs are compared. In the paper, the double-junction VCSELs with two oxide apertures exhibit a very high slope efficiency (SE) of 2.32 W/A at 25 °C, and the peak SE of 2.51 W/A is achieved at 10 °C. The power conversion efficiency (PCE) of 53.14% is achieved for double-junction individual VCSEL emitter. The peak SE of the triple-junction VCSELs reach 3.40 W/A with the PCE of 53.02% for individual VCSEL emitter. Under narrow pulse test conditions (400 Hz, 60 ns pulse width), the peak output powers of the designed double-junction and triple-junction VCSEL arrays reach 216.11 W and 325.77 W under the injection current of 80 A, respectively. Such high-performance multi-junction 808-nm VCSELs are very important for pumping solid state lasers and medical aesthetics.

Shear bond strength of orthodontic brackets bonded to a new version of zirconium all ceramic restoration: An in vitro comparative study

ObjectivesEsthetic restorations such as monolithic zirconia crowns are highly requested for adults nowadays. Bonding orthodontic braces on this type of material became a challenge for orthodontists, because of the special surface treatment needed. This study aims to assess the shear bond strength (SBS) of metal, and ceramic brackets bonded on two types of zirconia ceramics, surface roughness (SR) after different surface treatments for their surfaces, and adhesive remnant index (ARI). Materials and methodsBrackets’ base surface area (BSA) was scanned by an extra-oral scanner, then measured. The doubled labial surface of monolithic zirconia crowns (n = 30) and monolithic high translucent zirconia crowns (n = 30) were prepared and each was divided into three groups (n = 10) depending on surface treatment (hydrofluoric acid etching, no treatment, and rocatec airborne abrasion). Extracted lower central incisors (n = 20) were prepared. Each of them was divided into two subgroups depending on the type of bracket bonded on their surfaces (metal and ceramic). The SR, SBS, and ARI were assessed. Statistical analysis usedTests used are independent-samples t-test, Fisher's exact test, One-Way ANOVA, and Kruskal-Wallis test. ResultsThe highest SBS and SR were observed in Enamel/Metal and Zirconia/Metal/Rocatec subgroups, respectively. ConclusionAdequate bond strength could be obtained with the high translucent zirconia group if bonded with ceramic or metal brackets even if no treatment was used. Clinical significanceA proportion of simulation was done like practicing inside the dental clinic to reach the best results regarding the adhesion strength of orthodontic brackets.

Effect of double laser beam surface treatment on the surface morphological characteristics of Ti6Al4V at different heat source incidence angles

With the development of the high-end equipment manufacturing industry, the requirements for the surface performance of critical components are likewise increasing. To control the heat and mass transfer in the laser surface treatment process more efficiently and flexibly, the multiangle double laser surface treatment technology shows unique advantages. This study is focused on the experimental study of the laser surface treatment process for Ti6Al4V material. By changing the laser power and the incidence angle of the laser beam, the effects of single-laser beam surface treatment (SLST) and dual-laser beam surface treatment (DLST) on the surface morphology of the alloy were studied. The effects of laser treatment on the surface morphology, element distribution, roughness, surface chemical state, and surface structure of the alloy were emphatically analyzed. The mechanism of SLST and DLST at different incident angles of heat source and the effect of DLST on the formation of an oxide layer on the surface of the alloy were compared and analyzed. The results show that when the average power of the high-power nanosecond pulse width laser in DLST is 100 W and the incident angle is 135°, the surface oxygen content reaches the lowest, as low as 8.31%. The secondary effect of the laser makes the alloy surface remelt again, and then the best roughness after laser processing is obtained, with a roughness value of 2.801 μm. Finally, we obtain the optimal process for laser surface treatment and conclude that DLST can significantly optimize the surface state after a high-energy laser beam action.

