Single-layer Ones Research Articles

An analytical solution for settlement of jacked piles considering pile installation effects

This paper develops an analytical solution for the settlement of jacked piles induced by reconsolidation of the surrounding soil. The Terzaghi’s radial consolidation theory is utilised to model the dissipation of the installation-induced excess pore water pressure. A two-layer subgrade model, more general than single-layer ones and capable of being easily extended to multilayer soil systems, is adopted to analyse the settlement of the soil surrounding jacked piles so as to predict the additional settlement of the piles. The pile-soil interaction is properly considered in deriving the differential equations to formulate the problem considered. Example analysis is performed to illustrate the application of the proposed solution. Results indicate that the additional settlement of jacked piles, induced by reconsolidation of the surrounding soil, should be considered in calculation of the settlement of the pile after installation. Parametric studies are conducted to investigate the impact of the Poisson’s ratio, overconsolidation ratio, shear modulus and initial void ratio on the settlement of the pile due to consolidation of the surrounding soil. The results show that the Poisson’s ratio and the overconsolidation ratio of the upper stratum have pronounced effects on the settlement of the pile top.

Stability of breakwater roundhead protected with a Cubipod single-layer armor

This paper presents an analysis of the stability of breakwater roundheads protected with a Cubipod single-layer armor. This model was then subjected to a battery of 22 physical model tests, and the most significant variables were observed to be wave steepness (spr), the radius divided by the nominal diameter (Rn), and the relationship between the radius and wavelength at the breakwater toe (R/Lrp). It has been demonstrated that there are two behavioral patterns for stability according to the parameter R/Lrp, with large roundheads defined as R/Lrp ≥ 0.15 and small roundheads as R/Lrp < 0.15. The stability reserve (SR [%]) was also calculated and it was demonstrated that this parameter decreased with an increase in steepness. A design criterion was also defined based on the stability reserve (SR [%]) of these kinds of structures. The stability coefficient (Kd) was calculated to account for initial damage, destruction, and the design stage, and it was verified that this parameter depends primarily on wave steepness, to which it is directly proportional. Finally, a comparison with double-layer armors was made confirming that under certain conditions, the single-layer ones have the same stability as the ones with double layer armors, but their behavior is more rigid.

Enhanced absorbing properties and structural design of microwave absorbers based on Ni0.8Co0.2Fe2O4 nanofibers and Ni-C hybrid nanofibers

We have proposed a novel double-layer microwave absorber based on spinel ferrite Ni0.8Co0.2Fe2O4 nanofibers (NCFO NFs) and Ni-C hybrid NFs prepared via a facile electrospinning method combined with subsequent heat treatment. Electromagnetic and microwave absorption properties of the double-layer microwave absorbers, together with those of the single-layer ones, were systematically investigated in the frequency range of 2–18 GHz. The double-layer absorbers consisting of 50 wt% NCFO NFs/paraffin composite and 5 wt% Ni-C NFs/paraffin composite show superior microwave absorbing performance with stronger absorption and broader bandwidth as compared with the corresponding single-layer ones and many reported double-layer ones. As 1.5 mm thick NCFO NFs composite is used as the matching layer and 0.8 mm thick Ni-C NFs composite is employed as the absorption layer, the optimal reflection loss (RL) of the absorber reaches −84.9 dB at 17.0 GHz with an effective absorption bandwidth below −10 dB of 7.4 GHz ranging from 10.6 to 18 GHz. The enhancement of microwave absorption in the double-layer absorbers should be mainly ascribed to the improvement of impendence matching characteristics due to the efficient coupling and synergistic effect between two layers. These excellent properties demonstrate that our double-layer structures offer a new route to design microwave absorbers with lightweight and high absorption performance over a broad frequency range.

