Two-sided Surface Research Articles

Shell stand: Stable thin shell models for 3D fabrication

A thin shell model refers to a surface or structure, where the object’s thickness is considered negligible. In the context of 3D printing, thin shell models are characterized by having lightweight, hollow structures, and reduced material usage. Their versatility and visual appeal make them popular in various fields, such as cloth simulation, character skinning, and for thin-walled structures like leaves, paper, or metal sheets. Nevertheless, optimization of thin shell models without external support remains a challenge due to their minimal interior operational space. For the same reasons, hollowing methods are also unsuitable for this task. In fact, thin shell modulation methods are required to preserve the visual appearance of a two-sided surface which further constrain the problem space. In this paper, we introduce a new visual disparity metric tailored for shell models, integrating local details and global shape attributes in terms of visual perception. Our method modulates thin shell models using global deformations and local thickening while accounting for visual saliency, stability, and structural integrity. Thereby, thin shell models such as bas-reliefs, hollow shapes, and cloth can be stabilized to stand in arbitrary orientations, making them ideal for 3D printing.

Transverse Spin Hall Effect and Twisted Polarization Ribbons at the Sharp Focus

Transverse Spin Hall Effect and Twisted Polarization Ribbons at the Sharp Focus

Index of Minimal Hypersurfaces in Real Projective Spaces

Abstract We prove that for an embedded unstable one-sided minimal hypersurface of the $(n+1)$-dimensional real projective space, the Morse index is at least $n+2$, and this bound is attained by the cubic isoparametric minimal hypersurfaces. We also show that there exist closed embedded two-sided minimal surfaces in the 3-dimensional real projective space of each odd index by computing the index of the Lawson surfaces.

Visual Laboratory Tests: Effect of Operational Parameters on Proppant Transport in a 3D Printed Vertical Hydraulic Fracture with Two-Sided Rough Surfaces

Summary Hydraulic fracturing technology is an effective measure that can improve oil and gas production and achieve enormous economic benefits owing to it phenomenally increasing the oil recovery from the low intrinsic permeability of the compact rock. Good placement and distribution of the proppant in the hydraulic fractures can provide successful stimulation for a well, which is essential for applying the hydraulic fracturing process. Previous studies extensively explored proppant placement, distribution, and operational factors in simplified smooth surface fracture models. However, the operational factors such as pump rate, proppant concentration, proppant size, fluid viscosity, and inlet condition (pulse time) involved in proppant placement and distribution in realistic rough surfaces of fractures are not clearly understood. In particular, the law of proppant transport in a two-sided rough surface of fracture with changes in the aforementioned operational factors was unclear. Hence, in this study, we investigated the effect of these operational factors on proppant placement and transport in both the smooth surface fracture model and the two-sided rough surface fracture model. The results suggested that the traditional law of proppant transport drawn on the smooth surface fracture model did not apply to the two-sided rough surface model. It is suggested that selecting corresponding variables was needed to reduce the risk of proppant bridging and offer a better channel ratio.

Experimental study of fluid-particle flow characteristics in a rough fracture

Rough fractures can significantly affect particle-fluid flow in a stratum, but particle transport characteristics are still not fully understood. This paper proposes a novel method to combine three-dimensional laser scanning and casting technology for making rough transparent panels based on rock fractures. A large model with two-sided rough surfaces is constructed, and the inner sizes are 2 m × 0.3 m × 3 mm. The particle image velocimetry method is used to analyze slurry flow. The experimental results show that distorted irregular streamlines, vortexes, sand settling, and dispersion are primary characteristics of particles transported by low-viscosity fluid. Shear flow can induce prominent vortexes around the inlet and the fracture top. With the increase in fluid viscosity, sand-fluid flow along preferential flow paths, and particle clusters are easily formed due to sand aggregation in tortuous pathways. Increasing the fluid velocity avoids particles plugging around the inlet, and there is a threshold velocity. The vortex number has a negative relationship with fluid viscosity. With the dune accumulation, the vorticity intensity is significantly increased, and discrete vortexes are connected into a large vorticity region, which collapses sand aggregation along the whole fracture. Increasing fluid velocity and viscosity and reducing particle diameter are more effective ways to improve particle distribution than increasing particle concentration. The combination of multiple factors can enhance the more even distribution of particles in rough fractures. The investigation provides a fundamental understanding of slurry flow behaviors in fractured media and is a valuable reference for the simulation of particle-fluid flow.