Evolution mechanism of SO2 adsorption on palygorskite (1 0 0) surface modified by APTES: Effect of different grafting modification

The effects of 3-aminopropyltriethoxysilane (APTES) with different grafting modifications on the (100) surface of palygorskite (PAL) have been examined in the current work using the first principles method. Our finding results show that the chemisorption is probably occurring because the adsorption energies of the single, double, and three-tooth APTES-PAL (100) surface systems are −66.45, −199.55, and −153.63 kJ/mol, respectively, all below −18.86 kJ/mol (or −0.2 eV). Moreover, the different grafting structures of the APTES-PAL (100) surface have different adsorption characteristics, showing that H2O was produced in the double and three-tooth APTES-PAL (100) surface systems and H2 was produced in the single-tooth APTES-PAL (100) surface system. Additionally, the rate-determining step to adjust the effectiveness of the adsorbent is the H atom broken from the NH2 group of APTES combining with the O atom of SO2. These insights will be used to develop clay composite materials in the future for gas adsorption.

High-temperature oxidation and tribological behaviors of WTaVCr alloy coating prepared by double glow plasma surface alloying technology

Tungsten-based refractory high entropy alloys (RHEAs) are a potential candidate for plasma-facing materials (PFM) due to their excellent properties. However, the oxidation resistance of W-based RHEAs is poor. Moreover, there is still a lack of research on the evaluation of room temperature wear. In this work, several WTaVCr alloy coatings were fabricated by double glow plasma surface alloying (DGPSA) technology at different temperatures and different source ratios. The microstructure of WTaVCr coatings exhibited BCC solid solution phase. The coatings were compact and uniform. The scratch test indicates that the coating combines the substrate well. The surface hardness of the samples increases significantly after alloying, which is 5 times that of the substrate. Sliding wear tests were performed on the coating as well as the substrate. The fairly low specific wear rate of the coating (W31.7Ta13.3V42.9Cr12.2) proved its excellent wear-resisting property (The wear rate was 8 × 10−7 mm3/N∙m, which was two orders of magnitude lower than that of the substrate), and the dominant wear mechanism was abrasive wear and oxidative wear. The coating (W45Ta45.4V4.5Cr5.1) showed a favorable oxidation resistance, and a continuous Cr2O3 protective layer was formed on the surface. The oxidation resistance of the coating was approximately a quarter of the W-substrate.

Cooperative towing for double unmanned surface vehicles connected with a floating rope via vertical formation and adaptive moment control

The surface round-up and towing operations are essential for surface garbage removal, oil spill recovery and shipwrecked ship rescue. All of which are related to the national economy and the people’s livelihood, and it is urgent to improve operation efficiency. This work considers connecting double unmanned surface vehicles (DUSVs) with floating ropes to achieve efficiently autonomous round-up and towing. The core of this research is how to realize autonomous cooperative towing control of DUSV under the interference of floating rope hydrodynamic moment and wind, wave and current. Therefore, a vertical formation control algorithm was proposed to improve the control performance of the DUSV. The virtual leader–follower was treated as the guidance target, and the relative distance between the DUSV and the guidance target should be maintained properly. Next, to reduce the probability of drag separation of DUSV, on the basis of the sensors equipped on the floating rope, an adaptive moment control algorithm was designed via the control of the heading angle error and the adjustment of the moment correction. The results of the simulation and water experiments verified the excellent performance of our algorithms.

Investigation of physical phenomena during solidification in existence of nanomaterial

With a numerical method, the discharging process within a container with a double complex cold surface has been scrutinized in this paper. The inherent process makes conduction as the main mechanism and the temperature equation includes three terms and two of them are time-dependent which was discretized by means of implicit technique. Adding nanoparticles within water can enhance the rate of heat release and concentration of powders and their shapes can affect the properties of nanomaterial. Single phases for estimating the features of nanomaterial were applied. The maximum period of process takes 326.95[Formula: see text]s which is 1.36 times lower than the case of pure water. Increasing the shape factor can enhance the speed of process and its impact is less than concentration of additives.