Microwave absorption properties of double-layer absorbers based on spindle magnetite nanoparticles and flower-like copper sulfide microspheres

In this work, the spindle magnetite nanoparticles (SMNPs) and flower-like copper sulfide microspheres (FCSMSs) were synthesized via hydrothermal method. The structures, chemical composition and morphologies of samples were analyzed and characterized in detail. The microwave absorption properties of single-layer and double-layer absorbers were investigated based on the electromagnetic transmission line theory in the frequency range from 2 to 18 GHz. The results show that the double-layer absorbers consisting of FCSMSs as matching layer and SMNPs as absorbing layer display superior microwave absorbing performance compared to the single-layer ones due to the proper combination of magnetic loss of SMNPs and dielectric loss of FCSMSs, and the improved impedance matching characteristics. When the thicknesses of the absorbing layer and the matching layer are 1.6 and 0.4 mm, respectively, the minimum reflection loss reaches − 74.3 dB at 10.9 GHz, and the efficient absorption bandwidth is up to 5.34 GHz (8.46–13.8 GHz). The optimal SMNPs/FCSMSs double-layer absorbers can become a novel microwave absorption material with strong-absorption and broad-band.

Synthesis of core–shell single-layer MoS2 sheathing gold nanoparticles, AuNP@1L-MoS2

Nanoparticles, and more specifically gold nanoparticles (AuNPs), have attracted much scientific and technological interest in the last few decades. Their popularity is attributed to their unique optical, catalytic, electrical and magnetic properties when compared with the bulk. However, one of the main problems with AuNPs is their long-term stability. Two-dimensional materials like MoS2 (WS2) are semiconductors that exhibit a combination of properties which make them suitable for electronic, optical and (photo)catalytic devices. Few-layer MoS2 (WS2) nanoparticles (NPs), and in particular single-layer ones, show intriguing optical and electrical properties which are very different from those of the bulk compounds. Here we demonstrate the synthesis of AuNPs sheathed by a single layer of MoS2 (WS2), i.e. a core–shell nanostructure (AuNP@1L-MoS2). The hybrid NPs exhibit optical properties that are different from those of either constituent and are amenable for modulation via their chemistry, offering a myriad of applications.

Convective heat transfer in axisymmetric enclosures of different configurations under the conditions of their axial rotation and external heating

The phenomenon of the intensification of convective heat transfer through air cavities under the conditions of their axial rotation and external heating based on the rise of centrifugal body forces in differently heated air medium has been substantiated theoretically and confirmed experimentally. The criterion dependencies for convection coefficients of axisymmetric cylindrical and conical closed air cavities subjected to external heating and axial rotation have been obtained using the results of the physical and numerical experiments. Both single-layer cylindrical cavities and two-layer ones with perforating internal orifices have been considered.

Tribological characteristics of composite coatings formed by laser cladding of powders of nickel self-fluxing alloy and bronze

Microstructures, coefficients of friction, and relative wear of composite coatings based on the PG-12N-01 nickel self-fluxing alloy and PG-19M-01 bronze have been considered. It has been found that composite coatings have a complex structure. The bronze coating, which is deposited on the fillets of the nickel alloy, crystallizes in a form of dendrites with axes arranged under an angle of 45°. The nickel alloy has a globular-dendritic structure with the eutectic component crystallizing between its branches. Momentary coefficients of friction in conditions of the concentrated load are independent of the cladding rate, and their values are 0.08–0.12 depending on the load. In this case, the wear rate of coatings depends substantially on the laser cladding. Under conditions of the distributed contact, bilayer coatings have a considerable advantage, and the relative wear is reduced by several tens of times compared with single-layer ones.

Airstable near-infrared sensitive organic field-effect transistors utilizing erbium phthalocyanine as photosensitive layer

Near-infrared photosensitive organic field-effect transistors (PhOFETs) based on pentacene/erbium phthalocyanine (ErPc2) and copper phthalocyanine (CuPc)/ErPc2 heterojunction, as well as ErPc2 single-layer PhOFETs, were fabricated and characterized. The results showed that the heterojunction PhOFETs exhibit higher mobility, maximum photoresponsivity (Rmax) and maximum photo/dark current ratio (Pmax), comparing with the ErPc2 single-layer ones. Such a better performance of the heterojunction devices can be attributed to the higher mobility channel layer. And the pentacene/ErPc2 PhOFETs demonstrate an Rmax of 6498mA/W, Pmax of 2.6×103, hole mobility of 1.5×10−2cm2V−1s−1 and excellent air stability, its Rmax is 186 times larger than that of the ErPc2 single-layer PhOFETs. Therefore, ErPc2 can be used as an excellent NIR photoresponsive layer of heterojunction PhOFETs.