A flexible and hydrophilic hydrogel film based all-in-one supercapacitor

In recent years, the integrated supercapacitors have made remarkable progress, but it is still considered a huge challenge to obtain an ultra-flexible and stable all-in-one supercapacitor under diverse deformations. Herein, a novel all-in-one supercapacitor is constructed through preparing soft enough and hydrophilic polyacrylamide (PAM/LiCl) hydrogel film, subsequently, polymerizing and depositing of hydrophobic polypyrrole (PPy) nanocomposites onto the two-sided surfaces of the PAM/LiCl hydrogel. It is found that the all-in-one supercapacitor exhibits excellent flexible stretching up to 650 % of original length, high specific capacitance (229.8 mF cm−2 at 0.8 mA cm−2), and high ionic conductivity (29 mS cm−1). Interestingly, the all-in-one supercapacitor can remain 30 days without obvious deterioration in capacitance. Moreover, the all-in-one supercapacitor presents also eminent cycling performance. The capacitance can remain 80 % of initial capacitance after 5000 cycles. This all-in-one flexible supercapacitor provides great potential prospects in wearable energy devices involving mechanical impacts.

Essential surfaces in Seifert fiber spaces with singular surfaces

Two-sided incompressible surfaces in Seifert fiber spaces with isolated singular fibers are well-understood. Frohman [3] and Rannard [6] have shown that one-sided incompressible surfaces in Seifert fiber spaces which have isolated singular fibers are either pseudo-horizontal or psuedo-vertical. We extend their result to characterise essential surfaces in Seifert fiber spaces which may have singular surfaces, i.e., in S1-foliated 3-manifolds which have fibered model neighbourhoods that are isomorphic to either a fibered solid torus or a fibered solid Klein bottle.

Optimized Crystal Surface Treatment for Crosshair Light-Sharing TOF-DOI PET Detector

The coincidence resolving time (CRT) and DOI resolution of PET detectors are affected by the crystal surface treatment and the reflective material, and it is difficult to achieve a balance between their effects. We have developed the crosshair light-sharing (CLS) detector as a high-resolution TOF-DOI detector. The CLS detector uses a three-layered reflective material in a 2D crystal array to form a loop structure within a pair of crystals, allowing DOI information to be acquired even in the 2D crystal array. In this study, we investigated the relationship between the crystal surface treatment and the performance of the detector. Three types of LYSO:Ca were used: all crystal surfaces were mechanically polishing (MP), crystals with the one-sided saw-cut surface (1S), and crystals with the two-sided saw-cut surfaces (2S). The MP crystals showed the best CRT of 286 ps, but the worst DOI resolution of 7-8 mm. For the 1S crystals, the CRT was slightly degraded to 296 ps, but the DOI resolution of about 5 mm was obtained. For the 2S crystals, the CRT was significantly degraded to 332 ps and the DOI resolution was equivalent to that of the 1S. The crystal array with the 1S showed the best balance.

Spray Coated Cellulose Nanofiber (CNF) Film as an Eco-Friendly Substrate for Flexible and Printed Electronics

Cellulose nanofiber is an eco-friendly nanomaterial used for fabricating various functional materials. It is an alternative for synthetic plastic and other petroleum derived materials. Due to demand of CNF film, fast and rapid method for fabrication of CNF film is required. A new method on spray coating to prepare smooth cellulose nanofiber (CNF) films was developed. In this method, spraying CNF suspension onto a smooth and polished metal surface was carried out and then allowed the spray coated wet film to dry in air under standard laboratory conditions. Spraying has notable advantages such as contour coating and contactless coating with the base substrate. The basis weight and thickness of the CNF film is tailorable by adjusting CNF suspension in spraying process. CNF film prepared via spray coating has unique two-sided surface roughness with the surface in contact with the base substrate or metal side much smoother than the air-contact side. The surface roughness is one of the controlling parameter in the application of the CNF film as a substrate for flexible and printed electronics. The RMS roughness of the two surfaces investigated by Optical Profilometry [OP] was found to be 2087 nm on the rough side and 389 nm on the spray coated side, respectively. The spray coated CNF film has ultra-high smoothness on the side exposed to the polished stainless steel surface. The factors including the size of cellulose fibrils and surface smoothness of base surface that control the roughness of the film are currently being investigated and will be discussed in this chapter. The surface smoothness requirements for substrate applications in flexible and printed electronics will be discussed.

