Search Results (191)

As accuracy of the reflector surface of a space parabolic deployable antenna is an important factor to determine its electrical characteristics (transmission gain and side lobes), mechanical characteristics of parabolic antennas under various internal pressures should be studied. The objective of this paper is to explore the force analysis of parabolic antennas by theoretical method and to estimate the effect of different air pressures on the surface precision of parabolic antennas via experiments in horizontal and vertical directions, and then a numerical analysis of the vibration characteristics of the parabolic antenna is proposed to explore the transient response of parabolic antennas. It is found that the ratio of tension reduces as depth of the parabolic membrane increases and can infinitely converge to 1/2. For precision analysis, it is concluded that precision of the parabolic membrane surface in a vertical state is higher than that in a horizontal state. Full article

This article presents a mathematically grounded approach to increasing the operational reliability of current collectors in electric transport systems by ensuring a constant contact force between the collector shoe and the power rail. The core objective is achieved through the development and analysis of a mechanical system incorporating spring and cam elements, which is specifically designed to provide a nearly invariant contact pressure under varying operating conditions. A set of equilibrium equations was derived to determine the stiffness ratios of the springs and the geometric conditions under which the contact force remains constant despite wear or displacement. Additionally, the paper introduces a method for synthesizing the cam profile that compensates for nonlinear spring deformation, ensuring force constancy over a wide range of movement. The analytical results were validated through parametric simulations, which assessed the influence of wear depth, rail inclination, and external vibrations on the system’s force output. These simulations, executed within a numerical framework using scientific computing tools, demonstrated that the deviation of the contact force does not exceed a few percent under typical disturbances. Experimental verification further confirmed the theoretical predictions. The study exemplifies the effective use of mathematical modeling, nonlinear mechanics, and numerical methods in the design of energy transmission components for transport applications, contributing to the development of robust and maintainable systems. Full article

Tomato waste (TW) was employed as a sustainable source for the synthesis of fluorescent carbon dots (CDs) via a microwave-assisted hydrothermal carbonization (Mw-HTC) method, aiming at its valorization. Several amines were used as nitrogen additives to enhance the fluorescence quantum yield (QY) of CDs, and a set of reaction conditions, including additive/TW mass ratio (0.04–0.32), dwell time (15–60 min), and temperature (200–230 °C) of the HTC process, were scrutinized. The structural analysis of the tomato waste carbon dots (TWCDs) was undertaken by FTIR and ¹H NMR techniques, revealing their most relevant features. In solid state, transmission electron microscopy (TEM) analysis showed the presence of nearly spherical nanoparticles with an average lateral size of 8.1 nm. Likewise, the topographical assessment by atomic force microscopy (AFM) also indicated particles’ heights between 3 and 10 nm. Their photophysical properties, revealed by UV–Vis, steady-state, and time-resolved fluorescence spectroscopies, are fully discussed. Higher photoluminescent quantum yields (up to 0.08) were attained when the biomass residues were mixed with organic aliphatic amines during the Mw-HTC process. Emission tunability is a characteristic feature of these CDs, which display an intensity average fluorescence lifetime of 8 ns. The new TWCDs demonstrated good antioxidant properties by the ABTS radical cation method (75% inhibition at TWCDs’ concentration of 5 mg/mL), which proved to be related to the dwell time used in the CDs synthesis. Moreover, the synthesized TWCDs suppressed the growth of Escherichia coli and Staphylococcus aureus at concentrations higher than 2000 μg/mL, encouraging future antibacterial applications. Full article

As one type of critical load-bearing element in precast concrete structures, grouted sleeve (GS) connections enable efficient force transmission between reinforcing bars while maintaining structural integrity. Despite their growing global adoption, significant variations exist in design philosophies, construction specifications, and performance requirements among regional standards. Through bibliometric analysis, the most active countries and regions in GS application and research worldwide were identified, and the relevant technical standards established by these countries and regions were systematically reviewed. By comparing standards from Asia, the Americas, Europe, and Oceania, the main differences in design philosophy, construction quality control, material specifications, and performance requirements among these standards were analyzed and identified. The results show that different standards have a conceptual difference at the materials and quality control level, with one approach focusing on stricter management of sleeve materials and more detailed on-site construction requirements, and another approach emphasizing testing-based methods and third-party verification. These standards can be divided into the following two categories for the design limits of GS tensile performance: one category takes multiples of the yield strength of the connected reinforcing bars as the limit, and the other category takes multiples of the tensile strength of the connected reinforcing bars as the limit. Regarding mechanical performance requirements, standards using the ultimate tensile strength of the connected reinforcing bars as the control parameter differ from those using multiples of yield strength in their performance requirements for connections of low-strength and high-strength reinforcing bars. The variation in yield-to-tensile strength ratios among steel grades across different countries is a key factor leading to these different requirements. When using the uniform steel bar material properties specified in the standard for quantification, as the bar strength increases from approximately 240 MPa to 600 MPa, the minimum required ratio of the limits for standards based on multiples of yield strength and multiples of tensile strength increases from 0.79 to 1.07. When applying GS connections to reinforcing bars of varying strength levels, using fixed strength multiplier requirements may result in uneconomical designs or create technical challenges in achieving the required strength. Full article