Limited grain growth in multilayered Bi/Te thin films and the influence on the thermal and electrical conductivity

Bi2Te3 alloys were fabricated through thermal annealing of multilayered Bi/Te thin films as well as by co-sputtering of Bi and Te. In both cases, sharp X-ray diffraction peaks of Bi2Te3 were evidenced, indicating good crystallinity. It was found that the heterogeneous interface suppressed the grain growth in the multilayered samples considerably, and thus the thermal conductivity was reduced as a result of enhanced phonon scattering at the grain boundaries, but the electrical conductivity changed a little with temperature. However, the ZT figure (0.39) of the multilayered thin films was a little lower than that (0.43) of the single-layer ones at room temperature, suggesting the combined effect of power factor (PF) and thermal conductivity.

Test Apparatus for On-line Butt-Welding Evaluation of Aluminum Layer in PEX-AL-PEX Multilayer Pipes

Considering the advantages of multilayer pipes over metal and single layer ones as well as their new and increasing application in construction industry, testing these pipes has come into consideration to guarantee the quality of the pipes, and, consequently, prolong their life and increase the quality of building. A most prominent factor in multilayer pipes is the longitudinal seam-weld. If the aluminum layer is applied without welding, it may not affect the pipe’s strength. The welding normally employed involves butt or overlap using laser, ultrasonic, or tungsten inert gas (TIG) techniques. A defect-free weld can play a significant role in the pipe’s strength. Thus, a defect-free weld on the aluminum layer is a major factor in guaranteeing pipe’s quality. In this article, an apparatus for on-line testing of aluminum layer seam weld in multilayer pipes is presented which functions via an inductive proximity sensor. Finally, the results of several tests and defects detected are described.

Colloidal preparation and electrocatalytic hydrogen production of MoS2 and WS2 nanosheets with controllable lateral sizes and layer numbers.

Although layered transition metal dichalcogenide (TMD) nanosheets have attracted great attention due to their unique properties, it still remains challenge to develop a facile strategy for the precise control of the lateral sizes and layer numbers of TMD nanosheets. In this study, we demonstrate a solution-phase synthetic protocol to prepare colloidal MS2 (M = Mo, W) nanosheets which possess extremely small lateral dimensions from 15 to 40 nm and well-controlled odd numbers of layers, such as 1, 3, and 5 layers, as characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The size- and layer-dependence of the optical properties of colloidal MS2 (M = Mo, W) nanosheets are revealed by Raman and absorption spectra for the first time. These colloidal nanosheets, especially the single-layer ones, possess a large number of edge sites that serve as active sites for the hydrogen evolution reaction (HER). The catalysts exhibit a small HER overpotential and low Tafel slope of approximately 100 mV and 52 mV per decade for MoS2, and 80 mV and 46 mV per decade for WS2, respectively. Importantly, these products show enhanced stability after 500 potential cycles, and the current density remains almost unchanged during the test.

High-performance dual-layer channel indium gallium zinc oxide thin-film transistors fabricated in different oxygen contents at low temperature

In this work, fully transparent dual-layer channel amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates at low temperature. Dual-layer channel a-IGZO TFTs are studied by changing the partial pressure of oxygen while sputtering IGZO layers for comparison with single-layer channel TFTs which are fabricated with a constant oxygen content. All four types of dual-layer channel TFT sample demonstrate better performance, on-to-off ratios of ∼108 and low subthreshold swing (SS) of less than 200 mV/decade, than the single-layer ones. TFTs with two layers, a low-oxygen layer and a high-oxygen layer formed using oxygen partial pressures of 0.01 and 0.05 Pa, respectively demonstrate relatively better performance with a mobility of more than 60 cm2 V−1 s−1. Among them, the TFTs with a channel layer thickness ratio of 3 : 1 show the best transfer characteristics with a high on-to-off current ratio (Ion/off) of 1.8 × 108 and a low SS of 135 mV/decade.

Shock analysis and optimization of two-layered cellular materials subject to pulse loading

We present the method of characteristics with mass, momentum, and energy conservation to solve the nonlinear wave equation with shock formation in a two layer one-dimensional rod made of cellular material. We show that the rigid-perfectly-plastic-locking model cannot predict shock formation at a material interface, so we propose an elastic–plastic-densifying model to describe the stress–strain behavior of the cellular materials. The conditions for shock formation at a material interface are provided. We conduct a two-layer analysis to gain insights into the behavior of two layer cellular systems and to determine which material properties are most important for design. Finally, we optimize the significant parameters to reduce the length of one and two layered cellular systems with impulse and mass constraints subject to pulse loading. The results reinforce the concept of sandwich structures and show that two layer systems can achieve a 30% reduction in length over single layer ones.