A Dual stopband two-sided frequency selective surface for mobile shielding applications

A two-sided frequency selective surface (FSS) is proposed to shield two bands of the mobile frequencies (EGSM-900 and DCS-1800). The FSS consists of an array of square concentric-rings cells printed on both sides of the substrate to offer better shielding of the two mobile frequencies. The CST Microwave suit is used for the simulations. The equivalent circuit model for the two-sided FSS is analysed and the transmission frequency in terms of the two stop frequencies is estimated. The obtained shielding is better than 40 dB across the two bands. The proposed FSS can be used to reduce mobile radiation or to isolate halls from nearby mobile base stations. The bandwidth of the FSS cell can be increased by using ring pairs of unequal sizes on the two sides of the substrate.

On attached masses of panels oscillating in incompressible medium

The paper discusses small oscillations of a panel in an incompressible medium. Air can be considered an incompressible medium during modal tests of solar array panels for spacecraft deployed on the ground in a lab environment. A panel is represented as a two-sided boundary surface. Conditions are determined for applicability of the potential motion of the medium. Calculation of the attached mass is reduced to the solution of the Neumann boundary value problem. To solve the boundary value problem, the method of boundary elements is used in the piecewise constant approximation variant, which provides a solution of the hypersingular boundary integral equation. Numerical solutions are obtained for the three fundamental modes of rectangular panels. The obtained numerical values are refined using non-linear Shanks transformation. Dependence of attached mass on panel elongation and the amount of the gap between its fragments is studied. For any in-plane oscillation mode of a panel fragment, the attached mass is determined using the principle of linear superposition. An estimate is given of the effect of the distance from the panel to the wall on the attached mass value. Key words: oscillations, incompressible medium, air, attached mass, rectangular panels, boundary elements method.

ON ATTACHED MASSES OF PANELS OSCILLATING IN INCOMPRESSIBLE MEDIUM

The paper discusses small oscillations of a panel in an incompressible medium. Air can be considered an incompressible medium during modal tests of solar array panels for spacecraft deployed on the ground in a lab environment. A panel is represented as a two-sided boundary surface. Conditions are determined for applicability of the potential motion of the medium. Calculation of the attached mass is reduced to the solution of the Neumann boundary value problem. To solve the boundary value problem, the method of boundary elements is used in the piecewise constant approximation variant, which provides a solution of the hypersingular boundary integral equation. Numerical solutions are obtained for the three fundamental modes of rectangular panels. The obtained numerical values are refined using non-linear Shanks transformation. Dependence of attached mass on panel elongation and the amount of the gap between its fragments is studied. For any in-plane oscillation mode of a panel fragment, the attached mass is determined using the principle of linear superposition. An estimate is given of the effect of the distance from the panel to the wall on the attached mass value. Key words: oscillations, incompressible medium, air, attached mass, rectangular panels, boundary elements method.

Numerical and experimental study on the deformation of aluminum alloy ring treated by ultrasonic shot peen forming

Ultrasonic shot peen forming (USPF) is a promising and widely used forming technique for thin metallic parts. In this paper, detailed deformation behavior of the aluminum alloy ring caused by USPF was studied, which is of a great significance to industrial applications for roundness correction and reshaping of the ring parts, such as wheel hub, petrochemical containers, pressure vessels, and spacecraft shells. Firstly, the motion of the single pin during USPF was recorded by a high-speed camera. Then, by combining the recorded results and the stress wave theory, the firing pin motion was approximately described as an effective impact of 100 times per second and the average impact velocity of 5 m/s. By considering the firing pin movement, the 3D USPF FE model of a cell AA6061-T6 sheet was developed successfully for obtaining the accurate plastic strain field. Subsequently, a 2D USPF FE model of the ring part was developed, which is able to obtain similar residual stress profiles with the 3D cell’s FE model by inputting the plastic strain profiles induced by the firing pin impact. Based on the results of experimental and numerical simulation, it was observed that the convex deformation of the ring part increases as the wall thickness decreases and the central angle of the treatment area increases. In addition, a wave contour and a local deformation with a little influence on the other area of the ring part can be achieved by three USPF treatment areas distributed in one-sided surface and two-sided surface, respectively.