A continuously variable transmission can improve the energy efficiency of actuators with rotary output by providing an optimum transmission ratio. A continuously variable transmission based on circumferentially arranged disks (CAD CVT) is a new type of CVT that is highly beneficial for applications requiring large torques, like heavy road transport. However, its major drawback is that its efficiency drops in the low torque region. To overcome this problem, the current paper proposes an improved mechanical design in which the force on traction disks is changed according to the instantaneous torque requirement, thus resulting in improved efficiency in low torque regions. Furthermore, a hydraulic-actuation-based control system has been designed to ensure the optimum control of the improved mechanical design. The improved mechanical design of the CAD CVT is named CAD CVT-II, which is highly beneficial for variable torque applications such as road transport and wind turbines. Full article

The global transition toward clean energy has driven the extensive deployment of overhead tower-lines in desserts, where such structures face unique challenges from wind–sand interactions. The current design standards often overlook these combined loads due to oversimplified collision models and inadequate computational frameworks. These gaps are bridged in the present study through the development of a refined impact force model grounded in Hertz contact theory, which captures transient collision mechanics and energy dissipation during sand–structure interactions. Validated against field data from northwest China, the model enables a comprehensive parametric analysis of wind speed (5–60 m/s), sand density (1000–3500 kg/m³), elastic modulus (5–100 GPa), and Poisson’s ratio (0.1–0.4). Our results show that peak impact forces increase by 66.7% (with sand density) and 148% (with elastic modulus), with higher wind speeds amplifying forces nonlinearly, reaching 8 N at 30 m/s. An increased elastic modulus shifts energy dissipation toward elastic rebound, reducing the penetration depth by 28%. The dynamic analysis of a 123.6 m transmission tower under wind–sand coupling loads demonstrated significant structural response amplifications; displacements and axial forces increased by 28% and 41%, respectively, compared to pure wind conditions. These findings reveal the importance of integrating coupling load effects into design codes, particularly for towers in sandstorm-prone regions. The proposed framework provides a robust basis for enhancing structural resilience, offering practical insights for revising safety standards and optimizing maintenance strategies in arid environments. Full article

A high-gear-ratio anti-backlash 3K planetary gearbox with a preloaded flexure-based carrier is a suitable reducer for robot joints owning to its compact design and high transmission accuracy. However, to design such a 3K planetary gearbox with high bidirectional efficiencies for backdrivable robot joints, it is critical to develop an accurate transmission efficiency model to predict the effects of the preloaded flexure-based carrier on the efficiency of the 3K planetary gearbox. To determine the meshing forces of gear pairs in the 3K planetary gearbox, a quasi-static model is formulated according to tangential displacements of planet gears resulting from the preloaded flexure-based carrier. Considering the reverse meshing forces in the anti-backlash 3K planetary gearbox, a modified efficiency model is developed and the bidirectional transmission efficiencies are analyzed. Simulation results show that both forward and backward transmission efficiencies of the anti-backlash 3K planetary gearbox decrease as the preload increases, while they all increase with the increasing load torque. It is also revealed that the preload primarily affects the meshing efficiency of the sun–planet gear pair. Four different carrier prototypes are fabricated for experiments. The average errors between the predicted and measured results for forward and backward transmission efficiencies are 2.30% and 4.01%, respectively. Full article