Theory of spin-orbit coupling in bilayer graphene

Theory of spin-orbit coupling in bilayer graphene is presented. The electronic band structure of the AB bilayer in the presence of spin-orbit coupling and a transverse electric field is calculated from first-principles using the linearized augmented plane wave method implemented in the WIEN2k code. The first-principles results around the K points are fitted to a tight-binding model. The main conclusion is that the spin-orbit effects in bilayer graphene derive essentially from the single-layer spin-orbit coupling which comes almost solely from the d orbitals. The intrinsic spin-orbit splitting (anticrossing) around the K points is about 24\mu eV for the low-energy valence and conduction bands, which are closest to the Fermi level, similarly as in the single layer graphene. An applied transverse electric field breaks space inversion symmetry and leads to an extrinsic (also called Bychkov-Rashba) spin-orbit splitting. This splitting is usually linearly proportional to the electric field. The peculiarity of graphene bilayer is that the low-energy bands remain split by 24\mu eV independently of the applied external field. The electric field, instead, opens a semiconducting band gap separating these low-energy bands. The remaining two high-energy bands are spin-split in proportion to the electric field; the proportionality coefficient is given by the second intrinsic spin-orbit coupling, whose value is 20\mu eV. All the band-structure effects and their spin splittings can be explained by our tight-binding model, in which the spin-orbit Hamiltonian is derived from symmetry considerations. The magnitudes of intra- and interlayer couplings---their values are similar to the single-layer graphene ones---are determined by fitting to first-principles results.

Structure and dynamic properties of asymmetric vortexlike domain walls in inhomogeneous magnetic films with an in-plane anisotropy: I. Equilibrium structures. Nonlinear dynamics in two-layered films

Within the framework of a two-dimensional distribution of magnetization and exact allowance for the basic interactions, including dipole-dipole one, the static properties and nonlinear dynamic behavior of vortexlike domain walls in multilayer magnetically uniaxial films with an in-plane anisotropy have been studied. It has been shown that in such films, just as in single-layer ones, there exist asymmetric vortexlike walls; however, in this case the wall vortices prove to be moved toward the layers with a higher magnetization or toward the layers with a lower anisotropy. At some thicknesses of the layers and magnetization differences in them, the asymmetric Neel walls prove to be unstable. New scenarios of the dynamic transformation of the structure of the walls in multilayer films have been established, which in some cases differ significantly from the appropriate scenarios in the single-layer films.

Voltage–current and voltage–flux characteristics of asymmetric high TC DC SQUIDs

We report measurements of transfer functions and flux shifts of 20 on-chip high T C DC SQUIDs half of which were made purposely geometrically asymmetric. All of these SQUIDs were fabricated using standard high T C thin-film technology and they were single layer ones, having 140 nm thickness of YBa 2Cu 3O 7− x film deposited by laser ablation onto MgO bicrystal substrates with 24° misorientation angle. For every SQUID the parameters of its intrinsic asymmetry, i.e., the density of critical current and resistivity of every junction, were measured directly and independently. We showed that the main reason for the on-chip spreading of SQUIDs’ voltage–current and voltage–flux characteristics was the intrinsic asymmetry. We found that for SQUIDs with a relative large inductance ( L > 120 pH) both the voltage modulation and the transfer function were not very sensitive to the junctions asymmetry, whereas SQUIDs with smaller inductance ( L ≃ 65–75 pH) were more sensitive. The results obtained in the paper are important for the implementation in the sensitive instruments based on high T C SQUID arrays and gratings.