Improving the Efficiency of Solar Power Plants

Introduction. An urgent scientific problem is to increase the efficiency of using solar energy in solar power plants (SES). The purpose of the article is to study methods for increasing the efficiency of solar power plants. Materials and Methods. Solar power plants based on modules with a two-sided working surface are considered. Most modern solar power plants use solar modules. The reflection of solar radiation from the earth’s surface provides an increase in the production of electrical energy by 20% compared with modules with a working surface on one side. It is possible to increase the efficiency of using solar energy by increasing the annual production of electric energy through the creation of equal conditions for the use of solar energy by the front and back surfaces of bilateral solar modules. Results. The article presents a solar power plant on a horizontal surface with a vertical arrangement of bilateral solar modules, a solar power station with a deviation of bilateral solar modules from a vertical position, and a solar power plant on the southern slope of the hill with an angle β of the slope to the horizon. The formulas for calculating the sizes of the solar energy reflectors in the meridian direction, the width of the solar energy reflectors, and the angle of inclination of the solar modules to the horizontal surface are given. The results of computer simulation of the parameters of a solar power plant operating in the vicinity of Luxor (Egypt) are presented. Discussion and Conclusion. It is shown that the power generation within the power range of 1 kW takes a peak value for vertically oriented two-sided solar modules with horizontal reflectors of sunlight at the installed capacity utilization factor of 0.45. At the same time, when the solar radiation becomes parallel to the plane of vertical solar modules, there is a decrease in the output of electricity. The proposed design allows equalizing and increasing the output of electricity during the maximum period of solar radiation. Vertically oriented modules are reliable and easy to use while saving space between modules.

Visual lab tests: Proppant transportation in a 3D printed vertical hydraulic fracture with two-sided rough surfaces

An effective proppant placement in a hydraulic fracture system is the key to increasing the gas production of unconventional reservoirs. The fracture surfaces are generally rough, however, assumed to be smooth or rough only on one side for visualization in existing experimental fracture models, which may generate unrealistic results. This paper presents a two-sided rough fracture model for studying the proppant placement. This was realized by combining the digitalization of rough surface and 3D printing technology. Using this new fracture model, some distinct piling-up and transportation mechanisms of proppants in a vertical fracture with two-sided rough surfaces were demonstrated against the counterpart of the fracture that considers only one-sided rough surface or smooth surfaces. Particularly, a finger-like piling of proppants resulting from the collective effect of proppant gliding, aggregation and saltation was present in the two-sided rough fracture. Meanwhile, high-speed channel, particle wormhole, cavity and isolated pillars also occurred locally. To quantify these mesostructures, the concept of channel ratio was introduced and correlated with fluid viscosity. All the results suggest that the new fracture model is useful not only to better understand the proppant placement but also to optimally design and control hydraulic fracture systems.

On Waviness and Two-Sided Surface Features in Thermal Elastohydrodynamically Lubricated Line Contacts

Machine components are designed to endure increasingly severe operating conditions due to the strive for improved energy efficiency of mechanical systems. Consequently, lubricated non-conformal contacts must rely on thin lubricant films where the influence of surface topography on the lubricating conditions becomes significant. Due to the complexity of the multiphysical problem, approximate assumptions are often employed to facilitate numerical studies of elastohydrodynamically lubricated (EHL) contacts. In this work, the rough, time dependent, thermal EHL problem is solved with focus on two main analyses. The first analysis focuses on the influence of sinusoidal roughness and the difference between a thermal non-Newtonian approach and an isothermal Newtonian approach. The second analysis is focused on the lubricating mechanisms taking place when two-sided surface features overtake within the thermal EHL contact. The results indicate that the film thickness in the outlet of the contact may be significantly overestimated by an isothermal Newtonian approach and that differences in the high-pressure region may also occur due to viscosity variations in the inlet of the contact. Moreover, for the studied two-sided surface features, it became evident that not only the surface feature combination but also the overtaking position influence the film thickness and pressure variations significantly.