Chitosan is widely used in drug delivery applications, due to its biocompatibility, bio-degradability, and low toxicity. Nevertheless, its properties can be enhanced through the physical or chemical modification of its amino and hydroxyl groups. This work explores the electrostatic complexation of two chitosan samples of differing lengths with two poly(N-isopropylacrylamide) (PNIPAM) homopolymers of different molecular weight carrying a chargeable carboxyl end group. This interaction enables the electrostatic binding of PNIPAM side chains onto the chitosan backbone through the amino groups, and could be considered as an alternative grafting method. Dynamic and electrophoretic light scattering techniques were employed in order to study the solution/dispersion properties of the formed complexes as a function of the PNIPAM concentration, or, equivalently, the molar/charge ratio of the two components. The obtained results revealed that their mass, size, and charge mostly depend on the length of the two individual constituents, as well as their mixing ratio. Furthermore, their response to changes in their environment, namely temperature and ionic strength, was also examined, demonstrating the effect of either the thermoresponsiveness of PNIPAM or the electrostatic charge screening, respectively. Fluorescence spectroscopy, utilizing pyrene as a probe, provided information regarding the hydrophobicity of the formed complexes, while images from scanning transmission electron and atomic force microscopies further elucidated their morphology, which was found to be closely related to that of the corresponding chitosan molecule. Finally, their potential as drug delivery vehicles was also investigated, utilizing curcumin as a model drug at various loading concentrations. Full article

Since the early 20th century, dimensional analysis and similarity arguments have provided a critical tool for the analysis of scientific, engineering, and thermodynamic systems. Traditionally, the resulting dimensionless groups are categorized into those defined by (i) geometric similarity, involving ratios of length scales; (ii) kinematic similarity, involving ratios of velocities or accelerations, and (iii) dynamic similarity, involving ratios of forces. This study considers an additional category based on entropic similarity, with three variants defined by the following: (i) ratios of global or local entropy production terms Π entrop = σ ˙ 1 / σ ˙ 2 or Π ^ entrop = σ ˙ ^ 1 / σ ˙ ^ 2 ; (ii) ratios of entropy flow rates Π entrop = F S , 1 / F S , 2 or magnitudes of entropy fluxes Π ^ entrop = | | j S 1 | | / | | j S 2 | | ; and (iii) the ratio of a fluid velocity to that of a carrier of information Π info = U / c . Given that all phenomena involving work against friction, dissipation, spreading, chemical reaction, mixing, separation, or the transmission of information are governed by the second law of thermodynamics, these are more appropriately analyzed directly in terms of competing entropic phenomena and the dominant entropic regime, rather than indirectly using ratios of forces. This work presents the entropic dimensionless groups derived for a wide range of diffusion, chemical reaction, dispersion, and wave phenomena, revealing an entropic interpretation for many known dimensionless groups and many new dimensionless groups. Full article

The results of a comprehensive investigation into the structure and properties of nanodiamond soot (NDS), obtained from the detonation of various explosive precursors (trinitrotoluene, a trinitrotoluene/hexogen mixture, and tetryl), are presented. The colloidal behavior of the NDS particles in different liquid media was studied. The results of the scanning electron microscopy, dynamic light scattering, zeta potential measurements, and laser diffraction analysis suggested a similarity in the morphology of the NDS particle aggregates and agglomerates. The phase composition of the NDS nanoparticles was studied using X-ray diffraction, Raman spectroscopy, electron diffraction, transmission electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The NDS particles were found to comprise both diamond and graphite phases. The ratio of diamond to graphite phase content varied depending on the NDS explosive precursor, while the graphite phase content had a significant impact on the electrical conductivity of NDS. The study of the mechanical and tribological characteristics of polymer nanocomposites, modified with the selected NDS particles, indicated that NDS of various types can serve as a viable set of model nanofillers. Full article

The annealing process is one of the most common methods used to study the thermal stability of multilayers. To study the effect of the annealing process on the microstructural variation in NiV/B₄C multilayers, different annealing experiments were performed on NiV/B₄C multilayers with a d-spacing of 8 nm. This work provides a foundation for the fabrication of non-periodic NiV/B₄C multilayers. The NiV/B₄C multilayers were investigated by grazing-incidence X-ray reflectometry (GIXR), X-ray diffuse scattering (XRS), atomic force microscopy (AFM), X-ray diffraction (XRD), grazing-incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). The temperature-dependent experiments showed that annealing at 70–290 °C slightly increased the period thickness and interface width. Annealing at higher temperatures resulted in significant structural changes and thickness ratio (Г = d_NiV/d) changes from 0.4 to 1/3 at 340 °C. The time-dependent results showed that the microstructural variations primarily occurred after 60 min. The XRD, XRS, GISAXS and TEM were further used to study microstructural changes. It was found that the NiV/B₄C multilayers exhibited a microcrystal structure after annealing, and that enhanced crystallinity and an increase in interface roughness were the main reasons for the microstructural changes. Full article