Enhanced Phonon Scattering in Oxide Superlattices to Improve Laser Induced Thermoelectric Voltages

AbstractOptimizing the figure of merit for thermoelectric applications, ZT = S2σ2T/κ is currently at the core of materials oriented research in thermoelectricity. Here, one promising approach is to reduce ther thermal conductivity without sacrificing the electrical conductivity. Constructing superlattices of structurally compatible materials is one way to accomplish this goal. We report an enhanced laser induced thermoelectric voltage (LITV) effect observed in (YBa2Cu3O7/La1-xPbxMnO3)n multilayer thin films for the first time. Two groups of multilayer thin films grown on vicinal cut LaAlO3 substrates were prepared by pulsed laser deposition technique. The first group were grown on different substrates vicinal cut at different angles, and were used for checking the mechanism of the induced voltages. The second group samples were made at different period number n and for studying the number dependence of the peak values of LITV. The substrate angle dependence proved that this is a thermoelectric effect [1]. It was found that the LITV signals were enhanced significantly for these multilayer thin films comparing with the single layer ones. It is natural that the conductivity is going to be anisotropic due to the layered structure, and the same holds for the Seebeck coefficients. The enlarged Seebeck anisotropy will lead to higher induced voltages. Another possible reason is the reduced thermal conductivity in the layered structure. The maximum enhancement of LITV signals takes place at period number of 7, which seems in agreement with the prediction of minimum thermal conductivity in superlattices by Simkin and Mahan.

Selected problems in evaluating topography of coated abrasives

The paper presents some problems connected with the topography of coated abrasives. Various classes of coating are discussed, ranging from conventional single-layer ones to modern engineered coatings of the TRIZACT type. Actual parameters of the active face for various makes are given. Principal in-service properties of abrasive belts are discussed: instantaneous grinding efficiency and variation in surface roughness of the machined workpiece. A grinding process model is outlined which, after completion, will be capable of controlling precisely automated grinding operations using coated abrasives.

Measurement of the elastic moduli of dense layers of oriented carbon nanotubes by a scanning force microscope

A technique is developed for measuring the modulus of elasticity of a material with a Nanoscan scanning force microscope on the basis of measuring the dependence of probe vibration frequency on the penetration depth of the needle into the specimen. This technique makes it possible to study materials with elastic moduli from 50 to 1000 GPa. The Young moduli of dense films of carbon nanotubes oriented at angles of 45° and 90° to the quartz substrate are measured. From their ratio, the Young modulus in the direction perpendicular to the tubes and the anisotropy of the elastic moduli are determined. A comparison of these values with the corresponding values obtained for a nanotube film deposited on a silicon substrate is carried out. On the basis of this comparison, a conclusion is made concerning the interaction between single-layer nanotubes and between nanotubes in a mixture of single-layer and multilayer ones.

Fabrication of Matrimid/polyethersulfone dual-layer hollow fiber membranes for gas separation

We have developed almost defect-free Matrimid/polyethersulfone (PES) dual-layer hollow fibers with an ultra-thin outer layer of about 10 × 10 −6 m (10 μm), studied the effects of spinneret and coagulant temperatures and dope flow rates on membrane morphology and separation performance, and highlighted the process similarities and differences between single-layer and dual-layer hollow fiber fabrications. The compositions of the outer and inner layer dopes were 26.2/58.8/15.0 (in wt.%) Matrimid/NMP/methanol and 36/51.2/12.8 (in wt.%) PES/NMP/ethanol, respectively. It is found that 25 °C for both spinneret and coagulant is a better condition, and the fibers thus spun exhibit an O 2/N 2 selectivity of 6.26 which is within the 87% of the intrinsic value and a calculated apparent dense-layer thickness of about 2886 × 10 −10 m (2886 Å). These dual-layer membranes also have impressive CO 2/CH 4 selectivity of around 40 in mixed gas tests. The scanning electron microscopy (SEM) studies show that low coagulant temperatures produce dual-layer hollow fibers with an overall thicker thickness and tighter interfacial structure which may result in a higher substructure resistance and decrease the permeance and selectivity simultaneously. The elemental analysis of the interface skins confirms that a faster inter-layer diffusion occurs when the fibers are spun at higher spinneret temperatures. Experimental results also reveal that the separation performance of dual-layer hollow fiber membranes is extremely sensitive to the outer layer dope flow rate, and the inner layer dope flow rate also has some influence. SEM pictures indicate that the macrovoid formation in dual-layer asymmetric hollow fiber membranes is quite similar to that in single-layer ones. It appears that macrovoids observed in this study likely start from local stress imbalance and weak points.