Sandwich-like Catalyst-Carbon-Catalyst Trilayer Structure as a Compact 2D Host for Highly Stable Lithium-Sulfur Batteries.

Herein, we propose the construction of a sandwich-structured host filled with continuous 2D catalysis-conduction interfaces. This MoN-C-MoN trilayer architecture causes the strong conformal adsorption of S/Li2 Sx and its high-efficiency conversion on the two-sided nitride polar surfaces, which are supplied with high-flux electron transfer from the buried carbon interlayer. The 3D self-assembly of these 2D sandwich structures further reinforces the interconnection of conductive and catalytic networks. The maximized exposure of adsorptive/catalytic planes endows the MoN-C@S electrode with excellent cycling stability and high rate performance even under high S loading and low host surface area. The high conductivity of this trilayer texture does not compromise the capacity retention after the S content is increased. Such a job-synergistic mode between catalytic and conductive functions guarantees the homogeneous deposition of S/Li2 Sx , and avoids thick and devitalized accumulation (electrode passivation) even after high-rate and long-term cycling.

Two-sided ultrasonic surface rolling process of aeroengine blades based on on-machine noncontact measurement

As crucial parts of an aeroengine, blades are vulnerable to damage from long-term operation in harsh environments. The ultrasonic surface rolling process (USRP) is a novel surface treatment technique that can highly improve the mechanical behavior of blades. During secondary machining, the nominal blade model cannot be used for secondary machining path generation due to the deviation between the actual and nominal blades. The clamping error of the blade also affects the precision of secondary machining. This study presents a two-sided USRP (TS-USRP) machining for aeroengine blades on the basis of on-machine noncontact measurement. First, a TS-USRP machining system for blade is developed. Second, a 3D scanning system is used to obtain the point cloud of the blade, and a series of point cloud processing steps is performed. A local point cloud automatic extraction algorithm is introduced to extract the point cloud of the strengthened region of the blade. Then, the tool path is designed on the basis of the extracted point cloud. Finally, an experiment is conducted on an actual blade, with results showing that the proposed method is effective and efficient.

Market Theory and Capitalist Axiomatics

Producing a properly philosophical theory of capitalism as an open axiomatic system requires adding intensive multiplicities to the mathematical account of set theory, which allows only extensive multiplicities. Doing so enables us to understand pricing as a process of transforming intensive quantities into metric quantities, and thereby develop a diagram of the dynamics of axiomatisation and of the market as the two-sided and asymmetrical recording surface of the capitalist socius whose slope represents the infinite debt owed to finance capital. The capitalist market axiomatises four kinds of flows – flows of liquid capital and abstract labour, of course, but also flows of raw materials and energy and of human populations. At the same time that axiomatisation conjugates these flows in denumerable sets to extract surplus-value, it connects flows in minor, non-denumerable sets that escape axiomatisation and may become revolutionary. Such minor connections would constitute the fabric of a post-capitalist axiomatics.

Scattering suppression and cloak for electrically large objects using cylindrical metasurface based on monolayer and multilayer mantle cloak approach

The authors proposed analytical models applicable to monolayer and multilayer mantle cloaks for suppressing the scattering fields of electrically large conducting objects using printed ultrathin metasurfaces. To analyse the proposed structure, the two-sided impedance surface method is used and the scattering cross section (SCS) is obtained using Mie theory. It is shown that using surface impedance expression obtained from the analytical model for monolayer mantle cloak they can design a proper unit cell of a metasurface to reduce significantly total scattering from the cylinder. The proposed mantle cloaks in this work are mainly designed to minimise simultaneously several scattering multi-poles of a relatively large object around considerably broad bandwidth. Numerical results and full-wave simulation show good cloaking performance in designed frequency. The simulated results using their analytical models as well as the full-wave results show that the multilayer mantle cloak is an optimised candidate for cloaking of electrically large objects. The proposed multilayer mantle cloak confirms 3.6 dB SCS gain to cancel the scattering fields of a perfect electric conductor cylinder with a radius of 1.425λ0 at the designed frequency. Finally, they consider a cluster of closely spaced and overlapping three cloaked cylinders for suppression of electromagnetic fields.