This paper designs a spatial photoelectric scanning mechanism that utilizes the large transmission ratio and reverses the self-locking performance of worm gears and gears. The institution uses a stepper motor to drive the worm gear component, thereby driving the worm gear to drive the alarm camera for spatial alarm imaging work. The stepper motor provides the driving force for motion, and, simultaneously, the alarm camera image can be compared with the star map to achieve position feedback. Therefore, this mechanism can achieve closed-loop control without angle measuring devices, achieving the lightweight design of the photoelectric scanning mechanism. Although this driving mechanism has many advantages, due to the micro-vibration formed by the gear backlash between teeth during the operation of the worm gear and worm, micro-vibrations are generated in the system, which can interfere with satellites with high precision requirements and affect their normal operation. This paper analyzes and experimentally verifies the principle of micro-vibrations in the worm gear and worm movement mechanism, and takes a certain photoelectric scanning turntable as an example to suppress micro-vibrations. The micro-vibration momentum level has been reduced from 7 N (at its peak) to 3.5 N (at its peak), with the number of targets increased by 50%, resulting in an effective suppression effect. Full article

The article aims to describe the design and operation of a fundamentally new self-regulating planetary transmission, which, without a control system, changes the gear ratio under the influence of a variable external load. A self-regulating transmission can be created based on a kinematic chain with two degrees of freedom, having only one input. According to the laws of mechanics, such a chain has no definability of motion, since the number of inputs must be equal to the number of degrees of freedom. The equilibrium of a two-movable chain with one input can obtained by creating an additional constraint that substitutes a reaction in the instantaneous center of the intermediate link velocities by the friction moment in the hinge of the intermediate link. The friction moment creates a force constraint, which is taken into account in the equilibrium condition. The obtained equilibrium conditions ensure the definiteness of motion and the ability of self-regulation in the form of an inversely proportional dependence of the speed of the output link on the variable external load. The described method makes it possible to create a fundamentally new class of self-regulating mechanisms in all branches of technology. The interaction of kinematic and force parameters and the construction of parameter graphs was performed using the SolidWorks 2021 program with certain additions. The experimental studies performed confirm the reliability of the theoretical developments. Full article

Multicarrier navigation modulation is a trend within next-generation global navigation satellite systems (GNSS) aiming to enhance navigation performance, but it forces amplifiers to work in nonsaturation zones, resulting in low power efficiency. This paper presents constant-envelope multiplexing (CEM) based on clipping to overcome the low transmission efficiency of orthogonal multi-binary offset carriers (OMBOCs). The clip constant-envelope OMBOC (CCE-OMBOC) features a hard limit for the original OMBOC signal, and its cross-correlation function (CCF) has a fixed ratio with the CCF of the original OMBOC. Thus, the clipping process has no adverse effect on navigation performance. Additionally, the expression of transmission and multiplexing efficiency is presented according to OMBOC’s amplitude distribution. A low sampling rate is suggested for the CCE-OMBOC, which reduces the cost of signal generation. For OMBOC, the CCE-OMBOC provides multiplexing efficiency comparable to that of constant-envelope multiplexing via intermodulation construction (CEMIC). CCE-OMBOC has a straightforward generation process; in contrast, the complexity of CEMIC rises significantly with increasing subcarriers. Moreover, the CCE-OMBOC is a multicarrier CEM modulation tool that has good tracking performance and excellent compatibility. The greater the number of subcarriers, the more navigation services and the higher the navigation data rate. The CCE-OMBOC can be used in next-generation GNSS and integrated communication and navigation systems. Full article

We conducted experiments utilizing the scattering effect of zinc oxide (ZnO) to enhance the photoluminescence (PL) intensity of cesium lead bromide (CsPbBr₃) perovskite quantum dots (QDs). This study involved investigating the method for creating a CsPbBr₃ and ZnO mixture and determining the optimal mixing ratio. A mixture dispersion of CsPbBr₃ and ZnO, prepared at a 1:0.015 weight ratio through shaking, was fabricated into a film using the spin coating method. The PL intensity of this film showed a relative increase of 20% compared to the original CsPbBr₃ QD film without ZnO. The scattering effect of ZnO was confirmed through ultraviolet-visible (UV-Vis) absorption and transient PL experiments, and a long-delayed exciton lifetime was observed in the optimized mixture dispersion thin film. The morphology of the fabricated film was characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). For the CsPbBr₃-ZnO mixture (1:0.0015) film, crystal domains of approximately 10 nm were observed using TEM. Through AFM analysis, an excellent film roughness of 4.6 nm was observed, further confirming the potential of perovskite QD/ZnO composite films as promising materials for enhanced photoconversion intensity. In future studies, applying this method to other perovskite materials and metal oxides for the optimization of photoconversion composite materials is expected to enable the fabrication of highly efficient perovskite QD/metal oxide composite films. Full article